Lake-effect Snow

Lake-effect snow is produced during cooler atmospheric conditions when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor, which freezes and is deposited on the leeward shores. The same effect over bodies of salt water also occurs (e.g. ocean-effect snow, bay-effect snow). The effect is enhanced when the moving air mass is uplifted by the orographic influence 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 each hour, often resulting in copious snowfall totals.

The areas affected by lake-effect snow are called snowbelts. This effect occurs in many locations throughout the world but is best known in the populated areas of the Great Lakes of North America, and especially Western New York, northwestern Pennsylvania, northeastern Ohio, southwestern and central Ontario, northwestern and northcentral Indiana (mostly between Gary, IN and Elkhart, IN), and western Michigan. The Tug Hill Plateau of New York State has the most snow amounts of any non-mountainous location within the continental U.S., followed by the Upper Peninsula of Michigan, which can average over 200 inches (508 centimeters) of snow per year.

A lake-effect blizzard is the blizzard-like conditions resulting from lake-effect snow. Under certain conditions, strong winds can accompany lake-effect snows creating blizzard-like conditions. The wind chill and visibility values will often reach blizzard criteria; however the duration of the event is often slightly less than that required for a blizzard warning in both the US and Canada.

If the air temperature is not low enough to keep the precipitation frozen, it falls as lake-effect rain. For lake-effect rain or snow to form, the air moving across the lake must be significantly cooler than the surface air (which is likely to be near the temperature of the water surface). Specifically, the air temperature at an altitude where the air pressure is 850 millibars (85 kPa) (roughly 1.5 kilometers or 0.93 miles vertically) should be 13 °C (23.4 °F) lower than the temperature of the air at the surface. Lake-effect occurring when the air at 850 millibars (85 kPa) is much colder than the water surface can produce thundersnow, snow showers accompanied by lightning and thunder (caused by larger amounts of energy available from the increased instability).