Snow combined with high winds to whip up blizzard conditions in much of Minnesota on Thursday, closing roads, snarling traffic, shutting down schools and sending hundreds of cars careening into one another and off the road.

And now the state is once again waking up in a deep freeze. The high temperature Friday will barely break 0, with bitter windchills making it feel like 25 to 30 below, said Jacob Beitlich, meteorologist with the National Weather Service in Chanhassen.

"But it will be a bright, sunny day," he said.

And the worst of winter might be over, according to meteorologist Paul Douglas.

"This is the last really cold day in sight," he said. "This past week, for number of hours below zero and the severity of the windchill, this week was the coldest of winter. I may be an optimist but I think this was the worst of it."

That hopeful note could be exactly what Minnesotans need after 40-50 mph winds created white-out conditions in south-central Minnesota and slick roads throughout the state. The State Patrol reported 654 crashes — the troopers' busiest day this winter. There were 87 people hurt but no reported fatalities or serious injuries, said Lt. Tiffani Nielson.

Three of those crashes involved State Patrol troopers who had stopped to help other motorists. In each of those cases, a passing motorist lost control and hit the State Patrol squad car, Nielson said. One trooper suffered minor injuries and drove himself to the hospital, she said.

A driver who slid off the road on Interstate 35E at County Road 96 in White Bear Lake was hit when he got out of his car and another vehicle lost control, Nielson said. "Although he was injured, it wasn't serious, which is just amazing," she said.

"Anyone outside their vehicle has no protection and in these conditions you just need to stay in the car and call 911," she added. "People want to get out of their cars and check for damage, but it's not worth risking your life."

By evening, motorists were mired in gridlock, with evening commutes taking twice, sometimes three times longer than usual. "They were packed like sardines," Nielson said, which meant fewer accidents as rush hour became a crawl.

The morning commute could bring more trouble, though.

In bitterly cold weather, road salt and chemicals aren't effective, Douglas said. "The colder the storm, the more dangerous the storm."

Although many areas only received 1 to 3 inches of snow, high winds swirled it with what was already on the ground to create blizzard conditions throughout much of southwestern and south-central Minnesota. Whiteouts made travel hazardous and closed highways for a time, including Hwy. 60 from Mankato to Worthington and Hwy. 71 near Redwood Falls.

The Willmar School District called back buses that serve rural routes and alerted families that they'd have to pick up their kids from school instead.

Many school districts in the areas of the blizzard warning called off classes, including Blue Earth, Comfrey, Fairmont, Redwood Falls, Sleepy Eye, St. James, Tracy and Windom.

Schools in Mankato, public and private, decided to send students home at 1 p.m. In St. Peter, schools let out at noon.

The arctic blast this week produced one benefit — extra wind power. The electric grid for 15 mid-continent states, including Minnesota, reported strong wind generation, including a record level of wind power at 10:22 p.m. Tuesday. That represented 13 percent of the electricity on the grid, said Andy Schonert, spokesman for the system operator. Minneapolis-based Xcel Energy, the nation's leading wind power utility, said its wind farms had a good output but didn't set a record.

The forecast for bitter conditions wiped out a ski, walk and snowshoe event that was scheduled for Friday evening at Terrace Oaks Park in Burnsville. The NWS is calling for a high of no more than 1 degree Friday, with most of the day spent in minus territory amid continued strong winds.

Star Tribune staff writer David Shaffer contributed to this report.

marylynn.smith@startribune.com

paul.walsh@startribune.com