What’s behind the Nationwide Outbreaks of Deadly Tornadoes?

The enormous loss of life associated with the 2011 tornado season thus far is truly staggering.

After the Joplin, Mo., tornado May 22 and the recent outbreak in the southern Plains near the end of last week, the number of fatalities has risen to 504.

Over the last 31 years, only two times have tornado deaths risen above 100 for the full season: 130 in 1998 and 125 in 2008.

The unusually high death toll from this season’s storms is likely a result of the fact that some of the most intense storms have made direct hits on large populated areas (Tuscaloosa, Ala.; St. Louis, and Joplin, Mo., are standouts). It is also true that with 1,200 storms already reported, we may be seeing a record season for tornadoes. The current record is 1,819 storms in 2004 with the 31-year average being 1,105.

Currently we are investigating the hypothesis that tropical weather systems many days and thousands of miles upstream of the Midwest can play a central role in shaping the jet stream – a major ingredient necessary for tornado outbreaks. To the extent that this connection exists, then a warmer globe may well increase the likelihood of such outbreaks in the future as stronger springtime jet streams may result from a warming of the sea surface in the western tropical Pacific Ocean.

The atmosphere is a delicately balanced machine and, as hard as it may be to believe at times, slight perturbations to the global temperature may have such notable consequences.

Category: Severe Weather
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