Wednesday, September 17, 2025  2:10 AM 

Prepared by Bob Weisman, SCSU Meteorologist and Professor Emeritus

August Heat to Yield to Frequent Rain

90 Degrees in September Infrequent, But Not a Record

St. Cloud hit 91 degrees yesterday afternoon (see NWS: last 72 hours of St. Cloud observations). This was St. Cloud's 7th 90-degree high of the warm season, still more than 4 days fewer than average. Both Minneapolis-St. Paul International Airport and Mankato got to 92 degrees. 90 degrees in September is relatively rare, but not unheard of. Yesterday's record warm high was 94, set in 1948. There have been 112 September highs in the 139 Septembers on record, so the September average is close to 1 per year. 2012, 2013, 2018, and 2023 each had 2 September highs in the 90's. Only 9 of the 30 September dates have a record high cooler than 90. St. Cloud's record for the latest 90 degree high is October 2, with 2 of the 3 October 90 degree highs set in October of 2023. Since the low temperature was 64 degrees, yesterday's average temperature was 68 degrees, 18 degrees warmer than average. That's the third straight day during which the average temperature was at least 17 degrees above average. After yesterday, the September St. Cloud average temperature is more than a degree about average, completely wiping out the cool spell during the first week of the month. While I don't expect this kind of heat for the rest of the week, the persistent humidity will keep dew points between the upper 50's and the middle 60's, which will keep the average temperature above average.

Rainy Pattern to Begin, Especially Tonight

We won't get as warm during the rest of the week because the low pressure system that drifted into Wyoming yesterday (see College of DuPage North America mid-troposphere water vapor loop) will continue to drift closer to Minnesota through Saturday. There were a couple of showers and thunderstorms late yesterday afternoon in central Minnesota and in southern Minnesota last evening (set number of frames to 200 on the College of DuPage north central US radar loop), but the large blob of South Dakota grew into Nebraska and Iowa overnight, shutting down the showers further to the east. I don't expect a good chance for showers and thunderstorms in central Minnesota until tonight, but there will be more clouds pushing into central Minnesota from the leftovers of the thunderstorms to our south (see College of DuPage North America clean infrared satellite loop). That will knock our highs down 5-10 degrees today, but we are likely to see our 4th straight high in the 80's and 5th of September so far (average for the entire month is 6 days; set NWS Twin Cities NOWData to monthly summarized data for St. Cloud area, set range to por, period of record, variable to maximum temperature, summary to number of days, and threshold to greater than or equal to 80).

I have a 40 percent chance for a late afternoon shower or thunderstorm today.

However, we should reverse the trend of relatively dry weather since the start of August. During the past 60 days in Minnesota (set NWS Water Prediction Service to yesterday's date, and last 60 days), much of northern and central Minnesota has seen 4 inches or less (medium or neon green). Note that much of the yellow area in central Minnesota happened in mid-August, so it has been dry for the past month. However, there is the potential for 1 or even 2 inches of rain over the rest of the week (see NWS WPC quantitative precipitation forecast; total shown in this figure). The most likely time for showers and thunderstorms will be from tonight through Friday as we remain close enough to the northern edge of the warm and sticky air (now in eastern and southern Minnesota; see latest NWS WPC North America zoom-in map) so that the approaching low could trigger more widespread showers and thunderstorms. Even though we will be in slightly cooler air Friday through the weekend, the high dew points (upper 50's to lower 60's dew points) will remain, so there will be scattered showers and thunderstorms each afternoon as long as the upper air low remains close to Minnesota. Highs will be back in the 70's tomorrow through the weekend with lower 70's likely Friday and Saturday.

Slow Dry Out, Question About How Slowly

The rain chances will ease up when the upper air low pushes far enough to our east to reduce the temperature difference between the sun-heated ground and the pocket of cool air aloft. The computer forecast disagree about how quickly this will happen. The US forecast has the low pushing to our east by Saturday, but the European forecast keeps the low around longer. I am not going with the faster scenario, so I don't have highs back in the 80's each day of the weekend.

More Rain Chances Monday? Followed By Cool Down???

The long-range forecasts show another low with a stronger cold front due to come through Minnesota on Monday. That would again produce a chance for showers and thunderstorms, then bring considerably cooler air in for Tuesday and Wednesday.

Detailed St. Cloud, MN, and Vicinity Forecast

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

Wednesday 9/17/2025: Not quite as warm, but still uncomfortably humid. Mixed sun and clouds with a chance for late afternoon showers and thunderstorms. High: between 80 and 85. Winds: NE 5-15 MPH. Chance of measurable rainfall: 40%.

Wednesday Night: Showers and thunderstorms likely. Uncomfortable humidity. Low: between 60 and 65. Winds: E-NE 8-15 MPH. Chance of measurable rainfall: 70%.

Thursday 9/18/2025: A good chance for both early morning and afternoon showers and thunderstorms. Not as warm, but uncomfortably humid. High: between 73 and 78. Winds: ESE 8-15 MPH. Chance of measurable rainfall: 60%.

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

Thursday Night: Mostly cloudy with scattered rain showers, especially during the evening. Low: between 58 and 63. Winds: E 5-15 MPH. Chance of measurable rainfall: 50%.

Friday 9/19/2025: Mostly cloudy and humid with scattered showers and perhaps a thunderstorm. Best chance during the afternoon. High: between 70 and 75. Winds: SE 8-15 MPH. Chance of measurable rainfall: 60%.

Friday Night: Mostly cloudy with occasional rain showers, mainly during the evening. Low: between 60 and 65. Winds: SE 5-15 MPH. Chance of measurable rainfall: 40%.

Saturday 9/20/2025: Mixed clouds and sun with scattered afternoon showers. Still quite humid. High: between 70 and 75. Winds: SE 5-15 MPH. Chance of measurable rainfall: 50%.

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

Saturday Night: Mostly cloudy with occasional rain showers. Low: between 57 and 62. Winds: SE 5-15 MPH. Chance of measurable rainfall: 40%.

Sunday 9/21/2025: Mixed clouds and sun, perhaps some scattered afternoon showers. A bit warmer and still humid. High: between 75 and 80. Winds: SE 5-15 MPH. Chance of measurable rainfall: 30%.

Extended: Better chance of Monday afternoon showers and thunderstorms?? Cooler Tuesday and Wednesday??

Forecast Confidence (10 - "The Rabbits Will Thump Even Though I Fed Them"; 0 - "The Rabbits Will Offer To Groom My Bald Spot"): 7 Wednesday, 6 Wednesday night through Thursday, 5 Thursday night and Friday, 4 Friday night and Saturday, 2 Saturday night and Sunday.

Yesterday's High: 91°F; Overnight Low (through 2 AM Wednesday): 63°F
St. Cloud Airport 24-Hour Melted Precipitation (through 2 AM Wednesday): None; SCSU 24-Hour Precipitation (through 2 AM Wednesday): None

Next Update: Thursday, September 18, 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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