Ask Josh: Lake Effect Snow

Meteorologist Josh Fitzpatrick explains how and why it forms.

This is a subject that has always fascinated me!  I got an e-mail the other day from Linda Chambers in Spencer, WV and she asks: "How does lake effect snow form exactly and does it only happen along the Great Lakes?"

That's a very good question, Linda!  Here's how it forms: Lake effect snows occur when a mass of sufficiently cold air moves over a body of somewhat warmer water, creating an unstable temperature profile in the atmosphere.  The surface water temperature may be 40 degrees but the air moving over it could be 20 degrees or colder! 

As a result, clouds build over the lake and eventually develop into snow showers and squalls as they move downwind.  The intensity of the lake effect snow is increased when higher elevations downwind of the lake force the cold, snow-producing air to rise even further.

The most likely setting for this localized type of snowfall is when very cold Arctic air rushes over warmer water on the heels of a passing cold front, as often happens in the Great Lakes region during late fall and winter.

Winds accompanying Arctic air masses generally blow from a west or northwest direction, causing lake effect snow to fall on the east or southeast sides of the lakes.

Where an area gets a large amount of snow from lake effect is dependent on the direction of the winds, the duration they blow from a particular direction and the magnitude of the temperature difference between the water and air. 

Since cold air can hold very little moisture and the low level of the atmosphere is quite unstable, clouds form very rapidly, condensation occurs and snow begins to fall.

Areas of relatively higher elevation downwind of the Great Lakes generally receive higher amounts of lake effect snow than do other locations in the region.

For example, residents of the Tug Hill Plateau in New York State, east of Lake Ontario can spend the winter months digging out of anywhere from 200 to 300 inches of snow.  Likewise, the high mountains of West Virginia can receive more than 200 inches of snow in a winter helped by the lake effect.  In lake effect snow, you can get a localized snow squall that can dump a foot of snow but go a few miles in either direction of the snow band and you may have bare ground!

The only other lake that produces significant lake effect snow in the U.S. is the Great Salt Lake in Utah.

Cape Cod Bay in Massachusetts and Chesapeake Bay in Maryland and Virgina on occasion produce what is called bay effect snow.  Bay effect snow forms in the same manner as lake effect snow, only over the ocean.

I hope that answers all your questions on lake effect snow.  Keep those great questions coming!  If you have weather related question you'd like for me to answer, please submit it in a comment and I'll get back to you.  Remember to leave your name and what town you're from.

Thanks for reading!

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