A little more than a month ago, John Downing, a limnologist who heads the University of Minnesota Sea Grant program in Duluth, crunched some historical and meteorological data to predict a later-than-normal ice-out for northern Minnesota lakes.
Downing developed what he calls a lake ice-out “widget” where you can plug in a weather reporting station near your lake and figure, roughly, when ice out might occur.
In mid-March, with virtually no melting so far in winter, Downing predicted ice-out for north-central Minnesota lakes about a week or so later than average, but still in time for the May 13 fishing opener.
Now, past mid-April, Downing isn’t as sure all lakes will be ice-free by May 13, but he’s sticking with his prediction of mostly open water for the Minnesota opener. Last week’s spurt of unusually warm temperatures into the 70s across the Northland may have been enough to kick-start the melting process.
“Ice-out will still be late, but it would have been later without that week of hot weather,” Downing said.
Still, it’s going to take much more heat and many thawing-degree days to get the job done. Thawing-degree days are figured on a complicated formula: Add the daily high temperature to the daily low temperature, divide by 2 and then subtract 32. For every positive number, those are thawing-degree days. So if the air temperature is an average of 10 degrees above freezing during a day, that accumulates 10 thawing-degree days. (You don’t need to know that formula; the ice-out widget does it for you.)
You can track thawing-degree days for a weather station near your favorite lake at z.umn.edu/widget.
Downing’s ice-out widget figures that most north-central Minnesota lakes will lose their ice when the total thawing-degree days hit 220. But, as of Wednesday, lakes anywhere near the Hibbing weather reporting station were less than 110 thawing-degree days — not even halfway.
“Because so much snow had to be melted (before ice could start melting) for northern inland lakes, the models still point to May 6-8, plus or minus about five days for uncertainty due to weather,” Downing said. That makes the May 13 opener touch-and-go.
“If the weather (over the next three weeks) is warmer than usual, it will happen earlier,” Downing said. “If it is cooler than usual, it will happen later.”
The National Weather Service forecast is colder than normal temperatures for the next week.
As of Thursday, all lakes across the northern two-thirds of the state remained mostly ice-covered, with ice-out creeping as far north as the St. Cloud area. Lakes in southern Minnesota were on average losing their ice seven to 10 days later than their median dates, according to Pete Boulay, a climatologist in the Minnesota Department of Natural Resources’ state climatology office.
“Then the four days of 70s and 80s made up for lost ground, and now things are about five days to a week behind,” Boulay said.
Not a single southern Minnesota lake lost its ice in March this year, which is highly unusual, and only one did the first week in April, but the summer-like temperatures the second week of April boosted ice-out for some areas. Lake Minnetonka in the Twin Cities, with records dating back to 1855, loses its ice on average by April 13. This year it was April 19, Boulay said.
Moving north, Mille Lacs Lake on average loses its ice April 25, but it has been as late as May 16 back in 2013, the year most northern Minnesota lakes had their latest-ever ice-out. Big Sandy Lake near McGregor in Aitkin County, with nearly 100 years of records, loses its ice on average April 21, but it has been as late as May 12. Winnibigoshish on average loses its ice April 27, but it has been as late as May 17.
