About Jeff Masters
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
By: Bob Henson , 6:59 PM GMT on March 31, 2015
The first ten days of April could produce more severe weather than the modest amount racked up so far across the U.S. in 2015. The same upper-level pattern that kept the West warm and the East cold through most of the winter has also kept severe weather to a minimum, as northwest flow and a series of cold fronts pushed warm, unstable air off the U.S. mainland. This year through March 30, we’ve seen a preliminary total of a mere 38 tornadoes, compared to a January-March average over the preceding three years of 163. As of Tuesday morning, NOAA’s Storm Prediction Center had issued just four tornado watches and four severe thunderstorm watches for the year thus far. This compares to a long-term Jan.-Mar. average (1970 – 2014) of around 39 tornado and 24 severe thunderstorm watches, according to SPC’s Greg Carbin.
Figure 1. Severe-weather outlooks issued by NOAA’s Storm Prediction Center on Tuesday morning, March 31, valid for Tuesday (top), Wednesday (center), and Thursday (bottom). Image credit: NOAA/SPC.
The 2015 numbers look destined to rise over the next few days, as a major circulation change takes place over North America. The long-prevailing northwest flow is being replaced this week by more zonal (west-to-east) flow, with an embedded upper-level impulse reaching the Midwest on Wednesday and another targeting the Southern Plains on Thursday. A moist low-level air mass is already in place, with dew points close to 60°F from Tulsa, OK, to Birmingham, AL. Surface low pressure generated by the upper-level impulses should continue to pull the moisture pool northward and generate unstable conditions. SPC placed a broad belt from Oklahoma to Georgia under a slight risk of severe weather for Tuesday afternoon and evening, with large hail possible as the moisture continue to flow north.
A large swath of the Great Plains is under an slight risk for Wednesday, from northwest Oklahoma to southern Minnesota, with an slight risk in place for Thursday across part of the Southern Plains and mid-Mississippi Valley. The predominantly west-to-east upper flow combined with southerly low-level flow will enhance vertical wind shear, a key ingredient in the formation of supercell thunderstorms. The main threats appear to be high winds and large hail, although tornadoes can’t be ruled out. As was the case last Wednesday, when F2 tornadoes struck the Tulsa suburb of Sand Springs and the Oklahoma City suburb of Moore, the corridor from Interstate 44 into east central Oklahoma could be a particular focal point for supercell formation by late Thursday. Severe weather may continue into the lower Mississippi Valley on Friday before the associated cold front moves into the Gulf of Mexico.
Forecast models indicate a strong upper-level trough will settle across the Great Basin by early next week, setting the stage for what could be a more extensive multiday round of severe weather beginning as soon as Sunday. A strong surface low should develop over the High Plains by late in the weekend, pulling unstable air back northward across a large area beneath west-southwest upper flow. Strong thunderstorms could spread across the Midwest and South by early next week, with several days of focused severe weather possible.
Is El Niño about to make its presence known?
Surface waters have warmed dramatically over the far eastern tropical Pacific over the last several weeks, and the water temperatures are now assuming a more classic El Niño configuration that’s been absent for the last few months, with prominent warming just off the coast of South America. Computer models are remarkably consistent on projecting a strengthening of El Niño conditions over the next few months. All eight international models surveyed by the Australian Bureau of Meteorology on March 16 indicated that at least moderate El Niño conditions should be in place by August (i.e., sea-surface temperatures at least 1.0°C above average over the Niño3.4 region). However, in a March 31 update, the BOM cautions: “Model outlooks spanning February to May . . . have lower confidence than forecasts made at other times of year. Some models currently show some spread in their outlooks for tropical Pacific Ocean temperatures, indicating that while further warming is indeed very likely, there remains some ambiguity about the amount of warming expected.”
One hallmark of El Niño across the U.S. is split flow, with the polar jet stream retreating to the north and the subtropical jet stream intensifying across the southern tier of states. This pattern tends to keep unstable air shunted toward the Gulf Coast, hiking the chance of severe weather there (especially in Florida) but reducing the odds over the nation’s heartland.
Long-range models for mid-April are suggesting an El Niño-flavored pattern may emerge, with prominent split flow (see Figure 2, below). This is partly related to an intense Madden-Julian Oscillation event, the strongest on record (see our March 18 post), whose impacts are now reaching the eastern tropical Pacific and reinforcing the trend toward El Niño conditions. On its heels, a strong downwelling (or warming-phase) oceanic Kelvin wave will be pushing slowly eastward within the eastern equatorial Pacific over the next month, according to WSI’s Michael Ventrice. “This should favor increased organized thunderstorm activity over the eastern tropical Pacific basin, which will act to accelerate the subtropical jet stream over the U.S. through the end of spring,” says Ventrice. “This spells heavy precipitation threats (including some severe weather) across the southeastern tier of the nation over the upcoming months under the developing split-flow type pattern.”
Unfortunately, next week’s strong western trough may bypass California, further reducing hope of an “Awesome April” that might take a dent out of the severe drought and heat now plaguing the state. If a strong El Niño were to develop and persist, it could increase the likelihood of substantial rain in California during the 2015-16 wet season.
Figure 2. The GFS ensemble forecast issued at 1200 GMT on Monday, 30 March, and valid at 0000 GMT on Monday, 13 April, shows a pronounced split-flow pattern at the 200-millibar height (roughly 40,000 feet), with much of the United States lying between the polar and subtropical jet streams. Image credit: Michael Ventrice, WSI.
New insight on how El Niño, La Niña shape severe weather risk
A paper published this month in Nature Geoscience elaborates on how the odds of U.S. severe weather in late winter and spring tend to be boosted by La Niña and diminished by El Niño. The authors, led by John Allen (International Research Institute for Climate and Society, or IRI), acknowledge that it’s difficult to examine the connection between the El Niño/Southern Oscillation (ENSO) and severe weather. The datasets are imperfect (not all tornadoes or severe hailstorms get reported), and there’s a great deal of variability from year to year. “Trying to tease out an ENSO signal from both the natural noise and the human noise becomes quite complicated,” said coauthor Michael Tippett (Columbia University) in an IRI news release. “You can’t get a robust correlation using the observational record alone.” In this new study, the state of ENSO from 1979 to 2012 is compared not only with actual severe reports but also with the environmental factors associated with severe weather, such as instability and vertical wind shear, thus enabling the results to be analyzed more comprehensively. The study is the first to examine ENSO’s relationship to severe hail.
Figure 3. When ENSO is in a warm, or El Niño, phase (top), the frequency of springtime tornadoes goes down. When it is in a cool, or La Niña phase (bottom), tornadoes increase (indicated by red areas). The effect is strongest in the boxed area. Image credit: IRI, from Allen et al., Nature Geoscience, 2015.
In line with previous work by others, the largest influence found by the IRI team in winter (December-February) is across southern Texas and Florida, where the risk of tornadoes is roughly doubled during El Niño events. Prior studies had been inconclusive for springtime, but the IRI group found a significant ENSO influence focused across parts of northern Texas, Oklahoma, and Arkansas (see Figure 3), where the risk of tornadoes and severe hail rises dramatically during La Niña and drops during El Niño. There’s some asymmetry in this response: while not every El Niño event puts a dent in the region’s severe weather, La Niña events almost always push the likehood of tornadoes or severe hail above the climatological norm. “Naturally, this is only a simple model for the influence of ENSO on hail/tornadoes, and there needs to be more complexity added moving forward,” Allen told me in an email. He and colleagues are now looking into how variations in the strength of ENSO across a severe weather season might influence the outcome.
Given the weak El Niño event now under way, the IRI team is calling for slightly enhanced odds of a less-active severe season than usual. Allen explains the forecast in a video clip on IRI’s website.
Maysak maintains Category 5 strength
Jeff Masters posted a full report earlier today on Super Typhoon Maysak, now plowing across the Northwest Pacific east of the Caroline Islands. As of 8 am EDT Tuesday, Maysak’s top sustained winds were at 160 mph, according to the Joint Typhoon Warning Center. This makes the system one of only three Category 5 typhoons ever observed in the Northwest Pacific prior to April (the other two are Super Typhoon Ophelia of January 1958 and Super Typhoon Mitag of March 2002, both with 160-mph winds). The JTWC predicts some further strengthening of Maysak, with a projected top wind speed of close to 180 mph by Tuesday night. Any eyewall replacement cycle, if one occurs, could keep Maysak from getting stronger. Fortunately, Maysak is tracking north of Yap, the most populated of Micronesia’s Caroline Islands, and cooler water temperatures should lead to a fair amount of weakening by the time Maysak approaches the Philippines this weekend. At least 5 deaths and extensive damage have been reported on Chuuk State (Micronesia). The storm also passed just north of the sparsely populated islands of Fais and Ulithi while close to its top strength.
According to intensity estimates from the Joint Typhoon Warning Center, 2015 is the first year on record to have three Category 5 storms form in the Pacific Ocean during the first three months of the year. The other two Category 5 storms in 2015 were Tropical Cyclone Pam (165 mph winds), which devastated Vanuatu in mid-March, and Tropical Cyclone Eunice (160 mph winds), which affected ocean areas in the South Indian Ocean. Reliable satellite records of Southern Hemisphere tropical cyclones extend back to the early 1990s, so we only have about a 25-year period of good records for global tropical cyclones.
We’ll have a new post by Wednesday morning.
Figure 4. An infrared image of Super Typhoon Maysak from 0444 GMT on Tuesday, March 31. Image credit: NOAA/NASA and RAMBB/CIRA, courtesy Stu Ostro (The Weather Channel).
By: JeffMasters, 2:30 PM GMT on March 31, 2015
Extremely dangerous Category 5 Super Typhoon Maysak is pounding the islands of Yap State in Micronesia's Caroline Islands. At 8 am EDT Tuesday the Joint Typhoon Warning Center (JTWC) put Maysak's top sustained winds at 160 mph, making it one of only three Category 5 storms ever observed in the Northwestern Pacific prior to April. The Japan Meteorological Agency (JMA) put Maysak's central pressure at 905 mb, the lowest pressure they have estimated for any Northwestern Pacific typhoon occurring so early in the year (previous record: 930 mb for Typhoon Mitag of March 2002, Typhoon Alice of January 1979, and Typhoon Harriet of January 1959.) According to the NWS in Guam, the eye of Maysak has already passed very close to several of the smaller islands of Micronesia--Ulithi and Fais--bringing hurricane-force winds. Ulithi is an atoll about 12 feet above sea level, and Fais is 30 feet above sea level, so storm surge flooding is a huge concern on these low-lying islands. The 00 UTC Tuesday runs of the GFS and European models predict that the center of Maysak will pass about 100 miles northeast of Yap in the Caroline Islands (population 11,000) near 2 pm EDT Tuesday, which is near dawn local time on Wednesday. Since hurricane-force winds extend out about 45 miles from the center, Yap will likely only receive tropical storm-force winds. However, the significant wave heights in Maysak were estimated at 40 feet, and Yap will receive substantial coastal damage and flooding from the storm. Maysak has moderate wind shear of 10 - 20 knots and a large area of ocean with sea surface temperatures of 28 - 29°C (83 - 84°F) to work with through Wednesday, and will be capable of maintaining Category 5 strength until Thursday. As Maysak approaches the Philippines on Friday and Saturday, wind shear will rise, sea surface temperatures will cool, and the total heat energy in the ocean will decrease sharply, which should weaken Maysak significantly. The Joint Typhoon Warning Center (JTWC) is predicting that Maysak will be a Category 3 storm on Saturday, and at least a Category 1 typhoon when it hits Luzon Island in the Philippines on Easter Sunday.
Figure 1. MODIS satellite image of Super Typhoon Maysak taken at 03:55 UTC March 31, 2015. At the time, Maysak was a Category 5 storm with 160 mph winds. Image credit: NASA.
A record early start to typhoon season
According to the Joint Typhoon Warning Center (JTWC) database, 2015 is now the only season since records began in 1945 to feature three typhoons during the first three months of the year (January, February, and March), and also the first season to have two major typhoons (Category 3 or stronger) during the first three months of the year. The other major typhoon of 2015 was Typhoon Higos, which topped out as a Category 3 storm with 120 mph winds in February. Maysak is the fourth named storm so far in 2015 in the Northwestern Pacific, and only one other year since 1945 had more named storms by this point--1965, when there were five named storms by the end of March. The previous record for early season typhoons (during January, February, and March) was two, set in 2005, 1979, and 1955. Major typhoons of Category 3 or stronger intensity are rare before April, and only fifteen such storms have been observed between 1945 - 2014. Two of these were Category 5 super typhoons: Super Typhoon Ophelia of January 1958 with 160 mph winds, and Super Typhoon Mitag of March 2002, also with 160 mph winds.
The unusually early start to typhoon season is due, in part, to exceptionally warm waters in the typhoon breeding grounds just west of the International Date Line between 5 - 10° latitude, due to the weak El Niño event that is occurring. Water temperatures there are about 1 - 2°C (1.8 - 3.6°F) warmer than average. Also aiding typhoon formation this month was the strongest MJO event since record keeping began in 1974, which moved through the Western Pacific in mid-March. This MJO event generated an unusually strong band of west-to-east blowing surface winds near the Equator (a "westerly wind burst") that helped spin up Maysak and the storm that preceded it, Tropical Storm Bavi. This "westerly wind burst" will be strengthened by the counter-clockwise flow of air around Maysak, increasing the chances of El Niño lasting into the summer and potentially strengthening this fall. This process could potentially be aided by another tropical storm that the GFS model predicts will develop late this week from Invest 99W, in a location similar to where Maysak developed.
Maysak causes heavy damage to Chuuk
Maysak has already dealt a heavy blow to the islands in the Chuuk State in the Federated States of Micronesia, which have a population of about 50,000. Maysak passed through the islands as a Category 1 storm over the weekend, causing severe damage and five deaths. The eye of the storm passed directly over Weno Island, which recorded a wind gust of 71 mph and almost 7 inches of rain. Communications with Chuuk State are still difficult, so it is uncertain how much damage was done--though early reports indicate that up to 90% of the homes were damaged or destroyed by the storm.
Video 1. Damage in Micronesia's Chuuk State from Typhoon Maysak.
Wunderblogger Lee Grenci has a new post a new post about the upper-level environmentdiscussing how favorable the upper level winds were for allowing Maysak to intensify into a Category 5 storm.
High resolution visible loop of Maysak from March 31, 2015 from CIMSS
High resolution visible loop of Maysak until sunset on March 30, 2015 from CIMSS
Bob Henson will have a new post early this afternoon on the U.S. severe weather potential this week, a major "pattern shift" coming to our weather, and an update on El Niño.
By: JeffMasters, 3:22 AM GMT on March 30, 2015
It's been a record early start to typhoon season in the Western Pacific, where Category 2 Typhoon Maysak, with top sustained winds of 100 mph as of 8 pm EDT Sunday, is gathering strength in the waters a few hundred miles east of Yap State in the Caroline Islands. Maysak is the fourth named storm so far in 2015 in the Western Pacific, and the Joint Typhoon Warning Center (JTWC) database shows only one other year since 1945 with more named storms that formed during the first three months of the year--1965, when there were five named storms. Maysak is already the third typhoon of the year, setting a record for the most typhoons so early in the year. The previous record for early season typhoons (during January, February, and March) was two, set in 2005, 1979, and 1955. Major typhoons of Category 3 or stronger intensity are rare before April, and only fifteen such storms have been observed between 1945 - 2014. We already have had one major typhoon in 2015--Typhoon Higos, which topped out as a Category 3 storm with 120 mph winds in February. Maysak has moderate wind shear of 10 - 20 knots and a large area of ocean with sea surface temperatures of 29°C (84°F) before it, and appears destined to become a major Category 3 or stronger typhoon by Tuesday. If this indeed happens, it will mark the first time two major typhoons have been observed in the Western Pacific during the first three months of the year. Maysak has a ways to go to become the strongest early season typhoon, though--there have been two Category 5 super typhoons in the Western Pacific prior to the month of April. Super Typhoon Ophelia of January 1958 had 160 mph winds, and Super Typhoon Mitag of March 2002 also had 160 mph winds.
