UPDATE 12/22: Doesn’t look like it’s going to be a white Christmas unless you try to scrape out a little orographically-induced snow in the western Appalachians (which even then is a bit of a stretch unless the 500mb vort. from the northern stream intensifies like on the 12z GFS). I won’t put chances at 0% but it’s certainly very low.
There is still a lot of disagreement between the models concerning the potential Christmas Day winter storm. Right now the 12z Euro Op. is bringing front-end snow into the Mid-Atlantic followed by rain that lasts until the end of the event. While the Euro has trended northwestward with this system in recent runs, it is not worth looking into the trend too much at this range considering the high amount of uncertainty with this system and its ability to jump wildly in both position and time in ANY direction. It is my personal opinion that true run-to-run trends aren’t that telling of specific winter storm systems until we get within the 72 hour window.
This isn’t even bringing the GFS Op. into account, which over the last two runs has failed to produce a system even remotely like the Euro. The lack of support by the GFS is another good reason to dismiss any trends on the Euro at this stage of the game since there’s obviously a lot of different possibilities still on the table.
Having said all that, I have come to the conclusion that this potential storm needs to get “punted” for at least another day (more likely two days). There’s no reason to call for snow, rain, mix or whatever at this point since the models can’t even come up with similar enough solutions. Given what usually happens when there’s a huge disagreement between the models, I’m going to say that the GFS picks back up on the storm by the 00z Thursday run while the Euro starts to lose the “trend” it has displayed over the last couple of runs and become more random with its shifts. Right now the Euro typically has an edge on the GFS in sniffing out the general storm track and timing, so I’ll give the Euro a heavy lean for now, but by no means am I going to take it verbatim.
As far as January temperatures are concerned, I’m going to have to do a similar thing I did with December and basically flip my forecast around, resulting in a cool West and warm East. Aside from some blips in the stratosphere, there really isn’t anything to stop the eastern U.S. from “torching” in January. AO and NAO look to remain solidly positive going into the start of January as the PNA tries to shift negative (though I have a feeling it might stay neutral to slightly positive, which doesn’t have much an effect on the eastern U.S. given the much stronger AO/NAO signal). The forecast becomes a lot more uncertain heading into the second half of January, but confidence in a warm start to the month is higher than normal given what the medium range signals are forecast to be.
For the month as a whole, I currently have the East Coast around 2-3F above normal, but the first half of the month could easily be 3-5F above normal before any potential for a lasting period of cooler temperatures. I will post a U.S. forecast map for January at the end of the month.