Tuesday, December 11, 2018  3:00 PM (Updated for Air Quality Alert)

Quiet and Seasonably Mild Interlude to Continue Into Weekend

Seasonable Cold At the Ground, But Hard to Get Above Freezing Temperatures Down Here

While Virginia and North Carolina had winter weather advisories out last night (not for any storm, but because the wet spots from melted snow yesterday would ice up overnight as temperatures drop below freezing), Minnesota managed a bit of improvement yesterday. The patch of low clouds mostly pushed on to Wisconsin (see Shortwave Albedo loop from Colorado State satellite slider menu), allowing a good supply of sunshine. Even overnight, the fog development was rather limited (see UCAR Minnesota surface chart) despite low temperatures near 10 in central Minnesota and in the single digits across the northern half of Minnesota. It's more difficult for fog to develop overnight with the high clouds in the way, so we are only seeing some spotty fog.

Despite the additional sunshine, temperatures were about the same in the southern half of Minnesota yesterday (see Yesterday's High Temperature Map from NWS/SUNY-Albany). It was a bit milder in north central Minnesota with a few readings above freezing. Still, it is sobering to note that ground temperatures, even where it was the mildest, merely got to the temperature at 5,000 feet above the ground. Areas in the light blue had temperatures aloft between 32 and 36 degrees (0-2 degrees C) and in the duller blue-green, readings were between 35-40 degrees aloft (see Unisys N. Hemisphere 850 mb chart).

Update: Air Quality Alert for Central Minnesota Through At Least Thursday PM

The Minnesota Pollution Control Agency has issued an air quality alert for central Minnesota from now through 6 PM on Thursday. The area basically spans the region between I-94 and the Minnesota River and includes the Twin Cities, Willmar, Hutchinson, Stearns and Wright Counties and a piece of St. Cloud.

The fine particle concentration has risen to near the cutoff for unhealthful for sensitive groups in the Twin Cities and near that level in Rochester. The conditions trapping these particles, warmer air above cooler air, and generally light ground winds will continue to allow pollutants from vehicle exhausts and other sources to accumulate. Since it takes a strong cold front to usually clean out the low-level air, we are likely to see pollution problems into Saturday.

See https://www.pca.state.mn.us/air/current-air-quality for the latest advisory.

Warming is a Difficult December Task

It's always difficult to get milder air aloft down to the ground, since the warmer is less dense than the cold air underneath, so it tends to ride over the top of the cold air. This is particularly true in December and January because nearly every factor that might help mild air to the ground is going against us. The intensity of the sunshine is the weakest of the year, since the sun is lowest in the sky and the number of daylight hours are the smallest. So, sunshine has a lot of trouble heating the ground, even through thin clouds. Where there is snow cover (see snow depth map from NOHRSC), more of the sunlight that gets to the ground is wasted, either getting reflected back to space or being used up by melting the snow. It's no accident that yesterday's warmest highs were in the area of thinnest snow cover. Still, it's frustrating to see temperatures in the 20's and even some thirties in Montana, Alberta, and even western Nunavut (see NWS WPC Latest North American zoom-in surface map) while our readings our in the teens.

There is good news, however, on that NWS WPC Latest North American zoom-in surface map since it means really cold air is confined to eastern Canada. So, our seasonable temperatures will continue with a slight warming trend as the week goes on.

A Couple of (Not Much) Snow Threats Through Thursday

There are a few storm systems that will push through Minnesota over the next few days. The high and middle clouds moving into Minnesota this morning (see Shortwave Albedo loop from Colorado State satellite slider menu) are being produced by a storm system moving out of Alberta and into Saskatchewan (see Mid-Tropospheric water vapor loop from Colorado State satellite slider menu). However, the mild air is being produced by air flow down the eastern slopes of the Rockies, so that air in the lower half of the atmosphere is relatively dry. There are a few radar echoes from this system in North Dakota (see NWS Upper Mississippi Valley radar loop) and in southern Saskatchewan (see Environment Canada Prairie Provinces radar loop), but very little of that precipitation is making it to the ground (see UCAR Canadian Prairies map). So, we will see more high clouds dimming our sunshine with highs again in the upper 20's to perhaps near 30. The clouds will thicken tonight, but I only expect a short period late tonight into early tomorrow when the moisture will be deep enough to produce a little light snow or flurries. More clouds should keep low temperatures tonight in the teens. During the second half of tomorrow, we will have a chance to see some drying and some sunshine with temperatures again in the upper 20's to near 30.

