Lake-effect snow

Lake-effect snow is a meteorological phenomenon where snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated by the lake water, picks up water vapour from the lake and rises through colder air. The vapour then freezes and is deposited on the leeward (downwind) shores as snow.

[A band of lake-effect snow pictured from the city of Buffalo, New York]

If the air temperature is low enough to keep the precipitation frozen, it falls as lake-effect snow. If not, then it falls as lake-effect rain.

Some key elements are required to form lake-effect precipitation and which determine its characteristics: instability, fetch, wind shear, upstream moisture, upwind lakes, synoptic (large)-scale forcing, orography/topography, and snow or ice cover.

The same effect also occurs over bodies of saline water, but then it is termed ocean-effect or bay-effect snow. The areas affected by lake-effect and parallel ocean-effect phenomena are called snowbelts. These include areas east of the Great Lakes in North America, the west coasts of northern Japan, Lake Baikal in Russia, and areas near the Great Salt Lake, Black Sea, Caspian Sea, Baltic Sea, Adriatic Sea, the North Sea, and more.