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Lake-effect snow: What is it? Why does it happen?

Lake-effect snow as a person in black trudges through deep snow with an umbrella.
Lake-effect snow is common around the Great Lakes region. Image via NOAA.

According to the U.S. National Weather Service, an Arctic airmass brought cold temperatures and lake-effect snow to southwest Lower Michigan around January 6-7, 2022. Some eight to 14 inches (20 to 35 cm) of snow fell overnight across Michigan’s Berrien County – on the eastern edge of Lake Michigan – with 48-hour totals of 19 to 24 inches (48 to 61 cm) across far northern/ northeast Berrien County.

The cause was lake-effect snow, a common occurrence in the U.S. Great Lakes region during late fall through winter. It happens when cold air moves over a warmer body of water (such as a Great Lake). Then, the warmth and moisture of the lake transfers to the lower atmosphere. Ultimately, clouds build and release snow downwind. Places on the downwind side of the Great Lakes can easily get two to three inches (five to eight cm) of snow per hour.

The great video below shows moisture being pulled from Lake Superior around January 9, 2022, setting up conditions for lake-effect snow.

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Lake-effect snow: An interview with Tom Niziol

With this in mind, EarthSky interviewed Tom Niziol, a winter weather expert, a few years back. He said that accurate forecasting of lake-effect snow is a challenge because:

… [Lake-effect snow] occurs on such a small scale, almost on the scale of a summertime thunderstorm. One portion of a neighborhood or city might be under heavy snow, where a few miles away you may be under sunny skies.

He said Buffalo, New York, on the eastern shore of Lake Erie, is notorious for its lake-effect snowstorms. Niziol said cold air moving in from Canada triggers the snowfall.

As that air moves across the warm water of the Great Lakes, heat and moisture from the lake rises up into that air mass. That moisture eventually condenses out into snowflakes. And when we get to the downwind shores, we end up with lake-effect snow.

In addition, Niziol said similar snowstorms happen around the globe. The coasts of the United Kingdom, France, Japan and Korea, for example, get what’s called ocean-effect snow, from cold air moving across warm seas.

So at a whole range of latitudes in the Northern Hemisphere, right around the globe, we see the same activity.

Lake-effect snow causes locally heavy snowstorms

Previously, Niziol gave an earlier example of how dramatic lake-effect snow can be.

In early December 2010, in the western New York area around the city of Buffalo, one of these snow bands set up off Lake Erie. The band was about eight to 10 miles wide. The northern portion of Buffalo had green grass throughout most of this event. The southern portion of Buffalo, however, only about 10 to 12 miles away, picked up 40 inches of snowfall.

The timing of seasonal snowfalls

He said that lake-effect snow can begin in early fall and continue throughout the winter months.

Early in the fall, we see the same type of activity – cold air moving across a warm body of water – but it’s actually warm enough that we see lake-effect rain showers occur. As we get into November to early December, the air is cold enough to turn that into snow.

But, if the lake freezes over, it can bring a halt to these seasonal snowstorms.

Lake Erie is a very shallow lake. In January it develops a significant amount of ice cover. The ice cover acts as a cap, in a simple way, to limit the amount of heat and moisture that can come through that ice and then modify that air mass.

Graphic showing small cloud over water growing larger and lake-effect snow falling.
Lake-effect snow forms when cold air moves over warm water. You can see this effect most clearly with the Great Lakes, because most are too big to freeze. Smaller lakes freeze over and cut off the supply to form clouds and lake-effect snow. Image via NOAA.

How to prepare for lake-effect snow

Most importantly, Niziol said that people who experience lake-effect snow should know how to be prepared for an unexpected snowstorm.

Be prepared for winter weather conditions. Have extra clothes in your car, make sure your cellphone is charged, have a shovel in the car, some water, granola bars, extra food as well. Because you never know when you leave the house, even if you have a forecast with you, what it will be like when you drive through one of these snow bands.

Lake-effect snow belts may include portions of the Upper Peninsula of Michigan, northern and western portions of the Lower Peninsula of Michigan, northern Indiana, northeastern Ohio, northwestern Pennsylvania and western New York state.

Bottom line: 2022 has already seen examples of lake-effect snow in the northern U.S., around the Great Lakes. It happens when cold winter air moves over a relatively warm body of water. What you get are small-scale but intense snowstorms.

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