Category 6™

Haboob, Sandstorm, Dirt Storm? The Answer’s Blowing in the Texas Wind

By: Bob Henson , 3:02 PM GMT on May 31, 2016

Just as people come to America from around the world, so do the terms we use to describe wind--although some would prefer that the nation stick to homegrown meteorological verbiage. A good case of this linguistic angst emerged on Sunday evening with the arrival of a dramatic haboob in Lubbock, TX. Rain-cooled outflow from strong thunderstorms over the Texas Panhandle pushed across the Lubbock area from the northeast, plowing up a wall of dust that was captured on video from Lubbock’s National Weather Service office (see bottom of this post). The temperature at the Lubbock NWS office dropped from 82°F at 7:03 pm CDT to 64°F at 7:10 pm CDT, with winds gusting to 56 mph and visibility down to 0.5 mile in rain and blowing dust.

Haboobs are distinct from ordinary blowing dust because of the thick dust shoveled upward--sometimes more than half a mile--by the relatively cool, dense air at the leading edge. After a haboob’s front edge moves past a given location, the airborne dust quickly abates. In contrast, blowing dust refers more generally to the situation where hours of strong wind can kick up broad areas of reduced visibility, often for hours at a time during dry, hot weather. Extreme blowing dust episodes, or duststorms, typically cover a large area, as opposed to the narrow zone of a haboob. Sandstorms occur when sand grains are blown across the lowest few feet of the landscape, usually in true deserts rather than semiarid regions.


Figure 1. Intense thunderstorms located north of Lubbock at 6:15 pm CDT Sunday, May 29, 2016, pushed an outflow boundary (the faint line south of the storms) and associated haboob (not visible on radar image) toward the Lubbock area. Image credit: NWS/Lubbock.


Figure 2. Screenshot of the NWS/Lubbock Facebook entry noting that a haboob was approaching Lubbock International Airport from the north at 6:57 pm CDT Sunday, May 29, 2016. Image credit: NWS/Lubbock.


According to the AMS Glossary (American Meteorological Society), “haboob” is derived from the Arabic word “habb” (a verb meaning "to blow", as with the wind]. That fact has led to unrest on social media more than once over the last few years. The use of the term in media to (correctly) describe a massive haboob that plowed from southeast Arizona to Phoenix on July 18, 2011, caused enough of a local outcry to prompt an article about the controversy in the New York Times. When the NWS Lubbock office posted warnings on its Facebook page about an approaching haboob on March 11, 2014, many readers protested; when the warning was shared on a local TV station’s Facebook page, there were calls for the broadcast meteorologist to be fired. History repeated itself last Sunday when the approaching haboob was mentioned on the NWS Lubbock webpage. One commentor asked the NWS to “use the American term please.” Another said “I’ll find another weather service.”

What’s kicked up the haboob storm?
Why did it take until recently for residents of the Southwest U.S. to get excited about a once-obscure term? For one thing, intense, recurring drought over the last few years, coupled with record-warm, landscape-drying temperatures, could be making the region more prone to haboob formation at times, although this would be a difficult thing to quantify. Another factor: with their adoption of Twitter and Facebook, NWS offices now have a direct line to the public, together with the ability to introduce semi-technical terms that otherwise might not have made it through the filter of mass media. The ascent of online media has also made it more tempting for journalists and pundits to coin or promulgate terms that have a chance of going viral. Already, the age of social and online media has popularized “polar vortex,” “derecho,” and several others. It’s easy to see why a sensitized layperson might feel that certain foreign-sounding terms are being suddenly foisted on them.

Of course, there is Arabic influence throughout the world of scientific terminology. Every time you use 3, 5, or 8, you’re using an Arabic numeral. And though it’s only recently made it into public discourse, “haboob” is hardly a new term in the meteorological literature. As noted by Maryland weathercaster and AGU blogger Dan Satterfield, a 1925 paper in the Quarterly Journal of the Royal Meteorological Society was titled “Haboobs.”


Figure 3. The spectacular haboob that slammed into the Phoenix area on July 18, 2011, photographed in Maricopa. Image credit: wunderphotographer nukegm.

Other sources of wind names
Like the weather itself, weather words transcend national borders. The names we use in the United States for wind-related phenomena come from a wide array of sources. “Tornado” and “derecho” are both derived from Spanish (“thunder” and “straight,” respectively). The German-derived term “foehn wall” describes a wall of clouds that forms on the windward side of a mountain range, as seen from the leeward side; it’s often accompanied by a strong, mild “chinook” wind on the downwind side, named after several Native American peoples indigenous to the Pacific Northwest.

Even the all-American-sounding “downburst” and “microburst” were coined by a Japanese-American immigrant, the eminent meteorologist Theodore “Ted” Fujita (creator of the Fujita Tornado Damage Scale). First trained as a mechanical engineer, Fujita took a research flight in 1945 over the debris left by the bombs that struck Hiroshima and Nagasaki and observed starburst damage patterns emanating outward from the point of the bomb impact. Later, while surveying damage from the Super Outbreak of April 3, 1974, Fujita recognized similar starburst patterns, and he concluded that some of the damage must have resulted from descending wind bursts.

You’ll find a variety of haboob photos from around the world at the post filed by Jeff Masters on May 3, 2005. This was post #5 in this blog, out of 3317 posts to date!


Figure 4. Flooding at Lakeview Park in Humble, TX, on May 29, 2016. Image credit: wunderphotographer mcdsara1.

Continuing flood threat in southeast Texas this week
The National Hurricane Center issued its final advisory at 5:00 am EDT Tuesday on former Tropical Storm Bonnie, which had been declared post-tropical on Monday. High water resulting from more than 8 inches of rain in parts of South Carolina prompted the closure of Interstate 95 about 20 miles north of the Georgia border on Sunday, causing major traffic troubles. Flooding from a much larger area of heavy rain across Texas related to a stalled front and a slow-moving upper low has taken at least six lives since late last week. The Brazos River at Richmond, just west of Houston, was at a record-high flood stage of 53.19 feet at 7:15 am CDT Tuesday, and dozens of homes have been evacuated. More heavy rains are possible across southeast Texas later this week, which the Houston NWS office warns “will likely exacerbate flooding somewhere in our forecast area.”

Bob Henson


Extreme Weather Haboob

Bonnie Dies; Rampaging Flash Floods Kill 4 in Germany

By: Jeff Masters , 4:10 PM GMT on May 30, 2016

Tropical Depression Bonnie was declared post-tropical by NHC at 11 am EDT Monday, but the remains of Bonnie will continue to bring additional rainfall of 1 - 3" to eastern South Carolina, eastern North Carolina, and southeast Virginia through Wednesday. As of Monday morning, Bonnie had already brought total rainfall of more than 8 inches over portions of south-central South Carolina. Bonnie made landfall on the coast of South Carolina just east of Charleston at 8:30 am EDT Sunday morning as a tropical depression with top winds of 35 mph. Bonnie spent just 18 hours as a tropical storm, reaching peak intensity of 45 mph sustained winds on Saturday night when the center of the storm lingered over the warm waters of the Gulf Stream.


Figure 1. Two-day rainfall amounts from Bonnie for the period ending at 10 am EDT May 30, 2016.

Bonnie's legacy
The 2016 version of Tropical Storm Bonnie was the seventh incarnation of the storm, which made its first appearance back in 1980. My very first flight into a hurricane with the Hurricane Hunters was into the 1986 version of Hurricane Bonnie, which made landfall on the Upper Texas coast as a Category 1 storm--but wasn't powerful enough to cause notable damage. None of the versions of Bonnie over the years have been strong enough to get the name Bonnie retired, and this year's meager effort assures that there will be an eighth appearance of Bonnie in 2022. Only five other Atlantic storms have had more appearances than Bonnie--Arlene with ten (1959 - TS; 1963 - H2; 1967 - H1; 1971 - TS; 1981 - TS; 1987 - H1; 1993 - TS; 1999 - TS; 2005 - TS; 2011 - TS), Florence with nine (1953 - H3; 1954 - TS; 1960 - TS; 1964 - TS; 1988 - H1; 1994 - H2; 2000 - H1; 2006 - H1; 2012 - TS), Cindy with eight (1959 - H1; 1963 - H1; 1981 - TS; 1987 - TS; 1993 - TS; 1999 - H4; 2005 - H1; 2011 - TS), Dolly with eight (1953 – H1; 1954 – H1; 1968 - H1; 1974 - TS; 1996 - H1; 2002 - TS; 2008 - H2; 2014 - TS), and Frances with eight (1961 - H3; 1968 - TS; 1976 - H3; 1980 - H3; 1986 - H1; 1992 - H1; 1998 - TS; 2004 - H4, RETIRED). Thanks go to wunderground member Mark Cole for these stats.

Flash flooding in Germany kills four
A stationary low pressure system over Germany has led to massive amounts of hail and torrential rains in heavy thunderstorms, killing four people. Rainfall amounts in excess of four inches in two hours fell in some regions of southwest Germany, and this water was channeled and concentrated into narrow valleys upstream from the hard-hit town of Braunsbach in Baden-Württemberg's north. Some truly spectacular/frightening videos have come from that town:


Video 1. The flood waters from this video look sped up, but judging by the frequency of the emergency lights on the fire car being swept away and the way the water moves farther upstream, you can see that the speed is real.


Video 2. More incredible footage of cars being swept through the streets of Braunsbach in the May 30, 2016 flash flood.

The low will remain stationary over Germany during the next few days thanks to a jet stream weather pattern that has remained "stuck" in place, so additional extreme flash flooding is possible this week. Thanks go to wunderground contributor Michael Theusner for this information.

Jeff Masters

Hurricane Flood

Tropical Depression Bonnie Makes Landfall Near Charleston, SC

By: Jeff Masters , 3:28 PM GMT on May 29, 2016

The center of Tropical Depression Bonnie made landfall on the coast of South Carolina just east of Charleston at 8:30 am EDT Sunday morning. At the time, Bonnie had top winds of 35 mph. On Saturday night, Bonnie reached peak intensity with 45 mph winds as the center of the storm lingered over the warm waters of the Gulf Stream. However, early on Sunday morning, strong upper level winds created wind shear in excess of 40 knots over the storm, ripping away most of Bonnie's heavy thunderstorms, reducing the storm to tropical depression status.


Figure 1. Tropical Depression Bonnie making landfall near Charleston, South Carolina, as seen by the GOES-East satellite at 8:30 am EST May 29, 2016. Image credit: NASA/GSFC.

As Bonnie heads north at 9 mph on Sunday, the center will get farther from the warm ocean waters that fuel the storm, causing weakening. Nevertheless, Bonnie will be able to dump heavy rains of 2 - 4 inches over much of coastal South Carolina and adjacent areas of coastal Georgia and North Carolina through Monday. Radar-estimated rainfall from Charleston, South Carolina on Sunday morning showed several regions between Charleston, South Carolina and Savannah, Georgia had already tallied more than two inches of rain from the storm.


Figure 2. Radar-estimated rainfall from Charleston, South Carolina at 11:05 am EDT Sunday, May 29, 2016. Several coastal areas had received more than 2" of rain (yellow colors.)

Jeff Masters

Hurricane

TD 2 Expected to Become Tropical Storm Bonnie as it Crosses the Gulf Stream

By: Jeff Masters , 3:27 PM GMT on May 28, 2016

Tropical Storm Warnings continue for the coast of South Carolina as Tropical Depression Two chugs northwest at 13 mph towards the Southeast U.S. coast. Radar imagery from Charleston, South Carolina showed heavy rains from TD 2 had reached the coast late Saturday morning, and heavy rains will affect most of the coast of South Carolina by late Saturday afternoon. Satellite loops on Saturday morning showed that TD 2 had a relatively meager amount of heavy thunderstorm activity, which had increased in areal coverage only slightly since Friday. Strong upper level winds from the southeast were creating a high 20 knots of wind shear over TD 2 on Saturday morning, keeping the storm's heavy thunderstorms limited to the northeast side of the center. An Air Force hurricane hunter aircraft found top sustained winds of 35 mph in a small region near the storm's center on Saturday morning. Sea surface temperatures (SSTs) near TD 2's center were about 26°C (79°F)--marginally warm enough to support a tropical storm. A large area of dry continental air lay to the west of TD 2, and this dry air was interfering with development.


Figure 1. Ocean temperatures off the Southeast U.S. coast for the period May 25 - May 27, 2016, as sensed by AVHRR satellite instruments. On Saturday afternoon, TD 2 will be traversing the warm 27 - 28°C (81 - 82°F) waters of the Gulf Stream. Image credit: Ocean Remote Sensing Group, Johns Hopkins University Applies Physics Laboratory.

A heavy rain threat for the Southeast U.S. coast
On Saturday, TD 2 will be traversing warm Gulf Stream waters of 27 - 28°C (81 - 82°F), and these warm waters should provide enough of a boost to TD 2 to strengthen it into Tropical Storm Bonnie. However, there is dry air to the west of TD 2, and the SHIPS model predicted on Saturday morning that wind shear would rise to 20 - 25 knots on Saturday evening though Sunday. These conditions will likely keep TD 2 from becoming anything stronger than a 45-mph tropical storm. In their 11 am EDT Saturday Wind Probability Forecast, NHC gave Charleston, South Carolina the highest odds of any city on the coast of seeing tropical storm-force winds of 39+ mph: 43%. Heavy rain is the main concern from TD 2, and heavy rains of 2 - 4" are likely along the coast of South Carolina through Monday, with 1 - 3" amounts likely along the southeast coast of North Carolina through Tuesday. Water temperatures off the southeast coast of North Carolina are quite cool--near 24° C (75°F), so TD 2 should weaken as it progresses to the northeast along the coast on Sunday and Monday.

Jeff Masters

Hurricane

Tropical Storm Warnings for South Carolina as Tropical Depression Two Forms

By: Jeff Masters , 9:39 PM GMT on May 27, 2016

Tropical Storm Warnings are flying for the coast of South Carolina as newly-formed Tropical Depression Two moves west-northwest at 12 mph towards the Southeast U.S. coast. An Air Force hurricane hunter aircraft found a closed circulation and top sustained winds of 35 mph in a small region near the storm's center on Friday afternoon, leading NHC to start issuing advisories on the Atlantic's second tropical cyclone of the year. Sea surface temperatures (SSTs) near TD 2's center were about 25 - 26°C (77 - 79°F), which are only marginally warm enough to support a tropical storm. Wind shear on Friday afternoon was in the moderate range, 10 - 20 knots. A large area of dry continental air lay to the west of TD 2, and this dry air was interfering with development. Satellite loops on Friday afternoon showed that TD 2 had only a modest amount of heavy thunderstorm activity that had increased in areal coverage only slightly since Friday morning.


Figure 1. Tropical Depression Two as seen by the MODIS instrument on NASA's Terra satellite on Friday afternoon, May 27, 2016. Image credit: NASA.

A heavy rain threat for the Southeast U.S. coast
On Friday night and Saturday, TD 2 will be traversing waters of 25 - 26°C (77 - 79°F), and the 18Z (2 pm EDT) Friday run of the SHIPS model predicted that wind shear would stay in the moderate range, 10 - 20 knots. These conditions are barely favorable enough to allow slow development of TD 2 into a 45-mph Tropical Storm Bonnie. There is dry air to the west of the storm that will interfere with development, as well. TD 2 may get a small boost when it crosses the axis of the warm Gulf Stream current on Saturday afternoon, when SSTs will be 27 - 28°C (81 - 82°F), but a 55 mph tropical storm is probably the strongest that TD 2 can get. The NHC official forecast of a top intensity of 45 mph is a more likely scenario. In their 5 pm EDT Friday Wind Probability Forecast, NHC gave Charleston, South Carolina the highest odds of any city on the coast of seeing tropical storm-force winds of 39+ mph: 48%.

Heavy rain is the main concern from TD 2, and heavy rains should reach the coasts of South Carolina and southeastern North Carolina on Saturday afternoon or evening. In their Friday afternoon (12Z) runs, our two top two models for forecasting tropical cyclone tracks--the American GFS model and the European ECMWF model--showed TD 2 coming within 50 miles of the coast of South Carolina on Sunday morning. Steering currents will shift on Sunday evening, as TD 2 gets caught in the circulation associated with a trough of low pressure passing to the north. This shift will cause TD 2 to slow down as it reaches the coast of South Carolina, followed by a turn to the northeast. The center of TD 2 will likely track just inland along the coasts of South Carolina and North Carolina on Monday and Tuesday, spreading heavy rains of 2 - 4" along its path. It is uncertain at this time whether or not TD 2 will be able to spread heavy rains farther north into Virginia later in the week.

Jeff Masters

Hurricane

NOAA Calls for Near-Average 2016 Atlantic Hurricane Season; Other Groups Go Bigger

By: Jeff Masters and Bob Henson , 6:41 PM GMT on May 27, 2016

In its first outlook for the 2016 Atlantic hurricane season, issued Friday, NOAA’s Climate Prediction Center is calling for near-normal activity as the most likely outcome. The NOAA outlook predicts a 70 percent likelihood of 10 - 16 named storms, 4 - 8 hurricanes, and 1 - 4 major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale). These numbers include Hurricane Alex, which developed in January over the northeast Atlantic. If we take the midpoint of these ranges, NOAA is calling for 13 named storms, 6 hurricanes, and 2.5 major hurricanes. This is very close to the 1981-2010 seasonal averages of 12 named storms, 6 hurricanes, and 3 major hurricanes. NOAA/CPC forecaster Gerry Bell stressed: “This is a more challenging hurricane season outlook than most because it’s difficult to determine whether there will be reinforcing or competing climate influences on tropical storm development.” NOAA is projecting a 30 percent chance of an above-normal season and a 25 percent chance of a below-normal season.

