- 03/06/12

Parts of the Ohio and Tennessee Valleys are still in serious recovery mode from last week's deadly, one-two punch of severe weather.  144 tornadoes were reported last Friday, most occurring in Kentucky, Indiana, Illinois, and Tennessee.  The death toll stands at 39.  According to the Storm Prediction Center, there were more than 900 reports of severe weather (large hail, winds at or greater than 60 mph, large hail) on that day alone.

What might be forgotten in the crush of news from the outbreak on Friday is that just a few days prior, on the last day of February, another low pressure center took a similar path from the Plains toward the Great Lakes, spawning more than a dozen tornadoes in virtually the same places. 

Severe weather in March is not uncommon; in fact, the month typically heralds the beginning of the season.  However, what was uncommon about last week's outbreak is the number of tornadoes -- more in one day than typically reported in all of March -- and the location.  Usually, the severe weather season kicks off in the deep south: places like Texas and Oklahoma are first up.  That's because as warm air begins its annual northward march, it first encounters retreating winter air in southern locales before those further north.  But in this unusually warm winter, atypically warm air is making its way well north.  And it was in a zone of unusually warm air -- the high last Friday in Louisville, Kentucky, for example, was 74, twenty degrees above the average high for the date -- that the severe weather occurred.

Some scientists are saying that events like last week's severe weather outbreak will become more common earlier in the year, thanks to warming planet.  A story by the Reuters wire service earlier this week quoted a climatologist at the National Center for Atmospheric Research as saying that the severe weather may soon be begin in late February instead of early April, as it now typically happens.

The Reuters article also cited atmospheric experts at the Goddard Space Center and Purdue University as saying the central and eastern sections of the country can expect more thunderstorm days by the end of this century.  But the warmer atmosphere may also be a deterrent for tornadic storms, as a warmer, more uniform vertical temperature profile in the atmosphere is less conducive for the wind shear necessary to initiate the violently rotating winds. Read the entire Reuters article here: http://tinyurl.com/7f799f4