The Great Lakes are a valuable resource for drinking water, recreation and transportation, but did you know they also play a key role in our winter weather systems?  As the seasons change and the air grows colder, we often experience a weather phenomenon known as lake-effect.

During the summer months, the Great Lakes absorb heat from the sun and remain relatively warm as we move into winter.  When the cold winter air moves across warm lake water it heats the bottom layer of air and produces moisture. The lake moisture evaporates into the cold air, rises and begins to form clouds that produce snow.  This lake-effect snow only occurs with the right conditions. Air must be 13⁰C cooler than water temperatures and strong winds must carry the moisture across the lake.

Wintry Weather New York
A band of storm clouds moves across Lake Erie and into Buffalo, N.Y., Tuesday, Nov. 18, 2014. Parts of New York measured the season’s first big snowfall in feet, rather than inches, on Tuesday as 3 feet of lake-effect snow blanketed the Buffalo area and forced the closure of a 132-mile stretch of the state Thruway. (AP Photo/Gary Wiepert)

The further air travels over the warm lake, the more intense or heavy the snow will be.  Lake-effect snow falls on the leeward or downwind shore, and can produce narrow but intense bands of snow.  This is what the Buffalo area experienced last week.  This kind of snowstorm can leave behind more than 100 cm of accumulation  –  a lot of snow for winter enthusiasts!

Lake-effect snow is most common from November until January.  This winter system can happen until the lake freezes over or cools enough that there is little difference between water and air temperatures.

Southwestern Ontario gets a lot of lake-effect snow because we are surrounded by Great Lakes on three sides. This weather pattern can often cause blizzard-like conditions with reduced visibility and white-out conditions. The lake-effect is primarily why our geographical area is known as the ‘snowbelt’. It also explains why we can spend so much time in the winter digging out from under a heavy blanket of snow.

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