A bitterly cold air mass has formed far to the north, and it will rushsouthward through Canada Sunday and Monday. Expect the cold to reach thenorthern Plains and Upper Midwest Tuesday, then enter the eastern part of theUnited States during the middle of next week.This will be an extremely cold arctic outbreak with temperatures averaging 10to 15 degrees below normal across the Midwest, Ohio Valley and Northeast. Thecold air is here to stay.

Story by AccuWeather.com Meteorologist Rob Richards.