Category 6™

Did Hurricane Wilma have 209 mph sustained winds?

By: JeffMasters, 1:00 PM GMT on April 28, 2012

At last week's 30th Conference on Hurricanes and Tropical Meteorology of the American Meteorological Society, Dr. Eric Uhlhorn of NOAA's Hurricane Research Division presented a poster that looked at the relationship between surface winds measured by the SFMR instrument and flight-level winds in two Category 5 storms. Hurricane Hunter flights done into Category 5 Supertyphoon Megi (17 October 2010) and Category 5 Hurricane Felix (03 September 2007) found that the surface winds measured by SFMR were greater than those measured at flight level (10,000 feet.) Usually, surface winds in a hurricane are 10 - 15% less than at 10,000 feet, but he showed that in super-intense Category 5 storms with small eyes, the dynamics of these situations may generate surface winds that are as strong or stronger than those found at 10,000 feet. He extrapolated this statistical relationship (using the inertial stability measured at flight level) to Hurricane Wilma of 2005, which was the strongest hurricane on record (882 mb), but was not observed by the SFMR. He estimated that the maximum wind averaged around the eyewall in Wilma at peak intensity could have been 209 mph, plus or minus 20 mph--so conceivably as high as 229 mph, with gusts to 270 mph. Yowza. That's well in excess of the 200 mph minimum wind speed a top end EF-5 tornado has. The Joplin, Missouri EF-5 tornado of May 22, 2011 had winds estimated at 225 - 250 mph. That tornado ripped pavement from the ground, leveled buildings to the concrete slabs they were built on, and killed 161 people. It's not a pretty thought to consider what Wilma would have done to Cancun, Key West, or Fort Myers had the hurricane hit with sustained winds of what the Joplin tornado had.

Figure 1. Hurricane Wilma's pinhole eye as seen at 8:22 a.m. CDT Wednesday, Oct. 19, 2005, by the crew aboard NASA's international space station as the complex flew 222 miles above the storm. At the time, Wilma was the strongest Atlantic hurricane in history, with a central pressure of 882 mb and sustained surface winds estimated at 185 mph. The storm was located in the Caribbean Sea, 340 miles southeast of Cozumel, Mexico. Image source: NASA's Space Photo Gallery.

Figure 2. Damage in Joplin, Missouri after the EF-5 tornado of May 22, 2011. Image credit: wunderphotographer thebige.

Official all-time strongest winds in an Atlantic hurricane: 190 mph
The official record for strongest winds in an Atlantic hurricane is 190 mph, for Hurricane Allen of 1980 as it was entering the Gulf of Mexico, and for Hurricane Camille of 1969, as it was making landfall in Pass Christian, Mississippi. In Dr. Bob Sheets' and Jack Williams' book, Hurricane Watch, they recount the Hurricane Hunters flight into Camile as the hurricane reached peak intensity: On Sunday afternoon, August 17, and Air Force C-130 piloted by Marvin Little penetrated Camille's eye and measured a pressure of 26.62 inches of mercury. "Just as we were nearing the eyewall cloud we suddenly broke into a clear area and could see the sea surface below," the copilot, Robert Lee Clark, wrote in 1982. "What a sight! Although everyone on the crew was experienced except me, no one had seen the wind whip the sea like that before...Instead of the green and white splotches normally found in a storm, the sea surface was in deep furrows running along the wind direction....The velocity was beyond the descriptions used in our training and far beyond anything we had ever seen." So, the 190 mph winds of Camille were an estimate that was off the scale from anything that had ever been observed in the past. The books that the Hurricane Hunters carried, filled with photos of the sea state at various wind speeds, only goes up to 150 mph (Figure 2). I still used this book to estimate surface winds when I flew with the Hurricane Hunters in the late 1980s, and the books are still carried on the planes today. In the two Category 5 hurricanes I flew into, Hugo and Gilbert, I never observed the furrowing effect referred to above. Gilbert had surface winds estimated at 175 mph based on what we measured at flight level, so I believe the 190 mph wind estimate in Camille may be reasonable.

Figure 3. Appearance of the sea surface in winds of 130 knots (150 mph). Image credit: Wind Estimations from Aerial Observations of Sea Conditions (1954), by Charlie Neumann.

Figure 4. Radar image of Hurricane Camille taken at 22:15 UTC August 17, 1969, a few hours before landfall in Mississippi. At the time, Camille had the highest sustained winds of any Atlantic hurricane in history--190 mph.

The infamous hurricane hunter flight into Wilma during its rapid intensification
While I was at last week's conference, I had a conversation with Rich Henning, a flight meteorologist for NOAA's Hurricane Hunters, who served for many years as a Air Reconnaissance Weather Officer (ARWO) for the Air Force Hurricane Hunters. Rich told me the story of the Air Force Hurricane Hunter mission into Hurricane Wilma in the early morning hours of October 19, 2005, as Wilma entered its explosive deepening phase. The previous airplane, which had departed Category 1 Wilma six hours previously, flew through Wilma at an altitude of 5,000 feet. They measured a central pressure of 954 mb when they departed the eye at 23:10 UTC. The crew of the new plane assumed that the hurricane, though intensifying, was probably not a major hurricane, and decided that they would also go in at 5,000 feet. Winds outside the eyewall were less than hurricane force, so this seemed like a reasonable assumption. Once the airplane hit the eyewall, they realized their mistake. Flight level winds quickly rose to 186 mph, far in excess of Category 5 strength, and severe turbulence rocked the aircraft. The aircraft was keeping a constant pressure altitude to maintain their height above the ocean during the penetration, but the area of low pressure at Wilma's center was so intense that the airplane descended at over 1,000 feet per minute during the penetration in order to maintain a constant pressure altitude. By they time they punched into the incredibly tiny 4-mile wide eye, which had a central pressure of just 901 mb at 04:32 UTC, the plane was at a dangerously low altitude of 1,500 feet--not a good idea in a Category 5 hurricane. The pilot ordered an immediate climb, and the plane exited the other side of Wilma's eyewall at an altitude of 10,000 feet. They maintained this altitude for the remainder of the flight. During their next pass through the eye at 06:11 UTC, the diameter of the eye had shrunk to an incredibly tiny two miles--the smallest hurricane eye ever measured. During their third and final pass through the eye at 0801 UTC, a dropsonde found a central pressure of 882 mb--the lowest pressure ever observed in an Atlantic hurricane. In the span of just 24 hours, Wilma had intensified from a 70 mph tropical storm to a 175 mph category 5 hurricane--an unprecedented event for an Atlantic hurricane. Since the pressure was still falling, it is likely that Wilma became even stronger after the mission departed.

I'll have a new post by Tuesday at the latest.

Jeff Masters


Moderate Risk of tornadoes for Kansas; 1-year Super Outbreak anniversary

By: JeffMasters, 2:21 PM GMT on April 27, 2012

A dangerous severe weather threat is developing for Kansas today, where a small but potent storm system in the western part of the state will intensify and move east. By late this afternoon, the storm will spawn supercell thunderstorms capable of bringing large hail and strong tornadoes to eastern Kansas and extreme western Missouri. NOAA's Storm Prediction Center has placed this region in its "Moderate Risk" area for severe weather, the second highest level of alert. Cities in the Moderate Risk area include Topeka, Kansas, and Kansas City, Missouri.

Figure 1. Severe weather outlook for April 27, 2012, from our severe weather page.

One-year anniversary of the April 27, 2011 Super Tornado Outbreak
One year ago today, an astonishing outbreak of atmospheric violence unparalleled in world history hit the Southeast U.S. A total of 199 tornadoes touched down, including eleven violent EF-4s and four maximum-strength EF-5s. The 4-day period April 25 - 28 was the largest and most damaging severe weather outbreak in world history, with a total of 358 tornadoes, $10.4 billion in damage, and 321 deaths.

Video 1. Remarkable video of the tornado that hit Tuscaloosa, Alabama on April 27, 2011. Fast forward to 4:15 to see the worst of the storm.

Video 2. CBS42 meteorologist Mark Prater tracks the Tuscaloosa, Alabama tornado of April 27, 2011.

Video 3. Five-minute look at the Tuscaloosa tornado of April 27, 2011 and the damage it wrought.

