71.   Cold air in the panhandle will mark the leading edge of arctic air spilling south across the central Plains.

72.   Clouds and patchy light snow will occur in Montana and Wyoming near the boundary between the Arctic air and milder air to the south and west.

73.   Clouds will then increase from the southwest as the arctic air begrudgingly retreats from the approaching storm, while sunshine prevails across eastern New England.

74.   Despite the snow, temperatures will be milder than in recent days as Pacific air gradually replaces the arctic air in place over the region.

75.   Essentially, lake-effect snowstorms derive their energy from the large temperature contrasts that exist between the lake water and overriding arctic air.

76.   Every winter, moistened Arctic air crossing open waters is forced to rise over the ridge, setting the stage for a few hundred inches of snow.

77.   Farther north, snow showers will develop near the Great Lakes as Arctic air is moistened by evaporation from relatively tepid waters.

78.   Farther south, arctic air will retreat across parts of the southern New England and northern Middle Atlantic states, but the retreat will be short-lived.

79.   Farther west, a cold front marking the leading edge of a surge of Arctic air will move across the Great Lakes states.

80.   Farther north, Arctic air over Canada stood ready to knife south into near-record warmth.