Another storm system moving into British Columbia and the Pacific Northwest (see Pacific infrared satellite loop from University of Wisconsin/SSEC) will cross the mountains and throw clouds into Minnesota Wednesday night into Thursday. This system may have a bit more moisture with it, so we will have a better chance at seeing a light accumulation of snow late Wednesday night into Thursday morning. However, I'm only talking about a dusting to an inch at most.

Otherwise, Slow Warming Through Saturday

The generally mild weather will continue in Minnesota through Saturday. If we can keep the fog and low clouds to a minimum, we could see temperatures climb above freezing and Saturday. I'm still not sure we will be able to do this, especially as the snow to our south melts, but there is some hope. I don't expect any new precipitation until Saturday night when a cold front is due to move through. At this point, Sunday and perhaps Monday look to be a bit colder, but I don't see any highs in the teens nor lows below zero returning anytime soon.

A piece of that storm due on Thursday is expected to break off a southern stream storm that will track from Texas into the Gulf Coast states. This has the potential to produce heavy rainfall from Texas and Arkansas in the middle of the week to the entire eastern third of the country Friday into the weekend. Most of the precipitation from this storm should be rain, but that could cause problems with heavy rainfall over ground saturated by the recent snow.

Confidence Level: "The Bulb on That Hard-To-Reach Light in the Foyer Will Burn Out"

Tuesday 12/11/2018: Maybe some morning fog. Otherwise, some sunshine through thickening high clouds. Light winds and a shade colder. High: between 25 and 30. Winds: SE 5 MPH. Chance of measurable snowfall: 10%.

Confidence Level: "Every Time I Try to Put in a New Bulb, the Light Fixture Will Try to Detach From the Ceiling"

Tuesday Night: Mostly cloudy and not as cool. A chance of late night light snow or flurries. Low: between 15 and 22. Winds: E 5 MPH. Chance of measurable snowfall: 20%.

Wednesday 12/12/2018: Maybe some morning flurries or a little light snow. Perhaps some afternoon sun. Continued seasonably cold. High: between 25 and 30. Winds: SE 5-10 MPH. Chance of measurable snowfall: 20%.

Wednesday Night: Increasing clouds with a chance of light snow or flurries towards morning. Low: between 20 and 25. Winds: S-SW 5-15 MPH. Chance of measurable snowfall: 30%.

Thursday 12/13/2018: A chance of some morning steady light snow, then partly cloudy in the afternoon with a bit of a breeze. Milder. High: between 30 and 35. Winds: SW 5-10 MPH in the morning, NW 10-15 MPH in the afternoon. Chance of measurable snowfall: 40%.

Thursday Night: Partly clear, light winds, and perhaps some fog by morning. Low: between 15 and 22. Winds: SW 5 MPH. Chance of measurable snowfall: 10%.

Friday 12/14/2018: Morning clouds, some afternoon sun and seasonably mild. High: between 30 and 35. Winds: W 5-15 MPH. Chance of measurable snowfall: 10%.

Confidence Level: "The Only Way I'll Be Able to Change the Bulb and Hold the Fixture in Place Will Be to Yell At It

Friday Night: Clear and calm with some fog late at night. Low: between 15 and 22. Winds: SW 5 MPH. Chance of measurable snowfall: 10%.

Saturday 12/15/2018: Sunshine through high clouds, breezy, and milder. High: between 32 and 37. Winds: S 5-15 MPH. Chance of measurable snowfall: 10%.

Extended: Maybe some rain Saturday night? Not as warm on Sunday.

Forecast Confidence (10 - "The Rabbits Will Thump, Objecting to Me Yelling at the Light Bulb"; 0 - "I Will Be Hosting a DIY Show on Home Repairs"): 7 Tuesday, 5 Tuesday night through Thursday night, 4 Friday, 3 Friday night and Saturday, 2 Sunday.

Today's High (through 2 PM): 28°F; Overnight Low (through 9 AM Tuesday): 6°F
St. Cloud Airport 24 Hour Precipitation (through 7 AM Tuesday): Trace; SCSU Precipitation (through 7 AM Tuesday): Trace

Next Update: Wednesday, December 12, 2018 8 AM (or as needed)

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