TRAVERSE CITY, Mich. (AP) — For the second consecutive winter, bitter weather threatens to turn the surface of the Great Lakes into a vast frozen plain.

The federal Great Lakes research laboratory in Ann Arbor, Michigan reports Friday that nearly 81 percent of the five lakes' surface area is ice-covered. On Thursday, the ice cover exceeded 85 percent.

The lab's George Leshkevich says the small drop-off probably happened because winds broke apart some ice, creating open spots.

Still, satellite imagery shows this year's ice cover has grown rapidly, nearly doubling over the past couple of weeks.

Records show the lakes' most widespread freeze was 94.7 percent in 1979. The ice cover topped out at 92.2 percent last March.

Coast Guard spokesman Lorne Thomas in Cleveland, Ohio says another difficult season is in store for icebreaking vessels.