Lake effects: Snowbelts
Lake effect snow is one of the most impressive ways that Lake Erie affects our weather. It's an unusal phenomenon. Here's how it happens.
The frigid air pools along the eastern slopes of the Canadian Rockies.
Vast stretches of cold.
Waiting for the chance to roll south and east over the plains of Alberta, Saskatchewan and Manitoba. Waiting to roll through the mid-continental corridor between mountain ranges and into the low basin of the Great Lakes.
High in the sky, the jet stream is changing course. The stream of hurricane-force winds races around the globe, crossing North America from west to east, following the boundary between the warm and cold air masses. Now it loops farther south, deep into the midwestern United States. It pulls the polar air behind it. The leading edge forms a cold front, advancing, picking up speed. Dry, cold air rolling out of the north, and then crossing the warm waters of Lake Erie.
In the fall and early winter, the lake is warmer than surrounding land. The land is a spendthrift that rapidly fritters away its summer warmth. But the lake is a Scrooge. It hoards a vast fortune of heat during the summer and parts with it penny by penny during September, October, November, December.
As the surface water cools, it becomes more dense and sinks. Warmer water stored in the depths then rises to take its place. Until it reaches about 39 degrees F., the lake is a circulating reservoir of heat. The cold air from the north passes over this warm, open body. The air warms, takes on moisture, rises up in clouds. The clouds pile up on the cold southern shore of the lake and keep rising and cooling until they can no longer hold the water they stole from the lake.
Then it snows. The faster the clouds rise and cool, the faster it snows. To the west of Cleveland are low lake plains. The moisture-laden air meets no sudden elevation. It can slip inland and deposit snow gradually over some distance. But to the east of the city is the Portage Escarpment, the abrupt climb to the Heights, the last gasp of the Appalachian foothills. While the lake is about 570 feet above sea level and the city is 600 to 700 feet, the Heights are 1000 feet and, beyond, parts of Geauga County are over 1250.
As the air is driven up these elevations, it dumps snow suddenly, thickly. As a result of this lake effect snow, the snowbelt near Chardon gets two to three times the snowfall of the rest of northern Ohio. The location of any one of these snowfalls is hard to predict. The squalls often appear in narrow bands, like curtains of snow that extend inland 25 to 30 miles before depleting themselves. The bands may stay in one place or move with the shifting winds. One spot may be buried under two feet of snow, while a town just a few miles away may escape with light flurries.
The chances for lake effect snow depend largely on the temperature difference between lake and air (it needs to be at least 25 degrees), the elevation of the land, and the amount of open water the cold air crosses (the fetch). A northerly wind may travel only 50 or 60 miles over the narrow width of the lake before reaching Cleveland. Much more snow can be generated by a southwesterly wind blowing up the length of the lake to Buffalo and then climbing the mountains farther east.
This is unusual snow. The leeward shores of the Great Lakes are wondrously blessed (or cursed). Few other spots on Earththe eastern shore of Hudson Bay, the islands of northern Japancombine the right geographical conditions for so much lake effect snow. The right place must have a body of water large enough to warm the air, but not so large to warm it above the freezing point. It must have a large land mass upwind to supply cold air. And, finally, it must be far enough from the equator to have temperatures low enough for snow, but not so cold that the body of water freezes.
Later in the winter, when most of Lake Erie does freeze over, the lake effect snowmaking machine is turned off.