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Naturalist's data shows Minnesota lakes freeze later than they did 50 years ago

For the Minnesota Star Tribune

November 27, 2020 at 4:25AM

The general rule for walking, skating or fishing: 4 inches of ice. (BRIAN PETERSON • Star Tribune/The Minnesota Star Tribune)

The freeze-up dates for our Minnesota lakes are nearly impossible to predict because changing weather patterns feature warm and cold spells. Despite the variability, I can confidently say based on longtime data I've collected that lakes tend to freeze later than they did 50 years ago.

On and off since Oct. 24 here in southern Minnesota, we have seen ice on ponds and lake edges. Soon ice will form and then stay for months.

Listed below are some freeze-up dates for four Minnesota lakes. Note that 1991 was the year of the great Halloween snowstorm. I record freeze-up on the first day when at least 90% of a lake is frozen over and stays frozen over until the next spring.

Lake (county) freeze-up

19912015 2019

Cannon Lake (Rice County)

Nov. 3Dec. 19Dec. 2

Lake Waconia (Carver County)

Nov. 7Dec. 19Dec. 2

Lake Minnetonka (Hennepin County)

Nov. 25Dec. 31Dec. 2

Lake Bemidji (Beltrami County)

Nov. 4Dec. 19Dec. 3

For safety, remember it takes at least 4 inches of new solid ice in contact with stationary freshwater for safe skating, walking and ice fishing. A snowmobile takes 6 inches of ice, 8 to 12 inches are needed for a car, and 12 to 15 inches for a pickup truck. Going through the ice into cold water can quickly go bad. The cold water saps body heat 25 times faster than air of the same temperature. In 32-degree water, you have about 15 minutes before going unconscious.

Jim Gilbert's observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.