Lake Effect Snow

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Lake Effect Snow

Lake effect snow can cause large local variations in snow depth with 50 cm of snow accumulate over the course of a few days near the shore and a few miles inland from the lake shore there may be no snowfall at all. Lake effect snow does occur in regions away from the great lakes (for example along Lake Baikal in Russia) but it is far more pronounced and and destructive to ground and air transportation around the great lakes.

Lake effect snow occurs when a mass of freezing air moves down from the Arctic over a body of warmer water, creating instability in the atmosphere above the lakes. As a consequence, clouds build and develop over the lakes and, as they move downwind, develop into snow showers and squalls.

The water temperature of the Great Lakes lags behind the atmosphere in cooling through early winter, as water holds its heat far more readily than land. The heating from below results in instability in the air during cold outbreaks. This instability mixes warm, moist air near the surface of the lakes into the lowest 1 to 1.5 km of atmosphere. Rising air rapidly reaches saturation, and the result is shallow cumuliform clouds, frequently aligned in bands parallel to the low-level wind. By January, ice covers most of the lakes\’ surface area, cutting off or reducing the heat supply.

The distribution of lake effect snowfall in the Great Lakes area depends upon several factors: the position and direction of weather systems, the lake water temperatures and its variations, and the strength and direction of the winds. Topographic differences on the lee of the Great Lakes also affect the intensity and distribution of snowfall. On the eastern and southern shores of the Great Lakes, lake effect snowfall contributes between 30% and 50% of the total winter snowfall .

Winds from the Arctic generally blow from the west or northwest, causing lake effect snow to fall on the east or southeast sides of the Great Lakes. Whether or not an area gets a large fall of snow from lake effect snow is dependent on the direction of the winds, the duration they blow from a particular direction, and the size of the temperature differential between the lakes and the air above.

Cold air holds very little moisture and the low level of the atmosphere is quite unstable. Therefore clouds can form very quickly, condensation occurs and snow falls.

In late 1977 a storm hit the southeast of Lake Huron around London, Ontario. In just three days from December 7th to 9th 100cm (39 inches) of lake effect snow fell on the region. This snowfall was made worse by the 60mph winds causing huge drifts.

However the largest snowfall recorded that was attributed to lake effect occurred in January 1966. In a five day period from 27th to 31st, 259cm (102 inches) of snow fell in Oswego, New York. Half of that total fell on the 31st.

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