Tuesday, January 19, 2010

A taste of March in January

The rumors are true: the weather honeymoon is drawing to a close; Minnesota's weather will become stormier, travel more problematic as the week goes on. As is often the case, Mother Nature is about to throw us a curve. In spite of the St. Paul Winter Carnival kicking off the 10 coldest days of the year (on average) an unusually strong storm - tracking unusually far south and west of Minnesota - will pull enough warm air north for a period of rain and freezing rain (rain freezing into glaze ice on contact with cold surfaces) by Friday night and Saturday. Snow lovers are indignant, as well they should be: if this were a typical January with highs in the teens (north) and low 20s (south) we'd be looking at 12-16"+ of snow by Monday of next week. So close, and yet so far.

Icy possibilities. What month is this again? The maps look more like early March than mid January. An inch or two of slush is possible tomorrow, but the main event arrives this weekend, the atmosphere aloft just mild enough for snowflakes to melt into raindrops, potentially freezing on contact with cold surface. The best chance of icy headaches? Saturday morning (early). Again: Saturday night.

Potential for a "plowable snow"?
The GFS model is still hinting at 3-6" of snow Sunday into Monday, but precipitation Saturday should fall as a mix of snow, sleet, even some freezing rain (glaze ice) across central Minnesota. I still believe St. Cloud will pick up more snow than the Twin Cities, where more precipitation will fall as rain/freezing rain. Stay tuned for snowfall updates, but right now I'm leaning toward 3-5" for the St. Cloud area Saturday night into Monday morning. (For the record: I don' think the Twin Cities will see 6" of snow from this system, too much rain wrapping into the storm - I'm thinking more like 2-4" for Minneapolis & St. Paul by Monday).

Strange trends for the coldest week of winter. Check out the predicted temperature trend (top chart) showing temperatures at, even above freezing into the weekend. The bottom chart shows predicted snowfall amounts, spiking upward by Sunday/Monday as colder air filters back into the storm's circulation. In short: expect a king-size MESS this weekend!

Tuesday afternoon tornado warnings were issued for south central Los Angeles. No typo there - that's how violent and energetic the latest Pacific storm is, sweeping inland with torrential rains, hail and high water. One wrinkle of moisture and energy ejecting northeastward from the Four Corners region of the Desert Southwest will spark a little snow/sleet mix Wednesday night into Thursday, models still hinting at 1/2 to 2" of slushy/icy snow across much of Minnesota tomorrow. Give yourself some extra time to get around town, I expect commute times to be double, even triple normal, air temperatures holding in the mid/upper 20s, meaning potentially snow-covered secondary roads, let's hope treated major highways/freeways are mostly wet and slushy. Friday should be a better travel day, in-between storm systems, as we wait for the Main Event.

Guess the storm track! The heaviest snow is almost always 100-300 miles north/west of the actual storm track. Parts of the Dakotas may pick up 8-12"+ snow from the weekend storm, but a jog to the northwest may pull enough mild air northward for a changeover to sleet/rain/ice on Saturday, keeping amounts down, especially south/east of St. Cloud.

Anatomy of a slop-storm. By Saturday evening at 6 pm the storm is forecast to be stuck over southeastern South Dakota, moisture from the Gulf of Mexico pin-wheeling into Minnesota. This projected track would be far enough south/west of us for warm air to wrap completely around the storm circulation, triggering a mixed-bag of snow, ice, even a few hours of rain Saturday. Most of the accumulating snow should come Sunday into Monday morning, as the storm pushes east, toward the Great Lakes, and the entire column of the atmosphere begins to cool down.

The storm now slamming into California with gale force winds, mudslides and raging fits of thunder and lightning will cross the Rockies, gulping down vast quantities of moisture from the Gulf of Mexico late in the week, before turning almost due north over the weekend, pushing a shield of "precipitation" into Minnesota Friday night and Saturday. Notice I said precipitation, a wonderfully vague word, which could mean almost anything under the sun, except for the sun. To get all snow temperatures (usually) have to be colder than 32 throughout the lowest mile or so of the atmosphere. Even a thin layer of air > 32 F. can turn falling snowflakes into rain, dashing the hopes and expectations of snow-lovers stuck on the ground far below. A perfect storm track for snow runs from Kansas City and Des Moines to near La Crosse and Eau Claire, keeping Minnesota on the colder, northern side of the storm track. But this area of low pressure shows signs of "hooking" to the northwest, pushing into South Dakota (!) That, in turn, will probably yank enough mild air north for a significant period of sleet (ice pellets), changing to freezing rain (glaze ice) then finally over to plain-old-liquid-rain during the day Saturday, turning our snow to slush and mush (as I feared more than a week ago). As the storm does a big loop and finally tracks due east, then northeast across Wisconsin, toward the Great Lakes, a changeover back to mostly-snow is likely Sunday, finally tapering Monday. By then there may be 1-3" of new snow on the ground for southeastern MN, but a band of 3-6" is still very possible across central Minnesota (including St. Cloud), probably less near the Twin Cities - more like 2-3" - possibly 4" far northern and western suburbs.

The St. Paul (Messy) Carnival. Look at the bright side: no 40s or 50s this year. St. Paul may pick up an inch of sloppy snow Thursday, but rain may put a temporary damper on the fun Saturday, what may be the messiest day of the 10 day adventure. Temperatures cool back down into the 20s most of next week; the snow & ice sculptures should be in better shape by then.

We've been living on borrowed time in the temperature department, readings a good 10-15 degrees above average. The GFS model is now (strongly) suggesting a return to much colder weather next week (teens north, 20s south); an even colder push for the first few days of February, some single digits highs up north, maybe a week's worth of subzero lows for much of the state. I don't think it'll be as brutal as early January, but it will definitely get your attention. Our midwinter intermission was nice while it lasted, a welcome, nearly 2 week reprieve from the coldest, most controversial winds of winter. Old Man Winter got a "time out", but nights are (still) long, there's still a lot of snow lurking to our north - at some point the laws of physics kick in and the Yukon Express starts to roll once more. Give it about a week to 10 days, there will be no doubt in your mind that spring is NOT right around the corner.

Paul's Outlook for the Twin Cities

Today: Mostly cloudy - hanging onto good travel conditions. Winds: E 10-15. High: 27

Tonight: Chance of a little light snow, freezing drizzle. Low: 22

Thursday: Light snow, mixed with freezing drizzle at times, a slushy, slippery, icy inch possible. High: 28

Friday: Temporarily improving conditions - overcast, damp and gray. High: 30

Saturday: Wintry mix changes to mostly rain - very slippery/icy outside of town. High: 34

Sunday: Changeover back to mostly snow, starts to accumulate. Potential for 2-4" or more of snow by Sunday night. High: 31

Monday: Light snow quickly tapers to flurries, slowly improving travel conditions, turning colder. High: 20

Tuesday: Partly sunny and chilly, a few degrees cooler than average. High: 18

Wednesday: Yep, feels like a real January again. Intervals of sun, delightfully numb. High: 15

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