Lake Oaskis in Todd County has ice out records going back to 1867. May 13, 2013 was the second latest on record for Osakis. The latest on record for Osakis is 1950 with a May 14 date. Ironically, 2012 saw the second earliest ice out with March 21.
To set the stage for the long lasting ice cover, one can look into the month of April and the first half of May. Coming off the heels of a chilly meteorological spring, April started off with lows in the teens across Minnesota, along with some snow cover. Instead of gradually warming up to normal temperatures, April maintained below average temperatures and above average snowfall due to the placement of the jet stream, dragging cool air down from Canada.
The jet stream formed in a way in April that brought several low-pressure systems from northern Canada right into Minnesota. These storms brought unseasonably cool temperatures as well as snowfall. Since the temperatures were cool enough to sustain snow cover, it became an integral part to keeping the ice on the lakes. The snowfall contributed to ice over lakes as the snow layer kept the heat from reaching the ice. Additionally, the foggy and overcast conditions associated with many of the events enhanced the lifetime of the snowpack. The coolness eventually faded as some warmer events came through in late April, allowing the remaining ice on metro area lakes to melt away. Early May brought a return to the cold weather pattern and more snow. Typically, the jet stream retreats northward as the summer approaches due to large temperature gradients, yet Minnesota still saw pockets of cooler air sneaking into Minnesota at the beginning of the month. Many of the larger walleye lakes in northern Minnesota, and Mille Lacs as well remained ice covered for the fishing opener on May 11.
The weather became mild and then downright hot by mid May, with the 14th of May being a large catalyst for ice out dates. With dry air coming off of the Rockies, most areas around the state saw 80s and 90s and some locations reporting over 100 degrees for a maximum temperature. The large northern lakes lost their ice within a few days after this heat event and only the larger Boundary Waters lakes held onto their ice beyond May 17.
Here are some well-known lakes that have set new records in 2013 (Compiled with assistance from Climatology Volunteer John McCarty).
Lake Name County New Record Old Record Period of Record --------------------------------------------------------------------------------- Minnewaska Pope May 11, 2013 May 5, 1950 108 years Green Kandiohi May 8, 2013 May 7, 1951 83 years Mille Lacs Mille Lacs May 16, 2013 May 15, 1950 58 years Big Stone Big Stone May 8, 2013 April 29, 1950 62 years Calhoun Hennepin April 28, 2013 April 28, 1965 68 years (tie)
BWCA Ice Out Dates for 2013