Lake-effect snow on the way

Thursday 11th Feb 2016 by the Weather Club

Photo: Satellite image of the Great Lakes (27/01/2005) Source: Wiki

Lake effect snow is currently trending on Twitter, with up to 1ft of snow expected in areas of the United States lying downwind of the Great Lakes, such as Syracuse (NY) and Erie (PA).

But what causes it? Lake effect snow forms in the winter, as this is when there is the greatest difference in temperatures between land and water. As the wind direction shifts to a more northerly direction, Arctic air descends further south, towards the northern US states and over the Great Lakes. At this time of year, the surface of the Great Lake temperatures are around 1 to 6C (32 to 42F), a relatively warm temperature, compared to the much colder air aloft.

As the cold air moves over the surface of the lake, the air above starts to warm. This causes the air to become unstable, and triggers the ‘warmer’ air to start rising, as it is now less dense. As the air rises, it begins to cool, and condense, with clouds beginning to form, which can then produce precipitation in the form of snow. Because of increased friction over land, compared to water, once this parcel of air reaches the shoreline, it travels slower, allowing snow to “pile up”.

Lake effect snow is also affected by ‘fetch’ – the distance that the wind travels over a body of water. The longer the fetch, the greater the amount of heat and moisture the parcel of air can gather from the lake. In the case of the Great Lakes, this distance tends to be around 50-150 miles, depending on the wind direction.

Although the Great Lakes region is one of the most well-known areas for being affected by lake effect snow, several other areas in the world experience the phenomena. This includes areas close to the Black Sea, the Kamchatka Peninsula in Russia, and along the west coasts of the Japanese islands of Honshu and Hokkaido.