Category 6™

Tornadoes, Floods, and Severe Thunderstorms Continue in the Midwest

By: JeffMasters, 2:46 PM GMT on May 31, 2013

It was yet another active day for tornadoes, flooding, and severe thunderstorms in the Midwest on Thursday, with NOAA's Storm Prediction Center (SPC) logging 16 preliminary tornado reports. Twisters touched down in Oklahoma, Arkansas, and Illinois. The tornadoes missed heavily populated areas for the most part, but seven people were injured in Arkansas in two separate tornadoes, and two other people were hurt by lightning. The severe weather forced organizers of the outdoor Wakarusa Music Festival north of Ozark, Arkansas to delay the start of the festival. The band "Widespread Panic" was one of the groups scheduled to perform, leading to an Associated Press headline from yesterday titled, "Nine hurt in Arkansas storm; Widespread Panic delayed." Heavy rains from this week's thunderstorms have pushed the Mississippi River to major flood stage at most places from Burlington Iowa to Quincy Illinois, and the river is expected to crest near major flood stage at St. Louis early next week. In Iowa, the Cedar River at Cedar Falls, the Iowa River at Marengo, and the Skunk River near Sigourney and at Augusta are also in major flood. The latest forecast from NOAA's Storm Prediction Center calls for a "Moderate Risk" of severe weather today (Friday) over much of Oklahoma and Southwest Missouri, including Oklahoma City and Tulsa in Oklahoma, and Joplin, Missouri, with the potential for several strong EF-2 and EF-3 tornadoes.


Figure 1. Lightning strike from a severe thunderstorm near Guthrie, Oklahoma on May 30, 2013, as photographed by KFOR-TV. (AP Photo/KFOR-TV)


Figure 2. Severe weather outlook for Thursday, May 30, calls for a "Moderate Risk" of severe weather over much of Oklahoma and Southwest Missouri, including Oklahoma City and Tulsa in Oklahoma, and Joplin, Missouri. You can follow today's severe weather outbreak from our Severe Weather page.

A mostly quiet year for violent tornadoes
After a very quiet March, April, and first half of May, the U.S. tornado season has become very active during the last half of May, and is beginning to catch up to normal. TWC's tornado expert Dr. Greg Forbes has a preliminary count of 181 tornadoes for the month of May, through May 29, which is 35% below the 10-year average of 279 through May 29th. May 2012 had only 121 tornadoes. The 2013 tornado tally has risen significantly in the last half of May, due to 7 of the last 15 days having above-average numbers of tornadoes. Fortunately, we are well below-average for strong and violent EF-3, EF-4, and EF-5 tornadoes so far in 2013. According to NOAA, the U.S. has averaged 43 EF-3 or stronger tornadoes per year during the period 1954 - 2012. With tornado season nearly half over, only twelve EF-3 and EF-4 tornadoes have been recorded so far in 2013. An average year should have had at least twenty of these tornadoes by this point in the year. Here are the twelve EF-3 and stronger tornadoes so far in 2013, as detailed in Wikipedia's excellent Tornadoes of 2013 page:

EF-5, May 20, Moore, Oklahoma. 24 deaths, 377 injuries, $2 billion in damage.
EF-4, May 28, Ottawa County, Kansas. Intensity based on mobile Doppler radar data. See the Capital Weather Gang's description of this tornado.
EF-4, May 19, Shawnee, Oklahoma. 2 deaths, 6 injuries.
EF-4, May 15, Granbury, TX. 6 deaths, 24+ injuries.
EF-4, May 18, Rozel, Kansas.
EF-4, February 10, Hattiesburg, MS. 0 deaths, 82 injuries.
EF-3, Corning, KS, May 28.
EF-3, May 27, Lebanon - Esbon, KS. 1 injured. Wind gust of 175 mph measured by TIV2 intercept vehicle.
EF-3, May 15, Cleburne, TX. No deaths or injuries.
EF-3, January 30, Adairsville, GA. 1 death, 17 injuries, 363 buildings damaged or destroyed.
EF-3, April 11, Kemper County, AL. 1 death, 9 injuries.
EF-3, May 19, Luther - Carney, Oklahoma.


Figure 3. The annual number of EF-3 and stronger tornadoes, 1954 - 2012. The greatest number of these dangerous tornadoes was 131 in 1974, the year of the notorious "Super Outbreak." The minimum was just 15, set in 1987. The average is 43 per year. Image credit: NOAA.


Video 1. Impressive 2-minute timelapse of the Bennington, Kansas wedge tornado of May 28, 2013, as filmed by the Aussie Storm Chasers. As discussed in an excellent blog post by Jason Samenow of the Capital Weather Gang, the violent EF-4 tornado stood still for nearly an hour, and had wind gusts as high as 264 mph at an altitude of 300 feet measured by Doppler on Wheels.

Remains of Hurricane Barbara bringing heavy rains to Mexico
Hurricane Barbara died on Thursday as it attempted to cross Mexico's Isthmus of Tehuantepec into the southernmost Gulf of Mexico. While there is no low level circulation apparent on satellite loops this Friday morning, there is a bit of spin at middle levels of the atmosphere, and the remains of Barbara are kicking up some heavy thunderstorm activity over the southernmost Gulf of Mexico and adjacent land areas of Mexico. Wind shear is a high 20 knots in the region, and the area of disturbed weather is quite small, so I don't expect any development to occur over the next few days. Wind shear is predicted to remain high over the Gulf of Mexico for the next six days, and none of the reliable computers models is calling for tropical cyclone development in the Atlantic during that period. Late next week, wind shear is predicted to drop, and there is a better chance for tropical cyclone development in the Gulf of Mexico or Western Caribbean. Both the GFS and ECMWF models suggest that a strong tropical disturbance with heavy rains may affect Mexico's Yucatan Peninsula, Western Cuba, and the Southwest Florida by Friday next week.


Figure 4. Remains of Hurricane Barbara in the southernmost Gulf of Mexico as seen by MODIS at 12:05 pm EDT Thursday, May 30, 2013. Barbara had just been declared dead one hour prior to this photo. Image credit: NASA.

Saturday, June 1, is the first day of hurricane season, and I'll post a quick look at what we might expect to see in June.

Jeff Masters

Tornado

Hurricane Barbara Hits Mexico; Severe Weather Outbreak Continues in Midwest

By: JeffMasters, 3:29 PM GMT on May 30, 2013

The Eastern Pacific's Hurricane Barbara is still alive as a tropical depression at the edge of the Atlantic's Gulf of Mexico, and has the potential to gain new life as an Atlantic tropical cyclone later today. Barbara made landfall near 4 pm EDT (1 pm PDT) May 29, 2013, on Mexico's Bay of Tehuantepec coast, as a Category 1 hurricane with 75 mph winds. The storm killed two people, and brought heavy rains of 16.02" (407mm) to Arriaga in the state of Chiapas in an 18-hour period. Barbara remains a serious rainfall threat today. The storm intensified remarkably rapidly, becoming a hurricane just 21 hours after it became a tropical depression. According to NOAA's Historical Hurricane Tracks website, only one other Eastern Pacific hurricane has ever made landfall in May--Category 1 Hurricane Agatha of 1971, which hit Mexico west of Acapulco. Barbara is just the 2nd hurricane ever to make landfall in the Bay of Tehuantepec (the other: Category 1 Hurricane Rick of 1997.) Barbara's formation date of May 28 was the 2nd earliest appearance of the Eastern Pacific's 2nd named storm of the year; the record earliest second storm of the year occurred just last year, on May 21, 2012 (Tropical Storm Bud.) The average date for the formation of the Eastern Pacific's 2nd storm is June 25. Barbara's landfall location was the most easterly on record for an East Pacific hurricane. Records of Eastern Pacific hurricanes go back to 1949, but aren't really reliable until 1966.


Figure 1. MODIS satellite image of Hurricane Barbara taken at 4:30 pm EDT on May 29, 2013. At the time, Barbara was making landfall as a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Barbara survived its overnight crossing of Mexico's Isthmus of Tehuantepec with its circulation intact, but lost nearly all of its heavy thunderstorm activity. This morning, the center of Barbara was located just inland from the southernmost waters of the Gulf of Mexico's Bay of Campeche. Barbara was drifting northwest, towards open water, at 3 mph. With wind shear a moderate 10 - 20 knots over Barbara, the storm has the potential to be classified as an Atlantic tropical depression later today if its center emerges over water. However, latest satellite loops have shown a steady reduction in the storm's heavy thunderstorms this morning, and Barbara may lose its circulation before it has time take advantage of the Gulf of Mexico's warm waters. Since Barbara is a small storm, the moderate wind shear may be too great for it to withstand. None of the reliable computer models predict that Barbara will survive into Friday. If Barbara is able to re-intensify to a tropical storm, it would keep the name Barbara, becoming the first Atlantic storm ever to have an Eastern Pacific name. Formerly, Eastern Pacific storms crossing into the Atlantic would be given a new name, but a recent NHC policy change allows storms to keep their names when they cross from one ocean basin to another. If Barbara were to dissipate before reaching the Gulf, then its remnants regenerate into a tropical storm in the Gulf, it would be named Andrea. If you want to discuss this year's hurricane season via Twitter, AP will be doing a hurricane twitter chat today (Thursday) at 1 p.m. EDT: #APStormChat; the National Hurricane Center is doing a hurricane chat at 2 pm EDT: #HurriChat.

Double ocean tropical cyclones: a rare breed
According to the Hurricane FAQ, since 1923 there have been four East Pacific tropical storms or hurricanes that have maintained their circulations while crossing into the Atlantic Ocean, becoming tropical storms in the Atlantic Ocean:

Northeast Pacific Tropical Storm Alma (May 2008) became a remnant low in the Atlantic, where it merged with another tropical wave which generated Atlantic Tropical Storm Arthur. Arthur hit Belize as a tropical storm, killing nine and doing $78 million in damage.

Northeast Pacific Hurricane Cosme became Atlantic Tropical Storm Allison in June 1989. Allison hit Texas as a tropical storm, and heavy rains from Allison--up to 30" in some regions of Texas and Louisiana--triggered floods that killed eleven people and did $1 billion in damage. (A later incarnation of Tropical Storm Allison in 2001 also hit Texas, and caused such extensive flooding that its name was retired.)

An unnamed Northeast Pacific Tropical Storm (September-October 1949) became Atlantic Hurricane (Storm #10) and hit Freeport, Texas as a Category 4 hurricane, killing two people.

An unnamed Northeast Pacific Tropical Storm (October 1923) became Atlantic Hurricane (Storm #6) and made landfall as a Category 1 hurricane in Louisiana.

There have been eight Atlantic tropical storms or hurricanes that have maintained their circulations while crossing into the East Pacific Ocean, and were then tropical storms in that ocean.


Figure 2. Severe weather outlook for Thursday, May 30, calls for a "Slight Risk" of severe weather over much of the Midwest. You can follow today's severe weather outbreak from our Severe Weather page.

Multi-day severe weather outbreak in the Midwest brings more tornadoes and flooding
It was an active day for tornadoes in the Midwest on Wednesday, with NOAA's Storm Prediction Center (SPC) logging 23 preliminary tornado reports. Twisters touched down in Nebraska, Kansas, Texas, Oklahoma, Iowa, and Wisconsin. The tornadoes missed heavily populated areas, and no injuries and only minor damage was reported. The latest forecast from NOAA's Storm Prediction Center call for a "Moderate Risk" of severe weather today (Thursday) over much of Oklahoma, with the potential for several strong EF-2 and EF-3 tornadoes.


Figure 3. Five-day rainfall forecast for the period ending at 7am EDT Tuesday, June 4, calls for very heavy rains of 3 - 5" over much of Missouri. Image credit: NOAA/HPC.

As discussed by wunderground's weather historian Christopher C. Burt in his latest post, Some Phenomenal Rainfalls the Past Week in the U.S., the country has seen a lot of very heavy rainfall over the past week that has caused serious flooding. Of particular concern is Iowa, where Governor Terry Branstad issued a disaster proclamation on Tuesday for 13 Iowa counties, due to recent storms and flooding.The Iowa State Climatologist, Harry Hillaker, announced on May 29th that this has been the wettest spring (March-May) on record for the state since records began 141 years ago. A state average of 16.4” has been preliminarily reported. The previous wettest spring was 15.5” way back in 1892. He warned that “Iowa is at a tipping point for a major flood event”. Rains of 1 - 2" are expected over Eastern Iowa the remainder of the this week, which will keep most rivers above flood stage. Another round of rains of 1 - 2" are likely on Tuesday and Wednesday of next week, when the next storm system rolls through. That system also has the potential to bring a severe weather outbreak to the Midwest.

Jeff Masters

Hurricane Flood Tornado

Barbara Nearing Mexico at Hurricane Strength; Midwest Tornado Outbreak Today

By: JeffMasters, 2:02 PM GMT on May 29, 2013

Hurricane warnings are flying for the Pacific coast of Mexico, where Tropical Storm Barbara is rapidly intensifying as it makes landfall. Barbara should be ashore by 2 pm EDT (11 am PDT), and is expected to intensify to a Category 1 hurricane with 75 mph winds before landfall. Barbara formed on Tuesday night (May 28), an unusually early date for the formation of the Eastern Pacific's second storm of the year. The record earliest second storm of the year occurred just last year, on May 21 (Tropical Storm Bud.) The previous record was set in 1984, when the second named storm (Boris) formed on May 29. Reliable records of Eastern Pacific hurricanes go back to 1949. Barbara wasted no time getting organized, and is gathering strength in impressive fashion as it nears landfall in Mexico's Bay of Tehuantepec area. The storm's main threat is very heavy rains of up to a foot, which will be capable of causing dangerous flash floods and mudslides over the next 2 - 3 days. However, wind damage and the expected 3 - 5 foot storm surge are also a concern, since the area of the coast it is hitting, though not heavily populated, has very little hurricane experience. According to NOAA's Historical Hurricane Tracks website, only one Eastern Pacific hurricane has ever hit the Bay of Tehuantepec--Category 1 Hurricane Rick of 1997. Radar out of Puerto Angel, Mexico shows that Barbara has built a partial eyewall, and the storm has already spread heavy rains ashore along portions of the Mexican coast. Satellite loops show that Barbara is a relatively small storm, with a modest area of heavy thunderstorms.


Figure 1. Radar image of Barbara from Puerto Angel, Mexico, taken at 9:30 am EDT (6:30 am PDT) May 29, 2013. Image credit: CONAGUA.

May tropical storm landfalls are rare in the Eastern Pacific
Only eight named storms that formed in May have hit land in the Eastern Pacific since accurate hurricane records began in 1949--an average of one storm every eight years, according to NOAA's Historical Hurricane Tracks website. Just one of these May storms made landfall as a hurricane--Category 1 Hurricane Agatha of 1971, which hit Mexico west of Acapulco. But one of the deadliest and most destructive Eastern Pacific tropical cyclones of all-time was a May storm that never reached hurricane strength--Tropical Storm Agatha of May 29, 2010, which had top winds of only 45 mph at landfall. Agatha dissipated just one day after making landfall, but its remnants lingered over Central America for six days, dumping torrential rains that triggered deadly flash floods and landslides; Mazatenango, Guatemala, reported 22.27 inches of rain from May 25 - 30, 2010. At least 190 people died, mostly in Guatemala, making Agatha the 7th deadliest Eastern Pacific tropical cyclone in history. Agatha's $1.2 billion in damage made it the 6th most expensive Eastern Pacific tropical cyclone on record. Fortunately, Barbara is hitting a region of the coast that is relatively sparsely populated compared to where Agatha hit, and Barbara is not likely to cause anywhere close to the devastation that Agatha wrought.


Figure 2. Journey to the center of the Earth: a massive sinkhole 66 feet (20 m) across and 100 ft (30 m) deep opened up on May 29, 2010 in Guatemala City after heavy rains from Tropical Storm Agatha. The sinkhole collapsed suddenly, taking a three-story house that was used as factory, claiming fifteen lives. The sinkhole formed because Guatemala City is built upon volcanic pumice deposits, which are unconsolidated and of low density, allowing easy erosion. According to Sam Bonis, a geologist at Dartmouth College, because of lax city zoning regulations and building codes, leaking pipes went unfixed long enough to create the conditions necessary for this hole to form (it technically wasn't a sinkhole, since sinkholes form in limestone rock.) How do you patch something like this?

Tropical cyclone development unlikely in the Atlantic during the coming seven days
Barbara is expected to push northwards and cross into the Gulf of Mexico by Friday, but the storm is small enough and moving slowly enough that Barbara will likely dissipate before reaching the Gulf. If the storm were able to maintain at least tropical depression status and cross into the Gulf, it would keep the name Barbara. If Barbara were to dissipate before reaching the Gulf, then regenerate into a tropical storm in the Gulf, it would be named Andrea. However, conditions do not favor redevelopment of Barbara's remnants into an Atlantic tropical depression, since wind shear is expected to be quite high over the Gulf late this week. None of the reliable computer models is calling for tropical cyclone development in the Atlantic during the next seven days.

AP will be doing a hurricane twitter chat on Thursday at 1 p.m. EDT: #APStormChat

The National Hurricane Center is doing a hurricane chat on Thursday at 2 pm EDT: #HurriChat


Figure 3. Large tornado on the ground near Corning, Kansas, at 4:32 CDT May 28, 2013. Image credit: Ron Heinen, via twitter.


Figure 4. Radar reflectivity image of the tornado that hit Corning, Kansas at 4:32 pm CDT May 28, 2013.


Figure 5. Severe weather outlook for Wednesday, May 29, calls for a "Moderate Risk" of severe weather over much of Oklahoma and Kansas, plus portions of the Texas Panhandle. You can follow today's severe weather outbreak from our Severe Weather page.

Multi-day severe weather outbreak in the Midwest continues today
It was an active day for tornadoes in the Midwest on Tuesday, with NOAA's Storm Prediction Center (SPC) logging eighteen preliminary tornado reports, with twisters touching down in Nebraska, Kansas, Texas, Michigan, and Pennsylvania. No injuries were reported from these tornadoes, but damage was reported near Corning, Kansas, and Fenton, Michigan. The latest forecasts from NOAA's Storm Prediction Center call for a "Moderate Risk" of severe weather today (Wednesday), with the possibility of a significant tornado outbreak over much of Oklahoma and Kansas, plus portions of the Texas Panhandle.

Wunderblogger Lee Grenci has a post, The Moore Tornado, describing how the rapid intensification of the May 20, 2013 Moore, Oklahoma tornado occurred.

Jeff Masters

Hurricane Tornado

TD 2-E a heavy rain threat to Mexico; 150th anniversary of only U.S. May hurricane

By: JeffMasters, 4:06 PM GMT on May 28, 2013

Tropical depression Two-E has formed in the Eastern Pacific, centered about 200 miles west-southwest of the Mexico/Guatemala border. The storm will bring very heavy rains capable of causing dangerous flash floods and mudslides to Mexico's Bay of Tehuantepec area over the next 2 - 3 days. Radar out of Puerto Angel, Mexico shows that heavy rains have already pushed ashore along portions of the Mexican coast, and satellite loops show an impressive but moderately disorganized area of heavy thunderstorms associated with TD Two-E, with some spiral bands on the storm's south side. With wind shear a low 5 -10 knots and ocean temperatures a very warm 30°C, conditions are ripe for further development, and I expect TD Two-E will be a tropical storm when it makes landfall on Wednesday along the Mexican coast in the Bay of Tehuantepec. The storm is close enough to the coast that it is unlikely a hurricane can form before landfall.


Figure 1. Latest satellite image of TD Two-E.

Development unlikely in the Atlantic this week
If TD Two-E continues to push northwards late this week and cross into the Gulf of Mexico, conditions do not favor development of the disturbance into an Atlantic tropical depression, as wind shear is expected to be quite high over the Gulf late this week. None of the reliable computer models is calling for tropical cyclone development in the Atlantic during the next seven days. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, is currently located in the Eastern Pacific, but is weak and difficult to discern. According to NOAA's May 27 MJO discussion, there is an increased probability of tropical cyclone formation over both the Eastern Pacific and Caribbean this week, and over the Caribbean next week. The GFS model has been trying to spin up a tropical depression in the Western Caribbean or Gulf of Mexico next week in a number of its runs over the past few days, but these runs have been very inconsistent on the timing and location of such a development. Tropical cyclone genesis forecasts more than four days out are highly unreliable, and we should just view the GFS model's predictions of a tropical depression next week as a sign that we have an above-average chance of an Atlantic tropical cyclone forming then. The European (ECMWF) model has been much less enthusiastic about a tropical depression forming in the Atlantic next week.


