Geography
Lake-Effect Snow Belts Develop Downwind of Large Water Bodies
Quick fact
Some lake-effect snow belts, like those east of Lake Ontario, receive over 200 inches of snow per year, compared to less than 100 inches just a few miles away.
Why this is interesting
Imagine an area that gets three times more snow than neighboring towns, not because it's at a higher elevation, but because it sits downwind of a huge lake. Why does a lake, a body of water, turn some regions into snow magnets?
Read the full explanation
Understanding Lake-Effect Snow Belts Develop Downwind of Large Water Bodies
Lake-effect snow is a local weather phenomenon that happens when a large, unfrozen lake is much warmer than the air passing over it. As cold, dry air sweeps across the lake, it picks up heat and moisture from the water surface. This warm, moist air rises and cools, causing the moisture to condense into clouds. When these clouds reach the downwind shore, they dump the moisture as snow. This effect is strongest when the wind blows along the long axis of the lake, and the air is at least 13°C (about 23°F) colder than the water surface.
A deeper explanation
The core mechanism is the transfer of energy and moisture from the lake to the air. The air near the lake's surface warms and becomes more humid, making it less dense, so it rises. As it rises, it cools adiabatically, and the water vapor condenses, forming snow. The effect is amplified when the wind travels over a long stretch of open water (fetch), allowing more moisture to be absorbed. Additionally, the friction of the air over land can create bands of convergence, focusing the snowfall in narrow, intense bands. These conditions recur when cold, Arctic air masses push over the still-unfrozen Great Lakes, typically from late autumn until the lakes freeze over.