Friday, December 14, 2018  3:10 AM

A Breath of Fresh Air (Literally)

The cold front came through central Minnesota around midday yesterday. I did see a couple of stray snowflakes around 10-11 AM, but the big change was a supply of air from Alberta, chasing out the moist and dirty air that had been trapped near the ground. Temperatures briefly jumped to freezing late yesterday afternoon as skies even cleared out (see Shortwave Albedo from Colorado State satellite slider menu). It didn't dry out as fast as it did in western Minnesota, where high temperatures broke 40 degrees in places like Alexandria (see Yesterday's High Temperature Map from NWS/SUNY-AlbanyThat drier air has worked in enough to break up some dense fog that was over Princeton and St. Cloud earlier this evening ( see NWS: Last 72 hours of St. Cloud Observations), so temperatures have fallen back into the lower teens (see UCAR Minnesota surface chart).

Temperatures will begin to rise a bit in the early morning hours as the light southwest winds begin to kick in. That should actually push the western edge of the fog further to the east. Until that happens, a strip of eastern Minnesota is under a dense fog advisory. Some areas could have some ice spots due to spotty freezing drizzle.

The new air mass is also cleaner, allowing the Air Quality Index to drop to good levels in most of western Minnesota and to the low to middle part of the moderate range in eastern Minnesota (see hourly Air Quality Index from the Minnesota Pollution Control Agency).

More Sunshine, Still Mild Today

The air aloft isn't all that cool. In fact, even warmer air from Alberta, Saskatchewan, and Montana (greens are temperatures around 4-6°C, which are near or above 40 in Fahrenheit; see Unisys N. Hemisphere 850 mb chart) will be blowing over the top of this new air. However, having the air at the ground freshen up means that it will take longer for it to get stale. So, I think we will see some milder temperatures today and tomorrow than we saw earlier in the week. We should do well on sunshine. The air quality may creep into the moderate category this afternoon, but it will be cleaner than what we got rid of.

Perhaps a Few More Clouds Tomorrow

We will continue to be in this mountain air tomorrow. Temperatures will fall off quickly tonight into the teens with the possibility of fog, but the southwest winds will kick up a bit late tonight. Tomorrow, there will be a bit more of southwest wind. That means this air mass will spend some time over the leftover snow cover in southern Minnesota and northern Iowa (see NWS snow depth map from NOHRSC). Since there will be some actual melting in that area today and tomorrow, this air could see the moisture level creep up again, which would mean the possibility of low clouds when it gets here. This may knock a couple of degrees off the high temperature tomorrow, but I still think we can make into the middle 30's, at least. And with it being a weekend day, I don't think we will have as many problems with air quality.

Another Supply of Canadian Air Keeps Low Clouds At Bay Through Sunday

On Saturday night, another slightly cooler and drier air mass will move in behind a weak cold front. There is a slight chance of some light snow or flurries when that front comes through, but the main change will be to sweep out the old cool air and replace it with central Canada air, knocking the moisture and dirt particles out. There will be more of a northwest wind with this surge of cooler air, so we should see clearing on Sunday. Lows will stay in the 20's Saturday night and have a good chance to break freezing again on Sunday. We will be a bit deeper into the cool air mass on Monday, so lows could fall to the teens.

Fog and Low Clouds Back on Monday??

The computers are forecasting that air mass to develop low cloud and fog problems by late Sunday night into Monday. That's a bit far ahead, but the computer forecast have been doing fairly well with the low clouds in the current pattern. So, I've cut down on the potential sunshine on Monday. Moistening the air near the ground also means highs will be limited to the 20's. Milder air is forecast to push towards Minnesota on Tuesday and Wednesday, but that may simply trap the stale cold air near the ground. A bit of a southwest wind on Tuesday night could keep visibilities from getting too low as temperatures remain in the 20's all night. If the next cold front makes it into Minnesota by midday Tuesday, we might be able to see temperatures get to the freezing mark.

Still, nothing looks like a major storm affecting Minnesota through at least the middle of next week.

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

Friday 12/14/2018: Partly to mostly sunny, light winds, and seasonably mild. High: between 35 and 40. Winds: SW 5-10 MPH. Chance of measurable snowfall: 0%.

Friday Night: Partly clear and continued seasonably mild. Perhaps some fog. Low: between 15 and 20. Winds: SW 5 MPH evening, 5-15 MPH by early morning. Chance of measurable precipitation: 10%.

Saturday 12/15/2018: Sunshine through high clouds, breezy, and milder. High: between 35 and 40. Winds: S 10-20 MPH. Chance of measurable snowfall: 0%.

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

Saturday Night: Partly clear, breezy, and mild. A slight chance of a flurry. Low: between 25 and 30. Winds: SW 5-15 MPH, becoming NW 8-15 MPH late. Chance of measurable snowfall: 20%.

Sunday 12/16/2018: Partly sunny, breezy, and still seasonably mild. High: between 32 and 36. Winds: NW 10-20 MPH. Chance of measurable snowfall: 10%.

Sunday Night: Partly clear with diminishing wind late and a bit colder. Maybe some morning fog. Low: between 12 and 18. Winds: N 5-10 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

Monday 12/17/2018: Perhaps some low clouds or fog in the morning, then partly sunny in the afternoon. Seasonably cold with light winds. High: between 23 and 28. Winds: SE 5 MPH. Chance of measurable snowfall: 10%.

Monday Night: Partly clear, breezy, and not quite as cold. Perhaps some areas of fog. Low: between 18 and 23. Winds: SE 5-15 MPH. Chance of measurable snowfall: 10%.

Tuesday 12/18/2018: Low clouds and fog in the morning. Maybe a little afternoon sun. High: between 28 and 32. Winds: SE 8-15 MPH, becoming SW in the afternoon. Chance of measurable snowfall: 10%.

Extended: Relatively mild through Wednesday?

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 Friday through Saturday, 5 Saturday night and Sunday, 4 Sunday night, 3 Monday through Tuesday.

Yesterday's High: 32°F; Overnight Low (through 2 AM Friday): 11°F
St. Cloud Airport 24 Hour Precipitation (through 2 AM Fridayay): None; SCSU Precipitation (through 2 AM Friday): Trace

Next Update: Monday, December 17, 2018 8 AM (or as needed)

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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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