Figure 2. Track of the May 28, 1863 hurricane--the only hurricane on record to hit the U.S. in May. Image credit: Mike Chenoweth and the Bulletin of the American Meteorological Society.

150th anniversary of the only U.S. hurricane to make landfall in May
May 28 is the 150th anniversary of the only U.S. hurricane to make landfall in May--the May 28, 1863 hurricane that struck northwest Florida, killing at least 72 people. The hurricane hit nearly two weeks earlier than the next earliest U.S. landfalling hurricane, Hurricane Alma of June 9, 1966. (Tropical Storm Beryl of May 28, 2012 came close to being a May hurricane, bringing 70 mph winds to the coast near Jacksonville Beach, Florida.) According to a new paper by hurricane historians Mike Chenoweth and C. J. Mock, accepted for publication in the Bulletin of the American Meteorological Society, "Among the most unusual and unexpected hurricanes in United States history is the only hurricane to make landfall in the month of May. This recently re-discovered storm that struck northwest Florida on 28 May 1863 created a natural disaster in the area that became lost to history because it was embedded in a much larger and important manmade event, in this case the U.S. Civil War. We document the arrival of this storm both historically and meteorologically and anachronistically name it Hurricane “Amanda” in honor of the Union ship driven ashore by the hurricane. The hurricane revealed deficiencies and strengths in combat readiness by both sides. Meteorologically, the storm nearly achieved major hurricane status at landfall and its absence from modern data bases of tropical cyclone activity is a useful reminder to users of important gaps in our knowledge of tropical cyclones even in the best-sampled storm basins."


Figure 3. Severe weather outlook for Tuesday, May 28, calls for a "Slight Risk" of severe weather over portions of the Midwest. You can follow today's severe weather outbreak from our Severe Weather page.

Multi-day severe weather outbreak in the Midwest continues today
It was an active day for tornadoes in the Midwest on Monday, with NOAA's Storm Prediction Center (SPC) logging fourteen preliminary tornado reports, mostly in Nebraska and Kansas. No damage or injuries were reported from these tornadoes, as they stayed over unpopulated rural areas. One tornado in North Central Nebraska was intercepted by the Tornado Intercept Vehicle 2 (TIV2), which reported EF-3 to EF-4 winds before the tornado ripped off their weather instruments (Video 1.) The latest forecasts from NOAA's Storm Prediction Center call for an active severe weather period all week in the Midwest, with a "Slight Risk" of severe weather Tuesday and Thursday, and a "Moderate Risk" on Wednesday.


Video 1. Stormchasers Brandon Ivey and Sean Casey drove the Tornado Intercept Vehicle 2 (TIV2) into a violent EF-3 or EF-4 wedge tornado northeast of Smith Center, Kansas on Monday, May 27, 2013. They estimated that wind speeds were 150 - 175 mph before the tornado ripped the instruments off the top of the TIV2. This video captures the intensity of the storm as it moves over the TIV2. Since the storm occurred near sunset and the thick clouds blocked out much of the sun, it's tough to see much except thick debris. To license this footage, contact ‪http://www.StormChasingVideo.com‬.

Wunderblogger Lee Grenci has a new post this morning, The Moore Tornado, describing how the rapid intensification of the May 20, 2013 Moore, Oklahoma tornado occurred.

Jeff Masters

Hurricane

April 2013: Earth's 13th warmest April; 92E a threat to Mexico and Guatemala

By: JeffMasters, 3:15 PM GMT on May 27, 2013

April 2013 was the globe's 13th warmest April since records began in 1880, according to NOAA's National Climatic Data Center (NCDC). NASA also rated it the 13th warmest April on record. The year-to-date period of January - April has been the 8th warmest such period on record. April 2013 global land temperatures were the 17th warmest on record, and global ocean temperatures were the 7th warmest on record. April 2013 was the 338th consecutive month with global temperatures warmer than the 20th century average. Global satellite-measured temperatures in April 2013 for the lowest 8 km of the atmosphere were 13th or 11th warmest in the 35-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively. The Northern Hemisphere snow cover extent during April 2013 was the 9th largest in the 47-year period of record, and the first above-average April snow cover since 2003. Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of April 2013 in his April 2013 Global Weather Extremes Summary. He notes that The U.K. had its coldest April since 1989, and a storm felled the Pontfadog Oak, said by some to be Britain’s oldest tree. The historic tree dated back to at least 802 A.D., and was said to have served as a rallying point for a Welsh prince’s army that defeated England’s King Henry II in 1157 A.D.


Figure 1. Departure of temperature from average for April 2013, the 13th warmest April for the globe since record keeping began in 1880. Temperatures were much warmer than average across much of Mexico, the coastal regions of South America, most of Argentina, southern Europe, parts of coastal Africa, far eastern Europe, and western Australia. Record warm temperatures were observed across the southern tip of South America, far western Brazil, the southern Philippines, and some locales in far eastern Russia. It was much cooler than average across a swath of central North America, central Paraguay, part of northwestern Canada, and much of Alaska, where the southeastern portion of Alaska had record cold April temperatures. Image credit: National Climatic Data Center (NCDC) .

One billion-dollar disaster in April: floods in Buenos Aires, Argentina
Torrential rainfall fell across parts of Argentina’s city and province of Buenos Aires between the 2nd and 4th, triggering flash flooding that killed at least 70 and did $1.3 billion in damage, making it the deadliest and most damaging weather disaster world-wide in April. In the city of Buenos Aires, seven hours of heavy rains flooded subways and submerged low-lying neighborhoods. Hardest-hit was the La Plata region, where 400 millimeters (15.74 inches) of rain fell in just two hours. The total was more than the city had ever recorded during an entire month of April. Argentina’s largest refinery, Ensenada, also sustained damage from the floods, plus a fire.

The Argentinian flood in April brought the 2013 tally of billion-dollar weather disasters to six, according to the April 2013 Catastrophe Report from insurance broker AON Benfield. The six billion-dollar weather disasters through April 2013:

1) Drought in Central and Eastern China, 1/1 - 4/30, $4.2 billion
2) Flooding in Indonesia, 1/20 - 1/27, $3.31 billion
3) Flooding in Australia, 1/21 - 1/30, $2.5 billion
4) Winter weather in Europe, 3/12 - 3/31, $1.8 billion
5) Flooding in Argentina, 4/2 - 4/4, $1.3 billion
6) Severe weather in the Midwest U.S., 3/18 - 3/20, $1 billion

Preliminary damage estimates of $2 billion from the May 20, 2013 tornado in Moore, Oklahoma tornado will likely put that disaster on the list for May.


Figure 2. Severe flooding in Buenos Aires, Argentina, on April, 3, 2013 submerged half the city in waters up to 2 meters (6.6') deep. Image credit: focolare.org.

Neutral El Niño conditions continue in the equatorial Pacific
For the 13th month in row, neutral El Niño conditions existed in the equatorial Pacific during April 2013. NOAA's Climate Prediction Center (CPC) expects neutral El Niño conditions to last through summer. The large majority of the El Niño models predict neutral conditions will last through the fall of 2013. Temperatures in the equatorial Eastern Pacific need to be 0.5°C below average or cooler for three consecutive for a La Niña episode to be declared; sea surface temperatures were 0.4°C below average as of May 20, and have been +0.1 to -0.4°C from average since April 1, 2013.

Arctic sea ice falls to 7th lowest April extent on record
Arctic sea ice extent during April reached its seventh lowest extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). This was the 12th consecutive April and 143rd consecutive month with below-average Arctic sea ice extent. The last ten years (2004 to 2013) have seen seven of the ten lowest April extents in the satellite record.


Figure 3. Latest satellite image of Invest 92E.

Eastern Pacific tropical disturbance bringing heavy rains to Mexico and Guatemala
Invest 92E in the Eastern Pacific, centered about 100 miles southwest of the Mexico/Guatemala border, will bring very heavy rains capable of causing dangerous flash floods and mudslides to coastal Guatemala and Mexico's Bay of Tehuantepec over the next three days. Radar out of El Mozotal, Mexico shows that heavy rains have already pushed ashore along the Mexico/Guatemala border, and satellite loops show an impressive and expanding area of heavy thunderstorms associated with 92E, with some spiral bands beginning to develop on the storm's south side. In their 5 am PDT Tropical Weather Outlook, NHC gave 92E a 60% of developing into a tropical cyclone by Wednesday. I put these odds higher, at 80%. The 0Z Monday runs of the GFS and ECMWF both predict that 92E could develop into a tropical depression by Tuesday. With wind shear a low 5 -10 knots and ocean temperatures a very warm 30°C, conditions are ripe for further development, and I expect 92E will be a tropical depression or tropical storm when it makes landfall on Wednesday along the Mexican coast in the Bay of Tehuantepec.

In the Atlantic, the models are depicting high wind shear through June 1 over the majority of the regions we typically see May tropical cyclone development--the Caribbean, Gulf of Mexico, and Bahamas. The GFS and ECMWF models are showing a decrease in wind shear over the Western Caribbean after June 1, which would argue for an increased chance of tropical storm development then (though wind shear forecasts more than 7 days in advance are highly unreliable.)


Figure 4. Severe weather outlook for Monday, May 28, calls for a "Moderate Risk" of severe weather over portions of Kansas and Nebraska. You can follow this week's severe weather outbreak from our Severe Weather page.

Multi-day severe weather outbreak in the Midwest begins today
The latest forecasts from NOAA's Storm Prediction Center call for an active severe weather period Monday though Wednesday in the Midwest, with a "Moderate Risk" of severe weather today (Monday) over portions of Northern Kansas and Southern Nebraska. The severe weather outbreak will continue on Tuesday and Wednesday, though SPC is only highlighting a "Slight Risk" of severe weather on those days at present.

Have a great Memorial Day, everyone!

Jeff Masters

Climate Summaries

NOAA, TSR, UKMET, PSU, WSI, and WU Community Predict Active Atlantic Hurricane Season

By: JeffMasters, 9:11 PM GMT on May 24, 2013

NOAA forecasts an above-normal and possibly very active Atlantic hurricane season in 2013, in their May 23 outlook. They give a 70% chance of an above-normal season, a 25% chance of an near-normal season, and 5% chance of a below-normal season. They predict a 70% chance that there will be 13 - 20 named storms, 7 - 11 hurricanes, and 3 - 6 major hurricanes, with an Accumulated Cyclone Energy (ACE) 120% - 205% of the median. If we take the midpoint of these numbers, NOAA is calling for 16.5 named storms, 9 hurricanes, 4.5 major hurricanes, and an ACE index 162% of normal. This is well above the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2012 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median. Only five seasons since the active hurricane period that began in 1995 have not been above normal--including four El Niño years (1997, 2002, 2006, and 2009), and the neutral 2007 season.


Figure 1. Hurricane Michael as seen by NASA's Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a major Category 3 hurricane with 115 mph winds. Hurricane Sandy was the only other major Atlantic hurricane of 2012. Image credit: NASA.

The forecasters cited the following main factors that will influence the coming season:

1) Above-average sea surface temperatures (SSTs) are expected in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa between between 10°N and 20°N. SSTs in the MDR during April were 0.4°C above average, and were 0.33°C above the oceans in the remainder of the global tropics. Long-range seasonal computer model forecasts predict a continuation of above-average SSTs in the MDR during much of hurricane season.

2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multi-decadal Oscillation (AMO).

3) No El Niño event is expected this year. El Niño events tend to suppress Atlantic hurricane activity. Neutral conditions have been present since last summer, and are predicted to remain neutral through hurricane season by most of the El Niño computer forecast models.

NOAA said, "This combination of climate factors historically produces above-normal Atlantic hurricane seasons. The 2013 hurricane season could see activity comparable to some of the very active seasons since 1995." NOAA is increasingly using output from ultra-long range runs of the computer forecast models we rely on to make day-to-day weather forecasts, for their seasonal hurricane forecasts. These models include the NOAA Climate Forecast System (CFS), NOAA Geophysical Fluid Dynamics Lab (GFDL) model CM2.1, the European Centre for Medium Range Weather Forecasting (ECMWF) model, the United Kingdom Meteorology (UKMET) office model, and the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble.


Figure 2. Graphic from the 2013 NOAA Atlantic hurricane season forecast highlighting the reasons for this year's anticipated active character.

How accurate are NOAA's seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast. Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.


Figure 3. Forecast skill of the TSR, NOAA (National Oceanic and Atmospheric Administration) and CSU (Colorado State University) for the number of hurricanes in the Atlantic during 2003-2012, as a function of lead time. Forecast precision is assessed using the Mean Square Skill Score (MSSS) which is the percentage improvement in mean square error over a climatology forecast (six hurricanes in a given year.) Positive skill indicates that the model performs better than climatology, while a negative skill indicates that it performs worse than climatology. Two different climatologies are used: a fixed 50-year (1950-1999) climatology, and a running prior 10-year climate norm. NOAA does not release seasonal outlooks before late May, and CSU stopped providing quantitative extended-range December hurricane outlooks in 2011. Skill climbs as the hurricane season approaches, with modest skill levels by early June, and good skill levels by early August. Image credit: Tropical Storm Risk, Inc (TSR).

TSR predicts an active hurricane season: 15.3 named storms
The May 24 forecast for the 2013 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for an active season with 15.3 named storms, 7.5 hurricanes, 3.4 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 130. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. TSR rates their skill level as modest for these late May forecasts--11% - 25% higher than a "no-skill" forecast made using climatology. TSR predicts a 63% chance that U.S. land falling activity will be above average, a 21% chance it will be near average, and a 16% chance it will be below average. They project that 4.4 named storms will hit the U.S., with 2 of these being hurricanes. The averages from the 1950-2012 climatology are 3.1 named storms and 1.4 hurricanes. They rate their skill at making these late May forecasts for U.S. landfalls just 8% - 12% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.5 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR’s two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September 2013 sea surface temperatures in the tropical North Atlantic. Their model is calling for warmer than average SSTs and slower than average trade winds during these periods, and both of these factors should act to increase hurricane and tropical storm activity.

UKMET office predicts a slightly above normal Atlantic hurricane season: 14 named storms
The UKMET office forecast for the 2013 Atlantic hurricane season, issued May 13, calls for slightly above normal activity, with 14 named storms, 9 hurricanes, and an ACE index of 130. In contrast to the statistical models relied upon by CSU, TSR, and NOAA, the UKMET forecast is done strictly using two dynamical global seasonal prediction systems: the Met Office GloSea5 system and ECMWF system 4. In 2012, the Met Office forecast was for 10 tropical storms and an ACE index of 90. The actual numbers were 19 named storms and an ACE index of 123.

WSI predicts an active hurricane season: 16 named storms
The April 8 forecast from the private weather firm WSI (part of The Weather Company, along with The Weather Channel, Weather Central, and The Weather Underground), is calling for an active season with 16 named storms, 9 hurricanes, and 5 intense hurricanes.

Penn State predicts an active hurricane season: 16 named storms
The May 11 forecast made using a statistical model by Penn State's Michael Mann and alumnus Michael Kozar is calling for an active Atlantic hurricane season with 16 named storms, plus or minus 4 storms. Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the North Atlantic Oscillation (NAO), and other factors. The statistic model assumes that in 2013 the May 0.87°C above average temperatures in the MDR will persist throughout hurricane season, the El Niño phase will be neutral, and the North Atlantic Oscillation (NAO) will be near average.

The PSU team has been making Atlantic hurricane season forecasts since 2007, and these predictions have done pretty well, except for in 2012, when an expected El Niño did not materialize:

2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12.5, named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
2012 prediction: 10.5 named storms, Actual: 19

The wunderground community predicts an active hurricane season: 17 named storms
Over 100 members of the wunderground community have submitted their seasonal hurricane forecasts, which are compiled on trHUrrIXC5MMX's blog. The April 28 version of this list called for an average of 17 named storms, 8 hurricanes, and 4 intense hurricanes in the Atlantic. This list will be updated by June 3, so get your forecasts in by then! As usual, I am abstaining from making a hurricane season forecast. I figure there's no sense making a forecast that will be wrong nearly half the time; I prefer to stick to higher-probability forecasts.



NOAA predicts a below-average Eastern Pacific hurricane season: 13.5 named storms
NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 23, calls for a below-average season, with 11 - 16 named storms, 5 - 8 hurricanes, 1 - 4 major hurricanes, and an ACE index 60% - 105% of the median. The mid-point of these ranges gives us a forecast for 13.5 named storms, 6.5 hurricanes, and 2.5 major hurricanes, with an ACE index 82% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. So far in 2013, there has already been one named storm. On average, the 2nd storm of the year doesn't form until June 25.

NOAA predicts a below-average Central Pacific hurricane season: 2 tropical cyclones
NOAA's pre-season prediction for the Central Pacific hurricane season, issued on May 22, calls for a below-average season, with 1 - 3 tropical cyclones. An average season has 4 - 5 tropical cyclones, which include tropical depressions, tropical storms, and hurricanes. Hawaii is the primary land area affected by Central Pacific tropical cyclones.

The week ahead: 91E, and a heavy rainfall threat to Mexico
We're already behind last year's pace for named storms in both the Atlantic (where Tropical Storm Alberto formed on May 19, and Tropical Storm Beryl on May 26), and in the Eastern Pacific, where Bud formed on May 21 (the earliest date since record keeping began in 1949 for formation of the season's second named storm.) The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, is currently located in the Eastern Pacific. The MJO is relatively weak, but is helping boost the chances that Invest 91E in the Eastern Pacific will develop. On Friday, NHC was giving 91E a 20% of developing into a tropical cyclone by Sunday. The 12Z Friday runs of the GFS and ECMWF models were predicting that a weak circulation off the coast of Costa Rica, well east of the separate circulation currently called 91E, could develop into a tropical depression by Tuesday. This system is a threat to spread heavy rains to the coast of Mexico from Acapulco to Guatemala on Tuesday and Wednesday.

In the Atlantic, the models are depicting high wind shear through June 1 over the majority of the regions we typically see May tropical cyclone development--the Caribbean, Gulf of Mexico, and Bahamas. The GFS model is showing a decrease in wind shear over the Western Caribbean after June 1, which would argue for an increased chance of tropical storm development then (though wind shear forecasts more than 7 days in advance are highly unreliable.) The prospects for an early June named storm in the Atlantic are probably above average, though, given that the MJO may be active in the Atlantic during the first week of June.

Have a great holiday weekend, everyone!

Jeff Masters

Hurricane

Tornadoes and Climate Change: Huge Stakes, Huge Unknowns

By: JeffMasters, 4:05 PM GMT on May 23, 2013

In 2011, a series of violent severe storms swept across the Plains and Southeast U.S., bringing an astonishing six billion-dollar disasters in a three-month period. The epic tornado onslaught killed 552 people, caused $25 billion in damage, and brought three of the five largest tornado outbreaks since record keeping began in 1950. In May 2011, the Joplin, Missouri tornado did $3 billion in damage--the most expensive tornado in world history--and killed 158 people, the largest death toll from a U.S. tornado since 1947. An astounding 1050 EF-1 and stronger tornadoes ripped though the U.S. for the one-year period ending that month. This was the greatest 12-month total for these stronger tornadoes in the historical record, and an event so rare that we might expect it to occur only once every 62,500 years. Fast forward now to May 2012 - April 2013. Top-ten coldest temperatures on record across the Midwest during March and April of 2013, coming after a summer of near-record heat and drought in 2012, brought about a remarkable reversal in our tornado tally--the lowest 12-month total of EF-1 and stronger tornadoes on record--just 197. This was an event so rare we might expect it to occur only once every 3,000 - 4,000 years. And now, in May 2013, after another shattering EF-5 tornado in Moore, Oklahoma, residents of the Midwest must be wondering, are we back to the 2011 pattern? Which of these extremes is climate change most likely to bring about? Is climate change already affecting these storms? These are hugely important questions, but ones we don't have good answers for. Climate change is significantly impacting the environment that storms form in, giving them more moisture and energy to draw upon, and altering large-scale jet stream patterns. We should expect that this will potentially cause major changes in tornadoes and severe thunderstorms. Unfortunately, tornadoes and severe thunderstorms are the extreme weather phenomena we have the least understanding on with respect to climate change. We don't have a good enough database to determine how tornadoes may have changed in recent decades, and our computer models are currently not able to tell us if tornadoes are more likely to increase or decrease in a future warmer climate.


