The latest models are all over the place again as we head into the short term. The GGEM/Euro have backed down showing less accumulations while the GFS and NAM continue to show a more significant threat. Looking at our current observations I am favoring the NAM/WRF based on how far north this precip shield is already extending and the impressive convection in the Southeast.
However, all models are having trouble with the extension of the precip shield:
Notice in the first image we have few squall lines trying to develop along the Gulf Coast.
You can see a few inverted troughs extending from our low pressure system with a convectively enhanced warm front that will try to push north. The convection to the north has enhanced this to the point that the sharp thermal gradient is kicking off convection right along it and pushing it north. This is great news for a more impressive system and slightly north. But the most important thing here is how this convection pushes east. This batch of convection will slide east and depart from the precip in the Southern Plains. So don't panic when this happens as it is supposed too, the precip will redevelop in the NW quadrant as it approaches.
The squall lines trying to develop in the Deep South have caught my eye as they are entering an area of steep mid level lapse rates and MUCAPE values approaching 1000J/g. If this does develop more they could enhance the strength of the southern stream s/w by having an enhanced LLJ. This would support a stronger low.
I am not ready to make a snow map since I want one more run of the SREF, so I can get a better idea where this banding will set up. Above strong 700mb frontogenetic forcing coincides with moist potential vorticity, not seen here is the intense frontogenetic forcing in the lower levels to the southeast and the sounding from the NAM that shows upwards of 20J/Kg near this layer. The steep slope frontogenetic forcing suggest a very dynamic heavy band of snow will form where someone could see 4+". I highlighted the above area where my current thinking is currently.
I will also be watching the convection in the southeast. We want it to be slow and steady and not push too far east that quickly. It will push east but we want a gradual push east.
Dynamic cooling is the key here...i it is snowing heavily with a temperature of 34F it is going to stick, but factor in the cold low levels with the drag of some pretty big snow flakes we could easily see temps crash to 30F in heavy bands. The 18z NAM shows this banding as 35DBZ snow...
Frontogenic forcing has been mentioned. I have been trying to wrap my head around this concept this season and the whole idea of TROWAL. I was thinking this was a possibility all along (frontogenic forcing) but I'm not sure why......
I know that, but the prices they charge are on the verge on gauging. I am curious as to whether the new skew T's for tomorrow night show an atmosphere unstable enough to produce rapidly accumulating snow, (though over a short time), I suspect they will, the temperature profile is concerning but I think it will be alright.
It isn't that easy a fix though,the gfs runs four times a day the ecmwf only runs twice so that's one problem, and it would be very expensive to update the whole thing to initialize with the ecmwf and they would lose their big selling point if they were both equally accurate so I am not hopeful that anything will happen jointly in the near future.
Someone sent me an article a while back that talked about the ecmwf finally working with us to fix the gfs and get it on track with theirs, interestingly it was found that when the gfs was initialized with the ecmwf initialization data, it's results were much, much better.
Regarding the love affair forecasters seem to have with the gfs, it's there and there are reasons. One is that the ecmwf charges a quarter of a million dollars for the right to use their 25 day forecast (like put it on a site or something like that) and that quarter of a million doesn't even get you the right to use their 1 year forecast (which would be interesting to look at for trends), the ecmwf's big selling point is "we have the most accurate numerical weather forecast model in the world," and that's true, it has been more accurate then any other in all the time they have been compared. The gfs isn't that much less accurate though and it's free, so there's one big reason it's used so much.