Figure 1. Latest satellite image of Typhoon Maysak.
The unusually early start to typhoon season is due, in part, to exceptionally warm waters in the typhoon breeding grounds just west of the International Date Line between 5 - 10° latitude, due to the weak El Niño event that is occurring. Water temperatures there are about 1 - 2°C (1.8 - 3.6°F) warmer than average. Also aiding typhoon formation this month was the strongest MJO event since record keeping began in 1974, which moved through the Western Pacific in mid-March. This MJO event generated an unusually strong band of west-to-east blowing surface winds near the Equator (a "westerly wind burst") that helped spin up Maysak and the storm that preceded it, Tropical Storm Bavi. This "westerly wind burst" will be strengthened by the counter-clockwise flow of air around Maysak, increasing the chances of El Niño lasting into the summer and potentially strengthening this fall, boosting the odds of a quiet Atlantic hurricane season.
Maysak a danger to Yap
Maysak has already dealt a heavy blow to the islands in the Chuuk State in the Federated States of Micronesia, which have a population of about 50,000. Maysak passed through the islands as a Category 1 storm over the weekend. According to TWC's Stu Ostro, Weno Island recorded a wind gust of 71 mph (62 knots) and 5.60" of rain in three hours. All communications were down on in Chuuk State as of Sunday night U.S. time, so it is uncertain how much damage was done. Models predict the center of Maysak will come close to Yap in the Caroline Islands (population 11,000) as a major typhoon midday on Tuesday (U.S. time.)
There will be a new post by Tuesday morning at the latest.
By: Jeff Masters and Bob Henson , 2:58 PM GMT on March 27, 2015
The warmest temperature ever recorded on the continent of Antarctica may have occurred on Tuesday, March 24, 2015, when the mercury shot up to 63.5°F (17.5°C) at Argentina's Esperanza Base on the northern tip of the Antarctic Peninsula. According to weather records researcher Maximiliano Herrera, the previous hottest temperature recorded in Antarctica was 63.3°F (17.4°C) set just one day previously at Argentina's Marambio Base, on a small islet just off the coast of the Antarctic Peninsula. Prior to this week's remarkable heat wave, the hottest known temperature in Antarctica was the 62.8°F (17.1°C) recorded at Esperanza Base on April 24, 1961. (The World Meteorological Organization—WMO—has not yet certified that this week's temperatures are all-time weather records for Antarctica, though the Argentinian weather service has verified that the temperatures measured at Esperanza Base and Marambio Base were the highest ever measured at each site.) A new all-time temperature record for an entire continent is a rare event, and Weather Underground's weather historian, Christopher C. Burt, has full details in his latest post.
Figure 1. Argentina's Esperanza Base on the northern tip of the Antarctic Peninsula: the hottest place in Antarctica. Image credit: Wikipedia.
The Antarctic Peninsula is one of the fastest warming spots on Earth. A 2012 Climate Central post by Michael Lemonick documented how while the Earth as a whole warmed up by 1.3°F between 1900 and 2011, the Antarctic Peninsula warmed by 5°, forcing massive ice shelves to disintegrate and penguin colonies to collapse. A 2012 paper in Nature found that the recent warming is faster than 99.7% of any other given 100-year period in the last 2000 years.
New all-time national and territorial heat records set or tied in 2015
So far in 2015, five nations or territories have tied or set all-time records for their hottest temperature in recorded history. For comparison, only two nations or territories did so in 2014, and nine did in 2013. The most all-time national heat records in a year was nineteen in 2010 (21 records at the time, but two have been broken since.) Since 2010, 46 nations or territories (out of a total of 235) have set or tied all-time heat records, and four have set all-time cold temperature records. Since each of those years ranked as one of the top twelve warmest years in Earth's recorded history, this sort of disparity in national heat and cold records is to be expected. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on wunderground.com's extremes page. Here are the national heat and cold records set so far in 2015:
Antarctica set a new territorial heat record of 17.5°C (63.5°F) at Esperanza Base on March 24. Previous record: 17.4°C (63.3°F) at Marambio Base, set the previous day.
Equatorial Guinea set a new national heat record of 35.5°C (95.9°F) at Bata on March 17. Previous record: 35.3°C (95.5°F) at Malabo in February 1957.
Ghana tied the national record of highest temperature with 43.0°C (109.4°F) at Navrongo on February 12.
Wallis and Futuna Territory (France) set a new territorial heat record with 35.5°C (95.9°F) on January 19 at Futuna Airport.
Samoa tied its national heat record with 36.5°C (97.7°F) on January 20 at Asau. Previously record: same location, in December 1977.
Figure 2. Residents watch the rising flood waters of the Copiapo River, in Copiapo, Chile, Wednesday, March 25, 2015. Unusually heavy thunderstorms and torrential rains that began on Tuesday have caused destructive flooding that has killed seven and left nineteen others missing. (AP Photo/Aton Chile)
Amazing rains in the Chilean desert
Unwelcome rains fell this week in Earth's driest place--Chile's Atacama Desert--causing destructive flooding that has left seven people dead and at nineteen others missing. Antofagasta, which averaged just 3.8 mm of precipitation per year between 1970 - 2000, and has a long-term average of 1.7 mm of precipitation per year, received a deluge of 24.4 mm (0.96 inches) during the 24 hour period ending at 8 am EDT March 26. That's over fourteen years of rain in one day! The rains were due to an unusually strong and persistent "cut-off" low pressure system that was trapped over Chile by the exceptionally strong ridge of high pressure that brought the warmest temperatures on record to Antarctica early in the week. A cold front associated with the cut-off low hit the Andes Mountains, dumping rains over soils with very little vegetation (due to the dry climate.) Unusually warm ocean temperatures approximately 1°C (1.8°F) above average off of the coast meant that high amounts of water vapor were available to fuel the storm and generate exceptionally heavy rains. Heavy precipitation events are common in Chile during El Niño events, like we are experiencing now. El Niño brings warmer than average waters to the Pacific coast of South America where Chile lies.
By: Bob Henson , 4:03 PM GMT on March 26, 2015
Two Oklahoma suburbs took the brunt of damage from a rapid-fire severe weather outbreak that developed Wednesday afternoon. At least one person was killed and another critically injured when a tornado and/or accompanying downdraft winds moved across a manufactured home park in Sand Springs, just west of Tulsa. A number of mobile homes were reportedly destroyed in the high winds. Just south of Oklahoma City, the long-suffering town of Moore--struck by catastrophic F5/EF5 tornadoes in 1999 and 2013 and a deadly tornado that produced F3 damage in Moore in 2003--experienced yet another twister, though fortunately a much weaker one than its predecessors. Overall, the severe weather on Wednesday covered a swath from central Oklahoma to southeast Missouri, producing a preliminary count of 8 tornadoes and more than 110 reports of severe hail, some as large as baseballs.
Figure 1. First responders work to free a man from a pile of rubble after a round of severe weather hit a trailer park near 145th West Avenue and West 17th Street in Sand Springs, Okla., Wednesday, March 25, 2015. (AP Photo/Tulsa World, Matt Barnard)
Wednesday’s damage in Sand Springs is a painful reminder of our lack of national policy on mobile home safety in tornadoes. Winds of no more than 110 mph (a borderline EF1/EF2 on the Enhanced Fujita Damage Scale) can destroy the roof and walls of a typical manufactured home, or cause it to roll over. Although just 5% of Americans live in mobile homes, anywhere from 25% to 50% of tornado-related deaths in a typical year occur in such homes, including 17 of 47 U.S. deaths in 2014, 17 of 55 deaths in 2013, and 48 of 68 deaths in 2012, according to data from NOAA’s Storm Prediction Center. Thousands of mobile home residents live on acreages with no ready source of safe shelter, but even those who live in mobile home parks often lack an underground refuge. Although the state of Minnesota and some localities mandate shelters, safe rooms, and/or an evacuation plan when mobile home parks reach a certain size, there is no such national requirement. Where shelters do exist, they often fall prey to vandalism or are used for other purposes. One Sand Springs resident told the Tulsa World that as Wednesday’s tornado bore down, she discovered that her RV park’s designated shelter was “full of washing machines”.
Figure 2. The paths of the Moore, Oklahoma tornadoes from May 3, 1999 (green); May 8, 2003 (blue); and May 20, 2013 (red), together with the preliminary path of the March 25, 2015 tornado (yellow). This year’s tornado crossed the path of the 1999 tornado near the northwest edge of Moore and intersected the 2013 path near Interstate 35. Image credit: NWS/Norman and NWS.
Few if any cities have experienced the kind of protracted bad luck with tornadoes that Moore has had to deal with (see Figure 2). The city endured major twisters on May 3, 1999 (killing 36 and injuring 583 along its full path); May 8, 2003; and May 20, 2013 (killing 24 and injuring 377 along its full path). Wednesday’s tornado was far less destructive, mostly knocking out windows and destroying carports and trees, although it blew over some vehicles and knocked out the three transmission towers of the radio station KOKC (formerly KOMA, which broadcast from a separate tower in the mid-1950s that was the world’s largest structure at the time).
TWC's Jon Erdman has a nice article on the Moore and Oklahoma City Tornado History.
By: Bob Henson , 9:29 PM GMT on March 24, 2015
The fine art of weather watching at the nation’s capital, which goes all the way back to Thomas Jefferson, Philadelphia, and the Declaration of Independence, got a shot of adrenaline with the announcement that a CoCoRaHS rain gauge was being installed at 1600 Pennsylvania Avenue in Washington, D.C. The news broke on Monday as part of the fourth annual White House Science Fair.
CoCoRaHS, the Community Collaborative Rain, Hail and Snow network (CoCoRaHS), involves more than 20,000 volunteers across the U.S. and Canada who collect precipitation data and report it online each morning. The network is North America’s largest single source of daily precipitation data.
Figure 1. CoCoRaHS founder and Colorado state climatologist Nolan Doesken shows off a CoCoRaHS gauge at the White House Science Fair on Monday, March 23. Image credit: Darlene Cavalier.
CoCoRaHS originated in the wake of a deadly flash flood in Fort Collins, CO, on July 28, 1997. The disaster caused more than $200 million in damage, much of it at Colorado State University. State climatologist Nolan Doesken, whose office is at CSU, was frustrated by the lack of reliable data on the massive rainfall that fed the local floods. The experience led Doesken to develop a county-wide network of volunteer observers, starting in 1998. CoCoRaHS gradually spread to other parts of Colorado over the next several years; the second state (Wyoming) joined in 2003, and the 50th state (Nebraska) signed on in 2013. The network also extends to Puerto Rico and the U.S. Virgin Islands as well as Canada.
Automated observing systems have many strengths, including the ability to give quick notice on when precipitation starts or stops at a given location. However, CoCoRaHS uses only manual rain gauges, hail pads, and snowboards: these generally provide the highest accuracy for daily precipitation totals, provided the equipment is placed in an appropriate spot and used properly. CoCoRaHS offers extensive training through a network of county coordinators, as well as a collection of training videos and webinars available on YouTube.
Figure 2. A still image from one of the colorful CoCoRaHS training videos. Image credit: CoCoRaHS.
Because of the simplicity of CoCoRaHS volunteering--all that’s required aside from training is an inexpensive set of standard equipment and a good observing site--it plays well with other types of weather engagement, such as maintaining a personal weather station in the WU network. Data are entered through a CoCoRaHS interface and viewable through maps and station records on the CoCoRaHS website. (CoCoRaHS reports are received by WU, although the once-a-day readings are not currently displayed on the continually updated WunderMap.)
Figure 3. The White House station made its first official appearance on the CoCoRaHS map at 7:00 AM (the standard time for local data collection) on Monday, March 23. The gauge is located in the vicinity of the Kitchen Garden on the South Lawn of the White House. Image credit: CoCoRaHS.
Participants in the WU network and CoCoRaHS can also join NOAA’s venerable Cooperative Observer Program (COOP), which is celebrating its 125th anniversary this year. There are more than 8,000 COOP observers nationwide who collect and file daily reports of maximum and minimum temperature as well as precipitation totals. Several COOP participants have put in more than 70 years of service, and last summer 101-year-old Richard Hendrickson was the first to be honored for more than 80 years of volunteering.
First storm risk of spring Tues-Wed in southern Great Plains
A moderately strong upper-level trough moving through the central U.S., coupled with a strengthening surface low in Kansas, is triggering a two-day period of potential severe weather on Tuesday and Wednesday. A severe thunderstorm watch stretching from eastern Oklahoma to southern Missouri was issued Tuesday afternoon by NOAA’s Storm Prediction Center (SPC). The watch was more noteworthy than usual, since it’s the first watch of any type (tornado or severe thunderstorm) since February 25, and only the fifth watch of any type this year. In records going back to 1970, this is the latest we’ve gone in March before our first watch of any type. Stu Ostro (The Weather Channel) notes that by March 24 of last year, we were up to watch #32; in 2013, #63; and in 2012, #108.
SPC has issued “enhanced” risk areas for both Tuesday and Wednesday, a new rating between “slight” and “moderate” (see our explainer post from Monday for details on the new system). Moisture was still limited near the surface low on Tuesday afternoon, with dew-point temperatures only in the mid-50s. However, low-level wind shear was somewhat favorable near an east-west warm front, and a tornado or two is possible in any supercell thunderstorm that forms near the surface low this evening. As the surface low and upper trough shift east, a robust cold front will barrel across Oklahoma on Wednesday. There should be a short-lived risk of supercells close to the Oklahoma City-Tulsa corridor, likely followed by a southward-charging squall line.
Figure 4. The Day 2 outlook issued at 1730 GMT Tuesday, valid on Wednesday, March 25, shows much of Oklahoma with an enhanced risk of severe weather. Image credit: NOAA/SPC.
By: Bob Henson , 4:35 PM GMT on March 23, 2015
Now that spring is upon us, the odds are rising that millions of Americans will find themselves under a “slight,” “moderate,” or even “high” risk of severe weather at some point in the next few months. These terms have been used by NOAA’s Storm Prediction Center (SPC) since 1981 to describe the anticipated likelihood of large hail, damaging winds, and/or tornadoes. From seasoned emergency managers to budding weather geeks, many thousands of Americans follow each twist and turn of the SPC categorical risk maps, officially known as convective outlooks. The maps, along with accompanying expert discussions, are updated at five specified times (0600, 1300, 1630, 2000, and 0100 GMT) for same-day activity (Day 1), at 0600 and 1730 GMT for next-day activity (Day 2), and just once (0730 GMT) for Day 3.
Last fall the SPC risk categories underwent their first substantial revision in 33 years. The main change was to add two categories on either side of the “slight risk” designation.
Marginal: a stray severe storm is possible, but probabilities are too low to merit a slight risk. (This replaces the label “SEE TEXT”, which had been used to steer readers to the discussion accompanying each outlook for more details.)
