A BIT WARMER, AND SNOWIER
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EASING BACK ON THE CHILL
The overall weather pattern the past few days has been under the dominate control of a huge Arctic high. With a central pressure of 1049mb, it has provided sub-zero nights for 5 consecutive days. Follow the isobars, and you can see the pathway the cold has utilized to enter the Midwest.
Notice too how the frigid air has plunged deep into the heart of Texas, with freezing temperatures well past San Antonio.
At 9:00pm Tuesday, below zero temperatures covered about a third of the nation.
Wednesday, the high rapidly shifts SE and a return flow of southerly winds is established. After a sub-zero start and wind chills of 15-25 below zero, readings will climb into the low to mid-teens, perhaps close to 20 in the far SE where there is less snow cover.
FRESHEN UP THAT SNOW COVER...
With time, enough moisture gets into the pattern Wednesday night for models to begin the saturation process thanks to a weak moisture starved disturbance. A narrow band of light snow is shown developing, mainly near and along HWY 30. With high snow ratios, a fluffy 1/2 inch of snow is possible, with isolated 1" amounts possible.
That should be gone by daybreak Thursday. That makes room for a clipper that has better forcing and dynamics. Soundings are indicating better moisture and far less dry air at the surface. As a result, guidance has been trending a bit higher with snow accumulations. With QPF up to .20 on some of the CAMS, there may be a period of moderate snow where frontogenesis is maximized. There is still some doubt as to where this band sets-up, but with snow ratios of 20:1, it would not take much to get a localized swath of powdery 2-3" snows. The deterministic runs of the GFS and EURO are not as aggressive as other models and lower with amounts, which may or may not be correct. For now, I will stick with the low end of totals in the 1-2 inch range, with the option of slightly higher amounts if the trend of the higher CAMS holds on Wednesday's new data. Here's what guidance is currently suggesting. This includes the combined effects of any snow that falls Wednesday night as well as Thursday night.
The 3k NAM
The 12K NAM
The 10 K hi-res GEM
The NBM (national blend models)
The SREF short range ensembles.
On the backside of this disturbance, look for another surge of Arctic air to follow Friday and Saturday. Gusty NW winds to 30mph will usher in the frigid air, potentially generating pockets of blowing snow, especially in the open country. The winds will also send wind chills to 25-30 below Saturday morning.
These are low temperatures on the GFS Saturday morning.
Here are temperature departures Saturday night. Readings about 35 degrees below normal on the table again.
As promised, a warm-up is still coming next week as the pattern snaps back to one that is driven by Pacific air and the resurgence of El Niño's split flow. Notice all the blue from Alaska to Greenland. Two weeks ago, that was all red, indicating the dominance of high pressure and cold air. That's being drained, and the northern latitudes will need to be re-seeded with cold air before any harsh temperatures return to the Midwest.
You can see the impacts of next week's 500mb pattern clearly though, with above normal temperatures returning to much of the northern half of the United States next Monday. The difference this time compared to December is the deep snow cover that now exists. It will certainly temper the warm-up. The question is, how much?
That's all I have in my bag for now. Roll weather...TS! P.S. If you can swing a donation to the site, anything would be immensely appreciated. CLICK HERE TO CONTRIBUTE