Ice sheets put a lid on lake-effect snowfall

The Chicago Tribune (subscription required) carried this article on the current lake conditions:

February is the month when the spread of the winter ice packs reaches its farthest extent, forming a cap that--if wide enough--can prevent water from evaporating from the lake surface, condensing in winter winds and falling onshore as snow. The more ice on the lake, the less lake-effect snow.

And as scientists, runners, and weather watchers have pointed out last week, the ice this year is prodigious, even when compared to winters past. Meteorologists say it is thick enough to survive even the current warm spell.

From Waukegan to Gary, a vast, 60-mile plain a few inches to a foot thick has appeared along the southeastern shore of Lake Michigan. Shorelines along the rest of the Great Lakes have also frozen over, forming 800 nearly continuous miles of ice between Duluth, Minn., and Sackets Harbor, N.Y.

"It's a little more than normal. Traditionally, this time of year you don't get a lot of ice in the southern basin of Lake Michigan," said Raymond Assel, a physical scientist at the Great Lakes Environmental Research Laboratory in Ann Arbor.

Green Bay is frozen solid enough (theoretically) for trucks to drive from the Wisconsin city as far as Menominee in the Upper Peninsula of Michigan. In Lake Superior, Thunder Bay is a bay no more; now it is a broad field of ice nearly 2 feet thick. You could walk nearly all the way from Forestville, Mich., across Lake Huron to Goderich, Ontario. All of Lake Ontario's shores are iced in. There is no open water on Lake Erie, the shallowest of the Great Lakes.

Historically, the deepest part of the winter freeze has yet to descend on the Great Lakes, Assel said. That comes at the end of February or the beginning of March. Those hoping to escape the winter without more shoveling would do well to hope for a sustained cold snap.