Thursday, December 12, 2024  2:40 AM

Prepared by Bob Weisman, SCSU Meteorologist and Professor Emeritus

Bitterly Cold This AM, Then a Tricky (Foggy? Icy?) Path to Milder Temperatures

First Bout of Serious Wind Chills This Morning

It's finally cold enough to make headlines in central Minnesota. Skies cleared up early yesterday morning (see GeoColor satellite loop from Colorado State satellite slider), but with less than 9 hours of daylight (see St. Cloud sunrise and sunset times from timeanddate.com), and a cold air mass seeping in, clear days this time of year tend to be colder than cloudy days. Note that the arctic air has the telltale sign of cold air on the infrared satellite loop: the air under clear skies from the western shore of Hudson Bay into northwestern Minnesota has the same color as the lake effect snow clouds over Upper Michigan (see Clean Infrared satellite loop from Colorado State satellite slider), so the ground temperatures in the arctic air are as cold as that of middle clouds.

Temperatures fell all day yesterday through the plus single digits and have continued their fall overnight, getting well down into the minus single digits (see 7-day graph of St. Cloud temperatures from MesoWest) with some minus teens not far away (see NWS Aviation Weather Center METAR map). The winds have persisted at 8-15 MPH during the early morning hours, creating central Minnesota wind chills between -30 and -25 (see NWS Minnesota hourly weather round-up for the latest temperatures, winds, and wind chills). That's cold enough to freeze exposed skin in 30 minutes or less (light blue range). freeze exposed skin in 30 minusteady in the plus single digits yesterday ll be here shortly and continue through tomorrow morning (note area of dark blue moving into Minnesota today, use right arrows to advance the map, on the North America 850 mb temperature departure from average chart). It's even colder in northwestern Minnesota with temperatures in the minus teens and approaching -20 and wind chills in the -40 to -30 range.

The National Weather Service has changed its criteria for a cold weather advisory. Forecasters won't issue an advisory unless either the temperature or the wind chill is at least -30 (used to be -25 for a wind chill advisory). So, only northern Minnesota, north of Hwy. 210, has the advisory this morning.

The coldest of the cold air will push across Minnesota today. High temperatures will recover from the coldest low since January 20 to get back into plus territory today. Still, a high near 5 will be St. Cloud's coldest high temperature since either January 19 (5) or January 15 (0).

Warm-Up Could Include Wintry Mix Friday Night Into Saturday Night

Milder air will begin to move into Minnesota, especially tomorrow. The promised shift in the steering winds from the current northwest-to-southeast (seen from the Yukon through central Canada and into the Great Lakes on the Pacific mid-tropospheric water vapor loop from Colorado State satellite slider) to more west-to-east (as seen in the eastern Pacific) will take place. However, the warm-up is going to be tricky with a wintry mix of light precipitation possible between Friday night and Saturday.

The details: central Minnesota will be on the northern fringe of the storm approaching Oregon (see counterclockwise circulation on the Pacific mid-tropospheric water vapor loop from Colorado State satellite slider) as it moves from the central Rockies Friday to the Missouri-Iowa border by Saturday night. This track would be far enough to the south to keep the significant precipitation in Iowa (see Days 2-3 on the NWS WPC quantitative precipitation forecast). And, this system won't have that much cold air at upper levels, so even steady precipitation would most likely fall as freezing rain. Note the threat of measurable freezing is around 30 percent as of 00 UTC Sat, 6 PM CST Fri, with 70 percent plus (blue and orange areas) in Iowa and southern Minnesota during the 24 hours ending 00 UTC Sun, 6 PM CST Sat on the NWS WPC probabilistic winter precipitation guidance). Note that there is a chance of some light snow as well from southern Minnesota into Wisconsin (change precipitation type to snow for the period ending 00 UTC Sun, 6 PM CST Sat). The threat for a significant amount of snow or mixed precipitation in southern Minnesota is still a bit uncertain at this time.

Central Minnesota will be on the far northern fringe of the precipitation or just in the drizzle, but this would likely produce either light freezing rain or persistent freezing drizzle. The best chance for a period of steady freezing rain would be late Friday night into Saturday morning, but freezing drizzle could continue through much of Saturday, since temperatures will moderate to the 20's, but stay there all day and Saturday night.

On Saturday night, the winds will ease up. That would likely give us a threat for some dense fog Saturday night and still carry the threat for icy spots due to freezing drizzle.

In ice situations, the worst case scenario is either heavy precipitation (more than two tenths of an inch of ice), which can down tree branches and power lines, or very light precipitation (a few hundredths of an inch), which leaves an ice coating on all surfaces. The most likely threat in central Minnesota would be the lighter precipitation issue.

