Monday, September 15, 2025  3:15 AM 

Prepared by Bob Weisman, SCSU Meteorologist and Professor Emeritus

I Never Said There Would Be No Math

Do We Ever Get Average Weather During an Average Period?

So far, September's temperature swings are producing a September to remember and are providing a perfect example of how misleading temperature averages can be. From September 3 through 7, St. Cloud was having highs in the 60's and even a record cool 57 on September 4. We had 5 straight days with temperatures more than 10 degrees below average. At the end of this period, St. Cloud had a September temperature average more then 7 degrees below normal. You may have thought that it guaranteed posting the second cooler-than-average month since April 2023. However, the humidity got going on Friday with heat added on Saturday. Adding in yesterday's highs of 88 in St. Cloud and lower 90's in parts of southern Minnesota yesterday (see 4 PM Sunday NWS WPC North America zoom-in map), St. Cloud has now had two days during which the temperature was more than 10 degrees above average (yesterday was 18 degrees warmer than average). Adding in yesterday, St. Cloud's September average temperature nearly halfway through the month is back to 61.3 degrees, about a degree and a half below average.

An Example from Minnesota's Best Pro Team Playing Now

All of this is because average is not necessarily representative for a small group of temperatures. Let me give you an example from the most successful Minnesota team playing right now. Jessica Shepard, the 7th woman, second one off the bench, for the Minnesota Lynx, has widely varying statistics. My non-expert analysis of her game is that she takes up some of Napheesa Collier's inside game when Collier isn't playing, but leaves the lane to Collier when she is. Note that, during Shepard's last 10 games, she had one game with 22 points, 4 games in the teens, and 4 games with 4 points or less (her rebounding is much more consistent). Her average for those 10 games is close to 9 points, a figure that she has not put up during those 10 games. Only in one of the 10 games was she close to her average, the 8 points against Dallas. That can be typical in a small data set. If the variation is wild, then the average won't resemble the data very much. To give us an idea of how many points she is getting in any one game, it would be better to see the number of games that she scored 10-19 points, 20 or more, and less than 10.

Average temperatures are based on 30 years of highs and lows from that date. That's also a small data set, from a statistics point of view, so the average may again not represent the temperatures of several days. In fact, St. Cloud has only been within 3 degrees of average on 4 of the 14 days in September. That's because September so far has lived up to the wild extremes that can happen in any Minnesota fall (or spring) month (note the huge spread between the record high (top of red bar on the NWS Twin Cities St. Cloud September high-low temperature graph) and record low (bottom of blue column).

Since we are set to continue the extreme warmth for another day or two (and the high dew points likely throughout the week), St. Cloud will probably wipe out the below normal period from earlier this month by tomorrow. So, St. Cloud is going well beyond 'anything can happen Thursday' with our September weather.

This Week's Outlook: Very Humid All Week and Warm For A While, But Rain to Return

The main players in this week's weather are the ridge of high pressure (switch of upper-level winds from southwest-to-northeast in eastern Kansas, Nebraska, the Dakotas, and into Canada to northwest-to-southeast from Manitoba into eastern Minnesota, Wisconsin and Illinois; see College of DuPage North America mid-troposphere water vapor loop) and the series of lows to the west from the Canadian and US High Plains to the Pacific Northwest. The high produced the very warm and fairly humid conditions (highs in the upper 80's to lower 90's from southern Minnesota to Oklahoma, Texas, Missouri, and Arkansas; see 4 PM Sunday NWS WPC North America zoom-in map), while the lows triggered a number of showers and thunderstorms from the western and central Dakotas to Oklahoma (see College of DuPage north central US radar loop). The movement of weather systems will be painfully slow; despite the lows being so close to Minnesota, I don't have even a 50-50 shot for showers and thunderstorms until Tuesday evening.

Until then, we will continue with the August-like weather with another shot at upper 80's to near 90's highs today and highs well into the 80's, with a small chance for 90 if we stay relatively cloud-free tomorrow. The current dew points (near a Florida-like 70 degrees in parts of central and southern Minnesota; see dark orange and red on the UCAR hourly dew point map) will likely remain in the upper 60's to near 70, which produced heat indices above 90 yesterday in St. Cloud. There may be a few isolated showers today or tonight (1 chance in 5) with a 40% chance by late tomorrow afternoon. Lows will remain in the steamy 60's. A piece of north central Minnesota has a small (category 1 of 5) risk for severe thunderstorms today, but these are most likely going to be the southern edge of storms mostly in Manitoba.

Once we get into the showers and thunderstorms most likely Tuesday night or Wednesday morning, the rest of the week will see good chances for showers and thunderstorms Wednesday through Thursday with long periods of steady rain possible as the low is expected to weaken and stall out near the Dakotas-Minnesota border. That will keep the low level moisture with dew points in the 60's throughout the week. However, highs will be knocked back to the 70's since we will have a lot more clouds around and any sunny breaks will trigger a new outbreak of showers and thunderstorms. The most likely result is fairly heavy rainfall from late Tuesday night through Thursday (see Days 3-5 on the NWS WPC quantitative precipitation forecast). Still, the absence of rainfall of late has the NWS Weather Prediction Center showing only a category 1 risk of rainfall sufficient to cause flooding (see Days 4-5 Excessive Rainfall Outlook). There may be a shot at a severe thunderstorm, but that threat is likely to be small.

