St. Cloud, MN Weather Forecast

90's Throughout Minnesota; 100's on the Canadian Border

You don't need me to tell you that yesterday was hot again.  

The hottest temperatures were again in northern Minnesota. Crane Lake near the Boundary Waters hit 100 degrees (set time to 20Z-22Z, 4-6 PM, on the NWS Aviation Weather Center METAR map) with temperatures as high as 104 near the Canadian border (see map of cooperative reports from NWS Duluth) The main batch of 100's were in the western Dakotas to the Nebraska Panhandle and northeastern Colorado (see yesterday's 4 PM NWS WPC North America zoom-in map). 

In much of Minnesota, the intense heat allowed better mixing of the air from the ground, so the dew points stayed mostly in the upper 60's instead of Sunday's middle 70's. That kept the heat index only a couple of degrees warmer than the temperature, except a few pockets of northwestern Minnesota which had indices over 100 degrees (set time to 3-5 PM on the NWS Minnesota hourly weather round-up).

The exception was in southern Minnesota, where the afternoon dew points were still in the Florida-like middle 70's. The extra moisture in the air kept some of the sun's heat from getting to the ground, but made it harder for the evaporation of sweat to cool people, so heat indices were in the upper 90's. St. Cloud got to 92 degrees, the hottest temperature of the summer so far with a top heat index of 96 (see NWS: last 72 hours of St. Cloud temperatures).

You can see that the plume of hottest afternoon air ran from Montana and Wyoming to the Dakotas, Nebraska, and northern Minnesota (area of black turning to white each afternoon on the College of DuPage continental US clean infrared satellite loop).

Wildfires Now Spreading Large Smoke Plume and Poor Air Quality (BWCAW Closed)

The hot temperatures and breezy conditions were favorable for the wildfires burning in northeastern Minnesota. Note also the smoke symbol (symbol 04 on the NWS Jet Stream weather symbol chart) at Thunder Bay, Ontario (CYQT during 20Z-22Z, 4-6 PM, on the NWS Aviation Weather Center METAR map), as the plume from the wildfires blew in during the afternoon. The entire Boundary Waters Canoe Area Wilderness is now closed through at least Friday.

Some Smoke Reaching Into Central Minnesota By Tomorrow?

The southwest winds pushed that smoke plume over Thunder Bay and the Ontario shore of Lake Superior (see EPA fire and smoke map). The Minnesota Pollution Control Agency has issued an air quality alert in the eastern Iron Range, the Boundary Waters, and northeastern Minnesota through Thursday. These areas will suffer purple levels of air quality, affecting everyone, due to both the Minnesota wildfires and the smoke from the Manitoba and Ontario wildfires when the wind switches to north or northeast by tomorrow.  The EPA fire and smoke map also showed the moderate air quality levels in parts of eastern Minnesota (yellow) due to ozone, caused by the intense heating of vehicle pollutants. However, north or northeast winds could bring some of that smoke in northeastern Minnesota into parts of central Minnesota tomorrow.

Conditions Favorable for Wildfires Continue

The area close to the Minnesota-Ontario border will continue to be under a red flag warning, the highest category of fire danger, this afternoon and early evening. 

Worst of Heat Today, But Pockets of Slight Relief Tomorrow and Thursday(?)

The heat will go on during at least this work week, although there may be some pockets of relief. Today will be similar to yesterday (note the reds and purples on the NWS Heat Risk forecast in central and northern Minnesota today). Expect lots of highs in the 90's with upper 90's possible. Heat indices will be primarily between 95 and 102 (see NWS Minnesota hourly weather round-up for latest temperatures, dew points, and heat indices when over 87 degrees).

Note that the reds and purples on the NWS Heat Risk forecast are more scattered in pockets after today. That's because the cold front in Manitoba and Ontario on the latest NWS WPC North America zoom-in surface map will drift into northern Minnesota today and get into central Minnesota by tomorrow morning. Slightly less humid air (dew points in the 60's, maybe in the 50's in northern Minnesota) will build in, so the heat index and the temperature will likely be near the same. Still, I don't see much of a thunderstorm chance, since the warm pocket of air aloft will remain aloft. Note how little of the Canadian Prairie Provinces had thunderstorms or even clouds over the past day (see College of DuPage North America clean infrared satellite loop).

Extreme Heat Warning Continues Through Thursday Evening Due to Hot Days and Extremely Warm Nights

So, we will still have a chance for high temperatures in the 90's tomorrow through Friday, although a few pockets may have highs in the middle to upper 80's. Overnights, however, will continue to see low temperatures from the upper 60's into the 70's. That's the main reason that the National Weather Service has persisted the extreme heat warning from now all the way through 9 PM Thursday in central Minnesota and the Minnesota River Valley. 

There could be at least some relief after tonight in northwestern Minnesota (warning until 10 PM tonight) and northeastern Minnesota (warning until 9 PM tonight) as the slightly cooler and dry air will work in. On the other hand, the northeast winds raise the risk of spreading the wildfire smoke further to the south into central Minnesota.

Perhaps 'Only 90' Thursday, Middle 90's Friday

The forecast for Thursday into Friday is a bit more uncertain. The latest computer forecasts have another surge of the hotter air from Dakotas trying to get back in. Again, the warm plume of air will limit the chance for thunderstorms (I have a 1 in 3 shot on Thursday night), but we may have a shot at a high in the middle 90's rather than the lower 90's if we can stay relatively cloud free.

Relief on Track for Friday Night and Saturday....

A stronger cold front is due late on Friday with an uncertain chance (but not a huge chance) for thunderstorms late Friday into Friday night.

....But Even More Uncertain Sunday Into Next Week (and Canadian Air Flow Could Push More Smoke Here)

However, the latest computer forecasts still disagree about how strong the push of cooler and drier air will be. The latest forecast makes the drier trend uncertain after Saturday. I have knocked the highs back to the middle to upper 80's with dew points possibly in the 50's. Our air flow will come from the north central Canadian Prairie Provinces. That's where the most wildfire smoke is right now, so I have at least some chance of reduced air quality continuing through the forecast.

And, there is a chance that the flow of tropical moisture fueling the afternoon thunderstorms from Arizona to Idaho (see College of DuPage North America clean infrared satellite loop) could move to the lingering front. That's why the Days 4-5 NWS WPC quantitative precipitation forecast has more potential precipitation from northeastern Minnesota northward. The forecast uncertainty is high enough that the location of the precipitation could be really be anywhere in Minnesota, if we have the moisture arrive.