Monday, December 7, 2009

Ready, Set, Snow!

Snow enthusiasts and armchair meteorologists should be having fun with this one, I know I am. By all rights, this has been a classic, Upper Midwest, snowstorm in the making and it continues to develop. I have been impressed by the consistency in the weather models over the past few days and from run to run (Of the several weather models we pour over in situations like this, we get up to 4 runs from those specific models each day). Most of the time the weather models, crunching long mathematical and physical equations, bounce all over the place until the day of an event and even then, sometimes, they don't get it right. But this time, confidence is fairly high as we step out onto that ever growing "Limb". Winter Weather Headlines have been posted from here to Tim Buck Two, see image below:

Upper Midwest to See Heavy Snow:

Snow will begin Tuesday, but will pick up, in earnest, through the overnight hours tonight and early morning hours tomorrow. The Twin Cities will be on the northern fringes of this storm, so the brunt of the snow is likely to miss us, but we still are under a Winter Storm Warning until Wednesday afternoon. Here's a closer look at the Winter Weather Headlines for the Upper Midwest. Note the red colors in south central MN and northeastern IA, these are Blizzard Watches where heavy snow is expected to accumulate to near 6" to 10" through Wednesday with strong winds gusting from 40mph to 50mph by Wednesday afternoon creating near 0 mile visibility for several hours. Though, be advised that most everybody in the Winter Storm Warning (pink coloring) has the potential of 4" to 8" by Wednesday afternoon. Travel will be quite a headache for Tuesday evenings commute growing into an even bigger headache by Wednesday mornings commute and Wednesday evenings commute, but by the middle and end of the day Wednesday - blowing and drifting snow will be the biggest threat. Get that Winter Survival Kit in the car if your travel plans take you anywhere south and east Tuesday and Wednesday.

Rapid Intensification of a Low Pressure System or "Bombogenesis"

This is neat, we don’t see this too often in the Midwest. Take a look at the following forecast (surface maps) at these two different time periods and keep an eye on the low near the Oklahoma Panhandle in image #1 and near the Great Lakes in image #2. There is a term in the weather world for rapid intensification of a Mid-Latitude Cyclone or low pressure system and it is called “Bombogenesis” – classified as a low that drops its central pressure by 24mb or more in a 24hr period, essentially 1mb per hour for 24 hours. The typically happens with Nor’Easters, a little more rare for Midwest storms and to see it happen is always exciting.

Tuesday @ 6pm – Central Pressure 998mb

Wednesday @ 6pm – Central Pressure 973mb

As storms deepen/intensify the air rushes into the middle of the storm, converges and is sent upwards, causing "Lift" for precipitation to form. The stronger the storm, the stronger the winds blow. In our case, rapid intensification of this low will mean a steady increase in winds through the day, which will quickly become windy tonight through tomorrow.

Cold Air to Follow

The heart of the Arctic air is on our side of the globe and it found its way into the Canadian Prairie Provinces – note the crazy color scheme (turning yellowish and greenish) just north of Ontario and Saskatchewan – THIS IS REALLY COLD AIR - the coldest of the season so far. It will modify and head south into the lower 48 by the middle and end of this week. Temperatures, in fact, will be dropping through the day on Wednesday and overnight lows through the weekend will likely be in the single digits above and below zero.

Todd's Outlook for the Twin Cities

Today: Mostly cloudy with snow developing by mid to late morning. Accumulations of around 1" to 2" by 6pm. Becoming breezy by the afternoon. High 21

Tonight: Snow likely, accumulations of 2" to 4" - strong northwest winds causing blowing and drifting snow through the night. Low: 14

Wednesday: Snow continues through early afternoon with an additional 1" to 2" of fluff possible, but hard to measure as winds howl from the west/northwest 20mph to 40mph. Blowing and drifting snow continues. High: 14, falling through the day.

Thursday: Mostly cloudy with perhaps a few flurries. Not as windy, but much colder. High:10

Friday: Mix of clouds and sun. High: 14

Saturday: Still cold, flurries possible. High: 13

Sunday: Partly sunny, light snow. High: 16

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