Looking at the current wind patterns across the U.S. (see earth.nullschool.net), one notices a swath of west winds stretching from the northwestern Great Plains to New England. Dipping through the southern Great Lakes, this swath crosses Lake Michigan and Lake Huron and runs across the entire extent of Lake Erie.
Since the surface waters of the Great Lakes have not yet frozen (and often don't as our climate has warmed), the air is significantly colder than the water, causing the air to absorb moisture. As the air is forced to rise by land east of the Lakes, it cools below its dew point and precipitation occurs.
Buffalo, New York, at the east end of Lake Erie, is expected to receive up to five feet of snow. Three to four inches of snow per hour, accompanied by strong winds, lightening and thunder, will shut down the city and, perhaps, set an all-time record for a lake-effect snow event.
