As arctic air invades the Lower 48 states and spreads eastward through the week, lake-effect snow showers and squalls will likely develop downwind of the Great Lakes beginning late Wednesday or Thursday.
An upper-level low-pressure system will set up over southern Canada, spinning bitterly cold west to northwest winds over the relatively warmer Great Lakes.
For lake-effect snow to develop, the air temperature about 5,000 feet above the surface must be at least 23 degrees Fahrenheit (13 degrees Celsius) colder than the lake temperature.
The temperatures of the Great Lakes are currently in the 40s, and this incoming arctic air mass will be more than cold enough to irritate the mild lakes.
In fact, lake temperatures are running warmer than they have at this time each of the last five years, according to NOAA's Great Lakes Environmental Research Laboratory.
The cold, dry air will pick up moisture and heat from the lakes, which will condense into clouds and dump snow downwind of the lakes.
Some localized, intense snow bands may form, especially off Lakes Erie and Ontario, due to an upwind connection with the upper Great Lakes and possibly even the Hudson Bay at times.
https://www.wunderground.com/news/lake-effect-snow-forecast-great-lakes-early-december-2016
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