Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 15:13 GMT le 27 avril 2011
The nation's unprecedented April tornado-fest continued full force last night, with NOAA's Storm Prediction Center logging 57 tornado reports, 295 cases of damaging thunderstorm winds, and 254 reports of large hail. The 2-day tornado count from this latest huge April tornado outbreak is already 102. With another "high risk" forecast for tornadoes today, the tornado total for this week's outbreak may rival the April 14 - 16 tornado outbreak (155 confirmed tornadoes) as the greatest April tornado outbreak in history. It is unprecedented to have two such massive tornado outbreaks occur so close together, and the April preliminary tornado count of 654 is truly stunning. Even adjusting this number downwards 15% (the typical over-count in preliminary tornado reports) yields a probable April tornado total of 550. This easily crushes the previous April tornado record of 267, set in 1974. An average April has "only" 163 tornadoes, so we are already 300% over average for the month, and may approach 400% after today's outbreak. According to a list of tornado outbreaks maintained by Wikipedia, only two other tornado outbreaks have had as many as 150 twisters--the May 2004 outbreak (385), and the May 2003 outbreak (401). One positive note--there has only been one violent EF-4 or stronger tornado this year, despite the fact we've already had about 2/3 of the 1200 tornadoes one typically gets for the entire year. Over the past 20 years, we've averaged 7 violent EF-4 or EF-5 tornadoes per year, so we should have had 4 or 5 of these most dangerous of tornadoes so far this year.
Figure 1. Satellite image of last night's storm at 8pm EDT April 26, 2011. Image credit: NASA/GSFC.
Fortunately, no one was killed in last night's tornado frenzy, but four twisters caused injuries, with 7 injuries in Hesterman, Mississippi, and 3 in Beekman, Louisiana. Over 100 homes were damaged when a tornado struck Edom, Texas, approximately 75 miles East of Dallas. One woman was injured when her mobile home was destroyed. The only killer tornado of the current outbreak occurred on Monday night at 7:30 pm CDT when a 1/2 mile-wide EF-2 tornado struck the small town of Vilonia, Arkansas. Four people died in the town, where 50 - 80 buildings were destroyed. Tornado warnings were issued 30 minutes before the storm hit, contributing to the relatively low loss of life.
Figure 2. Storm chaser video of a tornado yesterday in Ben Wheeler, Texas.
Another very dangerous tornado outbreak expected today
The busiest April in history for tornadoes continues full-force today, as NOAA's Storm Prediction Center has issued their highest level of severe weather potential, a "High Risk" forecast, for Northern Alabama, Southern Tennessee, and adjoining portions of Georgia and Mississippi. This is the second day in a row, and third time this year, that SPC has issued a "High Risk" forecast. The devastating North Carolina tornado outbreak of April 16, which generated 52 confirmed tornadoes that killed 24 people in North Carolina and 2 people in Virginia, was the other "high risk" day. Numerous tornado warnings have already been issued in Tennessee, Kentucky, Georgia, Mississippi, Arkansas, Ohio, and Alabama this morning, but today's main action is expected to erupt late this afternoon as the cold front from a low pressure system currently over Arkansas moves eastwards over the "high risk" area. Strong daytime heating in a very moist, unstable airmass will allow a tremendous amount of energy to build up ahead of the front. The arrival of the cold front will force the warm, moist air upwards, allowing the pent-up energy to burst out and fuel supercell thunderstorms.
Related post: Are tornadoes getting stronger and more frequent?
Figure 3. Severe weather threat for Wednesday, April 27, 2011.
Unprecedented flooding predicted on Ohio River
This week's storm system, in combination with heavy rains earlier this month, have pushed the Ohio River and Mississippi River to near-record levels near their confluence. The Ohio River at Cairo, Illinois is expected to crest at 60.5 feet on May 1. This would exceed 100-year flood stage, and be the highest flood in history, besting the 59.5' mark of 1937. Heavy rains of 10 - 15 inches have inundated the region over the past few days, and one levee breach at Black River levee near Poplar Bluff, Missouri, has resulted in the evacuation of over 500 homes. Poplar Bluff has received 15.45" of rain since Friday morning. The greatest rain gauge-measured precipitation from the storm occurred in Springdale, Arkansas, where 19.70" inches has fallen since Friday morning.
Figure 4. The latest River Flood Outlook from NOAA shows major flooding is occurring over many of the nation's major rivers.
