Atmosphere And Weather

How Lakes Affect Snowfalls Lake Effect Snow

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Lake effect snow is a term that describes an unusual condition of snowfall.

Basically, cold temperature air flows over a body of warm water, causing an interaction with the heat. Bands of snow begin to form and follow the flow of cold-temperature air as they begin to drop. The bands, or formations, make room for warm air to rise and for the cold air and snow to fall. Bands are observed as separate bodies in the air because two things are happening at once, and thus make their space to continue. The difference in temperature between the two bands, or pairs of multiple bands over time, helps them to stay separate and maintain their form.

At wintertime, the rising warm air helps to create much more snow than might be possible if the cold air flows only over dry land. The difference can be measured in snow depths of more than a meters to several meters.

Lake effect snow is not just for winter. It can also take place in the fall and spring when cold air can still push over large bodies of water.

Common winter storms are associated with low pressure events. However, lake effect snows receive their flow from dry cold air, such as arctic air, known for pushing away clouds over dry lands.

As the air flows over the warm body of water and picks up rising moisture, then the distance the moisture travels and forms into snow is measured both in altitude and horizontal vectors. By the time the snow is formed and falls to the ground, it has already cleared the water and gone further inland in the same direction of flow as the cold air, downwind.

The nature of lake effect snow formation means that while other regions far from the bodies of water can clear up after a traditional snowfall, regions downwind from water bodies under the flow of cold air can still receive lake effect snow, even if they have already received traditional snow.

If the temperature difference is great enough, and if the cold air flows across the largest width of the warmer body of water, then extended snowfalls can occur from the lake effect. Snowfalls over two days are possible. Because cold air patterns tend to develop and the air flows predicable tracks, some regions and communities inland from warm water may receive more snow than surrounding areas as a result of being on track with the normal flow of cold air.

For example, there is a pattern of direction associated with cold air flow, trending from southwest to northwest. This pattern can yield lake effect snows more to the east and southeast sides of lakes and other water bodies where bands are able to slow down and dissipate over land. Such lake effect snowfalls can contribute more than half of annual winter snowfall over the communities east and south of the Great Lakes in the United States.

A helpful condition for setting up the lake effect snowfall is that the body of water be large enough to retain a lot of heat after the summer and fall. Without the ability to freeze over, such water is available to be scooped up into the cold air and begin the formation of bands that rise and then form snow and fall back down over time to traverse the altitude. The Great Lakes between Canada and the United States have this ability, as do some other bodies of water in Korea, Japan, Scandinavia, and others.

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