AccuWeather reports winter will sound the retreat of cold air and snow over much of the nation for the second week of January.

Snowcover that has reached about two-thirds of the nation to start the year will not last due to an upcoming shift in steering-level winds.

These high-flying, high-velocity winds, known as the jet stream, will pull northward during the second week of the month, allowing temperatures to moderate, which in turn will melt a substantial amount of snow outside of ski country.

As the polar air retreats, milder Pacific air will flow in to takes its place.

According to AccuWeather.com's Long Range Team, headed by Expert Senior Meteorologist Paul Pastelok, "Temperatures are likely to swing 15 to 25 degrees above normal or more from a several-day to perhaps a week or more period from the northern Rockies, eastward to the interior South and much of the Midwest and at least part of the Northeast."

Temperatures will range from near- to above-normal for several days over the balance of the West.

There will be at least one location where the cold air will resist for a little while longer: northern New England. Bubbles of Arctic air will slip over the region from central Canada into the first part of next week.

There are signs, however, that the pattern will be "progressive." The warm-up for next week may not have the staying power of last winter.

"The cold air is likely to start building southward from western Canada later next week, probably first entering the northern Rockies," Mr. Pastelok said.

From there, the cold may push southward through the Rockies and eastward onto the Plains.

As this happens, the warmth will come into full bloom over much of the eastern third of the nation, including New England.

Exactly how the jet stream finishes its shuffle is uncertain for the second half of the month.

It is possible it will set up a major southwest-northeast storm track somewhere from the Mississippi River to the East Coast later in week two to week three of the month.

"The key to the storm track may be if the cold air drives well southward in the West," Expert Senior Meteorologist Jack Boston said. "If this happens, the storm track will set up more in the middle of the nation, which would be a good thing as far as moisture is concerned for the upper Mississippi Basin."

If the cold pushes more to the east over the middle of the nation, it would likely set up the storm track somewhere from the Appalachians to the East coast.