All You’ve Ever Wanted to Know About Lake Effect Snow

2014-11-20 22:21:02.000 – Kaitlyn O’Brien, Weather Observer/Education Specialist

All eyes have shifted to western New York, where areas of the state have received crippling lake effect snow (and it’s not over yet!). But what exactly is lake effect snow and why does it occur? How can bodies of water have such a large influence on snowfall totals?

Every year between November and January, lake effect snow events bring several feet of snow to lake bordering cities such as Cleveland, OH, Erie, PA, and Buffalo, NY. While the Great Lakes region is not the only prime location for lake effect snow events to occur, it is perhaps the most well-known and heavily observed location within the United States. Take for example, this past Tuesday, November 18th (click here for a radar loop, courtesy of College of DuPage). If you’ve perused Twitter, Facebook, read any newspaper or watched any news channel in the last 48 hours, you’ve probably seen and heard about the colossal snowfall totals coming out of places like Lancaster, West Seneca, and other towns south of the Buffalo area. There are a few main ingredients needed for a significant lake effect snowstorm to occur, and each of these conditions was met, if not exceeded, for the event this past Tuesday.

The first thing to account for is the temperature of the body of water. Significant lake effect snow will develop if a warm body of water is present. Secondly, a cold air mass with limited wind shear will enhance the development of snow crystals. Lastly, the stretch of the lake that the air mass moves over, (known as the fetch) plays an important role too. Ultimately, for a large lake effect snow event, you want warm water temperatures, a cold air mass (so as to create a large temperature gradient between the water and air), with directionally consistent winds throughout the vertical levels of the air mass, and maximized time for this air mass to travel over the warm body of water, thus traveling the largest fetch distance. There are other influencing factors that shouldn’t be overlooked, such as the terrain surrounding the lake, the characteristics of the air sitting just above the water, and the amount of moisture present within the cold air mass, and the depth of the air mass.

With all of these specific ingredients, we now have the perfect setup for a lake effect snow storm to take place. Right above the warm body of water is a shallow layer of air that has been warmed through conduction. As the cold air mass moves over the water, this creates instability and the warm layer will be prompted to rise, since it is less dense than the cold air. This process is known as convection. When convection occurs, the air becomes saturated and condenses, producing snow crystals in low temperatures. As this process is occurring, it’s also important to factor in the differences in friction the air mass encounters on Earth’s surface as it travels from one area to another. Frictional drag between land and water are different, and the cold air mass will actually experience less friction as it travels across the body of water. This causes all of the condensation to converge in one area when the air mass travels over land again and experiences increased frictional drag. As a result, this air is forced to go up, rising higher into the atmosphere where the condensation process becomes enhanced. Similarly, any type of orographic lifting, or lifting of the air that occurs as a result of the terrain, can greatly increase those final snowfall totals after a storm.

Perhaps on a more local note, it is this orographic lifting process that has actually contributed to the few snow flurries we’ve seen in the higher elevations these past 48 hours. In fact, part of the residual moisture from the lake effect snow has been orographically lifted as a result of the mountainous terrain it encountered when continuing to stream off of Lake Erie and propagate eastward. This is not an uncommon occurrence and it is certainly a large contributing factor to the snowfall that can and has accumulated on the higher summits over the past few days.

Kaitlyn O’Brien, Weather Observer/Education Specialist