Average ice-out dates of interest to many in Minnesota

Reliable ice-out records for Lake Bemidji go back to 1932, written by a dentist on the wall of his garage. A local professor continued the tradition before passing the torch in 1992 to Lake Bemidji State Park naturalist John Fylpaa.

His prediction for 2016?

"It's quite possible we could have very early ice-out," Fylpaa said.

While ice-out dates in Minnesota have fluctuated wildly even within the past five years, close observers such as Fylpaa have noticed a long-term trend toward shorter periods of ice covering state lakes. The trend is more pronounced in the fall, with later and later ice-ups, Fylpaa said. But the average time for ice-out on Lake Bemidji has now crept into the second week of April after steadily arriving for many years during the third week of April, he said.

Records kept by the Minnesota Department of Natural Resources (DNR) show similar patterns on many other individual lakes. There's not enough statewide data to count as a statistically significant trend, experts say, but a rash of early ice-out dates since the late 1990s has clearly been noticed by fisheries managers, climatologists, naturalists and lake biologists.

Loons and other waterfowl species are returning earlier, hatcheries are meeting fish-stocking orders with more ease and boats are spending less time in storage.

On the other hand, spawning seasons are less predictable in early ice-out years and some worry that marginally cold-water lakes such as Lake Bemidji might warm up and lose cold-water species like tulibees, an important forage fish for walleye, northern and muskies.

Whatever the consequences of early or late ice-outs, Minnesotans are transfixed by them. Ice-out contests are about to gear up in some communities and DNR climatologist Pete Boulay said his interactive "Lake Ice Out" web page is a big hit annually, drawing 165,000 visitors in April 2014 — when ice-outs were late. You can click on your favorite lake and get a history of ice-out dates.

"People get excited about it because it's a sign of spring," Boulay said.

He said he learned years ago to stop predicting ice-out dates because projections can be very inexact. Snow cover on a frozen lake will slow the process while rain and balmy winds will speed it. Ice thickness has been below average this year on many Minnesota lakes, but Boulay said it's not always an indicator of early ice-out. The biggest factor is what temperatures are in March, April and May.

"There's no way to tell what's going to happen this spring yet," he said.

One constant is that Lake Pepin is one of the first to lose its ice, aided by flows from the Mississippi River. Feb. 29, 2000, is one of the earliest ice-outs on record for Minnesota and it happened on Pepin, Boulay said. The latest ice-out was June 3, 1936, on Gunflint Lake, near Grand Marais, he said.

Noah Lottig, a scientist at the University of Wisconsin's Center for Limnology, said 30 years of lake ice-out data gathered at the Trout Lake Station near Minocqua, where he works, is not enough to show a statistically significant trend. But that doesn't mean a trend doesn't exist, he said.

Lottig said there's evidence that north temperate lakes under study by the center in conjunction with the National Science Foundation are under ice for shorter periods of time than before.

On Lake Mendota in Madison, Wis., for instance, an unusually large amount of ice-out data shows that the lake's ice cover now lasts an average of about 100 days, 20 days shorter from the average long ago.

"In lakes where we have enough data," Lottig said, "we are seeing significantly shorter periods of ice-on days."

Minnesota DNR fisheries managers have noticed a trend toward early ice-outs since the late 1990s. But there have been exceptions as recently as 2014, when many northern lakes were frozen over for the mid-May fishing opener.

But on the flip side, DNR fisheries crews have more difficulty with fish surveys when ice-out is early or late. Average ice-outs are more prone to coincide with predictable spawning periods, when trap-netting can be most effective in measuring fish abundance and average sizes.

Fisheries supervisors Brad Parsons and Gary Altena said early ice-outs often trigger extended spawning seasons that are interrupted by cold fronts, making the survey work more challenging.

"The fish movement is less predictable when ice-out is early or late," Altena said.

Staff writer MaryJo Webster contributed to this report.