One factor that looks increasingly likely to push the system toward a more active season is the likelihood of weak to moderate La Niña conditions by late summer. La Niña favors hurricane development in the Atlantic by reducing the amount of vertical wind shear that tends to prevail over the region. The latest monthly NOAA/IRI probabilistic outlook, issued May 19, calls for a 70-75% chance of La Niña conditions by late summer/early autumn. Several other forecasting groups are now predicting a considerably busier-than-usual season, as detailed below.



TSR predicts an above-average Atlantic hurricane season: 17 named storms
The May 27 forecast for the 2016 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) is calling for a total of 17 named storms, 9 hurricanes, 4 major hurricanes, and an Accumulated Cyclone Energy (ACE) of 130 for the period June through December. This is a major shift from TSR’s April 9 forecast, which called for a near-average season with 12 named storms, 6 hurricanes, 2 major hurricanes, and an ACE of 80. The changes are the result of a trend toward negative North Atlantic Oscillation (NAO) conditions, which favor warmer peak-season waters in the main development region of the tropical Atlantic, as well as the increasing likelihood of La Niña.

CSU predicts a near-average Atlantic hurricane season: 13 named storms
A near-average Atlantic hurricane season is likely in 2016, said the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 14. They called for an Atlantic hurricane season with 13 named storms, 6 hurricanes, 2 major hurricanes, and an Accumulated Cyclone Energy (ACE) of 93 (these numbers all take Alex into account.) The next CSU forecast is due on June 1, and will receive a lot of media attention--it will be their first seasonal hurricane forecast issued without Dr. Bill Gray's authorship, as he passed away last month. Our April 14, 2016 blog post has more on CSU's most recent forecast.

UKMET office predicts a slightly above-average Atlantic hurricane season: 14 named storms
The UKMET office forecast for the 2016 Atlantic hurricane season, issued May 12, calls for slightly above-normal activity, with 14 named storms, 6 - 10 hurricanes, and an ACE index of 125 occurring during the period June - November. In contrast to the statistical models relied upon by CSU, TSR, and (to a lesser extent NOAA), the UKMET forecast is done strictly using a dynamical global seasonal model, the Met Office GloSea5 system.

The Weather Company predicts a slightly above-average Atlantic hurricane season: 14 named storms
The April 27 forecast from The Weather Company is calling for a near-average Atlantic hurricane season with 14 named storms, 8 hurricanes, and 3 major hurricanes.

Penn State predicts an exceptionally above-average Atlantic hurricane season: 19 named storms
Here's a forecast worth paying attention to: the April 25 forecast made using a statistical model by Penn State's Michael Mann and alumnus Michael Kozar called for an extremely active Atlantic hurricane season with 19 named storms (expected range: 14 to 24). Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the NAO, and other factors. The statistical model assumed that in 2016 the late-April +0.88°C departure of temperature from average in the Main Development Region (MDR) for hurricanes in the tropical Atlantic would persist throughout hurricane season, a moderate La Niña would form this fall, and the NAO would be near average. If no La Niña forms, their model predicts reduced activity: 16 named storms.

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

2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12 named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
2012 prediction: 11 named storms, Actual: 19
2013 prediction: 16 named storms, Actual: 14
2014 prediction: 9 named storms, Actual: 8
2015 prediction: 7 named storms, Actual: 11

NCSU predicts an above-average Atlantic hurricane season: 15 - 18 named storms
The April 15 forecast from North Carolina State University (NCSU), called for an above-average Atlantic hurricane season with 15 - 18 named storms, 8 - 11 hurricanes, and 3 - 5 major hurricanes. They use a statistical model encompassing more than 100 years of past Atlantic hurricane activity to make their forecasts.

Coastal Carolina University predicts a near-average Atlantic hurricane season: 13 named storms
The May 7 forecast from Coastal Carolina University called for a near-average Atlantic hurricane season with 13 named storms, 7 hurricanes, and 3 major hurricanes.

Cuban Met service predicts a near-average Atlantic hurricane season: 12 named storms
The May 4 forecast from the Cuban Meteorological Service, INSMET, called for a near-average Atlantic hurricane season with 12 named storms and 7 hurricanes. The forecast is based on a statistical prediction model developed by Ballester, González and Pérez (2010).

Little change to 91L approaching the Southeast U.S. coast
There hasn't been a lot of change to the story of Invest 91L, which we detailed in a post put up at noon EDT on Friday. An Air Force hurricane hunter aircraft was in the storm Friday afternoon, and we'll wait to make a new post on 91L until the mission is complete.

Jeff Masters and Bob Henson

Hurricane

Tropical/Subtropical Depression Could Form Today in Northwest Atlantic

By: Jeff Masters and Bob Henson , 3:50 PM GMT on May 27, 2016

Formation of a tropical or subtropical depression appears imminent on Friday or Saturday in the waters between the Bahamas and Bermuda as Invest 91L moves west-northwest or northwest towards the Southeast U.S. coast. Should it become a named storm, it would be called Bonnie.

Satellite loops show that 91L has a pronounced spin near the surface that has improved in organization since Thursday--the circulation is less elongated, and more circular. However, there was only a modest amount of heavy thunderstorm activity that was not changing much in areal coverage associated with 91L on Friday morning. The latest pass from the ASCAT satellite showed an area of surface winds near 35 mph in the heaviest thunderstorms to the north of the center. Sea surface temperatures (SSTs) near 91L's center were about 26°C (79°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are only marginally warm enough to support formation of a tropical storm, and 91L has taken on some characteristics of subtropical system instead of a tropical system. As I explain in my Subtropical Storm Tutorial, a subtropical storm typically has a large, cloud free center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate, but tropical storms generate more rain.

Wind shear on Friday morning had fallen to the moderate range, 10 - 20 knots, increasing the odds of development. A large area of dry continental air lies to the west of 91L, and this dry air is interfering with development. A hurricane hunter aircraft is scheduled to investigate 91L on Friday afternoon.


Figure 1. Latest satellite image of 91L.


Figure 2. Predicted wind speeds for the Southeast U.S. at 2 am EDT (06Z) Sunday, May 29, 2016 from the 00Z Friday, May 27 runs of the European model (left) and GFS model (right). Both models had the storm just off the coast of South Carolina. Image constructed using our wundermap with the "Model Data" layer turned on.

A heavy rain threat for the Southeast U.S. coast
The 12Z (8 am EDT) Friday run of the SHIPS model predicted that wind shear would stay generally in the moderate range, 10 - 20 knots, for the next five days, which should allow some slow development of 91L. On Friday and Saturday, 91L will be traversing waters of 25 - 26°C (77 - 79°F), which should be just warm enough to allow development. The storm may get a small boost when it crosses the axis of the warm Gulf Stream current on Saturday afternoon. The system will have trouble with the large area of dry air to its west; if wind shear remains in the moderate range, 91L may have difficulty moistening its inner core enough to wall off this dry air. In their Friday morning (00Z) runs, our three top models for forecasting tropical cyclone genesis--the American GFS model, the European ECMWF model, and the British UKMET model--all showed the potential for Invest 91L to develop into a tropical or subtropical depression on Friday or Saturday. In a special Tropical Weather Outlook issued at 7:45 am EDT Friday, the National Hurricane Center bumped up their development odds in the 2-day and 5-day time ranges to 90%.

The models are not very gung-ho about intensifying 91L, and the system will have too little time over water to become anything stronger than a 55-mph tropical storm. Thus, heavy rain is the main concern from this system. Heavy rains should reach the coasts of South Carolina and southeastern North Carolina on Saturday afternoon or evening--though the heaviest rains from 91L will likely stay out sea to the storm's east, in a large band of heavy rain typical for a subtropical system. The Friday morning runs of our two top models for hurricane tracking, the GFS and European models, showed the center of 91L reaching the central coast of South Carolina near Charleston early Sunday morning or late Sunday afternoon, respectively. Steering currents will shift on Sunday evening, as 91L gets caught in the circulation associated with a trough of low pressure passing to the north, forcing 91L to turn to the northeast. The center of 91L will likely track inland along the coasts of South Carolina and North Carolina on Monday and Tuesday, spreading heavy rains of 2 - 4" along its path. It is uncertain at this time whether or not 91L will be able to spread heavy rains farther north into Virginia later in the week.

We'll have a post later today analyzing the annual NOAA seasonal hurricane forecast, which will be released late this morning.


Figure 3. A large area of rains exceeding 10” fell between Austin and Houston between 7:00 am CDT Thursday, May 26, and Friday, May 27, 2016. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service.

From tornadoes to torrents: Rain records inundated in Texas
A large chunk of the upper-level low that lingered over the western U.S. most of this week began pushing onto the Southern and Central Plains on Thursday, triggering widespread severe weather. As opposed to the isolated, tornado-generating supercells earlier in the week, Thursday’s severe storms were far more widespread, but competition between the many storms helped cut down the ability of any one cell to become a cyclic tornado-producer. NOAA/SPC logged a preliminary total of 19 tornado reports on Thursday in Texas, Oklahoma, Colorado, Kansas, and Missouri, with no serious injuries or major damage reported. The highest-impact scare was at Kansas City International Airport, where passengers were herded from the three main terminals into tunnels and parking garages during a 20-minute evacuation. Near Dodge City, KS—not far from where multiple tornadoes struck on Tuesday—hail as large as softballs pelted an area south and east of Clark State Lake on Thursday evening.

Rain-cooled air from the Central and Southern Plains finally pushed back an incredibly rich southerly feed of low-level moisture from the Gulf of Mexico that had fueled severe weather all week. Shunted into Texas, the moisture fed several mesoscale convective systems (MCSs) that produced torrential rain on Thursday afternoon into Friday morning, especially between the Austin and Houston areas. The town of Brenham racked up an amazing calendar-day total of 16.62”, obliterating its previous record of 10.38” from October 17, 1994. Most of that rain fell in a 12-hour period from noon to midnight. All by itself, Thursday’s total would rank as the fourth wettest month in Brenham’s history, and it is larger than May's monthly record of 15.09” from May 2015 (the wettest month by far in state history). Weather records in Brenham extend back to 1897. The heavy rains led to several high-water rescues in the Austin and Bryan areas, and two people were missing as of Friday morning, according to weather.com. Flash flood warnings continued through noon CDT Friday just east of Austin, where 6” to 10” of rain had reportedly fallen. More heavy rain is possible across southern Texas with additional MCS development later on Friday and Saturday.

Overall, the severe weather threat will continue dropping through the Memorial Day weekend, as both vertical wind shear and instability will be much less favorable for supercell formation. However, with a still-respectable amount of low-level moisture in place, there will be plenty of showers and thunderstorms across the central states, making for a damp-at-times Memorial Day weekend from Texas to Minnesota and Wisconsin. Long-range models suggest that heavy rain may recur through next week in some areas, Texas in particular.

Jeff Masters (tropical), Bob Henson (severe)


Figure 4. Projected 5-day rainfall totals from 12Z (8:00 am EDT) Friday, May 27, through 12Z Wednesday, June 1, 2016. Image credit: NOAA/NWS Weather Prediction Center

Hurricane Flood Severe Weather Extreme Weather

Tropical/Subtropical Depression Likely off SE US Coast; Tornadoes Still Raking Kansas

By: Jeff Masters and Bob Henson , 3:51 PM GMT on May 26, 2016

Showers and thunderstorms have increased and grown more organized in association with an area of low pressure that has formed between the Bahamas and Bermuda (Invest 91L.) This low appears increasingly likely to develop into a tropical or subtropical depression as it moves west-northwest or northwest towards the Southeast U.S. coast over the next few days. Should it become a named storm, it would be called Bonnie.

Satellite loops show that 91L has developed a pronounced spin near the surface, though no well-defined low-level circulation center was in evidence yet on Thursday morning. Sea surface temperatures (SSTs) near 91L's center were about 26 - 27°C (79 - 81°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are only marginally warm enough to support formation of a tropical storm, and 91L is likely to take on the characteristics of subtropical system instead of a tropical system. As I explain in my Subtropical Storm Tutorial, a subtropical storm typically has a large, cloud free center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate, but tropical storms generate more rain.

Wind shear on Thursday morning was high, 20 - 30 knots, making significant development unlikely until the shear drops on Friday. A large area of dry continental air lies to the west of 91L, and this dry air will interfere with development. A hurricane hunter aircraft is scheduled to investigate 91L on Friday afternoon.


Figure 1. Lastest satellite image of 91L.


Figure 2. Predicted wind speeds for the Southeast U.S. at 2 pm EDT (18Z) Monday, May 30, 2016 from the 00Z Thursday, May 26 run of the European model (left) and GFS model (right). The GFS model predicted 91L would be inland over the South Carolina coast, while the European model had the storm just off the southern coast of North Carolina. Image constructed using our wundermap with the "Model Data" layer turned on.

A heavy rain threat for the Southeast U.S. coast
The 12Z (8 am EDT) Thursday run of the SHIPS model predicted that wind shear would fall to the moderate range, 10 - 20 knots, on Friday, then fall to the low range, below 10 knots, Saturday through Sunday. During this period, 91L will be traversing waters of 25 - 26°C (77 - 79°F), which should be just warm enough to allow the storm to spin up into a tropical or subtropical depression. The system will have to contend with a large area of dry air to its west, but if wind shear falls to the low range, 91L should be able to moisten its inner core enough to wall off the dry air and spin up. In their Thursday morning (00Z) runs, our three top models for forecasting tropical cyclone genesis--the American GFS model, the European ECMWF model, and the British UKMET model--all showed the potential for Invest 91L to develop into a tropical or subtropical depression on Friday or Saturday. In a special Tropical Weather Outlook issued at 8:25 am EDT Thursday, the National Hurricane Center bumped up their development odds in the 2-day and 5-day time ranges to 50% and 70%, respectively.

Invest 91L likely will not have enough time over water to become a strong tropical storm or hurricane, so heavy rain is the main concern from this system. Heavy rains should reach the coasts of South Carolina and southeastern North Carolina on Saturday night or Sunday morning, though the I expect the heaviest rains from 91L will stay out sea to the storm's east, in a large band of heavy rain typical for a subtropical system. The Thursday morning runs of our two top models for hurricane tracking, the GFS and European models, showed the center of 91L reaching the central coast of South Carolina near Charleston on Sunday afternoon. Steering currents will then shift, as 91L gets caught in the circulation associated with a trough of low pressure passing to the north early next week, forcing 91L to turn to the northeast by Sunday night. The center of 91L will likely track just offshore or just inland along the coasts of South Carolina and North Carolina on Monday and Tuesday, spreading heavy rains of 2 - 4" along its path. Ocean temperatures will cool as 91L pushes into the coastal waters of North Carolina, which should induce weakening on Monday and Tuesday.


Figure 3. One moment from the journey of a long-lived tornado that churned across central Kansas on Wednesday evening, May 25, 2016. A low-level inflow band is visible wrapping into the tornado from the right-hand side. See related video embedded at bottom. Image credit: Sam Ng, Metropolitan State University of Denver, used with permission.

Another day, another prolific tornado-producer in Kansas
After Tuesday’s sequence of highly visible tornadoes from a single supercell thunderstorm near Dodge City, KS, the atmosphere dropped countless jaws again on Wednesday as an isolated supercell marched along Interstate 70 in central Kansas. As was the case on Tuesday, this storm formed beneath relatively weak upper-level flow near the intersection of a dry line and an outflow boundary from earlier storms. Towering to 70,000 feet at one point, this all-alone storm generated 12 of the 14 preliminary tornado reports on SPC’s daily storm log by early Thursday. As it paralleled I-70 for much of its life, eventually angling across the highway, this storm produced what veteran storm chaser and damage expert Tim Marshall, who has filmed more than 200 twisters, called “the longest-lasting tornado of my chase career.” Update: This twister, roughly a half a mile wide, was rated EF4 and lasted for 90 minutes, according to the damage survey released on Friday afternoon by the NWS office in Topeka, KS. It is very rare when an individual tornado is confirmed to last more than an hour.

Almost miraculously, the tornado avoided any direct hits on large communities. It barely missed the tiny town of Talmage and passed just south of Abilene and the smaller town of Chapman; the latter was largely destroyed by a direct hit from a half-mile-wide EF3 tornado on June 11, 2008. About 20 homes were damaged or destroyed, but no serious injuries had been reported as of early Thursday.


Figure 4. A cyclic supercell spins just north of Enterprise, KS, as a long-lived tornado approaches the end of its hour-plus life cycle. Image credit: Victor Gensini, College of DuPage, used with permission.


Figure 5. The difference three hours can make: a clump of towering cumulus over central Kansas at 2215Z (5:15 pm CDT) Wednesday, May 25, 2016, had become a long-lived, tornado-spewing behemoth by 0115Z (8:15 pm CDT), as shown in this sequence of GOES visible satellite images. Preliminary tornado reports from this storm spanned the interval from 6:08 pm to 10:31 pm CDT, though tornadoes were not on the ground during that entire time. Image credit: NOAA and College of DuPage/NexLab.


