Name: How lake-effect snow forms
Uploaded: 2026-01-19T16:33:30.765Z
Duration: 1 min 57 s
Description: AccuWeather Meteorologist Geoff Cornish explains the current conditions of ice cover and lake-effect snow across the Great Lakes region as well as explain the conditions that causes the frequent snow.

AccuWeather Meteorologist Geoff Cornish explains the current conditions of ice cover and lake-effect snow across the Great Lakes region as well as explain the conditions that causes the frequent snow.

Lake-effect snow occurs when cold air moves over the relatively warm waters of the Great Lakes, causing moisture to rise and form clouds that produce snow. The process is most effective when there is a significant temperature difference—about 23 degrees—between the air a mile above the surface and the lake water.

As winter progresses and the lakes freeze, the temperature contrast diminishes, reducing the potential for lake-effect snow. When the lake water cools to near the temperature of the air above, the lake-effect snow season comes to an end.

How lake-effect snow forms

Ice is expanding on the Great Lakes and, you know, we've had a good start to winter back in December. Then we had that January thaw, and you can see the trend line here. The red line is the historical average percentage of the Great Lakes with ice coverage. Basically, if you look at all the area of the Great Lakes, what percentage of that area is covered in ice, and typically it's really the late part of winter when we get into the most expansive lake ice. We had an okay start, then we got that January thaw, and we lost a little bit of that ice coverage, but now it's increasing once again, and that's going to impact lake effect snow. Remember, lake effect snow is driven by the relatively mild water over the Great Lakes, and the contrast between really cold air upstairs versus the mild lake water. So as that lake water begins to cool down, we're going to begin to see a little bit lower octane fuel for lake effect snow. So we get this cold wind crossing the relatively mild Great Lakes. That gets the moisture increasing. We get these little rising currents of air, relatively weak but still rising currents of air, and that's enough to produce plenty of clouds and eventually some snow production as well, driven by that contrast between cold air upstairs and the relatively warm lake water. Well, a lot of the time we look for the contrast between about a mile up in the atmosphere and the lake surface to be about 23 degrees, so you want that air to be 23 degrees colder than that relatively mild lake water, and the wind direction is going to determine where the lake effect snow falls. But when the lakes begin to chill down, this is kind of the beginning of the end of lake effect snow season, so again, the contrast is reduced between the cold air upstairs and the warm lake water. When the lake water begins to chill down, temperatures are pretty similar between temperatures upstairs and near the lakes, ending lake effect snow season.

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