Friday, July 26, 2024  4:10 AM 

Prepared by Bob Weisman, SCSU Meteorologist and Professor Emeritus

Late Week Sweltering to Peak Saturday and Perhaps Sunday

Chance for Sunday Night Significant Rain(?), Severe Weather(??)

Heat and Fires in Black Hills and South and West

The heat got a bit closer to Minnesota yesterday with 100-plus temperatures in the western Dakotas, some even approaching 110 degrees, and in eastern Montana and points south (see 4 PM Thursday NWS WPC North America zoom-in map) and 90's continuing in much of Saskatchewan. Even though it was much cooler yesterday in Alberta (temperatures in the 50's and 60's in the clouds on the west flank of the Alberta low; see Mid-tropospheric water vapor loop from Colorado State satellite slider) and at least in western and central Washington and Oregon, the fire news continues to be serious, as one fire destroyed a good chunk of the Canadian Rockies resort town of Jasper and a man was arrested for beginning what has turned out to be a large California fire.

Florida-Like Humidity A Day and a Half Upwind of Minnesota

In Minnesota, our winds turned to the southeast yesterday (set time to 20Z-23Z, 3-6 PM, on the NWS Aviation Weather Center METAR map). We aren't in the really hot air, but note the spike to Florida-like humidity with dew points of 70 or above (see 4 PM Thursday NWS WPC North America zoom-in map) in those southeast winds from the eastern Dakotas into Iowa and Missouri (deep orange on the UCAR hourly dew point chart). Today and tomorrow, our strengthening southeast winds today and south to southeast winds tomorrow will allow dew points to climb from the merely uncomfortable lower 60's now (see latest readings on the NWS Aviation Weather Center METAR map) to the very uncomfortable middle to upper 60's by late today and the oppressive 70's tomorrow.

Heat Indices Serious Tomorrow and Possibly Sunday

We still have some of the wildfire smoke aloft over Minnesota (see hazy areas on the daytime photos from the GeoColor satellite loop on the Colorado State satellite slider), but will see a lot of sunshine today and most likely tomorrow. That will allow temperatures to climb into the upper half of the 80's this afternoon and into the lower 90's tomorrow. Given the increasing dew points, we will see heat indices in the upper 80's to perhaps 90 today with upper 90's and even low 100's possible tomorrow (see NWS Minnesota hourly weather round-up for current temperatures, dew points, and any heat indices of 90 or higher). Again, the smoke isn't likely near the ground (most air quality in Minnesota in the yellow moderate category on the new EPA fire and smoke map).

Scattered Thunderstorms Closer to Minnesota, But Not a Great Chance in Central Minnesota......

On the far northwestern edge of the hot air, there were some scattered showers and thunderstorms from Saskatchewan to Idaho and Nevada (see Shortwave Albedo satellite loop from Colorado State satellite slider) overnight as the Alberta low pushes a cold front to Saskatchewan and Montana. There will be a series of lows moving from the northeastern Pacific through the Pacific Northwest and into the western Canadian Prairies, but the main movement will continue to be southwest-to-northeast. Given the increasing humid air to the east of the warm front from the eastern Dakotas into Minnesota (see 4 PM Thursday NWS WPC North America zoom-in map), storms would have plenty of moisture to work with, but they will be scattered thanks to the hot air aloft over the hottest ground temperatures. And, with the main flow direction being southwest-to-northeast, the front will be able to more easily advance through Canada, but tend to hang up somewhere in North Dakota.

The NWS Storm Prediction Center has a threat for severe thunderstorms that overlaps part of northwestern Minnesota both today and tomorrow, but the threat level is relatively low (category 1 today, category 2 tomorrow) since the storms will be only scattered. This is why I have small chances for late night or morning thunderstorms both early tomorrow (1 in 5 chance) and early Sunday (1 in 3 chance). The chances are slightly better on Sunday, giving us the chance to have more lingering clouds around for part of the day. That's why I've backed off a bit on Sunday's high temperatures. Still, a high in the upper 80's, which is very possible, plus dew points of 70 or above, will push the heat index at least to the middle to upper 90's. So, I would not be surprised to see heat advisories in much of central and southern Minnesota both weekend days.

....Until Sunday Night

The computer forecasts have a stronger system pushing across the Pacific Northwest, getting closer to the Minnesota-Manitoba-Ontario border by Monday. The computers can't agree on the timing of this storm, but agree that there would be a better chance for showers and thunderstorms. We might see a few late Sunday afternoon, but the more likely time would be Sunday night into at least Monday morning. Even though the NWS Storm Prediction Day 3 severe weather outlook has the severe threat as only being category 1, the forecasts note that the low category is due to the differences in where the thunderstorms might be on Monday morning. This would also be the period with potential significant rain, even though the NWS WPC Day 3 quantitative precipitation forecast has more of it in northern Minnesota (note the heavier amounts in all of Minnesota on Day 3 versus Day 2). So, I have a 50-50 shot at Sunday night thunderstorms in the St. Cloud area.