Extraordinary intentional levee breach of Mississippi River halted by lawsuit
In a sign of just how extreme this flooding situation is, yesterday the Army Corps of Engineers, which is responsible for flood control efforts on the Mississippi River, announced plans to intentionally destroy a levee protecting the west bank of the Mississippi River in Southwest Missouri. The destruction of the levee is intended to relieve pressure on the levees at Cairo, Illinois, at the confluence of the Mississippi and Ohio Rivers. Cairo is currently under a voluntary evacuation order. The levee to be destroyed, located at Birds Point, is called a "fuse-plug" levee, and was designed to be destroyed in the event of a record flood. The levee protects 132,000 acres of prime farmland along the New Madrid Spillway, which is designed to take 550,000 cubic feet per second of water flow out of the Mississippi and redirect it down a 3 - 10 mile wide, 36 - 56 mile long path along the west side of the Mississippi. An 11-mile long section of the levee upstream at Birds Point, and 5-mile long stretch at the downstream end, are set two feet lower than the surrounding levees and filled with holes to accommodate dynamite. These levees will be destroyed if the Army Corps has its way, but a lawsuit by the state of Missouri is currently blocking the way. The Army Corps has now agreed to wait until Saturday to decide whether or not to blow the levee. The Army Corps' website has an unofficial damage estimate of $100 million for destroying the levees and flooding the New Madrid Spillway. At least 100 people live in the spillway and have been evacuated, and it would likely take many years for the farms to recover after flooding. The levees have been blown and the spillway opened only once before, back during the record flood of 1937.
Midwest deluge enhanced by near-record Gulf of Mexico sea surface temperatures
The deluge of rain that caused this flood found its genesis in a flow of warm, humid air coming from the Gulf of Mexico. Sea surface temperatures (SSTs )in the Gulf of Mexico are currently close to 1 °C above average. Only two Aprils since the 1800s (2002 and 1991) have had April SSTs more than 1 °C above average, so current SSTs are among the highest on record. These warm ocean temperatures helped set record high air temperatures in many locations in Texas yesterday, including Galveston (84°F, a tie with 1898), Del Rio (104°F, old record 103° in 1984), San Angelo (97°F, old record 96° in 1994). Record highs were also set on Monday in Baton Rouge and Shreveport in Louisiana, and in Austin, Mineral Wells, and Cotulla la Salle in Texas. Since this week's storm brought plenty of cloud cover that kept temperatures from setting record highs in many locations, a more telling statistic of how warm this air mass was is the huge number of record high minimum temperature records that were set over the past two days. For example, the minimum temperature reached only 79°F in Brownsville, TX Monday morning, beating the previous record high minimum of 77°F set in 2006. In Texas, Austin, Houston, Port Arthur, Cotulla la Salle, Victoria, College Station, Victoria, Corpus Christi, McAllen, and Brownsville all set record high minimums on Monday, as did New Orleans, Lafayette, Monroe, Shreveport, and Alexandria in Louisiana, as well as Jackson and Tupelo in Mississippi. Since record amounts of water vapor can evaporate into air heated to record warm levels, it is not a surprise that incredible rains and unprecedented floods are resulting from this month's near-record warm SSTs in the Gulf of Mexico.
Figure 5. Departure of sea surface temperature from average for April 25, 2001. Image credit: NOAA/NESDIS.
Fierce winds fan Texas, New Mexico fires
Fierce winds fanned raging fires across eastern New Mexico and Western Texas yesterday, thanks to a powerful flow of air feeding into the Midwestern storm system. Temperatures in the upper 80s and low 90s combined with humidities less than 10% combined to make yesterday a nightmare fire day for firefighters attempting to control the worst springtime fires in the history of the region. At 3:53 pm MDT yesterday in Carlsbad, New Mexico, the temperature was 87°F, winds were 38 mph gusting to 46, and the humidity was 8%--a perfect storm for extreme fire weather. In Fort Stockton, Texas near the huge Rock House fire, the temperature was 91°F, winds were 35 mph gusting to 44, visibility was reduced to 5 miles due to haze and smoke, and the humidity was 5% at 5:53pm CDT. According to the Interagency Fire Center, wildfires in 2011 have already burned nearly 2.3 million acres in the U.S. This is the greatest acreage on record so early in the year, and is more area than burned all of last year. The largest U.S. acreage to burn since 1960 was the 9.9 million acres that burned in 2007, so we area already 25% of the way to the all-time record fire year--with summer still more than a month away. The fire weather forecast for today is better then yesterday, with winds not expected to blow nearly as strong.
Figure 6. Major wildfires and smoke plumes as visualized using our wundermap with the "fire" layer turned on.
For those who want to lend a helping hand to those impacted by the widespread destruction this month's severe weather has brought, stop by the portlight.org blog.
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