Jeff Masters

Tornado Severe Weather

Extreme 111° heat hits Texas; floods kill 9 in Haiti

By: JeffMasters, 2:25 PM GMT on April 26, 2012

Another round of unprecedented April heat hit the U.S. yesterday, and this time it was Texas' turn to see large sections of the state with the hottest April temperatures in over a century of record keeping. Seven major airports in Texas set all-time April high temperatures yesterday:

Amarillo, TX: 99° (old April record 98° on 4/22/1989 and 4/22/1965)
Lubbock, TX: 101° (old April record 100° on 4/16/1925 and /22/1989)
Dalhart, TX: 96° (old April record 94° on 4/22/1989)
Borger, TX: 99° (tied April record set on 4/22/1965)
Midland, TX: 104° (old April record 101° on 4/21/1989)
Abilene, TX: 104° (old April record 102° on 4/16/1925)
Childress, TX: 106° (old April record 102° on three occasions, most recently on 4/3/2011)

According to wunderground's weather historian Christopher C. Burt, both Texas and Oklahoma came within 2°F of their all-time April state high temperature record yesterday. Altus, Oklahoma hit 104°, falling 2° short of the April state record of 106° set at the Magnum Research Station in 1972. In the Texas Mesonet, it hit 111° at Knox City 3NW, which is just 2° short of the Texas April state record of 113° set at Catarina in 1984. According to Mr. Burt, What is amazing is that Knox City is in the north-central part of the state, not down in the Rio Grande region like Catarina. The 111° would probably be pretty close to whatever the all-time hottest temp for ANY month might be in that location (probably around 115°). On Sunday this week, Nevada just missed setting their April state high temperature record, when the mercury hit 105° in Laughlin (April state record: 106° in 1989.)

Figure 1. At least 36 of the roughly 400 major U.S. cities that maintain automated weather sensors at their local airports (8%) have set or tied all-time April high temperature records so far this month. The records set yesterday in Texas are not yet in the database, and are not included on this map. Image taken from our new Record Extremes page.

Earlier this week, all-time record April heat hit large portions of Arizona, California, Nevada, Utah, Colorado, and Wyoming. At least 36 of the roughly 400 major U.S. cities that maintain automated weather sensors at their local airports (8%) have set or tied all-time April high temperature records so far this month; no all-time April cold records have been set. The U.S. has been on an extraordinary pace of setting high temperature records so far in 2012. During March 2012, an astonishing 32% of all the major airports in the U.S. set all-time March high temperature records. For the year-to-date, there have been 184 new all-time monthly high temperature records set at the major airports, and 6 all-time monthly low temperature records. Not surprisingly, the period January - March this year has been the warmest such period in the U.S. since record keeping began in 1895.

Figure 2. Total precipitable water (in mm) for this morning shows a surge of moisture moving westwards though the Caribbean. Precipitable water values in excess of 51 mm (2 inches, orange colors) are capable of generating heavy flooding rains. Image credit: University of Wisconsin CIMSS.

Heavy rains kill nine in Haiti
The rainy season has begun on the Caribbean island of Hispaniola, where heavy rains that began on Monday have triggered mudslides and floods that killed nine people. Nearly 500,000 people are still homeless in Haiti from the January 2010 earthquake, making the country highly vulnerable to flooding disasters. Heavy flooding was also a problem this week in the neighboring Dominican Republic, where 11,000 people were evacuated; no deaths were reported there, however. Precipitation forecasts from the GFS model suggest that the worst is over for Hispaniola, with the axis of greatest moisture expected to move west of the island today. This surge of moisture will bring heavy rains to Jamaica, Cuba, the Bahamas, Cayman Islands, and South Florida during the remainder of the week.

Jeff Masters

Heat Flood

March 2012: Earth's 16th warmest on record

By: JeffMasters, 1:30 PM GMT on April 25, 2012

March 2012 was the globe's 16th warmest March on record, but the coolest March since 1999, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center (NCDC). March 2012 was the 17th warmest on record, according to NASA. March 2012 global land temperatures were the 18th warmest on record, and ocean temperatures were the 14th warmest on record. The relatively cool global temperatures were due, in part, to the lingering effects of the La Niña event in the Eastern Pacific that is now ending. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were near average, the 17th or 11th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). March temperatures in the stratosphere were the 1st or 2nd coldest on record. We expect cold temperatures there due to the greenhouse effect and to destruction of ozone due to CFC pollution. Northern Hemisphere snow cover during March was near average, ranking 23rd largest (24th smallest) in the 46-year record. Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of March in his March 2012 Global Weather Extremes Summary. Notably, Norway, Iceland, and Scotland all recorded their hottest March temperatures on record, and it was the warmest March in U.S. history. Portions of Italy received no measurable precipitation whatsoever, and for most of southern Europe, it was the driest March on record. In the U.K. it was the driest March since 1953.

Figure 1. Departure of temperature from average for March 2012. The U.S. and Canada experienced the most extreme warmth of anywhere in the globe during March. Image credit: National Climatic Data Center (NCDC) .

La Niña conditions no longer present
La Niña conditions are no longer present in the equatorial Pacific, where sea surface temperatures were approximately 0.4°C below average during March and the the first half of April. The threshold for a La Niña is for these temperatures to be 0.5°C below average or cooler. NOAA's Climate Prediction Center forecasts that La Niña will be gone by the end of April. The majority of the El Niño computer models (48%) predict neutral conditions for this fall, during the August - September - October peak of hurricane season, though 35% of the models predict an El Niño will develop. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic.

Figure 2. Ice age data show that first-year ice made up 75% of the Arctic sea ice cover this March. Thicker multi-year ice used to make up around a quarter of the Arctic sea ice cover. Now it constitutes only 2%. Image credit: National Snow and Ice Data Center (NSIDC).

March Arctic sea ice extent ninth lowest on record
Arctic sea ice extent was at its ninth lowest extent on record in March, according to the National Snow and Ice Data Center (NSIDC). This was the highest since 2008 and one of the highest March extents in the past decade. Ice extent as of April 23 was close to average, one of the few times during the past decade that has occurred. However, ice in the Arctic is increasingly young, thin ice, which will make it easy for this year's ice to melt away to near-record low levels this summer, if warmer than average weather occurs in the Arctic. During the 1980s, more than 20% of the Arctic ice was more than 4 years old; this March, that fraction was just 2%. Satellite sea ice records date back to 1979.

I'll have a new post by Friday.

Jeff Masters

Climate Summaries

Death Valley's 113°: hottest April temperature on record in U.S.

By: JeffMasters, 2:37 PM GMT on April 24, 2012

An unprecedented April heat wave brought a second day of sizzling temperatures to the Western U.S. yesterday, where temperatures ranging 20 - 30 degrees above normal have toppled numerous all-time April heat records. Nearly every weather station in the Inter-mountain West has broken, tied, or come within 1 - 2 °F of their all-time record April heat record since Sunday. Most notably, the 113°F measured at Furnace Creek in Death Valley, California on Sunday, April 22 was tied for the hottest April temperature ever recorded in the U.S. According to wunderground weather historian Christopher C. Burt, the hottest reliable April temperature ever measured in the U.S. was 113°F in Parker, Arizona in 1898. A 113°F reading was also taken at Catarina, Texas in April 1984, and at Greenland Ranch in Death Valley on April 24, 1946. A hotter 118°F reading measured at Volcano Springs, CA in April 1898 is considered unreliable, since we don't know much about the exposure conditions or if the thermometers were even in shelters at remote California desert stations back in the 1880s and 1890s. The previous hottest April day in Death Valley was 111°F. Yesterday, the high temperature in Death Valley "cooled off" to 110°F, merely the fourth highest April temperature ever measured there. The heat wave peaked Sunday and Monday, and temperatures will be closer to normal for the remainder of the week.

Figure 1. All-time heat records for the month of April were set at 56 stations April 21 - 23, including at seven major cities. Image taken from wunderground's new extremes page.

As is often the case when a major Nor'easter is affecting the Eastern U.S., the record-breaking heat is due to a contortion of the jet stream that has created a strong ridge of high pressure over the Western U.S. Wunderground's extremes page lists 56 stations in the West in the past four days that have tied or broken all-time heat records for the month of April, including:

Phoenix, Arizona: 105°F (previous 105° April temperatures occurred on 4/20/1989 and 4/29/1992)
Las Vegas, Nevada: 99°F (tying old record set 4/30/1981)
Reno, NV: 90° (old record 89° 4/30/1981)
Elko, NV: 87° (old record 86° 4/30/1981). This also beat the previous so-warm-so-early-in-the-season record by 4°
Ely, NV: 84° (old record 82° 4/28/1992)
Winnemucca, NV: 90° (tying old record set 4/30/1981)
Grand Junction, CO: 89° (tying all-time April record also set on 4/29 and 4/30, 1992)

Boise, ID (91°) and Salt Lake City (88°) both came within 1°F of their record April max.

Figure 2. A late-season Nor'easter on April 23, 2012 leaves heavy snow on a farm in Penfield, NY. Image credit: wunderphotographer tvsportsguy.

Late-season Nor'easter winding down
The powerful late-season Nor'easter that brought snow, high winds, and heavy rains to the Northeast yesterday is winding down as it moves northwestwards into Canada. The storm brought an unusual amount of snow for so late in the season to western Pennsylvania, western New York, and the higher elevations in West Virginia. An earlier report posted by the NWS of 23.7” at Laurel Summit, Pennsylvania (elevation 2,770’) has now been scaled back to just 13.7”, according to the latest NWS Storm Summary. Many other higher-elevation locations saw snowfall amounts in the 6 - 12 inch range. Snow amounts were considerably lower in the major cities of the region; Buffalo, New York got 0.9", Rochester, New York, 2.8", and Erie, Pennsylvania, 0.5". The wet, heavy snow fell on regions where trees had already come into leaf, thanks to the surprise "Summer in March" heat wave that brought 80° temperatures to the Northeast over a month ago. High winds that accompanied the heavy snow caused extensive tree damage and power outages to at least 75,000 people in the region. However, the storm may have done more good than harm--widespread rainfall amounts of 2 - 4 inches occurred across Massachusetts, Rhode Island, New Jersey, Connecticut, and Southeast New York, which is under moderate to severe drought. Rainfall deficits in the region were generally 5 - 10 inches, so the Nor'easter's rains will make a significant dent in the drought. Wunderground's weather historian Christopher C. Burt has updated his post on Record Late Season Snowfalls with information from this storm.