The intensity of this tornado-generating machine may have surprised storm watchers, given that the NOAA Storm Prediction Center had indicated only a slight risk of severe weather for central Kansas as of Wednesday morning (and an even lower marginal risk at one earlier point). This is a good time to reiterate a key aspect of SPC convective outlooks: the risk categories are designed to emphasize probability, not intensity. The late morning outlook (issued at 11:30 am CDT) featured a 2% chance of tornadoes occurring within 25 miles of any given point (or about 1964 square miles) over a broad swath from North Dakota to Texas. This swath covered about 187,000 square miles, so the 2% odds across the swath were certainly of the right order of magnitude next to the modest amount of land area actually hit by tornadoes on Wednesday--even though nearly all of those twisters ended up occurring from a single storm.


Figure 5. Severe-weather risk areas for Thursday, May 26, 2016, issued at 8:00 am CDT Thursday by the NOAA/NWS Storm Prediction Center, include an enhanced risk for much of northern Kansas, southern Nebraska, and far southwest Texas, and a slight risk encompassing most of the southern and central Great Plains.

A serious severe threat for Thursday, with more Kansas tornadoes possible
A potentially volatile situation is lining up for Thursday, as upper-level winds strengthen and surface low pressure intensifies across western Kansas. Outside of thunderstorm-cooled areas, the air mass flowing north from the Gulf of Mexico remains unusually sultry, with dew points in the low- to mid-70s close to record levels for late May across Oklahoma and south-central Kansas. Wind shear should increase notably on Thursday, and instability will remain at extreme levels. As of Thursday morning, NOAA/SPC had placed much of Kansas and Nebraska, plus parts of southwest Texas, in the “enhanced” category of storm risk for Thursday, with a much larger slight-risk area (see Figure 5). Assuming the air mass recovers as expected, the greatest risk for tornadoes may once again be somewhere in western or central Kansas, near the intensifying dry line and surface low and a warm front expected to stretch eastward from the low. With more substantial upper energy flowing across the area today as opposed to earlier this week, storms will develop sooner and be a bit faster-moving, and severe weather should be much more widespread overall. I would not be surprised to see the enhanced-risk area upgraded and/or expanded as the day unfolds. Update: At 11:30 am CDT, NOAA/SPC enlarged the enhanced-risk area along the dry line from central Kansas to far southwest Texas. A moderate-risk area (fourth highest out of the five SPC categories] was introduced in central KS, reflecting a heightened chance of significant tornadoes in that area.

A large chunk of the stubborn upper-level low parked across the western U.S. all week will swing into the central U.S. on Friday, shunting the greatest severe threat into Texas. At least modest odds of severe weather could emerge during the holiday weekend across the southern Great Plains, as the soon-to-be-diminished western trough regains a bit of its strength.

Jeff Masters (tropical), Bob Henson (severe)



Video 1. A view of the long-lived tornado with a low-level inflow band that started out in Bennington, KS. Video credit: Sam Ng (@DocWX, Metropolitan State University of Denver, used with permission.

Hurricane Severe Weather Tornado Extreme Weather

Odds of a Weekend Tropical Depression Rise; Dodge City Dodges Multiple Tornadoes

By: Jeff Masters and Bob Henson , 3:36 PM GMT on May 25, 2016

Showers and thunderstorms continue over portions of the Bahamas and nearby waters in association with an upper-level trough interacting with a weakening cold front. On Wednesday morning, NHC designated this area of interest as Invest 91L. This activity is expected to coalesce into an area of low pressure on Friday a few hundred miles north of the Bahama Islands. This low has the potential to develop into a tropical depression as it moves northwest towards the Southeast U.S. coast over the weekend. Sea surface temperatures (SSTs) over the Bahamas are about 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are plenty warm enough to support formation of a tropical storm. Phase space diagrams from Florida State University have been consistently showing over the past few days that this storm will be a symmetric warm core system--technical lingo for a storm that is tropical in nature, rather than subtropical or extratropical.


Figure 1. The area of disturbed weather near the Bahamas that we're tracking, as seen by MODIS on Tuesday afternoon, May 24, 2016.


Figure 2. Predicted wind speeds for the Southeast U.S. at 2 pm EDT (18Z) Monday, May 30, 2016 from the 00Z Wednesday, May 25 run of the European model (left) and the 06Z Wednesday May 25, 2016 run of the GFS model (right). Both 5-day forecasts were predicting a possible tropical depression off the Georgia/South Carolina coast. Image constructed using our wundermap with the "Model Data" layer turned on.

Increasing model agreement on genesis
In my 2013 blog post, Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?, I explained that we have three models that have proven to be fairly reliable for predicting the genesis of tropical depressions up to four days in advance: the American GFS model, the European ECMWF model, and the British UKMET model. About 50% of the time, at least one of these models will successfully predict tropical cyclone genesis up to four days in advance. When all three models agree on genesis, confidence increases in the forecast. On Tuesday, the UKMET model was not forecasting genesis, while the GFS and European models were. However, the Wednesday morning (00Z) runs of all three of these models showed the potential for Invest 91L to develop into a tropical depression a few hundred miles north of the Bahamas this weekend; this increases our confidence that genesis will occur. In a special Tropical Weather Outlook issued at 8:15 am EDT Wednesday, the National Hurricane Center bumped up their development odds in the 2-day and 5-day time ranges to 10% and 50%, respectively.

Invest 91L likely will not have enough time over water to become a strong tropical storm or hurricane, so heavy rain is the main concern from this system. The 00Z Wednesday runs of the models indicated a possible threat to the coasts of northern Florida, Georgia, or South Carolina early next week--though the European model showed the storm staying just off the coast through next Wednesday. I'll keep you updated each day this week with the latest prognosis for this potential early-season storm. Should it become a tropical storm, it would be named Bonnie.

Close call for Dodge City: A marathon tornado sequence narrowly misses town
Tuesday produced one of the biggest tornado outbreaks of 2016 thus far, with 30-plus twister reports logged by the NOAA/NWS Storm Prediction Center as of early Wednesday. A long-lived supercell dropped several tornadoes across northeast Colorado, and a brief twister damaged several structures near Bristow, Oklahoma. More than 5 inches of rain fell from Tuesday to Wednesday morning across parts of eastern Oklahoma (see embedded tweet at bottom), and flash flood warnings were in effect Wednesday morning over parts of northeast Oklahoma and far northwest Arkansas. One person drowned early Wednesday morning after a car was swept off a roadway in high water near Davenport, OK.


Figure 3. One of the series of tornadoes that moved through Ford County, KS, along a north-south line just west of Dodge City. Image credit: Bob Henson.

The tornadic storm of the day on Tuesday was a monster supercell that ground its way northward across the Dodge City, Kansas, area. The storm formed near the intersection of the Southern Plains dryline and an outflow boundary from Monday night storms that had pushed through most of Kansas. Winds north of the outflow boundary were from the southeast, which provided plenty of low-level spin for the storm to ingest, and very warm, humid air (temperatures well above 80°F and dew points in the upper 60s) led to extreme levels of instability. With upper-level winds relatively weak, the Dodge City storm hung close to the slow-moving boundary intersection or “triple point”, spitting out more than a dozen tornadoes of various shapes and sizes (cone, wedge, elephant trunk, rope, etc.) in the space of 90 minutes along the storm’s track of about 30 miles. Observers reported at least three instances of two simultaneous tornadoes from this storm’s mammoth wall cloud--a la the twin tornadoes of Pilger, Nebraska, from June 2014--and there was reportedly a brief third tornado at one point. The sequence may end up ranking among the most prolific in the annals of cyclic tornado production from a single storm. At least a dozen structures were damaged or destroyed along the storm’s path, including several on the western outskirts of Dodge City, but no serious injuries had been reported as of early Wednesday--a very fortunate outcome for Dodge City’s closest tornado call in many years. Near sunset, an impressive light and cloud show unfolded on the storm’s west side.


Figure 3. A spectacular display of anticrepuscular rays opposite the setting sun near Dodge City on May 24, 2016. Image credit: Bob Henson.


Figure 4. The departing storm filled the eastern sky over Dodge City with mammatus at sunset on May 24, 2016. Image credit: Bob Henson.


Figure 5. Severe weather outlook for Thursday, May 26, 2016, from NOAA's Storm Prediction Center (SPC). SPC is calling for an enhanced risk of severe weather (orange) across portions of Nebraska, Kansas, and Oklahoma. This Day 2 outlook will be updated around 1:30 pm EDT Wednesday.

The severe weather outlook for Wednesday and beyond
The active pattern across the Southern Plains will take a partial breather on Wednesday, as very warm mid-level air will help suppress thunderstorms for much of the day. A few scattered supercells may pop up by evening across SPC’s broad slight risk area, which extends from Texas to Minnesota. Pockets of weakness in the upper-level wind pattern will be generally unfavorable for tornadic storms, leaving large hail as the main threat toward the south and strong winds toward the north along a cold front. Activity should refocus along the dry line from Texas to Kansas on Thursday, when a stronger upper-level wave may trigger another round of multiple tornadic supercells. SPC has placed the region just east of the dryline under an enhanced risk of severe weather for Thursday. The stubborn upper-level trough that’s driven four consecutive days of tornado activity will languish across the western U.S. through Memorial Day weekend into next week, but it will gradually weaken as it does so. As a result, the intensity of the Great Plains severe weather looks likely to ramp down as next week unfolds, with plenty of thunderstorms popping over the Southern Plains but less of an overall tornado threat.

Jeff Masters (tropical), Bob Henson (severe)



Hurricane Tornado

A Memorial Day Weekend Tropical System For the Southeast U.S.?

By: Jeff Masters , 4:13 PM GMT on May 24, 2016

We're fast approaching the official June 1 start of the Atlantic hurricane season, and we already have an area of concern to watch for possible genesis of a tropical depression during the coming Memorial Day weekend. An area of low pressure is expected to form on Friday near to or a few hundred miles north of the Bahama Islands, and this low has the potential for tropical development as it moves northwest towards the Southeast U.S. coast. Sea Surface Temperatures (SSTs) over the Bahamas are about 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are plenty warm enough to support formation of a tropical storm. Phase space diagrams from Florida State University have been consistently showing that this storm will be a symmetric warm core system, which is technical lingo for a storm that is tropical in nature, rather than subtropical or extratropical.


Figure 1. Departure of Sea Surface Temperature (SST) from average for May 24, 2016. The Bahamas had SSTs that were 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. Image credit: tropicaltidbits.com.

Figure 2. Surface pressure (black contours) and 6-hour precipitation (in mm/hr) predicted for Saturday, May 28, 2016 at 2 am EDT (06Z) from the 8 am EDT (12Z) Tuesday, May 24 run of the GFS model. An area of low pressure with the potential to develop into a tropical depression was predicted to be near the coast of South Carolina. Image credit: tropicaltidbits.com.

What the models say: a heavy rain threat for the Southeast U.S. coast
In my 2013 blog post, Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?, I explained that we have three models that have proven to be fairly reliable for predicting the genesis of tropical depressions up to four days in advance: the American GFS model, the European ECMWF model, and the British UKMET model. Over the past two days, the GFS and European models have been showing the potential for a tropical depression to form near or to the north of the Bahamas; the UKMET model has merely shown a tropical disturbance forming. The models have widely differing ideas on how much wind shear might be present, so it is too early to say if this weekend's system is a legitimate threat to develop into a tropical depression. The main concern for this weekend's low will be heavy rain over the northwest Bahamas and the Southeast U.S. coast, as the storm likely will not have enough time over water to become a strong tropical storm or hurricane. The GFS model is indicating a possible threat to the coasts of northern Florida, Georgia, or South Carolina early next week, while the European model takes the low farther to the north, to the coast of South Carolina or North Carolina. I'll keep you updated each day this week with the latest prognosis for this potential early-season storm. Should the storm over-achieve and become a tropical storm, it would be named Bonnie.

Jeff Masters

Hurricane

A Week of Storminess on the Southern Plains Dryline

By: Bob Henson , 4:26 PM GMT on May 23, 2016

With climatology in the driver’s seat, a busy week of potentially tornadic weather will take shape from Nebraska to Texas. This prototypical late-May pattern is being driven by a very slow-moving upper low centered near Montana and an upper trough extending to California. Moderately strong southwest flow ahead of this trough will persist nearly all week across the Southern Plains--a recipe for tornadic trouble this time of year, given the presence of very warm, moist low-level air streaming north from the Gulf of Mexico. The veering and strengthening of winds with height will lead to the vertical wind shear that favors tornadic supercells. In general, this week’s wind shear will not be as strong as seen in the worst tornado outbreaks, but there will be pockets of localized enhancement. In places where these coincide with areas of extreme instability, we can expect supercells to spit out very large hail, high winds, and tornadoes in some cases.

The pattern emerging this week is familiar to severe storm watchers. The persistent southwest flow at upper levels will help to perpetuate a sharp dryline separating dry air from the Desert Southwest and the moist Gulf air mass. This time of year, the dryline often “sloshes,” pushing east during the heat of the afternoon and then retreating back west overnight. Each afternoon’s push can be enough to trigger scattered severe storms along the dry line, with the locations determined by small-scale features that can be hard to predict until just hours before storms begin to develop. Storms are likely to congeal each night into sprawling, slow-moving mesoscale convective systems (MCSs) that roll across parts of the Plains. Morning cloudiness from the MCSs, and the boundaries of rain-cooled outflow air, will play a huge role in dictating where the next day’s storms will focus. Forecasters at the NOAA/NWS Storm Prediction Center and at local NWS offices will have their hands full this week pinning down those mesoscale details and identifying the highest-threat areas. Mesoscale models that are now commonly updated every hour will help greatly; for example, mesoscale runs on Monday morning have zoomed in on northwest and west-central Texas and southwest Oklahoma as one of the primary threat areas for late Monday (see Figure 3).


Figure 1. WU’s severe weather map for Sunday night, May 22, severe thunderstorm watches (yellow) and tornado watches (red) were strung along a boundary all the way from the Saskatchewan border with North Dakota to the Texas border with Mexico.


Figure 2. This large tornado, photographed in low light 15 miles east of Stinnett, Texas, around 6:30 pm CDT on Sunday, May 22, 2016, was one of several spun up by a long-lived supercell thunderstorm in northeast Texas. No major damage was reported. Photo credit: © John Monteverdi, used with permission.

The north-south spread of the activity was vast on Sunday evening: tornado and severe thunderstorm watches extended all the way from the Canadian to the Mexican border (Figure 1), with severe weather reported in every state from North Dakota to Texas. SPC logged 37 preliminary tornado reports from South Dakota, Kansas, and Texas as of Monday morning (reduced to 28 reports by late Monday morning), and hail up to 3” in diameter fell from several storms in Texas and Kansas. Fortunately, the severe weather was focused on sparsely populated areas, and no major damage or serious injuries were reported.


Figure 3. Areas of showers and thunderstorms projected by the 14Z (9:00 am CDT) Monday run of the HRRR model for 7:00 pm CDT Monday, May 23, 2016. Storm locations predicted by mesoscale models such as HRRR will vary from run to run and model to model, so forecasters watch for consistent messages across models and across time. Image credit: www.tropicaltidbits.com.


Figure 4. WU depiction of NOAA/SPC convective outlook areas in effect on Monday morning, May 23, 2016, for (left to right) Monday, Tuesday, and Wednesday, May 23 – 25. Dark orange denotes an enhanced risk of severe weather; yellow, a slight risk; and dark green, a marginal risk. The Day 1 area is updated several times each day; the Day 2 area is updated around 1:30 pm EDT. Full-sized maps can be found on the WU convective outlook page.

The outlook for Monday and beyond
On Monday, the eastward advance of a cool front is teaming up with rain-cooled air to help tamp down the threat of severe weather from Kansas northward. The air mass should have little trouble recovering in Texas and Oklahoma, where Monday’s severe threat will be focused. As of mid-morning Monday, SPC had an enhanced risk of severe weather extending southwest Oklahoma to far southwest Texas (Figure 4), with a slight risk into northwest Oklahoma and only a marginal risk further north. The big picture changes little on Tuesday, although the odds of severe weather may improve across parts of northeast Colorado and southern Nebraska as upslope surface winds increase and moisture shifts west. It now appears that a large chunk of the upper trough will swing across the Southern Plains on Thursday, which would heighten the chance of more concentrated severe weather and shift it toward more populated parts of eastern Kansas, Oklahoma, and Texas.

Localized flooding and flash flooding may become an increasing issue as the week rolls on, especially as the north-south boundary pushes into richer moisture over the eastern Great Plains. A flood watch is in effect through Wednesday morning for parts of southwest Oklahoma and northwest Texas adjoining the Red River, where additional heavy rain on Monday and Tuesday night may fall atop already saturated soils and rain-swollen creeks.

Bob Henson


Figure 5. The 5-day precipitation forecast from NOAA’s Weather Prediction Center, spanning the period from 8:00 am EDT Monday, May 23, 2016 to 8:00 am Saturday, May 28.

Severe Weather

Arctic Sea Ice Goes Far Beyond Record Low Extent for May

By: Bob Henson , 4:01 PM GMT on May 20, 2016

The sea ice that coats the Arctic Ocean each winter and erodes each summer is going through its most depleted spring since modern observing began. The Danish Meteorological Institute reported the lowest sea ice extent of any April in the Arctic’s 38-year-long satellite record. As luck would have it, the primary satellite sensor used by the National Snow and Ice Data Center (NSIDC) for extent measurement began producing spurious data in April. A similar microwave imager from another satellite is now in the process of being intercalibrated to ensure consistency of the long-term record. Even with that caveat, it’s clear that the unusually rapid ice loss from April is steaming ahead. NSIDC’s Mark Serreze confirmed in an email that the 2016 Arctic sea ice extent is indeed at record-low levels for May, as implied by Figures 1 and 2. Different agencies use different algorithms to measure sea ice extent, but the slight variations that result do not affect the big picture.


