If there's open water there can still be lake-effect snow (temperature is irrelevant in that aspect).
The only thing that limits lake effect snow is a frozen lake.
Ideally, a difference in temperature between the lake and the air of 15 degrees or more (the lake being the warmer of the two) creates this phenomenon.
Because the lakes are still relatively warm in the late fall months, lake-effect snow is often thought of as a late-fall/early-winter event.
While this may typically be the most active period, it is certainly not the only time lake-effect snow can occur.
A mild start to the winter that keeps the lakes warmer than normal coupled with an Arctic blast can keep the lake-effect machine running well into the winter months (as was the case in Oswego County New York in early February 2007).
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