Jeff Masters

Heat Winter Weather

Late-season Nor'easter socks Northeast U.S.

By: JeffMasters, 2:27 PM GMT on April 23, 2012

Heavy snow, high winds, and torrential rains are lashing the Northeast U.S. today, thanks to a powerful late-season Nor'easter approaching New York from the south. Wind gusts of 54 mph and 58 mph were recorded last night at New York City's La Guardia Airport and Staten Island, and heavy rains of 2 - 4 inches have been common across Massachusetts, Rhode Island, New Jersey, Connecticut, and Southeast New York since Sunday. The 2.45" that fell at Central Park in New York City yesterday broke the old record of 1.80" for the date set in 1969. The heavy rains are a boon for the region, which is under moderate to severe drought. The storm delayed the arrival of the space shuttle Enterprise, which was due to be flown into New York City's JFK Airport today and loaded on a barge to be shipped to the Intrepid Sea, Air & Space Museum on the Hudson River. The flight is now scheduled for Wednesday.

Figure 1. A late-season Nor'easter takes aim at the Northeast U.S. in this satellite image taken at 9:31 am EDT 4/23/12. Image credit: NASA/GSFC.

Heavy snow belting PA, NY, and WV
The big story with this Nor'easter is the heavy snow falling in Western Pennsylvania, Western New York, and the higher elevations in West Virginia. Wet, heavy snow of 6 - 12 inches will be common, particularly at elevations higher than 2,000 feet. Up to a foot of snow had already fallen in the Allegany Mountains of Western Pennsylvania as of 11 am EDT this morning, and 8.5" in the mountains of New York, according to the latest NWS Storm Summary. The wet, heavy snow is falling on regions where trees have already come into leaf, thanks to the surprise "Summer in March" heat wave that brought 80° temperatures to the Northeast over a month ago. High winds will accompany today's snow, and extensive tree damage and power outages can be expected. Winds have gusted as high as 39 mph this morning in Rochester, NY. Sustained north to northeast winds blowing off of Lake Ontario are expected to rise to 40 mph later today, creating waves up to 14 feet high, causing lake shore flooding problems.

History of late season snowfalls
Wunderground's weather historian Christopher C. Burt made a post last year on Record Late Season Snowfalls. He documents that the latest measurable snow in Buffalo, NY was 0.1" on May 20, 1907. Not including today, Buffalo has had ten calendar day snow events of an inch or more after the date of April 22nd. Recent events include May 7th, 1989 when 7.9 inches fell, and April 24th, 2005 when 1.2 inches of snow fell. In Rochester, NY, such events are slightly more common, with 18 such events of one inch of snow or greater after April 22nd. Recent events include April 25th, 1983, when 3.5 inches of snow fell, May 7th, 1989 when 10.7 inches of snow fell, and May 12th 1996, when 1.1 inches fell.

Two major Nor'easters this season: one in October, one in April
What's crazy about this Nor'easter is that it is only the second significant Nor'easter of the 2011 - 2012 snow season. The other major Nor'easter occurred October 30 - 31. It's pretty bizarre to have your only two significant Nor'easters of the season occur in October and April--and none in November, December, January, February, and March. I talked to a weather disaster expert in the insurance industry last week, who told me that NOAA's National Climatic Data Center will probably end up classifying last year's October 30 - 31 Nor'easter as 2011's fifteenth billion-dollar weather disaster.

Record April heat in Phoenix and Las Vegas
As is often the case when a major Nor'easter is affecting the Eastern U.S., the jet stream is contorted to bring a strong ridge of high pressure over the Western U.S., accompanied by record-breaking heat. Phoenix, Arizona hit 105°F yesterday, its tying its record for hottest April temperature (previous 105° April temperatures occurred on 4/20/1989 and 4/29/1992.) Las Vegas, Nevada hit 99°F yesterday, the hottest temperature on record for so early in the year, and tied for the hottest April temperature on record. The mercury climbed to a scorching 113° in Death Valley yesterday, a record for the date, and the hottest temperature measured in the U.S. so far in 2012.

Jeff Masters

Winter Weather Heat

Wunderground launches new Local Climate Change section

By: JeffMasters, 6:10 PM GMT on April 20, 2012

In honor of Earth Day on Sunday, wunderground has launched a new Climate Change Center, which gives people resources to understand how the climate is changing both globally and in their local neighborhoods. I am particularly pleased with our Local Climate Change feature, which allows one to see how temperature and precipitation have changed over the past 100+ years at the nearest station with a long period of measurements. Predictions from climate models on what the next 100 years may bring are overlaid for each station. Data for most U.S. stations goes back to 1895; we have data for a few stations in Europe that extend back to the 1700s. Berlin has the longest period of record in this database, with data back to 1702.

Figure 1. Screenshot of the Local Climate Change page for Washington, DC. Measured temperatures since 1820 are shown in grey. By clicking on the "Show post-1900 trend:" box, we see that the trend since 1900 has been for an increase in temperature of 1.5°C (2.7°F) per century. Moving the thin vertical red line over the image using the mouse shows that the warmest year on record in Washington D.C. was 1991. Predictions for a future with low emissions of heat-trapping gases like carbon dioxide are shown in yellow; the high emissions prediction is shown in red. Separate tabs are available to examine precipitation and snow.

Also included in the new Climate Change Center is a section addressing the common skeptical arguments made against climate change. We offer three levels of explanation. The "Basic" level is the default, but one can also see more technical in-depth discussions by clicking on the "See All Explanation Levels" link. The material was developed by physicist John Cook for his excellent web site, which is widely referenced in the climate science communication community.

Video 1. I'm featured in this video on extreme weather and climate change done by veteran videographer Peter Sinclair for the Yale forum on Climate Change and the Media this month. I'm also featured in Part 1 of this series. Our new Climate Change Center has a section for climate change videos, which includes a twice-monthly feature from GreenTV detailing the world's notable wild weather events of the past two weeks.

Earth: the Operator's Manual airs Sunday night
Penn State climate scientist Dr. Richard Alley hosts parts II and III of Earth: the Operator's Manual on PBS beginning at 7pm Sunday, April 22--Earth Day. Part I of this excellent series aired in April 2011. The series gives an overview of climate change, but primarily focuses on what we can do to help slow down climate change though smart energy choices. Dr. Alley, a registered Republican, geologist, and former oil company employee, is the Evan Pugh Professor of Geosciences at the Pennsylvania State University, and one of the most respected and widely published world experts on climate change. Dr. Alley has testified before Congress on climate change issues, served as lead author of "Chapter 4: Observations: Changes in Snow, Ice and Frozen Ground" for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and is author of more than 170 peer-reviewed scientific articles on Earth's climate. He is also the author of a book I highly recommend--The Two Mile Time Machine, a superb account of Earth's climate history as deduced from the 2-mile long Greenland ice cores. Dr. Alley is an excellent and engaging speaker, and I highly recommend listening to his 45-minute keynote speech, "The Biggest Control Knob: CO2 in Earth's Climate History", given at the 2010 American Geophysical Union meeting, via this very watchable recording showing his slides as he speaks in one corner of the video. If you want to understand why scientists are so certain of the link between CO2 and Earth's climate, this is a must-see lecture.

Have a great weekend, everyone, and I'll be back Monday with a new post. I'd like to thank Wunderground meteorologist, Angela Fritz for spearheading the creating the new Climate Change Center; it's a product I'll be referring to frequently in the future, and one we'll be updating in the coming months with data on local sea level rise, fire risk, and drought.

Jeff Masters

Climate Change

Southeast U.S. drought: another Tropical Storm Alberto needed

By: JeffMasters, 11:26 AM GMT on April 19, 2012

Today is my last day in Ponte Vedra Beach, Florida, where 700 of the world's hurricane experts are gathered to attend the 30th Conference on Hurricanes and Tropical Meteorology of the American Meteorological Society. It's been a great week of learning and catching up with old friends, and I present below a few final summaries of talks I attended.