Enhanced: activity may be more widespread than implied by a slight risk, but a moderate risk is not justified.
Each of the five categories used by SPC relates to a certain level of probability of various types of severe weather. These probabilities are issued by SPC forecasters in Norman, Oklahoma, based on a wide range of guidance from national- and storm-scale computer models and observations. Although the five risk categories aren’t used beyond Day 3, SPC does provide probabilities and discussions out to days 4 through 8, providing an important heads-up on threatening situations that show up consistently in long-range guidance. For example, the risk of a multi-day severe weather episode across the south central states was highlighted five days ahead of the devastating Super Outbreak that peaked on April 27, 2011.
Figure 1. Top: the Day 1 convective outlook issued by NOAA’s Storm Prediction Center at 1630 GMT on April 27, 2011. Bottom: how this outlook would have appeared in the newly expanded five-tier structure, with the categories “marginal” (MRGL) and “enhanced” (ENH) now included. Image credit: NOAA/SPC.
The pros and cons of risk terminology
For those with enough technical savvy, probabilities are very helpful, but other users need or prefer a more concise message. This is where the worded categories come in. It’s widely acknowledged that the terminology isn’t perfect--to an untrained ear, “slight” could sound dismissive, and “moderate” may not carry the gravity it deserves--but SPC opted to refine a familiar, widely trusted system rather than uproot it. As they explain: “The categorical words Slight, Moderate and High have been used by SPC for nearly 35 years and are generally understood by the weather risk communication community. Making measured changes, we believe, is more effective than a wholesale change.”
A separate concern with the risk categories is that the extent of severe storms doesn’t necessarily correspond with how strong they are. Sometimes you have enough widespread wind or hail to merit a moderate risk, but there are few tornadic thunderstorms and little major damage. Conversely, an isolated supercell might produce a destructive tornado even if it’s located in a slight-risk area. SPC attempts to capture these distinctions on Day 1 by breaking the probabilities for each threat into two categories: general severe weather and “significant” severe weather (see Figure 2 caption). The probabilities in each tier then determine which of the five risk categories is in effect, using the somewhat complicated table shown in Figure 2.
Figure 2. The risk categories (colored boxes) that correspond to various percentage probabilities of severe weather (left axis of figure) in the SPC Day 1 convective outlooks. Slightly different tables are used for Day 2 and Day 3 outlooks. When more than one category is valid in a given area, the highest category is used (e.g., an area with 45% probabilities of all three types of severe weather would be designated as high risk, but if the 45% probability only existed for hail and wind, the risk designation would be moderate). A severe thunderstorm produces hail at least 1” in diameter, wind gusts of at least 58 mph, and/or a tornado. “Significant” severe events include 2” diameter hail, wind gusts of at least 75 mph, and EF2 tornadoes. Image credit: NOAA/SPC.
How are they used?
“The convective outlooks are very important products to emergency managers,” says Kenneth Galluppi, associate director of the Advanced Technology Innovation Center at Arizona State University. Galluppi and colleagues have interviewed many hundreds of emergency managers over the years to analyze how they receive and communicate information. Weather is just one of the many threats an EM has to deal with, Galluppi notes, so there’s major pressure to look for clear break points that distinguish more-serious from less-serious weather days. His work suggests that that many EMs wait until a moderate risk is in effect. This is especially true in storm-prone parts of the country, where slight-risk days are commonplace in the spring and summer. The new “enhanced” category provides one way to alert EMs and others that a situation falling short of the moderate designation still deserves attention. However, it may take time for EMs and other users to adapt to the new system. In a few informal tests carried out at conferences, Galluppi found that EMs gravitated to the moderate-risk zones even when the new “enhanced” area was present. “In terms of triggering action, ‘moderate’ seems to be the flag,” says Galluppi.
How the SPC system began
The use of a multi-tiered labeling system for storm risk has deep roots. The first such system was in place not long after the 1952 establishment in Washington, D.C., of the Weather Bureau Severe Weather Unit, which eventually became the National Severe Storms Forecast Center in Kansas City, MO, and later moved to Norman as SPC. According to SPC forecaster Stephen Corfidi, the original outlooks included the following four categories:
Isolated thunderstorms (expected to cover less than 15% of the marked area)
Widely scattered thunderstorms (15 - 30%)
Scattered severe thunderstorms (31 – 45%)
Numerous severe thunderstorms (more than 45%)
By the mid-1970s, these outlooks were being featured on NBC’s “Today” show as part of NOAA’s SKYWARN program. This was one of the few ways in which the outlooks reached the general public in those pre-Internet, pre-Weather Channel days.
As far as Corfidi can tell, the “numerous” category was never used, but on the morning of the epic Super Outbreak of April 3, 1974, forecaster Roy Darrah placed a large section of the Ohio and Tennessee Valleys under a “scattered” risk. “ ‘Scattered’ was the default ‘high’ risk of that period,” Corfidi told me. “It was a pretty gutsy call. The forecast was very good, both spatially and temporally.” (See Figure 3). A total of 148 tornadoes occurred on April 3-4--the largest 24-hour total until the catastrophic Super Outbreak of April 2011--and more than 300 people were killed, a toll unmatched until the 2011 outbreak. Almost all of the U.S. tornadoes occurred within the “scattered” risk area. Bill Murray (Alabama Weather Blog) offers an evocative retrospective on that day’s outlooks.
Figure 3. Convective outlooks issued early on April 3, 1974, for the period from 1200 April 3 to 0000 GMT April 4 (left) and 0000 – 1200 GMT April 4 (right). The crosshatching on the left map shows watches already in effect. Image credit: Stephen Corfidi, NOAA/SPC.
By 1977, forecasters and researchers began to ponder whether the coverage-based labels such as “few” or “scattered” might leave users confused over whether the terms applied to severe storms or to thunderstorms in general. The result was a new system, adopted in 1980, with new labels and percentages that applied specifically to severe storms:
Low: 2-5% coverage of severe storms
Moderate: 6-10% coverage
High: greater than 10% coverage
(The category “low” was changed to “slight” in 1981.)
The first-ever “high risk” outlook, and the first tornado watch to bear the label “particularly dangerous situation,” were issued on April 2, 1982. Later that day, one of the nation’s worst tornado outbreaks on record produced 56 tornadoes from Texas to Illinois, killing 30 people and injuring more than 300. The toll could have been much higher were it not for the unusually strong early notice of the situation and the substantial lead time for warnings of some of the worst tornadoes. A Silver Medal from the U.S. Department of Commerce went to the seven meteorologists behind the successful forecast, including Bob Johns, whose longtime role at SPC is outlined in a fascinating open-access paper, “A Forecaster’s Story: Robert H. Johns,” available in the E-Journal of Severe Storms Meteorology.
Figure 4. The TOR:CON outlook issued on Feb. 8, 2015 (not today!). Image credit: The Weather Channel.
TOR:CON--another way to describe tornado risk
Regular viewers of The Weather Channel and users of weather.com will recognize the phrase TOR:CON (Tornado Condition Index). This frequently updated alert system was created by severe weather expert Dr. Greg Forbes and colleagues in 2009 to capture the risk of tornadoes on a simple 1-to-10 scale. A TOR:CON value of 3 corresponds to a 30% chance of a tornado within 50 miles of a given point, whereas the analogous SPC tornado probabilities apply within 25 miles.
“Since the area is four times larger for a 50-mile radius than for a 25-mile radius, the implied TOR:CON probabilities are generally higher than those of SPC,” says Forbes. He adds: “TOR:CON values reflect my own forecast and are not just mathematical translations of the SPC forecast.”
This week’s outlook
Severe storms with large hail and damaging winds are possible on Tuesday from eastern Oklahoma into Missouri, with the zone stretching on Wednesday from north Texas into southern Illinois. As of this morning (Monday), the odds of widespread severe weather or strong tornadoes appear low. SPC has slight-risk zones in effect for Tuesday and Wednesday. TOR:CON values reach a maximum of 3 on both days. The Weather Channel maintains a TOR:CON update page in addition to its severe weather tracking page.
By: Jeff Masters and Bob Henson , 4:35 PM GMT on March 20, 2015
No widespread major flooding is expected this spring in the U.S., NOAA said on Thursday in their annual spring flood risk forecast. Rivers in western New York and eastern New England have the greatest risk of spring flooding because of a heavy snowpack of 3 to 9 inches of snow water equivalent, coupled with the potential for heavy spring rain to fall on the snow and cause a sudden melt-water pulse. Significant river ice across northern New York and northern New England increase the risk of flooding related to ice jams and ice jam breakups if there is a quick warm-up with heavy rainfall. The latest 16-day forecast from the GFS model does not call for any heavy rainfall events capable of triggering widespread moderate flooding through the end of March, though.
Areas at risk of moderate flooding:
Eastern New England and western New York
Lower Missouri River basin in Missouri and eastern Kansas
Lower Ohio River basin including portions of southern Illinois, southwestern Indiana, and western Kentucky.
Figure 1. The NOAA spring flood forecast shows about one-third of the country is at risk of minor to moderate flooding, but there are no areas at high risk of major flooding. Image credit: NOAA Spring Flood Forecast.
Flood categories are defined by NOAA as follows:
Minor Flooding: Minimal or no property damage, but possibly some public threat (e.g., inundation of roads).
Moderate Flooding: Some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations.
Major Flooding: Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.
Drought a bigger concern than flooding in the U.S. this year
Meanwhile, widespread drought conditions are expected to persist in California, Nevada, and Oregon this spring as the dry season begins. “Periods of record warmth in the West and not enough precipitation during the rainy season cut short drought-relief in California this winter and prospects for above average temperatures this spring may make the situation worse,” said Jon Gottschalck, chief, Operational Prediction Branch, NOAA’s Climate Prediction Center. El Niño finally arrived in February, but forecasters say it’s too weak and too late in the rainy season to provide much relief for California, which will soon reach its fourth year in drought. Current water supply forecasts and outlooks in the western United States range from near normal in the Pacific Northwest, northern Rockies, and upper Colorado, to much below normal in the southern Rockies, portions of the Great Basin and in California:
· Columbia and Snake Rivers - Median forecast at The Dalles is 82% of average
· Missouri River - Median forecast at Toston is 86% of average
· Colorado River - Median forecast inflow to Lake Powell is 71% of average
· Rio Grande and Pecos River – Median forecasts generally range from 60% to 105% of average
· Great Basin – Median forecasts range from 35% to 75% of average for most locations
· California - Median forecasts range from less than 20% to 50% of average
Figure 2. The March 19 NOAA drought outlook calls for drought to persist in California, Nevada, and Oregon through June with the onset of the dry season in April. Drought is also forecast to develop in remaining areas of Oregon and western Washington. Drought is also likely to continue in parts of the southern Plains and in Minnesota. Image credit: NOAA Climate Prediction Center.
WunderPoster of the week: Sundog!
Even though it’s unclear how they got their name, we do know what it is that produces sundogs (also written “sun dogs”), the phenomenon highlighted in this week’s WunderPoster (Figure 3, right).
Normally seen as a pair of bright spots, and sometimes referred to mock suns, sundogs occur in the presence of very thin ice-crystal clouds such as cirrus or faint cirrostratus. They form when sunshine is refracted horizontally through the sides of plate-shaped crystals that face upward and downward within the cloud. Each sundog is located 22° away from the sun, with a visible halo often connecting the sundogs.
All WunderPosters can be downloaded in formats suitable for posters or postcards. There’s also still time for you to provide photographic inspiration for a new WunderPoster, as part of the 20th anniversary celebration of Weather Underground. The deadline for submissions is April 2. Our “picture yourself here” website has all the details.
Figure 4. This pair of sunrise sundogs appeared above snow-covered fields on Feb. 5, 2014, near Seward, Nebraska. Image credit: wunderphotographer lindag47.
Have a great weekend, everyone!
Jeff Masters and Bob Henson
By: Jeff Masters , 2:42 PM GMT on March 19, 2015
February 2015 was the second warmest February since global record keeping began in 1880, said NOAA's National Climatic Data Center (NCDC) on Wednesday. NASA also rated February 2015 as the 2nd warmest February on record, behind February 1998 (which was exceptionally warm due to the super-El Niño going on at the time.) February 2015's near-record warmth continues a trend of very warm months for the planet--2014 was Earth's warmest calendar year on record, the period spanning the Northern Hemisphere winter (December 2014 - February 2015) was the warmest such period on record, and the past twelve months have been the warmest 12-month period in recorded history. Global ocean temperatures during February 2015 were the 3rd warmest on record, and global land temperatures were the 2nd warmest on record. Global satellite-measured temperatures in February 2015 for the lowest 8 km of the atmosphere were the 6th or 3rd warmest in the 37-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively.
Figure 1. Departure of temperature from average for February 2015, the 2nd warmest February for the globe since record keeping began in 1880. Image credit: National Climatic Data Center (NCDC) .
No billion-dollar weather disasters in February 2015
No billion-dollar weather-related disasters hit the Earth during February 2015, according to the February 2015 Catastrophe Report from insurance broker Aon Benfield. February 2015 joins January 2015 and November 2014 as the only months since February 2012 to go without a billion-dollar weather disaster. However, damages from the series of winter storms and cold weather outbreaks that affected the eastern two-thirds of the U.S. during February killed 72 people and will likely add up to more than a billion dollars, Aon Benfield said.
Figure 2. The Alps of MIT: With more than 40 inches of snow blanketing the Boston area in a two week period in February 2015, snow removal efforts on the campus of the Massachusetts Institute of Technology in Cambridge created this five-story-high mountain of snow. It was the coldest month (any month) on record for some sites in the Northeast, including Syracuse, NY: 9.1°F; old record 12.1° (Feb. 1934); Buffalo, NY: 10.9°F; old record 11.6° (Feb. 1934); Rochester, NY: 12.2°F, old record 12.6°F (Feb. 1934); Bangor, ME: 6.1°F, old record 8.4°F (Jan. 1994); Worcester, MA: 14.2°F; old record 14.4°F (Feb. 1934); and Hartford, CT: 16.1°F; old record 16.5° (Feb. 1934). Blue Hill Observatory COOP site near Boston measured 83.6” of snowfall in February. This qualifies as the snowiest month on record for any site in Massachusetts records. The previous state record for such was 78.0” at Monroe in Feb. 1893. Image credit: Tom Gearty/MIT.
Deadliest disaster of February 2015: Afghanistan blizzards and avalanches
The deadliest disaster of February 2015 was the series of blizzards and avalanches that hit Afghanistan
February 24 - 28, killing at least 286. Some of the slides wiped out entire villages in the provinces of Panjshir, Badakhshan, and Bamyan, and 1,250 homes were destroyed.
Figure 3. Afghan survivors of an avalanche search their destroyed houses in the Abdullah Khil village of the Dara district of Panjshir province, north of Kabul on March 1, 2015. Afghan President Ashraf Ghani February 28 pledged to set up a relief fund for the victims of avalanches that claimed over 286 lives, and called for international help with the relief effort. Image credit: SHAH MARAI/AFP/Getty Images.
El Niño arrives in February 2015
NOAA issued an El Niño advisory in February 2015, heralding the official arrival of weak El Niño conditions in the equatorial Eastern Pacific. Sea surface temperatures were 0.6°C above average in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for an El Niño event to be declared. One more such period (Jan – Mar) is needed for the current event to go into record books as an El Niño episode. NOAA is giving a 50 - 60% chance of El Niño lasting through summer, and subsurface water temperatures are well above average through most of the equatorial Pacific. I gave a detailed analysis of the possibility of El Niño intensifying later this year in Wednesday's blog post.
