Lake Superior forecast calls for above average lake levels
Lake Superior will rise an inch above average in March and is expected to stay at that level at least through August, the U.S. Army Corps of Engineers said today.
The Corp's Detroit District released its annual water level forecast, saying a massive amount of water currently locked up in snow around Lake Superior will help push the lake level up.
"We forecast the lake to be at or just above long-term averages for the next six months,'' said Keith Kompoltowicz, the Corps' Detroit District chief of watershed hydrology.
Even before the snow began melting, the big lake on March 1 rose to its average level for the first time in nine years, according to the International Lake Superior Board of Control, continuing a year-long upward trend. The lake is more than a foot higher than it was one year ago.
Kompoltowicz said the snow on the ground around Lake Superior holds an estimated 9.5 inches of water equivalent, one of the highest levels on record.
"There's a lot of water on the ground waiting to melt,'' Kompoltowicz said in a teleconference with reporters.
That spring snowmelt is the greatest contributor to the lake's level each year, with water levels rising from April to August and then falling through each winter when moisture is locked up in snow and ice.
Officials also said the lake's extensive ice coverage this winter - at about 95 percent ice-covered as of today - could help keep more water in the lake come summer. If the lake ice continues into spring, it could keep summer water temperatures cooler, which would limit summer evaporation. But that evaporation also depends on summer air temperatures, and a warm summer could negate the impact of the ice on evaporation, said George Leshkevich, Great Lakes ice expert for the National Oceanic and Atmospheric Administration.
The trend seems to depart from a decade-long low period for the upper lakes. But officials stopped short of saying the lakes are nearing any sort of prolonged high-water period.
Lake Michigan and Huron is surrounded by 4-8 inches of water equivalent in the snowpack, with many cities around the lakes seeing near record snowfall this winter. The lakes are expected to continue a year-long trend away from near record low levels last winter. They remain a foot above last year's level at this time, when the all-time record low occurred, but still a foot below the long term average.
Experts said they expect Huron-Michigan to rise 14 inches from now through August, two inches more than normal. But they said the lakes will continue to remain just below long-term averages. That could change if wet conditions continue into spring and summer, Kompoltowicz said.
"Fourteen inches could be on the low side for the rise if wet conditions continue,'' he said.
The levels of the Great Lakes are important for shipping interests, which in recent years have seen lighter loads for Great lakes freighters, requiring more trips to carry the same amount of cargo. The lakes levels also impact things like shoreline erosion and fish spawning habitat.
Some 91 percent of the Great Lakes were covered in ice today, the most ice since 1973, officials said. Only in 1979, when ice coverage hit 94.7 percent of the lakes, was the level higher under modern records.
Lake Superior sat at 94.7 percent ice-covered today. The big lake has fluctuated between 80 and 95 percent in recent weeks, but could still freeze over entirely for the first time since 1996.
All that ice will make it tougher for the U.S. Coast Guard to clear shipping lanes for Great Lakes freighters for the expected opening of commerce on March 25, when the Soo Locks open.
The Coast Guard Cutter Alder began breaking ice Tuesday in the Twin Ports in advance of the coming shipping season.
"With the vast amount of ice we have on the lakes now... the Coast Guard is expecting a very tough go of it,'' Kompoltowicz said.