Impact of Tropical Cyclones on drought alleviation in the Atlantic and Gulf Coasts
Dr. Pat Fitzpatrick of the Stennis Space Center in Mississippi discussed how landfalling tropical storms and hurricanes can alleviate drought. The biggest winner tends to be the Southeast U.S. states of Florida, Georgia, South Carolina, and North Carolina, where about 20% - 50% of all droughts between 1960 - 2009 were busted by a landfalling tropical storm or hurricane. It is uncommon for Texas to see a drought busted; less than 10% of all Texas droughts have been ended by a hurricane or tropical storm. This occurs because the Southeast U.S. can receive heavy rains from hurricanes moving up the East Coast, or moving through the Gulf of Mexico, while relatively few storms track over Texas. Over the course of a year, hurricanes and tropical storms contribute 15 - 20% of rain along the Gulf Coast, and 3 - 16% along the East Coast. The length of a drought does not seem to affect whether a drought can be ended by a hurricane or not. Hurricanes have been able to end both short (< 3 month) and long (> 12 month droughts) equally well.

Figure 1. Example of a drought-busting tropical storm. Moderate drought (Palmer Drought Severity Index, PDSI, ≤ –2.0) was present in 52 percent of the Florida, Georgia, South Carolina, and North Carolina climate divisions in May 2006. The percentage decreased to 29 percent after Tropical Storm Alberto passed through on June 11 - 15, 2006. Image credit: U.S. Drought Monitor.

Figure 2. Rainfall in inches from the passage of Tropical Storm Alberto in 2006. Image credit: NOAA/HPC.

According to the U.S. drought monitor, over 90% of the area of Florida, Georgia, South Carolina, and North Carolina are currently in moderate to exceptional drought. There is 1 - 2 inches of rain coming to much of the region over the next few days, but that will not be enough to bust the drought. Based on Dr. Fitzpatrick's research, there is a 20% - 50% chance that the drought will be broken by a tropical storm or hurricane. The first storm on the list in 2012 is Alberto again; let's hope we get another Alberto this year that imitates the 2006 version of Alberto.

Patterns of rapid intensification
Peter Yaukey of the University of New Orleans studied patterns of hurricane rapid intensification in the Atlantic from 1950 - 2009. The Gulf of Mexico and Caribbean saw the most rapid intensification events, and the Northeast Atlantic the fewest. Interestingly, he found that rapid intensification events did not peak in September, but tended to be more common in June and July. Hurricane are less likely to intensify in the late afternoon and early evening (near 00 UTC), and more likely to intensify just after midnight, at 06 UTC.

Jeff Masters

Hurricane Drought

91L no concern; more postcards from the AMS hurricane conference

By: JeffMasters, 1:12 PM GMT on April 18, 2012

I'm in Ponte Vedra Beach, Florida this week, where the world's hurricane experts are gathered to attend the 30th Conference on Hurricanes and Tropical Meteorology of the American Meteorological Society. Most of the Hurricane Specialists from the National Hurricane Center are here, and they are keeping an eye on the waters a few hundred miles east of Bermuda, where an extratropical storm has cut off from the jet stream and is slowly acquiring tropical characteristics. This system was designated Invest 91L last night by NHC. Ocean temperatures are around 20°C (68°F) in the region, which is well below the 26°C usually needed for a tropical storm to form. Wind shear is a high 20 - 30 knots. Nevertheless, 91L has managed to develop a small amount of heavy thunderstorm activity near its center, and may continue to show more organization as it moves slowly southeastward over the next day or two. I give 91L a close to 0% chance of becoming a named storm in the next two days, and NHC seems to have stopped issuing new products for the system. By the end of the week, 91L should get picked up by a trough of low pressure and move off to the northeast. The storm is not a threat to any land areas.

Figure 1. Morning satellite image of Invest 91L. The island of Bermuda is seen at the left side of the image.

Global tropical cyclones and climate: current signal
Now, I'll summarize a few of the excellent talks given at this week's AMS hurricane conference. Dr. Greg Holland of the National Center for Atmospheric Research talked about the impact of global warming on hurricane intensities. Using data beginning in 1975, the beginning of the satellite era, he showed that while the total number of hurricanes globally has decreased in recent years, the proportion of hurricanes that are of Category 4 - 5 intensity has increased by 40%. He showed that this change could be related to a 0.8°C increase in global temperature during the period. He concluded that when hurricanes form, they are finding that it is easier for them to reach higher intensities.

Sensitivity of the strongest hurricanes to ocean surface warmth
Dr. Jim Elsner of Florida State University showed that observations indicate a sensitivity of hurricane winds of 8.2 m/s +/- 1.19 per degree Centigrade of ocean warmth, using data in the Atlantic from 1981 - 2010 (for oceans areas warmer than 25°C.) Using a high resolution model (HiRAM) with 50 km resolution, a sensitivity of only 1.5 +/- .6 m/s was found, calling into question the usefulness of current models for assessing future hurricane activity.

How will climate change affect hurricane tracks?
Angela Colbert of the University of Miami used 17 global climate models, the BAM hurricane tracking model, and the Atlantic historical HURDAT data base to see how hurricane tracks might change in the future. She classified storms as either straight moving (which tend to hit the Caribbean or U.S. Gulf Coast), recurving landfalling (U.S. East Coast impacts), or recurving ocean storms that miss landfall. She projected a 6% increase in recurving ocean storms and an 8% decrease in straight-moving storms by the end of the century, due to climate change. A decrease of 1- 2 storms per decade is predicted for the Caribbean and Gulf of Mexico, and an increase of 1 - 2 storms per decade in the waters of the mid-Atlantic, and along the East Coast of Florida. This occurs primarily because of an increase in westerly winds over the Central Atlantic, and to a lesser degree, an eastward change in genesis location closer to the coast of Africa. Both of these factors would tend to increase the number of recurving storms.

Jeff Masters


Postcards from the AMS hurricane conference: Bob Simpson honored

By: JeffMasters, 12:49 PM GMT on April 17, 2012

I'm in Ponte Verda Beach, Florida this week, where the world's hurricane experts are gathered to attend the 30th Conference on Hurricanes and Tropical Meteorology of the American Meteorological Society. The conference started out with a remarkable blast from the past, when Dr. Bob Simpson, one of the originators of the familiar Saffir-Simpson scale, gave the opening talk. Dr. Simpson has been a meteorologist since 1940, and is in amazing shape for someone who turns 100 years old later this year. Dr. Simpson served as director of the National Hurricane Center, and was joined in the audience by two other NHC directors, May Mayfield and BIll Read. Dr. Simpson described his work with civil engineer Herb Saffir, who worked for the United Nations to develop low-cost housing all over the world that could withstand strong winds. Saffir and Simpson worked together, using data from aerial surveys of hurricane damage that began with Hurricane Audrey in 1957, to help develop their famous scale, which assigns a Category 1 through 5 rating to a storm based on its winds. The Saffir-Simpson scale was finally published in 1973, and gained widespread popularity after Neil Frank replaced Simpson as the director of NHC in 1974. The audience gave Dr. Simpson a standing ovation for making the effort to travel here and give a talk.

Figure 1. Dr. Robert Simpson addresses the 30th Conference on Hurricanes and Tropical Meteorology of the American Meteorological Society on April 15, 2012, assisted by session chair Dr. Greg Holland.

Hurricane Andrew: 20 years later: What have we learned?
This year marks the 20th anniversary of the incredible devastation wrought in South Florida by Category 5 Hurricane Andrew. Hurricane Andrew was a wake-up call for how poorly buildings were constructed in hurricane-prone areas, and Dr. Tim Marshall of Haag Engineering discussed what we learned from the hurricane. Interestingly, much of Andrew's damage occurred in the storm's outer bands, before the peak winds arrived. The heaviest damage occurred in subdivisions that had poor building codes. Removal of asphalt shingles was a big problem. A lot of shingles were fastened with staples that ripped out, due to poor location, orientation, and depth. Often the secondary felt barrier below the shingles was not glued on, and was ripped away once the shingles ripped away. Once you lose your shingles, you often lose your house, since rain can then get into the house and destroy the interior. Andrew led to a complete revision of the building codes in South Florida, which are now the strongest in the nation. The new building codes, however, still allow for some dubious practices--like stapling shingles to roofs, and the placement of loose gravel on roof tops. Marshall concluded the talk by emphasizing that taping windows doesn't work. Board up your windows, or better yet, use steel shutters.

Figure 2. Hurricane Andrew as it closed in on South Florida 20 years ago. Image credit: NOAA.

Jeff Masters


Weekend tornado outbreak: 1 EF-4, 2 EF-3s, 6 dead, damage near $300 million

By: JeffMasters, 2:09 PM GMT on April 16, 2012

Damage surveys continue in the Plains in the wake of Saturday's major tornado outbreak. NOAA's Storm Prediction Center logged 110 preliminary tornado reports, with an additional 10 reports from Sunday. At least one tornado was a violent EF-4, which hit mostly unpopulated areas in Ellsworth County, Kansas. The only fatalities from the outbreak occurred in Woodward, Oklahoma, where an EF-3 tornado hit at night after lightning knocked out the town's tornado sirens. Six people were killed, three of them children. A preliminary rating of EF-3 has also been given to a tornado that hit the south and southeast portions of Wichita, Kansas near 10:30 pm CDT Saturday night. The tornado did significant damage to McConnell AFB and to a nearby trailer park. All of the residents of the trailer park were in the trail park's tornado shelter, which undoubtedly saved many lives. Two residents required hospitalization. Damage from the Wichita tornado has been estimated at $283 million.

