Sunday, April 17, 2011

La Nina and Tornadoes

With the destruction and deaths (43 so far) visited on the old Confederacy this weekend I was reminded of a few links that I had stored for a post and promptly forgotten.

La Nina is fading but NOAA's Climate Prediction Center doesn't expect ENSO neutral conditions until June.
Here's their most recent status and prediction report (April 11).
Here's the most recent Diagnostic Discussion.

Back on March 2 WVEC-Norfolk VA posted:
Spike in tornado activity likely in 2011 due to La Nina effect
NORFOLK – There’s new concern that Hampton Roads could see severe storms more often in this coming months.

It is well known that sea surface temperatures help shape the weather patterns around the world. Recent studies suggest that the coming months could bring increased bouts of severe weather to Hampton Roads.
The sea surface over the eastern Pacific Ocean is turning cooler, making conditions right for a La Nina event is developing. History suggests more severe storms and tornadoes may be in our forecast. In the last significant La Nina year, 2008, a tornado ripped through Suffolk on April 28, destroying homes and business. The damage was tremendous; the recovery continues to this day.

That tornado was one of 1,692 that spun across the United States that year.
In contrast, there 400 fewer tornadoes during 2010, an El Nino year.
The pattern is the same when reviewing conditions over several decades.

Nationally, there seems to be an increase in the intensity of the tornadoes and frequency of super outbreaks. Of the 15 largest tornado outbreaks between 1880 and 1990, all but one occurred during La Nina or neutral years. One of the largest more recent outbreaks also happened during a La Nina, on May 3, 1999 when 58 twisters devastated central Oklahoma.

Perhaps more troubling for our area is where the greater concentrations of tornadoes occur during La Nina years. Past events point to an increased focus of tornadoes right here in the Mid-Atlantic, along with the Ohio and Tennessee Valleys during the upcoming severe weather season....
There are a couple other sites that were on top of the connection, I'll link to them tomorrow.