Wednesday, July 9, 2025  2:50 AM 

Prepared by Bob Weisman, SCSU Meteorologist and Professor Emeritus

Single Number Doesn't Represent Forecast

Didn't Communicate Forecast Range to Emergency Officials...

I am still struggling with the Texas flood disaster. One aspect that bothers me is that local officials have 15 inches of rain stuck in their minds, noting how inaccurate the forecast was. I don't really want to be involved in placing blame; my focus is what can be done to avoid such devastating consequences.

Because a Forecast Number Has a Range of Possibilities....

In my opinion, this is another case of a lack of understanding about the possible range of a forecast. The last time I heard so much about a different number than was forecast was in during the immediate aftermath of the Red River Flooding in 1997. Grand Forks was flooded for a month when the river reached 54 feet. Local officials kept saying that the forecast was for merely 52 feet, so they didn't sandbag high enough. I don't want to get into the likelihood that a sandbag dike would hold up for more than a month under that kind of water pressure.

In math, a number is simply a number. In science, any single number doesn't represent the accuracy of that number. I can say that I am 5 feet 9 inches tall. If that was measured by a tape measure with markings every sixteenth of an inch, my measurement could be off by a sixteenth of an inch high or low, if I misread the reading. However, if I just used a crude stick with the only markings every foot, the number would be misleading, since I could only be sure that my height was closer to 6 feet than 5 feet.

This is Why Your Device Shouldn't Have a Single Number for Next Thursday's High

For forecasts, the inaccuracy of the number would be based on the average forecast error. Studies have shown that the average accuracy of a high or low temperature forecast is 1-2 degrees over the first 3 days of a forecast. That is why I give at least a 5 degree range on my high and low temperatures, because the number I come up with could be off by 2 degrees high or low. If we stretch out the forecast to 5-7 days, the average forecast error climbs to 3-5 degrees. That means there could be a 10 degree range of temperature, so my forecast for a high in the 80's for next Wednesday, for example, could produce a high in the upper 70's or even 90, based on this average error.

Meteorologists, especially those who make public forecasts, are being told by media consultants that people only retain a single number better than a range of numbers. TV producers and other social media creators use this logic to influence public forecasters to use a single number for a temperature forecast, mostly because meteorologists like having a job. And, don't get me started on having your device give a single number temperature forecast for 2 weeks or a month in advance.

We are actually used to a range of forecast numbers in certain situations. Snow forecasts usually carry a range, but recent studies have shown that we should probably widen our range. Hurricane forecasts have adopted the idea of a range, by showing the 'forecast cone.' The forecast has a central line of most likely track, but the cone widens to reflect the 60 mile possible error in eye placement in the first 3 days of the forecast and widens further for the 5 day forecast. Hurricane forecasters at the NWS Tropical Prediction Center have tried to encourage media people to use the entire cone for possible positions, rather than the line of forecast track.

River forecasts, especially in a flood situation, have a higher degree of uncertainty. A recent study of Iowa river stage forecasts from 1999 through 2014 (by faculty and graduate students at the University of Iowa) showed that river forecasts had an average error of 2-4 feet in cases when the river had above average flow (note peaks in 2002 and 2012). If the Red River flood in 1997 had the same pattern, then a forecast river stage of 52 feet could mean that the Red River could reach anything between 48 and 56 feet, so that forecast was more accurate than was credited.

Heavy Rainfall Predictions Just Aren't Accurate Enough to Focus on a Number

Rainfall predictions are even less accurate. The media attention has focused on that 15 inch rainfall total. Large ranges of possible rainfall are usually given in advance when a slow-moving hurricane comes ashore. Typical forecast ranges in heavy rainfall are given a range of a few inches, but they can be off. Once we get into amounts of 5 inches or more, probably a 5 inch range should be given.

So, meteorologists and local emergency officials have to get together so that the officials better understand that a number in a forecast means a possible range and the planning should take that possible range into account.

Central Minnesota Weather Discussion

Back to our forecast. The next storm on the horizon is still the Thursday night-Friday potential system. An initial low pressure system from the northeast Pacific has pushed through northern British Columbia and Alberta (see College of DuPage North American mid-tropospheric water vapor loop), finally bringing some needed rain to those fire-plagued areas (now from Alaska to Ontario). Note also the northward poke of the high (clockwise circulation) into southern Alberta and Saskatchewan. This is the system that will allow mid-week heat to take hold in Montana and the Dakotas today and tomorrow (see NWS Heat Risk). So, Minnesota will have another cycle of hotter and more humid air trying to move in, with peaking temperatures and oppressive humidity arriving tomorrow, and a slow-moving cold front breaking down the heat.

When temperatures and humidity are on the way up, I have 1 in 3 chance for showers and thunderstorms tonight into tomorrow morning. The only chance for severe weather will be in the Red River Valley and that threat will be relatively small. Dew points climbed back into the lower 60's yesterday in central Minnesota (see NWS: last 72 hours of St. Cloud observations) and will climb from those near 60 readings this morning (see NWS Aviation Weather Central METAR map) to the middle 60's tonight and into the oppressive lower 70's tomorrow.

