Everything you should know about lake-effect snow

Lake-effect snow can produce very heavy snowfall rates, sometimes exceeding several inches per hour. Snowfall totals from a single lake effect event can reach several feet in extreme cases.

When lake-effect snow hits regions of the Great Lakes during late fall and winter, you start to hear meteorologists use terms like "feet of snow," "whiteout conditions," "blizzard" and "travel trouble."

That's because lake effect often results in significant snowfall. While the intensity can vary, lake effect can create challenging conditions with heavy, localized snowfall that can significantly impact transportation and daily life.

"Lake-effect snow develops when cold air moves over a relative warm, large body of water, most typically found in the Great Lakes," AccuWeather Snow Expert Grady Gilman explained.

This process begins when cold, dry air, typically from Canada, sweeps across warmer waters. Lake-effect snow events typically occur from the late autumn to the first part of winter when the Great Lakes are still unfrozen and the waters are warm, relative to that colder air flowing across the region.

As the frigid air moves over the lakes, it absorbs warmth and moisture from the water, transferring these elements to the lower atmosphere. This process causes the air to rise and condense into clouds, which can develop into narrow bands capable of producing intense snowfall rates of 2 to 3 inches per hour or more. The narrow bands also mean some areas can get buried in snow, while little to no snow may fall just a few miles away.

"Additionally at the ground surface, a body of water has less friction than land, so when air flows from over the open bodies of water of the Great Lakes and then inevitably over land, i.e low friction to high friction, the additional friction of land causes 'frictional convergence', which compresses and condenses the moist air which increases precipitation," Gilman added 

One of the biggest lake-effect snowfall events on record hammered areas near Buffalo, New York, with 5 feet of snow in a span of two days back in November 2014, resulting in the deaths of more than a dozen people. Hundreds of roofs collapsed, nearly a thousand motorists were stranded and food and gas shortages occurred due to impassable roads.

Dashcam footage shot by extreme meteorologist Reed Timmer showed intense snowfall and whiteout conditions rivaling any blizzard. Meteorologists at the National Weather Service office in Buffalo described snow total disparity in the November 2014 snow event, saying, "Over 5 feet of snow fell over areas just east of the City of Buffalo, with mere inches a few miles to the north."

Another, more recent lake-effect snowstorm of epic proportions dumped nearly 7 feet of snow across parts of New York in November 2022. Orchard Park received the highest storm total snowfall with a staggering 77 inches of snow over a 24-hour span.

Locations “downwind” of the lakes are where lake-effect snow typically occurs, with the general wind flow being west to east. This means places like Buffalo, Watertown and Syracuse, New York; Cleveland; Erie, Pennsylvania; Grand Rapids, Michigan; and South Bend, Indiana; are all prime locations. But lake-effect snow can happen anywhere there is a large amount of relatively warm water that can collide with cold air.

"Lake-effect snow sometimes falls more than 100 miles downwind of the Great Lakes. The mountains of New York state, western, central and northern Pennsylvania, the West Virginia mountains and western Maryland can all get a visit from lake-effect snow," AccuWeather Senior Meteorologist Alex Sosnowski explained.

The Great Lakes are notorious for lake-effect snow due to their locations relative to cold air outbreaks and warmer summer months, but even smaller lakes like the Great Salt Lake of Utah and the Finger Lakes in New York can produce lake-effect snow given the winds are in a favorable direction and the difference in temperature from the air to the lake water is great enough.

"Lake-effect snow can be extremely dangerous due to the intensity of snow it can produces, where upwards of 6 inches an hour can happen, but also due to the sudden changes in conditions a shifting lake-effect snow band can cause from even the subtlest change in wind direction," Gilman noted. "One location can have zero visibility and total white-out conditions while a few miles down the road it is partly sunny. In a matter of miles, a traveler can go from blue skies and visibility to the horizon to blizzardlike conditions with near-zero visibility." 

Lakes aren't the only places this snowy phenomenon can occur, Gilman elaborated. There’s also sea-effect snow. "Sea-effect snow is also a common phenomenon in parts of the world, namely Japan, where the same mechanisms are in place as lake-effect, but the moisture source instead of a lake is the sea."

The Chesapeake Bay and southeastern Massachusetts, especially Cape Cod, are both areas in the U.S. that can receive ocean-effect snow when all the necessary ingredients are aligned.

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