Graph of summer days per year with a maximum daily Air Quality Index (AQI) value in Minnesota of 151 or higher ("Red" or "Unhealthy" category). Image produced by Minnesota State Climatology Office with data from Minnesota Pollution Control Agency.
The summers of 2021 and 2023 may have begun to normalize wildfire smoke pollution in Minnesota, but 2025 took it to a new level and was likely the smokiest year in five decades or more. The smoke and its harmful particulates degraded air quality and forced many Minnesotans indoors frequently throughout the summer.
Most of the problems arrived on northerly and northwesterly winds, which swept in smoke-filled air from large fires that burned through the summer in the forests of Manitoba and Saskatchewan. Northwesterly winds in the summer often spell relief from sultry air, but more than once this summer the heat was broken by cool but thickly-polluted air that smelled like burning tires.
From June through August, Minnesota experienced 15 days with at least one station recording a daily Air Quality Index (AQI) of 151 or higher, which is the "Red" or "Unhealthy for everyone" category. Nine additional days had AQI over 100 ("Orange" or "Unhealthy for sensitive groups") somewhere in the state. No recent year could match 2025 for its frequency of badly degraded air quality. The closest recent year was 2021, which had nine Red AQI days somewhere in Minnesota, meaning 2025 had two-thirds or 67% more Unhealthy days than 2021.
Three major events punctuated the smoky summer: one from late May into early June; a weekend outbreak July 11-13; and a prolonged, 9-day event from the end of July into the first week of August.
Although we can only extend the most basic comparisons with 2025 back into the 2010s, when the Minnesota Pollution Control Agency improved the coverage of its sensor network, weather observer notes and hourly observations also document the frequency and duration of smoky conditions. Looking at those supplemental sources, no year from 1978 through 2024 appears to have anything resembling 2025 in terms of smoke frequency. Both 1976 and 1977 had high fire frequencies in Minnesota, but hourly reports of smoke were much lower both years than 2025. It's difficult to say with certainty that this past year was smokier than those years, but at a minimum it was the smokiest since those years, and 2025 appears to be the smokiest year in Minnesota in five decades or more.
Posted December 15, 2025
KAB