Figure 1. Extent of Arctic sea ice for each year since 1979. The 2016 values in recent weeks through May 18 are shown as a dashed red line, denoting the provisional state of the data for the last few weeks. NSIDC cautions that “quantitative comparisons with other data should not be done at this time.” Image credit: NSIDC Charctic Interactive Sea Ice Graph.


Figure 2. Arctic sea ice extent for the past five years as tracked by the Danish Meteorological Institute. The 1979-2000 average is depicted as a gray line; the gray shading denotes one standard deviation from that average. Image credit: Danish Meteorological Institute.

This year’s hasty ice retreat has been fueled by incredibly mild temperatures across the Arctic during much of the winter and spring--a byproduct of El Niño atop longer-term warming from human-produced greenhouse gases. At Barrow, Alaska, every day since January 1 has been above average except for January 22, February 6, and a stretch from March 28 to April 3. Alaska’s Climate Division 1, which covers the North Slope, is having its warmest year to date by far (see Figure 3), with the January-to-April average of 2.7°F beating the previous record (–1.4°F, from 2014) by an eye-popping 4.1°F. Another red-letter data point: snow cover disappeared from the open tundra at the NOAA Barrow Observatory on May 13. Assuming that no snow cover returns this spring--an increasingly good bet--this is the earliest melt-out date by far in 74 years of recordkeeping at the Barrow lab, beating out May 24, 2002. Conditions have also been exceptionally mild on the other side of the Arctic. The town of Longyearbyen in Svalbard, Norway--the northermost civilian community on the planet--has had only one below-average day in 2016 thus far (see Figure 4).


Figure 3. Average January-through-April temperatures from 1925 to 2016 for Alaska’s Climate Division 1, covering the North Slope (which includes the Arctic Ocean coastline). Image credit: NOAA/NCEI.


Figure 4. Daily temperatures (red and blue traces) from April 2015 to April 2016 for Svalbard Airport, Norway. The black line shows normal (average) temperatures for each day. The smoothed average for Svalbard has been above normal for the entire 12-month period. Only one day in 2016 has fallen below average (denoted when the midpoint of a temperature bar for a given day is located below the solid black line]. Image credit: Norwegian Meteorological Institute.

Mild readings still on tap across the Arctic
Recent runs of the ECMWF and GFS models maintain high pressure over the central and western Arctic for the next 1 to 2 weeks. This implies plenty of sunlight over large parts of the ice pack, which will facilitate ice loss. The 00Z Friday run of the GFS model keeps warmer-than-average surface temperatures across the entire Arctic Ocean throughout the extended range. At times, the warmth will extend across large parts of boreal Siberia, Alaska, and Canada, which will keep land-based snow melting quickly. Northern rivers are already feeding large volumes of relatively mild water into the Arctic ahead of usual. April’s snow cover extent across the Northern Hemisphere was the lowest in 50 years of recordkeeping, according to the Rutgers University Global Snow Lab.

Another downside of premature snow cover loss is the potential for early-season wildfire across the far north. A prime example is Canada’s disastrous Fort McMurray fire, which exploded in early May as record heat swept over a snowless landscape. Although the fire still surrounds the city, some 85 to 90 percent of Fort McMurray’s structures were saved, and residents may be able to return beginning in early June. Media interest in the event has waned in recent days, but the fire continues to rage, with a new burst of growth this week. On Thursday, the fire covered some 1.2 million acres--twice the size of Rhode Island--and was beginning to extend into Saskatchewan. As noted by blogger Robert Scribbler, this fire already has spanned more area than all of Alberta’s fires in 2015 combined. Soot from the Fort McMurray fire, and from major wildfires burning across parts of Siberia, could exacerbate the loss of sea ice by falling atop the ice and darkening the surface, thus increasing its ability to absorb sunlight.


Figure 5. A group trying to rescue animals from Fort McMurray wait at road block on Highway 63 near as smoke rises from a forest fire near Fort McMurray, Alberta on May 6, 2016. Canadian police led convoys of cars through the burning ghost town of Fort McMurray Friday in a risky operation to get people to safety far to the south. Image credit: Cole Burston/AFP/Getty Images.


Figure 6. Satellite imagery showing the extent of sea ice on September 11, 2015, the date of the year’s minimum extent. The minimum of 4.41 million square kilometers was about 700,000 sq km below the 1981-2010 average, shown here as a gold line. Image credit: NASA Goddard Scientific Visualization Studio.

Record low sea ice extent this summer? Too soon to tell
Strange as it seems, there is no guarantee that this spring’s headlong melt will lead to the lowest Arctic sea ice minimum extent on record. Even with the unprecedented head start, more than two-thirds of the melting in a typical year has yet to occur. The final outcome of the melt season will hinge largely on the weather and the circulation patterns that unfold over the next three months or so--especially the amount of sunshine in June and July and the presence of winds and ocean currents that can shove thick, older ice toward lower latitudes. In 2012, the ice extent was just slightly below average in early June, but rapid melt later that month helped push the ice extent to its lowest value on record: 3.41 million square kilometers.

Some of the world’s top sea ice watchers will soon be putting their skills to work predicting the outcome of this year’s summer melt. A community forecasting project that began in 2008 has been operating as the Sea Ice Prediction Network since 2013. Each year SIPN compiles and releases outlooks from all interested parties who dare to predict the dates of ice-free conditions. Last year’s three monthly outlooks, issued in June, July, and August, included a total of 105 submissions employing various types of prediction (e.g., statistical techniques and modeling-based approaches). The forecasts issued in August 2015 spanned a vast range, from 0.98 to 5.6 sq km. The average of the August predictions--4.8 million sq km--was closer to the mark, but it still came in higher than the observed minimum of 4.41 sq km observed on September 11.

Sea ice prediction remains an embryonic science, and the SIPN website is an excellent place to follow that science as it evolves in real time. SIPN will be soliciting contributions several weeks ahead of its June, July, and August reports; here’s a tentative schedule.

Have a great weekend, everyone!

Bob Henson

Extreme Weather Arctic Sea Ice

April 2016: Earth's 12th Consecutive Warmest Month on Record

By: Jeff Masters and Bob Henson , 9:42 PM GMT on May 18, 2016

Keeping a year-long string of record-warm months going, April 2016 was by far the planet's warmest April since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Wednesday. In the NOAA database, April 2016 came in a full 1.10°C (1.98°F) warmer than the 20th-century average for April of 13.7°C (56.7°F), as well as 0.28°C (0.50°F) above the previous record for April, set in 2010. This is a huge margin for breaking a monthly global temperature record, as they are typically broken by just a few hundredths of a degree. The only months with larger warm departures from average were March and February 2016 and December 2015. NASA also reported the warmest April in its database (1.11°C above the 1951-1980 average), and the margin it broke the previous record by--0.24°C--was the largest margin ever recorded to break the April record by. The seven warmest months in NASA's database, relative to average, have been the past seven months (with data going back to 1880); these are the only months in the database with readings of at least 1.0°C above average.

April 2016 marked the twelfth consecutive month that the monthly temperature record was broken and the seventeenth consecutive month (since December 2014) that the monthly global temperature ranked among the three warmest for its respective month in the NOAA database. Both global ocean and global land temperatures were the warmest on record for any April. Global satellite-measured temperatures in April 2016 for the lowest 8 km of the atmosphere were the 2nd warmest for any April in the 38-year record, and the fourth-largest warm departure from average for any month, according to the University of Alabama in Huntsville (UAH). This breaks a string of six consecutive months the UAH database had registered a record monthly high.

The impressive global warmth in recent months is due to the steady build-up of heat-trapping greenhouse gases due to human activities, plus a spike due to a large amount of heat being released from waters in the Eastern Pacific due to the powerful 2015-16 El Niño event. This event peaked in December, but the warmest atmospheric readings (relative to average) usually lag the peak oceanic temperatures by a few months. NOAA’s global surface temperature for the year so far (January-April 2016) is an astounding 0.30°C (0.54°F) warmer than the previous record, set in 2015 (see Figure 2).


Figure 1. Departure of temperature from average for April 2016, the warmest April for the globe since record keeping began in 1880. Record warmth was observed over several land areas on Earth as well as most of the Indian Ocean, with especially warm readings over northern South America, northeast Africa, southeast Europe, southeast Asia, northern Australia, southern Greenland, and southern Alaska. Image credit: National Centers for Environmental Information (NCEI).


Figure 2. Departure from average for the global January-through-April temperature for the years 1880 - 2016. This year has seen by far the warmest temperatures on record for each of the four months. Image credit: NOAA/National Centers for Environmental Information (NCEI).

Will 2016 set another record high?
It’s increasingly probable that 2016 will eclipse 2015 as the warmest year in global temperature records that go back to 1880. When major El Niño events straddle two calendar years, the second year is often the warmer one globally, as there is a lag of several months between the peak oceanic and atmospheric warming. Here’s one way to look at the question: how cool would the rest of 2016 need to be to prevent an annual record? Let’s assume that a good analog for this year is 1998, when a very strong El Niño waned quickly in northern spring and was succeeded by a moderately strong La Niña by year’s end. That year, the departure in average global temperature was 0.71°C for January through April, and it dropped to 0.59°C for May through December. If we were to experience a similar drop in global temperature later this year—which is possible if we transitioned to a moderate La Niña, as predicted by several models—then the departure from average for the last eight months of the year could be in the neighborhood of 1.02°C. In that case, 2016 will still cruise handily to the title of warmest year on record. The drop from Jan-Apr to May-Dec would need to be twice as large this year as it was in 1998 in order to put this year’s annual average below that of 2015. Small wonder, then, that NASA/GISS director Gavin Schmidt has laid 99% odds on this year becoming the warmest in global records.


Figure 3. Global temperature in the year 2016 has left all recent years in the dust for the period January through April. Image credit: Climate Central.

El Niño on its way out
El Niño conditions weakened to the "moderate" classification during April 2016, and El Niño continues to weaken rapidly. The event peaked in strength in late November 2015, when the weekly sea surface temperatures (SSTs) in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W) peaked at a record 3.1°C above normal. By the week of May 16, 2016, the Niño3.4 SST anomaly had fallen to 0.6°C above average--barely above the 0.5°C threshold to be considered an El Niño. NOAA expects a transition to neutral conditions during early summer 2016, with a 65% chance of a transition to La Niña conditions by the August-September-October peak of the Atlantic hurricane season.

Arctic sea ice at its lowest April extent on record—and still plummeting
A key U.S. satellite sensor used to monitor sea ice extent failed in early April, and the National Snow and Ice Data Center (NSIDC) was unable to provide an estimate of the April sea ice extent in the Arctic. However, satellite data from the Danish Meteorological Institute, using a different instrument, showed that last month’s sea ice extent in the Arctic was the lowest for April across the 38-year satellite record. The unprecedented mid-spring melt is barreling ahead this month. Provisional data for early May from a replacement sensor now being calibrated by NSIDC closely resembles the data shown below in Figure 4, as well as analyses from the Japan Aerospace Exploration Agency (JAXA). “We are at a record low for this time of year,” confirmed Mark Serreze (NSIDC) in an email. We will have much more on this spring’s Arctic ice loss in an upcoming post.


Figure 4. Arctic sea ice extent through May 16, 2016. Arctic sea ice has been at record low levels from early April through mid-May 2016. Image Credit: Danish Meteorological Institute.

Three billion-dollar weather disasters in April 2016
According to the April 2016 Catastrophe Report from insurance broker Aon Benfield, three billion-dollar weather-related disasters hit the planet in April--two severe weather outbreaks in the U.S., and a flood disaster in South America. In addition, two other disasters from earlier in the year (Tropical Cyclone Winston in Fiji and a March 22-25 severe weather outbreak in the U.S.) accumulated enough damage claims to be rated billion-dollar disasters by the end of April. Between January - April 2016, there were twelve billion-dollar weather disasters. This is well ahead of pace of nine such disasters in January - April 2013--the year that ended up with the most billion-dollar weather disasters on record: 41. Last year had only five billion-dollar weather disasters through April. Here is the tally of billion-dollar weather disasters for January - April 2016:

1) Drought, Vietnam, 1/1 - 5/1, $6.7 billion, 0 killed
2) Severe Weather, Plains-Southeast U.S., 4/10 - 4/13, $2.75 billion, 1 killed
3) Winter Weather, Eastern U.S., 1/21 - 1/24, $2.0 billion, 58 killed
4) Winter Weather, East Asia, 1/20 - 1/26, $2.0 billion, 116 killed
5) Severe Weather, Rockies-Plains-Southeast-Midwest U.S., 3/22 - 3/25, $1.75 billion, 0 killed
6) Drought, Zimbabwe, 1/1 - 3/1, $1.6 billion, 0 killed
7) Flooding, Argentina and Uruguay, 4/4 - 4/10, $1.3 billion, 0 killed
8) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 3/4 - 3/12, $1.25 billion, 6 killed
9) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 2/22 - 2/25, $1.2 billion, 10 killed
10) Severe Weather, Plains-Rockies U.S., 4/15 - 4/19, $1.0 billion, 9 killed
11) Severe Weather, U.S., 3/17 - 3/18, $1.0 billion, 0 killed
12) Tropical Cyclone Winston, Fiji, 2/16 - 2/22, $1.0 billion, 44 killed

And here are the three disasters from April 2016:


Disaster 1. Heavy rains caused extensive flash flooding across parts of Texas on April 18, killing eight and leading to more than 1,800 water rescues in the greater Houston metropolitan area. The same storm also brought heavy snow and severe thunderstorms from April 15 - 19 to parts of the Rockies and Plains, killing one person. Damage was estimated at $1.0 billion. In this image, we see Kaicee Crowley walking through floodwaters to get belongings out of her stranded car at the North Main Street exit off I-45 in Houston on April 18, 2016, as White Oak Bayou came over its banks and floods the freeway. Image credit: Karen Warren/Houston Chronicle via AP.


Disaster 2. Severe thunderstorms caused catastrophic hail damage across parts of the Plains and Southeast from April 10 - 13, killing at least one person and injuring dozens more. The Dallas-Fort Worth and San Antonio metro regions in Texas were the hardest hit, where softball- and baseball-sized hail fell. Damage was estimated at $2.75 billion. In this photo, we see an impressive shelf cloud from a thunderstorm over Royce City, Texas, on April 11, 2016. Image credit: wunderphotographer Gweduc.


Disaster 3. Torrential rains led to severe flooding across portions of Argentina and Uruguay from April 4 - 10. No serious injuries or fatalities were reported. Hardest hit was northeast Argentina, where seven-day rainfall totals tallied as much as 750 millimeters (29.53 inches] in parts of the provincial regions of Entre Rios, Corrientes, Santa Fe, Chaco, Formosa, and Santiago del Estero. More than 15,000 people were affected, with most of the damage occurring along the overflowing Paraná and Salado rivers. Substantial damage occurred to 4 percent of the country’s soybean crop. Total economic losses to agriculture in Argentina alone were estimated at $1.3 billion. In this image, we see flooding in Villa Paranacito, Entre Rios, Argentina, on April 28, 2016. (AP Photo/Natacha Pisarenko)

Notable global heat and cold marks set for April 2016
Hottest temperature in the Northern Hemisphere: 48.5°C (119.3°F) at Titlagarh, India, 24 April
Coldest temperature in the Northern Hemisphere: -46.2°C (-51.2°F) at Geo Summit, Greenland, 7 April
Hottest temperature in the Southern Hemisphere: 43.2°C (109.8°F) at Onslow Airport, Australia, 2 April
Coldest temperature in the Southern Hemisphere: -79.1°C (-110.4°F) at Concordia, Antarctica, 24 April
(Courtesy of Maximiliano Herrera.)

