An unusual, fast-moving line of severe storms appears to have spawned numerous small, short-lived tornadoes across southeast Wisconsin on Wednesday, the National Weather Service said.
There were no immediate reports of major damage or injuries as a result of the storms.
Nearly 22,000 We Energies customers were left without power after the storms rolled across the region. By late afternoon on Wednesday, that number had been reduced to 2,600 customers without power, the Milwaukee-based utility said.
A tornado outbreak in mid-October is unusual for southeast Wisconsin, said Tim Halbach, warning coordination meteorologist with the National Weather Service in Sullivan.
“It’s nothing that’s unheard of, but it’s just not as often that we see this kind of activity this time of year,” Halbach said. Peak tornado season in southern Wisconsin typically occurs in June, July and August.
Halbach said the weather service was working on Wednesday afternoon to confirm how many tornadoes occurred.
Several of the storms on Wednesday produced what is known as tornado “debris signatures” on Doppler radar, Halbach said. Those radar images indicate that the storm was lofting debris into air as the radar was also detecting an area of rotating winds.
“We saw a number of those (debris signatures) as the line (of storms) came through,” Halbach said.
“Our expectation is that we had a bunch of very weak tornadoes,” Halbach said. “We haven’t had any reports of substantial damage. They were pretty short-lived.
“That is a typical scenario with the weaker-type tornadoes,” he added.
At midday on Wednesday, the national Storm Prediction Center said tornadoes had been reported in or near Brown Deer, Pewaukee, Whitewater, Elkhorn, Franksville and Burlington.
A 73 mph wind gust was reported near Cudahy in Milwaukee County and 60 mph gusts were reported near Hartford in Washington County and Delavan in Walworth County.
Residents posted images on social media from throughout the region of snapped and downed trees as well as patio furniture that was blown over and shingles ripped from roofs.
More:13 tornadoes touched down in Wisconsin in one day in June.
The storm system was the result of clashing air masses, with warm moist air out ahead of a strong cold front that swept through the region.
While forecasters were expecting unsettled weather on Wednesday, they were not expecting a tornado outbreak, Halbach said.
“The ingredients came together for about an hour or two here to produce these short-lived spin-ups,” Halbach said. “There was enough wind shear to produce these spin-ups along the cold front.
“We weren’t really forecasting tornadoes for today,” Halbach added.
There was little, if any, lightning with the storms, Halbach said.
資料來源：[Milwaukee Journal Sentinel]美國威斯康森州昨日受龍捲風吹襲 超過2萬民眾失去電力供應