Thursday, November 15, 2012

A Flip On Tornadoes

Despite our rather crazy weather this year in the Delaware Valley, you've probably noticed that there have been fewer severe weather episodes across Tornado Alley and across the Deep South, especially in comparison to last year when it seemed like there was a severe weather outbreak every other week.

2012 is on its way to possibly setting a statistical record for fewest tornadoes in the modern era (since 1950). As of November 13th, only 882 tornadoes have been officially registered as touching down in the US.

Last year had 1692, which was the second most on record to 2004's 1884.

Graphic courtesy of the Storm Prediction Center

One of the big factors in the tornadic drought this year has been...drought.

The heat ridge that permeated across the Midwest and Plains during the summer prevented supercell thunderstorms from developing across these areas. Supercell thunderstorms are the most common type of thunderstorm that produces tornadoes and the Plains is one of the larger tornado breeding grounds in the country thanks to its geography and access to Gulf of Mexico moisture, dry air punching downstream from the Rockies, and historical tendency for storm systems to track through the Plains to help produce severe weather.  The heat ridge bumped the primary storm track much farther north and limited tornadic outbreaks in prime severe weather season, late April on.

May, which is historically the busiest tornado month, was the quietest in the US since 2005 as roughly half of the historical average of tornadoes were reported.  Compared to 2011, when over 300 tornadoes were reported in May, 2012 was much quieter.  This trend continued into summer as June, July, and August were all significantly below average nationally in tornado counts. July, in fact, was the quietest of any month of July since the 1950's.

The lack of tornadoes is the unfortunate byproduct of a rather expansive dry spell over the Midwest and Plains that still continues...but the lack of tornadoes may ultimately lead to a record quiet year just a year after we flirted with a record active year.