Severe thunderstorm risk spreads after spate of tornadoes hits the Midwest

A widespread risk of severe weather covers parts of northeastern and central states into the weekend after an outbreak of tornadoes hit the Upper Midwest and Corn Belt earlier this week.

About 20 tornadoes slammed that region amid severe weather that also brought large hail and damaging winds. The strongest tornado, an EF3 with 140 mph winds, hit Tuesday near Hillsboro and Union Center in Vernon County, Wisconsin. An EF1 tornado hit Ann Arbor, Michigan, early Wednesday near Interstate 94, while hail between baseball and softball size pummeled the north side of Madison, Wisconsin.

A much broader severe weather risk is slated for Friday; that threat will once again stretch from Wisconsin to Oklahoma and unleash winds nearing 75 mph.

By Sunday, a brief lull in storm chances will ensue as cooler, drier air overspreads the nation’s midsection. But another batch of storms will arrive as early as Wednesday or Thursday next week and - as is typical this time of year - could be severe.

Outlook for Friday

A widespread risk zone stretches from Wisconsin to the central and southern Plains. A cold front will crash southeast into a mass of warm, humid air, helping to generate storms. There’s also a dryline, or the leading edge of dry air from the Desert Southwest, impinging on moisture to the east.

Both boundaries will effectively combine, plowing into a juiced-up air mass ahead of them and creating storms. Initial storms may be rotating supercells, and changing winds with height will help them to rotate. That’s why, early in storms’ life cycles, they may be able to produce a couple of tornadoes - especially in Wisconsin, near the surface low, and perhaps with any prefrontal storms that form to the east in Illinois.

However, the cold front will quickly overtake storms, causing them all to merge into a windy squall line. Tornado and hail risk will decrease, though a few spin-up tornadoes are still possible. Instead, widespread 60 to 75 mph wind gusts will accompany the squall.

Outlook for Saturday

A few leftover storms in Ohio may produce quarter-sized hail and 60 mph wind gusts, though tornadoes are not expected. Pittsburgh is also included in the risk zone.

A busy week for tornadoes

There have now been 356 tornadoes reported in the United States so far this year.

That’s an increase of more than 40 since last week.

On Monday, injuries were reported during tornadoes in Kansas. Then on Tuesday night and early Wednesday, eight tornadoes were reported in Michigan, with two causing damage near Detroit.

Ten tornadoes were also reported in southern Wisconsin on Tuesday evening, with structural damage occurring in some areas west of Milwaukee.