Figure 1. Radar reflectivity image of the EF-3 tornado that hit the south side of Wichita, Kansas, causing damage estimated at $283 million.

Video 1. Storm chaser video of one of Saturday's impressive tornadoes near Salina, Kansas. At about the 3 minute mark, you'll see what appear to be cows moving very fast in a mighty tail wind.

Video 2. Storm chaser video of the nighttime Wichita, Kansas tornado of April 14, 2012.

New dire language in tornado warnings
National Weather Service offices in several states in the Plains are experimenting this year with new wording in public advisories when a particularly dangerous tornado has touched down. If spotters confirm that a large and damaging tornado is on the ground, the NWS has the option of including some rather dire wording to get the public to take action. About 3/4 of all tornado warnings are false alarms. This primarily occurs because the NWS will issue a warning for a rotating thunderstorm spotted on radar, and these thunderstorms don't always have funnel clouds that reach to the ground. But when spotters actually verify that a tornado is on the ground, and that tornado has a long history of causing damage, issuance of one the new direly-worded advisories may help give the public the message that this tornado is not going to be a false alarm and they better take it seriously. Such an advisory was issued for Saturday's Wichita, Kansas tornado, which turned out to be an EF-3 that caused major but not catastrophic damage. The dire wording of the advisory predicted the type of damage associated with a violent EF-4 or EF-5 tornado, "with complete devastation likely." The damage from this tornado fell short of that mark, but I believe it was a reasonable usage of the new type of advisory:

1033 PM CDT SAT APR 14 2012












Jeff Masters

Tornado Severe Weather

Damaging Tornadoes Slam Plains

By: Shaun Tanner , 6:50 AM GMT on April 15, 2012

A devastating string of severe thunderstorms and tornadoes tracked through Texas, Oklahoma, Kansas, and Nebraska on Saturday. This severe weather outbreak was remarkable in its duration as supercell thunderstorms began to pop up in western Kansas late Saturday morning, and the dry line that was supposed to represent the end of the severe weather threat was only halfway through Kansas, Oklahoma, and Texas by 1:00 AM Central Time Sunday. The moisture difference on either side of this dry line was remarkable as well, with dew points in the upper 60's to the east, and a very dry 20's to the west.

SPC Storm Reports from Saturday

The SPC storm reports show the track of these storms, with Kansas being the hardest hit. Early in the afternoon, most of the supercell thunderstorms were consistently producing weak tornadoes that skipped across western and central Kansas. As the low-level jet stream kicked in late in the afternoon and into the evening, the thunderstorms strengthened considerably. Probably the most remarkable supercell thunderstorm began in western Oklahoma near Woodward as a stunning multi-vortex tornado. The tornado actually was several tornadoes that danced into southern Kansas and eventually threatened Wichita. The tornado passed just south and east of the city, producing an 84 mph wind gust at the Wichita Airport. It also did extensive damage at the airport. In addition, the Oaklawn area of Wichita was declared a disaster area very soon after the tornado passed. The Sedgwick County commissioner declared the county a disaster area. This wedge tornado eventually moved along the Kansas Turnpike northeast of Wichita before finally dissipating.

Figure 1. Double tornadoes in Oklahoma close to the Kansas border. Image credit:

Figure 2. This tornado sparked a fire in Oklahoma as it passed through the area northeast of Woodward. Image credit:

The deadliest tornado of the outbreak struck Woodward, OK early Sunday morning, as the main squall line moved through western Oklahoma. This tornado was very large and particularly dangerous since it occurred at night when most residents assumed the threat had ended. There were multiple reports of not hearing the city's siren, so it is entirely possible that the siren was either struck by lightning or hit by the tornado itself. At least five deaths have been confirmed in the Woodward area from this tornado. Probably the scariest video of a tornado I have ever seen was taken of this Woodward tornado as it moved into town. Note you can see the scale of the tornado as between power flashes.

Video 1. Storm chaser video of one of Saturday's impressive tornadoes near Salina, Kansas.

Figure 3. Radar reflectivity image of the tornado that hit the south side of Wichita, Kansas, causing damage at the Wichita airport.

Perhaps the most telling feature of this severe weather outbreak was its repetitive nature. Salina, KS was tornado warned three times by three separate severe thunderstorms. Similarly, areas from Medicine Lodge to Kingman, Kansas were warned for two separate thunderstorms, while Woodward itself was warned very early in the day before a different tornado moved through the city late in the night.

Last night's storms have weakened, but a new round of severe weather is expected Sunday afternoon over portions of Wisconsin, Minnesota, and Iowa. NOAA's Storm Prediction Center has put the region under their second highest level of alert, a "Moderate Risk."

Shaun Tanner

Tornado Severe Weather

Dangerous tornado outbreak expected Saturday; Gulf of Mexico SSTs warmest on record

By: JeffMasters, 2:57 PM GMT on April 13, 2012

A dangerous tornado outbreak is expected on Saturday over the Plains, says NOAA's Storm Prediction Center (SPC). Warm, moist air flowing northwards from a Gulf of Mexico that has record-warm waters will collide with cold air funneling down from Canada, creating a highly unstable air mass capable of creating strong thunderstorm updrafts. An impressive upper-level low, accompanied by a jet stream with 105 - 125 mph winds at middle levels of the atmosphere, will create plenty of wind shear, giving the air the spin it needs to form tornadoes. SPC has has issued their highest level of alert, a "High Risk," for much of Oklahoma, Kansas, and Nebraska for Saturday. Included in the "High Risk" area are the cities of Wichita, Oklahoma City, and Lincoln. This is the second time SPC has issued a "High Risk" forecast this year; the first "High Risk" forecast came for the March 2 tornado outbreak, which killed 41 people and did $1.5 - $2 billion in damage. It is very unusual for SPC to issue a "High Risk" forecast more than a day in advance of a suspected tornado outbreak; according to Wikipedia, today's "High Risk" forecast is only the second time SPC has ever done this. The other instance was for the April 6 - 8, 2006 tornado outbreak focused over Tennessee, which generated 73 tornadoes that killed 13 and did $1.5 billion in damage. People living in the threatened area need to pay close attention on Saturday to this dangerous severe weather situation.

Figure 1. Severe weather risk for Saturday, April 14, 2012, from NOAA's Storm Prediction Center.

Gulf of Mexico water temperatures the warmest on record
Temperatures in the states bordering the Gulf of Mexico were the 3rd - 7th warmest on record during the first three months of 2012, according to NOAA's National Climatic Data Center. This allowed Sea Surface Temperatures (SSTs) in the Gulf of Mexico (25 - 30°N, 85 - 90°W) to climb to 1.4°C (2.5°F) above average during March 2012, according to a wunderground analysis of the Hadley Centre SST data set. This is the warmest March value on record for the Gulf of Mexico, going back over a century of record keeping. During the first two weeks of April, Gulf of Mexico waters remained about 1.5°C above average, putting April on pace to have the warmest April water temperatures on record. Only one year in the past century has had April water temperatures in the Gulf of Mexico more than 1.1°C above average; that year was 2002 (1.4°C above average.) All that record-warm water is capable of putting record amounts of water vapor into the air, since evaporation increases when water is warmer. Because moist air is less dense than dry air, this warm, moist air flowing northwards from the Gulf of Mexico into the developing storm system over the Plains will be highly unstable once it encounters cold, dry air aloft. The record-warm waters of the Gulf of Mexico are a key reason for the high risk of severe weather over the Plains this weekend.

Figure 2. Departure of Sea Surface Temperature (SST) from average for April 12, 2012, as computed by NOAA/NESDIS. SSTs in the Gulf of Mexico are at their warmest levels on record for this time of year.

Follow Weather Underground on twitter for the latest on this potential severe weather outbreak.

Jeff Masters

Severe Weather Tornado

Damaging freeze hits the Midwest U.S.

By: JeffMasters, 1:46 PM GMT on April 12, 2012

Large portions of the Midwest U.S. shivered through a hard freeze (temperatures below 28°F ) this morning, and freezing temperatures extended as far south as Tennessee and North Carolina. Though the cold temperatures were not unusual for this time of year, they likely caused widespread damage to flowering plants fooled into blooming by last month's unprecedented "Summer in March" heat wave. Growers of apples, pears, peaches, nectarines, plums, and cherries worked during the night and early morning to minimize the damage by running large fans and propane heaters in their orchards, and some even rented helicopters in an attempts to keep temperatures a few degrees warmer. While freezing temperatures for an extended period will not kill the trees, they will destroy the flowers and fragile buds that are needed to produce fruit later in the year. Temperatures of approximately 28°F will kill about 10% of fruit tree buds and flowers, while temperatures of 25°F will produce a 90% kill rate. Temperatures of 25° were common over Michigan, Wisconsin, and Minnesota this morning, and I expect that this morning's freeze was severe and widespread enough to cause tens of millions of dollars in damage to the fruit industry. There have been numerous freezes and frosts over the Midwest's fruit growing regions since late March, and orchards are definitely taking a major beating from the weather. It will be several weeks before the extent of the damage is known, but I think that so far it is unlikely that the industry has suffered a billion-dollar disaster, such as occurred in 2007. A warm spell in March that year was followed by cold temperatures in early April that were 10 - 20 degrees below average, bringing killing frosts and freezes to the Midwest and South that caused $2.2 billion in agricultural damage, wiping out apple, peach, winter wheat and alfalfa crops.