Video 1. Remarkable video of the tornado that hit Tuscaloosa, Alabama on April 27, 2011, part of the largest and most expensive tornado outbreak in U.S. history--the $10.2 billion dollar Southeast U.S. Super Outbreak of April 25 - 28, 2011. With damage estimated at $2.2 billion, the Tuscaloosa tornado was the 2nd most expensive tornado in world history, behind the 2011 Joplin, Missouri tornado. Fast forward to minute four to see the worst of the storm.


Figure 1. Will climate change increase the incidence of these sorts of frightening radar images? Multiple hook echoes from at least ten supercell thunderstorms cover Mississippi, Alabama, and Tennessee in this radar image taken during the height of the April 27, 2011 Super Outbreak, the largest and most expensive tornado outbreak in U.S. history. A multi-hour animation is available here.

Changes in past tornado activity difficult to assess due to a poor database
It's tough to tell if tornadoes may have changed due to a changing climate, since the tornado database is of poor quality for climate research. We cannot measure the wind speeds of a tornado directly, except in very rare cases when researchers happen to be present with sophisticated research equipment. A tornado has to run over a building and cause damage before an intensity rating can be assigned. The National Weather Service did not begin doing systematic tornado damage surveys until 1976, so all tornadoes from 1950 - 1975 were assigned a rating on the Fujita Scale (F-scale) based on old newspaper accounts and photos. An improved Enhanced Fujita (EF) scale to rate tornadoes was adopted in 2007. The transition to the new EF scale still allows valid comparisons of tornadoes rated, for example, EF-5 on the new scale and F5 on the old scale, but does create some problems for tornado researchers studying long-term changes in tornado activity. More problematic is the major changes in the Fujita-scale rating process that occurred in the mid-1970s (when damage surveys began), and again in 2001, when scientists began rating tornadoes lower because of engineering concerns and unintended consequences of National Weather Service policy changes. According to Brooks (2013), "Tornadoes in the early part of the official National Weather Service record (1950 - approximately 1975) are rated with higher ratings than the 1975 - 2000 period, which, in turn, had higher ratings than 2001 - 2007." All of these factors cause considerable uncertainty when attempting to assess if tornadoes are changing over time. At a first glance, it appears that tornado frequency has increased in recent decades (Figure 2). However, this increase may be entirely caused by factors unrelated to climate change:

1) Population growth has resulted in more tornadoes being reported. Heightened awareness of tornadoes has also helped; the 1996 Hollywood blockbuster movie Twister "played no small part" in a boom in reported tornadoes, according to tornado scientist Dr. Nikolai Dotzek.

2) Advances in weather radar, particularly the deployment of about 100 Doppler radars across the U.S. in the mid-1990s, has resulted in a much higher tornado detection rate.

3) Tornado damage surveys have grown more sophisticated over the years. For example, we now commonly classify multiple tornadoes along a damage path that might have been attributed to just one twister in the past.


Figure 2. The total number of U.S. tornadoes since 1950 has shown a substantial increase. Image credit: NOAA/NCDC.


Figure 3. The number of EF-0 (blue line) and EF-1 and stronger tornadoes (maroon squares) reported in the U.S. since 1950. The rise in number of tornadoes in recent decades is seen to be primarily in the weakest EF-0 twisters. As far as we can tell (which isn't very well, since the historical database of tornadoes is of poor quality), there is not a decades-long increasing trend in the numbers of tornadoes stronger than EF-0. Since these stronger tornadoes are the ones most likely to be detected, this implies that climate change, as yet, is not having a noticeable impact on U.S. tornadoes. Image credit: Kunkel, Kenneth E., et al., 2013, "Monitoring and Understanding Trends in Extreme Storms: State of Knowledge," Bull. Amer. Meteor. Soc., 94, 499–514, doi: http://dx.doi.org/10.1175/BAMS-D-11-00262.1


Figure 4. Insured damage losses in the U.S. due to thunderstorms and tornadoes, as compiled by Munich Re. Damages have increased sharply in the past decade, but not enough to say that an increase in tornadoes and severe thunderstorms may be to blame.

Stronger tornadoes do not appear to be increasing
Tornadoes stronger than EF-0 on the Enhanced Fujita Scale (or F0 on the pre-2007 Fujita Scale) are more likely to get counted, since they tend to cause significant damage along a long track. Thus, the climatology of these tornadoes may offer a clue as to how climate change may be affecting severe weather. If the number of strong tornadoes has actually remained constant over the years, we should expect to see some increase in these twisters over the decades, since more buildings have been erected in the paths of tornadoes. However, if we look at the statistics of U.S. tornadoes stronger than EF-0 or F-0 since 1950, there does not appear to be any increase in their number (Figure 3.) Damages from thunderstorms and tornadoes have shown a significant increase in recent decades (Figure 4), but looking at damages is a poor way to determine if climate change is affecting severe weather, since there are so many human factors involved. A study in Environmental Hazards (Simmons et al., 2012) found no increase in tornado damages from 1950 - 2011, after normalizing the data for increases in wealth and property. Also, Bouwer (BAMS, 2010) reviewed 22 disaster loss studies world-wide, published 2001 - 2010; in all 22 studies, increases in wealth and population were the "most important drivers for growing disaster losses." His conclusion: human-caused climate change "so far has not had a significant impact on losses from natural disasters." Studies that normalize disaster data are prone to error, as revealed by a 2012 study looking at storm surge heights and damages. Given the high amount of uncertainty in the tornado and tornado damage databases, the conclusion of the "official word" on climate science, the 2007 United Nations IPCC report, pretty much sums things up: "There is insufficient evidence to determine whether trends exist in small scale phenomena such as tornadoes, hail, lighting, and dust storms." Until a technology is developed that can reliably detect all tornadoes, there is no hope of determining how tornadoes might be changing in response to a changing climate. According to Doswell (2007): "I see no near-term solution to the problem of detecting detailed spatial and temporal trends in the occurrence of tornadoes by using the observed data in its current form or in any form likely to evolve in the near future."


Figure 5. Wind shear from the surface to 6 km altitude in May on days with days with higher risk conditions for severe weather (upper-10% instability and wind shear) over the South Central U.S. has shown no significant change between 1950 - 2010. Image credit: Brooks, 2013, "The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data", Atmospheric Research Volumes 67-68, July-September 2003, Pages 73-94.


Figure 6. Six-hourly periods per year with environments supportive of significant severe thunderstorms in the U.S. east of the Rocky Mountains. The line is a local least-squares regression fit to the series, and shows no significant change in environments supportive of significant severe thunderstorms in recent decades. Image credit: Brooks, H.E., and N. Dotek, 2008, "The spatial distribution of severe convective storms and an analysis of their secular changes", Climate Extremes and Society

How are the background conditions that spawn tornadoes changing?
An alternate technique to study how climate change may be affecting tornadoes is look at how the large-scale environmental conditions favorable for tornado formation have changed through time. Moisture, instability, lift, and wind shear are needed for tornadic thunderstorms to form. The exact mix required varies considerably depending upon the situation, and is not well understood. However, Brooks (2003) attempted to develop a climatology of weather conditions conducive for tornado formation by looking at atmospheric instability (as measured by the Convective Available Potential Energy, or CAPE), and the amount of wind shear between the surface and 6 km altitude. High values of CAPE and surface to 6 km wind shear are conducive to formation of tornadic thunderstorms. The regions they analyzed with high CAPE and high shear for the period 1997-1999 did correspond pretty well with regions where significant (F2 and stronger) tornadoes occurred. Riemann-Campe et al. (2009) found that globally, CAPE increased significantly between 1958 - 2001. However, little change in CAPE was found over the Central and Eastern U.S. during spring and summer during the most recent period they studied, 1979 - 2001. Brooks (2013) found no significant trends in wind shear over the U.S. from 1950 - 2010 (Figure 5.) A preliminary report issued by NOAA’s Climate Attribution Rapid Response Team in July 2011 found no trends in CAPE or wind shear over the lower Mississippi Valley over the past 30 years.


Figure 7. Change in the number of days per year with a high severe thunderstorm potential as predicted by the climate model (A2 scenario) of Trapp et al. 2007, due to predicted changes in wind shear and Convective Available Potential Energy (CAPE). Most of the U.S. east of the Rocky Mountains is expected to see 1 - 2 additional days per year with the potential for severe thunderstorms. The greatest increase in potential severe thunderstorm days (three) is expected along the North and South Carolina coast. Image credit: NASA.

How will tornadoes and severe thunderstorms change in the future?
Using a high-resolution regional climate model (25 km grid size) zoomed in on the U.S., Trapp et al. (2007) and Trapp et al. (2009) found that the decrease in 0-6 km wind shear in the late 21st century would more than be made up for by an increase in instability (CAPE). Their model predicted an increase in the number of days with high severe storm potential for most of the U.S. by the end of the 21st century, particularly for locations east of the Rocky Mountains (Figure 7.) Brooks (2013) also found that severe thunderstorms would likely increase over the U.S. by the end of the century, but theorized that the severe thunderstorms of the future might have a higher proportion causing straight-line wind damage, and slightly lower proportion spawning tornadoes and large hail. For example, a plausible typical future severe thunderstorm day many decades from now might have wind shear lower by 1 m/s, but a 2 m/s increase in maximum thunderstorm updraft speed. This might cause a 5% reduction in the fraction of severe thunderstorms spawning tornadoes, but a 5% increase in the fraction of severe thunderstorms with damaging straight-line winds. He comments: "However, if the number of overall favorable environments increases, there may be little change, if any, in the number of tornadoes or hailstorms in the US, even if the relative fraction decreases. The signals in the climate models and our physical understanding of the details of storm-scale processes are sufficiently limited to make it extremely hazardous to make predictions of large changes or to focus on small regions. Projected changes would be well within error estimates."


Figure 8. From 1995 (the first year we have wind death data) through 2012, deaths from high winds associated with severe thunderstorms accounted for 8% of all U.S. weather fatalities, while tornadoes accounted for 13%. Data from NOAA.

Severe thunderstorms are capable of killing more people than tornadoes
If the future climate does cause fewer tornadoes but more severe thunderstorms, this may not end up reducing the overall deaths and damages from these dangerous weather phenomena. In 2012, the warmest year in U.S. history, the death toll from severe thunderstorms hit 104--higher than the 70 people killed by tornadoes that year. Severe thunderstorms occur preferentially during the hottest months of the year, June July and August, and are energized by record heat. For example, wunderground weather historian Christopher C. Burt called the number of all-time heat records set on June 29, 2012 “especially extraordinary,” and on that day, an organized thunderstorm complex called a derecho swept across a 700-mile swath of the Ohio Valley and Mid-Atlantic, killing thirteen people and causing more than $1 billion in damage. The amount of energy available to the derecho was extreme, due to the record heat. The derecho knocked out power to 4 million people for up to a week, in areas where the record heat wave was causing high heat stress. Heat claimed 34 lives in areas without power in the week following the derecho. Excessive heat has been the number one cause of weather-related deaths in the U.S since 1995, killing more than twice as many people as tornadoes have. Climate models are not detailed enough to predict how organized severe thunderstorm events such as derechos might change in a future warmer climate. But a warmer atmosphere certainly contributed to the intensity of the 2012 derecho, and we will be seeing a lot more summers like 2012 in coming decades. A future with sharply increased damages and deaths due to more intense severe thunderstorms and derechos is one nasty climate change surprise that may lurk ahead.


Figure 9. Lightning over Tucson, Arizona on August 14, 2012. A modeling study by Del Genio et al.(2007) predicts that lighting will increase by 6% by the end of the century, potentially leading to an increase in lightning-triggered wildfires. Image credit: wunderphotographer ChandlerMike.

Lightning may increase in a warmer climate
Del Genio et al. (2007) used a climate model with doubled CO2 to show that a warming climate would make the atmosphere more unstable (higher CAPE) and thus prone to more severe weather. However, decreases in wind shear offset this effect, resulting in little change in the amount of severe weather in the Central and Eastern U.S. late this century. However, they found that there would likely be an increase in the very strongest thunderstorms. The speed of updrafts in thunderstorms over land increased by about 1 m/s in their simulation, since upward moving air needed to travel 50 - 70 mb higher to reach the freezing level, resulting in stronger thunderstorms. In the Western U.S., the simulation showed that drying led lead to fewer thunderstorms overall, but the strongest thunderstorms increased in number by 26%, leading to a 6% increase in the total amount of lighting hitting the ground each year. If these results are correct, we might expect more lightning-caused fires in the Western U.S. late this century, due to increased drying and more lightning. Only 12% of U.S. wildfires are ignited by natural causes, but these account for 52% of the acres burned (U.S. Fire Administration, 2000). So, even a small change in lightning flash rate has important consequences. Lightning is also a major killer, as an average of 52 people per year were killed by lightning strikes over the 30-year period ending in 2012, accounting for 6% of all U.S. weather-related fatalities.

Summary
We currently do not know how tornadoes and severe thunderstorms may be changing due to climate change, nor is there hope that we will be able to do so in the foreseeable future. It does not appear that there has been an increase in U.S. tornadoes stronger than EF-0 in recent decades, but climate change appears to be causing more extreme years--both high and low--of late. Tornado researcher Dr. Harold Brooks of the National Severe Storms Laboratory in Norman, Oklahoma said in a 2013 interview on Andrew Revkin's New York Times dotearth blog: "there’s evidence to suggest that we have seen an increase in the variability of tornado occurrence in the U.S." Preliminary research using climate models suggests that we may see an increase in the number of severe thunderstorms capable of producing tornadoes over the U.S. late this century, but these thunderstorms will be more likely to produce damaging straight-line winds, and less likely to produce tornadoes and large hail. This will not necessarily result in a reduction in deaths and damages, though, since severe thunderstorms can be just as dangerous and deadly as tornadoes--especially when they knock out power to areas suffering high-stress heat waves. Research into climate change impacts on severe weather is just beginning, and much more study is needed.

Other analyses of tornadoes and climate change
Making Sense of the Moore Tornado in a Climate Context by Andrew Freedman of climatecentral.org

Tornadoes, Extreme Weather And Climate Change, Revisited by Joe Romm at climateprogress.org

Seeking Clarity on Terrible Tornadoes in a Changing Climate by Andrew Revkin of the New York Times has links to four other excellent blogs on the subject.


Video 2. Dr. Harold Brooks of the National Severe Storms Laboratory in Norman, Okla., gave a video interview at a tornado and climate research conference held at Columbia University earlier this year. He discusses why we don't issue seasonal tornado forecasts, but doesn't discuss climate change.

References
Brooks, H.E., 2013, "Severe thunderstorms and climate change," Atmospheric Research, Volume 123, 1 April 2013, Pages 129–138, http://dx.doi.org/10.1016/j.atmosres.2012.04.002.

Brooks, H.E., J.W. Lee, and J.P. Craven, 2003, "The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data", Atmospheric Research Volumes 67-68, July-September 2003, Pages 73-94.

Brooks, H.E., and N. Dotek, 2008, "The spatial distribution of severe convective storms and an analysis of their secular changes", Climate Extremes and Society, edited by Henry F. Diaz, Richard J. Murnane,

Doswell, C.A., 2007, "Small Sample Size and Data Quality Issues Illustrated Using Tornado Occurrence Data", E-Journal of Severe Storms Meteorology Vol 2, No. 5 (2007).

Del Genio, A.D., M-S Yao, and J. Jonas, 2007,
Will moist convection be stronger in a warmer climate?, Geophysical Research Letters, 34, L16703, doi: 10.1029/2007GL030525.

Kunkel, Kenneth E., et al., 2013, "Monitoring and Understanding Trends in Extreme Storms: State of Knowledge," Bull. Amer. Meteor. Soc., 94, 499–514, doi: http://dx.doi.org/10.1175/BAMS-D-11-00262.1

Marsh, P.T., H.E. Brooks, and D.J. Karoly, 2007, Assessment of the severe weather environment in North America simulated by a global climate model, Atmospheric Science Letters, 8, 100-106, doi: 10.1002/asl.159.

Riemann-Campe, K., Fraedrich, K., and F. Lunkeit, 2009, Global climatology of Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) in ERA-40 reanalysis, Atmospheric Research Volume 93, Issues 1-3, July 2009, Pages 534-545, 4th European Conference on Severe Storms.

Simmons, K.M., Dutter, D., and Pielke, R., 2012, "Normalized Tornado Damage in the United States: 1950-2011," DOI: 10.1080/17477891.2012.738642

Trapp, R.J., N.S. Diffenbaugh, H.E. Brooks, M.E. Baldwin, E.D. Robinson, and J.S. Pal, 2007, Severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing, PNAS 104 no. 50, 19719-19723, Dec. 11, 2007.

Trapp, R. J., Diffenbaugh, N. S., & Gluhovsky, A., 2009, "Transient response of severe thunderstorm forcing to elevated greenhouse gas concentrations," Geophysical Research Letters, 36(1).

U.S. Fire Administration, “2000 wildland fire season,” U.S. Fire Administration Topical Fire Research Series, vol. 1, Issue 2, 4 pp.

Jeff Masters

Tornado Climate Change

Moore Tornado an EF-5; $2 Billion Damage Estimate: 3rd Costliest Tornado in History

By: JeffMasters, 3:22 PM GMT on May 22, 2013

The Moore, Oklahoma tornado of May 20, 2013 is now ranked an EF-5, making it one of only 59 U.S. tornadoes to achieve that distinction since record keeping began in 1950. The National Weather Service in Norman, Oklahoma announced Tuesday that their damage survey teams found an area of EF-5 damage near Briarwood Elementary School, with winds of 200 - 210 mph indicated. There were no EF-5 tornadoes observed in 2012, and the last time the U.S. had an EF-5 was on May 24, 2011, when the Oklahoma towns of Calumet, El Reno, Piedmont, and Guthrie were hit by an EF-5 with 210+ mph winds that killed nine people. The maximum width of the 2013 Moore tornado's damage swath was a huge 1.3 miles. Detailed damage survey information in Google Earth Format provided by the Norman, OK NWS office shows that the typical width of the EF-0 and greater damage swath was about 0.6 miles, and the EF-4 damage area was about 0.1 miles across at its widest. EF-4 damage occurred along approximately 4 miles of the tornado's 17-mile long path. The damage swath from the May 20, 2013 tornado as it cut through the most densely built up portions of Moore was roughly 1.5 times as wide as the one from the May 3, 1999 EF-5 tornado. That tornado was the 4th costliest in history ($1.4 billion 2011 dollars), so it is a good bet that the 2013 Moore tornado will end up being even more expensive. This morning, the Oklahoma Insurance Department said the preliminary tornado damage estimate could top $2 billion. This would make the 2013 Moore tornado the 2nd most expensive tornado in history (as ranked by NOAA/SPC) or 3rd most expensive (as ranked by insurance broker Aon Benfield.) The nine billion-dollar tornadoes (2013 dollars) are:

1) Joplin, Missouri, May 22, 2011, $2.9 billion
2) Tuscaloosa, Alabama, April 27, 2011, $2.3 billion (not in SPC's list)
3) Moore, Oklahoma, May 20, 2013, $2 billion
4) Topeka, Kansas, June 8, 1966, $1.8 billion
5) Lubbock, Texas, May 11, 1970, $1.5 billion
6) Bridge Creek-Moore, Oklahoma, May 3, 1999, $1.4 billion
7) Hackleburg, Alabama, April 27, 2011, $1.3 billion (not in SPC's list)
8) Xenia, Ohio, April 3, 1974, $1.1 billion
9) Omaha, Nebraska, May 6, 1975, $1 billion


Figure 1. The Moore, Oklahoma tornado of May 20, 2013 (AP Photo/Alonzo Adams)


Figure 2. The damage swath of the Moore, Oklahoma tornado of May 20, 2013. EF-4 damage (red colors) occurred along roughly 4 miles of the 17-mile path, and the EF-4 damage swath was up to 0.1 miles wide. The tornado's maximum width of 1.3 miles (EF-0 and greater damage) occurred over a relatively small portion of the path, before the storm reached Moore. Image credit: NWS Norman.


