Windiest Mac start in years; front could ignite t-storms

Veteran Mac racers will tell you it’s been some time since the Chicago to Mackinac race kicked off amid 20 m.p.h. sustained winds. That’s what’s predicted as the race gets underway at noon Saturday—making today’s open potentially the windiest in years. The gusty winds precede a cold front which is racing southeastward beneath an abnormally strong July jet stream bearing winds as high as 125 m.p.h. at its core. These powerful upper-level winds (at the 18,000 to 36,000 ft. level) threaten to lift Saturday’s moderately humid low 60° dew point air, producing scattered-coverage t-storms in the process. Computer energy calculations, which take into account moisture, the rate the temperature declines with height and the tendency for wind directions to vary through the atmosphere, suggest some storms may become active. They may occur almost anywhere, probably becoming most numerous in areas just west and south of Chicago.
--By Tom Skilling, WGN-TV Chief Meteorologist