Warm and humid air surged across much of Minnesota on Friday July 11th, only to be replaced by dense smoke from wildfires in southern Canada. Smoky skies and a strong burning scent dominated the weekend over much of Minnesota.
A cold front moving into a typically muggy summer air mass on Friday ignited a round of strong afternoon thunderstorms across northern and central Minnesota. The normally refreshing breeze associated with rain-cooled air ahead of the storms also brought gusty waves of fine smoke particulates, along with a distinct "sour campfire" odor. As the storms produced heavy rain and even some hail, the smoky air and aroma persisted. The smoke had already been plaguing northwestern Minnesota earlier in the day, and after the storms moved on, clearing skies revealed smoke so thick the sun was reduced to a small red disk in the sky.
The smoke was generally thickest on Friday over northern and central Minnesota, where sensors monitored by the Minnesota Pollution Control Agency measured particle concentrations of up to 400 micrograms per cubic meter, putting them into worst category of air quality (called "Hazardous"). However, the smoke was most widespread on Saturday, when the majority of the state experienced daily-averaged Air Quality Index values in the Red or "Unhealthy for Everyone" category.
This major smoke event joins the ranks of another from this year and others from 2023, 2021, and 2016. During this event, several sensors broke their records for highest particulate concentrations from wildfire smoke. None broke the record of 476.2 micrograms per cubic meter, set on June 3rd this year at Grand Portage.
Posted July 15, 2025
KAB