That's the sound of the temperature dropping early this week as a batch of cold air moves from the Tennessee Valley and lower Midwest over to the East Coast.
There will be 3 to 9 inches of new snow to go along with that from the Virginias to Massachusetts, the National Weather Service said. Much of it is expected to fall in the daylight hours Tuesday.
Add the areas that are frigid already, and the eastern half of the nation will shiver through temperatures 10 to 25 degrees below average.
The vast area is expected to stay in the icebox until the weekend. That can mean lows in the teens in Memphis, Tennessee, and in the single digits from Louisville, Kentucky, to Boston.