Thirteen tornados were reported Thursday in Kentucky, Indiana and Michigan, said Bob Oravec, a meteorologist with the National Weather Center's Weather Prediction Center in College Park, Maryland, but no immediate reports of serious damage.
Meteorologists referred to the storm as a bomb cyclone, a winter hurricane that forms when the barometric pressure drops 24 millibars in 24 hours.
At the height of the storm, two feet of snow was dumped in the mountain regions of Colorado, forcing the cancellation of more than 1,300 flights in Denver and leading to more than 1,000 motorists trapped on roadsides, with many having to be rescued by police using school buses to ferry them to safety.
There were no remaining blizzard warnings Friday, Oravec said.
"There's still a good threat of thunderstorms in Louisiana, Mississippi and up into the Great Lakes region as the system pushes into Canada, but it's not like it was," he said.
Most power outages were cleared by early Friday, according to the tracking site PowerOutage.US and air traffic was returned to normal at Denver International Airport, a regional hub hardest hit by the storm.
Flood warnings and watches remained in effect for Nebraska, Iowa and Michigan, forecasters said.
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