When does ice cover shut down lake-effect snow?

An icy scene in Holland. (January 2018)


GRAND RAPIDS, Mich. (WOOD) — As of Monday, 23.5 percent of Lake Michigan was covered by ice — nearly double the ice cover this time last year and 20 times more than we saw at this time in 2016.

Map: Ice concentration on Lake Michigan as of Jan. 8, 2016, courtesy Great Lakes CoastWatch.
Map: Ice concentration on Lake Michigan as of Jan. 8, 2017, courtesy Great Lakes CoastWatch.
Map: Ice concentration on Lake Michigan as of Jan. 8, 2018, courtesy of Great Lakes CoastWatch.

But how much ice does there need to be to shut down lake-effect snow?

For lake-effect snow to form, cold air has to move over at least 62 miles of open, warm water. As our lakes freeze, different areas will see the lake-effect snow stop depending on what the wind direction is moving. Lake Michigan is so large that it takes a decent amount of ice to stop lake-effect snow from forming, especially when the wind is out of the northwest or the north-northwest.

Map: The distance a north-northwest wind covers over Lakes Superior and Michigan before reaching West Michigan.
Map: The distance a northwest wind covers over Lake Michigan before reaching West Michigan.
Map: The distance a west wind covers over Lake Michigan before reaching West Michigan.

Lake Erie also has an impressive fetch, but only when the wind is out of the south-southeast. When this happens, Buffalo, New York, gets hammered with snow, like it did in 2014.

Map: The distance a southeast wind travels over Lake Erie.

Not all of the Great Lakes are created equal. Lake Erie is the shallowest of the Great Lakes. This means it is usually the first to freeze. During this extensive outbreak of cold air over the eastern U.S., Lake Erie saw significant ice-gain. Last year at this time, Lake Erie had 22.1 percent ice concentration on its surface. This year, the cold has launched it to 87.2 percent ice coverage — much higher than any other Great Lake at this time.

Map: Ice cover on each of the Great Lakes as of Jan. 8, 2018.

The almost 90 percent ice coverage on the lake should be enough to stop the production of lake-effect snow. There is only a small span of open water left on the lake. It is difficult to tell for certain if it is shorter than the 62-mile threshold, but satellite imagery indicates the gap is too short for any lake-effect to form even if the wind was out of the favored southeast direction.

Map: Satellite imagery of ice cover puts the distance of open water at less than 60 miles.

This small area of open lake will likely grow and shrink in the coming days, but with so much ice already formed on Erie, it is highly possible this will be the end of the lake-effect for its shoreline residents.

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