BLOG: December 18th White Christmas Update
I'm on vacation this week but I can't NOT look at the weather! I thought I'd do a quick post with an update on our chances for a "white" Christmas this year.The snow pack reached a maximum of about 6-7 inches in parts of the Valley a few days ago but it has been receding since, thanks to milder temperatures and a little rain. Animation of the snow cover across the region over the last 2 weeks:
The snow will continue to vanish this week with temperatures like this: 
So the chances of the OLD snow still being on the ground come Christmas morning are looking slim. To get a White Christmas, we will need NEW snow. Will we get any?
MOST LIKELY WEATHER DECEMBER 23RD THROUGH 25TH
A cold front will cross the region Friday night into Saturday, bringing rain (and also balmy temperatures ahead of it). Here's a snapshot of the placement of precipitation Saturday morning, according to the European model: 
The key to predicting our weather for the rest of the weekend and into Christmas is: what happens to that front? 1) Does it keep sweeping east and unlock the doors to colder air, or 2) does it stall not far to our east....with waves of moisture coming northward out of the Deep South, keeping the coldest air to the west and making for a wet, not white Christmas Eve and perhaps Christmas Day?I lean toward idea #2 right now. Why? That's the solution favored by the "operational" European model and it has decent to good support from it's "ensembles", which leads to increased confidence.The average of all 51 members of the European ensemble model has little snow on the ground Christmas morning: 
With the "control" run showing even less: 
Basically the idea is that it's more likely to rain than snow Sunday night into Christmas morning.Meanwhile, the US counterpart to the European model, the "GFS", sweeps the front east over the weekend and the arctic air is allowed to drop anchor across the region. Check out the temperature difference Christmas Day between the European and GFS.European: 
GFS: 
By the way, look at those ridiculously cold temperature over the Upper Midwest. Ouch!Although the GFS is quite a bit colder, it does NOT bring much hope for a snow "storm" at Christmas. The best we could hope for would be some lake-effect. A couple of the GFS ensemble's "members" are interesting looking but they are the exception. 
Based on all this, I have lowered our White Christmas chances to 25%. 
Keep in mind we are still a week out and confidence in any forecast (and particularly one involving a wobbly front in the winter) this far out isn't high. Rely on human forecasters to give you the real story and not national weather apps that are usually based on ONE model.