Lake effect snow
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Lake effect snow is produced in the winter when cold winds move across long expanses of warmer lake water, picking up water vapor which freezes and is deposited on the lee shores. This effect is enhanced when the moving air mass is uplifted by the orographic effect of higher elevations on the downwind shores. This uplifting can produce narrow, but very intense bands of precipitation, which deposit at a rate of many inches of snow per hour. The areas affected by lake effect snow are called snowbelts.
Cold winds in the winter typically prevail from the northwest in the Great Lakes region, producing the most dramatic lake effect snow falls on the East to south shores of the Great Lakes. This lake effect produces a significant difference between the snow fall on the eastern and western shores of the Great Lakes. If the air temperature is not low enough to keep the precipitation frozen, it falls as lake effect rain. Lake effect snows at the Tug Hill Plateau on the southeastern side of Lake Ontario frequently set the daily records for snowfall in the United States. Lake Erie also produces a similar effect for a zone stretching from the eastern suburbs of Cleveland to Buffalo, but Lake Erie often freezes due to its shallowness, and ice cover stops the lake effect. In order for Lake Effect rain or Snow to form the temperature difference between the water and the air at 1500 meters above the surface must be at least 13 degrees C. The southern and southeastern sides of the Great Salt Lake also receive significant lake effect snow, but it is much more severe over the Great Lakes.
One area that receives the most lake effect snow is the snow belt in the Upper Peninsula (UP) of Michigan, near the cities of Houghton, Marquette, and Munising. These areas frequently average over 200 inches, and may receive close to 300 inches of snow a year (for comparison, on the western shore, Duluth, Minnesota receives only 77 inches). Due to the low populations of these areas, they do not get the publicity of the lake effect snows affecting Buffalo, Erie, Cleveland, or Upstate New York. Lake Superior and Lake Huron rarely freeze due to their size and depth; lake effect snow can fall continually in the UP and the Ontario, Canada snowbelts during the winter months. The most famous lake effect storm was the Blizzard of 1977, which struck the Buffalo area from January 28-February 1, 1977. It was the first instance of a region of the United States being declared a Federal Disaster Area because of excessive snowfall. Cities such as Toronto, Hamilton, Detroit and Chicago frequently miss out on lake effect events because they are not on the leeward shore of a lake during a Northwest oriented wind (wind coming from the Northwest, heading to the Southeast). However Toronto and Hamilton are often close enough to Georgian Bay and Lake Huron that they receive small amounts of Lake Effect Snow each winter.
Lake effect of extremely cold air over still warm water in early winter can produce thundersnow, snow showers accompanied by lightning and thunder.
Even when precipitation is not produced, any time cold air passes over warmer water it produces cloud cover. Fast moving cold fronts, known as Alberta clippers often cross the Great Lakes. After the passage of a cold front, winds tend to switch to northwest, and a frequent pattern is for a long lasting low to form over the Canadian Maritimes which may pull cold northwestern air across the Great Lakes for a week or more. Since the prevailing winter winds tend to be colder than the water for much of the winter, the southeastern shores of the lakes are almost constantly overcast, leading to the use of the term The Great Gray Funk as a synonym for winter. These areas have a high rate of seasonal affective disorder, a type of psychological depression thought to be caused by lack of light.
Similar snowfall can occur near large inland bays, where it is known as Bay effect snow. Note that Nor'easters are ocean effect storms produced by offshore lows on an Eastern coast, which bring moist, unstable air across land areas, often opposite to the usual prevailing winds. Areas such as Massachusetts' Cape Cod often experience a bay effect snow off the ocean, called ocean effect snow.