by Barb Hopkins

Created on: December 04, 2008   Last Updated: August 19, 2009

When Mother Nature wants to whip up a batch of lake effect snow she reaches for two main ingredients, cold air and warm water. Lake effect snow is the weather condition that occurs when a mass of cold Arctic air rushes over a body of warmer water creating unstable conditions that result in heavy localized snowfall.

Arctic air often hits areas like the Great Lakes between the U.S. and Canada and mixes with the warmer lake water. As the warmer lake water evaporates, it heats the bottom layer of cold air. Warm air is lighter than cold air so the warmed air rises and then cools. When it cools the evaporated moisture condenses to form clouds. Cold air can hold little moisture and clouds will form quite quickly. If the air is humid enough, snow will fall.

Typically, lake effect snow happens during the winter season but can occur during fall and even spring. If an area is going to experience a heavy snowfall because of this condition, three things must happen.

1. Wind direction. Arctic winds usually blow from a northwest or west direction which then cause heavy snow to fall on the southeast or east side of the lake.

2. The winds must maintain their strength for a long enough time.

3. There needs to be a temperature difference between the cold air and warm water, about 50 degrees Fahrenheit will do.

In addition, when the clouds move over the land, friction with the ground occurs. If the ground friction is stronger than the wind and lake friction, it will cause the winds to slow creating a convergence. A convergence may increase the amount of snow falling on land as compared to the amount falling over the water.

Areas of higher elevation found near the lakes tend to receive the largest amounts of lake effect snow. When the wind travels inland and meets hilly areas, the air is forced to rise. Then it cools. The more the air cools the more condensation, which to the delight of area children, creates even more snow. One example where this occurs is the area of the Tug Hill Plateau in New York State. Located just east of Lake Ontario, the residents can expect to have about 200 to 300 inches of snow per winter.

Predicting lake effect snow is not easy. Meteorologists study many variables. Wind shifts, temperature variations, and even the jet stream play integral parts of when and where the heaviest downfalls of snow will occur. For residents that live in the Great Lakes region, being prepared for this weather phenomenon is essential because it is never a question if the lake effect snow will come but when.

references: www.nature.org and www.das.uwyo.edu

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