Lower and/or drier air temperatures tend to reduce the number of thunderstorms.
With all the talk about last summer’s drought, most people may not have realized that another weather anomaly was also in play. Namely, the lack of moisture in the Plains and the Midwest suppressed tornado activity significantly. And Accuweather.com is reporting the cool spring weather might continue to suppress the number of tornadoes for 2013.
Current findings show that only 197 tornadoes of EF1 strength or greater occurred from May 2012 to April 2013. The year-to-date tornado count is currently less than half of the 8-year average.
"Since 1954, the previous low 12-month period was from June 1991 to May 1992, when 247 tornadoes with EF1 strength or greater occurred," says NOAA research meteorologist Harold Brooks.
One culprit may be the large storms emerging from the Rockies, which create a wedge of cool air that forces the base of the clouds much higher off the ground. The result not only limits tornado formation but also limits damaging wind gusts because the primary action is happening several thousand feet in the air. Unfortunately, the pattern can still produce storms with hail.
As spring temperatures continue to climb, Accuweather predicts a general uptick in the number of thunderstorms, severe thunderstorms and tornadoes. But the incidence of these events should remain "well behind the curve" of the average.
Weather watchers aren’t only looking at the number of tornadoes expected, but also where they might occur. Randy Mertens, a climate expert at the University of Missouri, says that higher sea temperatures in the central Pacific Ocean will shift the jet stream pattern eastward over Tennessee, Kentucky, eastern Missouri, Illinois and Indiana. That means that this year’s "Tornado Alley" is well eastward of where it normally lies.