Here’s what to know about the lake-effect snow set to wallop Buffalo

A lake-effect snowstorm hit Buffalo on Nov. 17 and is expected to bring waves of heavy snow off of Lake Erie and Lake Ontario for several days. (Video: The Washington Post)
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Residents across western and northern New York are bracing for historic “lake-effect snow,” a storm set to engulf most of the region in a crippling white cloak. Waves of heavy snow are expected to wash off of Lake Erie and Lake Ontario and bury the metro areas in Buffalo and Watertown — and as forecasters project upward of four feet of snow, Buffalo is expected to take the brunt of the bitter blizzard conditions.

The heaviest snow is expected late Thursday through Friday night with snowfall rates of four inches per hour. But the snow will continue to pound the area for at least 48 hours.

Lake-effect snow warnings have been issued in the counties surrounding lakes Erie and Ontario, which includes the cities of Buffalo, Watertown, Niagara Falls and Oswego. The warnings go into effect at 7 p.m. Thursday and lift Sunday at 1 p.m. New York Gov. Kathy Hochul (D) declared a state of emergency effective Thursday morning ahead of the intense snowfall.

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For residents near Buffalo, massive snowstorms from lake-effect snow are normal. But those unfamiliar with the phenomenon may be asking: What exactly is lake-effect snow? Here’s what to know.

How does lake-effect snow form?

Lake-effect snow forms when dry, freezing air picks up moisture and heat as it moves along warmer lake water. This causes some of the lake water to evaporate into the air, causing the air to be warmer and wetter. As the air cools and moves from the lake, it dumps all the moisture on the ground. When it’s cold enough, it results in a massive dumping of snow.

The perfect recipe for lake-effect storms occurs during the late fall and early winter, when there is the largest difference between the warm lake water and the colder air moving over it. The bigger the temperature difference, the heavier the storm.

The sweet spot for storm formation occurs when temperatures at 5,000 feet above a body of water are at least 25 degrees colder than the lake water. Temperatures lower than 25 degrees can sometimes add enough energy to create thundersnow. Thundersnow can be especially intense, sometimes falling at a clip of two to three inches per hour or more.

The direction of the wind is also important. If the wind is blowing in a direction that covers more of the lake, the air will act like a large sponge that gulps up water from the lake and wrings it onto the land, according to the National Oceanic and Atmospheric Administration.

Wind direction also determines which areas will receive lake-effect snow. In some cases, heavy snow may be falling in one location, while the sun may be shining just a mile or two away in either direction, according to the National Weather Service.

This cold air needs to blow at least 60 miles over the warmer water to produce significant snow.

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Where does lake-effect snow fall?

Normally the precipitation is dropped within 25 miles of the lake, but it can travel up to 100 miles.

This snow falls from bands of clouds that average roughly 10 miles wide and maybe 300 or more miles long. Amounts of snow vary across a region, with the most snow usually falling on hills inland from the lakes.

Who is impacted most by lake-effect snow?

The National Weather Service says lake-effect snow accounts for 30 to 50 percent of the annual snowfall on the eastern and southern shores of the Great Lakes, a region famous for large amounts of snowfall.

Lake-effect snow frequently pummels the Great Lakes with feet of wet snow that can trap people in their homes and covers cars. The chilling events generally occur during the late fall and winter season.

Thanks to lake-effect snow, cities on or close to the Great Lakes — such as Syracuse, Rochester and Buffalo in New York, plus Erie, Pa.; Cleveland; Grand Rapids, Mich.; and Duluth, Minn. — are among the snowiest large U.S. cities.

A good deal of the early winter lake-effect snow that falls on Buffalo and neighboring Niagara Falls occurs when westerly winds blow across Lake Erie. When the lake freezes over, it cuts off that source of lake-effect snow.

Some large Great Lakes cities, including Detroit, Toledo, Milwaukee and Chicago, receive little lake-effect snow because they are on the west side of their lake, and the prevailing winds are from the west.

The heaviest lake-effect snow in the United States falls on the Tug Hill Plateau, south of Watertown, N.Y., at the eastern end of Lake Ontario, making this region one of the snowiest places in the United States.

Syracuse, which is south of Tug Hill, is one of the snowiest bigger cities in the United States.

Lake Ontario (802 feet at its deepest point) stays warmer than the relatively shallow Lake Erie (201 feet at its deepest). In addition, water from all of the other Great Lakes flows past Buffalo, over Niagara Falls and into Lake Ontario all year. This continuous water movement also helps keep the lake from freezing.

Will climate change affect lake-effect snow?

Human-caused climate change has the potential to intensify lake-effect snow events, at least in the short term, according to the NOAA’s U.S. Climate Resilience Toolkit.

“Ice cover extent and lake water temperatures are the main controls on lake-effect snow that falls downwind of the Great Lakes,” the tool kit states. “As the region warms and ice cover diminishes in winter, models predict that more lake-effect snow will occur. The predictions change once lake temperatures rise to a point when much of what now falls as snow will instead fall as rain.”