A man walks in Laramie, Wyo., Wednesday, Dec. 4, 2013. Laramie, the home of the University of Wyoming, sits in a valley between two mountain ranges and could see temperatures dip to 29 below Wednesday night and early Thursday. The record low for Dec. 5 at Laramie is 33 below set in 1972. (AP Photo/Laramie Daily Boomerang, Jeremy Martin)

DENVER - The jet stream hunkered to the south Wednesday, promising to bring nearly a week of temperatures that could dip to -29 Celsius or worse in the northern midsection of the country, and forcing much of the rest of the nation to deal with unexpectedly cool temperatures.

The wintry blast delighted Rocky Mountain ski resorts, some of which surpassed 250 centimetres of snow for the season Wednesday. But the cold snap had public-safety officials warning of elevated avalanche risk and frostbite risk to anyone outside.

In Minnesota, the cold forced Salvation Army bell ringers inside and cancelled holiday parties, while dense, cold air sunk into Rocky Mountain valleys and kept some lower elevations freezing in the West. A Christmas parade planned for Friday in the Colorado town of Erie was cancelled.

The dip in the jet stream is allowing Arctic air to plunge deeper into the United States. To add to the cold weather trouble, AccuWeather senior forecaster Paul Walker said a new storm will likely develop in New Mexico and west Texas on Thursday and head east, bringing ice and potentially power outages.

Extreme cold is nothing new in the Rockies, with temperatures regularly dropping each winter to -29 or -32 annually. The difference this year is how long the cold snap is expected to last.

National Weather Service meteorologist Dave Bernhardt said the last extended cold period in Montana he could recall was in the winter of 1996.

Low temperatures in Denver were expected to drop below -18 through Friday but remain below -7 through the middle of next week. The storm dumped several centimetres of snow in Denver, and parts of Colorado's mountains could get up to 90 centimetres by the end of the day. Heavy overnight snow cancelled a men's World Cup downhill training in Beaver Creek because the skiers need a clean, slick surface to practice on.

Snowfall totals could also approach 90 centimetres in northeastern Minnesota, where the weather has contributed to hundreds of traffic accidents around the state, including at least five fatal crashes since Monday. Two other fatal crashes in Montana and North Dakota were blamed on the weather.

At the Denver Zoo, which was closed due to the weather, the polar bears were playing and lying in the snow and the Mongolian camels seemed friskier than normal, spokeswoman Tiffany Barnhart said. But many other animals remained in the indoor section of their quarters, close to their hay beds. Workers kept the lions occupied with toys and videos of African predators.

"It's a snow day for them too," she said.

The risk of frostbite was high for people doing every day activities, like waiting for a bus, unless they're bundled up. Tyler Elick wore a hat and gloves as he played with his dog, Coconut, in a parking lot downtown.

"It's fun, but my cheeks are frozen, so I may be slurring my words," he said.

Colorado homeless shelters opened extra beds, and Denver Police checked under bridges in search of homeless who may have been in danger.

Laramie, the home of the University of Wyoming, sits in a valley between two mountain ranges and could see temperatures dip to -34 early Thursday. The record low for Dec. 5 at Laramie is -36, set in 1972.

In Montana, the cold spot will be the northern city of Havre, with low temperatures expected to dip as low as -34 between Thursday and Saturday. The city isn't expected to get warmer than -21 degrees during that period.

In California's Central Valley, temperatures dropped into -7 overnight into Wednesday, not enough to cause any damage to citrus crops. Citrus farmers, however, are anticipating colder temperatures overnight and Thursday and are continuing to take precautions, said Bob Blakely, of California Citrus Mutual.

News from © The Associated Press, 2013