Cold Snap Proves Great Lakes Average Ice Cover Remains Unchanged Since 1973

A blast of frigid air from the Canadian Arctic over the last several days has the Great Lakes rapidly freezing over. After two straight winters of below-average ice cover, this one is shaping up to at least meet long-term averages, or be even icier.

The Great Lakes cumulatively went from 3.3% to 9.4% ice covered in just five days, from Dec. 22 through Wednesday, with continued cold temperatures expected to keep that number rising quickly. The Great Lakes at this time last year had just 3.2% ice cover — and a scant 0.3% ice cover at this time in 2015.

Despite an unusually warm fall, ice coverage started in spots on Lake Superior on Nov. 16, said George Leshkevich, a physical scientist at the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.

“With this cold weather we’re having now, I wouldn’t be surprised if, even before this weekend, there was ice on Saginaw Bay, a little bit in the western part of Lake Erie, and certainly Green Bay,” he said.

There’s not much relief in sight for ice-making conditions. After a brief “warm-up” to the high teens to start the weekend, Detroit’s forecast calls for high temperatures to drop back into the single digits to low teens well through next week.

The 225-foot Coast Guard cutter Hollyhock was scheduled to depart from Port Huron on Thursday morning, to travel down the St. Clair River and break ice in Lake St. Clair. The Detroit River has not yet iced up, according to a Coast Guard daily report, but they expected western Lake Erie to need ice-breaking by the weekend.

The Great Lakes Environmental Research Laboratory has kept Great Lakes ice coverage records since 1973. Over those 44 years, the average maximum ice coverage in a winter across the Great Lakes is about 55%.

During the positively polar winter of 2013-14, the Great Lakes neared total ice coverage, at 92.5%. The following winter was up there as well, at 88.8% covered. But then the mild winters of 2015-16 had the lakes only about one-third ice-covered at their peak, and last winter had only 19.7% coverage.

Full story

via The Global Warming Policy Forum (GWPF)

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December 29, 2017 at 11:46AM

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