The National Weather Service says the season's first lake effect snow is likely this weekend. That could be a harsh beginning to winter.
In the Great Lakes region, the effect kicks in when dry arctic air speeds over large expanses of warm water.
The air picks up evaporating moisture, freezes it and dumps it -- in great bands of snow -- over the land.
That means that cities that lie east of a lake -- like Buffalo, N.Y., Erie, Penn., and South Bend, Ind. -- can get hammered.
So how are conditions now?
Cold air -- check. A big blast is sweeping across the western plains, creating blizzard conditions in South Dakota, Nebraska and Iowa.
Meanwhile, the Great Lakes are much, much warmer than usual. Here are some recent harbor water temperatures:
Buffalo: 60, normal 54
Cleveland: 62, normal 56
Chicago: 60, normal 53
Duluth: 52, normal 44
That means ice isn't even likely to form on Lake Erie -- the shallowest of the Great Lakes -- for some time.
All that open water increases the chance for lake effect snow. So it could be a looooong winter.