The downwind sides of any large body of water—and especially the Great Lakes—can be perennial winners of the rotten-weather-in-winter prize. The air moving across them picks up moisture, then dumps it in the form of snow from heavy, ice-laden clouds over the downwind land area. The cloud cover almost invariably harbors ice and generates localized heavy snow fall, especially in the roughly 10-mile strip of land nearest the lake.
No matter what the forecast, there’s a safe rule of thumb for airports within 50 miles east or south of one of the Great Lakes: From November through March, it’s wise to be ready for lake effect clouds, ice and snow if the surface wind is stronger than a light breeze. It’s not unusual for such conditions to extend 100 miles or more downwind. Tops are usually at or below 10,000 feet and—generally, unless there’s an associated weather system—clear above.
Lake effect conditions can and do combine with warm and cold fronts, intensifying their effect. Should tops be reported above 18,000 feet, you’re not dealing with pure lake effect—there is another system involved. Unless we are flying something with known icing and decent performance in the low FL200s, there may be no ice-free altitude we can reach, so we’ll probably stay on the ground.
