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| Earth on Jan 20, 2013

What is lake-effect snow?

If you live on the downwind side of a large lake, you’re probably all too familiar with this weather phenomenon.

What is lake-effect snow? If you live on the downwind side of a large lake, you’re probably all too familiar with this weather phenomenon. It happens when cold winter air moves over a relatively warm body of water. What you get are small-scale but intense snowstorms. The typical lake-effect snow belts 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. EarthSky spoke to Tom Niziol, meteorologist-in-charge of the National Weather Service in Buffalo, New York. He said:

[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.

Photo credit: Square Foot Staffing

That makes accurate forecasting of lake effect snow a challenge for meteorologists, said Niziol. 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.

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.

Image Credit: pmarkham

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

Niziol gave an 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 8-10 miles wide. The northern portion of Buffalo had green grass throughout most of this event. The southern portion of Buffalo, however, only about 10-12 miles away, picked up 40 inches of snowfall.

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 rainshowers 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.

Niziol said that the most important thing for people who experience lake effect snow to know is 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.

Bottom line: Lake-effect snow happens when cold winter air moves over a relatively warm body of water. What you get are small-scale but intense snowstorms.