The difference between the computer forecasts also means that central Minnesota could be affected by redeveloping storms Monday afternoon, but others push the threat further to the east. We'll have to see about that part. The computer forecasts do not have a good track record at forecasting thunderstorms even a couple of days in advance, thus my low confidence in the forecast from Sunday on. In any case, there are likely to be more clouds around during Monday, so it will be very humid, but highs will likely stay in the 80's. If we have more clouds, we may be around 80. Only if the PM storms are well to our east will we have a shot at a Monday 90-degree high.

Tuesday Perhaps a Little Less Sweltering

The computers have some slightly drier air moving behind that front whenever it comes through on Monday. We will still have dew points in the uncomfortable 60's, but it won't be the Florida levels seen over the weekend. The air will also be slightly cooler, but the forecasts are hinting that we might be relatively free of clouds. Northwest winds will tap the larger supply of smoke both in the Canadian Prairies and increasing even in the US to our west (see EPA fire and smoke map), so highs could be tempered by smoke. But, the air won't be that much cooler, so we would have a chance for highs in the upper 80's to perhaps 90 if we had a good chance for Tuesday sun. The lower dew points would mean that heat indices would probably be no worse than the lower 90's, but by Tuesday, we will have seen 3 very warm nights, so the risk increases for those without air conditioning. (Much of Minnesota is back in the orange highlighted area on the NWS HeatRisk forecast on Tuesday and Wednesday).

Remaining At Least Humid Through Mid-Week With Storm Chances

The computers have the possibility of a storm moving near or through Minnesota by the middle of next week. They both agree that this system would be there, but have this system moving through Minnesota a day apart (Wednesday vs. Thursday). Given the typical forecast problems, my forecast is for at least the uncomfortable humidity levels to continue into the middle of the week with uncertain chances for thunderstorms. Also, I am uncertain whether we will have a clearer daytime period with highs of 90-plus. And, we will have to watch all of that smoke to our west and northwest to see if the area where it reaches the ground gets close to us.

Detailed St. Cloud, MN, and Vicinity Forecast

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

Friday 7/26/2024: Mixed clouds and sun, breezy, very warm, and uncomfortably humid.. High: between 85 and 90. Heat indices between 90 and 95. Winds: SE 10-20 MPH with higher gusts. Chance of measurable rainfall: 10%.

Friday Night: Partly clear, breezy, warmer, and oppressively humid. A slight chance for a late night shower or thunderstorm. Low: between 66 and 72. Winds: S 10-25 MPH. Chance of measurable rainfall: 20%.

Saturday 7/27/2024: Morning sun, mixed sun and clouds in the afternoon, windy, hot, and oppressively humid. A slight chance for a late day shower or thunderstorm. High: between 90 and 95. Heat indices between 95 and 105. Winds: S 15-25 MPH with higher gusts. Chance of measurable rainfall: 20%.

Saturday Night: Partly clear, breezy, sultry, and oppressively humid. A slight chance for a late night shower or thunderstorm. Low: between 68 and 73. Winds: S 8-15 MPH. Chance of measurable rainfall: 20%.

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

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

Sunday 7/28/2024: Perhaps an early shower or thunderstorm, then mixed sun and clouds, windy, hot, and oppressively humid. A better chance for a late day shower or thunderstorm. High: between 86 and 92. Winds: S 15-25 MPH with higher gusts, becoming SW late. Chance of measurable rainfall: 30% in the morning, 40% in the afternoon.

Sunday Night: Partly clear and oppressively humid with a good chance for showers and thunderstorms. Low: between 64 and 68. Winds: S 10-20 MPH with higher gusts, becoming SW late at night. Chance of measurable rainfall: 50%.

Monday 7/29/2024: Maybe a lingering morning shower or thunderstorm. Some smoky sunshine mixed with clouds midday and afternoon, not as windy, still very warm, but merely uncomfortable, rather than oppressive humidity. A chance for a late day shower or thunderstorm. High: between 80 and 85. Winds: NW 5-15 MPH. Chance of measurable rainfall: 30%.

Monday Night: Partly clear, light winds, and still warm. Some areas of fog by morning. Can't completely rule out a thunderstorm. Low: between 62 and 67. Winds: NW 5-10 MPH evening, SW 5-10 MPH late. Chance of measurable rainfall: 20%.

Tuesday 7/30/2024: Maybe an early thunderstorm. Otherwise, mixed clouds and hazy sunshine, continued very warm with uncomfortable to oppressive humidity. High: between 85 and 90. Winds: S 8-15 MPH. Chance of measurable rainfall: 20%.

Extended: Still very warm and very humid through the middle of next week?? Uncertain chances for showers and thunderstorms???

Forecast Confidence (10 - "The Rabbits Will Thump Even Though I Fed Them"; 0 - "The Rabbits Will Offer To Groom My Bald Spot"): 7 Friday, 6 Friday night through Saturday night, 3 Sunday and Sunday night, 1 Monday and Tuesday.

Yesterday's High: 83°F; Overnight Low (through 4 AM Friday): 66°F
St. Cloud Airport 24-Hour Melted Precipitation (through 4 AM Friday): None; SCSU 24-Hour Precipitation (through 4 AM Friday): None

Next Update: Monday, July 29, 2024 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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