Heavy snow and strong winds hammered parts of the central U.S. on Thursday and began moving into the Great Lakes region, knocking out power to tens of thousands of people and creating hazardous travel conditions a day after pummeling Colorado.

The spring blizzard — the second "bomb cyclone" storm system to hit the region in a month — left behind hundreds of canceled flights at Denver International Airport, along with wintertime temperatures and snarled traffic before blanketing parts of the Upper Midwest with up to 2 feet (0.61 meters) of snow.

Hundreds of schools canceled classes in Minnesota, Nebraska and South Dakota, where the governor closed state offices in much of the state for a second day Thursday because of dangerous road conditions.

The Minnesota State Patrol said it had responded to more than 500 crashes statewide since Wednesday, while the National Guard stood ready to rescue any stranded motorists.

"It's a mess out here. And that is an understatement," Minnesota State Patrol Lt. Gordon Shank said.

In Nebraska, the State Patrol sent additional troopers into the state's panhandle, and several highways were closed. Whiteout conditions were reported in western Nebraska and northwest Kansas.

Winter storm warnings were posted Thursday for northern Wisconsin and Michigan as heavy snow, strong winds, sleet and freezing rain moved into the region. The National Weather Service reported that daily snowfall records had already fallen in La Crosse, Wausau and Green Bay.

Records also were expected to fall in the Upper Midwest, Weather service meteorologist Steven Fleegel said. As much as 25 inches of snow had been reported in northeastern South Dakota, with snowfall forecast to continue into Friday in that state, Minnesota and southeastern North Dakota. Several highways and stretches of interstates were closed in the three states.

A "bomb cyclone" is a weather phenomenon that entails a rapid drop in air pressure and a storm strengthening explosively. Weather service meteorologist Mike Connelly said this week's storm system drew up moisture from the Gulf of Mexico as it moved out of the Rocky Mountains. He described the potential snowfall as "historic."

"This time of year (in) the central, southern Plains, you get severe weather — thunderstorms and tornadoes. Unfortunately in the Dakotas, we get feet of snow," he said.

Nearly 77,000 homes and business were without power across Minnesota, South Dakota, Iowa and Michigan Thursday, according to PowerOutage.us. The main culprit was snow and ice accumulating on power lines, along with strong winds, said Matt Lindstrom, spokesman for Minneapolis-based Xcel Energy.

In southwest Minnesota, the National Weather Service said there could be half an inch of ice accumulations and winds up to 50 mph (80.46 kph). At least three highways in the region had to be closed Thursday due to fallen power poles or lines on the roadway.

The system also created hazardous wildfire conditions in parts of Texas, Oklahoma and New Mexico.

The threat of severe weather will shift this weekend to southern states including Texas, Louisiana and Arkansas, including the cities of Houston, Dallas and New Orleans, according to the weather service's Storm Prediction Center. Threats will include damaging winds, large hail and tornadoes.

An unusual but not rare weather phenomenon known as "thunder snow" — snow accompanied by thunder and lightning — was reported Wednesday and Thursday in central South Dakota.

In addition to the immediate impacts, the storm threatened to swell rivers in the Midwest that flooded after March's drenching, which caused billions of dollars in flood damage in Nebraska, Missouri, Iowa and South Dakota. Forecasters aren't expecting similar flooding this time around thanks to the absence of a wet snowpack on frozen ground.

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Nicholson reported from Bismarck, North Dakota. Associated Press writers contributing to this report include Bob Moen in Cheyenne, Wyoming; Nelson Lampe in Omaha, Nebraska; Gretchen Ehlke in Milwaukee; and David Runk in Detroit.

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