Tomorrow, we will be in the steam bath. How hot we get will depend on sunshine and how likely late afternoon showers and thunderstorms will be. At this point, I have upped the chance to 1 in 3 tomorrow afternoon, so I have a larger temperature range (trying to reflect reduced confidence) with middle 80's if we have a lot of clouds and a few scattered showers and lower 90's if we are cloud-free. The case of 90's highs and 70's dew points would have the National Weather Service have some sort of heat advisory out tomorrow afternoon (see NWS Minnesota hourly weather round-up for temperature, dew points, and heat index, when it gets to the upper 80's or higher).

My confidence in the forecast goes down even further for Thursday night into Friday. I think that will be the most likely time for showers and thunderstorms of the next 5 days, but the different forecasts of the cold front's progress through Minnesota are keeping me to a 50-50 shot of Thursday night thunderstorms. I do think that central Minnesota is more likely to get wet on Friday (thus, a 70 percent chance for enough rain to coat the ground), but the different cold front speeds make it unclear whether we are most likely to get morning rain, afternoon showers and thunderstorms, or both. We would likely be cloudy all day Friday, but there would probably be a break in the storms with sunshine to our south. The NWS Storm Prediction Center has a level 1 severe weather forecast for much of Minnesota Friday. The NWS WPC Quantitative Precipitation Forecast has a better chance for central and southern Minnesota rain on Friday (day 3) than on Thursday, which includes Thursday night (day 2), or tonight (day 1). Southwestern Minnesota has the best chance (category 2 of 4 on the Day 3 NWS WPC excessive rainfall outlook) for enough rain that flooding might be a concern.

My best guess is that Friday will have temperatures either in the upper 70's or the lower 80's, the latter if we get some sun. Dew points will still be in the uncomfortable upper 60's to lower 70's.

Cooler and drier air from northwestern Canada will move in behind the Friday cold front, but the computer forecasts cannot agree on how dry and cool the air will be and the timing of more low pressure systems moving along the main storm track, which will be from the Canadian Prairie Provinces into Ontario, the Great Lakes, and perhaps Minnesota. I have more sunshine (for now) over the weekend and highs back to near 80 or above with dew points back in the 50's and merely a small chance of showers on Sunday. And, there might be a chance for Canadian wildfire smoke to move into Minnesota. Smoke levels are high right now in Winnipeg, but future rain could change that. However, my confidence in this forecast is low.

The only thing I can say about early next week is that we will continue to have frequent uncertain chances of showers and thunderstorms. There are some signs of another hot day, but they are inconsistent, so I will say little about temperatures at this point.

Detailed St. Cloud, MN, and Vicinity Forecast

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

Wednesday 7/9/2025: Mostly sunny with a few afternoon clouds, light winds, and continued warm and uncomfortably humid. A slight chance of an afternoon sprinkle. High: between 80 and 85. Winds: SE 5-10 MPH. Chance of measurable rainfall: 10%.

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

Wednesday Night: Partly cloudy, breezy, and warmer with increasing humidity. A chance for scattered showers or thunderstorms. Low: between 64 and 68. Winds: SE 5-15 MPH. Chance of measurable rainfall: 30%.

Thursday 7/10/2025: Perhaps an early thunderstorm. Otherwise, partly sunny with a stronger breeze and very warm with oppressive humidity. A chance for a late day shower or thunderstorm. High: between 84 and 92. Winds: SE-S 8-15 MPH. Chance of measurable rainfall: 30%.

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

Thursday Night: Continued warm with uncomfortable to oppressive humidity. A good chance of showers and thunderstorms. Low: between 63 and 68. Winds: S 8-15 MPH. Chance of measurable rainfall: 50%.

Friday 7/11/2025: Mostly cloudy with a good chance for both morning and afternoon showers and thunderstorms with a midday break possible. Not as warm, but still oppressively humid. High: between 75 and 80. Winds: SE 5-15 MPH, shifting to NW 10-20 MPH in the afternoon. Chance of measurable rainfall: 70%.

Friday Night: Still a chance for evening showers and thunderstorms. Then, partial clear, turning a bit cooler, with merely noticeable humidity. Low: between 55 and 60. Winds: NW 5-15 MPH. Chance of measurable rainfall: 40%.

Saturday 7/12/2025: Sunny to partly cloudy, breezy, and warm, but with more comfortable humidity. A slight chance of a shower. High: between 77 and 82. Winds: NW 8-15 MPH. Chance of measurable rainfall: 20%.

Saturday Night: Partly clear, still relatively dry, but breezy, and a bit warmer. Low: between 58 and 64. Winds: NW 5-15 MPH, becoming SW after midnight. Chance of measurable rainfall: 10%.

Sunday 7/13/2025: Sunny to partly cloudy, breezy, warmer, and becoming uncomfortably humid. A chance of a late day shower or thunderstorm. High: between 80 and 85. Winds: SW 8-15 MPH. Chance of measurable rainfall: 30%.

Extended: Continued uncertain temperatures, but likely humid into early next week??? Frequent chance of 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 Wednesday, 5 Wednesday night and Thursday, 3 Thursday night through Friday, 2 Friday night through Sunday.

Yesterday's High: 82°F; Overnight Low (through 2 AM Wednesday): 64°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, July 10, 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!

Are you interested in studying meteorology? If so, go to the Atmospheric and Earth Sciences Department home page.