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2016-12-25 EVENT: KS, NE, IA,MO,OK,TX

Oh it's happening sweetheart! The Xmas Event you've all dreamed of since you were storm chasing infants. Santa is going to bring us some severe weather 12/25 across much of the plains and lower MO/MS river valleys. SPC has a mention in their Day 6 long term, but no delineation due to low probs, and there are a few events to compare to, such as the Jan 7th, 1992 event in Central Nebraska (6 Tors, 5 F1's and 1 F2 in Nance and Merrick Counties) and the event in IA this November.

12Z GFS continues the trend of a narrow band of 100-500SBCAPE stretching from TX all the way up to Southeastern NE. Td's are likely to advect rapidly northward during the morning with low 50's and near 60 temps covering the target area. We had a similar setup in late November event this year in Central IA.

The low moving out of CO is forecast to be in the 990-988mb range, accompanied by an incredible DPVA lobe smashing into the area during max heating. Bulk shear values are 80-100kts, however helicity may not be terribly impressive due to the linear fashion of the shear. This being said, any right turning mini-supercells that can get embedded at the surface have the potential to drop tors, similar to the IA event.

Concerns: Low clouds may ruin diurnal heating, Linear Shear, heavy contingency on moisture advection
Bonus Factors: Extreme levels of DPVA, Divergence Aloft, Strong Jet, Powerful Low /w good return flow
X-Factor: Plains Winter events like this are rare, but have shown to produce tornadoes in bunches and often with very borderline conditions. The models appear to meet those borderlines and then some. GFS is tricky this far out as always, but the CFS has a noticeable peak on Sunday, so the GFS is not alone. Check it:


Target - Beatrice, NE. Good roads in all directions. The location of the low might be tricky, and GFS indicates we may have a leftover MCS that influences initiation in the Nebraska target. There will likely also be another solid target in SE KS where shear vectors are better, but I'm a DPVA man and I'm going to play the vorticity play every time. If the Southern Target blows up too big too early, the North Target dies, but if things stay way south down into OK or TX I think the North will have time to go. If it looks good Sunday Morning, I'm on the road, wish me some Xmas Luck.
What concerns me is a lack of run to run consistency in the models. Follow the bouncing low in GFS (18z Christmas):


Here in DFW this is starting to get a lot of comparisons to last year's Dec 26th events. As NWS FWD points out in the info graphic bellow, there are big differences:


We will have to watch this one closely, but I wouldn't cancel my Christmas plans yet (at least until a few more models come into range and we start getting some consistency).

Let's take a look at some really odd forecast soundings. This is Saunders Co, NE. <500 cape, 1000+ 0-3 SRH, 80+ Bulk Shear Vectors. LCL is at the treetops. Hodograph is literally off the chart. I've never forecasted a winter scenario before in Nebraska, but looking at previous events, that sound isn't too far off of the climatology.
They system is totally different for Texas. However Kansas may be looking at a classic low-med CAPE high shear event. Dixie Alley at night does not have a monopoly on those, far from it. Recent research shows the low CAPE high shear scenario happens as much or more often in the Plains and can be any time of day. Model consistency has improved in the last 24 hours. SPC is justified highlighting a Day 5 for Christmas Day.

Too far out to pinpoint locations, but the following is bullish for the central Plains. The 500 mb vorticity will be close enough to spark storms on the boundaries in the central Plains. Speed shear and directional shear is robust. Dewpoints will be a little just-in-time, normally a concern for springtime chasing. However in winter JIT is kind of how it goes with Tds. Figure localized higher helicity will be found on the lifting WF.
I'm still struggling to get on board with this setup. Models are more consistent now, shear is good, but it seems like southern plains targets are too capped and mid plains targets have too little moisture. If there is a silver lining it is moisture may be a little better than models portray. Today's 12Z GFS run had 45 Td at DFW at 21z and observed was 49. The Euro is also sliding the Low a little to the southeast with every run. Sure these low CAPE, high shear events can reward, but I'm not sold on this one. I hope I'm wrong and some of you get a good Christmas chase present.