Smoke plumes seen on radar loop from Duluth late afternoon on Monday May 12, 2025. Stationary, "streaming" echoes ( three to north and one to south of radar site) are particulates in smoke plumes from wildfires.
Radar loop courtesy of College of DuPage; data from NOAA/National Weather Service
A hot, dry air mass overspread Minnesota beginning on Saturday May 10th, with record high temperatures and an outbreak of wildfires in parts of the state.
A warm, sunny, and dry pattern had dominated Minnesota's weather since May 2nd or 3rd, but a much hotter and drier air mass moved in over the weekend of the 10th and 11th, as winds from the southwest increased along the gradient between low pressure in Montana and high pressure over the northeastern US.
Saturday May 10th was warm and sunny in most areas, but hot in western and southwestern Minnesota, with temperatures reaching the upper 80s to near 90 degrees F.
The heat reached its greatest intensity on Sunday May 11th, as winds increased and relative humidity dropped into the 15-25% range. The highest temperatures exhibited an atypical, geographically inverted pattern, with far northern Minnesota coming in as the hottest part of the state. International Falls reached a maximum temperature of 96 F, which shattered the old daily record of 83 F, and became the highest temperature ever recorded so early in the season at that station. St. Cloud, the Twin Cities, and Duluth all set daily records, at 93, 90, and 87 F, respectively.
The heat continued through Wednesday May 14th, though at slightly lower intensity but with even drier air in place on Monday, when relative humidity of 10-20% was common throughout Minnesota. The geographical inversion of temperatures continued, with the hottest air generally up near the Canadian border. International Falls broke daily high temperature records each day through Wednesday, and its run of four straight days with high temperatures of at least 90 F was the first during May in the history of the station. Duluth also broke a daily maximum temperature record on Monday, but none of the other first-order climate stations broke daily records after Sunday.
The excessively dry heat, combined with gusty winds and emergent or dormant vegetation, led to a high risk for wildfires. The first major fire, the Camp House Fire, formed near Brimson in St. Louis County, damaging structures and requiring some evacuations. By Monday another large fire developed about 10 miles away near Jenkins Creek, and the Duluth radar showed the plumes of four separate fires--three in St. Louis County and one in eastern Pine County near the border with Wisconsin.
The heat and fire risk dropped off appreciably starting on Thursday as higher humidity, thunderstorms, heavy rains, and eventually cooler air swept into the state, in association with a potent spring cyclone in the Dakotas.
May 15, 2025
KAB