Major weather stations that set (not tied) new all-time heat or cold records in April 2016
Record heat waves in Southeast Asia and Africa caused a remarkable five nations to set all-time heat records in April 2016 (see below). The excessive heat gives us an uncommonly long list of all-time local heat records in more than a dozen nations to report:

Keningau (Malaysia) max. 37.3°C, 7 April
Batu Embun (Malaysia) max. 38.6°C, 9 April; followed by 39.2°C on 10 April
Bua Chum (Thailand) max. 43.2°C, 10 April
Surin (Thailand) max. 42.2°C, 10 April; followed by 42.8°C on 11 April; followed by 42.9°C on 12 April; followed by 43.1°C on 17 April
Chok Chai (Thailand) max. 41.3°C, 10 April; followed by 42.5°C on 11 April
Tak Fa (Thailand) max. 41.6°C, 10 April; followed by 41.7°C on 22 April
Nang Rong (Thailand) max. 41.9°C, 10 April; followed by 42.8°C on 11 April; followed by 43.0°C on 12 April
Banteay Ampil (Cambodia) max. 42.2°C, 11 April: New national record high for Cambodia
Saravanh (Laos) max. 41.2°C, 11 April; followed by 41.5°C on 16 April
Nakhon Ratchasima (Thailand) max. 43.2°C, 11 April
Tha Phra (Thailand) max. 42.7°C, 11 April
Kosumphisai (Thailand) max. 42.5°C, 11 April
Ubon Ratchathani (Thailand) max. 42.5°C, 11 April; followed by 42.6°C on 15 April
Roi Et (Thailand) max. 42.3°C, 11 April
Aranyaphrathet (Thailand) max. 42.2°C, 11 April
Nan (Thailand) max. 42.2°C, 11 April; followed by 42.4°C on 12 April; followed by 43.3°C on 14 April
Nong Phlub (Thailand) max. 42.0°C, 11 April
Chainat (Thailand) max. 41.8°C, 11 April
Surat Thani (Thailand) max. 41.3°C, 11 April
Kho Hong (Thailand) max. 39.9°C, 11 April
Hat Yai (Thailand) max. 39.3°C, 11 April; followed by 39.7°C on 28 April
Koh Samui (Thailand) max. 38.0°C, 11 April
Pattani (Thailand) max. 38.3°C, 12 April; followed by 38.5°C on 19 April; followed by 38.7°C on 21 April
Lom Sak (Thailand) max. 41.9°C, 12 April; followed by 42.0°C on 18 April
Sakon Nakhon (Thailand) max. 42.5°C, 12 April
Nakhon Sawan (Thailand) max. 43.2°C, 12 April; followed by 43.4°C on 19 April
Seno (Laos) max. 42.3°C, 12 April: New national record high for Laos
Long Island (India) max. 37.6°C, 12 April
Sagaing (Myanmar) max. 43.8°C, 12 April
Phonm Penh (Cambodia) max. 41.0°C, 13 April
Temerloh (Malaysia) max. 38.8°C, 13 April
Dori (Burkina Faso) max. 47.5°C, 13 April: New national record high for Burkina Faso
Dedougou (Burkina Faso) max. 45.2°C, 13 April
Boromo (Burkina Faso) max. 44.2°C, 13 April
Tillabery (Niger) max. 47.0°C, 13 April
Bougouni (Mali) max. 44.0°C, 13 April
Banjul (Gambia) max. 44.4°C, 14 April
Mersing (Malaysia) max. 37.4°C, 14 April
Malaybalay (Philippines) max. 36.4°C, 15 April
Kozhikode (India) max. 39.1°C, 15 April; followed by 39.2°C on 30 April
Preah Vihea (Cambodia) max. 42.6°C, 15 April: New national record high for Cambodia
Attapeu (Laos) max. 42.0°C, 15 April
Houei Sai (Laos) max. 40.8°C, 15 April; followed by 41.0°C on 28 April
General Santos (Philippines) max. 39.4°C, 16 April
Hanimaadhoo (Maldives) max. 34.9°C, 16 April: New national record high for the Maldives; followed by 35.0°C on 30 April
Walvis Bay Airport (Namibia) max. 42.8°C, 16 April
Danxian (China) max. 40.4°C, 17 April
Changjiang (China) max. 40.5°C, 17 April
Satun (Thailand) max. 39.6°C, 20 April
Kottayam (India) max. 39.9°C, 20 April
Car Nicobar (India) max. 35.4°C, 22 April
Bengaluru (India) max. 39.2°C, 24 April
Mysore (India) max. 39.9°C, 24 April
Palakkad (India) max. 41.9°C, 26 April
Phetchabun (Thailand) max. 43.3°C, 26 April
Bhumibol Dam (Thailand) max. 43.9°C, 27 April
Sayabouri (Laos) max. 40.8°C, 27 April
Cannur (India) max. 39.2°C, 27 April
Jaffna (Sri Lanka) max. 37.0°C, 27 April
Mae Hong Son (Thailand) max. 44.6°C, 28 April: New national record high for Thailand
Yalla (Thailand) max. 40.1°C, 28 April
Magwe (Myanmar) max. 46.5°C, 29 April
Yamethin (Myanmar) max. 45.0°C, 29 April
Thayawady (Myanmar) max. 43.9°C, 29 April
Loikaw (Myanmar) max. 39.5°C, 29 April

(Courtesy of Maximiliano Herrera.)

Five all-time national heat records set in April 2016
From January through May 16, 2016, a total of nine nations or territories tied or set all-time records for their hottest temperature in recorded history--which is a huge number of records for so early in the year. One all-time cold temperature record has been set so far in 2016 (in Hong Kong.) "All-time" record here refers to the warmest or coldest temperature ever reliably reported in a nation or territory. The period of record varies from country to country and station to station, but it is typically a few decades to a century or more. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. Our data source is international weather records researcher 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. Here are 2016's all-time heat and cold records as of May 16:

Maldives set its all-time hottest record on April 30, 2016, when the mercury hit 35.0°C (94.8°F) at Hanimaadhoo.

Thailand set its all-time hottest record on April 28, 2016, when the mercury hit 44.6°C (112.3°F) at Mae Hong Son.

Cambodia set its all-time hottest record on April 15, 2016, when the mercury hit 42.6°C (108.7°F) at Preah Vihea.

Burkina Faso set its all-time hottest record on April 13, 2016, when the mercury hit 47.5°C (117.5°F) at Dori.

Laos set its all-time hottest record on April 12, 2016, when the mercury hit 42.3°C (108.1°F) at Seno.

Vanuatu in the South Pacific set its all-time hottest record on February 8, 2016, when the mercury hit 36.2°C (97.2°F) at Lamap Malekula.

Tonga set its all-time hottest record on February 1, 2016, when the mercury hit 35.5°C (95.9°F) at Niuafoou.

Wallis and Futuna Territory (France) set a new territorial heat record with 35.8°C (96.4°F) on January 10, 2016 at Futuna Airport. This is the second year in a row that Wallis and Futuna has beaten its all-time heat mark; the previous record was a 35.5°C (95.9°F) reading on January 19, 2015 at the Futuna Airport.

Botswana set its all-time hottest record on January 7, 2016, when the mercury hit 43.8°C (110.8°F) at Maun.

Hong Kong Territory (China) set its all-time coldest mark on January 24, 2016, when the mercury dipped to -6.0°C (21.2°F) at Tai Mo Shan.

Heat records continue to tumble across India
Wednesday, May 18, brought the hottest reliably measured temperature on record for a populated location in India, as Phalodi soared to 50.5°C (122.9°F). The hottest temperature in India’s history as recognized by the India Meteorological Department is just 0.1°C warmer: 50.6°C (123.1°F) at Alwar, Rajasthan, on May 10, 1956. There was also a 50.6°C (123.1°F) measurement taken at Pachpadra (an uninhabited saline depression) on May 25, 1886. According to Herrera, the Pachpadra reading in 1886 is not that reliable, because the screen used on the instrument shelter was of questionable quality. He also believes that the official record at Alwar is junk—that record was set during what was not an exceptional heat wave, just a few months after the station was installed. Temperatures were constantly overestimated by 5 - 6°C during the first few years of operation of the station, after which it was probably fixed, since its temperatures fell in line with neighboring stations.
Update: On Thursday, May 19, Phalodi reached a high of 51.0°C (123.8°F]--a clear record for the highest temperature ever observed in India.

Jeff Masters and Bob Henson

Climate Summaries

Deadly Rains From Tropical Cyclone One Kill 34 in Sri Lanka, Leave 134 Missing

By: Jeff Masters , 3:28 PM GMT on May 18, 2016

One of the deadliest weather-related disaster of 2016 is unfolding in Sri Lanka, where heavy rains from Tropical Cyclone One have triggered flash floods and landslides that have killed at least 34 people and left 134 missing. The rains began on Monday, when an area of low pressure that formed on the leading edge of the advancing monsoon began to consolidate just to the southeast of Sri Lanka. Hours of torrential rains triggered massive mudslides Tuesday evening that buried homes and people in the villages of Siripura, Pallebage and Elagipitya in Kegalle District, about 45 miles north of the capital of Colombo. The Sri Lankan Red Cross said 220 families were reported missing on Wednesday, but that the situation was unclear.

According to the April 2016 Catastrophe Report from insurance broker Aon Benfield, four weather-related disasters so far in 2016 have killed over 100 people:

1) Heat wave in India, 4/1 - 4/30, 300 deaths
2) Flooding in Pakistan and Afghanistan, 4/2 - 4/8, 152 deaths
3) Flooding in Pakistan, 3/9 - 3/29, 141 deaths
4) Winter Weather in China, Taiwan, Korea, Japan and Thailand, 1/20 - 1/26, 116 deaths


Figure 1. Sri Lankan military personnel take part in relief and rescue efforts following a landslide in the village of Bulathkohupitiya on May 18, 2016. (STR/AFP/Getty Images)


Figure 2. Radar image of Tropical Cyclone One from Chennai, India at 02:20 UTC Wednesday, May 18, 2016. Heavy rains from the storm were affecting the Bay of Bengal coast of India.

Forecast for Tropical Cyclone One
Tropical Cyclone One had top sustained winds of 45 mph at 8 am EDT Wednesday, according to the Joint Typhoon Warning Center (JTWC). The India Meteorological Department (IMD) gave the system top winds of 35 mph (but IMD uses 3-minute average winds for tropical cyclones instead of the 1-minute averaging time used by the U.S., resulting in winds that will be perhaps five percent lower than JTWC's.) Radar images from Chennai, India on Wednesday showed the storm was not well-organized, but was bringing heavy rains to the east coast of India. Moderate wind shear near 20 knots and warm ocean temperatures near 30 - 31 C (86 - 88°F) should allow some modest intensification through Thursday. By Thursday evening, the storm will be passing over an ocean eddy with low total heat content and unusually cool water, which should discourage development. At that time, the storm will also be getting embedded in a trough of low pressure with high wind shear, which should cause weakening. Relatively cool waters with low total heat content also lie in the the extreme northern portion of the Bay of Bengal, so the storm will likely continue to weaken as it approaches landfall in the northern Bay of Bengal on Saturday. The Wednesday morning run of the HWRF model goes along with this idea, showing little change in strength for the storm on Friday and Saturday, with TC One making landfall on Saturday as a tropical storm.

The global weather summary for April 2016 will be posted later today.

Jeff Masters

Flood Hurricane

An Oklahoma Tornado Rewrites the Rule Book

By: Bob Henson , 5:17 PM GMT on May 16, 2016

Overshadowed by the mighty EF4 and EF3 tornadoes that tore across south-central Oklahoma last Monday, May 9, another less damaging twister--from the same thunderstorm--has left seasoned scientists both astonished and fascinated. This tornado, which struck near Roff, OK, was rated an unexceptional EF1 on the Enhanced Fujita Tornado Damage Scale. However, the Roff tornado stands out in several other ways.

—It was an anticyclonic tornado, meaning that it rotated clockwise rather than counterclockwise. A few such twisters probably occur each year, but they account for only perhaps 1% of all U.S. tornadoes—and that’s a very rough estimate, according to tornado climatology expert Harold Brooks (NOAA National Severe Storms Laboratory). In fact, the Storm Data procedures maintained by NOAA include no specific requirement or methodology for reporting whether or not a tornado is anticyclonic.

—It developed in the “forward flank” part of the storm, enveloped in rain-cooled air. “This is the first time I’ve ever heard of a well-developed anticyclonic tornado buried inside the forward-flank core,” said Roger Edwards (NOAA Storm Prediction Center), who has predicted and observed tornadoes for more than 25 years.

—Its damage path was initially estimated to be as much as 13 miles long, as documented in a preliminary storm survey conducted by the National Weather Service in Norman, OK. If confirmed, this path length will likely be a record; I have been unable to find evidence of any other anticyclonic tornado with a path this long. The estimated duration of 35 minutes might also end up as a record-setter for anticyclonic tornadoes. However, reanalysis of the damage could reduce the estimated path length and duration, as the radar signature of the tornado was shorter-lived, according to Gabriel Garfield (University of Oklahoma/CIMMS/NWS), who participated in the storm survey.


Figure 1. An example of the relatively light damage inflicted by the anticyclonic tornado near Roff, OK, on May 9, 2016. Photo credit: Courtesy Gabriel Garfield, OU/CIMMS/NWS.


Figure 2. Doppler radar image of the supercell thunderstorm that contained a large EF3 cyclonic tornado (the Sulphur tornado) and a weaker EF1 anticyclonic tornado (the Roff tornado). The reflectivity image (top, with reds indicating heavy precipitation) shows the classic hook echo in connection with the EF3 tornado (labeled in the velocity image at bottom). The anticyclonic tornado (labeled in the bottom image) is firmly embedded in the heavy rain core along the storm’s forward flank, as shown in the top image. Image credit: Courtesy Roger Edwards and his Weather or Not blog.


The scarcity of anticyclonic tornadoes is not a direct result of the Coriolis effect, which makes tropical cyclones spin cyclonically. The Coriolis force actually has little direct influence on circulations as small as tornadoes (not to mention toilets or other drains that happen to cross the equator). What appears to be the main driver is the wind shear that produces rotating supercell thunderstorms. In the Northern Hemisphere, a blossoming supercell will often split in two, with one cell angling to the right of the mean upper-level wind, spinning cyclonically, and the other angling leftward and rotating anticyclonically. Rightward-moving, cyclonically-spinning cells are the ones better positioned to ingest warm, moist air and grow more vigorously. Thus, most tornadoes are cyclonic, spawned by mesocyclones within cyclonically rotating supercells. (This Wikipedia page includes a nice conceptual diagram of a supercell thunderstorm.) Toward the outer edge of a storm’s rear-flank gust front, there can be anticyclonically rotating features; very rarely, one of these will spin up an anticyclonic twister.

What happened in Oklahoma last week doesn’t quite fit the classic picture: the anticyclonic Roff tornado developed right in the rain-cooled heart of the storm rather than on its periphery. The Roff tornado was embedded in rain for most or all of its lifespan. “We saw no evidence of it in the gray murk of heavy rain to our [west], nor any suspicious wind shifts,” reported Edwards, who was on the same storm photographing the nearby Sulphur tornado. As for what caused the anticyclonic Roff tornado, “we can offer only speculation and conjecture at this point,” said Edwards in a blog post. The smoking gun could end up being a stray left-moving storm, evident on radar, that zipped northward and became embedded in the larger, stronger supercell that produced the Roff and Sulphur tornadoes. It’s conceivable that this left-moving cell injected some anticyclonic spin into the forward flank of the storm.

Deducing what happened will take some doing, as this storm was more than 50 miles from the Oklahoma City NEXRAD radar. Data from mobile radar, including the RaXPol unit operated by Howard Bluestein and colleagues (University of Oklahoma), may shed some light on the oddly positioned Roff twister. “Having a tornado in that location is worrisome for my team,” said Doppler on Wheels chief scientist Joshua Wurman in an email, “because we count on being able to transect cores safely. That's not where we expect to find danger.”

Edwards mused: “The odds are extraordinarily tiny of ever seeing another anticyclonic tornado entombed in the forward-flank core of even a violently tornadic supercell. Yet now we know it’s possible, and we must be vigilant of that.”

Some clockwise pioneers
There are extremely rare cases where a left-moving, anticyclonically rotating thunderstorm generates an “anti-mesocyclone” that spawns an anticyclonic twister, as occurred near Sunnyvale, CA, on May 4, 1998. However, the best-known examples of anticyclonic twisters occur in conjunction with more powerful cyclonic twisters as part of a single supercell thunderstorm, as was the case in Oklahoma last week. Sometimes these are weak, short-lived satellite twisters very close to the companion cyclonic tornado; others are stronger and more separated. Wurman unraveled DOW data for several of these in a 2013 Weather Analysis and Forecasting paper. “Our paper does not include any observations of [forward-flank] anticyclonic tornadoes, so this current one is certainly an outlier,” Wurman told me.

One classic case—probably the first anticyclonic tornado ever filmed—unfolded just west of Ames, IA, on June 13, 1976. In this storm, a powerful F3 anticyclonic tornado (the strongest anticyclonic tornado documented to date) closely paralleled the path of an F5 that ripped through the town of Jordan and the nearby countryside. The twisters were only about a mile apart as they moved largely in sync (see Figure 3). The YouTube clip at bottom shows both tornadoes.

A few years later, Ted Fujita and Roger Wakimoto examined the mammoth, nearly stationary supercell that tormented Grand Island, NE, for nearly three hours on June 3, 1980. (This is the storm that inspired the book and movie “Night of the Twisters”). Of the seven tornadoes that emerged that night, three were found to be anticyclonic. “This storm produced the most complex damage patterns imaginable,” wrote James McDonald (Texas Tech University) in the Bulletin of the American Meteorological Society. “No one but Ted Fujita could have sorted them out.”


Figure 3. Damage paths from the tornadoes that struck just west of Ames, Iowa, on June 13, 1976. The F5 tornado is in purple, the anticyclonic EF3 tornado is in green, and a cyclonic F2 satellite tornado that rotated around the F5 is in yellow. Rows of dots are separated by one mile each. Image credit: NWS/Des Moines, IA.



Figure 4. Reflectivity imagery from mobile radars operated by Howard Bluestein and colleagues (University of Oklahoma) reveals cyclonic [C] and anticyclonic [A] circulations that were each associated with tornadoes in (a) eastern Colorado on May 25, 2010; (b) eastern Colorado on June 10, 2010; and (c) western Kansas on May 25, 2012. Image credit: Bluestein et al., 2016: Doppler radar observations of anticyclonic tornadoes in cyclonically rotating, right-moving supercells, Monthly Weather Review 144. ©American Meteorological Society. Used with permission.


Doppler radar sharpens the picture, but the process remains fuzzy
The growth of mobile radar over the last few years has yielded much more data on the evolution of anticyclonic tornadoes, although plenty of questions remain about how and why they form. A group led by Bluestein examined four such events in a paper published in April in Monthly Weather Review.

