Of all the images of ice last winter, one of my favorites was a friend’s photo of crumpled sheets of blue ice on the west side of Beaver Island in northern Lake Michigan. With her smartphone, Denise McDonough snapped a photo that looked like it was taken by a polar explorer, not by one of the proprietors of McDonough’s Market, the family-owned grocery store on the island.
Her photo evoked childhood memories of the ice and snow in the Great Lakes region, so it makes sense to me that the forecast for this summer is for some of the coldest surface water we’ve seen since 1979.
At the end of May, small icebergs were still being spotted from a webcam mounted on Granite Island, an aptly named small, rocky island with a lighthouse about 5 miles from shore near Marquette, Michigan, on Lake Superior. The lake is normally ice-free by the end of April.
With more than 90 percent of the Great Lakes covered in ice last winter, it should come as no surprise that summer water temperatures are expected to be colder than normal, but just how cold was anyone’s guess until now.
Researchers studying evaporation on the Great Lakes have developed a new forecasting tool for seasonal water temperatures on Lake Superior, funded in part by the University of Michigan.
Surface water temperatures above the deepest parts of Lake Superior are expected to be at least 6 degrees Fahrenheit colder than normal by August, the research team says. This temperature difference is about three times greater than at present, which was only about 2 degrees below normal at the end of May.
Why the big amplification by late summer? It has something to do with thermal memory and the way the lake mixes before and after 39 degrees Fahrenheit, the temperature that water reaches its maximum density, according to John Lenters of LimnoTech, one of the lead researchers on the project.
“Before 39 degrees, the lake mixes very deeply, which causes it to warm slowly, especially in deep, offshore waters,” said Lenters. “After 39 degrees, the top layer of the lake will warm much more rapidly. But this year, that rapid surface warming is not likely to happen in the offshore waters until well after the fourth of July. And it’s all because we started out just a few degrees below normal.”
My last post on this topic was about how “Ice Cover Affects Water Levels in Surprising Ways.” To summarize what this latest information means for lake levels, the cooler water this summer is good news because it will delay the evaporation season, allowing the lakes to continue their recovery from record lows last year.
The Summer of Fog
Ice sightings are giving way to another weather phenomena: fog. Just the other day, my mom sent me the above photo of a thick, white fog bank taken from her deck overlooking Lake Michigan.
A fisherman’s video of a fog bank rolling in off the lake went viral after it was posted to YouTube on May 21:
Fog events are likely to continue with the combination of chilly water and warm, humid air.
“It’s going to be the summer of fog,” said Peter Blanken, a study co-investigator from the University of Colorado. “The water will stay really cold, but summer air tends to be warm and humid. And any time you get that combination, you’re going to have condensation and fog – basically evaporation in reverse.”
For more information about the new water temperature forecast tool and to view forecast maps, visit the U-M website.
Lisa Borre is a lake conservationist, freelance writer and avid sailor. With her husband, she co-founded LakeNet, a world lakes network, and co-wrote a sailing guide called “The Black Sea” based on their voyage around the sea in 2010. A native of the Great Lakes region, she served as coordinator of the Lake Champlain Basin Program in the 1990s. She is now an active member of the Global Lake Ecological Observatory Network.