National Weather Service United States Department of Commerce

A potent cyclone brought rather harsh weather to the Upper Midwest on November 11 & 12. Though the most extreme weather occurred in Iowa (On the 11th, the Des Moines airport saw a tornado, followed by snow 6 hours later!), southern Wisconsin got in on the action as well. In southern Wisconsin, the primary impacts were from the winds, which came in two different phases; thunderstorm winds during the evening of Nov 11, and gradient (low pressure induced) winds through the day of November 12.


Round 1: Thunderstorms

Typically in November, southern Wisconsin struggles to get enough warmth and moisture to support thunderstorms, but usually has no trouble with the other requirements for thunderstorms (lift, wind shear). That proved to be the case yet again on Wednesday, as extreme amounts of lift and wind shear were in place, but there was very little in the way of warmth and moisture. However, the approaching low pressure system was able to pump just enough warmth and moisture into the state (and plenty of lift and shear to compensate for the lack of moisture) to initiate a few lines of thunderstorms.

Surface analysis, 8 pm, Nov 11 Radar loop from 6 - 10 pm, Nov 11


By evening on the 11th, a severe thunderstorm watch had been issued for portions of southern Wisconsin. Shortly thereafter, the storms pushed into the area and severe thunderstorm warnings were issued over the next few hours. While most of the severe weather occurred just to the south and west of Wisconsin, there were several reports of winds to around 50 mph in southern Wisconsin, and a few reports of damage, likely coming from winds in excess of 55 mph. Additionally, there were multiple reports of pea sized hail around the Milwaukee metro area, and 1 report of quarter sized hail in Big Bend.

Storm reports from Nov 11


Round 2: Gradient Winds

By sunrise on the 12th, the deep low had moved to the northeast of Wisconsin, leaving a substantial pressure gradient in its wake. This can be seen by the tightly packed isobars in the below image. The force resulting from this pressure gradient gave rise to very blustery winds across the region. In fact, wind advisories were in effect for much of the Upper Midwest, and gale or storm warnings were in effect for all of Lake Michigan. Across south central and southeastern Wisconsin, there were several reports of wind gusts in excess of 45 mph, and a few greater than 50 mph.

Surface analysis, 8 pm, Nov 11 Storm reports from Nov 12