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Posted at 10:10 AM ET, 04/27/2012

Super tornado outbreak of April 27, 2011: one year anniversary


Tornado touchdowns in the U.S. from April 25-28, 2011. Map by Katie Wheatley. View bigger. (USTornadoes.com)
Today marks the one year anniversary of one of the most violent, widespread and deadly tornado outbreaks in U.S. history. 208 tornadoes touched down - the most on record in a single day. 316 people died - the 5th most in a single day.

April 27 marked the pinnacle of what was actually a multi-day outbreak spanning April 25-28, with 358 confirmed tornadoes in 21 states. With total damages around $11 billion, it was the costliest outbreak in U.S. history.

What made the outbreak so devastating was not as much the number of tornadoes, but the number of highly destructive tornadoes. As the website USTornadoes.com documents:

On April 27, 15 violent tornadoes rated EF-4 [on 0-5 scale] or higher (including four EF-5s) struck the states of Mississippi, Alabama, Tennessee and Georgia. Alabama was the hardest hit, with 9 violent tornadoes touching down there, and 11 total crossing within its boundaries. The top two deadliest tornadoes in April since modern records began hit that day.

Link: Videos of the violent EF-4 and EF-5 tornadoes of April 27, 2011

Prior to the 4 EF-5 twisters on April 27, 2011, there had only been two confirmed EF-5 tornadoes since the implementation of the Enhanced Fujita (EF) scale in February 2007.


Radar sequence of tornado supercell thunderstorms that tracked from western Mississippi into southwest North Carolina. (Brian Tang)
Alabama, the state affected most profoundly by the outbreak, suffered 252 fatalities. The long-track EF-4 tornado (on the ground for 80.7 miles) that struck both Birmingham and Tuscaloosa killed 64 people and injured more than 1500.

Link: Alabama tornado outbreak visuals: jaw-dropping radar and satellite imagery

Alabama T.V. meteorologist James Spann, who earned widespread recognition for his outstanding coverage of the outbreak, worked with his station (ABC 33/40) to produce the following dramatic and moving video:

Video from ABC 33/40: Alabama’s generational tornado outbreak of April 27, 2011. Death toll was 252, so much suffering.

Link: Alabama tornado outbreak: why did so many people die?

The outbreak was triggered by a powerful jet stream carving a deep trough in the western U.S. before charging East towards the South Central U.S. Warm, moist air out ahead of the jet collided with cooler, drier air behind it setting up a volatile, unstable atmosphere.

Link: Tornado outbreak for the record books: how did deadly, destructive event happen and what does it mean?

Video: Jet stream evolution (500 mb loop) of April 25-28 outbreak from USTornadoes.com

According to the Weather Channel’s Dr. Greg Forbes, the combined paths of all the tornadoes from the outbreak totaled over 2,600 miles - greater than the distance from Atlanta to San Francisco.

Northern Virginia-Maryland effects

On April 27 and 28, 19 tornadoes touched down from northern Virginia to northern Maryland. Most of these tornadoes were not destructive, but small spin-ups, rated EF-0 or EF-1. In the Washington, D.C. metro area, tornado watches were in effect for nearly 24 consecutive hours. 38 tornado warnings were issued during this time frame.

Link: April 27-28, 2011 tornado outbreak: Numerous tornadic storms impacted the D.C. region as well

By  |  10:10 AM ET, 04/27/2012

 
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