DENVER - The jet stream hunkered to the south Wednesday, promising to bring nearly a week of temperatures that could dip to 20 below or worse in the northern midsection of the country, and forcing much of the rest of the nation to deal with unexpectedly cool temperatures.

In Minnesota, the cold has forced Salvation Army bell ringers inside and canceled holiday parties, while dense, cold air sank into Rocky Mountain valleys and kept some lower elevations below freezing in the West.

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 potential power outages.

Extreme cold is nothing new in the Rockies, with temperatures regularly dropping each winter to minus 20 or minus 25 degrees. 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 are expected to drop just below zero through Friday and remain below 20 through the middle of next week. The storm dumped several inches of snow in Denver, and parts of Colorado's mountains could get up to 3 feet by the end of the day. Heavy overnight snow canceled a men's World Cup downhill training in Beaver Creek because the skiers need a clean, slick surface to practice on.