Perhaps the most notorious case was the El Reno, OK, storm of May 31, 2013, the one that killed storm researchers/photographers Tim Samaras, Carl Young, and Paul Samaras. That mammoth EF3 tornado, which lasted 41 minutes, was accompanied for 12 minutes by an anticyclonic EF2 tornado, several miles to its east, whose path arced southeastward (see Figure 5 below).

All four cases analyzed by Bluestein and colleagues involve anticyclonic tornadoes that developed on the rear, or trailing, end of a supercell’s rear-flank gust front. Each case also featured a mesocyclone producing a companion cyclonic tornado that was either weakening or had just dissipated. However, there was little consistency in the timing or in other aspects of these four cases, and "no characteristic stands out as being unusual,” the authors wrote. Multiple mechanisms could be at work in producing such anticyclonic tornadoes, they added. High-resolution computer simulations may tell us more about these clockwise mavericks in the years to come.


Figure 5. Damage track of the long-lived EF3 tornado that struck near El Reno on May 31, 2013 (T2, with the damage path outlined in orange) and the companion anticyclonic EF1 tornado that arced southeast (T3, in yellow). Image credit: Bluestein et al., 2016: Doppler radar observations of anticyclonic tornadoes in cyclonically rotating, right-moving supercells, Monthly Weather Review 144. ©American Meteorological Society. Used with permission.


Figure 6. WU depiction of convective outlooks issued early Monday morning, May 16, 2016, for Monday (left) and Tuesday (right).

A localized severe threat on Monday and Tuesday
There’s no rest for the storm-weary in Oklahoma and Texas, as another week will begin with a round of potentially severe weather. This time the threat will be focused in the eastern Texas Panhandle into northwest Oklahoma, where a warm front will be lifting north and a dry line pushing east. Storms may cover a fairly broad swath along the warm front and dry line, but the strongest will likely be close to the intersection point, where NOAA/SPC has placed an enhanced risk area. A few tornadoes are possible, especially as low-level winds crank up toward late afternoon and early evening; the storms will likely congeal into a southeastward-moving complex late Monday. The pattern should repeat itself in south Texas on Tuesday, though tornadoes may be less likely, with upper-level energy increasingly separated from an advancing cold front. This cool, dry air mass will sweep across most of the eastern U.S. by midweek, pinching off the prospects of widespread severe weather through at least the end of the week.

We'll be back on Wednesday with our next post.

Bob Henson


Figure 7. One of the best illustrations I’ve seen of the life-saving value of tornado safety practice, drawn from the Sulphur tornado pictured above. From a Facebook post by the NWS office in Norman, OK: “We ran across this young man about 5 miles northwest of Sulphur, OK who was home alone at the time of the tornado. He was able to survive by doing exactly what we always tell people to do—he went to a small room in the center of his home away from outside walls and windows. He walked away without a scratch. There are no guarantees when it comes to tornado safety, but in most cases, the advice works!” Image credit: NWS/Norman.


Video 1. This mini-documentary on Theodore “Ted” Fujita’s research into the Iowa tornadoes of June 13, 1976, includes commentary from Fujita and high-quality (for the era) film footage of both the cyclonic and anticylonic tornadoes. The relevant segment extends from about 3:25 to 5:20.



Tornado Severe Weather

A Quiet Start to the Eastern Pacific Hurricane and Northwest Pacific Typhoon Seasons

By: Jeff Masters , 3:13 PM GMT on May 13, 2016

The 2016 Eastern Pacific hurricane season officially begins on Sunday, May 15, and should be quieter than the crazy 2015 season. Last year set a record for the most major hurricanes (Category 3 or higher) ever recorded in the Eastern Pacific east of 140°W, with nine such storms (reliable records go back to 1971.) One of those 2015 hurricanes was Earth's strongest tropical cyclone ever measured, Hurricane Patricia of October 2015, which reached astonishing sustained wind speeds of 215 mph. The year 2016 should see fewer major hurricanes in the northeast Pacific, thanks to cooler sea surface temperatures (SSTs) and less favorable upper-level winds brought on by what appears to be an emerging La Niña event. In their May 12 update, NOAA predicted a 70% chance of La Niña conditions emerging by the August-September-October peak of the Northern Hemisphere hurricane season. SSTs off the Pacific coast of Mexico this week were about 1°C (1.8°F) cooler than what they were last year in mid-May (Figure 1), and will likely continue to cool (relative to average) during the next few months. The forecast for the 2016 Eastern Pacific hurricane season, issued on May 6 by Mexico's Servicio Meteorológico Nacional (SMN), predicted 17 named storms, 9 hurricanes, and 4 major hurricanes. This is close to the average numbers (east of 140°W) from 1981 - 2010, which were 15 named storms, 8 hurricanes, and 4 major hurricanes. The 2015 Northeast Pacific hurricane season (east of 140°W) featured 18 named storms, 13 hurricanes, and 9 major hurricanes.


Figure 1. Change in Sea Surface Temperature (SST) between May 11, 2015 and May 11, 2016. Ocean temperatures are much cooler this year along the equator in the Pacific, signifying the transition from El Niño to La Niña conditions. SSTs are also much cooler off the Pacific coast of Mexico. Image credit: NOAA/ESRL.

A quieter hurricane season likely for Hawaii
Hawaii, which has been under the gun during the past two hurricane seasons--with one direct hit by a tropical storm (Iselle in 2014) and a number of close calls--should get a bit of a break in 2016. About half as many named storms form in the Central Pacific between 120°W and 180°W in a La Niña year, compared to an El Niño year. Hawaii is about three times less likely to be impacted by a tropical cyclone in a La Niña vs. an El Niño year, according to Phil Klotzbach, a hurricane forecaster at Colorado State University.

We've already had one hurricane in the Central Pacific this year--Category 2 Hurricane Pali became the earliest hurricane on record in the Central Pacific on January 11, 2016, and later dissipated on January 14. This storm was more a carry-over from the record-breaking Central Pacific hurricane season of 2015, though, which had exceptionally low wind shear and record-warm ocean temperatures. In 2015, the Central Pacific (between 140°W and 180°W) had 14 named storms, 8 hurricanes, and 5 major hurricanes form in or track through the basin--all of which were new records. Between 1981 - 2010, the Central Pacific had an average of 3.4 named storms, 1.5 hurricanes, and 0.7 major hurricanes form or track through the basin per year.


Figure 2. MODIS visible satellite image of Hurricane Pali taken on the afternoon of January 12, 2016. At the time, Pali was at peak strength--a Category 2 storm with 100 mph winds. Hurricane Pali became the earliest hurricane on record in the Central Pacific Ocean on January 11, 2016, and dissipated on January 14. The previous record for the earliest hurricane in the Central Pacific was Hurricane Ekeka on January 30, 1992. El Niño played a role in the formation of Pali. According to the discussion issued January 7, 2016 by the Central Pacific Hurricane Center, "This low-latitude out-of-season system has tapped into significant directional shear of the low-level winds, with an El Niño related westerly wind burst south of the system, and prevailing easterly trade winds to the north providing the large scale conditions conducive for development." Image credit: NASA.

Look for the season's first storm in early June
Several recent runs of the 16-day GFS model forecast have shown a tropical depression or Tropical Storm Agatha forming in the Eastern Pacific between Mexico and Hawaii during the last week of May, though these forecasts are too far in the future to be reliable. According to the Weather Company's long-range forecasting expert Dr. Mike Ventrice, the Eastern Pacific has a good chance of seeing its first storm of the season during the period May 30 - June 5, though. A Madden-Julian Oscillation (MJO) event is currently gaining amplitude over the Indian Ocean, and the European weekly model projects this MJO will pass through the Eastern Pacific during May 30 - June 5. The MJO often provides the necessary kick to spin up a tropical storm, especially over the Eastern Pacific and Atlantic Basins.


Figure 3. Super Typhoon Maysak as seen from the International Space Station at approximately 6 pm EDT Tuesday March 31, 2015 (just after dawn local time.) At the time, Maysak was a Category 5 storm at peak intensity, with sustained winds of 160 mph (as estimated by the Joint Typhoon Warning Center) and a central pressure of 905 mb (as estimated by the Japan Meteorological Agency.) Maysak was the strongest typhoon ever observed in the Northwest Pacific prior to April, and one of only three Category 5 typhoons ever observed in the Northwest Pacific so early in the year. Maysak killed nine and did $8.5 million in damage to several small islands in the Federated States of Micronesia, making it Micronesia's second deadliest and second most expensive storm in recorded history.

TSR predicts a below-average Northwest Pacific typhoon season
Last year was one of the busiest typhoon seasons on record in the Northwest Pacific, with a record number of Category 3 and stronger storms--sixteen--and an ACE index that was the third highest on record (479, behind only 2004's ACE of 481 and 1997's ACE of 568). This year should be much quieter, though. The May 7 forecast for the 2016 Northwest Pacific typhoon season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for a below-active season with 22 named storms, 13 Category 1 or stronger typhoons, 6 major Category 3 or stronger typhoons, and an Accumulated Cyclone Energy (ACE) of 217. The long-term averages for the past 51 years are 26 named storms, 16 typhoons, 9 major typhoons, and an ACE of 298. TSR rates their skill level as modest for these late May forecasts--13% to 30% higher than a "no-skill" forecast made using climatology. TSR’s main predictor for their typhoon season forecast is the forecast sea surface temperatures (SSTs) during August - September 2016 in the region 5 ̊S - 5 ̊N, 140 ̊W - 180 ̊W, which they expect to be moderately cooler than average (-0.8°C from average.) Cool waters in this region are typically associated with stronger trade winds over the region 2.5°N-12.5°N, 120°E-180°E, the Northwest Pacific region where most major typhoons form. Stronger trade winds in that region tend to interfere with the amount of spin developing typhoons can get, leading to quieter typhoon seasons.

Using Dr. Phil Klotzbach's handy new Tropical Cyclone Activity stats page, we can see that the Northwest Pacific is off to a slow start this year. There have not been any named storms yet, and typically, we should have seen two by now. Last year, there had already been seven named storms in the Northwest Pacific by this point in the year, including three storms that became Category 5 typhoons.

Northern Indian Ocean tropical cyclone season underway
An area of disturbed weather formed on Thursday evening in the North Indian Ocean about 400 miles east of Sri Lanka. According to the Tropical Weather Discussion from the Joint Typhoon Warning Center, the disturbance has favorable conditions for development--low wind shear and very warm ocean waters about 2°C above average. Recent runs of the GFS and European model show this storm moving over Sri Lanka and South India on Sunday and Monday. The disturbance may have enough time over water to become the first tropical depression of the season in the North Indian Ocean, before interaction with land halts development. The Northern Indian Ocean has two tropical cyclone seasons--one that peaks in late May, just before the arrival of the Southwest Monsoon, and one that peaks in November, after the monsoon has waned. During the June - October peak of the monsoon, tropical cyclone formation is suppressed by the atmospheric circulation associated with the monsoon. This year's May tropical cyclone season has the potential to produce some unusually intense tropical cyclones, since SSTs across the basin are at record to near-record warm levels, 1 - 2°C above average.

Jeff Masters

Hurricane

April Keeps the Warm, Wet U.S. Trend Going for 2016

By: Bob Henson , 6:58 PM GMT on May 11, 2016

Although the warmth was notched down a bit from the year’s first quarter, April was still much milder and moister than average, according to the monthly U.S. climate roundup released on Wednesday by the National Centers for Environmental Information. The monthly average for the contiguous 48 states came in at 53.2°F, which is 2.2°F above the 20th-century average and the 18th warmest among the 122 Aprils since records began in 1895. Outside of New England, New York, Pennsylvania, and Michigan, every state came in above its long-term average (see Figure 1), and it was a top-five warmest April for Idaho, Oregon, and Washington. The only place that saw record statewide warmth in April was Alaska, which merits a separate discussion (see below).


Figure 1. Statewide rankings for average temperature during April 2016, as compared to each April since 1895. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 122 the warmest. Image credit: NOAA/NCEI.


Figure 2. Statewide rankings for average precipitation during April 2016, as compared to each April since 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 122 the wettest. Image credit: NOAA/NCEI.


There were plenty of April showers this year, especially across the Great Basin and Great Plains. The month came in as the 21st wettest on record for the 48 contiguous states, with a 48-state reading of 2.95” (0.43” above the 20th-century average). It was a top-ten wettest April for the entire Plains corridor from Texas to North Dakota (Figure 2). The apex of last month’s precipitation was the phenomenally heavy rain and severe flash flooding in Houston on April 18. More than than a foot of rain fell in northwest parts of the Houston area, and the city officially saw its second wettest day on record (9.92”, topped only by 10.34” during Houston’s “first” Tropical Storm Allison in 1989). Across the southwest U.S., where moisture was scant earlier this year despite the strong El Niño, generous precipitation finally arrived.

Daily record highs are far outpacing record lows this year
It’s no longer quite the warmest year on record for the United States thus far (although the planet is still demolishing year-to-date records--stay tuned for our global roundup next week). The average temperature for the contiguous U.S. (January-April 2016) now ranks second behind only 2012. The tally of daily record highs and lows across the nation reinforces this warm picture: as of Wednesday morning, the year-to-date tallies on NOAA’s Daily Weather Records site show a total of 10,328 record daily highs and just 1286 record lows, a ratio of just over 8:1. Last year’s ratio ended up close to 3:1, after two oddly chill years in which the nation saw more daily record lows than highs (no such years had occurred since 1993).

By this date in 2012, the contiguous states had already seen thousands more record highs than in 2016, thanks to the Great Warm Wave of March 2012. However, 2016 has by far the lowest number of daily record lows to date of any year in the century-plus database--a reflection of this winter’s moist, mild El Niño conditions on top of long-term warming.


Figure 3. A picture of Alaska’s warmth in the first 110 days of 2016 as projected in the 6-10 day NOAA outlook for each day (advancing from left to right in each row and then from top row to bottom row). Orange and red colors denote above-average readings and blue below average. Nearly every day ended up with above-average readings throughout all or most of the state. Only one day--February 19--saw below-average readings the state as a whole. Image credit: Brian Brettschneider.


Crazy Alaskan warmth
The nation’s 49th state is setting the pace this year for temperature extremity. Alaska’s average for April of 33.3°F beat the previous record of 32.9°F (1940) and was a full 10°F above the 1925-2000 average, a huge margin for a state so large. For the year to date through April, Alaska’s 21.7°F came in almost 2°F above its previous record (18.9°F, 1981) and 11.4°F above the state’s long-term average. The consistency of this year’s warmth has been nothing short of amazing, with most Alaskan towns and cities recording only a handful of days below average thus far.


Figure 4. January through April 2016 is running far milder than all other years in the weather history of King Salmon, Alaska. Image credit: Brian Brettschneider.


Figure 5. Based on data through early May drawn from 25 locations across Alaska, this year’s consistent mildness has put 2016 ahead of all other years since 1955. Image credit: Brian Brettschneider.

Melting, melting
Rivers across Alaska are feeling the heat, with some showing record-early ice melt. “This is an under-appreciated issue, as most of Alaska is off the road network and frozen rivers are the most efficient method of travel,” noted meteorologist Brian Brettschneider in an email. At the town of Circle in east central Alaska, the Yukon River began flowing freely on April 29, the earliest ice break-up date on record and well in advance of the average date (since 1980) of May 10.

The break-up of the Tanana River at the town of Nenana provided a major windfall for 28 participants this year in the annual Nenana Ice Classic. Each year a jackpot is split among the hundreds of thousands of guesses as to which day the Tanana will experience its spring break-up at downtown Nenana. This year’s $330,330 winnings were divided evenly among the 28 entrants who correctly pegged the date as April 24. It was the seventh earliest breakup in the 99-year history of the contest, which began when a group of railroad engineers pooled $800 (in 1917 dollars). The average break-up date is now about a week earlier than it was in the early 1900s, as shown in this climate.gov feature.

Bob Henson


Figure 6. A tripod sits atop the Tanana River during the 2008 Nenana Ice Classic. When the river begins flowing, it moves the tripod and triggers a clock to stop, serving as the official marker of the ice break-up. Image credit: Wikimedia Commons/Frank K.


Figure 7. As of May 10, 2016, only a few rivers across far northern Alaska remained ice-choked. Image credit: NOAA/NWS Alaska-Pacific River Forecast Center.

Climate Summaries

Tornadoes Kill Two in Oklahoma; Severe Weather Outbreak in Ohio Valley on Tuesday

By: Jeff Masters , 3:10 PM GMT on May 10, 2016

A significant tornado outbreak hit the Plains on Monday night, killing two people in Oklahoma and causing significant damage in several towns, including Wynnewood, Oklahoma. NOAA's Storm Prediction Center (SPC) logged 22 preliminary reports of tornadoes, with touchdowns occurring in Oklahoma, Kansas, Iowa, Arkansas, Illinois, and Nebraska. There were more than 90 reports of large hail at least 1" in diameter, with softball-sized hail 4.25" in diameter reported in Lincoln, Nebraska. Chester Barnes, 76, was killed in his rural Garvin County home when a violent tornado touched down south of Oklahoma City, according to KFOR.com. A second death occurred in Johnston County near Connerville, whom KXII.com identified as 76-year-old Jackie Brooks. The two deaths bring the 2016 tornado death toll in the U.S. to twelve, according to the Storm Prediction Center. Survey crews from the National Weather Service will go to the tornado-damaged areas on Tuesday to determine the EF ratings of the twisters. Some impressive YouTube videos of Monday's twisters can be seen from severestudios.com and from stormchasingvideo.com.


