Here’s the science behind how lake effect snow forms

Late fall into winter is the prime time for lake-effect snow in the Great Lakes, and while it is most common in this region, it can also develop on other bodies of water.

There’s a classic pattern that meteorologists look for before heavy lake snow. The pattern shows a sharp, sustained southward plunge of the jet stream anchored over the eastern United States by a low pressure vortex over or near Canada’s Hudson Bay. In this pattern, repeated rounds of cold air pour over the Great Lakes, producing bands of heavy lake-effect snow off Lakes Erie, Ontario, Huron, Michigan and Superior.

Warmer lake water contrasted with colder air aloft results in snowfall. By warm we don’t mean that the lake’s water is suitable for swimming, but rather that it is mild enough to create the right temperature contrast with the colder air above the ground to form clouds and then snowflakes.

Ideally, this environment will have temperatures about 5,000 feet above the ground that are at least 23 degrees Fahrenheit (13 degrees Celsius) colder than lake temperature. The lake adds heat and moisture, which evaporates into the colder air above, causing condensation that forms clouds and streaks of lake-effect snow.

This temperature contrast is most likely to occur from late fall to early winter, before lake waters become colder or even at least partially ice over, particularly in Lake Erie.

The snow bands are often narrow, but can at times extend far inland. Lake effect snow bands are much longer than they are wide. For example, a driver could go from wide visibility and no snow to near snow-free conditions within a 10 mile distance and then return to no snow again after leaving the band.

The length of the snow bands varies from tens of miles to more than 200 miles, depending on the strength of the wind that carries them inland.

Extreme sums are possible in hours or over many days. In the most persistent lake effect snow events, where bands lie over an area for an extended period of time, snowfall totals of several inches in a single hour are not uncommon. This is why many of the most extreme snowfall rate records in the United States occurred during lake-effect snow events.

December 2022 was a reminder that widespread snowfall in the form of lakes can have serious impacts. A blizzard-triggering band of snow from Lake Erie swept across Buffalo, New York, for nearly 72 hours around Christmas, dropping up to 51 inches of snow across the metropolitan area, burying roads, blocking motorists and closing the city’s airport.

Over a 10-day period from February 3 to 12, 2007, Lake Ontario produced an incredible 141 inches of snow in the town of Redfield, New York, about 50 miles northeast of Syracuse.

The lake effect can also occur in smaller bodies of water. Most winters we see occasional bouts of lake-effect snow from the Great Salt Lake and Lake Tahoe in Utah along the California-Nevada border.

Even smaller lakes can produce snow in rare cases during extreme Arctic cold outbreaks. A recent example was during a cold snap in mid-January 2024 that allowed lakes in the Dallas-Fort Worth metroplex to produce light snow accumulations.

Marine snow also occasionally occurs on the East Coast of the United States, particularly along Cape Cod in Massachusetts.

Chris Dolce has been a senior meteorologist at Weather.com for over 10 years, having started his career at The Weather Channel in the early 2000s.