What is “lake effect snow”? Warm air from large bodies of water is the key ingredient

When cities along the Great Lakes become buried in drifts of blowing snow, as many have in recent days, weather experts start talking “the lake effect”.

Lake effect snow often forms in relatively narrow bands that dump large amounts of snow. The weather phenomenon can significantly increase snowfall totals, and it can hit one area and leave another untouched just a few miles away.

Over the weekend, parts of upstate New York, Pennsylvania, Ohio and Michigan saw nearly 4 feet of lake-effect snow.

Here is an overview of how it works:

In the United States, the lake effect typically begins when cold air – often from Canada – blows over the warmer waters of the Great Lakes.

The warm air from the lakes then pushes the moisture in the sky higher into an area more conducive to snowfall due to its temperature. This creates clouds capable of dumping lots of precipitation downwind, said Phillip Pandolfo, a meteorologist at the National Weather Service office in Buffalo, New York.

Most of the moisture needed for lake effect snow doesn’t actually come from the lakes, but rather from the cold air blowing over them.

“It’s a common misconception that lakes are a tremendous source of moisture,” Pandolfo said. “In practice, we actually need the air to contain enough moisture before it actually starts to flow across the lakes.”

Under the right conditions, rising, moisture-laden air causes clouds to form that could lead to “very intense snowfall,” Pandolfo said.

The results are usually thin bands of clouds that can produce heavy snowfall – 2 to 3 inches (5 to 8 centimeters) per hour and sometimes more. And because the bands are narrow, cities near each other could experience significant differences in snowfall totals.

Lake effect snow can be difficult to predict; Slight changes in wind direction can have a major impact on where the heaviest snow falls, according to the weather service.

Lake effect snow goes hand in hand with living near a Great Lake. In many cases a foot or two (30 to 61 centimeters) of snow will fall, but sometimes it can get out of hand.

In November 2022Lake-effect storms dumped more than 6 feet of snow in Western New York. These winter storms were the worst in New York since at least November 2014, when some communities south of Buffalo were hit with 7 feet (2.1 meters) of snow in three days, collapsing roofs and trapping drivers on a part of New York. York State Highway.

In parts of Michigan’s Upper Peninsula, snowfall can total more than 20 feet per year because the lake effect strengthens storms, according to researchers at the University of Michigan and Michigan State University.

The phenomenon can also occur with other very large lakes, including Utah’s Great Salt Lake.