Figure 3. On May 20, 2013, a supercell thunderstorm in central Oklahoma spawned a destructive tornado that passed just south of Oklahoma City. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this natural-color image of the storm system at 2:40 p.m. Central Daylight Time (19:40 Universal Time), just minutes before the devastating twister began. The red line on the image depicts the tornado’s track. Image credit: NASA Earth Observatory.

There have been bigger tornadoes
The 1.3 mile maximum width of the 2013 Moore tornado's damage swath was not a record. Wikipedia documents that the EF-3 Edmonson, Texas tornado of May 31, 1968 had a damage path width between 2 and 3 miles (3.2 and 4.8 km) wide. The EF-4 Wilber - Hallam, Nebraska tornado on May 22, 2004 was of similar size, with a damage path up to 2.5 miles wide. Doppler radar measurements indicate that the May 4, 1999 Mulhall, Oklahoma EF-4 tornado--which thankfully passed mostly over farmland--would have caused damage over a path 4 miles wide at its peak size, had it encountered a built-up area. The EF-5 tornado that devastated Greensburg, Kansas on May 4, 2007 was 1.7 miles wide.


Figure 4. Damage swath of the Wilber - Hallam, Nebraska EF-4 tornado of May 22, 2004 was up to 2.5 miles wide, making it one of the largest tornadoes on record.


Figure 5. Severe weather outlook for Wednesday, May 22, calls for a "Slight Risk" of severe weather over portions of the Ohio Valley and Northeast U.S. You can follow today's severe weather from our Severe Weather page.

No tornadoes reported on Tuesday; "Slight Risk" of severe weather on Wednesday
The severe weather outbreak of May 18 - 22 peaked on Sunday and Monday. We did not record any tornadoes on Tuesday, though there were many reports of large hail and damaging winds, including three thunderstorms with wind gusts over 74 mph. Tuesday was the first day since May 14 that no tornadoes were recorded in the U.S. And after issuing four consecutive "Moderate Risk" outlooks for severe weather, NOAA's Storm Prediction Center (SPC) is going with only a "Slight Risk" for severe weather on Wednesday in the U.S., with the main severe weather action expected to affect portions of the Ohio Valley and Northeast U.S. The primary threat will be straight-line wind damage and large hail, though we can't rule out a few tornadoes. During the three-day period May 18 - May 20, 70 tornadoes (preliminary) were recorded by SPC.


Video 1. Charles Cook caught the birth of the May 20, 2013 tornado at Newcastle, OK. It moved from there to Moore where it caused catastrophic devastation.


Video 2. NOAA's GOES-East satellite collected this view of the storm system that spawned a deadly tornado over Moore, Oklahoma on May 20, 2013. The animation runs from 10:45 a.m. through 6:45 p.m., Central Daylight Time. Images courtesy NASA GOES Project Science: ‪http://goes.gsfc.nasa.gov/‬

The Norman, OK NWS office has an excellent page with detailed info on the Moore tornado.

I did a 10-minute Skype interview with democracynow.org on Tuesday morning, discussing the Moore tornado.

I greatly appreciate all the valuable links members of the WU community have posted here, and I have used many of them in my posts over the past day. Keep up the great work!

How to help
Portlight Strategies, an organization that supports disaster victims with disabilities, will be working with shelter operators and disability stakeholder organizations in Oklahoma to serve the needs of people with disabilities. Further information and how to offer additional support can be found on their website.

Donations can be made to American Red Cross disaster relief at redcross.org/weather or by texting WEATHER to 90999 to donate $10.

Donations can be made on The Salvation Army's website or by texting STORM to 80888 to donate $10. You can also call to make donations of other monetary amounts at (800) 725-2769.

Jeff Masters

Tornado

Violent EF-5 Tornado Causes Catastrophic Damage in Moore, Oklahoma

By: JeffMasters, 4:00 PM GMT on May 21, 2013

A massive and violent tornado 1.3 miles wide smashed through Moore, Oklahoma near 3 pm CDT Monday, causing catastrophic damage along a 17-mile long path. The National Weather Service in Norman, Oklahoma announced that it has found at least one area of EF-5 damage near Briarwood Elementary School, with winds of 200 - 210 mph. Damage was extreme and covered a huge area, and many buildings swept away down to their foundations. The tornado was on the ground for 51 minutes, from 2:45 - 3:36 pm CDT. This averages out to a 20 mph forward speed, and the tornado was initially moving even slower--20 mph. Violent tornadoes typically move considerably faster, sometimes at speeds in excess of 60 mph, and the relatively slow motion of the Moore tornado contributed to the extreme damage by exposing buildings to a longer period of violent winds than usual. A tornado warning for the storm was issued at 2:40 pm CDT, sixteen minutes before it touched down. On average, a tornado warning comes about thirteen minutes before touchdown. A tornado emergency was declared for Moore at 3:01 pm, about twenty minutes before the tornado entered the west side of the city. The debris ball from the tornado, as seen on Doppler radar, expanded to over two miles in diameter, and debris was carried over 100 miles from Moore. The National Weather Service office in Tulsa, Oklahoma reported at 4:13 pm CDT that they were "seeing reports of light tornado debris falling in the Tulsa metro area again this evening, likely from the Moore area." Tulsa is 100 miles east-northeast of Moore.


Figure 1. The Moore, Oklahoma tornado of May 20, 2013. Image credit: WIkipedia.


Figure 2. A fire burns in the Tower Plaza Addition in Moore, Oklahoma, following a tornado on Monday, May 20, 2013. Photo: Sue Ogrocki, ASSOCIATED PRESS.


Figure 3. Flipped vehicles are piled up outside the heavily damaged Moore Medical Center in Moore, Oklahoma, after a powerful tornado ripped through the area on May 20, 2013. On the enhanced Fujita Scale, the maximum degree of damage (11), indicating EF-5 winds of 210 mph, is "Significant damage to building envelope" on an institutional building like a hospital or government office. The damage to the Moore Medical Center may qualify as EF-5 damage. Image credit: Brett Deering/Getty Images)

Here is the tornado warning that was issued at 2:40 pm CDT, sixteen minutes before the tornado touched down:

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE NORMAN OK
240 PM CDT MON MAY 20 2013

THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A

* TORNADO WARNING FOR...
NORTHWESTERN MCCLAIN COUNTY IN CENTRAL OKLAHOMA...
SOUTHERN OKLAHOMA COUNTY IN CENTRAL OKLAHOMA...
NORTHEASTERN GRADY COUNTY IN CENTRAL OKLAHOMA...
NORTHERN CLEVELAND COUNTY IN CENTRAL OKLAHOMA...

* UNTIL 315 PM CDT

* AT 238 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED NEAR NEWCASTLE...AND MOVING EAST AT 20 MPH.

IN ADDITION TO A TORNADO...LARGE DAMAGING HAIL UP TO GOLF BALL SIZE IS EXPECTED WITH THIS STORM.

* LOCATIONS IMPACTED INCLUDE...NORMAN...MOORE...NEWCASTLE...BRIDGE CREEK AND VALLEY BROOK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW IN A STORM SHELTER OR AN INTERIOR ROOM OF A STURDY BUILDING. STAY AWAY FROM DOORS AND WINDOWS.


At 3:01 pm CDT, five minutes after the tornado touched down and about twenty minutes before the tornado hit the west side of Moore, the NWS issued a "Tornado Emergency" advisory:


BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE NORMAN OK
301 PM CDT MON MAY 20 2013

THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A

* TORNADO WARNING FOR...
NORTHWESTERN MCCLAIN COUNTY IN CENTRAL OKLAHOMA...
SOUTHERN OKLAHOMA COUNTY IN CENTRAL OKLAHOMA...
NORTHERN CLEVELAND COUNTY IN CENTRAL OKLAHOMA...

* UNTIL 345 PM CDT

* AT 259 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS AND STORM SPOTTERS WERE TRACKING A LARGE AND EXTREMELY DANGEROUS TORNADO NEAR NEWCASTLE. DOPPLER RADAR SHOWED THIS TORNADO MOVING NORTHEAST AT 20 MPH.

THIS IS A TORNADO EMERGENCY FOR MOORE AND SOUTH OKLAHOMA CITY.

IN ADDITION TO A TORNADO...LARGE DESTRUCTIVE HAIL UP TO TENNIS BALL SIZE IS EXPECTED WITH THIS STORM.

* LOCATIONS IMPACTED INCLUDE...MIDWEST CITY...MOORE...NEWCASTLE...STANLEY DRAPER LAKE...TINKER AIR FORCE BASE AND VALLEY BROOK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THIS IS AN EXTREMELY DANGEROUS AND LIFE THREATENING SITUATION. IF YOU CANNOT GET UNDERGROUND GO TO A STORM SHELTER OR AN INTERIOR ROOM OF A STURDY BUILDING NOW.

TAKE COVER NOW IN A STORM SHELTER OR AN INTERIOR ROOM OF A STURDY BUILDING. STAY AWAY FROM DOORS AND WINDOWS.


Figure 4. The annual number of EF-3 and stronger tornadoes, 1954 - 2012. The greatest number of these dangerous tornadoes was 131 in 1974, the year of the notorious "Super Outbreak." The minimum was just 15, set in 1987. The average is 43 per year. Image credit: NOAA.


Figure 5. Violent EF-4 and EF-5 tornadoes make up only 1% of all tornadoes, but account for well over half of all deaths. Image credit: tornadoproject.com.

A very bad tornado in an otherwise quiet year for violent tornadoes
According to NOAA, the U.S. has averaged 43 EF-3 or stronger tornadoes per year during the period 1954 - 2012. With tornado season nearly half over, we are well below the average pace for these most dangerous tornadoes--only nine EF-3 and EF-4 tornadoes have been recorded so far in 2013. An average year should have had at least fifteen of these tornadoes by this point in the year. Here are the nine EF-3 and stronger tornadoes so far in 2013:

EF-5, 200 - 210 mph winds, May 20, Moore, Oklahoma. Many deaths and injuries.
EF-4, 166 - 200 mph winds, May 19, Shawnee, Oklahoma. 2 deaths.
EF-4, 180 mph winds, May 15, Granbury, TX. 6 deaths, 24+ injuries.
EF-4, 165 - 185 mph winds, May 18, Rozel, Kansas.
EF-4, 170 mph winds, February 10, Hattiesburg, MS. 0 deaths, 82 injuries,
EF-3, 140 mph winds, May 15, Cleburne, TX. No deaths or injuries.
EF-3, 160 mph winds, January 30, Adairsville, GA. 1 death, 17 injuries, 363 buildings damaged or destroyed.
EF-3, 145 mph winds, April 11, Kemper County, AL. 1 death, 9 injuries.
EF-3, 136 - 165 mph winds, May 19, Luther - Carney, Oklahoma.

Moore tornado likely to be one of the five most damaging tornadoes in history
Moore has the unenviable distinction of having previously experienced the 4th costliest tornado in world history, the notorious May 3, 1999 Bridgecreek-Moore EF-5 tornado. There have been only six billion-dollar (2011 dollars) tornadoes in history:

1) Joplin, Missouri, May 22, 2011, $2.8 billion
2) Topeka, Kansas, June 8, 1966, $1.7 billion
3) Lubbock, Texas, May 11, 19780, $1.5 billion
4) Bridge Creek-Moore, Oklahoma, May 3, 1999, $1.4 billion
5) Xenia, Ohio, April 3, 1974, $1.1 billion
6) Omaha, Nebraska, May 6, 1975, $1 billion

The May 3, 1999 Bridge Creek-Moore tornado killed 36 people and injured 583. It damaged or destroyed 8132 homes, 1041 apartments, 260 businesses, 11 public buildings and seven churches. According to rough estimates of the size of the damaged area made by helicopters operated by news9.com and kfor.com, the damage footprint from the May 20, 2013 tornado is easily twice as large. I expect that after the damage tally from the May 20 tornado is added up, Moore will hold two of the top five spots on the list of most damaging tornadoes in history, and the May 20 tornado may approach the Joplin tornado as the costliest twister of all-time.


Figure 6. Severe weather outlook for Tuesday, May 21, calls for a "Moderate Risk" of severe weather over Northeast Texas, Southwest Arkansas, and small portions of Southeast Oklahoma and Northwest Louisiana. You can follow today's severe weather outbreak from our Severe Weather page.

Here we go again: Another big severe weather day today in the Midwest
The Moore tornado was the first of twenty tornadoes reported on May 20--the third consecutive day with twenty or more tornadoes in the Midwest. Each of these days had a "Moderate Risk" of severe weather, as advised by NOAA's Storm Prediction Center (SPC.) The SPC is calling for a fourth consecutive day with a "Moderate Risk" of severe weather today (Tuesday), with the greatest danger occurring over Northeast Texas, Southwest Arkansas, and small portions of Southeast Oklahoma and Northwest Louisiana. Once again, we can expect to see isolated supercells capable of spawning dangerous violent tornadoes during the late afternoon and early evening hours. The severe weather outbreak moves east and will begin to wind down on Wednesday, when only a "Slight Risk" of severe weather is expected over New York, Ohio, Pennsylvania, plus northern portions of Kentucky, West Virginia, and Maryland.


Video 1. Remarkable time-lapse sequence of the Moore, Oklahoma tornado on May 20, 2013, taken from a news helicopter.


Video 2. Stormchasers caught the dramatic sounds and sights of the Moore, Oklahoma tornado of May 20, 2013 as it moved through the city.


Video 3. Video of the Moore, Oklahoma tornado of May 20, 2013 taken from a smartphone as the tornado moved across an open field.

Jeff Lechus filmed this remarkable video from his car while trying to get to his son. The flying debris near his car was extremely dangerous, and he is lucky he is alive.

Wunderground's weather historian Christopher C. Burt discusses the deadliest tornadoes of all time in his April, 2011 post. Since that post, the Joplin, Missouri tornado of May 22, 2011, killed 158 people, making it the 7th deadliest tornado in history.

My post, 2011: Year of the Tornado from December 2011, detailing the remarkable tornado records set in 2011.

I saved a 10-frame animation of the radar reflectivity image from the Moore tornado here.

I greatly appreciate all the valuable links members of the WU community have posted here, and I have used many of them in my posts over the past day. Keep up the great work!

How to help
Portlight Strategies, an organization that supports disaster victims with disabilities, will be working with shelter operators and disability stakeholder organizations in Oklahoma to serve the needs of people with disabilities. Further information and how to offer additional support can be found on their website.

Donations can be made to American Red Cross disaster relief at redcross.org/weather or by texting WEATHER to 90999 to donate $10.

Donations can be made on The Salvation Army's website or by texting STORM to 80888 to donate $10. You can also call to make donations of other monetary amounts at (800) 725-2769.

Jeff Masters

Tornado

Violent tornado devastates Moore, Oklahoma

By: JeffMasters, 12:48 AM GMT on May 21, 2013

A massive and violent tornado at least a mile wide smashed through Moore, Oklahoma near 3 pm CDT Monday, causing catastrophic damage along a 20-mile long path. The National Weather Service in Norman, Oklahoma has rated the tornado at least an EF-4 (166 - 200 mph winds), and detailed damage surveys may upgrade this rating to the top-end EF-5 level in the coming days. Damage was extreme and covered a huge area, and many buildings swept away down to their foundations. The tornado was on the ground for 40 minutes, from 2:56 - 3:36 pm CDT, and a tornado warning for the storm was issued at 2:40 pm CDT, sixteen minutes before it touched down. The debris ball from the tornado, as seen on Doppler radar, expanded to over two miles in diameter, and debris was carried over 100 miles from Moore. The National Weather Service office in Tulsa, Oklahoma reported at 4:13 pm CDT that they were "seeing reports of light tornado debris falling in the Tulsa metro area again this evening, likely from the Moore area." Tulsa is 100 miles east-northeast of Moore.


Figure 1. The news helicopter from kfor.com caught this image of the shocking near-total destruction of a huge area of Moore, Oklahoma, on May 20, 2013.


Figure 2. Radar reflectivity image taken at 3:06 pm CDT May 20, 2013 of the supercell thunderstorm that spawned the Moore, Oklahoma tornado. A classic "hook echo" terminates in a sphere of colors with high-reflectivity purple at its core, the signature of a "debris ball" of debris hurled into the air by a violent tornado.


Figure 3. Terminal Doppler Weather Radar velocity image taken at 3:06 pm CDT May 20, 2013 of the supercell thunderstorm that spawned the Moore, Oklahoma tornado. Note the couplet of dark red colors right next to dark blues, showing that the air was moving both towards the radar and away from it within a short distance, indicating a tight rotation of the tornado's parent mesocyclone. The velocity folding inside this couplet is extremely unusual to see in Doppler radar data and shows that the winds were so fast, the radar misidentified their speed. This, along with the extremely low beam height (0.5°), suggests that the radar was scanning the upper parts of the tornado and its immediate environment. Thanks go to wunderground's tornado expert, Dr. Rob Carver, for annotating this image.

Moore tornado likely to be one of the five most damaging tornadoes in history
Moore has the unenviable distinction of having previously experienced the 4th costliest tornado in world history, the notorious May 3, 1999 Bridgecreek-Moore EF-5 tornado. There have been only six billion-dollar (2011 dollars) tornadoes in history:

1) Joplin, Missouri, May 22, 2011, $2.8 billion
2) Topeka, Kansas, June 8, 1966, $1.7 billion
3) Lubbock, Texas, May 11, 19780, $1.5 billion
4) Bridge Creek-Moore, Oklahoma, May 3, 1999, $1.4 billion
5) Xenia, Ohio, April 3, 1974, $1.1 billion
6) Omaha, Nebraska, May 6, 1975, $1 billion

The May 3, 1999 Bridge Creek-Moore tornado killed 36 people and injured 583. It damaged or destroyed 8132 homes, 1041 apartments, 260 businesses, 11 public buildings and seven churches. According to rough estimates of the size of the damaged area made by helicopters operated by news9.com and kfor.com, the damage footprint from the May 20, 2013 tornado is easily twice as large. I expect that after the damage tally from the May 20 tornado is added up, Moore will hold two of the top five spots on the list of most damaging tornadoes in history, and the May 20 tornado may approach the Joplin tornado as the costliest twister of all-time.


Figure 4. Comparison of the tracks of the May 3, 1999 and May 20, 2013 tornadoes in Moore, Oklahoma. Both tornadoes caused near-total destruction along a significant portion of their paths. Image credit: ‪NWS Norman, #Okwx‬ ‪pic.twitter.com/4BmUWIyNbo‬


Video 1. Short storm chaser clip of the May 20, 2013 Moore, Oklahoma tornado. The video is notable for the large amount of flying debris seen swirling around the funnel.

I urge you to give generously to the victims of this tragedy, whether through your monetary donations to disaster relief organizations like redcross.org or portlight.org, or with your prayers to those afflicted.

Jeff Masters

Tornado

Tornadoes Slam 5-State Area, Killing Two; Outbreak Continues Today

By: JeffMasters, 1:29 PM GMT on May 20, 2013

The Midwest U.S. is under the gun again today, as a potent storm system that spawned a preliminary count of 24 tornadoes in five states on Sunday reloads and prepares to dish out another afternoon and evening of atmospheric mayhem. Sunday's tornadoes swept through Oklahoma, Kansas, Iowa, Missouri, and Illinois, with Oklahoma bearing the brunt of the assault. The outbreak's only deadly tornado--preliminarily rated as en EF-5 with 166 - 200 mph winds--hit Shawnee, Oklahoma, a town of 30,000 located 35 miles southeast of Oklahoma City. The twister leveled a trailer park, killing two people, and blew a semi-trailer off of an expressway overpass on I-40. At least 21 people were injured and 300 homes destroyed over the five-state area by the tornadoes. The 24 tornadoes from May 19 make it the biggest day for tornadoes in the U.S. this spring, and the highest number reported in one day since January 30, when 44 tornadoes touched down from Georgia to Indiana.


