Tuesday, July 11, 2017

Heavy Rainfall and Wind Threat for Some Tuesday night/Wednesday Morning

A Flash Flood Watch has been issued for Rock and Walworth counties beginning at 10pm Tuesday evening.  Current indications suggest that as a warm front begins to advance east out of Iowa, thunderstorms will develop along and north of the front late Tuesday evening.  This storm development looks to occur over south-central and southeast Wisconsin after 10pm Tuesday night, before shifting northeast over Lake Michigan.  Heavy rainfall, possibly due to training thunderstorms, strong winds and hail would all be possible overnight. 

However, this scenario isn't set in stone.  It's possible thunderstorms could develop a little further to the southwest, closer to Rockford and Janesville, before lifting northeast overnight.  If that happens, then our storm threat would increase after 10pm, but decrease once the warm front moved further north.

To complicate matters even more, thunderstorms are rapidly developing over Northern Dakota and western Minnesota this evening.  These thunderstorms are also forecast to form into a complex of storms after sunset and quickly race southeast through Wisconsin during the overnight.  Expected arrival time in southern/southeast Wisconsin would be just before or right around sunrise.  This, too, would pose a hail, wind and heavy rain threat through the morning commute, especially right near the Wisconsin/Illinois border.

Wherever the combination of thunderstorms from Tuesday night and Wednesday morning come together, rainfall totals will be very high.  Right now the highest threat for heavy rainfall, and possibly flash flooding, appears to be over southeast Wisconsin where three to four inches of rain could occur.

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