Monday, October 3, 2022 4:35 AM 

Sprinkly and Mild Early Week, Coolest Air of the Season Late Week

Spelling Out What We Don't Know

Meteorology is still a relatively young science, compared to biology or physics. Weather forecasting has made strides, especially from the second half of the 20th century on. However, forecasters are increasing trying to communicate what we don't know as well as what we know.

We just saw an example with huge real-life implications with Hurricane Ian. Nothing would have changed the huge amount of damage, but many of the lives lost could have been prevented. Over the past few years, the NWS Tropical Prediction Center has been setting up their forecasts, including the average error in their forecasts. So, they are trying to get media and public safety officials to look at the "cone," the white area surrounding the "best track" forecast (archive of track and "cone" forecasts from the NWS Tropical Prediction Center). That represents all the possible positions of the center of the storm at various times. While the track itself showed a landfall near Tampa Bay when Ian was over western Cuba, having an eye on the eastern edge of the forecast cone put the storm over the Fort Myers area, so a landfall there would have only taken an average forecast error. And, since the worst storm surge is in the thunderstorms outside of the eye along and to the right of the track, the area hit the hardest was included in the worst potential effects as early as Monday. Another way of putting numbers on the uncertainty is not to use a single number, but to use a range, and even give a probability of even the less likely amounts. This happened with the storm surge forecasts. Only a few feet was the forecast early on Monday, but there was still a 40 percent chance of a devastating storm surge, especially when the elevation of the islands and the Fort Myers area are only 5-8 feet. The most important factor is that it takes 36-48 hours to evacuate all the vulnerable areas, so waiting until the day before to issue an evacuation order was not a good idea.

All of this still doesn't account for the people who chose to ride out the storm in vulnerable areas.

I also use these "known unknowns" in my forecast. That's why I have a range of temperatures, not one value. I know the average error on a high or low temperature forecast is still 2-3 degrees for tomorrow and 10 degrees a week out. That's why I use chance for precipitation. I'm not thrilled with my forecast of the persistent clouds and occasional sprinkles or light rain, but I had at least a 1 in 5 chance for measurable rainfall through most of the weekend. That's why I use a range of snow accumulations in those forecasts. You will also see the National Weather Service put out both a minimum and maximum snowfall map (representing the accumulations with a 10% chance either high or low) as well as the forecast. And, the recent research has shown that snow is even harder to forecast, so the few studies done suggest a wider range of accumulations.

So, what I annoys me is the weather apps which have a single temperature from tomorrow all the way to three months in advance, hour by hour rainfall accumulation, forecasts of snowfall to the inch, and hiding the probability numbers. That's not following the science.

Still Patches of Light Showers in Warm Air Through Tomorrow...

Note that I snuck in there the trouble I've been having pinning down the rain chances. The low pressure system in Montana has been blocked by the leftovers from Hurricane Ian, now two lows, one departing the Northeast and one pushing into the Ohio Valley (see Mid-level water vapor satellite loop from Colorado State satellite slider). Despite the dry air still at the ground (dew points only reaching 50 in a few parts of the western Dakotas and Minnesota; see UCAR hourly dew point chart), there has been some moisture moving from the Desert Southwest aloft, so there have been patches of radar echoes over the Dakotas and Minnesota since Thursday and some of them generated rain or sprinkles. The thicker clouds also kept high temperatures in the 60's Saturday (see NWS: 3-days of St. Cloud temperatures). We managed more sunshine yesterday, so highs reached into the lower 70's, in the Labor Day range of average temperatures

The leftover Ian low is going to linger around the Mid-Atlantic until the second half of the work week. The Montana low will edge eastward during the first half of the week, not reaching Minnesota until Wednesday. So, we will continue to see patches of thicker clouds (see Shortwave Albedo satellite loop from Colorado State satellite slider) and more scattered showers (see College of DuPage north central US radar loop). I have a 1 in 5 shot at showers today, but a better chance of more persistent clouds tonight and tomorrow with a 40 percent chance of rain. So, I think temperatures will break into the 70's again today after a mild start in the 50's (see NWS Aviation Weather Center METAR map), but I am keeping enough clouds around tomorrow so that highs will be in the upper 60's to perhaps near 70.

Best Chance of Rain Tuesday Night and Wednesday?

That Montana low will be in Minnesota on Wednesday, so I have the best chance for rain Tuesday night and Wednesday. Still, with the initially dry air, I don't expect a large rainfall. We might have some sunshine on Wednesday afternoon, so highs could still make it into the lower 70's.

