Snow, cold, ice drive predictions for significant rise in Michigan-Huron water level
A harsh winter of cold, snow and ice has finally yielded some good news — more water for the Great Lakes.
Just 14 month after hitting a record low, the Lake Michigan-Huron water level, already 13 inches higher than last year at this time, is expected to rise at least another 14 inches by August, according to predictions released this week by the U.S. Army Corps of Engineers.
That would put the water level about eight inches higher than last year, although it would still be 10 inches below the average for August and 41 inches below the record high in 1986.
The prediction comes just days after scientists reported that the ice cover on the Great Lakes peaked at 90.5% on March 2. That is closing in on the record of 94.7% set in 1979, although ice surveys only date to 1973, according to George Leshkevich, a physical scientist with the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory.
Lake Michigan is 90.5% covered by ice, while lakes Superior, Huron and Erie are at least 95% covered. Only 45% of Lake Ontario is covered by ice.
And for the first time in 18 years, ice on the lakes reached a “double max,” topping out at 88% on Feb. 13 and 14, then decreasing during a brief respite from freezing temperatures before peaking again, this time at 90.5% on March 2, Leshkevich said.
“That hasn’t happened since 1996,” he said. “Usually ice on the lakes will reach a max in mid-February, then start to break up and decay. Not this year.”
Ice is a factor in the complex lake level equation, but snow is driving predictions for a significant increase, according Keith Kompoltowicz, chief of water hydrology for the Army Corps.
“The snow cover across the Great Lakes, especially in the Lake Michigan-Huron basin, has the highest water equivalency we’ve seen in 10 years,” he said.
The correlation between water trapped in snow and lake levels is relatively straightforward — much of that moisture will reach the lakes when the snow melts.
The impact ice has on lake levels is not as clear, experts say.
“Certainly an extensive ice cover can reduce evaporation on the Great Lakes,” Leshkevich said. “That hopefully stabilizes water levels.”
During the last few years, evaporation monitoring stations have been set up around the Great Lakes in an effort to better quantify the amount of water lost to evaporation, he said.
But ice also plays an important role in lakes levels by affecting water temperatures, Leshkevich said.
Because colder water evaporates at a slower rate than warmer water, the longer ice persists, the longer the lake water remains cold and less prone to evaporation, Leshkevich said.
“If the ice persists into spring, and that is a big if, the more impact it will have on water levels,” Leshkevich said. “The longer ice persists, the longer it takes for the heating season to begin.”
A delayed increase in spring water temperatures combined with a cool and cloudy summer can keep water temperatures relatively cool heading into fall, which is when the greatest evaporation occurs because of the significant difference between water and air temperatures, Kompoltowicz said.
Last fall, the decline in Michigan-Huron water levels was only six to seven inches, about half the normal decline, due in part to a cool, wet fall, he said.
The cold weather then set the stage for the early onset of ice, Leshkevich said.
“We started receiving reports of ice on the lakes as early as late November,” he said.
But over the next several months, precipitation will be the most significant factor, Kompoltowicz said.
“In 2013, we had very heavy rainfall in April. Unfortunately that caused some flooding, but it was good for lake levels,” he said. “That, combined with a heathy snow cover, although one that was nothing like this winter’s, produced a 20-inch seasonal increase in lake levels.
“If we have another wet spring, another increase of 20 inches would not be unexpected.”
Image information: ICE ON LAKE MICHIGAN as seen from the bluffs at Lion’s Den Gorge Nature Preserve in the Town of Grafton. Photo by Bill Schanen IV