Arctic sea ice falls to 3rd lowest February extent on record
Arctic sea ice extent during February 2015 was the 3rd lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). However, during the first half of March, Arctic sea ice extent fell to its lowest level on record, and set a record for the lowest winter maximum, as discussed by Bob Henson in a March 9 blog post.
Notable global heat and cold marks set for February 2015
Hottest temperature in the Southern Hemisphere: 49.2°C (120.6°F) at Roebourne Airport (Australia), February 21
Coldest temperature in the Southern Hemisphere: -61.5°C (-78.7°F) at Dome Fuji (Valkyrjedomen), Antarctica, February 27
Hottest temperature in the Northern Hemisphere: 43.0°C (109.4°F) at Navrogno, Ghana, February 12
Coldest temperature in the Northern Hemisphere: -60.9°C (-77.6°F) at Summit, Greenland, February 13
On February 21, Wittenoom, Australia recorded a minimum temperature of 35.1°C (95.2°F), which is a new world record of highest minimum temperature for the month of February.
Major stations that set new all-time heat or cold records in February 2015
Ottosdal (South Africa) max. 40.6°C, February 9
Llay Llay (Chile) max. 40.2°C, February 12
Lynchburg (Pennsylvania, USA) min. -23.9°C, February 20
Lamap Malekula (Vanuatu) max. 34.8 °C, February 24
New all-time national and territorial heat records set or tied in 2015
Ghana tied the national record of highest temperature with 43.0°C (109.4°F) at Navrongo on February 12.
Wallis and Futuna Territory (France) set a new territorial heat record with 35.5°C (95.9°F) on January 19 at Futuna Airport.
Samoa tied its national heat record with 36.5°C (97.7°F) on January 20 at Asau. Previously, the record was set at the same location in December 1977.
A big thanks goes to Maximiliano Herrera for providing the global heat and cold records. He maintains a comprehensive list of extreme temperature records for every nation in the world on his website.
The Climate Change Elevator Pitch
Climate change videographer Peter Sinclair, whom I've done a number of interviews with, interviewed scientists in San Francisco in December 2014 at the annual American Geophysical Union's annual meeting. Climate scientist John Cook, who asked the actual questions during the interviews, had the brilliant idea to ask each of them one last question:
“Ok, you’re getting on an elevator with someone, and they say, “So you’re a climate scientist--what’s all this about climate change and global warming? You’ve got 10 floors. Go.”
The Elevator Pitch series has been pretty well received. Al Gore’s Climate Reality group uploaded some of these to their facebook page where glaciologist Eric Rignot's piece got more than a quarter million views. Here are the Climate Change Elevator Pitches that have been released so far:
NASA glaciologist Eric Rignot
Penn State glacier expert Richard Alley
Texas Tech's Katherine Hayhoe
Ken Caldeira, Carnegie Institution for Science
Simon Donner, University of British Columbia
Another interesting collection of short videos by climate scientists has just been released by morethanscientists.org. Featured are hurricane scientist Kerry Emanuel, Texas Tech's Katherine Hayhoe, and more than 100 others. The videos offer a unique glimpse into the real life stories, personal views and feelings of the experts on climate change, emphasizing not the science itself, but why it matters--and what it will mean for our children and grandchildren. "I'm very excited about this new campaign. Too few people have seen the lighter and more personal side of climate scientists," said climate scientist Michael E. Mann, director of Penn State's Earth System Science Center and advisory board member of More Than Scientists. "Many of us are science nerds. But we are ordinary people too, and like anyone else, we care about our children and grandchildren, and the health of the world we leave behind for them. So I'm very excited about this new campaign and the promise it holds for communicating that message to the public."
By: JeffMasters, 2:11 PM GMT on March 18, 2015
The Madden Julian Oscillation (MJO) is a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, and has many important impacts on weather patterns world-wide. For example, when the area of increased thunderstorms associated with the MJO is located in a particular ocean basin, the odds of tropical cyclone formation increase there. Scientists use the Wheeler-Hendon MJO index to monitor how strong the MJO is, and this week, the amplitude of the MJO set a new all-time record for the strongest MJO event observed since record keeping began in 1974 (with no data available from 3/17/1978-12/31/1978 due to satellite problems). The MJO index hit 4.09 on March 15, 2015, beating the old record of 4.01 set on February 14, 1985. On March 16, 2015, the MJO index set an even higher mark--4.67. That was likely the peak of this record MJO event, as the MJO index fell to 4.51 on March 17, and is forecast to drop significantly over the coming week. Thanks go to CSU's Phil Klotzbach for alerting me to the MJO record.
Figure 1. Wind flow diagram from March 13, 2015, when counter-rotating tropical cyclones on each side of the Equator in the Pacific created strong westerly winds along the Equator. Image credit: http://earth.nullschool.net/.
This record-strength MJO event began increasing in intensity last week, and aided in the formation of twin tropical cyclones, one on each side of the Equator (an event that tends to happen at least once per year.) The Southern Hemisphere storm that formed was Tropical Cyclone Pam, which intensified to Category 5 strength and devastated the island nation of Vanuatu. The Northern Hemisphere tropical cyclone, Tropical Storm Bavi, was not as strong since it had cooler waters to navigate, but still managed to attain peak winds of 60 mph before decaying to a tropical depression this Wednesday. These two tropical cyclones were counter-rotating--the Northern Hemisphere storm spun counter-clockwise, while the Southern Hemisphere storm spun clockwise. As a result of having two counter-rotating storms on either side of the Equator, very strong west-to-east blowing winds formed along the Equator, opposing the usual east-to-west blowing equatorial trade winds. The westerly winds from the counter-rotating tropical cyclones were strong enough and persistent enough that they boosted the odds of the current weak El Niño event staying on through the summer and into fall, since these "westerly wind bursts" tend to move warm water from the Western Pacific into the Eastern Pacific (the presence of warmer-than-average water in the Eastern Pacific is needed for an El Niño event to occur.) According to an email I received from University at Albany El Niño expert Paul Roundy, he expects an 80% chance that there will be a strong El Niño late this year, based on the latest model forecasts, and the evolution of the present event--which is being boosted by the current record-strong MJO, and was helped along by the counter-rotating tropical cyclones in the Pacific last week. He cautions, though, that "failure of El Niño could occur this year if sufficient warm water volume is expelled up and down the coasts of the Americas before June, without maintenance of westerly wind burst activity into June (when the equatorial easterly winds typically amplify with the seasonal cycle and bring the cold tongue back.) "
Figure 2. Projections of sea-surface temperature in the Niño 3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for an El Niño event to be declared. These forecasts are for August 2015 in terms of departure from average (degrees C), as compiled from eight international climate models and released by the Australian Bureau of Meteorology in a March 17 update. Each model’s projection on the graph above is based on the average of multiple runs in an ensemble. The threshold for El Niño conditions for Australia is 0.8°C above average, as shown on the chart, while the NOAA threshold (not shown) is 0.5°C. Image credit: Australia Bureau of Meteorology .
In a March 17 outlook, Australia's Bureau of Meteorology bumped up their El Nino odds. They stated, "The past fortnight has seen unusual conditions in the tropical Pacific, which may increase the chance of El Niño in 2015. In the western Pacific, severe Tropical Cyclone Pam and Tropical Storm Bavi straddled the equator, producing one of the strongest reversals in the trade winds in recent years. This change is expected to increase the already warm sub-surface temperatures currently observed in the tropical Pacific Ocean, which may in turn raise tropical Pacific Ocean surface temperatures in the coming months. All eight international models surveyed by the Australian Bureau of Meteorology project that water temperatures will increase by August to at least 1.0°C above average in the Niño 3.4 region (see Figure 2), which would suggest at least a moderately strong El Niño event by NOAA’s definition.
NOAA's Climate Prediction Center is saying that there is an approximately 50-60% chance that El Niño conditions will continue through Northern Hemisphere summer 2015. This outlook was issued before the recent record-strength MJO and counter-rotating Pacific tropical cyclones emerged, so it will interesting to see how their outlook changes in the next update on April 9.
If El Niño is present this fall, it increases the odds that we will have a quiet Atlantic hurricane season. El Niño typically brings high wind shear to the tropical Atlantic, disrupting hurricanes and tropical storms as they try to form or intensify. Conversely, El Niño favors a more active than usual Eastern Pacific hurricane season, by lowering wind shear there and increasing water temperatures. If we get a strong El Niño this winter, it would increase the odds of breaking California's streak of four consecutive dry winters, and put a decent dent in their crippling drought. As we saw this past winter, California can still get low precipitation and drought conditions during a weak El Niño event. If El Niño builds and stays through the summer, warmer waters in the Pacific could lead to a wide-scale coral bleaching event, resulting in massive die-off of coral.
By: Bob Henson , 3:14 PM GMT on March 17, 2015
Four days after Category 5 Tropical Cyclone Pam unleashed its fury on the island nation of Vanuatu, the full extent of damage and casualties is not yet known. Unsettled weather made it impossible for relief flights to reach many of the hardest-hit islands until Tuesday. The United Nations Office for the Coordination of Humanitarian Affairs attributed at least 11 deaths to the storm, revising its toll downward from an earlier estimate of 24 deaths. Somewhat ironically, the nation’s president, Baldwin Lonsdale, was attending the third UN World Conference on Disaster Risk Reduction in Sendai, Japan, when Cyclone Pam struck Vanuatu. In a news conference before returning home, Lonsdale referred to the cyclone as “a monster, a monster. It's a setback for the government and for the people of Vanuatu.” At its peak, Pam's 165 mph winds made it one of only ten Category 5 storms ever rated by the Joint Typhoon Warning Center (JTWC) in the waters east of Australia, and one of only two such storms to make landfall--the other being Cyclone Zoe of 2002, which struck the Solomon Islands. Pam and Zoe are the two most intense cyclones observed in the region since records began in 1970.
Some of the worst damage is expected to be found on the southern islands of Erromango (population 2,000) and Tanna (population 29,000), which were struck head-on by the stronger southeastern portion of the eyewall. Gusts may have topped 160 mph on the western sides of these islands, according to analyses by the British firm Tropical Storm Risk. On Tuesday, Australian military planes reported that more than 80 percent of structures on Tanna Island were partially or completely destroyed. The storm’s weaker southwest eyewall hit the island of Efate, and it appears the capital city, Port Vila, was just far enough west to avoid the worst winds. Still, aerial photos indicate many homes in Port Vila were destroyed, and some 15,000 people on Efate are homeless due to the storm.
Figure 1. This resident of Port Vila, Vanuatu, was injured when hit by masonry due to a shipping container breaking through a concrete wall during Cyclone Pam. Image credit: MR Roderick J. Mackenzie/New Zealand Defence Force, via Getty Images.
How you can help
Relief efforts for Cyclone Pam are still in the process of being organized, but food and water are among the most urgent requirements. The Weather Channel posted this set of agencies that are already welcoming donations to help those affected by Cyclone Pam:
• Red Cross Australia | New Zealand
• UNICEF Australia | New Zealand
• Oxfam Australia | New Zealand
• TEAR Fund
• CARE USA
• World Vision
• Save the Children
• Act for Peace
Was climate change a factor?
While there is no sign of any significant increase in tropical cyclone activity across the southwest Pacific in recent decades, Cyclone Pam developed over waters that were up to 2°C warmer than average, boosting the storm’s potential strength. The rise in sea level due to warmer oceans also exacerbates any ocean-related flooding produced by tropical cyclones. At Mashable, Andrew Freedman posted this comprehensive look at the connections between Cyclone Pam and climate change.
Records wilt after another day of summer-like heat across Central Plains
The hottest late-winter airmass on record across the central Great Plains sent temperatures on Monday to absurd values for mid-March. As a trough of low pressure strengthened over the northern Plains, westerly winds were driven downslope from the Colorado Rockies. Already very warm for the elevation and time of year, the air mass warmed even more as it descended toward lower elevations. Both Nebraska and Iowa saw the only 90°F temperatures known to have occurred before the spring equinox in more than a century of record-keeping at the states’ major reporting stations. The heat also persisted in California, where downtown Los Angeles endured its fourth 90°F day in a row--the first time any March has produced four 90°F days, consecutive or otherwise, in records going back to 1877.
Figure 2. High temperatures in the 80s and 90s were widespread across the central U.S. on Monday, March 16. Image credit: NOAA, via Florida State University.
Among the Monday records compiled by Jon Erdman and Nick Wiltgen of the Weather Channel:
All-time March records:
North Platte, NE: 91°F (previous record 88°F on Mar. 31, 1946)
Norfolk, NE: 92°F (tied record 92°F set on Mar. 22, 1910)
Grand Island, NE: 90°F (tied record set eight times before)
Warmest so early in the year:
Lincoln, NE: 90°F
Sioux City, IA: 90°F
Broken Bow, NE: 90°F
Goodland, KS: 89°F
Concordia, KS: 89°F
Omaha, NE: 88°F
Des Moines, IA: 84°F (tie)
Denver, CO: 81°F
Colorado Springs, CO: 80°F
Canada's Charlottetown and Saint John trump Boston in snowiest-winter sweepstakes
The same nor’easter that put Boston over the top for its snowiest winter on record produced the same result--with much more drama--in the largest cities of two Canadian provinces. By late Monday, the paralyzing storm had delivered an estimated 55 cm (21.7”) to the provincial capital of Prince Edward Island, Charlottetown. The city's official total snowfall on Sunday of 47.6 cm (18.7") sent the city’s snow total for the winter to 463 cm (182”), almost twice the total observed in Boston. Charlottetown’s previous seasonal record, 451.3 cm (177.7”), had been set just last winter. In the province of New Brunswick, Saint John climbed to a seasonal total of 431 cm (170”) on Sunday, beating the record of 424 cm (167”) set in 1962–63. Yet another storm will paste the Canadian Maritimes on Wednesday, bringing as much as 20 cm (8”) of additional snow to Charlottetown.
Figure 3. Several feet of snow can be found in the backyards of Charlottetown, Prince Edward Island, where the latest snowstorm pushed the city’s seasonal snowfall total above 15 feet. Image credit: Ann Thurlow.
By: Jeff Masters and Bob Henson , 2:13 PM GMT on March 16, 2015
A tropical cyclone catastrophe of nearly unprecedented dimensions is unfolding in the unlucky South Pacific island nation of Vanuatu, as relief teams reach the hardest-hit areas from the Friday the 13th strike by Category 5 Tropical Cyclone Pam. The latest situation report from the government of Vanuatu lists 24 deaths and "widespread severe damage". The death toll is sure to grow as relief efforts reach some of the more remote areas that received the brunt of the storm. Cyclone Pam is almost certainly the most destructive tropical cyclone in Vanuatu's history--and possibly for the entire South Pacific east of Australia. At its peak, Pam's 165 mph winds made it one of only ten Category 5 storms ever rated by the Joint Typhoon Warning Center (JTWC) in the waters east of Australia. The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam's central pressure bottomed out at 896 mb, making it the second most intense tropical cyclone in the South Pacific basin after Cyclone Zoe of 2002.