Figure 1. The Shawnee, Oklahoma tornado at 6:44 pm CDT May 19, 2013, as it passed just NW of Shawnee. The tornado killed two people in a mobile home park in Shawnee. Viewer submitted photo. #okwx pic.twitter.com/UCH9e8o9G8 Matt Mahler@themahler


Figure 2. The Shawnee tornado hurled a semi-trailer off of an expressway overpass at Highway 117 and I-40 in Oklahoma, and toppled another semi. Four people who sheltered under this overpass were injured, one seriously, and taken to the hospital. Highway overpasses can act to amplify a tornado's winds, and are very dangerous places to be during a tornado. According to the NWS in Norman Oklahoma, during the tornado outbreak of May 3, 1999, tornadoes crossed three highway overpasses, and at all three locations, there was a fatality. One of the fatalities occurred from an EF-2 tornado in a rural area, which suggests that a tornado need not be a large, violent tornado with a considerable debris cloud to cause fatal injuries to people seeking shelter from storms under overpasses. In addition to the fatal injuries to three people, there were also many severe, potentially life-threatening and gruesome injuries inflicted upon people underneath the overpasses, that in some cases, has left these people with permanent disabilities. Don't take shelter under a highway overpass from a tornado! Image credit: KFOR.com.


Figure 3. Radar reflectivity image taken at 6:08 pm CDT May 19, 2013 of the supercell thunderstorm that spawned the Shawnee, Oklahoma tornado.


Figure 4. Doppler velocity image taken at 6:08 pm CDT May 19, 2013 of the supercell thunderstorm that spawned the Shawnee, Oklahoma tornado. Note the couplet of dark red colors right next to light blues near the center of the image, showing that the air was moving both towards the radar and away from it within a short distance, indicating a tight rotation of the tornado's parent mesocyclone.

Iowa's record tornado-free streak ends at 359 days
A tornado touched down near Slater, Iowa at 6:10 pm CDT on Sunday, May 19, one of six tornadoes reported in the state that day. Remarkably, it was the first tornado recorded in the state since May 24, 2012 (Fayette County.) The 359-day streak without a tornado was the longest tornado-free period in state history. The previous record was 355 days, set between May 5, 1955, and April 26, 1956. The new streak is far more impressive because digital technology and spotter networks today are so comprehensive, resulting in far fewer missed tornadoes. There was a much higher likelihood back in the 1950s for tornadoes to be missed. The exceptional tornado-free period was due to the combination of the state's dry summer of 2012 (3rd driest on record) and cold spring of 2013 (8th coldest March - April on record). Thunderstorms like heat and moisture to form, and its tough to get a tornado if you're experiencing a top-ten driest or coldest spring or summer.


Figure 5. Radar reflectivity image of the tornado-spawning supercell thunderstorm that dropped an EF-1 tornado just to the southwest of Wichita, Kansas, on May 19, 2013.

Wichita gets lucky
At 3:30 pm Sunday, Kansas' largest city, Wichita, got a major scare when a large supercell thunderstorm spawned a half-mile wide tornado to the southwest of the city. The tornado headed directly for the airport and downtown Wichita, prompting the issuance of "Tornado Emergency" for the city. In the wake of the deadly EF-5 tornado that leveled Joplin, Missouri in 2011, the NWS decided to give local NWS offices the option to issue special, strongly worded tornado warnings to let the population know when a particularly dangerous tornado--one that has been confirmed by spotters to be on the ground--is approaching. The NWS issued one of these very strongly-worded tornado warnings on Sunday for Wichita:

Statement as of 3:47 PM CDT on May 19, 2013
... A Tornado Warning remains in effect for southern Sedgwick County until 415 PM CDT...

... Tornado emergency for Wichita...

At 345 PM CDT... a confirmed large... violent and extremely dangerous tornado was located on the southwest side of Wichita... and moving northeast at 30 mph.

This is a particularly dangerous situation.

Hazard... deadly tornado.

Source... weather spotters confirmed tornado.

Impact... you could be killed if not underground or in a tornado shelter. Complete destruction of neighborhoods... businesses and vehicles will occur. Flying debris will be deadly to people and animals.

Locations impacted include...Maize... downtown Wichita... Wichita... Bel Aire... McConnell Air Force Base…east Wichita and Oaklawn.

Precautionary/preparedness actions...

This is an extremely dangerous tornado with complete devastation likely. You could be killed if not underground or in a tornado shelter. Do not delay... seek shelter now! If no underground shelter is available seek shelter in an interior room of the lowest level of a structure... or if time allows... consider moving to an underground shelter elsewhere. Mobile homes and outbuildings will offer no shelter from this tornado.

Tornado... observed
Tornado damage threat... catastrophic
Hail... 2.75in

Wichita TV station KSNW did an excellent job covering the tornado, but were forced to abandon the studio during the height of the storm, as seen on this video clip. You can hear hail pounding the roof as the news crew scrambles for shelter. Station meteorologist J.D. Rudd has this to say: "We are okay. I'll tell you though, it got intense. That thing passed right over our studio. Luckily, it had lifted. But I truly thought the roof of our studio was about to peel off. And the sound of the hail was deafening. What a day. Three hours of coverage with the largest city in the state under a TOR warning for a long time. Weather service called it a Tornado Emergency…'Large, violent tornado on the ground'. Words that gave me chills when I read them." Preliminary damage surveys from the NWS indicate that the Wichita tornado was an EF-1 with a path length 4.6 miles that lifted two miles south of the Wichita airport.


Figure 6. Severe weather outlook for Monday, May 20, calls for a "Moderate Risk" of severe weather over much of Oklahoma, and portions of surrounding states. You can follow today's severe weather outbreak from our Severe Weather page.

Another big severe weather day today in the Midwest
The latest forecasts from NOAA's Storm Prediction Center call for an active severe weather day again on Monday, with a "Moderate Risk" of severe weather over much of Oklahoma, plus portions of Southwest Missouri, Northwest Arkansas, and extreme North Texas. The highest threat for tornadoes will be in Southern Oklahoma and into North Texas. The severe weather outbreak will continue on Tuesday and Wednesday, progressing eastwards into the Ohio Valley and Great Lakes. Only a "Slight Risk" of severe weather is expected those days.


Video 1. Impressive footage (peaking at 4:30 of the video) of the huge tornado that devastated Carney, Oklahoma on May 19, 2013.


Video 2. The "Dominator 3" armored tornado intercept vehicle saw plenty of action on Sunday, as seen in this video, taken just northeast of Edmond, Oklahoma. From the ‪http://tvnweather.com/‬ description of the video: "This tornado was one of the strongest ever intercepted, and we needed all 10,000k pounds of the new Dominator because I have never felt vibration like that before as we were slammed by suction vortices wrapping all around the vehicle. Jim Cantore was on board and he's hooked. All part of #TornadoChasers, Season 2013 coming up this fall on ‪http://tvnweather.com/ondemand‬"

Additional info
Wunderblogger Lee Grenci has an interesting post discussing how last Wednesday's Granbury, Texas tornado was able to form in an atmosphere that seemingly had too little wind shear to get a supercell thunderstorm spinning. The Granbury tornado was an EF-4 with 166 - 200 mph winds that killed six people, and was part of a weather system separate from the one that is generating the current Midwest U.S. tornado outbreak.

news9.com out of Oklahoma City had some excellent live helicopter coverage of Sunday's storms, and will likely be out there again today.

Jeff Masters

Tornado

U.S. has its 23rd coolest April; 16 tornadoes confirmed from Texas outbreak

By: JeffMasters, 2:29 PM GMT on May 17, 2013

It was an unusually cool April over much of the U.S. during April 2013, said NOAA's National Climatic Data Center (NCDC) in their latest State of the Climate report. It was the coolest April since 1997, and ranked as the 23rd coolest April in the 119-year record for the contiguous U.S., putting the month in the coldest 20% of all Aprils on record. North Dakota had its coldest April on record, and six additional states--South Dakota, Nebraska, Kansas, Oklahoma, Minnesota, and Wisconsin--had top-ten coldest Aprils on record. No state recorded a top-ten warmest April. Over three times as many record cold highs and lows occurred than record warm highs and lows during April. For the year-to-date period January - April, both temperatures and precipitation over the contiguous U.S. have been near average.

According to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top-10% and bottom-10% extremes in temperature, precipitation, and drought, April extremes were near average, and the year 2013 has been slightly below average for extremes. The CEI during January - April 2013 was 18.5%, and on average, about 19.5% of the contiguous U.S. experiences top-10% extreme weather as defined by the CEI.


Figure 1. Historical temperature ranking for the U.S. for April 2013. North Dakota had its coldest April on record, and six additional states--South Dakota, Nebraska, Kansas, Oklahoma, Minnesota, and Wisconsin--had top-ten coldest Aprils on record. No state recorded a top-ten warmest April. Image credit: National Climatic Data Center (NCDC).


Figure 2. Historical precipitation ranking for the U.S. for April 2013. Iowa and Michigan both had their wettest April on record, and Tennessee, Illinois, Indiana, and Wisconsin each had one of the ten wettest Aprils on record. Connecticut had a top-ten driest April. Image credit: National Climatic Data Center (NCDC).

Iowa and Michigan record their wettest Aprils
It was a very April for the continuous U.S., ranking as the 19th wettest April since 1895. Iowa and Michigan both had their wettest April on record, and Tennessee, Illinois, Indiana, and Wisconsin each had one of the ten wettest Aprils on record. The heavy precipitation in the watershed of Lake Huron and Lake Michigan caused those lakes to rise 9.8", one of the largest monthly rises on record. These lakes were at their all-time lowest water levels on record in January 2013. Drought conditions improved across the Southeast, Midwest, and along the northern and eastern periphery of the core drought areas of the Great Plains during April, but worsened for parts of the Southwest. According to the May 16 Drought Monitor report, about 48% of the U.S. is still in moderate or greater drought, down from 52% at the beginning of April. Improvement in drought conditions is expected from Northern Texas to South Dakota during May and June, but drought is expected to spread into Oregon and Idaho.

According to data from the Rutgers Global Snow Lab, the March snow cover extent for the contiguous U.S. was the 6th largest April snow cover extent in the 47-year period of record. However, snowpack, an important water resource in the West, was dismal in part of the West, with only 18 percent of normal snowpack reported in the Sierra Nevada Mountains.


Figure 3. This image of Texas taken by the GOES East satellite at 0045Z on May 16, 2013 shows the vicinity around Granbury, TX approximately 21 minutes before an EF-4 tornado hit Granbury, Texas. Image credit: NOAA Viz Lab.

Sixteen tornadoes confirmed from Texas tornado outbreak
Sixteen tornadoes have now been confirmed from Wednesday night's tornado event in Texas (fifteen on the 15th, and one just after midnight on the 16th.) The most powerful tornado was an EF-4 with 166 - 200 mph winds that tore through Granbury, killing six and leaving seven missing. The outbreak also had a huge EF-3 tornado, 3/5 of a mile wide, that hit Cleburne, causing extensive damage and a state of emergency. The fifteen tornadoes from May 15 make it the biggest day for tornadoes in the U.S. this spring, and the highest number reported in one day since January 30, when 44 tornadoes touched down from Georgia to Indiana. The data we have on the May 15 - 16 tornadoes so far:

Wednesday, May 15, 2013:
1739 CDT  1 W Belcherville, Montague Co TX - EF?, spotter
???? CDT  Nocona Lake, Montague Co - EF?, photos
1835? CDT Millsap, Parker Co TX - EF-1, 100 mph; 5 homes significantly damaged
1841 CDT  3.5 SSE Mineral Wells, Palo Pinto Co TX - EF-0; brief; 4 NW Millsap
???? CDT  West of Annetta South, Parker Co TX - EF?, brief, from Millsap storm
???? CDT  NW Cresson, Hood Co TX - EF? - determined to be in southern Parker Co
1859 CDT  Sunset, Montague Co TX - EF-1, 100 mph, 1 injured, near Hwy 287; 5 homes damaged south of Lake Amon G. Carter, one of them destroyed
1900? CDT Mills Co TX - EF?, spotters
1922 CDT  3 E Millsap, Parker Co TX - EF-0; brief; photograph
???? CDT  Alvord, Wise Co TX - EF?, public and spotter reports
2006 CDT  Granbury, Hood Co TX - EF-4, 6 killed, dozens injured; only foundations left in places; 200 homes damaged/destroyed; 5 dozen of them Habitat for Humanity. First EF-4 in DFW area since the Lancaster tornado in 1994
2006 CDT  6 SE Granbury, Hood Co TX - EF-1, 90-100 mph; near Pecan Plantation; separate path from Granbury tornado
2130 CDT  Cleburne, Johnson Co TX - EF-3, 140 mph, 8.5 mi path, 1060 yds wide
2142 CDT  6 ESE Cleburne, Johnson Co TX - EF-0, 85 mph; separate from Cleburne tornado
2257? CDT North of Evant, Hamilton Co TX - EF?, brief; #1 of two that occurred simultaneously
2257? CDT North of Evant, Hamilton Co TX - EF?, brief; #2 of two that occurred simultaneously

Thursday, May 16, 2013:
0010 CDT  Ennis, Ellis Co TX - EF1, 90 mph, 6 mi path; significant damage in Ennis; began west of I-45 and crossed I-45 south of Ennis Ave

The latest forecasts from NOAA's Storm Prediction Center call for an active severe weather pattern Saturday - Tuesday. The threat will be highest on Sunday and Monday, when conditions may align to bring about a classic spring severe weather outbreak, as a powerful spring weather system gathers strength over the center of the country.

Saturday's main threat areas: northwest KS, southwest NE
Sunday : east SD, east NE, east half KS, central OK, northwest MO, west and central IA, south half MN.
Monday : central OK, east IA, northwest IL

Jeff Masters

Climate Summaries Tornado

Study: 97% Agreement on Manmade Global Warming

By: angelafritz , 7:36 PM GMT on May 16, 2013



The scientific agreement that climate change is happening, and that it's caused by human activity, is significant and growing, according to a new study published Thursday. The research, which is the most comprehensive analysis of climate research to date, found that 97.1% of the studies published between 1991 to 2011 that expressed a position on manmade climate change agreed that it was happening, and that it was due to human activity.

The study looked at peer reviewed research that mentioned climate change or global warming. Peer review is the way that scientific journals approve research papers that are submitted. In peer review, group of scientists that weren't involved in the study, but who are experts in the field, look at the research being submitted and have approved that it meets scientific process standards, and the standards of that journal.

In 2011, 521 of those peer reviewed papers agreed that climate change is real, and that human activity is the cause. Nine papers in 2011 disagreed.

John Cook, founder of skepticalscience.com and the lead author on the study, said the motivation for the analysis was the importance of scientific consensus in shaping public opinion, and therefore policy. "When people understand that climate scientists agree on human-caused global warming, they're more likely to support climate policy," Cook said. "But when the public are asked how many climate scientists agree that humans are causing global warming, the average answer is around 50%."

This "consensus gap" is what Cook and the research team is trying to close. "Raising awareness of the scientific consensus is a key step towards meaningful climate action," Cook said.

This study is not the first to examine the overwhelming agreement among climate scientists. Surveys of actively publishing climate scientists as well as analyses of climate change papers have shown similar results.

In 2004 Naomi Oreskes, Professor of History and Science Studies at the University of California San Diego, published what many scientists consider the seminal study on climate change consensus. She also co-authored the book Merchants of Doubt, which identifies and examines the similarities between today's climate change conversation and previous controversies over tobacco smoking, acid rain, and the hole in the ozone layer.

Oreskes believes that the public isn't aware of the consensus because of deliberate efforts to cause confusion. "There has been a systematic attempt to create the impression that scientists did not have a consensus, as part of a broader strategy to prevent federal government action," Oreskes said. "The public have been confused because people have been trying to confuse us."

The study published Thursday is the first to take so many papers and authors into account. Doing a search on the popular science article website Web of Science for "climate change" or "global warming" produces over 12,000 results. Of these, 4,014 papers were identified to state a position on climate change. Among those, 3,896, or 97.1% endorsed the consensus that climate change was happening and that it was caused by human activity.

In an interesting result, Cook and his team found that over time, scientists tend to express a position on climate change less and less in their research papers. This is likely a result of consensus -- that if a scientific conclusion has been reached, there's no need to continue to state that conclusion in new research. "Scientists tend to take the consensus for granted," says Cook, "perhaps not realizing that the public still think it's a 50:50 debate."

Climate Change

EF-4 tornado kills 6 in Texas; Mahasen makes landfall in Bangladesh, killing 10

By: JeffMasters, 3:34 PM GMT on May 16, 2013

After going twelve months with a record-low tornado death toll of just seven people, last night we received a jolting reminder that tornadoes typically kill a lot more people than that in the U.S. A deadly tornado swept through Granbury, Texas near 8 pm CDT, killing six and injuring up to 100. The weather system that spawned the Granby tornado also unleashed a mile-wide twister that hit Cleburne, about 25 miles southeast of Granbury. Damage was heavy in Cleburne and a state of emergency declared, but only seven minor injuries were reported. A third tornado hit the small town of Millsap, about 40 miles west of Fort Worth, causing roof damage a destroying a barn, but caused no injuries. Preliminary figures indicate that a total ten tornadoes touched down in Texas last night, and NWS damage survey teams are out today to determine the exact total and how strong they were. The National Weather Service out of Fort Worth has issued a preliminary rating of EF-4 to the Granbury tornado, making it the first tornado stronger than EF-0 reported in May 2013. The storms also dumped softball-sized hail up to 4" in diameter in Mineral Wells, TX.


Video 1. The Granbury, Texas tornado of May 15, 2013.

Thursday's tornado was the deadliest U.S. tornado in over a year. The last time six people died in a U.S. tornado was on April 14, 2012, during an EF-3 tornado that hit Woodward, Oklahoma. The last Texas tornado that was deadlier occurred on April 24, 2007 in Maverick County, when an EF-3 tornado hit Eagle Pass, Texas, killing seven. Texas has had one other tornado death in 2013, from a twister that hit on February 21, 2013, in Sabine County. The region of Texas hit by last night's tornadoes has few basements, which may have contributed to the death toll. According to underground member Seattleite, "In this part of Texas basements are very uncommon. The reason is due to the soil, it is basically clay. It contracts and expands with temperature and moisture levels on the order of a foot or more in a typical year. The pressure from this can cause basement walls to cave. They can be built, but it costs at least an extra $20,000+, as they surround the basement with a sand-like barrier to handle the changes in the ground."


Figure 1. Softball, anyone? One of the 4" hailstones that fell near Mineral Wells, Texas on May 15, 2013. Image from Patrick Vondra via Twitter.

Is the 2012 - 2013 tornado drought over?
Thanks to the cold spring in the Midwest during 2013, and the 2012 Midwest drought, the 197 EF-1 and stronger tornadoes that occurred during May 2012 - April 2012 was an all-time minimum for any twelve-month period since at least 1954, wrote tornado researcher Harold Brooks at the U.S. Severe Weather Blog (previous minimum: 247 tornadoes from June 1991-May 1992.) The death toll of just seven was also a record low for any twelve-month period since 1950. Amazingly, this tornado drought occurred less than two years after the record maximum: 1050 EF-1 and stronger tornadoes from June 2010 - May 2011. The extraordinary contrast underscores the crazy fluctuations we've seen in Northern Hemisphere jet stream patterns during the past three years. Call it "Weather Whiplash" of the tornado variety. A blog post by meteorologist Patrick Marsh of NOAA's Storm Prediction Center argues that the record 12-month tornado maximum of 1050 EF-1 and stronger tornadoes from June 2010 - May 2011 was a 1-in-62,500 year event. The record 12-month minimum of 197 EF-1 and stronger tornadoes that occurred from May 2012 - April 2013 was a 1-in-3000 to 1-in-4000 year event. In Marsh's words: "Anyway you look at it, the recent tornado "surplus" and the current tornado "drought" is extremely rare. The fact that we had both of them in the span of a few years is even more so!"

Our tornado drought may be at its end, as the latest forecasts from NOAA's Storm Prediction Center call for an active severe weather pattern Saturday - Monday. The current forecast calls for just a "Slight Risk" on Saturday over the Northern Plains, but the threat will grow on Sunday and Monday as a powerful spring weather system gathers strength over the center of the country.