Figure 1. A tornado south of Wynnewood, OK taken from the west at 4:18 pm on May 9, 2016.  The tornado was dwarfed by the massive spinning updraft of its parent supercell which stood out in amazing clarity owing to its almost complete separation from the core of rain and large hail. The Oklahoma Highway Patrol closed I-35 near Wynnewood for 15 minutes when the tornado turned towards the freeway, the Associated Press said. Image credit: James LaDue.


Figure 2. A tornado rips through a residential area after touching down south of Wynnewood, Oklahoma on May 9, 2016. (JOSH EDELSON/AFP/Getty Images) 


Figure 3. Preliminary storm reports for Monday, May 9, 2016, from NOAA's Storm Prediction Center.

More severe weather coming on Tuesday
The storm system responsible for Monday's severe weather has moved eastwards, and Tuesday's greatest severe weather threat will be focused over the Ohio Valley in southern Indiana and northern Kentucky, where SPC has issued their "Enhanced" probability of severe weather. A very moist and unstable airmass is in place there, which should fuel a round of severe thunderstorms capable of causing widespread wind damage. Upper level winds are marginally favorable for allowing a few supercell thunderstorms with tornadoes to occur, as well.


Figure 4. Severe weather outlook for Tuesday, May 10, from NOAA's Storm Prediction Center.

Jeff Masters

Tornado

Six U.S. Billion-Dollar Severe Weather Disasters in 2016; More Severe Weather Today

By: Bob Henson and Jeff Masters , 3:40 PM GMT on May 09, 2016

Hail and water were the most destructive forces at work in U.S. severe weather during April 2016. According to the April 2016 Catastrophe Report from insurance broker Aon Benfield,  two billion-dollar weather disasters hit the U.S. in April: a severe weather outbreak from the Plains to the Southeast on April 10 - 13 that cost at least $2.75 billion and killed one person, and a severe weather outbreak from April 15 - 19 in the Rockies and Plains that cost $1 billion and killed nine. (Note that Aon Benfield includes flash flood damage in its “severe weather” category.) The highly publicized severe weather of April 27 in the Southern Plains failed to make the billion-dollar threshold, although it did generate hundreds of millions in damage. 




Figure 1.  Heavy rains caused extensive flash flooding across parts of Texas on April 18, killing eight and leading to more than 1,800 water rescues in the greater Houston metropolitan area. The same storm also brought heavy snow and severe thunderstorms from April 15 - 19 to parts of the Rockies and Plains, killing one person. Damage was estimated at $1.0 billion. In this image, we see residents of an apartment complex in the Greenspoint area of north Houston use an air mattress to evacuate their flooded homes on Monday, April 18, 2016.  Image credit: AP Photo/David J. Phillip.




Figure 2. Severe thunderstorms caused catastrophic hail damage across parts of the Plains and Southeast from April 10 - 13, killing at least one person and injuring dozens more. The Dallas-Fort Worth and San Antonio metro regions in Texas were the hardest hit, with softball and baseball-sized hail. Damage was estimated at $2.75 billion. In this photo, we see an impressive shelf cloud from a thunderstorm over Royce City, Texas, on April 11, 2016. Image credit: wunderphotographer Gweduc.



These events brought the tally of billion-dollar severe weather disasters so far in the U.S. to six. This ties 2016 with 2013 for the third-most billion-dollar severe weather disasters in one year. The record is nine billion-dollar severe weather disasters in 2011, with 2012 in second place with seven, according to NOAA/NCEI. There was also a $2 billion dollar winter storm in the Eastern U.S. in January, bringing the total number of U.S. billion dollar weather disasters so far in 2016 to seven:



1) Winter Weather, Eastern U.S., 1/21 - 1/24, $2.0 billion, 58 killed

2) Severe Weather, Plains-Southeast U.S., 4/10 - 4/13, $2.75 billion, 1 killed

3) Severe Weather, Rockies-Plains-Southeast-Midwest U.S., 3/22 - 3/25, $1.75 billion, 0 killed

4) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 3/4 - 3/12, $1.25 billion, 6 killed

5) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 2/22 - 2/25, $1.2 billion, 10 killed

6) Severe Weather, Plains-Rockies U.S., 4/15 - 4/19, $1 billion, 9 killed

7) Severe Weather, U.S., 3/17 - 3/18, $1.0 billion, 0 killed

Tornado impacts on the low side this spring
Thus far in 2016, the most destructive and deadly tornadic activity occurred in February with a swarm of early-season twisters, straight-line winds, and large hail across the eastern United States on February 23-24. The damage toll from the month’s severe weather was expected to top $1 billion, according to Aon Benfield in its February 2016 Catastrophe Report. Seven tornado-related deaths were recorded by NOAA’s Storm Prediction Center (SPC) on the February 23-24 outbreak. Otherwise, there have been only two killer tornadoes thus far in 2016: an EF2 twister in Manatee County, FL, that took two lives on January 17, and a weak EF0 tornado that killed one person in Houston, TX, during the April 27 outbreak. Seven of this year’s ten deaths have been in manufactured homes.
 
Through May 8, SPC has tallied a total of 394 preliminary tornado reports. Once this number is “inflation-adjusted” for comparison with earlier decades, when fewer people were looking for tornadoes and reporting them, 2016’s tornado total for the year thus far is lower than about 3 out of 4 years since 1950--although it only takes a single multi-day outbreak to change those numbers significantly.
 

Figure 3. Killer tornadoes for 2016 thus far. The yellow icon denotes EF1 strength; green, EF2, and blue, EF3. Not shown is the EF0 tornado that produced one fatality in Harris County, TX, on April 27. Image credit: NOAA/SPC.
 

Figure 4. WU depiction of NOAA/SPC’s convective outlook, showing the severe-weather risk areas as of mid-morning Monday for Monday and Tuesday, May 9 and 10, 2016.

This weekend’s severe weather and the outlook going forward
An upper-level storm sweeping from the western U.S into the Plains over the past weekend brought plenty of dynamics to trigger severe thunderstorms. However, moisture return from the Gulf of Mexico was relatively slow and anemic, which kept the severe weather relatively limited. Several highly visible twisters occurred in association with two supercell storms over the high plains of far northeast Colorado on Saturday, with five injuries reported. The strongest tornado, with a preliminary rating of EF2, damaged several homes and businesses along its eight-mile path north of the town of Wray. About a dozen tornadoes struck on Sunday along a dry line stretching from Nebraska to Oklahoma, with no major damage reported.
 

Figure 5. The spectacular EF2 tornado that struck just north of Wray, Colorado, on Saturday, May 7, 2016. Image credit: Bob Smith/Tempest Tours, used with permission.


More severe weather is possible as the upper-level storm system lumbers eastward Monday and Tuesday. SPC has placed a large swath from southern Iowa to northeast Texas under a slight risk (Figure 4), with an enhanced-risk area including Little Rock, AR, and Texarkana, TX. Remnant clouds and storms from Sunday night will complicate Monday’s setup, but upper-level cold air will favor very large hail over eastern OK and northeast TX. Late Tuesday, a mesoscale convective system of MCS (a large cluster of strong thunderstorms, often extending through the night) may develop near the mid-Mississippi Valley and race eastward through the Ohio Valley, with a repeat possible in the same general area on Wednesday evening. MCSs can produce damaging straight-line winds and large hail. Northwest upper-level flow should predominate later in the week, quashing the odds of any widespread severe weather until next week at the earliest.

WU contributor Lee Grenci has an interesting new post discussing the extremely dry air that fed the catastrophic spread of the Fort McMurray wildfire on Wednesday, May 4.

Bob Henson and Jeff Masters
 



 

Severe Weather Tornado

Hurricane Intensity Forecast Models Are Improving

By: Jeff Masters and Bob Henson , 4:30 PM GMT on May 06, 2016

Forecast accuracy in predicting where a hurricane will go has improved dramatically over the past 20 years, with official NHC track errors for 1 - 5 day Atlantic forecasts improving by more than a factor of two (Figure 1). Improving hurricane intensity forecasts, though, has proved to be very difficult--there has been very little improvement in official NHC intensity forecasts over the past 20 years (Figure 2). However, the models used to predict hurricane intensity have steadily improved over the past six years, and this improvement may herald the arrival of significantly improved hurricane intensity forecasts in the coming years. A good portion of this credit goes to the Hurricane Forecast Improvement Project (HFIP), a ten-year project that began in 2009 with the objective of reducing hurricane track and intensity errors by 20% over five years (by 2014) and by 50% over ten years (by 2019.)


Figure 1. Verification of official NHC hurricane track forecasts for the Atlantic, 1990 - 2015. Over the past 15 years, 1 - 5 day track forecast errors have been reduced by approximately 50%. Image credit: 2015 National Hurricane Center Forecast Verification Report.


Figure 2. Verification of official NHC hurricane intensity forecasts for the Atlantic, 1990 - 2015. Intensity forecasts have shown much slower improvement that track forecasts. There is some support for the idea that 1-day and 2-day intensity forecasts since 2010 (red and green lines) have shown a modest increase in improvement. Image credit: 2015 National Hurricane Center Forecast Verification Report.

Improvements in NOAA's HWRF model
The main focus of development efforts in HFIP have been to improve NOAA's HWRF model, which was the top-performing hurricane intensity model in 2015 and 2012 - 2015. If we consider the HWRF model alone, its improvement over the five-year period ending in 2014 has been 20% (Figure 3), meeting the HFIP goal of a 20% improvement in hurricane intensity models in a five-year period. (Note that HFIP cannot take full credit for the improvement of the HWRF model during this period, since the National Weather Service made independent substantial improvements to NOAA's GFS model, which supplies the initial conditions needed to run the HWRF model.) Official NHC intensity forecasts have also improved since 2009, though the numbers in 2015 for 3 - 5 day forecasts did not follow this trend. The 2015 numbers may be skewed because of the relatively few number of forecasts made last year, as NHC made forecasts as far out as five days for only four storms, two of which proved difficult to forecast--Danny and Joaquin. This allowed a few ugly forecasts to have an unrepresentative influence on the yearly stats. Perhaps most encouraging, the HWRF model showed significant progress in 2015 in making the most important intensity forecasts there are--ones of rapid intensification (RI). The model's probability of detection of an RI event increased, and the false alarm rate went down, compared to forecasts from previous years.


Figure 3. Intensity forecasts from NOAA's HWRF model for Atlantic tropical cyclones for the 2015 version of the model have shown a 20% improvement, meeting the 5-year improvement goal for the Hurricane Forecast Improvement Project (HFIP), a ten-year project that began in 2009 with the objective of reducing hurricane track and intensity errors by 20% over five years (by 2014). Image credit: Vijay Tallapragada, NOAA/EMC.

Improvements coming in 2016 for NOAA's HWRF model
The HWRF model should be even better this year. In July of 2016, the HWRF model is scheduled to receive a major upgrade to its code to improve the boundary layer and surface physics and vertical wind structure. The model will also increase the size of the "zoomed-in" region where its highest-resolution calculations are performed immediately surrounding a hurricane, and HWRF will be connected to a separate hurricane wave model which will allow the two models to interact and improve the forecasts of both models. I look forward to seeing if the HFIP program can meet its goal of a 50% improvement of hurricane intensity forecasts by 2019; I think 2016 will be a crucial test. Even if this goal is not met, HFIP has shown its worth in training a new generation of hurricane scientists. Many of these researchers will be moving into operational weather forecasting in the next few years in support of NOAA's latest modeling effort, the Next Generation Global Prediction System (NGGPS).


Figure 4. Skill of computer model intensity forecasts of Atlantic named storms in 2015, compared to a "no skill" model called "Decay-SHIFOR5" that uses just climatology and persistence to make a hurricane intensity forecast (persistence means that a storm will tend to maintain its current behavior.) The official NHC intensity forecasts were close in skill to three of their four main intensity models. These four models were the dynamical Hurricane Weather Research Forecasting (HWRF) and Geophysical Fluid Dynamic Laboratory (GFDL) models, which subdivide the atmosphere into a 3-D grid around the storm and solve the atmospheric equations of fluid flow at each point on the grid, and the statistics-based Logistic Growth Equation Model (LGEM) and Decay Statistical Hurricane Intensity Prediction Scheme (DSHIPS, the SHIPS model with inland decay of a storm factored in.) The GFDL model did poorly in 2015. Note also that NOAA's Global Forecast System (GFS) and the European Center for Medium Range Weather Forecasting model (ECMWF) made lousy intensity forecasts relative to climatology and persistence except at 5 days; these models are generally disregarded by NHC when making intensity forecasts. Image credit: 2015 National Hurricane Center Forecast Verification Report.

It’s PWS Owner Appreciation Week--and your chance to win a personal weather station!
Our thousands of members with personal weather stations (PWSs) are the heart and soul of Weather Underground; it’s the data they provide that helps give WU forecast apps their hyper-local edge. Our first-ever PWS Owner Appreciation Week, running through next Wednesday, May 11, pays tribute to our backyard observer-members. You’ll find profiles of PWS owners and their stations posted on the WU PWS blog. On Thursday, WU’s Madeline Rae introduced us to GoodGreen House, located in central New York between Binghamton and Ithaca, where Jeff White and Liz Smith use a PWS to keep track of conditions both outside and inside the working greenhouse that also serves as their home. Check out the profile to learn more. Earlier this year, Madeline spotlighted Koe Kellen, a firefighter in northern Illinois whose PWS helps Koe and his fellow volunteers assess fire risk.

There’s still time for you to participate in our PWS giveaway. By taking a quick quiz, you’ll have a shot at winning one of 10 personal weather stations or 500 WU T-shirts. Winners will be announced on Wednesday, May 11, so don’t delay!


Have a great weekend, everyone!

Jeff Masters and Bob Henson

Hurricane

The Fort McMurray Disaster: Getting Beyond “Is It Climate Change?”

By: Bob Henson and Jeff Masters , 3:49 PM GMT on May 05, 2016

In just two days, the fire engulfing the Canadian city of Fort McMurray in Alberta has seared itself into the North American consciousness. This appears to be the first time in the continent’s history we have seen a city of more than 60,000 residents (officially an “urban service area” rather than a city), located hundreds of miles from any comparable population center, forced to evacuate a furious wildfire. The fact that a city this large is also so remote owes everything to the presence of vast oil sands, the driver that has increased Fort McMurray’s population more than twentyfold since the 1960s. As of Thursday morning, May 5, more than 1,600 structures had been destroyed and 7,500 hectares (18,500 acres) burned as the fire continued to burn out of control. According to Reuters, a hotel north of the airport's main terminal had caught fire, but as the sun rose on Thursday, there was no obvious damage to the airport. There were no deaths from the blaze, but fatalities were reported in at least one vehicle crash along the evacuation route. Weather conditions in Fort McMurray on Wednesday were hellacious for firefighting--a high of 89°F, humidities as low as 7%, and powerful winds sustained at speeds as high as 34 mph, gusting to 45 mph. Thursday's weather is not going to be as bad, with highs in the upper 60s and west-northwest winds of 10 - 20 mph. There is no rain in the forecast until next Wednesday, and temperatures are predicted to once again rise above 80°F in breezy conditions on Saturday. The average high for this time of year is just 59°F.


Figure 1. Smoke rises at Fort McMurray in Alberta, Canada on May 4, 2016. Pyrocumulus clouds formed by major wildfires can sometimes develop into pyrocumulunimbus clouds intense enough to generate lightning, hail, high winds, and tornadoes. Image credit: @tamarackaspenbirch/Instagram.

A fire wildly out of season
The Fort McMurray fire arrived months ahead of when summer wildfire typically races through the boreal forests of northern Alberta. A low-pressure center arcing far north of a typical early-May track brought hot southwest winds across the Fort McMurray region, which lies within the southern edge of the great boreal forests of northern Canada. Fort McMurray saw record daily highs of 91°F on Tuesday and 89°F on Wednesday. The city gets this warm on only about five days in a typical year, and those days are usually in July or August (even then, the average daily high is between 70°F and 75°F). The hot weather struck at an uncommonly bad time for wildfire risk: after winter snows had disappeared, but before the summer green-up had taken hold. Normally the window between these would be quite narrow, but snowfall was light this winter across the region, and it disappeared quickly during record warmth in April. From December through April, Fort McMurray recorded only 1.69” of precipitation, compared to the 1981-2010 average for that period of 3.22”.


Figure 2. Wildfire danger for Canada on May 5, 2016, from the Canadian Wildland Fire Information System. Record heat, strong winds, and dryness due to below-average winter snows and the lack of spring snow cover have conspired to produce extreme fire danger over much of Alberta and Saskatchewan.

El Niño, climate change, and The Question
It’s not rocket science to connect the dots between the preconditions for the Fort McMurray fire and large-scale, long-term trends. High northern latitudes are among the planet’s most rapidly warming regions, just as predicted by climate models that incorporate human-produced greenhouse gases. The advance of Northern Hemisphere snowfall in autumn and winter has seen little significant change--if anything, there is a bit more autumn snow cover (see Figure 3 below)--but in springtime, the snowpack is vanishing far more quickly than it did in decades past, another outcome well predicted by global climate models. On top of all this, El Niño tends to produce warm Canadian winters, so the strong 2015-16 El Niño event added a hot spike to the long-term drumbeat of winter warming across western Canada. This year’s warmth has extended from the Pacific Northwest (where Portland, OR, and Seattle, WA just completed their warmest April on record) to Alaska (where Anchorage saw below-average temperatures on just 3 of the year’s first 124 days, a truly remarkable stretch).


