The Arctic chill that has gripped the Upper Midwest and Rockies is spreading.

Other parts of the U.S. are expecting sharp drops in temperature in the coming days from a powerful weather system that hit Alaska with hurricane-force winds over the weekend. The system has dumped 2 feet or more of snow in some places.

A look at the system and its effects:

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SNOW, SNOW AND MORE SNOW

As much as 25 inches of snow blanketed parts of Michigan's Upper Peninsula, and more is expected before the storm ends Wednesday. Up to 18 inches fell in northern Wisconsin and parts of central Minnesota saw more than 16.

Upper Peninsula residents are a hardy bunch, accustomed to snowy conditions. Houghton County's roads were snow-covered and slippery Tuesday night, but sheriff's Sgt. Cort Rajala said most people were taking the weather in stride, driving cautiously or staying inside.

The National Weather Service said the snow would taper Wednesday except for some lake-effect snow, mainly in Michigan.

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SNOW DAY DREAMS DASHED

The early wintry weather in the Midwest this week gave Principal Lynn Grewing an opportunity to test a virtual classroom; she asked students of St. Cloud Cathedral high school in central Minnesota to work from home using laptops or iPads.

Grewing said her students' cherished snow days are now a thing of the past.

"This is what we will be doing every single snow day going forward," she said. "I'll be honest. There has been some grumbling."

Private schools such as Cathedral, as well as some public school districts nationwide, are starting to use the flexibility that technology provides to meet school mandates without needing makeup days when bad weather keeps students at home.

Cathedral senior Tommy Auger said doing classwork at home using his school-provided MacBook Air didn't feel very different to a day in class. Once they got over the initial disappointment of missing a snow day off, Auger said he and his classmates agreed they would rather skip a day of sledding than make up the missed school days in the summer.

"It's hard to think ahead, but it's definitely better," he said.

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THE COLD

The unseasonably low temperatures were spreading, with the cold air in the Rockies and Midwest spilling into the Pacific Northwest. The chill was expected to hit the Appalachians and mid-South by Wednesday morning and the East Coast by Thursday.

In Billings, Montana, where temperatures fell from the high 60s into the single digits on Tuesday, Patsy Kimmel said she was warned about the weather before arriving from Oklahoma to celebrate her 70th birthday with family.

"Yesterday I was wearing sandals and a short-sleeve shirt, and today I'm wearing a coat and scarf and turtleneck and sweatshirt and gloves," she said.

In the Texas Panhandle, temperatures plunged from 70 degrees into the teens overnight. Oklahoma City went from a high of 80 degrees Monday to a low of 30 Tuesday morning.

In the Dakotas, wind chills made it feel like 20 below in some places. That was good news for Action Mechanical Inc. of Rapid City, South Dakota, a heating and ventilation business that was doing booming trade.

"Bang! We get this arctic blast, and it just opens the floodgates," said John Hammond Jr., a department head. "We're behind right now as we're sitting here talking."

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DON'T BLAME THE POLAR VORTEX

Meteorologists are adamant the weather isn't because of the polar vortex, a giant upper air pattern that normally pens in cold air in the Arctic in the winter. Instead, they say it's pushed in by a different weather phenomenon more related to the remnants of a powerful typhoon.

"The polar vortex itself has not moved south. It's still in the Arctic where it always is," said National Weather Service spokeswoman Susan Buchanan.

Whatever the case, the cold is expected to linger. Some regions will go from record warm to record cold in just two days, with temperatures dropping 15 to 20 degrees below normal on the East Coast Friday and Saturday. Freezing temperatures will likely dip as far south as Atlanta on Friday, said Jeff Masters, meteorology director of the Weather Underground.

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Nord reported from Pierre, South Dakota.

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Associated Press writers contributing to this report include Kyle Potter in St. Paul, Minnesota; Seth Borenstein in Washington; Matt Brown in Billings, Montana; Kevin Burbach in Bismarck, North Dakota; David Runk in Detroit; and Gretchen Ehlke in Milwaukee.