In Chicago and heard that term. I don’t know what that means.
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The lakes aren’t covered with ice yet and are still above 32 degrees. When really cold air comes across the warmer water of the lakes, it picks up and carries the moisture to land where it falls as snow.
Moisture from the lakes augment the snowfall amounts depending on which direction the storm is moving.
The Great Lakes are massive. Cold air comes down from Canada, and picks up the moisture from the not yet frozen lakes. Then dumps all the snow (or any precipitation) on cities like Rochester or Buffalo.
Cities with lake effect snow will always get hit harder, basically because there’s more water nearby that can be evaporated and turned to snow
When you have warm, moist air that collides with freezing air, the moisture in the air is frozen and drops to the ground. So you get a bit of snow. However, ultimately there’s only so much moisture the air can hold. Once it runs out of moisture, it stops snowing and you just get cold, dry weather.
However, when the weather system is moving over a large body of water (in this case, Lake Michigan), it is continually being fed new moisture and the process can continue as long as the weather system is in the region.
In the Midwest, the ‘Lake Effect’ primarily hits Western Michigan, the Upper Peninsula and Canada because the prevailing weather is West-to-East. You can see this with the upcoming holiday storm. Milwaukee is projected to get a few inches of snow. The Upper Peninsula will probably get well over a foot.
Chicago is on the Western edge of Lake Michigan, so normally the Lake Effect is a good thing – it provides cooling in summer and warming in winter since water has a much higher heat capacity than air (and thus prevents rapid changes in temperature). However, when you get the rare storm that goes from East-to-West, Chicago suffers the same massive snowfalls that you’ll be seeing in Western Michigan soon. That ‘Lake Effect snow’ is rare but devastating.
Note that you see a similar situation with the Northeast and the Atlantic Ocean. Normally the weather is West-to-East and you get somewhat temperate climates. When a “Nor’easter” arrives – with East-to-West winds – the Northeast gets absolutely hammered due to the massive amounts of moisture being taken up into the storm.
Winds whipping across large bodies of water (like Lake Michigan) pick up and disburse moisture in a localized area often close to the shores.
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