Figure 3. Trends in Northern Hemisphere snow cover since the late 1960s, shown as departures from the monthly average extent in millions of square kilometers for October and November (top) and April and May (bottom). The snow cover last month was the least extensive for any April in the 50-year record. Image credit: Rutgers Global Snow Lab.

Wildfire: the climate plot thickens
Catastrophic wildfire is more than a temperature or precipitation anomaly. Time and again, an intense spell of record heat after weeks of warm, dry weather sets the stage for devastating wildfire. Along with this, there are other preconditions: Is the landscape packed with tinder-dry trees? Has the area burned in recent years or decades? Are local firefighters well equipped to put out small fires quickly? Are there arsonists and copycats lurking in the wings? All of these cofactors make it more difficult to draw a straight line from climate change to specific wildland fires. It’s much the same with flooding, another natural disaster influenced by how humans shape the landscape. Study after study has established that bursts of intense rainfall are becoming heavier in many parts of the world, as predicted by climate change research. Yet the human factors that feed into flooding (urban pavement, river channeling, and the like) complicate the task of attributing a particular flood to climate change.

None of this absolves human-produced greenhouse gases from loading the dice toward fire- and flood-friendly conditions. Rather, it’s to say that even the most elaborate, carefully conducted attribution studies (research designed to show how and when climate change has made a particular event more likely) may not always give the conclusive results people crave when it comes to specific fires and floods--although such work can say quite a bit about long-term trends. In fact, one of the first major attribution studies was ”Detecting the effect of climate change on Canadian forest fires,” a 2004 paper led by Nathan Gillett, which showed a detectable human influence on the area burned by wildfire in Canada between 1959 and 1999. In its February report ”Attribution of Extreme Weather Events in the Context of Climate Change”, the National Academies notes that fire season has lengthened by an average of 19% globally, with increases noted across more than 25% of Earth’s vegetated land area. “What is less clear,” the report adds, “is how climate warming is driving changes in the atmospheric circulation and its teleconnections, resulting in persistent areas of high pressure that lead to large fire years on regional scales. Similarly, it is unclear how climate warming is regulating the shorter-term weather patterns that control extreme fire periods during which fires expand rapidly.”

What do we do?
We don’t need attribution studies to realize that our struggling firefighting resources must be brought up to speed to match the evolving picture of longer fire seasons and more dangerous fires. A U.S. Forest Service report issued last summer sounded the alarm: “...within a decade, the agency will spend more than two-thirds of its budget to battle ever-increasing fires, while mission-critical programs that can help prevent fires in the first place such as forest restoration and watershed and landscape management will continue to suffer. Meanwhile...these catastrophic blazes are projected to burn twice as many acres by 2050.” It is no small irony that Wednesday, May 4, was International Firefighters Day.

In their deadline coverage of the Fort McMurray event, journalists such as Andrew Freedman (Mashable) have done a laudable job pointing out the complex but real connections between climate change and wildfire. We have much more to learn about exactly why and how the atmosphere is moving in directions that favor devastating fire--but for now, perhaps it’s enough simply to know that the dice are being loaded. Together with the many other threats posed by climate change, this should be more than enough motivation to get serious about emission cuts. The vast and profound effects of human-produced greenhouse gases--from intensified downpours and drought impacts to ocean acidification and sea-level rise--call for a sustained commitment to change that transcends any single disaster, even one as compelling as the nightmare unfolding in Fort McMurray.

Bob Henson and Jeff Masters


Video 1. Dashcam footage taken by Michel Chamberland as he evacuates the hard-hit Beacon Hill neighborhood of Fort McMurray, Alberta, on May 3, 2016, at 2 pm. Huge flames leap out along the roadside, and embers fall over the traffic. Chamberland told CBC he was feeling "pretty empty, saddened, devastated, shocked. Still trying to take in the whole situation and what happened. You just never, never expect this."


Climate Change Fire Drought Extreme Weather

Brutal Heat Intensifies Across India; Generous Monsoon on the Way?

By: Bob Henson , 3:24 PM GMT on May 04, 2016

There are encouraging signs of a wetter-than-average monsoon in the cards for India this year--but until it arrives, millions of residents will have to deal with torrid pre-monsoon heat assaulting South and Southeast Asia this spring. More than 300 fatalities have been reported in the east-central Indian states of Odisha and Telangana. On May 1 and 2, at least 12 Indian locations broke or tied their all-time highest May temperatures. Accentuating the premature nature of this year’s heat, most of the prior records had been set during the last week of May. (Thanks to meteorologist Michael Theusner of Klimahaus for these statistics.) Extra weeks of heat stress are an ominous portent in this highly vulnerable nation. Some 2500 people were killed in 2015 by India’s second-deadliest pre-monsoonal heat wave on record, close behind 1998 (2541 deaths).

The pre-monsoon season is naturally a hot period in India: it’s the increasing contrast between land and sea that eventually brings the heat-quenching, life-giving summer monsoon. Yet even by pre-monsoonal standards, April was extraordinarily hot across the region, as reported by WU weather historian Christopher Burt. On April 24, it hit 48.5°C [119.3°F] in the east-central town of Titlagarh--the highest temperature ever reliably measured in India during April. “You can say there is an undeclared curfew in Titlagarh after 10 am. If you go out, you are either a very brave person or you are an outsider,” local Congress member Upendra Bag told the Hindustan Times. Titlagarh’s all-time high is 50.1°C (122.2°F) on June 3, 2003, and India’s hottest reliably measured temperature is 50.6°C (123.1°F) at Pachpadra on May 25, 1886.


Figure 1. Residents of New Delhi endure another day of sizzling heat on Monday, May 2, 2016. Monday hit a record 46°C (114.8°F) at Indira Gandhi International Airport and 44°C (111.2°F) at the city’s Safdarjung observatory. Image credit: Ramesh Sharma/India Today Group/Getty Images.


Figure 2.Departures from average in land-surface temperature across South and Southeast Asia for April 2016, as calculated from MODIS data (the Moderate Resolution Imaging Spectroradiometer aboard NASA’s Terra satellite). Some landscapes in Cambodia averaged more than 12°C (22°F) above normal for the month. Land-surface temperatures can vary significantly from air temperature. In this case, both air and land have been baking in relentless sunshine and record warmth. Image credit: NASA Earth Observatory.


Scorching in the Silicon Valley of India
One place where pre-monsoonal heat tends to be a bit less extreme is the highlands of southwest India’s Kerala state. The tech-oriented city of Bengaluru (Bangalore) is perched at near 900 meters (3000 feet), which helps keep a typical April day maxing out at no more than around 33°C (91°F). Yet on April 24, the city soared to 39.2°C (102.6°F), breaking the all-time record of 38.9°C for Bengaluru that extended all the way back to May 22, 1931. Schools in Kerala’s capital city of Thiruvananthapuram will be closed until at least May 20. In another Indian state, Bihar, the use of indoor cookstoves in rural areas has been banned between 9 am and 6 pm in response to heat- and drought-driven fires that burned 2500 houses and took 36 lives.

Some good news: outlook for the 2016 Indian monsoon
With El Niño now in its death throes, large-scale conditions are lining up favorably for above-average rains during the 2016 Indian monsoon. According to the India Meteorological Department (IMD), 71% of monsoon seasons that follow an El Niño produce near- or above-normal rainfall. The IMD’s initial outlook for the 2016 monsoon, issued on April 12, calls for 106% of long-term average rainfall for the nation as a whole, with a margin of error of plus or minus 5%. In probabilistic terms, the IMD is giving only 6% odds of below-average rains and a 64% chance of above-average rains.

Similar to the techniques used in many seasonal hurricane outlooks, the IMD employs a statistical forecast scheme for its April monsoon outlooks. The five variables are:

--SST gradient between North Atlantic and North Pacific (Dec + Jan)
--Equatorial South Indian Ocean SST (Feb)
--East Asia mean sea level pressure (Feb + Mar)
--Northwest Europe surface air temperature (Jan)
--Equatorial Pacific warm water volume (Feb + Mar)

Along with its statistical technique, the IMD is now collaborating with the Indian Institute of Tropical Meteorology and other agencies, including NOAA, on model-based monsoon prediction, using a research version of the NCEP Climate Forecast System (CFS). This coupled dynamical system paints an even brighter picture for the 2016 monsoon, projecting that it will produce 111% of India’s long-term national rainfall average (again plus or minus 5%). IMD will issue an updated outlook in June, including region-by-region forecasts. The private firm Skymet is also calling for an above-average summer monsoon, with 105% of average rainfall (plus or minus 4%).


Figure 3. Some parts of southern and eastern India that average 20 to 50 mm of rain (0.8” to 2.0”) from March 1 to May 3 (center) have received little or no rain this year (left), helping temperatures to soar well beyond typical pre-monsoon levels. Image credit: India Meteorological Department.


After two disappointing monsoons, hopes are high
As long as destructive flooding can be minimized, a generous summer monsoon would be a boon to India after the tepid outcome of the last two summer monsoons: 88% of average in 2014 and 86% of average in 2015. Far southeast India has its own monsoon in autumn, which is often boosted by El Niño and tamped down by La Niña--the opposite of the typical effects of these phenomena on India’s summer monsoon. As El Niño surged in strength last autumn, record rainfall caused devastating floods in Chennai and other parts of South India.

Thanks go to international weather records researcher Maximiliano Herrera for India heat statistics above. Herrera maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

Bob Henson



Figure 4. People wade through a flooded street in Chennai, in the southern Indian state of Tamil Nadu, on Wednesday, December 2, 2015. Image credit: AP.

Extreme Weather El Niño La Niña

The Life-Saving Bonus from Greenhouse Gas Emission Cuts: Better Air Quality

By: Jeff Masters and Bob Henson , 3:21 PM GMT on May 02, 2016

Climate change mitigation is often portrayed as a burden, with any long-term benefits far in the future. That’s a misleading and inaccurate picture, as emission cuts can produce many benefits right out of the gate. Chief among those is the potential for improved air quality. When we burn less of the oil, coal and gas that produce heat-trapping gases such as carbon dioxide, there’s also an immediate reduction in the witch’s brew of other compounds that these fuels add to our atmosphere. Cutting this pollution could pay phenomenal benefits in public health, saving hundreds of thousands of lives. In the year 2013, outdoor air pollution was connected to about 2.9 million deaths globally, and about 80,000 deaths in the U.S., according to a 2016 study carried out by the University of British Columbia as part of the Global Burden of Disease project. The global toll was even larger when considering both indoor and outdoor air pollution: more than 5.5 million premature deaths. Two of the worst culprits are coal plants in China and indoor cookstoves in India, according to the report.



Figure 1. Pupils cover their noses after school in heavy smog on December 23, 2015, in Binzhou, China. According to the Ministry of Environmental Protection of the People's Republic of China, more than 50 cities, including Beijing, Tianjin, Shanghai and Guangzhou, were affected by severe air pollution. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

Clean Air Act has made a big impact in the United States
The U.S. has already made great progress in cutting back on some of our worst air pollutants. Lead--a terrible health hazard that still plagues water in cities around the nation, including Flint, Michigan--was once an airborne scourge as well: it poured into the atmosphere every time we pumped leaded gasoline into our vehicles. But a federally mandated switch to unleaded gas has almost eliminated unsafe levels of lead in the atmosphere, with reductions of more than 90% since 1980. More recently, updates to the Clean Air Act have led to big cuts in the emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC), which team up in the presence of sunlight to produce dangerous ground-level ozone. From 2004 to 2014, U.S. fossil-fuel emissions of NOX dropped 13%, and VOC a whopping 42%, according to EPA data.


Figure 2. Juxtaposed with the growth in many other indices of our industralized society--including carbon dioxide emissions--the United States has made noteworthy progress since 1970 in reducing the combined emissions of six common pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Image credit: EPA, courtesy American Lung Association.


Particulates are a particular concern
It’s been harder to cut down on the tiny airborne solids and liquids called aerosols, or fine particulate matter. These are produced by fossil fuel burning as well as wildfires and natural sources. Particulates smaller than 2.5 microns in diameter (0.0001 inch) can accumulate in the lungs and cause both short- and long-term trouble. This includes asthma, lung cancer, and other respiratory ailments, as well as cardiovascular disease, an air-pollution threat that’s gone from obscurity to infamy in the last 20 years. You may be surprised to learn that, according to the WHO, roughly 80% of the deaths related to outdoor air pollution in 2012 were from heart disease or stroke.


Figure 3. Particulates that enter our atmosphere from fossil fuel burning, wildfires, and other sources can be less than 2.5 microns (0.0001 inch) in diameter--smaller in diameter than beach sand or a human hair. These particles are small enough to enter the bloodstream and contribute to cardiovascular disease. Image credit: EPA, courtesy American Lung Association.

How many people does pollution kill?
Why is it that air pollution episodes that kill thousands of Americans don't receive the media attention that, say, hurricanes get? It’s because "premature deaths" caused by air pollution are only partly attributable to breathing bad air, while drowning in a hurricane's storm surge is entirely due to the hurricane, and is a much more dramatic event. Nevertheless, a great many children die of pollution-induced asthma attacks who would not have died otherwise, and the mortality due to air pollution in the general U.S. population is in the tens of thousands each year. The only way to see air pollution deaths is to analyze death rate statistics for multiple years, carefully filtering out other influences such as weather extremes. Over two thousand studies have been published in the scientific literature documenting the link between air pollution and higher death and hospitalization rates. Most of these studies concern fine particulate matter; recent studies have also documented higher death rates from ozone pollution.

Cutting emissions could prevent nearly 300,000 U.S. air pollution deaths by 2030
The startlingly large death toll related to pollution means there is great potential to save lives. A February 2016 study published in Nature Climate Change, "Climate and health impacts of US emissions reductions consistent with 2 °C", found that reducing U.S. emissions in the energy and transport sectors could prevent almost 300,000 early deaths caused by air pollution in the U.S. between 2015 and 2030, or about 20,000 per year. The reductions in pollution would also lead to about 29,000 fewer asthma attacks per year in children under 18 requiring emergency room visits, and save 15 million lost adult work hours per year. These benefits would require a reduction of air pollution emissions averaging 2.7% per year beginning in 2015, consistent with the U.S. pledge made at the Paris Climate Summit in 2015 to keep global warming less than 2 °C above pre-industrial levels. The researchers estimated that the saved lives and reduced health care costs would benefit the U.S. economy by $250 billion per year, and estimated that "benefits seem to outweigh costs by at least a factor of 5–10." Once you include the benefits of emissions cuts for reducing global climate change, these economic gains “roughly quintuple”, they said.

When one adds in the huge health and environmental costs associated with fossil-fuel extraction--such as oil spills, mountaintop removal for coal mining, and failures of coal ash ponds--the benefits of switching away from fossil fuel energy sources are even more dramatic.

How climate change could shape the face of U.S. air pollution
In case we need still more motivation to cut back on fossil fuels, there is also evidence that climate change itself may exacerbate certain types of air pollution. In the U.S., urban air pollution appears to be getting “spikier,” with heat waves, droughts, and wildfires worsening the worst episodes even as many cities experience cleaner air overall. In its 2016 State of the Air report, the American Lung Association noted that most of the cities plagued with high year-round particulate levels made real progress in 2015. Los Angeles had its record-lowest number of unhealthy days for both ozone and particulates. Yet seven cities saw their highest-ever number of days with unhealthy short-term levels of particulates. California’s Central Valley was the epicenter of this syndrome, with persistent high pressure, record heat, and a fourth year of drought gripping the region for much of 2015.


Figure 4. A view of the Los Angeles city skyline as heavy smog shrouds the city on May 31, 2015. Image credit: Mark Ralston/AFP/Getty Images.


More perspective comes from a major report released by the Congressionally-chartered U.S. Climate Change Research Program in April, The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. The report covers a wide range of health impacts, from heat and cold waves to vector-borne disease. Among the key findings in the chapter on air quality:

• Climate change will make it harder for any given regulatory approach to reduce ground-level ozone pollution in the future as meteorological conditions become increasingly conducive to forming ozone over most of the United States [Likely, High Confidence]. Unless offset by additional emissions reductions, these climate-driven increases in ozone will cause premature deaths, hospital visits, lost school days, and acute respiratory symptoms [Likely, High Confidence].

• Wildfires emit fine particles and ozone precursors that in turn increase the risk of premature death and adverse chronic and acute cardiovascular and respiratory health outcomes [Likely, High Confidence]. Climate change is projected to increase the number and severity of naturally occurring wildfires in parts of the United States, increasing emissions of particulate matter and ozone precursors and resulting in additional adverse health outcomes [Likely, High Confidence].

• Changes in climate, specifically rising temperatures, altered precipitation patterns, and increasing concentrations of atmospheric carbon dioxide, are expected to contribute to increasing levels of some airborne allergens and associated increases in asthma episodes and other allergic illnesses [High Confidence].

Check out WU’s Air Quality Awareness Week website
The U.S. Environmental Protection Agency (EPA) has designated the week of May 2-6, 2016, as Air Quality Awareness Week. Check out our special WU website with more background on AQAW, including the major pollutants tracked by EPA as well as safety tips to help reduce the risk of health impacts from outdoor and indoor pollution affecting you and others around you.

Jeff Masters and Bob Henson

Air and Water Pollution Climate Change


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

Category 6™

About

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