12/23 all rain for the NE right? well probably but there is an scenario

I will try to make this addition of shorter than the last few posts but I usually end up saying so much that such an endeavor never really works out.
The first issue to deal with it is the cold front that comes through the Northeast sometime on 12/20. The overnight run of the European has brought back the Wave development on the front a little bit. This idea is generally supported by the 0z Ukmet
http://www.meteo.psu.edu/~gadomski/UKHEMI_0z/f96.gif

http://www.meteo.psu.edu/~gadomski/UKHEMI_0z/f120.gif

but the operational runs of the GFS in the Canadian show NO development until the northern stream short wave is way out to sea. However if one were to look at the GFS ensembles we would see that many of the members to show a somewhat more amplified short wave moving through the Northeast when compared to the 0z operational GFS
Please note c000 p001 o002 p003 p004 p008
http://www.meteo.psu.edu/~gadomski/ENSHGT_0z/f132.html

CMC of 0z ensembles
http://www.meteo.psu.edu/~gadomski/ENSCMCHGT_0z/f120.gif

In any event this potential feature is not going to be a big deal or even a significant event for that matter. It wasn't for the fact that we are enjoying a very mild December here in the Middle portions of the month this wave development would not get much if any mention at all.

All right lets move on to major closed cut off 5h Low over the Southwest states coming out in one piece. I think at this point in time we can safely rule out the idea that the system is going to turn N into the Central and/or Upper Plains. It looks like it as this upper Low tracks across southern New Mexico and Central Texas it's going to produce a major snowstorm for many of the livestock areas in the lower Plains possibly as far north as southern Nebraska 12/19-20. Once the system crosses the Mississippi River the temporary surge of cold air in the Northeast will be gone and as a result the large rainstorm we are likely to see from this upper low crossing the Deep South will spread into the Middle Atlantic states.

At this point it would seem safer to forecast a complete rainstorm for a major cities of I-95 and I don't see any real reason to go against that idea. As I mentioned in the winter forecast the stormy pattern we saw in October and early November was an indication of the type of winter pattern we could see in January February & March. But more importantly this is a really textbook case of why certain features have to be in place in the upper levels of the atmosphere for a major snowstorm or even a significant snowstorm concur on the East Coast. It's not simply just a matter of how in a large deep slow-moving low pressure area during the winter months.

That being said there is a scenario where as the SE Low begins to move up the coast on the 23rd fact we may yet see significant snow over some portions of the Interior middle Atlantic --- ie mtns -- and the Northeast -- well inland. here is How that COULD happen:

First lets deal with 192 hrs -- the 0z European model as the primary Low pushing fairly far to the north... across the Ohio River. Without a large cold High-pressure area in place over southeastern Canada or northern New England IF the primary Low tracks that far north and is below say 1008 MB then you often have a significant warm air problem for the big cities of the Northeast. Indeed that is what the operational European is showing but I'm curious as to why the primary Low tracks that far north given the ULL stays fairly far to the south. So that's one aspect to keep mind over the next several days.

Second and again this is on many of the medium-range models as well as the ensembles... is the appearance of a important short wave which appears to drop into the Northeast just as the 5H Low is over the SE. Now this sort of scenario is what I call a " timing problem" and by that I mean everything has to work out just right -- "in the nick of time" to get the cold air into the Northeast while the Low is still close enough to the coast to change things over snow. We see weather models do this an awful lot in the medium-range and it's exciting to watch but for the most part its very uncommon .

Recall that in yesterday's post I mentioned how none of the ensemble members were showing the confluence zone PJ (Polar Jet) close enough to the Northeast to produce source for a cold HIGH to form.... all the members on that the data yesterday showed that Polo get region still north of the Great Lakes and over Central Ontario and Québec... hence no cold air source

However that is not the case on this morning 0z GFS ensembles. For instance if we were to take a look at the 180 hr GFS ensembles members we would see several members trying to drop the PJ much further south and phase a northern short wave into the 5h closed Low over the SE states. P007 P008 P009 and c000 all show the phasing occurring in the "Nick of time" scenario I mentioned above.
http://www.meteo.psu.edu/~gadomski/ENSHGT_0z/f180.html

This is probably the ONLY way given such a warm régime that one can get a snowstorm in East Coast. If you want to see an analog as to how the 500 pattern could phase and let me emphasize again this is COULD not certain... not likely... not reasonable... just COULD then take a look in your KU snowstorm books at February 8-10 1969. That being said the odds are NOT good for and event like that happen. Every winter I see MR and LR models showing this type of development and every winter is often falls apart.

Interestingly prefer the 6z op GFS is closer to this idea than the 0z and matches those more aggressive 0z GFS ensembles.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_180.shtml
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_192.shtml

For the time being I think there is a good possibility that the Interior portions of the Mid Atlantic and by that I mean the mountains and the inland areas over New England have a CHANCE of seeing a decent snow event in this but I'm still in the speculation stage and I am not committed to this idea.

Even as we go beyond this possible event on 12/23 the overall ensembles look very impressive... with regard to storminess. The operational 0z GFS at day 10 looks very similar to what we saw on the THURS 12Z run and almost every single member in the GFS ensembles shows some sort of major short wave on the verge of phasing or about to phase between the two branches. I still see that the overall pattern in the last week at December has a lot of potential.

http://www.meteo.psu.edu/~gadomski/ENSHGT_0z/f240.html