I'm trying something new tonight: I'll post quick thoughts as the different computer models stream in as well as other odds and ends (about every 15-30 minutes). Keep your finger near the refresh button...
1:15 a.m. update: European model a tad more out to sea and not as intense as last several runs. Would be a big hit for the coast, but just light snow for us. Little support now for a super snowstorm in D.C. Pretty huge for New England though. Right now, (considering everything) the forecast we've held onto since basically Sunday for a 50-60% of 1" or more, and 20% or so chance for more than 4" seems about right. And the possibility of a miss is still out there.
12:50 a.m. update: European model starting to come out. Hang tight.
12:20 a.m. update: The GFS ensemble mean (the average of the various versions of the GFS model runs with slightly different initial conditions) is a bit west of the primary operational run and produces a little more precipitation.
12:00 a.m. update The Canadian model tracks everything too far to the south and east and the D.C. metro region gets nada. I'm not a big fan of the Canadian model, but it definitely shows we're not near a consensus about what's going to happen.
11:30 p.m. update: Another takeaway from the models coming in so far tonight is that they are unified in at least giving the mid-Atlantic some snow and phasing the northern and southern stream energy - albeit fully a little late for a big snow here. But the details in the timing/phasing will still evolve so my confidence is a little higher we'll get some snow given the direction of the models. Plus, still awaiting the Euro model coming out at 1 a.m. Who's staying up???
11:15 p.m. update: Both the GFS and the NAM suggest a big storm will develop but not until it passes north and northeast of D.C. The dip in the jet stream in these models doesn't amplify enough for the storm to come up the coast in the mid-Atlantic - probably because they advance the southern stream too quickly and not as far south. However, both models would suggest some light accumulating snow would fall late on Christmas day into early Sunday morning.
11:00 p.m. update: GFS run is also speeding up the southern stream and bringing back the threat of snow on Christmas. But it doesn't look like it's going to develop the storm explosively until it passes north of D.C.
10:50 p.m. update: Another perspective - Henry Margusity at AccuWeather is predicting 6"+ for the metro region...
10:45 p.m. update: One thing about the NAM model is that it does look like it's primed to bomb (develop rapidly) the low after 84 hours - so it does suggest a big storm will form - just a little late for DC, but maybe not so further north. But at this time frame, it's very close. And this model - again - is not real skillful at this timeframe.
10:20 p.m. update: One meteorologist, Dave Tolleris, at WxRisk.com has released some snowfall probabilities for the East Coast. You can see them here. He's pretty bullish about the storm threat, indicating a 50-70% chance of 4-8" for the metro region. Ours aren't that high (20-30% for 4" or more) but we'll be updating them tomorrow after we digest tonight's models and tomorrow morning's.
10:00 p.m. update: The latest NAM model is in - this is a short-range model that goes out just 84 hours. It actually brings back the idea of light snow on Christmas day as it advances the southern stream system more quickly. By the end of its run (84 hours, Sunday morning), it's trying to develop a storm off the coast of the Carolinas as the southern stream system interacts with a disturbance diving in from the northwest, but probably too far to the east to come up the coast and produce significant snow. I don't think this model, which is pretty poor with its forecasts beyond 48 to 60 hours, has a lot of support. Still, we'll need to see if its quicker timing is shown in other models coming out.