U.S. — (CNN) -- A blizzard that has hammered the Midwest is expected to weaken Friday.

But the road closures, school cancellations, power outages and travel delays spawned by the storm continue to cause widespread havoc and inconvenience.

Many people planning Christmas trips have been stuck at Chicago's two airports -- O'Hare and Midway -- because of flight cancellations.

"There is a long line of very unhappy people," said an air traveler quoted by CNN affiliate WLS. "It's not a good experience."

The heavy snows will "finally begin to wind down by Friday," the National Weather Service said. But heavy winds are expected to hammer the region Friday and Saturday as holiday travelers take to the roads and head to airports.

The storm is expected to move to the U.S. Northeast and southern Canada on Friday, but blizzard warnings have been discontinued. Light snowfall is expected to continue in a large area from the Ohio Valley to New England, forecasters say.

The severe weather has caused problems in many areas in the past few days.

Blinding snow is blamed for a 30-car pileup on Interstate 35 near Fort Dodge, Iowa. Two people died, including a 43-year-old Arkansas woman, Sgt. Scott Bright of the Iowa State Patrol said Wednesday.

At least 20,000 customers were without power in Iowa early Friday, most of them in the Des Moines area, MidAmerican Energy said.

The storm -- the first blizzard of the season -- made travel treacherous throughout the region. Nebraska authorities temporarily closed much of snow-packed Interstate 80 Thursday as blowing snow dangerously reduced visibility. The interstate was reopened later, but motorists were advised to be cautious.

Things were not much better in Iowa, Bright said.

"When the winds start to blow, you can see about 5 feet in front of your vehicle" he said. "We've had major issues all over the place. We got around 10 to 12 inches throughout the state, and it's a wet snow. We have around an inch of ice on our roadways."

Close to 100 accidents had been reported in Iowa by late Thursday morning, Bright said.

In Wisconsin, Gov. Scott Walker declared a state of emergency, put the National Guard and state patrol on standby and closed state offices to the public in 20 counties most likely to be affected by the storm. Employees were still expected to report for work.

As much as 7 inches was already on the ground Thursday in parts of southern Wisconsin. The Wisconsin State Patrol and National Weather Service urged people to avoid traveling.

CNN's Stefan Simons, Jim Kavanagh, Jareen Imam, Laura Smith-Spark, Carma Hassan and Joe Sutton contributed to this report.

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