Lake Effect Snow. You have probably heard about it before. But what actually causes it? Where does it occur and under what conditions does it occur?

“BBC Broadcast Meteorologist Everton Fox takes a look at ‘lake effect snow’ and how it is formed. “

Inland areas of water, such as the Great Lakes in North America, can actually create their own circulation systems. This is due to the large specific heating capacity of water, which results in water heating up (or cooling down) much more slowly than the surrounding land.

As a result, this modifies the climate and weather of the surrounding land. In the spring and Summer, when the water is cooler than the land, air temperatures downwind of the lake are slightly cooler than they would be if the lake wasn’t there. The cooler water also inhibits cloud formation, so the days are often sunnier as well.

In the winter, the lakes can produce an effect known as ‘lake effect snow’. Cold, dry Arctic air often spills southwards into the northern parts of North America. Where the cold air meets the warmer water, evaporation occurs and the air is warmed. This makes the air unstable and turbulent.

The warm moist air near the surface of the lake rises, which causes it to cool. However, it doesn’t cool as much as the surrounding air that hasn’t passed over the warmer lake waters. This effect is similar to that experienced when a hot bath is run and the cold air above the bathwater readily condenses.

The cooling air forms clouds of ice-crystals, which eventually form snowflakes. The prevailing cold wind blows the clouds over land, the heat source is lost and the air can no longer retain the moisture it’s holding, causing heavy snow showers downwind of the lake. These heavy showers can leave up to 30cm (12 inches) of snow in just a few hours.

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