Stalling weather patterns are traditionally difficult for the computers to forecast, especially when the upper air flow is so weak. Most likely, the upper air low will hang around Minnesota into the weekend. It will slow weaken and the main feed of showers and thunderstorms will eventually drift further to the east, so we will see a slow decrease in the number of rain showers on Friday and Saturday and how many that will be around at times besides the midday and afternoon, but I can't forecast any day without at least a chance for afternoon showers through Saturday (see Minnesota still within the area with a chance for rainfall on the Days 4-7 NWS WPC quantitative precipitation forecast). We won't see much drying out, so lows are likely to remain near 60 into the weekend. Highs may decrease into the upper 60's to near 70 Friday and possibly Saturday. Eventually, the reduced moisture caught up in the low should allow at least some periods of sunshine, but I am not sure how quickly that will happen.

The cool highs will end the daytime heat, but continued lows near 60 will continue to contribute to above average temperatures through the weekend. But, this period should ease the dryness we've seen since early August.

Detailed St. Cloud, MN, and Vicinity Forecast

Confidence Level: "The Bugs Are Waiting for Me to Mow the Lawn"

Monday 9/15/2025: Mixed clouds and sun, very warm and still uncomfortably humid. A slight chance of a late day shower or thunderstorm. High: between 85 and 90. Winds: SE 10-20 MPH with higher gusts. Chance of measurable rainfall: 20%.

Monday Night: Partly clear, breezy, warm, and sticky again. A slight chance for a shower or thunderstorm. Low: between 62 and 67. Winds: S 5-15 MPH. Chance of measurable rainfall: 20%.

Tuesday 9/16/2025: Mixed clouds and sun, breezy, still very warm, and uncomfortably humid. A chance of a late day shower or thunderstorm. High: between 83 and 90. Winds: SW 10-20 MPH with higher gusts. Chance of measurable rainfall: 40%.

Confidence Level: "Extra Bugs Will Come From Every Home on the Block to Hover Around My Head"

Tuesday Night: Cloudy with a better chance for showers and thunderstorms. Partly clear, breezy, and turning a bit less humid late at night. Low: between 58 and 63. Winds: SW 10-20 MPH, becoming NE 8-15 MPH by late evening. Chance of measurable rainfall: 50%.

Wednesday 9/17/2025: Lots of clouds with a good chance for showers and thunderstorms both during the morning and late afternoon. Not as warm, but uncomfortably humid. High: between 76 and 82. Winds: E-SE 8-15 MPH. Chance of measurable rainfall: 50%.

Wednesday Night: Showers and thunderstorms likely. Uncomfortable humidity. Low: between 60 and 65. Winds: NE 8-15 MPH. Chance of measurable rainfall: 80%.

Thursday 9/18/2025: Mostly cloudy with occasional showers and perhaps a thunderstorm. Still uncomfortable humidity. High: between 70 and 75. Winds: E 8-15 MPH. Chance of measurable rainfall: 50%.

Thursday Night: Mostly cloudy with scattered rain showers. Low: between 58 and 63. Winds: NE 5-15 MPH. Chance of measurable rainfall: 40%.

Friday 9/19/2025: Continued mostly cloudy and humid with scattered showers and perhaps a thunderstorm. Otherwise, partly sunny, breezy, and warmer with uncomfortable humidity. Maybe a scattered late day shower or thunderstorm. High: between 70 and 75. Winds: E-SE 8-15 MPH. Chance of measurable rainfall: 40%.

Confidence Level: "Enough Bugs Will Fly into My Mouth to Throw Off My Diet"

Extended: Continued cloudy through the weekend with a slow trend towards fewer scattered rain showers (still best chance in the afternoon) Highs in the upper 60's to lower 70's?? Eventually drying and turning warmer, but uncertain how quickly next week??

Forecast Confidence (10 - "The Rabbits Will Thump Even Though I Fed Them"; 0 - "The Rabbits Will Offer To Groom My Bald Spot"): 7 Monday and Monday night, 6 Tuesday, 4 Tuesday night, 5 Wednesday night and Thursday, 4 Thursday night and Friday.

Yesterday's High: 88°F; Overnight Low (through 3 AM Monday): 73°F
St. Cloud Airport 24-Hour Melted Precipitation (through 3 AM Monday): None; SCSU 24-Hour Precipitation (through 3 AM Monday): None

Next Update: Tuesday, September 16, 2025 6 AM

Let me know what you think about this forecast and discussion by emailing SCSU meteorology professor Bob Weisman. Please note that I make the forecast, not the weather!

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