A bitterly cold air mass has formed far to the north, and it will rush southward through Canada Sunday and Monday. Expect the cold to reach the northern Plains and Upper Midwest Tuesday, then enter the eastern part of the United States during the middle of next week.

This will be an extremely cold arctic outbreak with temperatures averaging 10 to 15 degrees below normal across the Midwest, Ohio Valley and Northeast. The cold air is here to stay.

Story by AccuWeather.com Meteorologist Rob Richards.