Figure 1. Temperatures this morning dipped below freezing across most the northeast quarter of the country, extending into Tennessee and North Carolina. Image taken from our wundermap with the new "go back in time" feature turned on.

History of billion-dollar U.S. freezes
Freezes can cause big damage to agriculture. According to NOAA's National Climatic Data Center, there have been six billion-dollar U.S. freezes since 1980, accounting for 5% of all billion-dollar weather-related disasters. Five of these freezes affected California or Florida; one hit the Midwest. Ranked by damages (in 2011 dollars), here are the six billion-dollar U.S. freeze events since 1980:

1) California Freeze of December 1990. Severe freeze in the Central and Southern San Joaquin Valley caused the loss of citrus, avocado trees, and other crops in many areas. Several days of subfreezing temperatures occurred, with some valley locations in the teens. $5.9 billion in direct and indirect economic losses, including damage to public buildings, utilities, crops, and residences.

2) Florida Freeze of December 1983. Severe freeze central/northern Florida; about $4.5 billion damage to citrus industry.

3) California Freeze of December 1998. A severe freeze damaged fruit and vegetable crops in the Central and Southern San Joaquin Valley. Extended intervals of sub 27° F temperatures occurred over an 8-day period; $3.5 billion estimated damages/costs.

4) Florida Freeze of January 1985. Severe freeze in central/northern Florida; about $2.5 billion damage to citrus industry.

5) East/Midwest freeze of April 2007. Widespread severe freeze over much of the East and Midwest (AL, AR, GA, IL, IN, IA, KS, KY, MS, MO, NE, NC, OH, OK, SC, TN, VA, WV), causing significant losses in fruit crops, field crops (especially wheat), and the ornamental industry. Temperatures in the teens/20's accompanied by rather high winds nullified typical crop-protection systems. Over $2.2 billion in damage/costs.

6) California Freeze of January 2007. For nearly two weeks in January, overnight temperatures over a good portion of California dipped into the 20's, destroying numerous agricultural crops, with citrus, berry, and vegetable crops most affected. $1.5 billion estimated in damage/costs; 1 fatality reported.

Record warmth in the Western U.S.
As is often the case when one part of the country is experiencing much cooler than average temperatures, the other half is seeing record warmth, due to a large bend in the jet stream that allows warm air to flow northwards. Much of Wyoming, Montana, Idaho, and Colorado experienced record warm temperatures yesterday. Most notably, Jackson, Wyoming hit 72°F, the earliest 70° reading in their history, and 27° above their normal high of 45°.

Figure 2. Severe weather risk for Saturday, April 14, 2012, from NOAA's Storm Prediction Center.

Tornado outbreak possible Saturday in Kansas and Oklahoma
A significant tornado outbreak is possible on Saturday, says NOAA's Storm Prediction Center. A warm, unstable airmass will collide with cold air funneling down from Canada, and strong jet stream winds will create plenty of wind shear. There is the potential for long-track strong tornadoes over Oklahoma and Kansas on Saturday, and SPC has has issued their second highest level of alert, a "Moderate Risk," for the region.

First named storm in the Atlantic possible next week
Both the GFS and ECMWF models are predicting that an extratropical "cut-off" low will separate from the jet stream early next week several hundred miles east of Bermuda, and linger for several days over subtropical waters with temperatures in the 22 - 24°C range. These ocean temperatures may be warm enough to allow the storm to organize into a named subtropical storm. However, climatology argues against such an occurrence; there has been only one named April storm in the Atlantic since 1851. If a subtropical storm does form next week, it would probably not affect any land areas.

Jeff Masters

Winter Weather

March 2012: warmest in U.S. history

By: JeffMasters, 2:12 PM GMT on April 10, 2012

Not only was March 2012 the warmest March in the U.S. since record keeping began in 1895, it was also the second most extreme month for warmth in U.S. history, said NOAA yesterday, in their monthly "State of the Climate" report. The average temperature of 51.1°F was 8.6 degrees above the 20th century average for March, and 0.5°F warmer than the previous warmest March in 1910. Of the more than 1,400 months that have passed since the U.S. weather records began in 1895, only one month--January 2006--had a larger departure from its average temperature than March 2012. A remarkable 25 states east of the Rockies had their warmest March on record, and an additional 15 states had a top-ten warmest March. Only four states were cooler than average, with Alaska being the coldest (tenth coldest March on record.)

Figure 1. Temperature rankings for March 2012 in the Contiguous U.S. Twenty five states set records for warmest March in the 118-year records (red colors.) Image credit: NOAA.

March 2012: most daily records broken of any month since July 1936
A wunderground analysis of weather records from NOAA's National Climatic Data Center temperature record database reveals that more daily high temperature records were broken in March in 2012 than for any month except July 1936, going back at least 100 years. Fully 11.3% of all daily high temperature records for the month of March in the U.S. are now held by the year 2012, for the 550 stations in NOAA's National Climatic Data Center database that have weather records extending back at least 100 years. The only month in U.S. history holding a higher percentage of daily temperatures records is July 1936. That month holds 14.4% of all the U.S. high temperature records for the month of July. That month occurred in the great Dust Bowl summer of 1936, the hottest summer in U.S. history.

Summer in March 2012: records not merely smashed, but obliterated
Among the 15,000 daily records for warmth set in March 2012 were 21 truly astonishing ones: cases where the low temperature for the day beat the previous high temperature for the day. It is quite rare for a weather station with a 50+ year period of record to break a daily temperature record by more than 10°F. During "Summer in March, 2012", beating daily records by 10° - 20°F was commonplace, and NOAA lists 44 cases where a daily record was broken by more than 22°F. Extraordinarily, four stations broke a record for the date by 30°F or more. Canada holds the most surreal record of this nature during the "Summer in March, 2012" heat wave: Western Head, Nova Scotia hit 29.2°C (85°F) on March 22, breaking their previous record for the date (10.6°C in 1969) by 18.6°C (33.5°F.) Canada also had several stations break their all-time warmest April temperature records in March.

Last 3 months and 12 months were the warmest on record
The previous 12-month period (April 2011 -March 2012), which includes the second hottest summer (June-August) and fourth warmest winter (December-February), was the warmest such period for the contiguous United States. The year-to-date period (January - March) was also the warmest on record. NOAA's U.S. Climate Extremes Index, an index that tracks the highest 10 percent and lowest 10 percent of extremes in temperature, precipitation, and drought, was 39 percent, nearly twice the long-term average and the highest value on record for the January - March period. The predominant factor was the large area experiencing extremes in warm daily maximum and minimum temperatures.

Analyzing the "Summer in March, 2012" heat wave
Dr. Martin Hoerling of NOAA's Earth System Research Laboratory in Boulder has posted a thorough analysis of the heat wave, which he calls, "Meteorological March Madness 2012". He explains that the event was probably a natural phenomenon, one that was predicted more than a month in advance by NOAA's long-range CFS model. A similar, though not as intense heat wave occurred in March 1910. However, he notes that the approximate 0.5 - 1°C warming in the Ohio Valley/Midwest U.S. in recent decades--due to human-caused emission of heat trapping gases like carbon dioxide--has significantly increased the odds of major heat waves occurring. He speculates that the odds of a 1-in-40 year heat wave in the Midwest may have increased by about 50% due to human-caused global warming, but that we really don't know how much global warming may have increased the odds of the March 2012 heat wave, saying "This issue of estimating reliable statistics of extreme, rare events continues to be a matter of active research." He estimates that human-caused global warming likely increased the intensity of the March 12 - 23, 2012 heat wave by about 5 - 10%, and concludes by saying, "The probability of heatwaves is growing as [human-caused] warming continues to progress. But there is always the randomness."