Figure 1. Samuel, only his first name given, kicks a ball through the ruins of their family home as his father, Phillip, at back, picks through the debris in Port Vila, Vanuatu in the aftermath of Cyclone Pam Monday, March 16, 2015. Pam destroyed or damaged 90 percent of the buildings in the capital. Other portions of Vanuatu received much stronger winds. (AP Photo/Dave Hunt, Pool)
Pam was at its peak strength, with 165-mph Category 5 winds, when it passed over several small Vanuatu Islands to the north of Efate Island, Vanuatu's most populous island (population 66,000.) Pam is one of only two Category 5 cyclones in recorded history to make landfall on a populated island in the waters east of Australia. The only other Category 5 landfall event among the nine other Category 5 storms to affect these waters since 1970 was by the strongest tropical cyclone on record in the basin, Cyclone Zoe of 2002. Zoe made a direct hit as a Category 5 storm on several small islands in the Temotu Province of the Solomon Islands with a total population of 1700. There was one other close call: the eye of Category 5 Tropical Cyclone Percy passed 15 miles east of Ta'u, American Samoa, on February 16, 2005, but caused minimal damage.
Pam's weaker southwest quadrant eyewall hit Efate on Friday the 13th, bringing terrible damage there. Continuing to the south, Pam hit the southern islands of Erromango (population 2,000) and Tanna (population 29,000), Even though Pam had weakened slightly to 155 mph winds by this time, these islands took a catastrophic pounding, since they were hit by the stronger southeastern portion of the eyewall, where the clockwise spin of the storm aligned with its southerly forward motion to create the strongest winds.
Figure 2. Tropical Cyclone Pam as seen on March 13, 2015, as its southeast eyewall battered the Vanuatu island of Tanna. At the time, Pam was a high-end Category 4 storm with 155 mph winds. Tanna (population 29,000) probably took the worst punishment from the storm, due to the fact it was hit by the stronger southeast eyewall, where the clockwise spin of the storm aligned with its southerly forward motion. At least five people are confirmed dead on the island. Thanks go to wunderground member barbamz for saving this image.
Cyclone Olwyn: a costly event for Western Australia
Though much weaker than Pam, Severe Tropical Cyclone Olwyn made its presence known on Friday as it raked a lengthy portion of Australia’s western coast, with peak winds of 100 mph near landfall. Olwyn’s path--paralleling the coast and gradually inland, with the strongest winds on the landward side--is roughly analogous to a hurricane moving slowly north-northeast up the west coast of Florida.
Figure 3. Track of Cyclone Olwyn. Image credit: Wundermap.
Olwyn produced winds of 70 mph, gusting to 87 mph, in the town of Carnarvon (thanks to Weather Channel senior meteorologist Matt Crowther for this report). The region’s banana crop, part of an agricultural system that produces roughly $70 million US in value each year, was reportedly wiped out, and more than 1,000 residents were still without power on Monday. Olwyn accomplished the rare feat of passing almost directly over a profiler (an upward-pointing, wind-measuring radar) located at Carnarvon’s airport. The profiler detected 115-mph winds at about 3000 feet above ground, according to Sarah Fitton (Australia Bureau of Meteorology).
Record-melting heat across western U.S.
From California to North Dakota, a large part of the nation’s northwest half experienced summer-like heat over the weekend. Some of the more ominous reports came from fast-drying California, where the rainy season is limping to a halfhearted end. Many stations around Los Angeles and San Diego set record highs near or above 90°F on each day Friday through Sunday. In the San Francisco Bay area, all-time monthly heat records were notched on Saturday at Salinas Airport (92°F), San José (89°F), Monterey (87°F), and on Sunday in Fresno (91°F). The heat pushed into the northern Rockies and northern Great Plains on Sunday, with the all-time March record falling at Rapid City, SD (84°F). Many other locations saw their warmest day for so early in the season. In North Dakota, both Fargo (75°F; normal high 35°F) and Grand Forks (70°F; normal high 33°F) had their earliest 70°F readings on record--though by just one day, as the Great Warm Wave of March 2012 headed toward its amazing apex starting on March 16. More records appear certain to fall over the central Great Plains on Monday, with even the impressive numbers from 2012 in jeopardy at some locations.
At last: a seasonal snow record for Boston
The snowy onslaught that gripped Boston in late January and February smashed records for the most snow observed there in any single month (64.8”, besting the 43.3” from January 2005). After a reprieve in early March, a quick shot of snow on Sunday afternoon secured this winter’s place in city history as the snowiest on record. Sunday’s 2.9” pushed the seasonal total to 108.6”, breaking the record of 107.6” set in 1995–96. In a Sunday article, the Weather Channel’s Jon Erdman highlighted these and many other noteworthy aspects of Boston’s snow siege of 2014–15. The city’s snow records date back to 1891–92.
What about the 250-plus years between the arrival of the Puritans and the launch of modern snow-data collection in Boston in 1891? According to Weather Underground historian Christopher Burt, very few sites across New England maintained regular monthly and seasonal snowfall data prior to 1891. According to Burt: ”Cotton Mather noted that 36” - 42” of snow on level buried Boston between February 27 and March 9, 1717, as related in one of the first publications of the Massachusetts Historical Society. But there is no record of how much snow may have accumulated in the city over the course of that season. The same goes for all the winter seasons in Boston until we have the modern record. Bottom line: although we don’t know how much snow may have fallen each season prior to 1891-82, there is no positive or even anecdotal historical evidence to indicate that this season is not likely the snowiest on record since the founding of the city and, of course, in the modern record.”
Figure 4. Boston’s Beacon Hill on February 15, during the city’s record-setting streak of January/February snowstorms. Image credit: wunderphotographer Orfeo.
Our next post will be on Wednesday at noon at the latest.
Bob Henson and Jeff Masters
By: Jeff Masters and Bob Henson , 11:13 PM GMT on March 13, 2015
Tropical Cyclone Pam has weakened slightly to a top-end Category 4 storm with top sustained winds of 155 mph, according to the 2 pm EDT Friday advisory from the Joint Typhoon Warning Center (JTWC). The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam's central pressure remained at 899 mb at 2 pm EDT Friday, the same value as at 8 am. Satellite loops show that Pam is still a huge and intimidating storm, with a prominent 14-mile diameter eye and a very large area of intense eyewall thunderstorms with extremely cold cloud tops. The clouds have warmed in recent hours, as the strong updrafts in the eyewall have weakened and are no longer pushing the cloud tops to the base of the stratosphere. Steady weakening should continue over the weekend, but Pam will still be capable of bringing tropical storm-force winds and destructive waves to the northern portion of New Zealand on Sunday.
Figure 1. Tropical Cyclone Pam as seen by the VIIRS instrument on the Suomi satellite at 10:42 am EDT March 13, 2015. At the time, Pam was a Category 5 storm with 165 mph winds, and was just southeast of Efate Island, where the capital of Vanuatu, Port Vila, lies. Image credit: @NOAASatellites.
Pam's eyewall clobbered three major islands of the South Pacific island nation of Vanuatu on Friday. Even though Pam had weakened slightly to 155 mph winds, the southern islands of Erromango (population 2,000) and Tanna (pop 29,000) likely took the worst punishment from the storm, due to the fact these islands were hit by the stronger right-front quadrant (southeast) side of the storm. Pam was at its peak strength, 165 mph Category 5 winds, when its weaker left (southwest quadrant) eyewall passed over the eastern side of Efate Island, Vanuatu's most populous island (population 66,000.) However, since the weather station in the capital city of Port Vila survived the storm and reported winds below tropical storm force, this most populous (southwest) portion of the island may have escaped severe damage. Despite this fact, there is a good chance that Pam will be the most expensive natural disaster in Vanuatu's history.
25 Years Ago Today: An Early Outbreak for Tornado Alley
The U.S. is in the midst of an extremely quiet March for severe weather thus far, with no tornadoes and only three reports of large hail. Things looked far different 25 years ago today, as the central Great Plains endured its worst late-winter tornado outbreak on record. From March 11 to 13, 1990, more than 60 tornadoes plowed across Tornado Alley, from north Texas to Iowa. The meteorological setup for this outbreak was classic, but the seasonal timing wasn’t. Never before or since have such strong tornadoes been observed so far northwest so early in the year.
Figure 2. Tracks and intensities of the tornadoes observed on March 13-14, 1990, across the central Plains. Image credit: National Weather Service.
The standouts of this outbreak were two long-lived F5 tornadoes that raked central Kansas on the late afternoon of March 13. The twisters were the first in a family of five generated by a single supercell thunderstorm. The first one developed near the town of Pretty Prairie, west of Wichita, and went on to strike the town of Hesston near the end of its 48-mile path, destroying more than 200 homes. As this F5 tornado narrowed and dissipated, a new one formed about a mile to its north within the same larger-scale circulation. An analysis by eminent tornado scientist Theodore “Ted” Fujita found that the two twisters likely rotated around a common axis as the first one dissipated and the second one expanded, delivering a glancing blow to the town of Goessel along its 22-mile path. There have been only four other days since 1950--and none so early in the year--with at least two tornadoes producing F5 or EF5 damage (May 25, 1955; May 15, 1968; April 3, 1974, and April 27, 2011).
Despite the strength and longevity of the Hesston and Goessel tornadoes, they caused only two fatalities. The low death toll becomes even more impressive when you consider the limits of communication and warning technology circa 1990. At that time, the National Weather Service office in Wichita still relied on a 1957-vintage, pre-Doppler weather radar that tracked precipitation but provided no wind data. ”We would draw what we saw on a reflection plotter and then trace contours on a paper map overlay to locate a storm geographically,” recalled Randy Steadham, who was filling in as meteorologist in charge of the Wichita NWS office. The emergence of a classic hook echo on radar, plus a number of eyewitness reports, helped the office to track the storm closely and issue updates roughly every 9 minutes, which made it to the public via radio, TV, and NOAA Weather Radio.
Video 1. A compilation of videos of the F5 tornado that ended up striking Hesston, KS, on March 13, 1990.
The long-lived Hesston tornado was one of the first to be widely captured on videotape, a feat made possible by the new availability of affordable video cameras. According to storm-chase documentarian Blake Naftel, the only previous F5 to be videotaped from multiple perspectives was the one that struck near Wheatland, PA, on May 31, 1985. After the March 1990 outbreak, a team led by Jonathan Davies drew on a number of photos and videos and a post-storm ground survey to carry out detailed analysis of the Hesston tornado’s evolution and structure and its “handoff” to the the Goessel twister. Their results appeared in a 1994 paper in the Bulletin of the American Meteorological Society (PDF available at top of linked page). The group’s work touched on several longstanding challenges, including the task of distinguishing between tornadoes and sub-vortexes. ”In a sense, the more information we have, the more confusing and problematic the events become,” they wrote. And though the notion of high-resolution digital video cameras tucked within cellphones lay far in the future, the authors did note: “Given the proliferation of inexpensive, simple video cameras, it is increasing(ly) likely that at least some video images will be obtained for many, if not most, significant tornado events.”
The Wichita NWS office maintains a page on the Hesston/Goessel tornadoes with a number of photos, videos, and writeups. A slideshow from the Wichita Eagle captures the tornadoes’ devastation. Another long-lived supercell to the north produced an F4 tornado or tornado family that tracked across more than 120 miles in Nebraska. The NWS office in Hastings, NE, covers the outbreak’s northern extent in more detail.
This week’s WunderPoster: Frost flowers
As winter winds up in the Northern Hemisphere and flowers begin to dot the landscape, this week’s WunderPoster (Figure 3, right) harks back to the cold-season beauty of frost flowers. These intricately branched features can blossom where very cold, dry, and calm air settles over a thin layer of lake ice or sea ice. All WunderPosters can be downloaded in formats suitable for posters or postcards.
Now it’s your turn: help us create a WunderPoster!
To celebrate our 20th anniversary, we’re looking to you to provide inspiration for a new WunderPoster. Our “picture yourself here” website has all the details.
By: JeffMasters, 3:01 PM GMT on March 13, 2015
The South Pacific island nation of Vanuatu is taking an extreme pounding from the 165 mph winds of Category 5 Tropical Cyclone Pam, one of the strongest tropical cyclones ever recorded in the waters east of Australia. According to microwave satellite images from the Navy Research Lab, the eye of Pam passed directly over several small islands north of the main Vanuatu island of Efate near 4:05 am EDT March 13, making Pam Earth's first landfalling Category 5 tropical cyclone since Super Typhoon Haiyan hit the Philippines in November 2013. Pam is continuing southwards, and its western eyewall passed over the eastern side of Efate Island near 8 am EDT. Efate is the most populated island in Vanuatu, with a population of 66,000, and is home to the capital city of Port Vila. With top sustained winds of 165 mph as of 8 am EDT Friday, as estimated by the Joint Typhoon Warning Center (JTWC), eastern Efate likely experienced severe to extreme damage from Pam, even though the island was on the weaker (left front) side of the eyewall. Fortunately, Port Vila is on the southwest side of the island, and missed the strongest winds of the eyewall. Observations from Port Vila remained online through Pam's closest approach, and a minimum pressure of 942 mb was recorded, with top winds of 31 mph, gusting to 59 mph. A Personal Weather Station in Port Vila had received 4.69" of rain from the storm as of 4 am EDT Friday, before going off-line. The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam bottomed out with a central pressure of 899 mb at 8 am EDT Friday.
Figure 1. Tropical trouble: four tropical cyclones churn the Pacific in the this afternoon VIIRS image from March 12, 2015. Pam is in the right center of the image. Image credit: NOAA Visualization Lab.
Figure 2. Tropical Cyclone Pam approaching Vanuatu's capital city of Port Vila on Efate Island, as seen by the MODIS instrument on the Aqua satellite at 10:20 pm EDT March 12, 2015. At the time, Pam was a Category 5 storm with 160 mph winds. Image credit: NASA.
Satellite loops show that Pam is a huge and fearsome-looking storm, with a prominent 17-mile diameter eye and a very large area of intense eyewall thunderstorms with extremely cold cloud tops. These clouds have cold tops due to the fact that the strong updrafts in the eyewall are pushing the cloud tops to the base of the stratosphere. Sea surface temperatures are near 30°C (86°F), which is about 1°C (1.8°F) above average. Warm waters extend to great depth beneath the cyclone, giving Pam a huge amount of heat energy to draw upon. Wind shear Friday morning was low, near 10 knots, and is expected to be low to moderate though Saturday morning, which should allow Pam to remain an extremely dangerous Category 4 or 5 storm. The 8 am EDT Friday official intensity forecast from the Joint Typhoon Warning Center (JTWC) did not forecast any additional intensification of Pam. Intense tropical cyclones like Pam typically undergo one or more eyewall replacement cycles, during which a second, outer eyewall forms and contracts inward toward the eye, choking off the old, inner eyewall. During this time, the cyclone's intensity typically weakens. However, Friday morning microwave satellite images showed no signs that Pam is ready for an eyewall replacement cycle. These cycles are not predictable by current forecast models.
Figure 3. Track of all Category 5 storms in the South Pacific (east of 135°E) since satellite records began in 1970. Pam is one of only ten Category 5 storms ever recorded in the basin since satellite records began in 1970. The strongest tropical cyclones in the Joint Typhoon Warning Center’s records are Zoe (2002/2003) and Monica (2006), which topped out with 180 mph winds (thanks go to Phil Klotzbach of CSU for this stat.) Image credit: Michael Lowry, TWC.