Saturday's main threat areas: SD to NE, and northern KS
Sunday : IA, parts of MO/KS, to central/eastern OK
Monday : IL/MO to OK/TX border


Figure 2. MODIS image of Tropical Cyclone Mahasen taken at 06:50 UTC Thursday May 16, 2013. Mahasen made landfall about two hour prior to this image as a tropical storm with 50 mph winds. Image credit: NASA.

Tropical Storm Mahasen hits Bangladesh
Tropical Storm Mahasen hit the Bangladesh coast near 08 UTC Thursday, May 16 near a place called Feni north of Chittagong. Mahasen was a tropical storm with top winds of 50 mph at landfall. Satellite observations suggest that the storm was becoming much more organized just before landfall, and it is fortunate that the storm ran out of time to intensify when it did. Mahasen likely brought a storm surge of up to a meter (3.3 feet) to the coast of Bangladesh, but it is the storm's rains that are causing the main problems. Satellite rainfall forecasts made at landfall show that Mahasen could dump up to 20 inches of rain along a swath through Bangladesh and into Northeastern India. These rains will be capable of causing destructive flooding, and ten deaths have already been reported in Bangladesh from the storm. At least eight people have been killed in Sri Lanka due to landslides triggered by Mahasen's heavy rains, and a boat carrying refugees capsized on Monday, killing eight and leaving 50 missing.

First tropical storm of the year, Alvin, forms in the Eastern Pacific
The official start of hurricane season in the Eastern Pacific is Wednesday, May 15, and Mother Nature emphatically agreed, bringing us the first named storm of the year, Tropical Storm Alvin. With wind shear a moderate 10 - 20 knots and the storm currently struggling to hold itself together, it currently appears unlikely that we will see a Hurricane Alvin. The storm is moving west-northwest into the Central Pacific, and is not a threat to any land areas.

I'll have a new post this afternoon, on an important climate change study released today.

Jeff Masters

Tornado Hurricane

Extreme Weather Whiplash: 106° in Iowa on the Heels of Record May Snows

By: JeffMasters, 5:48 PM GMT on May 15, 2013

Does not compute! That must be what residents of Iowa and the Midwest have have been saying to themselves on Tuesday as a ferocious heat wave unprecedented in intensity for so early in the year sent temperatures soaring as high as 108°. Just two weeks ago, the deepest snowfall ever measured during any May of record buried a wide swath from Arkansas to Minnesota, with Iowa breaking its all-time snowfall record for May (13” accumulation at Osage on May 1 - 3.) And how's this for a definition of "Weather Whiplash": Sioux City, Iowa had their first-ever snowfall on record in the month of May on May 1 (1.4"), but hit an astonishing 106° yesterday. Not only was this their hottest temperature ever measured in the month of May, but only two June days in recorded history have been hotter (June, 10, 1933: 107° and June 21, 1988: 108°.) On May 12th they registered 29°, and thus had a 77° rise over 56 hours (from 6 a.m. May 12 to 1:30 p.m May 14.)


Figure 1. Intense heat and strong winds fanned a wildfire in northwestern Wisconsin's Douglas County near Gordon on Tuesday, May 14, 2013. The fire spread to 8,700 acres and forced dozens of residents to leave their homes. Image credit: Kevin Harter/Wisconsin Department of Natural Resources, and courtesy of wisconsinrapidstribune.com.

The hottest temperature of all on Tuesday was 108° at Tekamah, Nebraska. This is just 2° short of warmest temperature ever recorded in the state of Nebraska during May: 110° at Broken Bow in 1895 (exact day unknown.) Numerous all-time early season heat records were set on Tuesday, making the event the most notable May wave in the Midwest since a multi-day event in 1934. That heat wave was not preceded by unusually cold weather, which is what makes the May 2013 Midwest heat event truly extraordinary. A few notable cases of "Weather Whiplash" from the May 14, 2013 heat wave:

- Chicago, Illinois hit 91°, after hitting a low of 36° the previous morning. The 1-day temperature swing of 52° was the city's greatest on record for the month of May.

- Rochester, Minnesota, where 14.5” of snow fell just 10 - 12 days ago (4th greatest snowstorm for any month on record), saw an all-time early season heat record of 97° on May 14th. The previous day, May 13th, it was 32° in Rochester--a 65° rise in temperature over the course of 36 hours.

- Omaha, Nebraska hit 101°, the earliest 100° on record (old record 102° on May 29, 1934). It was 32° in Omaha on May 12th! That tied for the coldest so late in the season with 32° on 5/13/1997 and also on 5/15/1983.

- Albert Lea and St. James, Minnesota hit 102° (hottest in the state on Tuesday.) Both cities had May snow less than two weeks previously. Tuesday morning, it was 27° at Crane Lake and Silver Bay, for a same-day state temperature spread of 75° in Minnesota. This is a relatively common figure for California or Texas, but almost unprecedented for a Midwestern state.

- Minneapolis hit 98°, the hottest so early in season (next is 99° on May 22, 1925). May record is 106° on May 31, 1934 (the only time 100° has been measured during May).

- Norfolk, Nebraska hit 103°, the hottest temperature ever measured so early in the year (previous record: 103° on May 25, 1967. A daily record low of 29° was recorded on May 12th, just two days previous.

Fires in Wisconsin and Minnesota
The intense heat was accompanied by strong winds, which fanned multiple fires in Minnesota and Wisconsin. One fire, near Gordon, Wisconsin, burned 8,700 acres, making it the largest fire in Wisconsin since the Cottonville fire on May 5, 2005, and the largest fire in Northern Wisconsin since the Oak Lake fire of April 22, 1980 (11418 acres.) The Gordon fire destroyed 47 structures, including 17 homes, and forced the evacuation of several dozen people. The fire was 90% contained Wednesday morning. At least 25 smaller wildfires were reported in Minnesota, and Governor Mark Dayton signed an emergency order on Tuesday to help the Minnesota Interagency Fire Center fight wildfires around the state.

Why the crazy extremes? Blame the jet stream
The position of the jet stream is a critical controller of weather regimes across the U.S., Europe, and Asia. Precipitation-bearing low pressure system ride along the axis of the jet, and the jet marks the boundary between cold, Canadian air to the north, and warm, subtropical air to the south. On average, the jet flows from west to east, but the jet often departs from average. The jet is continually rippling with U-shaped troughs of low pressure that allow cold air to spill southwards. The troughs are counterbalanced by upside-down-U-shaped ridges of high pressure that bring warm air northwards. When these ridges and troughs grow to unusually large amplitude, record extremes of both cold and heat occur adjacent to each other. Often times, the jet will have multiple extreme loops that result in unusual extremes over large portions of the Northern Hemisphere. That was the case Tuesday in Europe, where an unusually strong ridge of high pressure was present over Western Russia, with a companion strong trough of low pressure over the U.K. Moscow, Russia hit 29.7°C (85.5°F) on Tuesday, and several locations within the city rose to 31°C (88°F). According to weather records researcher Maximiliano Herrera, this has never happened in the first half of May before. At the same time, up to 3" of snow fell in the U.K. on Tuesday, a rare occurrence for mid-May. Could climate change be a factor in the extreme gyrations of the jet stream this year? It could, and I discussed some of the possible connections in my April 2013 post, Unusually cold spring in Europe and the Southeast U.S. due to the Arctic Oscillation.


Figure 2. Monday afternoon's jet stream shows the pronounced ridge (upside-down U-shaped curve to the jet stream) over the Midwest U.S., which led to all-time record high temperatures for so early in the year. At the same time, a sharp trough of low pressure (U-shaped dip in the jet stream) was present over the East Coast, which allowed cold air from Canada to spill southwards and set record lows--for example, 44° at Tallahassee, Florida on May 14.

Jeff Masters and Christopher C. Burt

Extreme Weather Heat

Mahasen not Strengthening; Eastern Pacific's First Tropical Depression Forming

By: JeffMasters, 1:34 PM GMT on May 15, 2013

Tropical Cyclone Mahasen in the Bay of Bengal continues to show little change as it steams north-northeastward at 14 mph towards the Bangladesh coast just north of the border with Myanmar. Though the storm is no longer expected to reach hurricane strength, Mahasen's storm surge and heavy rains represent a significant threat to people living in low-lying areas along the Bangladesh and Myanmar coasts. At least 70,000 people have been asked to evacuate, and a boat carrying refugees capsized on Monday, killing eight and leaving 50 missing. The ocean bottom is shallow and allows storm surges to pile up to great depths on the Bangladeshi coast, and Mahasen is expected to bring a storm surge of 3 - 5 feet (1 - 1.5 meters) to the Bangladesh coast on Thursday, according to the Regional Specialized Meteorological Center in Delhi, India. The Bangladesh Meteorological Department is warning of a 5 - 7 foot (2 meter) storm surge for their coastal districts. The greatest storm surge will occur to the right of where the center crosses the coast, in northern Myanmar. The Myanmar Department of Meteorology and Hydrology is warning of a 6 - 10 foot (2 - 3 meter) storm surge there. Accompanying the surge will be torrential rains of 3 - 7 inches that have the potential to cause dangerous flooding. At least seven people have been killed in Sri Lanka due to landslides triggered by Mahasen's heavy rains.


Figure 1. MODIS image of Tropical Cyclone Mahasen taken at 07:45 UTC Wednesday May 15, 2013. At the time, Mahasen was a tropical storm with 50 mph winds. The storm appears disorganized due to wind shear keeping the heavy thunderstorms to the west of the center. Image credit: NASA.

The 10 am EDT Wednesday advisory from the Joint Typhoon Warning Center put Mahasen's top sustained winds near 50 mph. Satellite loops show that Mahasen continues to struggle with wind shear. The low-level circulation center has become exposed to view several times, with an intense area of thunderstorms with very cold cloud tops just to the west of the center. The cloud pattern is not well-organized, with little spiral banding. Wind shear remains a moderate 10 - 15 knots, but Mahasen is now over cooler waters with a much reduced total heat content, and it appears unlikely that the storm will change much in intensity before landfall. Landfall is expected to occur near 18 UTC on Thursday.


Figure 2. Storm-total rainfall from Tropical Cyclone Mahasen as predicted by the 12 UTC May 14, 2013 run of the HWRF model. Rainfall amounts of 3 - 7" are expected along a wide swath of Bangladesh and Myanmar. Image credit: India Meteorological Department.


Figure 3. Bathymetry of the Bay of Bengal. The shallow waters of the Continental Shelf (mostly shallower than 200 meters) are shaded whitish-grey. From Kolkata, India to Cox's Bazar, Bangladesh, the ocean bottom is shallow and allows storm surges to pile up to great depths. Fifteen of the twenty deadliest tropical cyclones in world history have been Bay of Bengal storms that have hit Bangladesh, India, or Myanmar, bringing catastrophic storm surges. Image credit: geomapapp.org.

Resources
Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models

India Meteorological Department's tropical cyclone page

Radar out of Chennai, India

Bangladesh Meteorological Department Warning

Myanmar Dept. of Meteorology and Hydrology Warning


Figure 4. Latest satellite image of Invest 90E.

First tropical depression of the year forming in the Eastern Pacific
The official start of hurricane season in the Eastern Pacific is Wednesday, May 15 (today!), and Mother Nature is playing along with this idea. The first "Invest" of the year, Invest 90E, has become well-organized on satellite loops, and NHC has set in motion the process to name this system Tropical Depression One-E (or possibly Tropical Storm Alvin) at 11 am EDT. Wind shear is a low 5 -10 knots, and is predicted to remain low for the next five days. Ocean temperatures are a warm 29 - 30°C, and it is possible that this could become Hurricane Alvin late this week. The storm is moving west-northwest into the Central Pacific, and is not a threat to any land areas.

I'll have a new post late this morning or early this afternoon on yesterday's remarkable heat wave in the Midwest. Can you believe 106° in Iowa and 108° in Nebraska, after unprecedented May snows were falling less than two weeks ago? Unbelievable!

Jeff Masters

Hurricane

Little Change to Tropical Storm Mahasen; First Eastern Pacific Tropical Disturbance

By: JeffMasters, 2:23 PM GMT on May 14, 2013

Tropical Cyclone Mahasen in the Bay of Bengal continues to show little change, and the storm is running out of time to undergo rapid intensification into a dangerous major hurricane. The 10 am EDT Tuesday advisory from the Joint Typhoon Warning Center put Mahasen's top sustained winds at 50 mph, with a motion northeast at 8 mph towards Bangladesh. Satellite loops show that Mahasen has been struggling with wind shear over the past day. The low-level circulation center has become exposed to view several times, with an intense area of thunderstorms with very cold cloud tops just to the west of the center. The cloud pattern is not well-organized, with little spiral banding. The upper-level outflow channels have degraded some since Monday, even though wind shear has decreased to a moderate 10 - 15 knots. Ocean waters have cooled some, to 29 - 30°C (84 - 86°F). The warm ocean waters extend to great depth, though, and the Tropical Cyclone Heat Potential (TCHP) is over 90 J/kg/cm^2, which is favorable for rapid intensification.


Figure 1. MODIS image of Tropical Cyclone Mahasen taken at 05:35 UTC Tuesday May 14, 2013. At the time, Mahasen was a tropical storm with 50 mph winds. Wind shear has caused the low-level center to become exposed to view on the east side, with a clump of heavy thunderstorms to the west of the center. Image credit: NASA.


Figure 2. Storm-total rainfall from Tropical Cyclone Mahasen as predicted by the 00 UTC May 14, 2013 run of the HWRF model. Rainfall amounts of 3 - 7" are expected along a wide swath just to the right of where the storm makes landfall. Bangladesh's two largest cities, Dhaka and Chittagong, are shown. Image credit: India Meteorological Department.

Forecast for Mahasen
The most favorable conditions for Mahasen to intensify would appear to be today, as the storm will be moving over cooler waters with a much reduced total heat content beginning about 06 UTC on Wednesday. Wind shear is expected to remain in the moderate range through Wednesday, so there is still time for Mahasen to reach Category 1 strength, as the official JTWC forecast calls for. There is a lot of hot, dry air to the storm's northwest over India, though, and if this dry air gets wrapped into Mahasen's circulation, it could put the brakes on intensification. Landfall is expected to occur in Bangladesh near the Myanmar border on Thursday near 18 UTC, and wind shear is predicted to increase on Thursday, so the opportunity to Mahasen to undergo rapid intensification into a major Category 3 or stronger hurricane is growing short. I give a 10% chance that Mahasen will undergo rapid intensification to a Category 3 or stronger storm before landfall. There is a precedent for this sort of event: in October 2010, Tropical Cyclone Giri, which was approaching the coast of Myanmar near Bangladesh, underwent explosive deepening from a 60 mph tropical storm to a top-end Category 4 hurricane with 155 mph winds in just 30 hours. Even a Category 1 storm has the potential to bring a destructive storm surge to the coast of Bangladesh, where the ocean bottom is shallow and allows storm surges to pile up to great depths. Heavy rainfall will present a major flooding threat regardless of the storm's final intensity at landfall. The 00Z May 14 run of the HWRF model predicts that the Mahasen will dump a significant area of heavy rains of 3 -7" over Maynmar and Bangladesh. The storm surge, high winds, and heavy rains of Mahasen are a particular concern for the 140,000 Myanmar refugees living near the coast in makeshift camps. Evacuations of 70,000 of these refugees has been recommended, and a boat carrying refugees capsized on Monday, killing eight and leaving 50 missing.


Figure 3. Bathymetry of the Bay of Bengal. The shallow waters of the Continental Shelf (mostly shallower than 200 meters) are shaded whitish-grey. From Kolkata, India to Cox's Bazar, Bangladesh, the ocean bottom is shallow and allows storm surges to pile up to great depths. Fifteen of the twenty deadliest tropical cyclones in world history have been Bay of Bengal storms that have hit Bangladesh, India, or Myanmar, bringing catastrophic storm surges. Image credit: geomapapp.org.

Resources
Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models

India Meteorological Department's tropical cyclone page

Radar out of Chennai, India

Bangladesh Meteorological Department Warning

Myanmar Dept. of Meteorology and Hydrology Warning

Weather Whiplash in the Midwest: a 70° warm-up in just one day
It's been a "Topsy-Turvy Temperature Regime for U.S. this May" says underground's weather historian Christopher C. Burt in his latest post. After record May cold and snows hit the Great Lakes over the weekend, a ferocious May heat wave is in full bloom today. Several cities are poised to experience their greatest 1-day May temperature swing on record today. Chicago bottomed out at 36° on Monday morning, and this afternoon's high is predicted to be 88°--a spectacular 52° change in temperature in just one day. The all-time record for a one-day warm-up in the Windy City during May is 50°, set May 1, 1992. A 50°+ temperature swing is also expected in Minneapolis, where the high today is predicted to be 94°, coming on the heels of a 41° low Monday morning. The most dramatic "Weather Whiplash", though, came in Aberdeen, South Dakota, where the mercury hit 22° on May 12, then shot up to 92° on May 13--an astonishing 70° rise in just one day!

Alvin coming? First "Invest" of the year forms in the Eastern Pacific
The official start of hurricane season in the Eastern Pacific is Wednesday, May 15, and it looks like Mother Nature is playing along with this idea, with the appearance yesterday of the year's first "Invest" (Invest 90E) in the Eastern Pacific. Invest 90E is moving west-northwest into the Central Pacific, and is not a threat to any land areas. Satellite loops show a modest area of disorganized heavy thunderstorms. Wind shear is a low 5 -10 knots, and is predicted to remain low for the next four days. Ocean temperatures are a warm 29 - 30°C, and I give a 30% chance that 90E will become a tropical depression by Thursday morning, as predicted by the GFS model. If the system reaches tropical storm strength, it would be called Alvin.

What is an "Invest"?
When a National Hurricane Center forecaster sees a tropical disturbance that may be a threat to develop into a tropical depression, the forecaster may label the disturbance an "Invest" and give it a tracking identification number. There is no formal definition of what qualifies as an "Invest". Declaring an "Invest" is merely done so that a set of forecasting aids like computer model track forecasts can be generated for the disturbance. The "Invest" is given a number 90-99, followed by a single letter corresponding to the ocean basin--"L" for the Atlantic, or "E" for the Eastern Pacific. Other warning agencies assign "Invests" for the other ocean basins--"W" for the Western Pacific, "A" for the Arabian Sea, etc. Detailed microwave and traditional satellite images are available for all "Invests" across the globe at the Navy Research Lab web site.

Jeff Masters

Hurricane

Bay of Bengal Tropical Storm Mahasen remains a dangerous threat

By: JeffMasters, 2:39 PM GMT on May 13, 2013

It's always a nervous time when a tropical cyclone with the potential to intensify marches through the Indian Ocean's Bay of Bengal. That's because fifteen of the twenty deadliest tropical cyclones in world history have been Bay of Bengal storms that have hit Bangladesh, India, or Myanmar. The most recent of these horrifying storms was 2008's Cyclone Nargis, which killed 146,000 people in Myanmar. The Bay of Bengal's notorious history is why hurricane forecasters are watching Tropical Cyclone Mahasen a little nervously today. Even though there has been little change to the 55 mph tropical storm over the past two days, the storm remains a potential threat to undergo rapid intensification into a dangerous major hurricane. The 11 am EDT Monday advisory from the Joint Typhoon Warning Center put Mahasen's top sustained winds at 55 mph, with a motion northwest at 11 mph towards India. Satellite loops show that Mahasen has a large area of intense thunderstorms with very cold cloud tops that reach high into the atmosphere. The cloud pattern is not well-organized, with little spiral banding. This lack of organization is also apparent on radar out of Chennai. However, the cyclone has developed a respectable upper-level outflow channel to the northwest. Wind shear has decreased to a moderate 10 - 20 knots, and is continuing to decrease. Ocean waters that are an exceptionally warm 31°C (88°F), about 1°C warmer than average for this time of year. The warm ocean waters extend to great depth, and the Tropical Cyclone Heat Potential (TCHP) is over 90 J/kg/cm^2, which is favorable for rapid intensification.


