Traffic moves through the falling snow down southbound I79 near Evans City, Pa. on Monday, Jan. 26, 2015. The snowstorm had already dropped three inches in the area as it moves across the northeast of the country. (AP Photo/Keith Srakocic)

PHOTOS: Northeast blizzard of 2015

The National Weather Service says accumulations of 18 to 24 inches are possible by Tuesday afternoon in several Northeast states.