Tuesday, January 5, 2010

Risk of a Snowy Clipping

Good news (for anyone attempting to travel later today): the latest clipper is tracking about 50-75 miles farther west, taking the heaviest ("plowable") amounts of snow into far western and southwestern Minnesota, where more than 6" may pile up by breakfast Thursday. The odds of significant snow for St. Cloud and the Twin Cities have diminished; we'll be lucky to pick up an inch of powder tonight as the heaviest snow amounts slide off south and west of the Minnesota River.

Why Minnesota Meteorologists Have Gray Hair. Then again I'm happy to have ANY hair at this stage in my life, color is optional. But check out the extremes in expected snow later today. Virtually no snow expected north/east of I-94, maybe .5 to 1" for St. Cloud and the Twin Cities, 2-4" for Rochester, 4-6" Mankato, with a band of 8-12" of powdery snow possible near Windom and Pipestone. A foot of snow in the span of 80 miles, give or take. You can see how a slight wobble in the storm track can make a HUGE difference in expected snowfall.

Time-out. Forecasting Alberta Clippers is exceedingly difficult. They move quickly, moisture is usually very limited, a slight gyration in the storm track of just 50 miles can make the difference between flurries and 8" of flurries. The computer models don't do a very good job in this kind of a pattern, where a slight zig or zag in the track can make a HUGE difference in how much snow winds up in your yard - my confidence is lower than usual. For a time I was tempted to assign a "Confidence Level" for each day of the 7-Day forecast, using a scale from 1 to 10 to convey just how comfortable I was with the forecast for that specific day. The idea may have some merit, certain weather patterns have "high bust potential", there is a LOT that can go wrong. Other forecasts (in quiet patterns with relatively light jet stream steering winds aloft) are as close to "sure things" as they ever get, although in all honesty and candor: days when the forecast is truly black and white (and simple) are few and far between, maybe 50 days/year that are truly no-brainers. I thought about issuing a "Confidence Factor", and then thought again. We already hit people with too many numbers. Forecast recall is already an issue. Including another number, no matter how good the intention might be, would probably cause more confusion than anything else. So I came up with a compromise: when the forecast is unusually tough, loaded with potential "gotchas", I try to come clean and communicate this as clearly and honestly as I can.

A Very Close Call. Here is the NAM output valid 6 pm Wednesday evening, showing expected snow accumulation from noon through 6 pm - 3-6" of powder expected over far western and southwestern Minnesota, from Windom and Pipestone to Breckenridge, Wheaton and the Moorhead area. In general the farther west you drive out Highway 7, 12 or I-94 the worse travel conditions will be - the very worst conditions within 50-75 miles of the Dakota line.

Think twice before driving into southwestern Minnesota later in the day Wednesday, snow falling with temperatures this cold will result in very icy roads, with a layer of ice underneath the snow; MnDOT's salt/sand mix fairly inefficient when the mercury is flirting with zero. The good news: winds won't be too strong, that should limit blowing and drifting. This does NOT appear to be a blizzard situation shaping up out west. One thing is painfully evident, virtually certain: another body-blow of arctic air will swirl into Minnesota on the backside of today's clipper, we probably won't see zero Thursday, much of Minnesota will enjoy (wrong word) a day of negative numbers on Friday as well. Something to look forward to.

2009 Recap. The National Weather Service has put together an exhaustive, comprehensive review of 2009. Overall daytime highs averaged about .6 F. cooler than average, but nighttime lows were 1.1 F warmer than average, continuing a trend we've seen in recent decades of warmer nighttime lows. The complete recap is here.

Get ready for another potentially painful encounter with air that was drifting over the Yukon just a few short days ago, I'm expecting 3 or 4 subzero nights (as cold as -20 F Saturday morning). But it won't be quite as cold as last weekend, and all the models are still adamant about a nice little warming trend next week. I know this sounds ridiculous (and looks even dumber in print) but you will be AMAZED how good 20s will feel next week. 30 is still a possibility, and I want to believe that the coldest of the cold wave will be behind us as of Sunday. I hope that's the case, and I'm reasonably confident that (looking at the number of hours below zero and the wind chills we've been experiencing) the WORST of winter may be in our rear view mirror within 96 hours, give or take. The pattern definitely seems to be shifting to more of a "zonal", west to east wind flow. Canada is literally running out of Nanook air, at least for the short term, looking out 10-14 days. Maybe public musing that "the worst is behind us now" is just wishful thinking. All I know is that all those official NOAA forecasts of El Nino resulting in a milder winter for much of the USA, including Minnesota?

Hahahahahahaha! Oh brother.

Sorry. Not very professional. Ah, the perils of long-range prognostication. 7 days into the future is tough enough, most days. I can sympathize.

Paul's Outlook for the Twin Cities

Today: Cloudy with light snow and flurries developing (heaviest west of Cold Spring, Albany and Kimball). Potential for about 1" of light, powdery snow by tonight. Winds: NE 5-15. High: 12

Tonight: Light snow tapers, turning colder. Very icy roads (as much as 4-8" over far western MN, heaviest amounts west of Alexandria). Low: 2

Thursday: Cold sun returns, dangerously cold wind chills. High: 5 (feels like -20 to -25 F).

Thursday night: Numbing again. Low: -12

Friday: Bright sun, less wind, still bitter. High: 0 Low Friday night: -14

Saturday: Blue sky, temperatures moderating a bit. High: 12 (above)

Sunday: Partly cloudy, more tolerable again. High: 22

Monday: Patchy clouds, a few flakes. High: 21

Tuesday: Mostly cloudy, noticeably "milder". High: 27

Wednesday: Grilling weather! More clouds than sun, above average. High: near 31 ! ! !

1 comment:

  1. If the well-informed weather heads in the Washington, DC area use confidence assessments within the forecast (see also capitalweather.com), it seems like they should be used here as well.