DETROIT — 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.

"It's very dramatic," Leshkevich said. "The variability has become much greater."

Though some seasonal forecasts called for another mild winter on the Great Lakes, others predict a La Niña weather pattern in the Pacific, which tends to lead to colder temperatures and more precipitation in the Great Lakes region.

It matters because open water in winter has significant effects on local weather, generally keeping things warmer and with more precipitation. Some Great Lakes fish species, including whitefish, spawn in fairly shallow areas that can be destroyed by wave action, so ice cover improves their reproduction. And a host of ice-fishing tournaments and festivals were canceled across Michigan over the last two winters, impacting local economies.

"For our fruit-growers on the west side of the state, an extended ice season into the spring will accompany cooler temperatures," Leshkevich said. "If that extends long into the spring, it cuts down the chance of a killing frost."

The amount of ice on the Great Lakes impacts perhaps no one greater than the shipping industry. Those big ships moving iron ore, coal and other products through the Great Lakes to other Midwest states, the Atlantic Ocean and the world rely on ice-free passageways.

Less ice means more shipments in that window of opportunity, said Glenn Nekvasil, vice president of the Lake Carriers Association, a trade group representing U.S. freighters operating on the Great Lakes.

"The winters of '13-'14 and '14-'15 were basically Arctic," he said.

An iron ore freighter left the Duluth-Superior port on the Minnesota-Wisconsin border in western Lake Superior on March 26, 2014, bound for Gary, Ind. The trip typically takes 62 hours, but ice buildup that winter caused it to take 11 days, Nekvasil said. Another ore freighter leaving Escanaba, Mich., that month took 12 days to reach Cleveland, typically a 50-hour trip.