Why Are We Getting So Many Tornadoes?

Bill's Blog
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There’s been 371 tornadoes in the U.S. in the last two weeks. 

  The total for the year is 855 through May 29 (add two from yesterday – one in Maryland and one in New Mexico).  Yesterday was a relatively quiet day and we still had 108 severe reports, including 3″ diameter hail near Llano TX and winds over 70 mph at Gainesville VA.   The map below shows all the tornado warnings that were issued over a 7-day period from May 23-29.  In just a week 45 local NWS forecast offices issued a combined 423 Tornado Warnings for portions of 27 states.

What’s causing all the tornadoes.  Here’s two maps that show the difference in U.S. temperatures between May 2018 and May 2019:

This is May 2018.  Almost the entire country was warmer than average.  The contrast in below and above average temperatures was in the desert Southwest – where they hardly ever get thunderstorms in the spring.  With the desert being a little cooler than average and the surrounding areas warmer than average, there would have been less temperature difference between the hot lower elevations and the surrounding higher elevations…the result was a calm month with little severe weather.  Now look at this month:

Wow!  Look at the difference.  It’s quite the contrast from record heat in the Southeast to significantly colder than average from the Canadian border to the Southwest.  Look at where the warmer than average meets the colder than average…from TExas and Louisiana north to the Ohio Valley and the mid-Atlantic.  That’s been the thunderstorm superhighway this month with flooding rains and lots of tornadoes and severe weather. 

The latest 8-14 day temperature outlook from the Climate Prediction Center has less contrast, but some…so the tornado and severe storm count nationwide should settle down to at least average (if not a little below average) numbers. 

This is the severe weather probability map for June 17.  This is near the maximum time for severe weather in Lower Michigan over the course of the year.  Note the highest probabilities remain in the Plains states (Kansas).  ‘There is also a relatively high probability over E. Indiana and Ohio (where they just had several EF3 tornadoes).

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