AccuWeather forecasters issue a high risk for severe thunderstorms in Midwest

The atmosphere will remain primed for severe weather in portions of the central and eastern United States this week, and a large portion of the Heartland from central Iowa to the Upper Peninsula of Michigan will be at the greatest risk for damaging thunderstorms into Wednesday night, AccuWeather meteorologists warn.

The bulk of the thunderstorm activity in the Central and Eastern states this week has been on the periphery of a large dome of extremely hot air anchored over the Mississippi Valley and Plains. The heat dome has produced many 100-degree Fahrenheit high temperatures and uncomfortably warm nights for millions.

There were more than 340 reports of severe weather Monday, with most stemming from high wind incidents that extended from southern Wisconsin and northern Illinois to western Virginia and North Carolina, according to the Storm Prediction Center.

Winds damage reports across the central and eastern U.S. in the aftermath of severe weather that unfolded from Monday night into Tuesday.

Two long-track but small complexes of thunderstorms formed on the rim of the heat instead of one large intense derecho Monday. However, both complexes tracked over 240 miles and produced widespread high wind incidents which would suggest the storm system met derecho criteria along the way. More than 200,000 homes and businesses remained without power as of Wednesday midday in the wake of the storms, according to PowerOutage.us.

The ring-of-fire pattern will continue through Wednesday night as thunderstorms are forecast to extend from the northern tier of the Plains and Great Lakes southeastward to the central and southern Appalachians and portions of the Atlantic coast.

Another round of spotty thunderstorms, some locally severe, will pulse into Wednesday evening from South Carolina to Alabama.

However, a rare occurrence, with a high risk of damaging thunderstorms is forecast to ramp up by AccuWeather meteorologists for much of eastern, central and southern Wisconsin into Wednesday night. The high risk extends into the southeastern corner of Minnesota and the northeastern portion of Iowa. The majority of Wisconsin is under a tornado watch until 10 p.m. CDT Wednesday, per the National Weather Service.

"The main threat to lives and property in Wisconsin into Wednesday night will stem from high winds and large hail, but there is a risk for tornadoes as well," AccuWeather Meteorologist Matt Benz said. "The risk of tornadoes may be greatest in any thunderstorm that develops ahead of a solid line of storms." These discrete thunderstorms would stand the best chance of strong rotation.

The first tornado produced by the severe thunderstorms touched down in Oakdale, Wisconsin in the late afternoon hours Wednesday. Multiple tornadoes were reported between Oakdale and neighboring Tomah, Wisconsin, with a large tornado causing a partial closure of local highways I-90 and I-94. Highway I-90 continued to be stuck in a standstill in the early evening hours Wednesday, rerouting traffic for miles amid damage that includes multiple tipped over semi trucks.

In Mauston, Wisconsin, law enforcement confirmed tornado damage to a local hospital, with the severity of the damage unknown as of 6 p.m. CDT Wednesday evening. As of 6:53 p.m. CDT, over 100,000 Wisconsin residents were without power, according to PowerOutageUS.

"Right now there looks to be a corridor from near the Mississippi River on northeast into the Upper Peninsula of Michigan that should see at least some sunshine break through the clouds which then will charge up the atmosphere for thunderstorms to develop from Wednesday afternoon through the evening," Benz said.

Wausau, Rhinelander and La Crosse, Wisconsin, will be smack in the middle of the tornado and high wind threat into Wednesday evening, forecasters say.

After 4 p.m. CDT, the National Weather Service called for residents in northern Juneau County, Wisconsin, to take shelter immediately, warning of a "very strong, dangerous tornado on the ground."

"The tornado is rain-wrapped! You may not see it approaching. Do not risk it -- take shelter!" the NWS office in La Crosse, Wisconsin, said over Twitter.

At Chicago O'Hare Airport, travellers were advised to stay away from windows as a tornado warning hit the area at approximately 5 p.m. CDT.

Rapidly changing weather conditions that include a moderate risk of severe thunderstorms will extend ahead of a cold front from Lake Superior to central and southern Iowa. Locally severe storms will be possible as far south as southern Kansas and as far north as central Ontario, Canada.

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Wind gusts in the strongest storms, aside from any potential tornadoes, will range between 40-70 mph with an AccuWeather Local StormMax™ wind gust of 90 mph possible. Hail the size of golf balls or larger, which can dent siding on homes and vehicles as well as break glass, can also occur in the more intense storms.

The worst of the storms are likely to occur well north and west of Chicago through Wednesday evening. The Windy City was peppered with tornado warnings as a complex of severe thunderstorms rolled through Monday evening. Winds gusted to 84 mph at O'Hare Airport and the same complex brought wind gusts to 98 mph in Fort Wayne, Indiana, late Monday evening. Locally severe storms could make there way to the Chicago Lakefront later Wednesday night.

Cooler and less humid air in the wake of the front on Thursday will mark an end to excessive heat that resulted in a string of days that produced highs well into the 90s and low 100s over the central U.S.

While the intensity of the severe weather is likely to peak over the Upper Midwest into Wednesday evening, storms are likely to re-fire and still pack a punch farther to the east Thursday.

Rising air ahead of a strong cold front will trigger potentially damaging and dangerous thunderstorms and perhaps isolated tornadoes from much of New York to southern West Virginia and western Virginia during Thursday afternoon and evening, according to AccuWeather meteorologists. Potent storms may also extend farther to the south over the Appalachians.

The forward speed of the cold front may prevent significant thunderstorm activity along the Eastern Seaboard Friday. As a result, New York City and Boston may totally avoid the threat of severe weather that has plagued so many locations in the Midwest and the East this week.

Thunderstorms that erupt in parts of the Southeast could become locally severe Friday. Thunderstorms may also pester parts of the central Plains and middle Mississippi Valley as warm and more humid air tries to return at the end of the week.

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