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WSHS Environmental Biology

 Lake effect snow is caused when very cold air flows over the relatively warmer water of a large lake.  Intense evaporation from the lake surface forms convective clouds that can not contain all of this water, and some of it falls back to the surface as snow. WHAT CAUSES LAKE EFFECT SNOW?

 Lake effect snow showers often form into bands, with abrupt edges to the falling snow.  One location can receive a foot of snow, while another location just a few miles away receives only flurries.  Once the lake surface cools to near 32 o F, the lake effect snow slows considerably. When the lake freezes, the snow stops altogether.

The Greater Cleveland area is the largest population center that is routinely impacted by heavy lake-effect snowfall (LES) within the Great Lakes region. Cleveland Hopkins airport receives about 50" of snow annually, and about 40% can be attributed to LES from Lake Erie. Some 35 miles due east, Chardon is known as the snow capital of northeast Ohio and receives over 100" annually - the majority as a result of LES. WOW

Radar observations

Satellite visible imagery

These are the mechanisms to make Lake Effect Snow, ranked in usual order of importance

HEATING: The water in the Great Lakes does not cool off as quickly as the atmosphere in the fall and early winter. This warmer water heating the cooler air results in instability, especially during early cold outbreaks. The warmer air rises and quickly reaches saturation, and the result is shallow cumuliform clouds, often aligned in bands parallel to the low-level wind.

By January, ice covers most lakes, at least in part, cutting off or reducing the heat supply. Lake Erie often freezes entirely because it is more shallow than the other Great Lakes.

MOISTURE: The lake surface evaporates, which is very effective when the wind is strong and the air dry The cold air from Canada has a very low pressure. Also, strong winds cause spray, facilitating evaporation.

WIND FETCH: The greater the distance that wind blows over the warm water, the greater the snow fall. Three of the five lakes are relatively long and narrow. Winds blowing the length of these lakes have a long route over water and will produce a lot of snow, but a 30 degree wind shift brings the winds across the lake. The shorter routes will produce less lake-effect snow and move the snow to a different site.

Click on Map

Related Web Sites NOAA Coast Watch - Great Lakes Node Information about current conditions of the Great Lakes including current and past water temperature and ice cover. WW2010 Summary of the Veterans Day Snowstorm Learn more about the Veterans Day Lake Effect Snowstorm that produced record amounts of snow in northern Ohio. Nowcasting Lake Effect Snow Learn to forecast lake effect snow via a lab exercise from the Cooperative Program for Operational Meteorology, Education, and Training (COMET). Click on Map

FRICTIONAL DIFFERENCE: The effect of the land surface on the moving air is much greater over rough land than it is over relatively smooth lake water. The rougher land slows the surface wind, causing more surface convergence and lifting. This effect is much greater with stronger winds.

UPSLOPE LIFT: In some localities, wind blowing from a lake onshore is forced to climb up hills. As the air rises, it cools and precipitates.

LARGE-SCALE FORCING: The general cyclonic nature of an air mass supports development of precipitation anywhere, and may also enhance lake-effect snow.

What Is Snow? When falling from the sky, snow is in the form of crystalline ice, and ice crystallizes into six-sided objects. After reaching the ground, snow loses it's crystalline shape and becomes granular. So falling snow and snow on the ground should be considered two different forms.

Formation of Snow Crystals Snow crystals are crystals of ice formed within the atmosphere at temperatures below freezing. They form due to condensation of water vapor on a very small ice crystal or dust particle. Typical Snow crystals are see through like glass, and are typically from.02 to.5 inches in diameter.

Lower levels of cumulonimbus clouds consist mostly of water droplets while at higher elevations, where temperatures are well below 0 degrees Celsius, ice crystals dominate.

Even though it is the rarest of storm types, the supercell is the most dangerous because of the extreme weather generated. This storm was producing baseball hailhail

Thundersnow viewed from space

Ground Snow Once snow hits the ground, it cannot keep its crystalline shape. The shape changes into more of a rounded form, even if the temperature remains below freezing. The ground snow will eventually become ice granules.

Can You Look Cross- Eyed??? Cross your eyes and stare at the next 3 Slides. You will be able to see a 3-Dimension image in the center.

After several days in a snow pack

From a melting snow pack

Hexagonal snow crystal with broad branches, composed of 2 offset 3 branched snow crystals.

Hexagonal snow crystal with broad branches, composed of 2 offset 3 branched snow crystals.

The needle crystal is often associated with heavy snowfall in the Northeastern United States.