Why is it so…
Why is it so snowy near the Great Lakes?
When frigid air blows across a big, unfrozen lake, the warmer water heats and moistens the air from below. It rises into narrow bands of clouds that dump heavy snow on the downwind shore, sometimes several inches an hour, while places a few miles away see sunshine.
~23°F+lake warmer than air aloft
Inches/hoursnow rates in a band
Downwind shoregets buried
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The recipe
- A big temperature gap: forecasters look for the lake surface to be roughly 23°F or more warmer than the air about 5,000 feet up.
- A long trip over water: the more miles of lake the wind crosses (the fetch), the more moisture it gathers.
- Steady wind direction: a constant wind keeps the snow band over the same towns for hours.
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Who gets buried
Cold outbreaks usually come from the northwest, so the eastern and southern shores catch the snow: Buffalo, Erie, western Michigan, and New York's Tug Hill Plateau, one of the snowiest places east of the Rockies. Hills just inland squeeze out even more.
Why it fades in late winter
Once a lake freezes over, the water can't heat and moisten the air anymore, so lake-effect snow drops off. That's why it's often heaviest in late fall and early winter, when the lakes are still relatively warm.
Questions people ask
- Does lake-effect snow happen elsewhere?
- Yes, near other large lakes and seas when very cold air crosses open water, such as Utah's Great Salt Lake and the Sea of Japan.
- Why can it snow heavily in one town and not the next?
- Lake-effect bands are often only a few miles wide, so the snow piles up under the band and stops sharply at its edges.