Impacts of Pam
Pam is likely to be one of the most destructive natural disasters in Vanuatu's history. According to EM-DAT, the international disaster database, the previous most expensive disaster in Vanuatu history was Cyclone Eric of 1985, which did $173 million in damage (1985 dollars.) Though it appears the capital of Port Vila avoided the worst of Pam, the east side of Port Vila's Efate Island was not so fortunate. Pam will also pass very close to or over the three small, southernmost islands of Vanuatu on Friday and Saturday. These islands are Erromango (population 2,000), Tanna (pop 29,000) and Aneiytum (pop 900). Even if the islands miss a direct hit by Category 4 - 5 eyewall winds, hurricane-force winds will extend out 35 miles from the center, and likely cause heavy damage to all of these islands. Regardless of Pam's track, its waves will cause major coastal damage; the significant wave height of the storm was 45 feet at 8 am EDT Friday. The NOAA WaveWatch III model predicted significant waves height of up to 50 ft, as documented by storm surge expert Hal Needham in his latest blog post. Storm surge is a major concern, as well as extreme flash flooding from Pam's torrential rains. After passing Vanuatu, Pam is likely to weaken significantly, but the storm may still be capable of bringing tropical storm-force winds to New Zealand on Sunday. High surf causing erosion and coastal damage will be the main threat from Pam to New Zealand, though.
Pam has already caused significant damage to several islands in the Solomon Islands, just to the north of Vanuatu. According to Radio New Zealand International, Tikopia and Anuta Islands bore the full force of the storm, with people injured from falling trees and houses destroyed by strong winds. Tikopia lost 90 percent of its food crops and fruit trees and the water was contaminated, but the weather was still too rough to launch a boat with emergency supplies. All phone lines to Anuta were down and there was no information about how the island had fared.
Bob Henson will have a new post late this afternoon.
By: JeffMasters, 9:20 PM GMT on March 12, 2015
Residents of the South Pacific island nation of Vanuatu are bracing for the impact of Category 5 Tropical Cyclone Pam, one of the strongest tropical cyclones ever recorded in the waters east of Australia. Pam has rapidly intensified over the past two days and reached top sustained winds of 160 mph as of 2 pm EDT Thursday, making it one of only ten Category 5 storms ever recorded in the basin since satellite records began in 1970. The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam had a central pressure of 918 mb at 2 pm EDT Thursday.
Figure 1. The eye of Cyclone Pam as seen by the VIIRS instrument on the Suomi satellite at 10:11pm EDT March 11, 2015. At the time, Pam was a Category 4 storm with 135 mph winds. Image credit: @NOAASatellites.
Figure 2. Track of all Category 5 storms in the South Pacific (east of 135°E) since satellite records began in 1970. The strongest tropical cyclones in the Joint Typhoon Warning Center’s records are Zoe (2002/2003) and Monica (2006), which topped out with 180 mph winds (thanks go to Phil Klotzback of CSU for this stat.) Image credit: Michael Lowry, TWC.
Satellite loops show that Pam is a huge and fearsome-looking storm, with a prominent 17-mile diameter eye and a very large area of intense eyewall thunderstorms with extremely cold cloud tops. These clouds have cold tops due to the fact that the strong updrafts in the eyewall are pushing the cloud tops to the base of the stratosphere. Sea surface temperatures are near 30°C (86°F), which is about 1°C (1.8°F) above average. Warm waters extend to great depth beneath the cyclone, giving Pam a huge amount of heat energy to draw upon. Wind shear is currently moderate, 10 - 15 knots, and is expected to be low to moderate though Friday morning, which may allow Pam to undergo additional intensification. The 2 pm EDT Thursday official intensity forecast from the Joint Typhoon Warning Center (JTWC) has Pam topping out with 175 mph winds, which would make it the 3rd strongest storm on record in the waters east of Australia. Intense tropical cyclones like Pam typically undergo one or more eyewall replacement cycles, during which a second, outer eyewall forms and contracts inward toward the eye, choking off the old, inner eyewall. During this time, the cyclone's intensity typically weakens, and Pam will likely reach its peak intensity once one of these cycles begins. However, Thursday afternoon microwave satellite images showed no signs that Pam is ready for an eyewall replacement cycle. These cycles are not predictable by current forecast models.
Impacts of Pam
Pam is likely to be one of the most destructive natural disasters in Vanuatu's history. The storm will likely pass over or very close to the three small, southernmost islands of Vanuatu on Friday, and these islands will suffer extreme devastation if a direct hit occurs. These islands are Erromango (population 2,000), Tanna (pop 29,000) and Aneiytum (pop 900). The 12Z Thursday run of the usually-reliable European model shows a direct hit occurring on the more northerly island of Efate, the most populated island in Vanuatu (66,000), where the capital city of Port Vila is located. Even if the islands miss a direct hit by Category 4 - 5 eyewall winds, hurricane-force winds will extend out 40 miles from the center, and will likely cause heavy damage to all of these islands. Regardless of Pam's track, its waves will cause major coastal damage; the significant wave height of the storm was 44 feet at 2pm EDT Thursday. Storm surge is also a concern, as well as extreme flash flooding from Pam's torrential rains. After passing Vanuatu, Pam is likely to weaken significantly, but the storm may still be capable of bringing tropical storm-force winds to New Zealand on Sunday. High surf causing erosion and coastal damage will be the main threat from Pam to New Zealand, though.
Pam has already caused significant flooding on the low-lying island of Tuvalu, located over 700 miles northeast of the storm, as documented by storm surge expert Hal Needham in his blog. Since Tuvalu is located in an area with very deep water offshore, this flooding was likely due to large waves crashing onshore and running up inland, rather than an actual storm surge from winds piling up water over a shallow coastal shelf.
Port Vila, Vanuatu webcam (thanks go to wunderground member Huracan94 for posting this link.)
Vanuatu weather from the Australian BOM
Porta Vila info -- Click on "Details" in the wind section to view past wind data.
Vanuatu Meteorological Service
A Personal Weather Station at Port Vila, Vanuatu is in the path of Pam, and had received 0.57" of rain from the storm as of 4 pm EDT Thursday.
By: Bob Henson , 11:14 PM GMT on March 11, 2015
Despite huge west-to-east differences, the nation’s meteorological winter of 2014-15 (December through February) ended up warmer and drier than average, according to NOAA’s National Climatic Data Center. NCDC reported on Wednesday that the contiguous 48 U.S. states saw their 19th mildest winter in records that go back to 1895. The average of 34.3°F came in a full 2.1°F above the 20th-century average. Over the last century, winters have warmed more than 2.0°F across the 48 states, with seven of the last 10 winters placing warmer than average (see Figure 1).
Precipitation came in as the 27th lowest on record, with the 48-state average of 6.12” falling 0.67” below the 20th-century norm. Although seven of the last 10 winters have been drier than average nationwide, there is no discernable trend in winter precipitation for the 48 states as a whole (see Figure 2).
Figure 1. Winter temperature rankings (December-February) for the period 1895-96 through 2014-15. Image credit: NOAA National Climatic Data Center
Figure 2. Winter precipitation rankings (December-February) for the period 1895-96 through 2014-15. Image credit: NOAA National Climatic Data Center.
In many ways, this was a tale of two winters, both in time and space. December was extremely warm nationwide, second only to 1939, while January and especially February featured a split between record or near-record warmth across much of the West and intensifying cold over most of the East. More than half of the 48 states saw either a top-ten warmest or top-ten coldest February (see Figure 3). Five states had their warmest February on record. Interestingly, although every state from Ohio, Pennsylvania, and New York through New England had its second-coldest February, no state set a monthly record, with 1934 holding on to top billing (except in Ohio, where the coldest February remains 1978). Nevertheless, as we reported in a post last week, a number of locations had their coldest single month or their coldest February on record, while some Western cities had their warmest winter month on record.
Figure 3. Temperature rankings for February 2015. A value of 1 indicates the coldest February in the 121-year record, whereas 121 indicates the warmest. Image credit: NOAA National Climatic Data Center
Overall, last month’s Northeast chill was remarkable given that February has been warming at a rapid clip over that region: more than 4°F since 1900. The West has only been warming at about half that rate in the long term during February, but the heat was on last month in many areas, especially California, where February was 1.3°F warmer than the previous record-holder (1962).
In spite of the relentless snowfall that buried New England in February—especially eastern Massachusetts, where Boston and Worcester had their snowiest month on record—the Northeast as a whole had its 12th driest February on record. The main reason was the absence of rain. Typically, heavy rains can drench the Northeast even in midwinter, whereas little rain occurred there with the persistently cold pattern this past month. Two snowy places that did manage to set records for their highest February precipitation were Boulder, CO (3.69”, including 54.8” of snow) and Riverton, WY (1.28”, including 17.8” of snow). Across most of the West, precipitation ended up well below the winter norm, and the amount of moisture locked up in snowpack by early March was far below average from California through Washington and southwest British Columbia all the way to southern Alaska.
For much more detail, see the NOAA summaries for December, January, and February (which includes winter 2014-15), and our WU posts for December and January.
How well did the seasonal forecasts do?
For those courageous forecasters who attempt to predict how each winter will fare, the last few years have been challenging indeed. This time, the impacts of what’s been a marginal El Niño ended up weaker and patchier than expected. The west-to-east temperature contrast noted above overwhelmed the more prototypical El Niño winter pattern of milder-than-average weather across the northern tier of states and cooler-than-average conditions over the Sunbelt.
Figure 4. A comparision of seasonal temperatures forecasts for winter 2014-15 issued by NOAA (left) and WSI (center) with actual temperatures (right). Image credit: Todd Crawford, WSI, with data from NOAA.
Several private forecasting firms went for more widespread cold across the East than was projected by NOAA, including WSI. According to chief meteorologist Dr. Todd Crawford, WSI’s forecasters believed that the weak El Niño would push the influence of the tropical Pacific farther east than it was in the winter of 2013-14. “This resulted in an eastward shift of the poleward-and-downstream ridging relative to last year, which meant that the largest negative temperature anomalies ended up farther east than last year,” Crawford told me.
Another closely watched factor is the extent of snow cover across Siberia in the autumn. Studies led by Judah Cohen (Atmospheric and Environmental Research) suggest that greater October snow extent may trigger surface high pressure and lead to stratospheric disruptions that produce spells of winter cold and snow over eastern North America and Eurasia, linked to negative phases of the Arctic Oscillation (AO). Last October, snow cover in Siberia was close to a record-high extent in October, implying an enhanced risk of midwinter cold and snow in the U.S. Northeast. Although a sudden stratospheric warming (SSW) did occur, and AER’s U.S. temperature forecast verified well, the AO ended up positive rather than negative during most of the winter, especially in February. In an email, Cohen explained: “I do believe that the tropospheric pattern from late January though February was reflective of the stratospheric circulation forced by the SSW in early January. We are trying to understand why the AO stayed positive, and I think that we have some good leads.”
Jan Null (Golden Gate Weather Services) takes a closer look at how NOAA’s temperature and precipitation forecasts verified for winter 2014-15. Another useful tool is the interactive verification website provided by NOAA’s Climate Prediction Center. It’s worth noting that CPC’s seasonal forecasts are probabilistic: the areas marked “A” are not blanket forecasts of above-average conditions, but rather denote a shifting of the odds toward above-average and away from below-average, with the odds of near-normal conditions fixed at 33.3% except where huge departures are expected. More explanation can be found at a CPC tools page.
By: Jeff Masters , 4:25 PM GMT on March 11, 2015
A rare subtropical storm, with characteristics of both a tropical and a non-tropical system, has formed in the South Atlantic waters off the coast of Brazil, according to the 8 am EDT March 11, 2015 analysis by the Navy Hydrographic Center in Brazil. The storm has top wind speeds near 45 mph, according to an 3:40 pm EDT Tuesday pass from the Rapidscat instrument on the International Space Station. The surface pressure was near 1000 mb, and a modest amount of heavy thunderstorm activity was firing up near the center of circulation, and a more substantial amount on its southeast side, in a band well removed from the circulation center. Sea surface temperatures are near 27°C, which is about 0.5°C above average, and 1°C above what is typically needed to support a tropical storm. Phase space diagrams from Florida State show the storm has a weak warm core at low levels which should get better defined through Thursday morning, but by Thursday evening the storm will begin losing its tropical characteristics as wind shear increases and Cari moves to the southeast, away from Brazil, over cooler waters. It is unlikely the storm has time to become fully tropical, and Cari is not a threat to make landfall.
Here are the recent IR and VIS satellite loops from GOES-East, courtesy of NOAA's Dan Lindsey.
Figure 1. MODIS satellite image of Subtropical Storm Cari off the coast of Brazil, taken at approximately 9:00 am EDT Wednesday, March 11, 2015. Image credit: NASA.
Figure 2. Surface winds off the coast of Brazil according to an 3:40 pm EDT Tuesday pass from the Rapidscat instrument on the International Space Station. The center of circulation of Subtropical Storm Cari is seen, along with top winds near 45 mph in a band well southeast of the center of circulation.
South Atlantic tropical storm history
Tropical and subtropical storms are so rare in the South Atlantic that until 2011, there was no official naming of depressions or storms done. In 2011, the Brazilian Navy Hydrographic Center instituted a naming system with nine names, of which three have been used so far (Arani in 2011, Bapo in February 2015, and now Cari.) Brazil has had only one landfalling tropical cyclone in its history, Cyclone Catarina of March 2004. Catarina is one of fewer than ten tropical or subtropical storms to form in the South Atlantic, and the only one to reach hurricane strength. Tropical cyclones rarely form in the South Atlantic Ocean, due to strong upper-level wind shear, cool water temperatures, and the lack of an initial disturbance to get things spinning (no African waves or Intertropical Convergence Zone exist in the proper locations in the South Atlantic to help spawn tropical storms). It is uncertain whether climate change may cause an increase in South Atlantic tropical storms in the future. While today's storm formed over waters that were about 0.5°C above average in temperature, Catarina in 2004 formed over waters that were 0.5°C cooler than average. Sea surface temperature is not the main limiting factor inhibiting these storms--wind shear is. How climate change might change wind shear over the South Atlantic has not been well-studied.
Pam hits Category 4 in the South Pacific
In the South Pacific Ocean about 1,800 miles east of Australia, Tropical Cyclone Pam has rapidly intensified to a Category 4 storm with top sustained winds of 135 mph as of 8 am EDT Wednesday. Pam has generated quite a bit of hype over the past few days, thanks to eye-popping model projections by the GFS and European models which show the cyclone intensifying into a Category 5 monster with a central pressure less than 880 mb by late this week. If this forecast verifies, it would make Pam one of the strongest tropical cyclones ever recorded, world-wide. However, these models are not known for making reliable intensity forecasts, and are generally disregarded by NHC for intensity forecasts in the Atlantic and Eastern Pacific. The HWRF model, which is one of our better intensity forecast models, predicted with its 06Z (2 am EDT) Wednesday run that Pam would reach a central pressure of 907 mb by Friday, which would make it a still-formidable Category 5 cyclone. The Tuesday morning official intensity forecast from the Joint Typhoon Warning Center (JTWC) goes along with this idea, making Pam a Category 5 storm by Thursday evening. Pam is an unusually large cyclone over extremely deep warm water, with widespread surface temperatures above 30°C (86°F). Wind shear is currently high, 30 knots, but is expected to fall to the moderate range by Thursday night, which may allow Pam to undergo additional intensification into a Category 5 storm. A westward shift in the predicted track means that Pam will likely pass over or very close to some of the islands of Vanuatu on Thursday and Friday. In particular, a Personal Weather Station at Port Villa appears to be directly in the path of Pam.
Figure 3. Latest satellite image of Pam.
