Dear Tom,
You’ve mentioned that winter thunderstorm tops are lower than those in summer. How tall were the thunderstorms that spawned last month’s Poplar Grove tornado?
David Franks, Elmhurst
Dear David,
The devastating twisters that raked areas from Rockford to Kenosha on Jan. 7 were spawned by severe thunderstorms that towered to 50,000 feet.
Normally in this area, winter thunderstorms seldom reach 35,000 feet — considerably lower than those of their summer counterparts, which often soar to more than 50,000 feet. Less surface heating and limited atmospheric instability are two of the primary reasons for the diminished winter cloud heights.
But on Jan. 7, as temperatures rose to 65 degrees, enough lift was generated to allow the thunderstorms to reach 10 miles into the atmosphere.
In comparison, the highest cloud tops in Tuesday night’s tornado outbreak across the South reached 55,000 feet, an impressive level any time of the year.
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