Sunday Will Be Milder, But Still Cloud Problems?

On Sunday, we will get deeper into the mild air, but there may be problems clearing out the low clouds. So, I am keeping the high temperatures only near freezing.

Drier, Colder, Wind-Whipped Air Monday, But Not as Cold as Now

The forecasts agree that a cold front will push through Minnesota early Monday. The winds will shift into the northwest on Monday morning and kick into high gear, producing blustery conditions. The immediate cold air behind the cold front won't be nearly as cold as what we have now, so morning temperatures near 30 will fall only slowly into the middle or lower 20's. There might be a chance of some light snow or flurries, but any precipitation is likely to be light.

We will be in a quickly moving storm track, but it will remain close to west-to-east through mid-week. Early next week, any cold period would likely keep us merely seasonably cold (highs in the 20's). The timing and track of weather systems change so much from one model to another that the European forecast has a high pressure over Minnesota Wednesday evening, while the main US forecast has a storm in northeastern Minnesota at the same time. Punting time!

Detailed St. Cloud, MN, and Vicinity Forecast

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

Wednesday Night Pre-Dawn: Clear, breezy, and colder with serious wind chill. Low: between -15 and -8. Winds: NW 8-15 MPH. Wind chill: between -33 and -25. Chance of measurable snowfall: 0%.

Thursday 12/12/2024: A new candidate for the coldest day of the winter thus far. Mostly sunny, not nearly as windy, but continued arctic cold. High: between 2 and 7. Winds: NW 5-15 MPH. Wind chill: between -28 and -14 during the morning, between -15 and -5 during the afternoon. Chance of measurable snowfall: 0%.

Thursday Night: Clear with light winds and quite cold during the evening. Partly clear with a biting breeze, but steady or rising temperatures after midnight. Low: between -10 and 0, rising to near 5 by morning. Winds: light evening, becoming SE 5-10 MPH after 3 AM. Late night wind chill: between -15 and -5. Chance of measurable snowfall: 10%.

Friday 12/13/2024: Sunny in the morning, sunshine through high clouds in the afternoon, not quite as ridiculously cold, but a biting breeze returns. High: between 13 and 18. Winds: SE 8-15 MPH. Wind chill: between -20 and 0 in the morning, in the plus single digits during the afternoon. Chance of measurable snowfall: 10%.

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"

Friday Night: Cloudy, breezy, and not as cold. A chance of patchy fog or spotty freezing drizzle late at night. Temperatures between 10 and 15 early in the evening, rising to between 20 and 25 by morning. Winds: SE 8-15 MPH. Wind chill: between 0 and +15. Chance of measurable precipitation: 30%.

Saturday 12/14/2024: Cloudy, breezy, and seasonably cold. A chance of dense fog or occasional freezing sprinkles, especially during the morning. High: between 23 and 28. Winds: SE 5-15 MPH, becoming E in the afternoon. Wind chill: between +12 and +25. Chance of measurable precipitation: 20%.

Saturday Night: Continued cloudy with a better chance for dense fog. Perhaps some spotty freezing drizzle. Milder. Low: between 23 and 28. Winds: E 5 MPH. Chance of measurable precipitation: 20%.

Sunday 12/15/2024: Early low clouds and fog, perhaps some sunny periods in the afternoon, a bit of a breeze, and slightly milder. High: between 30 and 35. Winds: SE 5-15 MPH. Chance of measurable precipitation: 10%.

Sunday Night: Partly cloudy and still quite mild. Low: between 25 and 30. Winds: SE 5 MPH. Chance of measurable precipitation: 10%.

Monday 12/16/2024: Turning blustery and colder during the day. Perhaps a little light snow or flurries. Early temperatures near 30, falling back to the middle 20's for most of the day. Winds: becoming NW 15-30 MPH with gusts to 40 MPH from late morning through afternoon. Wind chill: between 0 and +15. Chance of measurable snowfall: 20%.

Extended: Milder Sunday (30's)???? Not as mild 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"): 9 Thursday, 8 Thursday night and Friday, 3 Friday night through Monday.

Yesterday's High: 19°F (set at midnight Tuesday night); Yesterday's Daytime High: 13°F; Overnight Low (through 2 AM Thursday): -9°F; Yesterday's Top Wind Gust (through 3 AM Thursday): 35 MPH at 1:18 and 3:00 PM Tuesday;
St. Cloud Airport 24-Hour Melted Precipitation (through 2 AM Thursday): None; SCSU 24-Hour Precipitation (through 2 AM Thursday): None; Yesterday's Worst Wind Chill (through 2 AM Thursday): -27°F, set at 7 and 10 PM Tuesday, and 2 AM Wednesday

Next Update: Friday, December 13, 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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