Monday, October 18, 2021 3:20 AM

Bask in the Warmth While You Can

My Lawn Reflected the Contrasts of the Warm Season

I spent the weekend doing yard work. My yard shows the ups and downs of the warm season. I have now taken 54 city of St. Cloud yard bags of leaves out of the yard (of the usual 100-120). Most of the leaves I've seen in my back yard had relatively dull colors and some were shriveled, reflecting the rainfall deficit that still hasn't been completely made up. As of 1 AM this morning, the St. Cloud Airport was still 5.49 inches short since May 1 (actual rainfall 14.14 inches; average rainfall 19.63 inches). Most trees still had about half their leaves, since my yard hasn't had its first frost. Only yesterday morning was there a widespread frost in central Minnesota with many reporting stations between 29 and 32 degrees (see 8 AM Sunday UCAR Minnesota map). There was frost in some rural areas on Friday and Saturday mornings, but yesterday had the most stations with a temperature below freezing, including the first one at the St. Cloud Airport. However, my yard was merely wet. And, despite the rainfall rate slowing during October, my lawn was the greenest it has been all warm season and there were plenty of mushrooms from the moist conditions due to the rains of the past two months and the frequency of dew (and how long it stays on my lawn with the weaker sun and the shade from the trees). My purpose is not to complain about my weekend, but to note that plants with shallow roots are tapping plenty of moisture, but the trees with deeper roots are seeing the effects of the lingering dryness.

These are signs of the moisture conditions in the weekly Minnesota Crop Progress and Condition reports. There will be a new report later today, but last week's showed only 25 percent of the top soil short or very short on moisture, but still 47 percent of the subsoil short or very short.

Temperatures Finally Rebounded Yesterday Afternoon

We are done with the frosts for now. Despite lots of clear sky across Minnesota (see Shortwave Albedo from Colorado State satellite slider), the high pressure that produced our sunny weekend has drifted into Texas and Tennessee (see NWS WPC Latest North American zoom-in surface map). The cool air it once carried has been warmed by the high's trip to the southern US. With our winds from the southwest, yesterday afternoon's temperatures rebounded well above average with highs in the upper 60's in central Minnesota and even lower 70's in central and southern Minnesota (see 4 PM Sunday NWS WPC North American zoom-in map). That's more than 10 degrees warmer than the mid-October average high temperature, now in the middle 50's. The temperature rebound continued overnight, despite clear skies, as the persistent southwest wind has helped to keep low temperatures in the 40's in central Minnesota (see NWS Aviation Weather Center metar map) with even some 50's in southwestern Minnesota. The winds did calm down (circle around the station circle) in northeastern Minnesota, so temperatures are again below freezing. And, some light winds in central Minnesota have allowed lows in the upper 30's.

The warming has come as the upper-air low pressure system that produced the rain in the Red River Valley and the snow in the Black Hills moved into eastern Canada (see Mid-tropospheric water vapor loop from Colorado State satellite slider). The upper air high (center of clockwise circulation on the Mid-tropospheric water vapor loop) moved from the Rockies into the central US, allowing steering winds from the west or even southwest to support warmer air in the Plains. Still, the lingering effects of the cool high dominate the central US. Even though this air has been warmed by the stronger sunshine in the central Plains, it retained its dryness with dew points no higher than the 40's across the entire Continental US (green on the UCAR hourly dew point map), except central and south Florida. That dryness has kept the center of the country cloud-free (see Shortwave Albedo from Colorado State satellite slider). Even under the clouds in the Intermountain West and the Northeast, there are very few areas of precipitation (only California and New York; see College of DuPage national radar loop).

Warmth to Continue Today, Dimmed by Some Clouds From an Approaching Storm Tomorrow

We will have a couple of more warm days today and tomorrow. Today will likely be the warmest, since we will enjoy the most sunshine. High temperatures climb above 70 degrees in much of central and southern Minnesota and will approach 70 even in northern Minnesota. The south winds will be strong at 15-25 MPH.

The storm producing the rain in central and northern California is a strong one (see the counterclockwise circulation coming onshore on the Mid-tropospheric water vapor loop from Colorado State satellite slider), and it is scheduled to move right over Minnesota on Wednesday. However, the dry air in the center of the country all the way to the Gulf Coast means that it will have trouble getting enough moisture to produce substantial rain. By Tuesday, the low pressure will already be lifting the air over Minnesota, but with the dry leftover air at low levels, all that will do is move some of the high and middle "colored clouds" in the Rockies (see Shortwave Albedo from Colorado State satellite slider) over us. The clouds may look impressive, but the infrared satellite picture only shows us how high the tops of the clouds are. The dry air underneath means these clouds are mostly high clouds, but not deep ones. So, the main effect will be to dim some of the sunshine. In mid-October, that does mean knocking a few degrees off our high temperatures, so 60's are more likely than 70's tomorrow afternoon.

Strong Storm With Limited Moisture Will Produce Narrow Band of Wednesday Significant Rain (S MN?)

The California storm is strong enough to create a narrow band of significant rainfall on the northern flank of the storm. Since the low will track across northern Iowa and southern Minnesota on Wednesday, some parts of southern and perhaps central Minnesota could see some substantial rainfall, but the computer forecasts have to be right on to pin that area down. The National Weather Service forecasters note that the trend in the computer forecasts has been to push the band of significant rainfall further to the south, so by the time we get to Wednesday, the rain might be more limited to southern Minnesota. For the rest of us, the low will pull our winds around to northeast on Tuesday night and they will blow quite strongly at 10-25 MPH with gusts over 30 MPH on Wednesday (the low is a strong one, just moisture-starved). After temperatures fall back to the middle to upper 40's late Tuesday night, they will generally remain no higher than 50 degrees during the day on Wednesday. There will be a chance for rain when the front comes through late Tuesday night, but the best chance for rain will be during Wednesday into Wednesday evening. Right now, it appears that St. Cloud will be on the northern fringe, so we may only see sprinkles or occasional showers, but that band of more important rain will be close.

