Tornadoes and giant hail kick off weeklong severe storm threat across Central US

By Meteorologists Chris Dolce, Briana Waxman and CNN’s Hanna Park

(CNN) — A week of severe storm threats across the Central US started with a bang Monday, with multiple tornadoes demolishing buildings in Kansas, heavy rain stranding vehicles on flooded streets in Wisconsin and hail up to softball size battering parts of four states. It’s part of a weeklong severe weather threat across the region – and today has the potential to be the most dangerous.

Tornadoes were confirmed Monday in eastern Kansas, northern Iowa, southern Minnesota and northern Wisconsin. Nearly softball-sized hail fell south of Minneapolis and damaging winds toppled power lines and trees in northeast Illinois.

On Tuesday, tens of millions of people from the Texas-Mexico border to the Great Lakes are at risk of seeing a severe storm, including in Chicago, Milwaukee and Des Moines, Iowa, where there’s a Level 3 of 5 threat for large hail, damaging wind gusts and tornadoes.

About a dozen states from Texas to the Upper Midwest and Great Lakes will see a threat of severe storms on one or more days through Friday. The threat zone will shift each day depending on where surges of jet stream energy mix with warm, humid air to trigger intense thunderstorms.

Dangerous flooding is also a concern, especially where rivers are already running high in water-logged northern Michigan and northern Wisconsin.

Tornadoes and giant hail

Monday’s most intense severe storms produced several tornadoes in eastern Kansas and dropped hail ranging in size from golf balls to softballs across southern Minnesota and central Wisconsin. More than 80,000 customers are without power in Wisconsin early Tuesday, according to PowerOutage.us, after rounds of severe thunderstorms blasted through overnight.

Multiple buildings were “demolished” after a tornado touched down in Kansas’ Linn County, Randy Hegwald, the county’s emergency management director, told CNN. A lake community southeast of Mound City “took a direct hit,” but only a few minor injuries have been reported, Hegwald said.

About 45 miles north, a tornado impacted dozens in the city of Hillsdale, Miami County Undersheriff Matthew Kelly told CNN. One minor injury has been reported, and emergency officials are working to arrange shelter for those displaced from their homes.

The storm also caused structural damage in nearby Ottawa, most of which was without power Monday night, according to Franklin County Emergency Management.

Senator Jerry Moran, who represents Kansas, said he was “hearing reports of potential tornado damage” in Ottawa and urged residents to heed warnings from weather officials.

Timing the severe storms

Going forward, the biggest concern continues to be large hail, which could dent cars, shatter windshields and damage roofs. The storms could also produce a few more tornadoes and winds strong enough to down trees and power lines.

Tuesday could have the most widespread number of severe storms. The storm threat zone spans from West Texas into Oklahoma and the Great Lakes.

Chicago, Milwaukee and Des Moines, Iowa, are under a Level 3 of 5 risk of severe thunderstorms that includes more than 14 million people.

The supercell thunderstorms that fire up in this corridor by late afternoon could have damaging hail the size of limes or bigger. A few tornadoes are also possible and they have the potential to be strong — rated EF2 or higher.

Strong winds capable of knocking out power and damaging or even uprooting trees are also possible as the storms blast eastward into the evening across Michigan and northern parts of Ohio and Indiana.

Wednesday is expected to bring yet another round of strong storms, but Tuesday’s leftover storms could affect how potent the threat becomes — the longer they stick around, the less time the sun has to heat the air and provide energy for new storms. Either way, wind damage and hail appear to be the biggest concerns rather than tornadoes.

And that’s not the end of this daily onslaught.

One more surge of jet stream energy will fire up a final round of potent thunderstorms on Friday, especially from Oklahoma to Iowa, but it’s too soon to determine how big of a punch they will pack.

The storm-weary central US will finally get a breather over the weekend because of a weather pattern change that will also usher in a temperature drop.

Flooding woes hit the Great Lakes

Flood watches are in effect for more than 3.5 million across northern parts of Wisconsin and Michigan, where multiple rounds of rainfall this week could aggravate ongoing river flooding and send more rivers surging.

As rain continues to fall early Tuesday morning, more than 1 million people are under flash flood warnings, including residents of Green Bay, Wisconsin and Traverse City, Michigan.

Significant street flooding has stranded vehicles and shut down several roads across central Wisconsin, according to the National Weather Service.

Authorities are urging residents near the Cheboygan County Lock and Dam in Michigan to prepare for possible evacuations as the dam’s water levels have risen due to melting snow and recent heavy rain.

Residents should prepare a “go-bag” with essentials, review evacuation plans with family members and be ready to act, the sheriff’s office said Monday.

“Water levels remain unpredictable,” the sheriff’s office noted in a post showing potential flooding projections. The areas at risk are along the Cheboygan River.

Water levels had reached 13.75 inches from the top of the dam as of 7 a.m. Monday. An evacuation order would be triggered if water levels reach an inch below the top, according to the Michigan Department of Natural Resources.

Flash flood warnings are in effect following water releases from the Tippy Dam on the Manistee River and thee Mio Dam on the Au Sable River in northern Michigan. Locations downstream from both dams “should be prepared for flooding,” the alerts said.

The Muskegon River near Evart, Michigan, is forecast to hit major flood stage — 14 feet — by Wednesday. Subdivisions along the river upstream from the town would see major flooding at that level and it could trigger “significant evacuations,” according to the National Weather Service.

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Meteorologist Dakota Smith contributed to this report.