Jeff Masters

Climate Summaries Climate Change

First U.S. billion-dollar disaster of 2012: March 2-3 tornado outbreak

By: JeffMasters, 1:17 PM GMT on April 09, 2012

The first billion-dollar weather disaster of 2012 for the U.S. was the March 2 - 3 tornado outbreak in the Midwest and Southeast, said NOAA today. They put the total cost of the tornadoes that killed 41 people in Kentucky, Indiana, Ohio, and Alabama at 1.5 billion. Global reinsurance company AON Benfield, in their latest monthly Global Catastrophe Recap Report, put the damage at $2 billion. The outbreak spawned two EF-4 tornadoes, one which devastated Henryville, Indiana, and another that plowed through Crittenden, Kentucky. The two other tornado outbreaks of note that occurred in February and March had damages less than $1 billion: the Leap Day tornadoes in Illinois and surrounding states ($475 million), and the Dexter, Michigan tornado EF-3 tornado of March 15 ($275 million.) I expect that the tornadoes that swept through the Dallas, Texas region last week will likely have a damage tally in the hundreds of millions, but fall short of the billion-dollar mark. In 2011, we already had two billion-dollar weather-related disasters by the first week of April, so we are behind last year's pace. NOAA's National Climatic Data Center logged a record fourteen billion-dollar weather disasters in 2011. There has been just one other billion-dollar disaster in the world this year, according to AON Benfield--severe flooding in Australia's New South Wales and Victoria states in late February and early March that caused $1.58 billion in damage. A separate flooding episode in late January and early February caused an additional $920 million in damage in Australia.

Figure 1. A school bus mangled by the EF-4 Henryville, Indiana tornado of March 2, 2012. Image credit: NWS Louisville, Kentucky.

A week for severe severe weather across the Plains and Midwest
Expect severe weather and tornadoes every day this week across the Plains and Midwest U.S., says NOAA's Storm Prediction Center (SPC). A warm, unstable airmass will collide with cold air funneling down from Canada most of the week, creating conditions ripe for severe thunderstorms and tornadoes all week. The main focus of severe weather today will be over Western Oklahoma and portions of the Texas Panhandle, where SPC has issued their lowest highest level of alert, a "Slight Risk."

Figure 2. Severe weather threat for Monday, April 9, 2012.

Video 1. Wunderground tornado expert Dr. Rob Carver alerted me to this remarkable railroad surveillance video recently posted to YouTube that captures a train derailed by a Tornado January 7, 2008 in Harvard, IL. The tornado moved across the Chicago and Northwestern railroad where it blew 12 railroad freight cars off the track. The train was moving at the time the tornado hit it, so as the main engine stopped, the remaining cars on the track continued along it and slammed into the front part of the train. No one was injured, but 500 residents in the nearby unincorporated town of Lawrence were evacuated because of the potential for a hazardous materials situation.

Jeff Masters

Extreme Weather

CSU: expect a quiet 2012 Atlantic hurricane season; EF-3 tornado confirmed in Texas

By: JeffMasters, 2:47 PM GMT on April 05, 2012

Expect one of the quietest Atlantic hurricane seasons since 1995 this year, say the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 4. They call for an Atlantic hurricane season with below-average activity: 10 named storms, 4 hurricanes, and 2 intense hurricanes. An average season has 10 - 11 named storms, 6 hurricanes, and 2 intense hurricanes. The 2012 forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (24% chance, 31% chance is average) and the Gulf Coast (24% chance, 30% chance is average). The Caribbean is forecast to have a 34% chance of seeing at least one major hurricane (42% is average.) Four years with similar pre-season March atmospheric and oceanic conditions were selected as "analogue" years that the 2012 hurricane season may resemble: 2009, 2001, 1965, and 1957. These years all had neutral to El Niño conditions during hurricane season. The average activity for these years was 9.5 named storms, 4.8 hurricanes, and 2.3 major hurricanes.

Figure 1. Departure of sea surface temperature (SST) from average for April 5, 2012, as computed by NOAA's NESDIS branch. SSTs in the hurricane Main Development Region (red box) were near average to below-average.

Why the forecast of a quiet season?
The CSU team cited two main reasons why this may be a quieter than average hurricane season:

1) La Niña has weakened rapidly over the tropical Eastern Pacific over the past month, and is expected to be gone by the end of April. In its wake, El Niño conditions may develop in time for the August - September - October peak of hurricane season. If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. The CSU team is leaning towards putting their trust in the ECMWF model, which is predicting that a weak El Niño event will be in place by fall.

2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were near average to below average in March 2012. Virtually all African waves originate in the MDR, and these African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. This year's SSTs in the MDR are among the coolest we've seen since our current active hurricane period began in 1995. The cool temperatures are largely due to strong surface winds that blew during the winter over the tropical Atlantic in response to the positive phase of the North Atlantic Oscillation (NAO.) The strong winds stirred up the water, bringing up cooler waters from the depths.

How good are the April forecasts?
The forecasters are using a new statistical model developed last year for making April forecasts, so we don't have a long enough track record to judge how good the new model is. The new model correctly predicted a more active than average season for last year, though called for more activity than was actually observed. However, April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño, conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart.

CSU maintains an Excel spreadsheet of their forecast errors ( expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology) for their their April forecasts. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due by June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.

Preliminary NWS survey of the April 3rd, 2012 Dallas, Texas tornadoes
The Fort Worth Weather Service office began surveying tornado damage yesterday from three tornadoes that ripped through the Dallas metro area on Tuesday afternoon. Official storm surveys will be released in the next few days. The Arlington/Kennendale tornado has a preliminary rating of EF-2. They suspect wind speeds peaked around 135mph, a path length of 4.6 miles, and a maximum width of 400 yards (1/4 mile). The Lancaster/Hutchins tornado has a preliminary rating of EF-2, and they suspect it had a maximum width of 200 yards (1/8 mile). The Forney tornado has a preliminary rating of EF-3, with suspected winds up to 150 mph. Surveys are ongoing--there's a lot of damage to see along the tornado paths. These ratings reflect the most severe damage the teams have seen so far. Eighteen tornado warnings were issued by the National Weather Service in Fort Worth on Tuesday, which saved hundreds of lives. There were no fatalities Tuesday, which is welcome news in the wake of 2011's deadly tornado season.

Figure 2. This photo was taken by a NWS Storm Survey team in Lancaster TX on April 4, 2012. It shows EF-2 tornado damage that occurred in parts of Lancaster on April 3, 2012.

Figure 3. From the Weather Service: This is an aerial photograph of a tornado damaged area in Arlington TX. The damage from the tornado that affected Kennedale and Arlington on April 3, 2012 has been given a preliminary rating of EF-2. The photo was taken on Wednesday, April 4, looking to the east.

Portlight disaster relief charity responds to this year's tornadoes
Disaster relief charity sent Thomas Hudson to the DFW area yesterday to do damage assessment and determine whether there is a need for Portlight's services in the wake of the tornadoes. Check out the Portlight blog to see the latest updates, and catch up the great work they've been doing in Harrisburg, Illinois in the wake of the devastating EF-4 tornado that hit the town on Leap Day, 2012.

Jeff Masters

Hurricane Tornado

Tornadoes rip through Dallas metro area

By: AngelaFritz , 9:36 PM GMT on April 03, 2012

At least three tornadoes have ripped through the Dallas metro area this afternoon, one passing between Dallas and Fort Worth, bearing down on the Dallas-Fort Worth airport but narrowly missing to the east. The other two tornadoes passed east of Dallas, one touching down near the town of Forney, where there were reports of impacts to the high school. The DFW airport issued a ground stop for all incoming flights and grounded all planes at their airports, and a spokesman said they were sheltering passengers. The airport is now closed while they inspect the planes for hail damage, and can accept no incoming flights for lack of a place to put them.

Residential neighborhoods were completely destroyed in the Arlington tornado, and tractor trailers were tossed like toys. Extensive damage was done to the Green Oaks nursing home and rehab center, which is just east of Lake Arlington. The Arlington tornado was on the ground for approximately 30 minutes. In addition to the tornadoes, trained storm spotters were reporting hail up to three inches in diameter, which is approximately the size of a baseball.

The mayor and city council of Arlington, Texas declared a state of disaster for the city when, just an hour after the tornado had passed through, it was obvious that the area had sustained incredible damage.

Tornado warnings continue to be issued, and the potential for severe thunderstorms with and tornadoes will continue through the evening in eastern Texas, Oklahoma, southern Arkansas, and Louisiana. The convective outlook paints a good picture of the tornado potential for the rest of the evening. If you're in one of these regions, stay alert for tornado watches or warnings that may be issued.

Radar reflectivity of the tornadic thunderstorms as they passed over the Dallas metro area this afternoon. The storms that produced tornadoes are circled, and Arlington, Texas has been pointed out on the map.

Tornado warnings (red) and severe thunderstorm warnings (yellow) at the time two tornadoes were passing to the east and west of Dallas, Texas.

Video of the Arlington tornado developing as it crosses US-287 near Sublett Road, from Twitter user @wesstevens.

Video 2. Dramatic video of semi-trailers being tossed more than 100 feet in the air by the Lancaster, Texas tornado of April 3, 2012.