Bob Henson will have a new post Wednesday afternoon, summarizing the U.S. winter of 2014 - 2015.
By: Bob Henson and Jeff Masters , 7:28 PM GMT on March 10, 2015
There’s a calm across the nation’s tornado-prone regions, a quietness that seems odd when you consider the calendar. By crunching numbers from the monthly and yearly severe weather summaries produced by the NOAA Storm Prediction Center (SPC), it becomes clear that tornadoes are just part of the story.
Through March 9, the U.S. has racked up only 28 preliminary tornado reports, compared to an average of 95 for the same time span (Jan. 1 to Mar. 9) during the years 2000 – 2014. (Note that the 2014 data remain preliminary.) We’ve had quiet starts to tornado seasons before--in 2002, there’d been only 5 tornadoes by this point in the year--but 2015 stands out even more for its utter lack of strong thunderstorms. The most notable convective excitement of the year has been Jim Cantore’s amped-up encounters with thundersnow in New England (now Auto-Tuned for posterity). If you happened to encounter ice falling from the sky, it was more likely sleet than hail.
The dearth of severe weather comes into focus when we look beyond tornadoes. Through March 9, we’ve seen 119 preliminary reports of severe wind, compared to a 15-year average of 708. Even more striking is the almost-complete absence of large hailstones. The 15-year average up to this point in the year is 362 reports of severe hail (at least 1” in diameter), but in 2015 thus far, we’ve had only two such reports, both occuring in northern Louisiana on Feb. 1.
Figure 1. Total counts of tornadoes, severe hail, and severe wind for the period Jan. 1 – Mar. 9 in each year from 2000 to 2015. The national criterion for severe hail was raised from ¾” to 1” in 2010. Image credit: Jerimiah Brown, Weather Underground; data from NOAA Storm Prediction Center.
It’s pretty easy to see what’s caused the severe-weather drought of early 2015. A stubborn upper-level trough over Hudson Bay has kept northwest flow dominant across the eastern half of the country, shunting potentially unstable air masses well out to sea before they have a chance to generate thunderstorms. Even high-contrast fronts, like the one that plowed through the South last week, haven’t enough upper-level support ahead of the cold air in order to produce severe weather. The large-scale patterns have been so clear-cut that even the ambiguity that might prompt a tornado or severe thunderstorm watch has been in short supply. So far this year, SPC has issued just four watches (all tornado watches). This is the latest we’ve gone without at least one severe thunderstorm watch, and the lowest total number of watches through March 9, in records that go back to 1970. On average, more than 30 watches have been issued by this point. The first nine days of March 2015 didn’t see a single severe weather report or a single watch; no March in the official record has gone past March 10 without at least one watch.
Figure 2. Persistent northwest flow kept severe weather set-ups to a minimum across the central and eastern U.S. from late January through February. Image credit: The Weather Channel.
Variability in tornado seasons is increasing
After the catastrophic tornado season of 2011, which took more than 550 U.S. lives, the pendulum swung hard in the other direction. The period 2012 – 2014 saw the fewest tornadoes of any three-year period going back to 1950, when reliable tornado records began. As for 2015, the odds appear slim for any major severe outbreaks in the U.S. over at least the next week. “I would, in fact, not be surprised if we do not see a significant tornado in the month of March,” tornado researcher Victor Gensini (College of DuPage) told me in an email. It’s important to remember that a season that gets off to a slow start can still become active by spring, as noted by the Weather Channel’s Jon Erdman in this overview. And even a below-average season, such as 2013, can feature a few devastating days, such as the deadly outbreaks in late May 2013 that struck in and near Shawnee, Moore, and El Reno, Oklahoma.
Figure 3. Cloud-to-ground lightning near Tulsa, OK, on May 31, 2013, a day that also brought deadly tornadoes and flash flooding to the Oklahoma City area. Image credit: wunderphotographer mrwing13.
If it seems like tornado seasons are getting more variable, your impression is backed up by research. Harold Brooks (NOAA National Severe Storms Laboratory) led a study published last autumn in Science that details the increased ups and downs in tornado occurrence on a variety of time scales. Looking only at twisters with at least F1/EF1 strength on the Fujita/Enhanced Fujita damage scale, the study found that the number of days with at least one F1/EF1 tornado has dropped since the 1980s, while the number of days with at least 30 such tornadoes has risen dramatically. As a result, twisters are becoming more concentrated into a few high-intensity days each year. About 20% of all tornadoes in the decade 2004 - 2013 occurred on the three biggest days of each year, whereas this was the case for only 10% of all tornadoes before that decade. The reasons behind the shift aren’t yet clear, but the authors observe, “If the variability continues to increase, it could lead to an even greater concentration of tornadoes on fewer days.”
Seasonal timing is becoming more variable too, according to the study. For example, in all but three years from 1954 to 1996, the 50th F1/EF1 tornado of the year was reported between March 1 and April 10. But in the subsequent period (1997 – 2013), just 6 of 17 years saw the 50th twister occur in that early-spring interval, which implies that seasons are getting off to faster and/or slower starts. We’ll have more on climate change and tornadoes in an upcoming post.
Pam becomes a powerhouse in the South Pacific
In the South Pacific Ocean about 1,800 miles east of Australia, Tropical Cyclone Pam has quickly intensified to a Category 1 storm with top sustained winds of 90 mph as of 8 am EDT Tuesday. Pam has generated quite a bit of hype over the past few days, thanks to eye-popping model projections by the GFS and European models which show the cyclone intensifying into a Category 5 monster with a central pressure less than 880 mb by late this week. If this forecast verifies, it would make Pam one of the strongest tropical cyclones ever recorded, world-wide. However, these models are not known for making reliable intensity forecasts, and are generally disregarded by NHC for intensity forecasts in the Atlantic and Eastern Pacific. The HWRF model, which is one of our better intensity forecast models, predicted with its 06Z (2 am EDT) Tuesday run that Pam would reach a central pressure of 902 mb by Friday, which would make it a still-formidable Category 5 cyclone. The Tuesday morning official intensity forecast from the Joint Typhoon Warning Center (JTWC) goes along with this idea, making Pam a Category 5 storm by Friday. Pam is an unusually large cyclone over extremely deep warm water, with widespread surface temperatures above 30°C (86°F). With wind shear a moderate 10 - 20 knots and expected to be in the low to moderate range this week, Pam should be able to undergo a period of rapid intensification into at least a Category 4 storm. Fortunately, no major populated areas are in the projected path of Pam, although a westward shift in track could threaten the islands of Vanuatu.
Figure 4. MODIS satellite image of Pam taken at 23:00 UTC Monday March 9, 2015. Image credit: NASA.
Rare subtropical depression off the coast of Brazil
A rare subtropical depression, with characteristics of both a tropical and a non-tropical system, has formed in the South Atlantic waters off the coast of Brazil, according to the 8 am EDT March 10, 2015 analysis by the Navy Hydrographic Center in Brazil (thanks go to wunderground member Tropicsweatherpr for alerting us to this.) The unnamed storm has top wind speeds near 35 - 40 mph, according to an 8:20 am EDT pass from the ASCAT satellite. The surface pressure was near 1008 mb, and a modest amount of heavy thunderstorm activity was on its east side, in a band well removed from the circulation center. Sea surface temperatures are near 27°C, which is about 0.5°C above average, and 1°C above what is typically needed to support a tropical storm. Phase space diagrams from Florida State show the storm has a warm core at low levels which should get better defined through Wednesday, but by Thursday the storm will begin losing its tropical characteristics as it moves over cooler waters, and it is unlikely the storm has time to become fully tropical. The unnamed storm is not a threat to make landfall.
Figure 5. Surface analysis from 8 am EDT Tuesday March 10, 2015, from the Navy Hydrographic Center in Brazil showing a 1008 mb subtropical depression off the coast of Brazil.
South Atlantic tropical storm history
Tropical and subtropical storms are so rare in the South Atlantic that until 2011, there was no official naming of depressions or storms done. In 2011, the Brazilian Navy Hydrographic Center instituted a naming system with nine names, of which two have been used so far (Arani in 2011, and Bapo in 2015.) If this week’s storm becomes a subtropical storm, it will be called Cari. Brazil has had only one landfalling tropical cyclone in its history, Cyclone Catarina of March 2004. Catarina is one of fewer than ten tropical or subtropical storms to form in the South Atlantic, and the only one to reach hurricane strength. An unnamed February 2006 storm may have attained wind speeds of 65 mph, and a subtropical storm brought heavy flooding to the coast of Uruguay in January 2009, killing fourteen people. Tropical cyclones rarely form in the South Atlantic Ocean, due to strong upper-level wind shear, cool water temperatures, and the lack of an initial disturbance to get things spinning (no African waves or Intertropical Convergence Zone exist in the proper locations in the South Atlantic to help spawn tropical storms).
Climate change and South Atlantic storms
It is uncertain whether climate change may cause an increase in South Atlantic tropical storms in the future. While today's storm formed over waters that were about 0.5°C above average in temperature, Catarina in 2004 formed over waters that were 0.5°C cooler than average. Sea surface temperature is not the main limiting factor inhibiting these storms--wind shear is. How climate change might change wind shear over the South Atlantic has not been well-studied.
Bob Henson and Jeff Masters
By: Bob Henson , 3:37 PM GMT on March 09, 2015
Instead of easing toward its typical March maximum in coverage, the Arctic’s sea ice appears to be more inclined toward getting a head start on its yearly summer melt-out. As of Sunday, March 8, Arctic sea ice as calculated by Japan’s National Institute of Polar Research extended across 13.65 million square kilometers (Figure 1, red line). This value is more than 450,000 sq km--roughly the size of California--below the record extent for the date.
Figure 1. Arctic sea ice in 2015 (red trace) may have already reached its maximum extent for the year. Image credit: National Institute of Polar Research (Japan).
Even more striking is the consistency of the ice loss over the last couple of weeks. March is often a time of rapid gains and losses in ice cover, as seasonal warming and melting battle it out with quick refreezing when shots of cold air return. This year, the ice extent peaked on February 15 at 13.94 million sq km, and it looks increasingly unlikely that the ice will manage to return to that very early peak over the next couple of weeks. No season in the Japanese database has fallen short of the 14-million mark, so if the February peak stands, it will mark the lowest maximum in the Arctic since satellite monitoring began in 1979.
Using a slightly different formula for calculating extent, the National Snow and Ice Data Center comes up with a similar record low for the date (Figure 2). In an update on March 4, NSIDC stated: “The Arctic maximum is expected to occur in the next two or three weeks. Previous years have seen a surge in Arctic ice extent during March (e.g., in 2012, 2014). However, if the current pattern of below-average extent continues, Arctic sea ice extent may set a new lowest winter maximum.” (As explained by NSIDC, “extent” measures the outer edge of where ice covers most of the ocean surface, with at least 15 percent of ice coverage required in a given grid cell. It’s a bit like measuring the size of a slice of Swiss cheese. “Area” is a more direct index of where ice actually exists--the cheese itself--but it’s also more prone to difficulty in satellite measurement.)
Figure 2. A closer look at Arctic sea ice extent for each year since 2007. Image credit: National Snow and Ice Data Center/Charctic.
Not only is Arctic sea ice essential to many ecosystems: it serves as a powerful tracer of recent warming, and its absence in summer allows open water to absorb much more heat from sunlight. While the ice has seen some modest recovery in recent years, it has failed to fully mend the fabric torn by the record-setting drop of 2007. The overall thickness of the ice, and the fraction that’s survived for multiple years (multiyear ice), have both suffered major losses. A comprehensive survey just published in The Cryosphere found that ice thickness in the central Arctic dropped by 65 percent from 1975 to 2012.
Experts differ strongly on when we might see a summer that melts nearly all of the Arctic’s ice (typically defined as less than a million sq km of extent by the normal September minimum). Computer models suggest this point might not be reached till the 2040s or later, while simple extrapolation from recent years would produce an effectively ice-free September by the 2020s, perhaps even sooner. Sea ice around Antarctica has increased somewhat in recent years, but that ice plays a vastly different role in global and regional climate.
A lot can happen during a particular Arctic warm season to accelerate or mute ice loss. Melt ponds scattered across the ice play a vital role in absorbing sunlight and hastening further melt, and cloud-free, sunny weather--especially near the summer solstice--can make a huge difference. Because of these and other intervening factors, there’s little correlation between the size of the March (or February) maximum and that of the September minimum. Even so, the magnitude of the current record low for the date is jarring, and weather patterns this week could raise eyebrows even further. A string of intense cyclones is now riding the jet stream northward between Greenland and Norway. The flow around these storms is close to ideal for pushing large amounts of ice to their doom through the Fram Strait east of Greenland. Such export of ice is more common when the Arctic Oscillation is positive, as it’s been most of this winter. NOAA’s daily AO index reached an extremely high value over the past weekend, exceeding 5.5.
Figure 3. The daily Arctic Oscillation index was nearly off the charts on the high side during the weekend of March 7-8, 2015. Image credit: NOAA Climate Prediction Center.
The current weather pattern is also pushing a huge pulse of extremely mild late-winter air across the central Arctic (see Figure 4). Temperatures on Sunday, March 8, reached 15.8°C (60.4°F) in Stockholm. Senior climatologist Sverker Hellström (Swedish Meteorological and Hydrological Institute) observed today in an email forwarded by weather records researcher Maximiliano Herrera that the 15.8°C is the warmest reading prior to March 19 in records at Stockholm that go all the way back to 1756! If there is any major refreezing of Arctic sea ice in the next few days, it’s most likely to occur in the Bering Sea, but the freeze-up there would have to be vast and quick to counterbalance the major ice losses we’ve seen across the Arctic as a whole since February. Even if a new peak is reached this month, it’s unlikely to be enough to keep 2015 from setting the record for the lowest maximum Arctic ice extent.
The Arctic Sea Ice Blog offers extensive coverage of this topic, including an excellent compilation of graphics updated daily. Blogger Jim Hunt examined the current situation in a detailed post on Sunday.
Figure 4. A surge of relatively mild air may send temperatures 35°F or more above average over the central Arctic by Tuesday, March 10. Image credit: ClimateReanalyzer.org.
By: Bob Henson , 4:55 PM GMT on March 06, 2015
More than a year after the prospect of a 2014–15 El Niño event first surfaced, NOAA’s Climate Prediction Center (CPC) issued a long-awaited El Niño Advisory on Thursday. We’re still a long way from a textbook example of El Niño: ocean warming is barely above the standard threshold, and the atmospheric response is not yet fully formed and consistent. One thing we do know is that sea-surface temperatures in the crucial Niño3.4 region of the eastern tropical Pacific have now met the El Niño threshold (0.5°C above average) across four overlapping three-month periods (Sept- Nov, Oct-Dec, Nov-Jan, and unofficially Dec-Feb). A total of five such periods are required before the title “El Niño episode” is bestowed by NOAA, so we could be there by April.
Figure 1. Weekly departures from average in sea-surface temperature (degrees C) across the Niño3.4 region of the eastern tropical Pacific. Image credit: NOAA Climate Prediction Center.
