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A Wisconsin tornado… in February?!

What was expected to be a low end severe threat yesterday across Illinois and southern Wisconsin became so much more. Wisconsin saw its first ever recorded February tornado. Here is the breakdown of this event.

This map shows a low pressure system bringing warm, moist air to Illinois and southern Wisconsin.

The morning of the event:
Off to the west in Minnesota, an intense low pressure system was set up, with a warm front draped over southern Wisconsin, Illinois, and Indiana, bringing multiple record high temps for that day as well. In the upper levels of the atmosphere, elongated high pressure, denoted by the zig-zags in the images below, were feeding in more warmth for the region.

Most notably, a warm and moist sector was noted across northern Illinois and southern Wisconsin, which could provide enough to spark some thunderstorms as the low pressure provided ample amounts of low-level shear and upper-level shear. Ahead of this event, The Storm Prediction Center issued a marginal risk (level 1 of 5) for the potential of damaging winds, some large hail, and perhaps a tornado. Much uncertainty lied in how much energy there would be for storms that could form.

Showers were noted across most of southern WI in the early afternoon, as seen in the radar loop below. Following a few hours of quiet weather, thunderstorms would spawn from Dubuque, Iowa to Quincy, Illinois, marching eastward. These storms occasionally had low-level rotation, especially in Illinois, where two tornadoes were reported near Henry, Illinois and Magnolia, Illinois. The thunderstorms that meandered in Wisconsin were no different, with some rotation being noted, and multiple tornado warnings having been issued for extreme southern Wisconsin. The thunderstorms continued to tap into the intense wind shear in the atmosphere, and one storm intensified and produced a tornado for the first time in February in Wisconsin’s history near Evansville, WI. This tornado would strengthen, and gain a level 2 tornado warning, denoting this tornado as “large and extremely dangerous” as it moved northeast across Rock County, and into Jefferson and Walworth Counties before weakening.

Radar loop courtesy of Weather Underground: https://www.wunderground.com/maps/radar/yesterday/spi

According to the National Weather Service in Milwaukee/Sullivan, Wisconsin, no tornado warnings had been issued in Wisconsin in February until this event. In fact, Wisconsin has never recorded a February tornado in its history. This NWS office issued 5 tornado warnings. Only 17 Severe Thunderstorms Warnings have been issued in WI prior to this event in February. 8 more Severe Thunderstorm Warnings would be added from this event.

This event is very intriguing, as for the past few weeks, the Midwest has been notably warm, but can be typical of an El Niño, and the El Niño pattern this year has been one of the stronger patterns ever recorded.

We’ve been warm and occasionally dry, which are typical El Niño conditions for our area.

The current warm stretch across the region will come to and end this weekend as a cold front moves through. For those who have been wanting snow this season, this year may continue to disappoint. Last year we were in a La Niña pattern. Compare that to the start of this year, where we are still in an El Niño pattern. For those enjoy these warm temps you have enjoyed this season so far, but for those snow lovers, it’s been a rough year.

—Cardinal Weather Service Forecaster Lance Huffman—

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