DETROIT (AP) — The Arctic chill is gripping the Rockies and Upper Midwest — and it’s crawling east.

Sharp drops in temperature are expected in other parts of the U.S. in the coming days, thanks to a powerful weather system that hit Alaska with hurricane-force winds over the weekend before blanketing several states in snow.

A look at the system and its effects:

THE LINGERING COLD

Dangerously cold weather was expected to linger until Thursday in eastern Montana, where temperatures could reach as low as negative 30 degrees. Denver’s high was only was 5 degrees on Wednesday, a day after the snow-covered city broke a nearly century-old record for the lowest temperature ever recorded on a Nov. 11.

The frigid air was expected to crawl into the Appalachians, mid-South and the East Coast by Thursday. Forecasters have issued freeze and cold-weather warnings across parts of Texas, Louisiana, Mississippi and Alabama.

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.

Temperatures fell more than 30 degrees overnight in northern Illinois, from a high of 58 on Tuesday to 26 degrees on Wednesday. Similar swings hit Oklahoma City, where temperatures went from 80 degrees Monday to a low of 30 on Tuesday.

In the Dakotas, wind chill made it feel like 20 below in some places. But 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.”

SNOW, SNOW AND MORE SNOW

Parts of Michigan’s Upper Peninsula were buried in more than 3 feet of snow on Wednesday, with more snow forecast through the weekend, along with temperatures that dipped in the 20s and 30s. Up to 18 inches fell in northern Wisconsin, while parts of central Minnesota saw more than 16 inches of snow.

Many roads were snow-covered and slippery Wednesday in the Upper Peninsula, where residents are accustomed to snowy conditions. Of his drive into work, National Weather Service meteorologist Justin Titus said that roads were “just rutted out and kind of felt like you were driving over a washboard.”

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 being 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.

James Nord reported from Pierre, South Dakota.