Along with the increased certainty of warm SSTs, the atmospheric response is gradually becoming more coherent, according to CPC forecaster Emily Becker. “For the last few months, we’ve been seeing some suggestions of borderline atmospheric El Niño conditions, but until this month we were below that borderline. This month, we’ve finally crept above it,” said Becker in a blog post at climate.gov. She points to a weakening of equatorial trade winds, as expressed in the Equatorial Southern Oscillation Index, as well as an increase in rainfall across the central tropical Pacific. NOAA’s advisory pegs the odds of El Niño conditions extending into northern summer at 50-60%. Weak El Niño events are much less likely to produce reliable effects on U.S. weather than stronger events, although there could be a El Niño–boosted enhancement of rainfall across the Gulf states this spring. With California’s rainy season winding down, there’s little hope of any major benefit from El Niño.
Seven of the eight global computer models surveyed this week by the Australian Bureau of Meteorology indicate that Niño3.4 temperatures will be above the NOAA threshold (0.5°C) in July. Predictions are most challenging during northern spring, when El Niño episodes are usually on the wane. If this event does mature and extends into next autumn, then 2015 could become one of the rare calendar years that sees continous El Niño conditions from January to December (as measured by the oceanic index described above). Going back to the start of NOAA records in 1950, the only other such years are 1953, 1969, and 1987. A prolonged El Niño event isn’t necessarily a strong one, but several models do push the Niño3.4 index above 1.0°C by this summer. An event under way in July typically strengthens by the end of the year, as climatology becomes more favorable.
Twin tropical cyclones possible next week
The incipient El Niño could get a shot in the arm from a major westerly wind burst that models are consistently developing next week around 5°S in the western Pacific. As they push against the prevailing east-to-west trades, westerly wind bursts can help nudge the ocean-atmosphere linkage toward the direction of El Niño. The atmospheric set-up that favors a westerly wind burst can also encourage the development of twin tropical cyclones to its north and south, and models are indicating this may also occur next week. In fact, multiple runs of the GFS and ECMWF models are suggesting that a tropical cyclone east of Australia could become one of the strongest on record for that region. It’s far too soon to take any model forecast literally, with the event still nearly a week out, but the consistency across multiple models lends credence to the idea of a powerful cyclone that could threaten islands in the southwest Pacific north of New Zealand sometime late next week.
Figure 6. Snowfall on Thursday, March 5, in Glasgow, Kentucky, east of Bowling Green. Much of central Kentucky saw more than a foot of snow from Wednesday into early Thursday. Image credit: wunderphotographer tightwad6972.
Winter’s last gasp back East?
March came in like the proverbial lion this week across the eastern U.S., taking one last swipe at the region before a much-anticipated warm-up. Heavy sleet and snow developed on Thursday from Texas to New York--including many of the same areas struck last week--within a band of moist upper-level flow extending from the tropical Pacific to the U.S. East Coast. The Dallas-Fort Worth airport received 2.5” of snow, yielding the snowiest March since 1947; amounts of 5+” were reported in the north DFW area. Central Kentucky was again buried in foot-plus accumulations: Lexington saw its heaviest 24-hour total (14.6”) and two-day total (17.1”) on record.
Figure 3. Temperatures ran the gamut across the Southeast as a strong cold front plowed across the region at 6 AM EST on Thursday, March 5. Image credit: WunderMap.
Parts of the Southeast got a brief taste of spring warmth before the cold roared back, leading to some unusually dramatic cool-downs. In Jackson, MS, the reading sank from a humid 81°F at 3 PM CDT Wednesday to a blustery, damp 28°F at 10 AM Thursday. On Friday morning, unprecedented cold for so late in the winter struck several locations, especially snowbound Kentucky.
All-time record lows for March:
Frankfort, KY: –10°F (old record –3°F, Mar. 7, 1960)
Urbana, IL: –7°F (old record –5°F, set Mar. 1906)
Paducah, KY: –6°F (old record –2°F, last set Mar. 6, 1960)
Pittsburgh, PA: –4°F (old record –1°F, last set Mar. 2, 1980)
Lexington, KY: –2°F (tied old record, last set Mar. 6 ,1960)
Harrisburg, PA: 0°F (old record 5°F, last set Mar. 10, 1984)
Toasty in Spain; howling in Italy and Croatia
Temperatures soared to summer-like readings along Spain's east coast early this week. On Monday, March 2, the towns of Sagunto and Elche both reached 30.4°C (86.7°F), a reading that’s close to the average daily high in August at the nearby coastal city of Valencia. These are the warmest temperatures known to have occurred on the Iberian peninsula (mainland Spain) so early in the year, according to weather records researcher Maximiliano Herrera. The nearest rival is the 32.4°C (90.3°F) reported at Almeria on March 3, 1987. Warmer temperatures have occurred in wintertime on Spanish territory beyond the peninsula, including 34.2°C (93.6°F) at Melilla (a Spanish enclave on the north African coast, adjoining Morocco) on Feb. 27, 2010.
Figure 4. Firemen inspect a truck overturned by heavy winds, near Split, Croatia, Thursday, March 5, 2015. Winds caused traffic disruptions in much of coastal Croatia. Image credit: AP Photo/Ivo Cagalj, PIXSELL.
This week’s heat in Spain preceded a strong Mediterannean cyclone that produced extreme bora (cold downslope) winds and extensive damage, including many downed trees, in Italy and Croatia on Wednesday night (see Figure 4, above). According to Herrera, a gust to 209 km/h (130 mph), one of Italy's strongest on record, was reported at Gigliana, Tuscany. Even stronger gusts were reported in parts of Croatia, with heavy mountain snowfalls. Severe Weather Europe’s Facebook page includes a number of dramatic photos and videos of pounding waves along the Croatian coastline.
This week’s WunderPoster: Lenticular clouds
The latest installment in our WunderPoster series (Figure 5, right) pays homage to the surreal structure of lenticular clouds. These clouds form when a strong jet stream impinges on a mountain range and the resulting wavelike motion is trapped within a layer of stable air. An isolated peak can produce lenticulars resembling a stack of dinner plates (or flying saucers). All WunderPosters can be downloaded in formats suitable for posters or postcards.
Now it’s your turn: help us create a WunderPoster!
To celebrate our 20th anniversary, we’re looking to you to provide inspiration for a new WunderPoster. Our “picture yourself here” website has all the details.
Figure 6. These sunset lenticulars along Colorado’s Front Range were featured by the U.S. Postal Service in 2004 in its “Cloudscapes” stamp series. Image credit: Carlye Calvin.
By: Jeff Masters , 1:08 PM GMT on March 04, 2015
On the night of August 17, 1969, Hurricane Camille roared towards the Mississippi coast with sustained winds of an incredible 175 mph. Residents all along the coast fled the wrath of this mighty Category 5 hurricane, but a few unfortunate holdouts chose to ride the storm out rather than evacuate. Legend has it that many of the 23 residents of the infamous Richelieu Manor Apartments in Pass Christian who chose to stay held a hurricane party, in defiance of the hurricane's might (and common sense!) An ABC TV made for TV movie called Hurricane, starring Frank Sutton (of Gomer Pyle USMC fame), Larry Hagman (of Dallas fame), Martin Milner, and Michael Learned, was loosely based on the supposed hurricane party. Legendary TV anchorman Walter Cronkite perpetuated the hurricane party story during one of his broadcasts after the hurricane. As the camera panned over the cement slab littered with debris that marked the former location of the Richelieu Apartments, Cronkite narrated:
"This is the site of the Richelieu Apartments in Pass Christian, Mississippi. This is the place where 23 people laughed in the face of death. And where 23 people died."
Figure 1. The Richelieu Manor Apartments in Pass Christian, Mississippi before Hurricane Camille (top) and after (bottom.) Image credit: NOAA photo library.
Camille pushed its record 24.7-foot storm surge through Pass Christian, completely leveling the Richelieu Apartments. The 1989 PBS NOVA show, Hurricane, interviewed Mary Ann Gerlach, who claimed to be the lone survivor of the ill-fated hurricane party. She provided lurid details of the booze and pills at the party, after which she and her sixth husband fell asleep in their second-floor apartment. When Camille's storm surge smashed through, the building disintegrated, and she landed in the chaotic sea. Gerlach survived by clinging to pieces of floating debris and furniture. Gerlach, however, was not exactly a reliable witness. In 1982, when on trial for murdering her 11th husband, Gerlach's lawyer used an insanity defense, claiming her Camille experience and the resulting drug and alcohol abuse caused her to kill. She was found guilty, sentenced to life in prison, and paroled in 1992.
Figure 2. A boat driven inland by Hurricane Camille's record storm surge in Mississippi. Image credit: NOAA photo library.
According to an article published in 2000 by Mississippi Sun Herald reporter Kat Bergeron (kindly forwarded to me by Dr. Patrick Fitzpatrick, Mississippi State University professor and author of Hurricanes: A Reference Handbook), watching Cronkite's broadcast was Josephine Duckworth, whose 24-year-old son had ridden out the storm in the Richelieu Apartments. Her husband, Hubert Duckworth, certain that their son had been killed, headed down to Pass Christian the next day to claim their son's body. Hubert Duckworth encountered Mike Gannon, who had also ridden out the storm in the Richelieu Apartments.
"Where can I find my son's body?" the father asked.
"Why, Ben Duckworth isn't dead," Gannon told him. "I've seen him, and he's all right."
Indeed, father was reunited with son. And, according to survivor Ben Duckworth, only 8 out of the 23 residents of the Richelieu Apartments died in the storm, and the hurricane party never happened. Duckworth recounted,
"We were exhausted from boarding up windows and helping the police move cars. We were too tired to party. I cannot tell you why the story persists, or why people didn't put two and two together. I guess the hurricane party makes a good story." While he was boarding up and helping others prepare for the storm, a traveling salesman that some residents knew stopped by the complex. "Let's get some beer and have a hurricane party," the salesman said. "We were too exhausted. and when he couldn't find any takers, he got in his car and headed toward New Orleans," Duckworth remembered. "That probably saved his life, but I've wondered if that man isn't the origin of the legend. Maybe someone heard him and thought the party really happened."
Former Wunderblogger Margie Kieper, now working on her Ph.D. in hurricane science at Florida International University, has researched the party myth, and had this to add:
"The building was a designated civil defense shelter. One of the survivors interpreted that to mean he thought it was built with steel beams, but it was stick built. The sheriff did come by several times and ask them to evacuate, but the landlord convinced them it would be safe to stay. The young guys had promised to stay and look after some of the older people. They spent the day helping the landlord get the property ready, like boarding all the first floor windows with sheets of plywood (for a building that size you can imagine how much work that was!) After that and moving furniture upstairs to the second and third floor vacant apartments, they were all pretty exhausted. They had also helped ferry the residents back and forth to get all their cars parked in a different location where they believed the cars would be safe from surge. There were older people in the apartments including at least one in a wheelchair. The younger men tried to look after the older people. They were simply sheltering the storm and made a bad choice. Eight people in the building died and six lived. The building held a lot more than 23 residents."
More details on the experiences of the Richelieu Apartments survivors can be found at the passchristian.net website.
Our next post will be on Friday.
By: Bob Henson , 4:11 PM GMT on March 02, 2015
We won’t have the full state-by-state picture of February’s U.S. climate for a few days, but the outlines are abundantly clear from city climate summaries issued on Sunday. It’s been almost 40 years since the nation has seen a month so starkly divided between a cold east and warm west. The statistics bring to mind early 1977, when snowflakes fell for the first and only time on Miami Beach’s art deco buildings while skiers in the Rockies found themselves hunting in vain for fresh powder. A more distant analog for the sharp eastern cold is January 1934, as evident in the records broken below. This year millions of people experienced either the warmest or coldest February for their locations, with records in some cases going back more than 100 years. A number of cities had their coldest average temperature for any month on record—truly stunning in a climate that’s running close to a record-high global air temperature. Meanwhile, February proved to be the warmest winter month ever documented across a huge swath of the West. Alaska wasn’t as consistently warm as parts of California through the month, but a few extremely mild air masses pushed into the state, helping produce the first thundersnow on record in Nome and an all-time monthly high of 53°F in the town of Homer.
Figure 1. Instead of slowly rising through February, as climatology would have it, daily highs and lows in Syracuse, NY, sagged into colder and colder realms as the month went by. Each dashed column represents one month, with dark blue traces showing observed highs and lows. The green band indicates 30-year average highs and lows, with pink and blue showing daily record highs and lows, respectively. Image credit: NWS/Binghamton, NY.
Below is just a sampling of the many monthly records set at various points in the past four weeks. One hint of the state records to come: according to the Northeast Regional Climate Center, Maine had its coldest average temperature of any February, with a mere 2.5°F for the entire state.
Coldest month on record
Bangor, ME: 6.1°F, old record 8.4°F (Jan. 1994)
Syracuse, NY: 9.1°F; old record 12.1° (Feb. 1934)
Buffalo, NY: 10.9°F; old record 11.6° (Feb. 1934)
Rochester, NY: 12.2°F, old record 12.6°F (Feb. 1934)
Worcester, MA: 14.2°F; old record 14.4°F (Feb. 1934)
Coldest February on record
Caribou, ME: 2.8°F; old record 4.1°F (1993)
Portland, ME: 13.8°F; old record 13.9°F (1934)
Youngstown, OH: 13.7°F; old record 15.2°F (1934)
Cleveland, OH: 14.3°F; old record 15.2°F (1875)
Chicago, IL: 14.6°F; tied with Feb. 1875
Hartford, CT: 16.0°F; old record 16.5°F (1934)
Harrisburg, PA: 20.9°F; old record 21.4°F (1934)
Warmest winter month on record (Dec., Jan., Feb.)
Salt Lake City, UT: 43.9°F; old record 42.9°F (Feb. 1907)
Reno, NV: 46.3°F; old record 46.0°F (Feb. 1995)
Seattle, WA: 48.8°F; old record 48.7°F (Feb. 1977)
Portland, OR: 49.2°F; old record 48.8°F (Feb. 1991)
San Francisco, CA (downtown): 59.5°F; old record 58.9°F (Feb. 1986)
Las Vegas, NV: 60.0°F; old record 58.6°F (Feb. 1995)
Warmest February on record
Flagstaff, AZ: 39.7°F; old record 38.2°F (Feb. 1947)
Figures 2 and 3. The nation’s split climate of the last month is captured in these contrasting images taken near (left) Hollister, CA, on Feb. 24 and (right) Freeport, ME, on Feb. 19. Image credits: Jan Null (left), wunderphotographer capritaur (right).
How it felt on the ground
The most concentrated impacts were felt in Boston, where multiple storms left a record snow total for any month (64.8”, smashing the previous record of 43.3” from Jan. 2005) and a year-to-date total of 103.9” as of Sunday night, March 1. That’s less than 6 inches from the all-time seasonal snow record of 107.6” set in 1995-96. The scrappy residents of Boston coped with the snow as best they could, drawing on more than a few dashes of bleak humor, but this event was truly a disaster for countless people in the Boston area who lost days or weeks of pay because of transportation snarls. Though fewer in number, residents of Maine dealt with cold and snow that were arguably the worst in a lifetime for many who are accustomed to dealing with harsh winter weather.
If we pull back to examine the winter as a whole, it’s the western warmth that really stands out. More than 20 reporting stations saw their warmest winters on record, including San Francisco, Las Vegas, Seattle, Salt Lake City, and Portland, Oregon. December was very mild nationally (the 2nd warmest in 120 years of U.S. record keeping), which blunted the ability of the last few frigid weeks to set any coldest-winter records in the eastern U.S. Flowers are blooming on California hillsides weeks ahead of schedule. Pleasant as all this might seem to folks freezing in the East, the warmth and relative dryness have left much of the West vulnerable to major drought impacts in the coming summer.
The next post will be Wednesday at the latest.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather