Tornadoes, severe thunderstorms kill nine in OK, AR; more severe weather today

Posted by: JeffMasters, 1:07 PM GMT on April 15, 2011

Tornadoes and deadly severe thunderstorms tore through Oklahoma and Arkansas last night, killing at least nine people. The action began Thursday afternoon, when a powerful spring low pressure system intensified over western Kansas. The intensifying storm pulled in frigid Canadian air behind it and warm, moist Gulf of Mexico air in front of it, and where two air masses collided over eastern Oklahoma, a powerful cold front spawned a dangerous squall line of severe thunderstorms late Thursday afternoon. Doppler radar indicated the spinning signatures of mesocyclones inside numerous thunderstorms, and the National Weather Service began issuing multiple tornado warnings. At 6:22pm CDT, storm spotters reported a wide "stovepipe" shaped tornado had touched down in south-central Oklahoma four miles south of Milburn in Johnson County. Huge hailstones up to 4 1/2 inches in diameter--the size of softballs--began pelting the ground. The tornado roared to the northeast, ripping through the small town of Tushka, population 350, at 7:23pm. The powerful twister ripped off the roof of the local high school and destroyed dozens of buildings in Tushka, killing two people and injuring 25. The tornado moved over farmland and dissipated a short time later, but the squall line that spawned the tornado moved into Arkansas overnight, spawning severe thunderstorm winds that killed seven more people. The nine deaths made yesterday the deadliest severe weather outbreak of 2011.

Figure 1. Radar reflectivity image of the Tushka, Oklahoma tornado at 7:16pm CDT in Atoka County, seven minutes before the twister hit the town. Note the classic hook-shaped echo of the parent mesocyclone in the rotating severe thunderstorms that spawned the tornado.

Figure 2. Doppler radar velocity image of the Tushka, Oklahoma tornado at 7:16pm CDT in Atoka County, seven minutes before the twister hit the town.

The Tushka tornado brings this year's tornado death tally to five people, which is low for mid-April. In total, yesterday's severe weather outbreak had 10 tornado reports, 122 instances of large hail greater than 2" in diameter, and 91 reports of damaging winds. The action shifts eastwards to Mississippi and Alabama today, which NOAA's Storm Prediction Center have placed under its "moderate risk" region for severe weather. This is the same risk Oklahoma had during yesterday's tornado outbreak. You can follow today's outbreak using our severe weather page and interactive tornado map. This map now shows links to Youtube storm chaser videos of tornadoes, plus any wunderphotos taken of the storm. Tornado warnings have already been posted in Louisiana, Alabama, and Mississippi today. A report visible on our tornado page indicates that a tornado touched down just west of Jackson, Mississippi near noon EDT today, crossing Interstate 20 and ripping the roof off of a bank in Clinton, MS.

Figure 3. Satellite image from 23:03 UTC (5:03pm CDT) April 14, 2011, showing the strong low pressure system over the Plains that brought yesterday's severe weather outbreak. Image credit: NASA/GSFC.

Figure 4. Storm chaser video of the Tushka tornado.

Jeff Masters