Tornado Extreme Weather

Arctic sea ice loss tied to unusual jet stream patterns

By: JeffMasters, 2:40 PM GMT on April 02, 2012

Earth has seen some highly unusual weather patterns over the past three years, and three new studies published this year point to Arctic sea loss as a potential important driver of some of these strange weather patterns. The record loss of sea ice the Arctic in recent years may be increasing winter cold surges and snowfall in Europe and North America, says a study by a research team led by Georgia Institute of Technology scientists Jiping Liu and Judith Curry. The paper, titled "Impact of declining Arctic sea ice on winter snowfall", was published on Feb. 27, 2012 in the online early edition of the journal Proceedings of the National Academy of Sciences. "Our study demonstrates that the decrease in Arctic sea ice area is linked to changes in the winter Northern Hemisphere atmospheric circulation, said Judith Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech, in a press release. "The circulation changes result in more frequent episodes of atmospheric blocking patterns, which lead to increased cold surges and snow over large parts of the northern continents."

Figure 1. Arctic sea ice in September 2007 reached its lowest extent on record, approximately 40% lower than when satellite records began in 1979. Sea ice loss in 2011 was virtually tied with the ice loss in 2007, despite weather conditions that were not as unusual in the Arctic. Image credit: University of Illinois Cryosphere Today.

Figure 2. The extent of Arctic sea ice loss in the summer July - August - September period in 2007 was about 1.4 million square miles (3.6 million square kilometers) greater than in 1980, according to the University of Illinois Cryosphere Today. For comparison, the lost ice coverage (orange colors) was equal to an area about 44% of the size of the contiguous U.S., or 71% of the non-Russian portion of Europe.

Summertime Arctic sea ice loss: 40% since 1980
The Arctic has seen a stunning amount of sea ice loss in recent years, due to melting and unfavorable winds that have pushed large amounts of ice out of the region. Forty percent of the sea ice was missing in September 2007, compared to September of 1980. This is an area equivalent to about 44% of the contiguous U.S., or 71% of the non-Russian portion of Europe. Such a large area of open water is bound to cause significant impacts on weather patterns, due to the huge amount of heat and moisture that escapes from the exposed ocean into the atmosphere over a multi-month period following the summer melt. The Georgia Tech study found that Arctic sea ice loss had caused a 20 - 60% weakening of the west-to-east belt of winds circling the pole in recent years, producing broader meanders in the jet stream that allowed it to get "stuck" in place 20 - 60% more often. When the jet stream gets stuck in place for a long period of time, we say a "blocking pattern" has set up. Since the jet stream marks the boundary between cold, Arctic air to the north, and warmer subtropical air to the south, areas on both sides of the jet are subjected to extended periods of unusually warm or cold weather during a blocking episode. Such a blocking pattern began on January 26, 2012 and lasted until February 11, bringing and exceptionally cold and snowy conditions to much of Europe, which lay on the cold side of an elongated loop of the jet stream that got stuck in place. Conversely, most of North America and northern Siberia saw unusually warm temperatures during this period, since they were on the warm side of the jet stream. Lead author Jiping Liu, a senior research scientist in the School of Earth and Atmospheric Sciences at Georgia Tech, added, "We think the recent snowy winters could be caused by the retreating Arctic ice altering atmospheric circulation patterns by weakening westerly winds, increasing the amplitude of the jet stream and increasing the amount of moisture in the atmosphere. These pattern changes enhance blocking patterns that favor more frequent movement of cold air masses to middle and lower latitudes, leading to increased heavy snowfall in Europe and the Northeast and Midwest regions of the United States." The paper concludes: "if Arctic sea ice continues as anticipated by climate modeling results, we speculate that episodes of the aforementioned circulation change will become more frequent, along with more persistent snowstorms over northern continents during winter."

Figure 3. Waiting for the warm-up after a rare snowfall in Italy during the February, 2012 European cold blast. Image credit: wunderphotographer cathykiro.

Two other studies link Arctic sea ice loss to atmospheric circulation changes
"The question is not whether sea ice loss is affecting the large-scale atmospheric's how can it not?" That was the take-home message from Dr. Jennifer Francis of Rutgers University, in her talk "Evidence Linking Arctic Amplification to Extreme Weather in Mid-latitudes, presented at December's American Geophysical Union meeting in San Francisco. Dr. Francis presented new research that has just been published in the journal Geophysical Research Letters, which shows that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions. Dr. Francis describes her work in a March 5, 2012 post on the Yale environment360 web site.

"Even if the current weather situation may seem to speak against it, the probability of cold winters with much snow in Central Europe rises when the Arctic is covered by less sea ice in summer." That was the opening sentence of a January 26, 2012 press release by a group of European scientists, led by Ralf Jaiser of the Alfred Wegener Institute in Germany. The words proved prescient, because that day marked the beginning of a brutal two-week cold air outbreak over Central and Eastern Europe that killed 823 people and did over $660 million in damage, according to preliminary estimates by insurance broker Aon Benfield. Dr. Jaiser's team, using modeling studies, showed that Arctic sea ice loss weakens upper-level winds over the Arctic in winter, allowing an increased chance of cold air surges over Europe.

Figure 4. Digging out in Maryland after "Snowmageddon" on February 4, 2010. Image credit: wunderphotographer chills.

Why was the winter of 2011 - 2012 so warm in the U.S.?
The winter of 2011 - 2012 in North America was unusually warm--the fourth warmest on record. The cold air spilling out of the Arctic during the winter was confined to Europe, unlike that previous two winters, which were unusually cold and snowy in the Eastern U.S. Obviously, loss of Arctic sea ice is not having the same impact each winter; such factors as El Niño/La Niña, the phase of the 11-year sunspot cycle, and the amount of snow cover in Siberia also have strong influences on the winter weather pattern that sets up. Cold air is less likely to spill out of the Arctic during a solar maximum, as we are now headed towards, so this factor may tend to reduce the odds of getting big cold blasts in the U.S. during the coming two winters. However, cold air may be more likely to spill out of the Arctic in winter due to the decades-long pattern of warming and cooling of Atlantic Ocean waters known as the Atlantic Multidecadal Oscillation (AMO). A 2012 study by NASA scientists found that the warm phase of the AMO (like we have been in since 1995) causes more instances of atmospheric blocking, where the jet stream gets "stuck" in place, leading to long periods of extreme weather. It will be interesting to see how all these factors play out in the coming years. If these three newly-published studies are correct, the U.S. should see more winters like 2010 - 2011 and 2009 - 2010 in coming decades, as Arctic sea ice continues to melt and affect global atmospheric circulation patterns more strongly.

Francis, J.A., and S.J. Vavrus (2012), "Evidence linking Arctic amplification to extreme weather in mid-latitudes," Geophysical Research Letters, 21 February, 2012.

Jaiser, R., K. Dethloff, D. Handorf, A. Rinke, J. Cohen (2012), Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation, Tellus A 2012, 64, 11595, DOI: 10.3402/tellusa.v64i0.11595

Liu et al. (2012), "Impact of declining Arctic sea ice on winter snowfall", Proc. Natl. Academy of Sciences, Published online before print February 27, 2012, doi: 10.1073/pnas.1114910109

Jeff Masters

Climate Change Winter Weather

April Fools weather humor; all-time March warmth in WY, NE

By: JeffMasters, 3:41 PM GMT on April 01, 2012

I don't have an April Fools blog post for you this year, but instead thought I share with you two of the funniest weather-related stories of the year. Firstly, it turns out that you don't need to be a human to enjoy a little snowboarding. The snowy conditions in Russia this winter gave the opportunity for an intrepid crow to take up the sport in this remarkable Youtube video. I found the video over at Andy Revkin's DotEarth blog at the New York Times. The bird is a hooded crow, and has evidently been doing quite a bit of snowboarding, judging by the multiple tracks on the rooftop. Too bad us humans can't use a flap-assist from our wings while snowboarding, it might cut down on injuries!

Video 1. A crow in Russia goes snowboarding on a snow-covered rooftop.

The most insane letter ever written by a child to a TV weatherman
I've done a lot of talks about the weather to schools, and have gotten hundreds of thank-you letters from the kids afterwards. But I've never gotten a letter quite like the one KVUE morning and midday meteorologist Albert Ramon in Austin, Texas recently received after talking at a local school. A sampling:

"Some day when I become supreme Ultra-Lord of the universe I will not make you a slave, you will live in my 200 story castle where unicorn servants will feed you doughnuts off their horns."

And this: "Thank you again for teaching us about meteoroligy, you're more awesome than a monkey wearing a tuxedo made out of bacon riding a cyborg unicorn with a lightsaber for the horn on the tip of a space shuttle closing in on Mars while ingulfed in flames."

Check out the letter here.

Finally, has a funny April Fool's blog post today called ‘Wrong sign paradox’ finally resolved?

All-time March warmth records in Wyoming, Nebraska
Most of Wyoming and much of Nebraska set or tied their record for all-time warmest March temperatures yesterday, no fooling. A strong ridge of high pressure that generated a strong flow of warm air from the southwest was responsible. Some of the records included:

Omaha, NE: 91°F
Lincoln, NE: 91°F
Casper, WY: 77°F
Lander, WY: 76°F
Rock Spring, WY: 72°F
Worland, WY: 81°F
Laramie, WY: 71°F
Rawlins, WY: 73°F
Chadron, WY: 83°F
Sidney, WY: 83°F

Jeff Masters

Humor Heat

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

Category 6™


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