Here's The Science Behind How Lake-Effect Snow Forms

L​ate-fall into winter is prime time for lake-effect snow in the Great Lakes, and while it's most common in that region, it can develop on other bodies of water as well.

There's a classic pattern meteorologists look for ahead of heavy lake-effect snow. The pattern features a sharp, persistent southward plunge of the jet stream anchored over the eastern U.S. by a gyre of low pressure over or near Canada's Hudson Bay. In this pattern, repeated rounds of cold air spill over the Great Lakes and manufacture bands of heavy lake-effect snow off of lakes Erie, Ontario, Huron, Michigan and Superior.

Warmer lake waters contrasting with colder air aloft creates the snowfall. By warm, we don't mean the lake waters are prime for swimming, but rather they are mild enough to create the proper temperature contrast with colder air above the ground in order to form clouds, then snowflakes.

Ideally, that setup will feature temperatures around 5,000 feet above ground that are at least 23 degrees Fahrenheit (13 degrees Celsius) colder than the lake temperature. The lake adds warmth and moisture which evaporates into the colder air above, resulting in condensation that forms clouds and bands of lake-effect snow.

This temperature contrast is most likely to happen from late fall into early winter before lake waters turn colder or even at least partially ice over, especially Lake Erie.

The bands of snow are often narrow, but can spread far inland at times. Lake-effect snow bands are much longer than they are wide. For example, in a span of 10 miles a driver might go from wide open visibility and no snow to near-whiteout conditions and then back to no snow after exiting the band.

Extreme totals are possible in hours or over many days. Multi-inch snowfall totals in a single hour are not unheard of in the most persistent lake-effect snow events where bands sit over one area for an extended time. It's the reason why many of the most extreme U.S. snowfall rate records have occurred during lake-effect snow events.

December 2022 was a reminder that extended bouts of lake-effect snow can create serious impacts. A blizzard-inducing snow band from Lake Erie waffled over Buffalo, New York, for almost 72 hours around Christmas, dumping up to 51 inches of snow on the metro area, burying roads, trapping motorists and shutting down the city's airport.

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

Lake effect can happen on smaller bodies of water too. We see occasional bouts of lake-effect snow from Utah's Great Salt Lake and Lake Tahoe along the California/Nevada border most winters.

Even smaller lakes can produce snow on rare occasions during extreme arctic cold outbreaks. One recent example was during a mid-January 2024 cold snap that allowed lakes in the Dallas-Fort Worth Metroplex to produce light accumulating snow.

O​cean-effect snow is also seen on occasion along the U.S. East Coast, especially along Cape Cod in Massachusetts.

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.