Understanding Lake Effect Weather

March 12, 2014

When you live nearby a lake, you become familiar with a weather pattern known as ‘lake effect’. This phenomenon occurs when cold wind tracks along warmer lake water. This enables the air to pick up water vapor, gather energy, and eventually freeze as it hits the shores. Cities and towns that lie alongside lakes are all too familiar with the massive quantities of snow that often fall during the winter as a result of this atmospheric effect.

The area known as the ‘lake belt’ in the northeastern U.S and Great Lakes region, extending into Canada, is one of the most frequently affected by lake effect precipitation. Southwest Ontario, in particular, is extremely vulnerable to devastating storms from lake effect since the city is surrounded by water on three sides. Here is a brief look at how lake effect occurs.

How Lake Effect Works

Lake effect can produce everything from light rain to heavy snow to thundersnow that combines a thunderstorm with heavy snowfall. Depending on the conditions, lake effect can be the sole contributor to severe blizzards in lake regions. The principle determiners of lake effect are: instability, fetch, windstream, moisture, topography, and snow and ice cover.

Instability- This refers to the difference between the lake temperature and the height in the atmosphere. When barometric pressure reaches a certain point, conditions in the atmosphere become ideal for a higher precipitation rate.

Fetch- The distance an airmass travels over a body of water is known as it’s fetch. In general, the larger the fetch, the more precipitation produced since more water vapor and energy travel from water to air. Depending on the size of the lake, lake effect precipitation may be more or less likely or intense.

Wind Shear- The direction in which the wind passes between the surface of the water and the height of the atmosphere will determine the intensity of the precipitation. The degree of barometric pressure is again a determinant of type and degree of precipitation–such as the difference between snow flurries and a blizzard.

Moisture- Upstream moisture has to do with the relative humidity along the lake. High humidity enables condensation, clouds, and precipitation to form more easily and in larger number.

Topography- The elevation of the lake has everything to do with precipitation levels. Just as mountains receive more snowfall, so too do lakes with elevation gains.

Snow and Ice Cover- Finally, snow and ice cover along the lake can gradually reduce precipitation since the distance an airmass can travel over the lake is reduced and there is less energy in frozen water to produce squalls that generate storms over land.