St. Cloud, MN Weather Forecast

How Air Got Cleaner Second Half of Yesterday

"The solution to pollution is dilution." That's a quote from Professor Volker Mohnen when I took his Air Pollution class in graduate school. This batch of smoke-filled air that has irritated Minnesota since Tuesday night got all the smoke from the northeastern Minnesota wildfires, then that air sank behind the cold front that moved through central Minnesota Wednesday night. That combination concentrated the smoke plume at the ground. And, the northeast winds behind the front blew the smoke-filled air into central and eastern Minnesota (see graph of St. Cloud air quality index when you set tab to 'hourly time series,' pollutant to PM2.5, particles, date to 7/15/2026, and location to St. Cloud on the MPCA past Air Quality Index). The air quality indices were pushed over 1000 at Ely (off the scale) and over 1600 at Hibbing.

The best way to ease the problem of polluted air is to spread the pollutants into a larger portion of air. The atmosphere can do this in two ways: 1) have low-level winds blow in air with less pollutants and 2) have the low-level air mix upward through a deeper air, thinning out the concentration of pollutants near the ground. Both things happened in St. Cloud and central Minnesota from mid-morning on yesterday. The wind direction switched to south (see NWS: last 72 hours of St. Cloud observations) and picked up during the afternoon, so the cleaner air south of the Minnesota River Valley returned to central Minnesota. And, the development of puffy cumulus clouds by late morning meant that more air was being mixed upward than earlier in the week when our sky was clear. That's because the plume of very warm air at 5,000 to 10,000 feet above the ground earlier in the week had cooled, allowing more than a few thousand feet of mixing.

That combination has allowed the air quality index to ease back (see loop of AQI on the EPA Airnow.gov interactive map, when you push the loop button) into the moderate (yellow) category from the south of Alexandria, Little Falls, and most of the Twin Cities (see latest Minnesota Pollution Control Agency Minnesota air quality index map). Conditions are still bad from Brainerd and Hinckley northward, particularly in northeastern Minnesota where the AQI is still as high as 1000 in the Duluth area.

Essentially, the Air Quality Alert will only remain in effect for the parts of Minnesota in the purple or worse ratings. As the south winds continue to blow into Friday, the worst pollution will retreat into northeastern Minnesota, but these areas aren't likely to see any relief.

Central Minnesota will likely have another shot at the smoke plume. After a cold front pushes through this evening, our winds will switch to northwest, likely blowing the pollutants from Winnipeg and the leftover smoke plume to our north back into the rest of Minnesota (see forecast smoke plume from firesmoke.ca). The sinking air behind the front will help concentrate them again near the ground. So, I expect major air quality issues from Friday night at least into Saturday. 

Back and Forth From Hot (Today, Sunday and Monday) to Warm (Tomorrow)

We will be in a back-and-forth pattern of lingering heat from today until Monday. Today, most of central,  southern, and northeastern Minnesota is in a heat advisory (orange), while the continuing overnight hot temperatures has the Twin Cities metro in an extreme heat warning (red on the NWS Twin Cities watch-warning map). the leading edge of the hotter and more humid air (see 24-hour loop of NWS WPC surface maps) will remain to our north, so the south winds will continue. Dew points will remain in the upper 60's to Florida-like lower 70's (see orange on the UCAR hourly dew point map), so we will see highs back in the lower half of the 90's with those uncomfortable dew points producing heat indices from the upper 90's to the lower 100's (see NWS Minnesota hourly weather round-up for the latest temperatures, dew points, and heat indices when 88 or over).

The hotter and breezier conditions will also aggravate the fire danger to our north, although the higher dew points will offset the issue somewhat. Still, the high fire danger should continue in parts of far northern Minnesota.

Scattered Storms Perhaps Tonight (More in N MN)

The front to our south will push southward through the rest of Minnesota by tomorrow morning. Satellite imagery is now back (see College of DuPage clean infrared satellite loop since yesterday afternoon), showing a few scattered thunderstorms in northern Minnesota (see College of DuPage north central US radar loop). The weather system that will push the front southward tonight is causing storms over Montana. That system will allow new storms to develop this afternoon and evening, but the bulk of them will remain over northern Minnesota (see Day 1 of the NWS WPC quantitative precipitation forecast). There could be some isolated severe weather (best chance being large hail or damaging winds, but a tornado can't be ruled out), but the threat is small (category 1 of 5 on the NWS Storm Prediction Center convective outlook).

Leftover Smoke Likely Tonight and Tomorrow

Tomorrow, the Manitoba air will push into Minnesota. Dew points will fall into the more comfortable 50's and we will see hazy sunshine through the smoke. I am going for the smoke to persist all day, so I have highs back in the 80's. The combination of warm, windy, and drier air will likely crank up the northern Minnesota fire danger to extreme. I wouldn't be surprised to see red flag warnings again issued in at least northern Minnesota. Saturday's smokier air will likely end the St. Cloud heat wave (5 straight days with a 90-degree high including yesterday's 92, likely to reach 6 today). St. Cloud's last 6-day heat wave was during June 5-10, 2021.

Another Shot at 90 Sunday (A Bit More Humid)

Another storm system will turn our winds back to the south on Sunday. The air will also get slightly more humid, but I think the dew points will be limited to the 60's. We will again have a good shot at a high in the 90's, but the heat index will likely be close to the temperature, so the worst I would expect is a heat advisory.

Storms Possible Sunday Night

A stronger cold front will push through on Sunday night. There will again be a chance of a few scattered thunderstorms (I have a 40% chance for those storms). There will be a small chance of severe weather (see NWS Storm Prediction Center Day 3 convective outlook) and only a limited chance for rain (see Day 3 of the NWS WPC quantitative precipitation forecast). If we have dry thunderstorms tonight or Sunday night, lightning strikes could start new wildfires in northern Minnesota.

Longer Period of Drier, Eventually Cooler, and Perhaps Smoky Air Next Week

The longer surge of cooler and drier air during the first half of next week is coming into better focus. The drier air will arrive on strong north winds Sunday night, but the air will still be warm, so we could have another 90-degree plus high on Monday. The cooler air will move in Monday night. For the middle portion of next week, we will see highs in the lower 80's or even the upper 70's. Overnight lows could drop into the 50's.

It is still uncertain how much of the smoke from the fires from the Yukon and Nunavut into the northern Canadian Prairie Provinces will push into Minnesota or how close to the ground the smoke will be, but there will be the potential for more air pollution issues. And, the still warm, dry, and breezy air will pose the risk of new wildfires. Still, the potential for significant rainfall during the upcoming week is uncertain, but likely small (see Days 4-7 of the NWS WPC quantitative precipitation forecast).