And Then, For Temperatures Complete Different (Late Week into Weekend)

Still, Tuesday night will mark the major change for the week as the northwest-to-southeast air flow behind the low will be dominant. Our air during the second half of the work week will actually be coming from the Canadian islands along the Arctic Coast in north central Canada. So, the temperature roller coaster will plunge with temperatures having a hard time getting past 50 degrees for a high. Any clear, calm night will have the potential of producing the first hard freeze of the season (low of 28 degrees or colder) for those areas that have been without a freeze.

Hard Freeze Potential Thursday Night?

On Wednesday night, the clearing is likely to come during the second half of the night, so I have low temperatures remaining in the 30's, but that could change if we clear out earlier. Highs on Thursday will be in the upper 40's to near 50. The northwest winds won't be as strong as they will be on Thursday, but the 10-20 MPH winds will still make it feel cool in the shade. At this point, Friday morning has that potential for a hard freeze, after a clear and calm night. Lows will be in the 20's to near 30.

Maybe Some Instability Showers Friday, Which Could Produce Snow Flakes

The computer forecasts are actually moving the upper-level low containing the coldest of the early season cold air into at least southwestern Ontario on Friday. Depending on how close it gets to Minnesota, some parts of the state will see instability showers due to the large temperature difference between the ground and the middle atmosphere, much as was the case last Friday. However, this time the low level air will be cold enough to allow some of the light showers to fall as sleet pellets or snowflakes. Highs will be in the chilly 40's in central Minnesota, so I don't see a chance for any snow to stick, but northern Minnesota might even see a brief coating, depending on how close the upper-level low gets to Minnesota. There is disagreement among the computer forecasts, so the snow showers are not guaranteed.

Eventually, a wetter storm is forecast to move inland into the western US next weekend, bringing an end to the stark nationwide dryness. That may eventually give Minnesota a better chance for rain early next week, but it's too soon to tell.

Measurable Snow (Not Indicated for This Week) in October Shouldn't Surprise You

However, after last year, we shouldn't be surprised by October snow. A year ago Wednesday, on October 20, St. Cloud got the second heaviest snowfall of last season with 7.0 inches, setting a daily record. The heaviest daily snow fell on November 10 with 7.2 inches. The 15.8 inches of snow picked up in October and November last season were about a third of the snow total for the entire cold season. The storm that is due to produce some rain in at least southern Minnesota on Wednesday will produce a second major snowfall of this season in Wyoming tomorrow and could produce some measurable snow in the Black Hills Wednesday, although it won't be anything like the storm a week ago.

Detailed St. Cloud, MN, and Vicinity Forecast

Confidence Level: "I Will Walk into the Doorknob at Least Twice A Day"

Monday 10/18/2021: Sunny, breezy, and warmer (typical of early September). High: between 72 and 77. Winds: S 15-25 MPH. Chance of measurable rainfall: 0%.

Monday Night: Partly clear, light winds, but seasonably mild. Low: between 42 and 47. Winds: S 5-10 MPH. Chance of measurable rainfall: 10%.

Tuesday 10/19/2021: Sunshine through high clouds, light winds, and still warm. High: between 65 and 70. Winds: S 5-15 MPH. Chance of measurable rainfall: 10%.

Confidence Level: "At Least Once, My Fingernail Will Get Pulled Back and Start Bleeding"

Tuesday Night: Clouding up with a chance of showers late. Breezy and still mild. Low: between 45 and 50. Winds: S 5-15 MPH early, becoming NE 10-25 MPH. Chance of measurable rainfall: 30%.

Wednesday 10/20/2021: Cloudy, breezy, and much cooler. Occasional rain or showers. High: between 48 and 53. Winds: NE 10-25 MPH. Chance of measurable rainfall: 50%.

Wednesday Night: Evening sprinkles, then partial clearing and much cooler late. Low: between 32 and 37. Winds: N 8-15 MPH, becoming NW 5-10 MPH late. Chance of measurable rainfall: 20%.

Thursday 10/21/2021: Sunny, breezy, dry, but cool for mid-October. High: between 46 and 52. Winds: NW 10-20 MPH. Chance of measurable rainfall: 10%.

Thursday Night: Partly clear and calm. A hard freeze is possible in areas that have avoided it so far. Low: between 25 and 30. Winds: NW 5 MPH. Chance of measurable rainfall: 10%.

Confidence Level: "We Will Be Out of Bandages"

Friday 10/22/2021: Mixed clouds and sun, breezy, and continued cool. Maybe a sprinkle or even a stray snowflake? High: between 42 and 50. Winds: NW 10-20 MPH. Chance of measurable precipitation: 20%.

Extended: Average to colder than average temperatures continue over the weekend??

Forecast Confidence (10 - "The Rabbits Will Thump Even Though I Fed Them"; 0 - "The Rabbits Will Offer To Groom My Bald Spot"): 8 Monday, 7 Monday night and Tuesday, 5 Tuesday night, 4 Wednesday through Thursday night, 2 Friday.

Yesterday's High: 68°F; Overnight Low (through 3 AM Monday): 42°F
St. Cloud Airport 24-Hour Precipitation (through 3 AM Monday): None; SCSU Precipitation (through 3 AM Monday): None

Next Update: Monday, October 18, 2021 8 AM

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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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