Fast Forward to Halloween-Like Temperatures Late Week

However, a major weather pattern change will take place over North America. The low in the eastern Pacific is going to be moved out by a stronger jet stream in the central Pacific (see contrast between red and white over the Aleutian Islands of Alaska on the Pacific Mid-tropospheric water vapor loop from Colorado State satellite slider). That will build a high across all of western North America, shifting the flow over northwestern interior Canada to northwest-to-southeast. That will be able to tap a pocket of early season polar air in the Northwest Territories and Nunavut (see 4 PM Sunday NWS WPC North America zoom-in map) and drag into the Northern Plains, Great Lakes, and Northeast for the second half of the upcoming week. We may have another shot at rain showers as the cold front pushes in Wednesday evening, but the colder air will roar in after 1-2 AM early Thursday morning. Temperatures will fall back from the 50's to near 60 down into the 40's by sunrise and only recover to between 45 and 50 during Thursday's daylight hours. There still could be a sprinkle with the front Wednesday evening. And there will be occasional sprinkles from the cold air aloft on Thursday. It could easily be cold enough to allow some accumulating snow in northern Minnesota and to produce the first snowflakes of the season in central Minnesota, although any snow should melt on contact with the warmer ground.

Fri AM Hard Freeze Likely for Those Not Hitting 20's So Far

The coldest temperatures of the season are likely to follow the cold front with daytime highs in the 40's on Thursday and Friday. On Friday morning, central Minnesota is likely to see widespread temperatures in the 20's, which will produce a hard freeze in areas that stayed out of the 20's in last week's frost. Friday night could have persistent wind, so I am not sure about a second night in the 20's, but a low in the 30's with a stiff southeast wind won't feel all that great. Below average temperatures will continue into at least Saturday. A second northern Canada cold push could take place Sunday and continue into early next week, but I am not sure if that second cold shot will be as cold as the first one.

Detailed St. Cloud, MN, and Vicinity Forecast

Confidence Level: "I Will Have to Remove Five-Foot High Snow Piles to Put Out the Trash"

Monday 10/3/2022: Mixed clouds and sun, breezy, sunny, breezy, and warmer. A slight chance of a shower. High: between 70 and 75. Winds: S 10-20 MPH. Chance of measurable rainfall: 20%.

Confidence Level: "The Continuing Snow Melt Will Make It Icy Right Where I Have to Change My Balance and Throw the Snow"

Monday Night: Cloudy, breezy, and mild with a chance of scattered showers. Low: between 50 and 55. Winds: S-SE 10-20 MPH evening, 5-15 MPH late. Chance of measurable rainfall: 40%.

Tuesday 10/4/2022: Mostly cloudy and a bit cooler with a chance of occasional showers. High: between 65 and 70. Winds: SW 5-15 MPH. Chance of measurable rainfall: 40%.

Tuesday Night: Cloudy with a better chance of rain or showers. Low: between 53 and 58. Winds: NW 5-15 MPH. Chance of measurable rainfall: 70%.

Wednesday 10/5/2022: Cloudy with morning showers, then becoming a mixture of clouds and sun, breezy, and continued warm. A chance of an afternoon sprinkle. High: between 66 and 72. Winds: NW 8-15 MPH. Chance of measurable rainfall: 50%.

Wednesday Night: Partly clear and mild with light winds through midnight, then becoming blustery and turning much cooler late at night. A slight chance of a shower. Low: between 45 and 50. Winds: NW 5-15 MPH through early morning, NW 15-30 MPH with higher gusts after 2 AM. Chance of measurable rainfall: 20%.

Thursday 10/6/2022: Mixed clouds and sun, blustery, and much cooler. Maybe a sprinkle. Daytime temperatures falling to the middle 40's, then holding between 45 and 50. Winds: N 15-30 MPH with higher gusts. Chance of measurable rainfall: 20%.

Confidence Level: "The Melting Maven Will Magically Make My Sidewalk Ice Disappear Overnight"

Thursday Night: Clearing with diminishing wind and the coldest night of the season so far. Good chance for a hard freeze. Low: between 23 and 28 (record cold low: 19 in 1976). Winds: NW 5-15 MPH evening, 5 MPH late. Chance of measurable rainfall: 10%.

Friday 10/7/2022: Much more sunshine, much lighter winds, but still Halloween-like temperatures. High: between 45 and 50. Winds: NW 5-15 MPH. Chance of measurable rainfall: 10%.

Extended: Cool but breezy Friday night??? Cloudy and not quite as cool Saturday??? Continued average to cooler than average into early 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, 5 Monday night through Thursday, 3 Thursday night through Saturday.

Yesterday's High: 73°F; Overnight Low (through 4 AM Monday): 56°F
St. Cloud Airport 24-Hour Precipitation (through 4 AM Monday): Trace; SCSU 24-Hour Precipitation (through 3 AM Monday): TBA

Next Update: Monday, October 3, 2022 7 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 Hydrologic Sciences Department home page.