Figure 1. MODIS image of Tropical Cyclone Mahasen taken at 07:55 UTC Monday May 13, 2013. At the time, Mahasen was a tropical storm with 55 mph winds. Image credit: NASA.


Figure 2. Storm-total rainfall from Tropical Cyclone Mahasen as predicted by the 00 UTC May 13, 2013 run of the HWRF model. Rainfall amounts of 16 - 30 cm (6 - 12") are expected along a wide swath just to the right of where the storm makes landfall. Bangladesh's two largest cities, Dhaka and Chittagong, are shown. If Mahasen's track occurs farther to the left, as suggested by some models, these two cities will receive Mahasen's heaviest rains. Image credit: India Meteorological Department.

Forecast for Mahasen
The official forecast brings Mahasen to Category 1 strength before landfall occurs in Bangladesh near the Myanmar border on Thursday near 18 UTC. However, the model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models continue to show wide disagreement on the future intensity, speed, and landfall location of the storm. It is possible that wind shear will keep the storm disorganized and below hurricane strength until landfall, as suggested by the ECMWF model. However, other model guidance, such as the 00 UTC May 13 forecast from the HWRF model, bring Mahasen to Category 2 strength by Tuesday. Mahasen is currently approaching a trough of low pressure to its northwest that is expected to recurve the storm to the northeast into Bangladesh. As the recurvature process progresses today through Tuesday, wind shear should relax to a low to moderate 5 - 15 knots, and a strong upper-level outflow channel will intensify to the storm's north, aiding intensification. There is a lot of hot, dry air to the storm's northwest over India, and if this dry air gets wrapped into Mahasen's circulation, it could put the brakes on rapid intensification, though. Considering all these factors, I give a 30% chance that Mahasen will undergo rapid intensification to a Category 3 or stronger storm by Wednesday. The storm should experience higher wind shear and less oceanic heat content in the waters beneath it in the 12 hours before landfall, which should cause some weakening. But even a weakening Category 1 storm has the potential to bring a devastating storm surge to the coast of Bangladesh, and torrential rainfall will be a major flooding threat regardless of the storm's final intensity at landfall. The 00Z May 13 run of the HWRF model predicts that the Mahasen will dump a significant area of heavy rains of 16 - 30 cm (6 - 12") over Maynmar and Bangladesh. The storm surge, high winds, and heavy rains of Mahasen are a particular concern for the thousands of Myanmar refugees living near the coast in makeshift camps, as reported by the New York Times.

MJO pulse that spawned Mahasen headed towards the Atlantic
Mahasen spun up in response to an active phase of the Madden Julian Oscillation (MJO) that has been moving through the Indian Ocean during the past week. The MJO is a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. The strong MJO pulse coincided with a convectively coupled atmospheric Kelvin wave (CCKW), a wave of increased heat and moisture propagating along the Equator, which helped increase thunderstorm activity. The active pulse of the Madden Julian Oscillation is expected to reach the Western Caribbean (in a somewhat weakened state) May 21 - 25, and there will be a heightened chance of an early-season tropical storm forming in the Eastern Pacific and Western Caribbean during that time period.

Resources
Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models

India Meteorological Department's tropical cyclone page

Radar out of Chennai, India

Bangladesh Meteorological Department Warning

Myanmar Dept. of Meteorology and Hydrology Warning

Jeff Masters

Hurricane

Dangerous Cyclone Mahasen gathering strength in the Bay of Bengal

By: JeffMasters, 4:25 PM GMT on May 11, 2013

Dangerous Tropical Cyclone Mahasen is gathering strength over the Indian Ocean's Bay of Bengal, and is a potential major threat to Bangladesh and Myanmar. The 11 am EDT Saturday advisory from the Joint Typhoon Warning Center put Mahasen's top sustained winds at 55 mph, with a motion northwest at 19 mph into the center of the Bay of Bengal. Satellite loops show that Mahasen has a large area of intense thunderstorms with very cold cloud tops that reach high into the atmosphere. The cloud pattern is not well-organized, with little spiral banding. However, the cyclone has developed respectable upper-level outflow channels to the north and east, which are ventilating the storm by carrying away air converging to the center near the surface. High wind shear of 20 - 25 knots is affecting the storm, which is keeping the system disorganized. However, wind shear has declined about 5 knots since Friday, and is predicted to fall to the moderate range, 10 - 20 knots, by Sunday. This should allow organization into a Category 1 storm on Sunday. Aiding this process will be Mahasen's motion away from the Equator, which will help the cyclone leverage the Earth's spin to get itself spinning faster. Also aiding the intensification process will be ocean waters that are an exceptionally warm 31°C (88°F). This is about 1°C warmer than average for this time of year.


Figure 1. Latest satellite image of Tropical Cyclone Mahasen gathering strength over the Indian Ocean's Bay of Bengal.

Forecast for Mahasen
The official forecast brings Mahasen to Category 1 strength before landfall occurs in Bangladesh near the Myanmar border on Wednesday. Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models show wide disagreement on the future intensity and speed of the storm, though. It is possible that wind shear will keep the storm disorganized and below hurricane strength until landfall, as suggested by the GFS and ECMWF models. The 06 UTC forecast from the HWRF model brings Mahasen to Category 3 strength on Monday, but weakens the storm to tropical storm strength at landfall. The model predicts that the storm will dump a significant area of heavy rains of 32 cm (12.6") over Maynmar and Bangladesh. The storm surge, high winds, and heavy rains of Mahasen are a huge concern for the thousands of Myanmar refugees living near the coast in makeshift camps, as reported by the New York Times.


Figure 2. Double trouble: Tropical Cyclone Jamala (lower) and Tropical Cyclone Mahasen (upper storm) spin on opposite sides of the Equator in this in this MODIS image taken at 04:25 UTC May 10, 2013. Mahasen is the name of a King of Sri Lanka from the 3rd century. Image credit: NASA.

MJO pulse that spawned Mahasen headed towards the Atlantic
Mahasen spun up in response to an active phase of the Madden Julian Oscillation (MJO) that has been moving through the Indian Ocean during the past week. The MJO is a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. The strong MJO pulse coincided with a convectively coupled atmospheric Kelvin wave (CCKW), a wave of increased heat and moisture propagating along the Equator, which helped increase thunderstorm activity. The active pulse of the Madden Julian Oscillation is expected to reach the Western Caribbean sometime May 22 - 26, and there will be a heightened chance of an early-season tropical storm forming in the Eastern Pacific and Western Caribbean during that time period.

There is a small disturbance a few hundred miles north of Puerto Rico today that has developed some spin and a bit of heavy thunderstorm activity. This system is over cool waters of 77 - 79°F, and will likely be torn apart by high wind shear on Sunday.

Resources
Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models

India Meteorological Department's tropical cyclone page

Bangladesh Meteorological Department Warning

Myanmar Dept. of Meteorology and Hydrology Warning

Tutorial on Equatorial Waves in the COMET program's Introduction to Tropical Meteorology, plus their case exercise built around the May 2002 "twin twins" case, for use in a tropical synoptic course.

Jeff Masters

Hurricane

Double Trouble: twin tropical cyclones spin up in the Indian Ocean

By: JeffMasters, 3:27 PM GMT on May 10, 2013

There's double trouble in the Indian Ocean today, with a pair of counter-rotating tropical cyclones spinning away on either side of the Equator. In the Southern Hemisphere, we have Tropical Cyclone Jamala, a tropical storm with 45 mph winds that is headed southwards at 3 mph. Jamala is expected to intensify into a Category 1 storm over the weekend, but is not a threat to any land areas. In the Northern Hemisphere, it's Tropical Cyclone 01B, a tropical storm with 40 mph winds that is dumping heavy rains over western Sumatra. This storm much larger and far more dangerous than its Southern Hemisphere twin brother. Cyclone 01B is under high wind shear of 20 - 30 knots, which is keeping the system disorganized, with the heaviest thunderstorms displaced from the center of rotation. However, Cyclone 01B is expected to move generally northwestwards over the next few days through the Bay of Bengal, where wind shear is lower and ocean temperatures are an exceptionally warm 31°C (88°F). This is about 1°C warmer than average for this time of year. The official forecast brings the storm to Category 1 strength before landfall occurs in Myanmar just south of the border with Bangladesh early next week. Comparative model forecasts of Cyclone 01B from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models show poor agreement on the intensity of Cyclone 01B, though, and it is possible that wind shear will keep the storm disorganized until landfall, with heavy rain being the main threat.


Figure 1. Double trouble: Tropical Cyclone Jamala (lower) and Tropical Cyclone 01B (upper storm) spin on opposite sides of the Equator in this infrared satellite image taken at 12 UTC (7 am EDT) Friday May 10, 2012. Image credit: University of Wisconsin CIMSS.

Twin tropical cyclones: how unusual?
Twin cyclones forming on either side of the Equator are surprisingly common in the Indian Ocean. They tend to spin up in May and November--the months immediately preceding and following the annual monsoon (the monsoon dominates the circulation patterns during June - October, making tropical cyclones rare in the Northern Indian Ocean during those months.) The most recent occurrence of twin developments happened unusually late: the end of December 2011, when Tropical Cyclones Thane and Benilde developed. Both storms became mature hurricanes, with Thane hitting the southeast coast of India on December 30, making it the second latest landfalling cyclone in India (thanks go to Meteo-France's Philippe Caroff of RSMC La Reunion for this info.)

Usually, the twin storms spin up when the active phase of the Madden Julian Oscillation (MJO) is present. The MJO is a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. The area of increased thunderstorms associated with the MJO currently straddles the Equator in the Indian Ocean, and is helping boost thunderstorm activity in both Cyclone 01B and Tropical Cyclone Jamala. The strong MJO pulse coincides with something called a convectively coupled atmospheric Kelvin wave (CCKW), which is helping increase thunderstorm activity as well. The tutorial on Equatorial Waves in the COMET program's excellent Introduction to Tropical Meteorology, (free, but registration required) gives several examples of twin tropical cyclones forming on either side of the Equator. One of these cases occurred in November 2007, when the notorious Tropical Cyclone Sidr formed in the North Indian Ocean at the same time that Tropical Cyclone Lee-Ariel formed on the other side of the Equator. Sidr struck Bangladesh as a Category 4 storm, killing up to 10,000 people. Dr. Michael Ventrice of wsi.com gave me these examples of other twin Indian Ocean tropical cyclones that formed between 1990 - 2009:

1. mid Oct 1992
1. early November 1993 
2. late April 1994
3. mid Nov 1995
4. late April/early May 1995 
5. late October 1995
6. mid March 2000
7. early May 2002 (*Great Example, two sets of twins*) 
8. early Nov 2002
9. mid Dec 2002
10. early Dec 2003
11. early July 2004 
12. late April 2008
13. mid Oct 2008
14. mid Nov 2008
15. early Nov. 2009 

These twin cyclone events tend to  most commonly occur during strong MJO events over the Indian Ocean (strong equatorial lower tropospheric westerly winds), but it's not the only time that they can occur. To look at these years with MJO and Kelvin wave type filtered anomalies overlaid (contours), please visit http://www.atmos.albany.edu/student/ventrice/ncep/5S-5N/. Here, blue shaded TCs represent the tropical depression category forming south of the equator, whereas red TC symbolizes depressions that have formed north of the equator. 

It's worth mentioning that the active pulse of the Madden Julian Oscillation is expected to reach the Western Caribbean sometime May 22 - 26, and there will be a heightened chance of an early-season tropical storm forming in the Eastern Pacific and Western Caribbean during that time period.


Figure 2. The most spectacular case of twin cyclones in the Indian Ocean: "twin twins" on May 9, 2002. A strong MJO event superimposed with a strong convectively coupled atmospheric Kelvin wave passed the Indian Ocean and two sets of twins developed, the first over 60E on May 1-3, and the second pair of twins over 90E May 8-10. The eastern pair of twins are Tropical Cyclone Errol (Southern Hemisphere) and Tropical Cyclone 02B (Northern Hemisphere.) The western pair had quite a significant impact, with Tropical Cyclone Kesiny in the Southern Hemisphere making landfall in northern Madagascar as a hurricane, which was the first occurrence of a hurricane making landfall in the month of May in the Southwest Indian Ocean in at least 40 years (though Kesiny was followed the next year by Tropical Cyclone Manou, which hit the east coast of Madagascar at an even higher intensity.) Kesiny affected half a million people in Madagascar and caused numerous fatalities (at least 33), with people being drowned due to severe flooding in the aftermath of the TC-related rain event (Toamasina the major harbour of the country and main city of the east coast of the island received 891 mm (35.08") of rainfall in 3 days--although being quite far to the south from the landfalling point). At the same time, Tropical Cyclone 01A finished its life on the arid land of the Arabian Peninsula, also generating a severe rain event (unprecedented in at least 30 years), which caused devastation in the Dhofar region of western Oman. An observing station reported 251 mm (9.88") of rainfall (the equivalent of 4 to 5 years of average rainfall for this arid region). At least 9 fatalities were attributed to this unusual storm and rain event. Thanks go to Meteo-France's Philippe Caroff of RSMC La Reunion for this info and image.

Resources
Comparative model forecasts of Cyclone 01B from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models.

India Meteorological Department's tropical cyclone page


Tutorial on Equatorial Waves in the COMET program's Introduction to Tropical Meteorology, plus their case exercise built around the May 2002 "twin twins" case, for use in a tropical synoptic course.

Equatorial Rossby Waves and Twin Tropical Cyclogenesis

Dynamical Aspects of Twin Tropical Cyclones Associated with the Madden-Julian Oscillation

Shen, B.-W., W.-K. Tao, Y.-L. Lin, and A. Laing, 2012: Genesis of twin tropical cyclones as revealed by a global mesoscale model: The role of mixed Rossby-gravity waves. J. Geophys. Res., 117, D13114, doi:10.1029/2012JD017450


Have a great weekend, everyone!

Jeff Masters

Hurricane

Tornado drought: only 3 U.S. tornadoes during May's first week

By: JeffMasters, 3:55 PM GMT on May 08, 2013

With just three tornadoes during the period May 1 - 7, 2013 has had the third-fewest U.S. tornadoes during the first week of May since record keeping began in 1950. The only year with fewer tornadoes during the first week of May were 1970 (zero) and 1952 (two.) During the ten year period 2003 - 2012, the U.S. averaged 73 tornadoes during the first week of May, with a high of 239 during May 1 - 7, 2003. The three May 2013 tornadoes have all been week EF-0 twisters, and none have hit the Midwest's tornado alley:

May 2: An EF-0 tornado with 70-mph winds hit Boca Raton, Florida, tossing lawn furniture around, downing a few trees and fences, and breaking one window. The tornado stayed on the ground for just four tenths of a mile and was only 50 yards wide; nobody was hurt.

May 4: An EF-0 tornado damaged barns and outbuildings near Elkton, Florida.

May 6: An EF-0 tornado with 50 mph winds passed through Bakersfield, California. The 25-yard wide tornado lasted two minutes and stayed on the ground for 1/4 mile. This tornado was not related to a supercell thunderstorm like most tornadoes are, but instead was a "landspout" tornado, caused by the interaction of the inflow into a thunderstorm with a ground-based swirling area of winds.


Video 1. One of May 2013's scant total of three tornadoes during the month's first week: an EF-0 tornado with 50 mph winds passes through Bakersfield, California at 7:10 pm PDT on May 6, 2013. The 25-yard wide tornado lasted two minutes and stayed on the ground for 1/4 mile.

Here are the record low years for the May 1-7 period, as I tabulated using 1950 - 2012 data from the Tornado History Project:

1970 - 0
1952 - 2
2013 - 3
1951 - 3
2011 - 4
1966 - 5
1957 - 7
1963 - 8
1962 - 8


Figure 1. Running 12-month total of (E)F1+ tornadoes starting in January 1954 and ending in April 2013. The record high and record low have both occurred during the past three years. EF-1 and stronger tornadoes are better to use when studying long-term trends in tornadoes, since weaker EF-0 tornadoes were significantly undercounted in the first few decades of the historical record. Image credit: Dr. Harold Brooks, U.S. Severe Weather Blog

Unusually cold spring weather to credit for the 2013 tornado drought
The low May tornado numbers come on the heels of an usually quiet March and April for tornadoes. The cause? Unusually cold weather in the Midwest, including last week's remarkable May snowstorm. Thanks to the cold spring in the Midwest during 2013, and the 2012 Midwest drought, the 197 EF-1 and stronger tornadoes that occurred during May 2012 - April 2012 was an all-time minimum for any twelve-month period since at least 1954, wrote tornado researcher Harold Brooks at the U.S. Severe Weather Blog (previous minimum: 247 tornadoes from June 1991-May 1992.) The death toll of just seven was also a record low for any twelve-month period since 1950. This is all the more remarkable since this record minimum in tornado numbers occurred less than two years after the record maximum: 1050 EF-1 and stronger tornadoes from June 2010 - May 2011. The extraordinary contrast underscores the crazy fluctuations we've seen in Northern Hemisphere jet stream patterns during the past three years. Call it "Weather Whiplash" of the tornado variety. A blog post by meteorologist Patrick Marsh of NOAA's Storm Prediction Center argues that the record 12-month tornado maximum of 1050 EF-1 and stronger tornadoes from June 2010 - May 2011 was a 1-in-62,500 year event. The record 12-month minimum of 197 EF-1 and stronger tornadoes that occurred from May 2012 - April 2013 was a 1-in-3000 to 1-in-4000 year event. In Marsh's words: "Anyway you look at it, the recent tornado "surplus" and the current tornado "drought" is extremely rare. The fact that we had both of them in the span of a few years is even more so!"


Figure 2. A reminder that May tornado seasons that start out quietly don't always end that way: the May, 2011 tornado season had only four tornadoes during the first week of May. However, the EF-5 tornado that hit Joplin, Missouri on May 22, 2011 cost $2.8 billion, making it the most expensive tornado in world history.

The forecast: quieter than usual during the coming week
The weather will warm up over tornado alley the remainder of the week, but tornado activity should will stay well below average--NOAA's Storm Prediction Center is forecasting a "Slight Risk" of severe weather over isolated portions of the country Wednesday through Friday, with damaging winds, not tornadoes, expected to be the primary threat. But things can change in a hurry in the Midwest. The first week of May in 2011 only had four tornadoes, yet that month ended up as one of the most devastating tornado months in history: 326 tornadoes, 178 deaths, and well over 1,000 injuries. The EF-5 tornado that hit Joplin, Missouri on May 22, 2011 cost $2.8 billion, making it the most expensive tornado in world history.

Jeff Masters

Tornado

Survey says: 97% of climate scientists agree that humans cause global warming

By: JeffMasters, 4:14 PM GMT on May 07, 2013

Two studies done in 2009 and 2010 found that 97% of actively publishing climate scientists agree that humans cause global warming. But what would a larger sample of the scientific literature show, extended all the way up to 2011? You're invited to help find out, by participating in an anonymous 10-minute survey where you will be reading the abstracts (summaries) of ten randomly selected technical papers on Earth's climate published between 1991 and 2011. The survey was created by physicist John Cook of The Global Change Institute at Australia's University of Queensland. Mr. Cook is the creator of one of my favorite climate change websites, skepticalscience.com. He authored one of our special Earth Day 2013 essays, Closing the Consensus Gap on Climate Change, from which I have pulled Figure 1 below. Mr. Cook is lead author on a new paper called "Quantifying the consensus on anthropogenic global warming in the scientific literature," to be published in the next month or so in Environmental Research Letters. The paper analyzes the same papers included in the survey you're asked to participate in, and the researchers plan to compare the results. Each of these 11,944 papers written by 29,083 authors and published in 1,980 journals included the keywords "global warming" or "global climate change" in their listing in the ISI Web of Science database. After reading each abstract, you will be asked to rate the level of endorsement within the abstract for the proposition that human activity (i.e., anthropogenic greenhouse gases) is causing global warming. There will be these choices available on a drop-down menu for you to choose from:

1. Explicit Endorsement with Quantification: abstract explicitly states that humans are causing more than half of global warming.
2. Explicit Endorsement without Quantification: abstract explicitly states humans are causing global warming or refers to anthropogenic global warming/climate change as a given fact.
3. Implicit Endorsement: abstract implies humans are causing global warming. E.g., research assumes greenhouse gases cause warming without explicitly stating humans are the cause.
4. Neutral: abstract doesn't address or mention issue of what's causing global warming.
5. Implicit Rejection: abstract implies humans have had a minimal impact on global warming without saying so explicitly. E.g., proposing a natural mechanism is the main cause of global warming.
6. Explicit Rejection without Quantification: abstract explicitly minimizes or rejects that humans are causing global warming.
7. Explicit Rejection with Quantification: abstract explicitly states that humans are causing less than half of global warming.
8. Don't know.

