What causes lake-effect snow?

November 25th, 2012 at 9:59 am by under Weather

A satellite photo of a lake-effect snow event. Notice northwest winds blowing over the Great Lakes, causing clouds to form and deposit large amounts of snow in downwind locations. (Photo courtesy of xweather.org)

With an ongoing lake-effect snow event in the Great Lakes area today, it’s a good time to take a moment and learn about what exactly causes this phenomenon.

The basis of the concept lies in the high specific heat capacity of water. This means that, compared to air, water takes a longer time to cool off – or to warm up.

Because of that physics principle, during the fall and early winter months, the Great Lakes are still relatively warm from all of the sunlight they absorbed during the summertime.

At the moment, cold, dry Arctic air is spilling southwards into the northeastern parts of the US.

When this cold air blows over 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. As it rises and cools, clouds are formed.

As the warm, moist air continues to rise and form clouds at colder (higher) levels above the lake surface, snowflakes form inside of the cloud. This process is referred to as convection, and is one of the causes of precipitation.

The prevailing cold wind blows the clouds over land eventually, bringing them over the land area that is downwind from the lake. As these clouds move from over the lake surface to over land, the convective heat source is lost and the air can no longer retain the moisture it’s holding.

All of the moisture (snowflakes) in the cloud suddenly have nothing to keep them airborne, producing an area of heavy snowfall as the moisture is dumped out of the clouds. Lake effect snow has caused some of the highest snowfall totals in history, with rates of several inches per hour fairly common.

Incredible snowfall totals can result from lake-effect snowfall. (Photo courtesy of xweather.org)

Comments are closed.