Monday, hurling cows into the sky, flattening buildings and killing three people in the area, officials and witnesses said Tuesday.
But police who did have notice took to the streets honking horns and shouting warnings for residents to take cover, a move that may have saved dozens of lives as the storm, which struck around 9 p.m. (10 p.m. EDT), demolished the business district in the northwest Wisconsin town of 900.
An 80-year-old woman, an elderly man of undetermined age and a 60-year-old man died in a rural area outside the town, said Byron Higgin, editor of the Burnett County Sentinel in nearby Grantsburg.
The Burnett County Sheriff's Office confirmed the three deaths.
Higgin said the tornado warning siren at Siren was knocked out of commission several weeks ago by a lightning strike but the town's police chief, Dean Roland, "went through the community like a town crier" before the storm and people "had enough warning."
Higgin said the town now "looks like World War Three. On the main street there's maybe one or two buildings not touched. They had built a brand new hockey arena and it's gone, completely gone.
"There's a gas station that's nothing but a frame. The laundromat's gone, the garage. The community theater - a fourplex - collapsed and people had to be rescued from it. Almost all the trees are gone."
Higgin estimated that perhaps 150 people were made homeless by the storm.
He said there was severe damage to two settlements west of Siren - Falun and Alpha.
"There were cows flying through the air and landing dead" at Alpha, he said. The scene along state Route 70 from Grantsburg to Siren is about 12 miles of "pure destruction," Higgin said.
"It's 10 times worse than the worst explosion you can imagine," said Patrick Taylor, Burnett County's medical examiner.
Tom Wick, chief executive of the Burnett Medical Center in Grantsburg said the hospital had treated about a dozen people during the night for minor cuts and bruises and all had been released.
Two elderly people had been stuck in their basement until Tuesday morning, more than 12 hours after the Monday evening storm, but they were fine, said Dennis Quinn, a firefighter from a nearby town who came to help.
Search teams were still checking other homes and businesses Tuesday to make sure no one else was injured or trapped, Quinn said.
Wisconsin Gov. Scott McCallum declared a state of emergency Tuesday in Burnett and neighboring Washburn counties.
The twister cut a path of damage about a half-mile wide and at least 20 miles long, sheriff's officials said.
The same storm also spun out a tornado that struck a few minutes earlier in Braham, Minn. No injuries were reported but some 600 customers lost electrical service.
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