As new information comes in this evening and I digest it, I'll post updates every 30 to 45 minutes...
1:20 a.m. update: The bottom line: all guidance has trended toward a stronger storm, closer to the coast. This stunning shift cannot be ignored and the risk of a significant snowstorm on Sunday is real. The two operational models we trust the most - the European and GFS models - suggest the possibility of between several inches and up to a foot of snow. However, a slight shift in the track to the east could still result in little to no snow (1 in 3 chance) so this is NOT a done deal. On the other hand, any additional shifts in the track west could mean a crippling storm on a busy shopping and travel day. Considering all of this information, I think we have about a 60-65% chance of more than 1" of snow, and 35-40% chance of more than 4" of snow Sunday into Sunday night. We will have lots of coverage tomorrow, so please check back.
1:10 a.m. update: Euro has trended significantly west and suggests 2-4" or so for the D.C. metro region (but we are very close to getting a lot more or very little) Sunday, but much more toward the coast and a serious storm for southern New England. Give me a few minutes to digest everything I've seen tonight. I'll sign off with some final thoughts around 1:20 a.m.
1:00 a.m. update: Raise the roof, snow lovers. Euro looks like it may show a biggie... More in 10 minutes...
12:45 a.m. update: As we await the Euro, view this great video on the model evolution by Glenn "Hurricane" Schwartz in Philly - cut at midnight tonight: Big changes in snowstorm forecast
12:30 a.m. update: The average of the GFS ensembles (the GFS model run multiple times with slightly different initial conditions) also, taken literally, would suggest 6"+. But, again, the folks at NOAA who run this model think it may be overdoing things.
12:10 a.m. update:: NOAA says: "THE 18Z AND 00Z GFS RUNS ARE SHOWING SIGNS OF CONVECTIVE/GRIDSCALE FEEDBACK AS THE SYSTEM MOVES ALONG THE GULF COAST WHICH COULD BE MAKING ITS SOLUTION AT THE SURFACE AND ALOFT TOO STRONG." Translation: the GFS - which would, taken literally, indicate 6-12" of snow for the D.C. metro region - may be overdone. NOAA prefers a compromise between the NAM (dusting) and SREF (5" or so) - which would suggest a couple inches as most likely.
11:50 p.m. update: The Canadian model has also shifted slightly west from earlier runs but still just fringes the metro region with probably up to an inch or so but more toward the eastern shore.
11:40 p.m. update: A model from the United Kingdom, known as the UKMET, is now out. It suggests a near miss for the D.C. metro region with just light snow or flurries - similar to the NAM. However, its storm track is considerably west of earlier runs following the unanimous shift closer to the coast among all models today.
11:15 p.m. update: The latest guidance continues to support a storm track closer to the coast (further west), although the models have yet to reach consensus on how much precipitation will make it into the metro region.
Possibilities for Sunday still include just a dusting to 6" or more. The NAM model shows a glancing blow (light snow/flurries) whereas the GFS would suggest a major winter storm Sunday. The GFS is supported by the Short Range Ensemble Forecast (SREF) model which indicates about a 50% chance of five or more inches of snow.
In light of the latest model trends, we now believe there is a 50-60 percent chance of at least 1", and about a one in three chance of more than four inches.
However, we eagerly await the output from non-U.S. models (such as the Canadian and Euro) to see if there is more support for the snowier or drier solutions.