When you are all done, the survey will let you know how your average score for the ten papers compares to the rating given by the authors. The survey took me about 8 minutes to complete, and it was interesting to see the tremendous diversity of research being done on global warming in my random sample. I'll post about Mr. Cook's results when his paper is published in the next few months.


Figure 1. Two recent studies have sought to measure the level of agreement in the scientific community in different ways and arrived at strikingly consistent results. A 2009 study led by Peter Doran surveyed over 3,000 Earth scientists and found that as the scientists' expertise in climate change grew, so did the level of agreement about human-caused global warming. For the most qualified experts, climate scientists actively publishing peer-reviewed research, there was 97% agreement. Alternatively, a 2010 analysis led by William Anderegg compiled a database of scientists from public declarations on climate change, both supporting and rejecting the consensus. Among scientists who had published peer-reviewed climate research, there was 97% agreement. However, it is worth pointing out that science is not decided by majority vote. This is articulated concisely by John Reisman who says: "Science is not a democracy. It is a dictatorship. It is evidence that does the dictating." Figure and text taken from Mr. John Cook's special Earth Day essay, Closing the Consensus Gap on Climate Change.

Thanks for participating!

Jeff Masters

Climate Change

Extreme Drought to Flood in Georgia: Weather Whiplash Strikes Again

By: JeffMasters, 3:57 PM GMT on May 06, 2013

The remarkable storm that brought record-breaking May snows and cold to the Midwest last week continues to spin over the Southeast U.S. The storm is unleashing flooding rains, bringing a case of "Weather Whiplash" to Georgia: flooding where extreme drought had existed just a few months ago. The storm formed when a loop in the jet stream of extreme amplitude got cut off from the main flow of the jet over the weekend, forming a "cutoff low" that is now slowly spinning down as it drifts east over the Southeast U.S. On Sunday, the storm dumped 3.4" of rain on Atlanta, Georgia--that city's sixth heaviest May calendar day rain storm since record keeping began in 1878. Remarkably, the rains were also able to bring rivers in Central Georgia above flood stage. This portion of the country was in "exceptional drought"--the worst category of drought--at the beginning of 2013.


Figure 1. The record May snowstorm that hit the Midwest U.S. on May 1 - 3, 2013, got cut off from the jet stream and was seen spinning over the Southeast U.S. on Sunday, May 5, in this image from NASA's MODIS instrument. The 3.4" of rain that fell on Atlanta, Georgia on May 5 was that city's sixth heaviest May calendar day rainfall since record keeping began in 1878.

Weather Whiplash
Weather Whiplash--a term originally coined by science writer Andrew Freedman of climatecentral.org to describe extreme shifts between cold and hot weather--is also a excellent phrase we can use to describe some of the rapid transitions between extreme drought and floods seen in recent years. I brought up a remarkable example in mid-April, when a 200-mile stretch of the Mississippi River north of St. Louis reached damaging major flood levels less than four months after near-record low water levels restricted barge traffic, forcing the Army Corp to blast out rocks from the river bottom to enable navigation. As the climate warms, the new normal in coming decades is going to be more and more extreme "Weather Whiplash" drought-flood cycles like we have seen in the Midwest and in Georgia this year. A warmer atmosphere is capable of bringing heavier downpours, since warmer air can hold more water vapor. But you still need a low pressure system to come along and wring that moisture out of the air to get rain. When natural fluctuations in jet stream patterns take storms away from a region, creating a drought, the extra water vapor in the air won't do you any good. There will be no mechanism to lift the moisture, condense it, and generate drought-busting rains. The drought that ensues will be more intense, since temperatures will be hotter and the soil will dry out more.


Figure 2. Weather Whiplash in Georgia, 2013: the center of the state was in exceptional drought as the beginning of the year, but heavy rains in February, March, and April busted the drought. Heavy May rains have now brought flooding. Image credit: U.S. Drought Monitor.

Weather Whiplash in the Southeast U.S. more likely due to an intensification of the Bermuda High
This year's "Weather Whiplash" in Georgia is the second time in the past decade the state has gone from exceptional drought to flood. In September 2007, Atlanta, Georgia was in the midst of a 1-in-100 year drought, and was just weeks away from running out of water. Yet just two years later, the drought had been busted, and a phenomenal 1-in-500 year flood ripped through the city, killing ten and causing $500 million in damage. According to a 2011 study by a Duke University-led team of climate scientists, "Changes to the North Atlantic Subtropical High and Its Role in the Intensification of Summer Rainfall Variability in the Southeastern United States", the frequency of abnormally wet or dry summer weather in the southeastern United States has more than doubled in recent decades, due to an intensification of the Bermuda High. The scientists found that the Bermuda High, which is centered several hundred miles to the east of the Southeast U.S., has grown more intense during summer and has expanded westwards over the past 30 years. Since high pressure systems are areas of sinking air that discourage precipitation, this has made abnormally dry summers more common over the Southeast U.S. However, in summers when the Bermuda High happens to shift to the east, so that high pressure is not over the Southeast U.S., the stronger winds blowing clockwise around the Bermuda High bring an increased flow of very moist subtropical air from the south to the Southeast U.S., increasing the incidence of abnormally wet summers. Thus, the intensification of the Bermuda High has made extreme droughts and extreme floods more likely over the Southeast U.S. Using climate models, the scientists determined that human-caused global warming was likely the main cause of the significant intensification in the Bermuda High. Thus "Weather Whiplash" between drought and flood will probably become increasingly common in the coming decades over the Southeast U.S.


Figure 3. Observed June-July-August departure of precipitation from average over the SE United States for a 60-yr period (mm day−1). Horizontal dashed lines represent 1 standard deviation of the summer rainfall. Note that summer precipitation extremes exceeding one standard deviation have more than doubled during the most recent 30-year period compared to the previous 30-year period. Image credit: Li et al., 2011, Journal of Climate.

New climate change blog at The Guardian
In these days of steadily decreasing media coverage of climate change (and all science, in general), its good to see a fresh new source of good science appear in a major newspaper. The Guardian, a prominent UK news source, has a new blog called Climate Consensus – The 97%. The primary authors are Dana Nuccitelli of SkepticalScience and John Abraham, Associate Professor at the University of St. Thomas in Minnesota. The first post at the new blog is titled “Why is Reuters puzzled by global warming’s acceleration?”

Related Links
Don't miss the summary post on last week's remarkable snow storm by wunderground's weather historian, Christopher C. Burt, The Phenomenal May Snowstorm of May 1-3, 2013

Extreme Drought to Extreme Flood: Weather Whiplash Hits the Midwest: my April 19, 2013 blog post.

Southeast U.S. drought: another Tropical Storm Alberto needed: my April 2012 post describing how 20% - 50% of all droughts in the Southeast U.S. are broken by tropical storms or hurricanes.

Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse: October 2010 post by Joe Romm at climateprogress.org.

Jeff Masters

Flood Drought Climate Change

Fires, Floods, and Heavy Snow: an Extreme May Weather Situation

By: JeffMasters, 3:23 PM GMT on May 03, 2013

A highly unusual jet stream pattern is bringing a bizarre combination of heavy May snows, flooding, extreme fire danger, and well below average severe thunderstorm activity to the U.S. A strong "blocking" high pressure system has set up over Greenland, blocking the normal west-to-east progression of weather systems. A truly unusual situation has developed where the blocking high has forced a low pressure system near Greenland to move southwestwards to a point just off the New England coast. The blocking high has also forced an unusually sharp southwards dip in the jet stream over the Central U.S., where all-time May snowfall and cold temperature records are being set. This loop in the jet stream will get cut off from the main flow of the jet over the weekend, forming a "cutoff" low that will drift over the Southeast U.S., bringing cold, flooding rains of 2 - 4" over a wide swath of the Southeast. But over the Western U.S., an unusually sharp ridge of high pressure has set up, bringing record high temperatures, a strong Santa Ana wind event, and dangerous fire weather. The Santa Ana wind event has entered its second day over Southern California, where a clockwise flow of air has brought offshore winds, record high temperatures in the 90s, powerful winds gusting from 40 - 75 mph, and relative humidities less than 5%. Three destructive fires have erupted since Wednesday. The largest of these fires is called the Springs fire, and has burned 10,000 acres near Camarillo, California, about 50 miles west-northwest of Los Angeles. According to Cal Fire, the blaze was 10% contained at 6:30 am PDT May 3. The hourly observations from Thursday, May 2 at Camarillo show the onset of the Santa Ana winds impressively. The temperature jumped from 54° to 81° between 7 am and 8am, and the wind went from calm to sustained 35 mph, gusting to 43 mph, by 9 am. The temperature Thursday afternoon topped out at 98°--a new record high for the date--and the humidity dropped to a desiccating 4%. The Santa Ana wind event will not be quite as strong Friday, but will still be powerful enough to keep firefighters from gaining the upper hand on the blaze. The situation will improve dramatically over the weekend, when a low pressure system will bring in air 10 - 15° cooler, onshore winds, and rain.


Figure 1. Residents look on as a back fire set by firefighters consumes the hillside behind their homes as a wildfire burns on May 2, 2013 in Newbury Park, Calif. (Photo by Kevork Djansezian/Getty Images)


Figure 2. A bad day to be on the Channel Islands. Offshore winds blow smoke from the Springs fire, burning about 50 miles west of Los Angeles on May 2, 2013, over the Channel Islands, where the smoke mixed with brighter marine stratocumulus clouds. Image credit: NASA.

A early start to the California wildfire season
According to the National Interagency Fire Center, as of April 26, the U.S. had the fewest fires and the lowest acreage burned by wildfires in 2013 for any year-to-date period over the past ten years. But in just the past two days, the acreage burned for 2013 has jumped by 20%. Severe drought conditions across much of the Western U.S. are likely to help fuel an early and severe wildfire season during 2013, they said in their latest monthly outlook, issued May 1. Fire season is expected to be in full swing during May--a full month earlier than usual--in Southern California, California's Sacramento Valley and adjacent lower foothills, and South Central Oregon. In California, “precipitation pretty much shut off at the beginning of the year,” NIFC wildfire analyst Jeremy Sullens said during a conference call with reporters. “Since they’re not expecting a lot more precipitation for the remainder of the summer, conditions are going to worsen as we go into the hotter part of the year.” Significant fire potential will increase to above normal during May in southeastern Arizona, much of western New Mexico, and northern Virginia. Late-season snows across the Rocky Mountains in Wyoming and Colorado have dumped enough moisture to delay wildfire season until its usual June start. However, these storms have largely missed southern Colorado, where the wildfire risks remain elevated.


Figure 3. Predicted May fire activity from the National Interagency Fire Center.

Water a precious commodity in California in 2013
As of May 2, California's Sierra Mountain snowpack was just 17% of average for the date, with a water content more typical of what is seen in early July. That's bad news for a state that relies on a steady stream of meltwater to keep reservoirs filled during the summer. The poor 2012 - 2013 snow season comes on the heels of a poor 2011 - 2012 snow season, as well. But thanks to good water years leading up to 2011 - 2012, two key reservoirs are above 80% capacity: Lake Oroville, the main reservoir for the State Water Project (86%), and Lake Shasta, the main reservoir for farmers in California's Central Valley (83%.) So, California will likely weather the dry conditions of the summer of 2013--but the snows of the winter of 2013 - 2014 had better be plentiful, or the state could be looking at a serious water shortage in 2014.


Figure 4. The water content of the snowpack in the Southern Sierra Mountains of California, from San Joaquin through Kern and Owens, was 9% of average for the date on May 2, 2013 (and 7% of the average for April 1.) The snowpack is usually not this thin until early July. Statewide, the snowpack was 17% of average for the date. Image credit: California Department of Water Resources.

Amazing May snowstorm smashes more records
A rare and historic May snowstorm continues to set all-time snow and cold records for the month of May. Winter Storm Achilles brought Arkansas its first May snowfall in recorded history this morning, and four other states have set unofficial new May snowfall records for a 2-day storm: 18" in Blooming Prairie Minnesota (previous record of 15"); 17" in Rice Lake, Wisconsin (previous record, 15.4"); 12" in Chariton, Iowa (previous record: 8"), and 6" in Warrensburg, MO (previous record: 4.5".)

Here are the latest peak snowfall totals by state as of 11am EDT May 3:

Buckhorn Mtn., CO: 28.2"
Near Warren AFB, WY: 22.3"
Blooming Prairie, MN: 18"
Rice Lake, WI: 17"
Bessemer, MI: 13"
Chariton, IA: 12"
Dalton, NE: 8.5"
Beresford, SD: 6"
Warrensburg, MO: 6"
Traer, KS: 5.3"
Maysville, AR: 3"
West Siloam Springs, OK: 1.5"

And here is a partial list of cities that have set all-time low temperature records for the month of May:

Shreveport, LA: 41° on May 3 (previous May record: 42°) Records for the city go back to 1874.
Abilene, TX: 33° on May 3 (tied with 33° on May 4, 1907.)
Denver, CO: 19° on May 2 (tied with 19° on May 3, 1872)
Fort Benton, MT: 14° on May 2 (tied with 14° on May 10, 1946)
Denton, MT: 9° on May 2 (previous May record: 13° set on May 1, 2005.) Denton's records began in 1948.

Wunderground's weather historian Christopher C. Burt plans to fully document the records from this week's epic storm in his post coming on Saturday.


Figure 5. The jet stream pattern for Winter Storm Achilles showed a very high-amplitude trough over the Midwest U.S., which allowed record-breaking cold air to flow southwards out of Canada.

Nor'easter for Northeast Florida
Adding to Mother Nature's unusually varied bag of tricks for the U.S. today is a very wet and windy Nor'easter centered just east of Melbourne, which is lashing the east coast of Florida with heavy rains and rough surf. The storm brought 8.29" of rain to St. Augustine, Florida in the 24 hours ending at 8 am EDT May 3, and a daily record deluge of 1.7" of rain to Orlando, 3.1" to Fort Lauderdale, and 4.14" to Key West on May 2. The storm also spawned an EF-0 tornado with 70 mph winds that touched down in Boca Raton on May 2, causing minor damage. Radar loops out of Melbourne, Florida show disorganized heavy rain bands with a bit of rotation just offshore, and satellite loops show disorganized heavy thunderstorms extend from Cape Canaveral to Georgia. Development into a subtropical depression is unlikely due to very high wind shear of 40 knots, but this system will hang around through Saturday, generating heavy rains of up to three inches along the northeast coast of Florida. Gale warnings and flood watches are posted along much of the East Central and Northeast coasts of Florida.

Jeff Masters

Extreme Weather Winter Weather Fire Drought Achilles

Historic May snows hit Minnesota, Wisconsin, and Iowa

By: JeffMasters, 1:37 PM GMT on May 02, 2013

A rare and historic May snowstorm continues to pelt Iowa, Minnesota, and Wisconsin with snowfall amounts unprecedented in the historical record for the month of May. Winter Storm Achilles has brought 15.5" of snow to Owatonna, Minnesota, about 50 miles south of Minneapolis. This is (unofficially) the largest May snowstorm in state history, surpassing the 3-day total of a 15" snowstorm at Sandy Lake Dam/Libby. The 14.7" of snow that has fallen at Baldwin, Wisconsin is just shy of Wisconsin's May state record snowfall of 15.4". Minneapolis just missed getting heavy snow, as bands of heavy snow with thunder and snowfall rates over one inch per hour set up over Northeast Iowa and Southeast Minnesota early this morning. There are multiple reports of tree damage across Red Wing, Owatonna, and other locations in eastern Minnesota and western Wisconsin, with power outages in the thousands across the Red Wing area. I-35 is closed in both directions just north of Owatonna due to snow cover and downed power lines.

Here are the latest peak snowfall totals by state as of early Thursday morning:
• Buckhorn Mtn., Colo.:  28.2"
• Near Buford, Wyo.:  20"
• Near Harrisburg, Neb.:  6.1"
• Ringsted, Iowa:  6.5"
• Owatonna, Minn.:  15.5"
• Beresford, S.D.:  6"
• Baldwin, Wisc.:  14.7"


Figure 1. Not yet! "Looks like I got the deck furniture out a little early," writes wunderphotographer MikePic in his caption for this photo taken on May 1, 2013 in Wheat Ridge, Colorado.


Figure 2. Observed snowfall amounts in inches from the May 1 - 2, 2013 snowstorm as of 9am EDT May 2. Image credit: NWS Minneapolis.

A historic May snowstorm for many locations
Rochester, Minnesota has received 7" of snow, smashing their all-time May snowstorm record of 2", set on May 4 - 5, 1944.

Over 3" of snow has fallen in Omaha, Nebraska, breaking their all-time May snowstorm record of 2" on May 9, 1945.

It was the first one-inch-plus May snowfall anywhere in the state of Iowa since 1967. A storm-high 6.5" fell in Iowa at Ringsted.

The 1.5" of snow that fell on Sioux Falls, South Dakota Wednesday was that city's first May snowfall since 1976, the first May snowfall of greater than one inch since 1944, and the 3rd highest May snowfall on record.

Topeka, Kansas, Kansas City, Missouri, and Des Moines, Iowa are all expected to get an inch or more of snow on Thursday through Friday. This would be only the second May snowstorm in recorded history for those cities. Their only other May snowstorm occurred on May 3, 1907 (3.2" at Topeka, 1.7" at Kansas City, and 1.2" at Des Moines.)

Jeff Masters

Winter Weather Achilles

Rare May snowstorm bringing heavy snows from Colorado to Wisconsin

By: JeffMasters, 2:42 PM GMT on May 01, 2013

"Not the typical May forecast." That's the lead-in for today's National Weather Service forecast discussion for Minneapolis, where Winter Storm Achilles is expected to bring 6 - 9" of snow by Thursday morning. Snowfall rates as high as 1 - 3" per hour may occur in snow bands in East Central Minnesota this afternoon, and an 8 - 10" swath of snowfall is expected from South Central Minnesota into East Central Minnesota and West Central Wisconsin. With ratios of snow to liquid water an exceptional 5:1 or even 4:1 (normal is 10:1), the wet, heavy snow will be capable of downing power lines and tree limbs. However, the ground is warm, and accumulation on roads will be less of a problem than for the usual storm of this magnitude. The storm has already brought 7.3" of snow to Cheyenne, Wyoming, and 12 - 14" to locations 10 - 15 miles to the WNW of Cheyenne. Cheyenne's greatest May snowstorm on record was 18.3" on May 5 - 6, 1978. Denver, Colorado is expected to get 3 - 6" of snow from the storm; Boulder, Colorado has already received 8" of snow, Fort Collings got up to 9", and up to 28" has fallen in the Northern Rocky Mountains of Colorado.


Figure 1. Snow plasters trees in Fort Collins, Colorado, on May 1, 2013. Up to 9" of snow has fallen on Fort Collins from the storm. Image credit: wunderphotographer pkkeya.

A historic May snowstorm for some locations
According to the Minnesota Climatology Working Group, the greatest May snowstorm in Minneapolis is 3" on May 20, 1892, so today's winter storm has the potential to be the greatest May snowstorm in city history.

The 1.5" of snow that fell on Sioux Falls, South Dakota this morning was that city's first May snowfall since 1976, the first May snowfall of greater than one inch since 1944, and the 3rd highest May snowfall on record.

On Thursday, after the cold front from Achilles passes through Topeka, Kansas, up to one inch of snow is forecast to fall. May 3, 1907 was the only measurable snowfall at Topeka on record (3.2") during the month of May!


Figure 2. Snow on a Deserted Street in Dawson, Minnesota in Lac Qui Parle County on May 20, 1892. The storm brought Minneapolis its greatest snowfall on record, 3.0". Image courtesy the Minnesota Historical Society.

Jeff Masters

Winter Weather Achilles


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather