LAKE-EFFECT SNOW—

The lake-effect snow machine runs on warm lake water. Surface water temperatures in the Great Lakes can be relatively warm compared to cold air flowing over them this time of year.

When the difference in temperature between the surface and the air aloft reaches a threshold value, typically between 18 and 23 degrees, lake effect snow becomes possible.

As cold air flows over the warm water, the lake warms and moistens the air. Since warm, moist air is less dense than cold air, the heated air rises. Rising air cools and water vapor condenses into cloud droplets.

Water vapor can turn to snow when it rises above the freezing level.

These clouds can produce snow over the lake, but the efficiency of snow production increases when the wind pushes the clouds over land. Friction with the ground causes air to pile up. This creates lift and enhances snowfall.

The lifting produced when these clouds run into the inland hills further enhances the snow production. That’s exactly what happens in the higher terrain east of Cleveland.

Winds accompanying these cold air masses in this area generally blow from a west or northwest direction causing lake effect snow to fall on the east or southeast sides of the lakes.

In order to have heavy lake-effect snow, cold air must travel over at least 60 miles of relatively warmer open water.

Lake Erie is the shallowest of the Great Lakes and, because of that, it is the warmest which means it can generate impressive snows early in the winter. However, it cools rapidly during the winter and is the only lake prone to freezing over.

When that happens lake-effect snows are effectively turned off.

The most notorious area for prodigious amounts of lake-effect snow around here is Buffalo, NY. This is because a west wind has some 250 miles of open water over which to gain moisture before it collides with the rising terrain at Buffalo’s east end of the lake.

They like to claim the title of the World’s Record City for Snowfall based on their 5 day record for continuous snow at 82.3 inches which fell in December 2001. (1)

Cleveland, by comparison, has a seasonal snowfall average of but 52 inches. (2)

The photo was taken recently from the computer screen of an image produced by the radar of Intellicast.com. Lake effect snows are clearly visible flowing from Lake Superior across the Upper Peninsula of Michigan and along the entire eastern shoreline of Lake Michigan. Note also the band of lake effect snow flowing south from Lake Huron across Lake Erie where it intensifies and grows into a huge area of snow in northeastern Ohio and covering much of western Pennsylvania. Winds throughout the area were from the north-northwestNotes:

(1) Click! The Buffalonian

(2) Click! City-data

Otherwise compiled from USATODAY.com and www.Weather.com/encyclopedia/winter/lake.html.