Over the next 90 minutes or so, I'll post updates every 15 to 30 minutes right here that include model updates, new insights, and other interesting information streaming into the Weather Gang lab....
11:30 p.m. update:It's been a really long day so I'm going to try to get some sleep before getting up early again. Some final thoughts: Despite the trend toward less shown by the latest models tonight, we still believe we'll have some accumulating snow tomorrow. The higher end totals seem least likely at this point but enough uncertainty remains such that we will be closely following the evolution of the storm and will keep you up-to-date with the latest developments during the day tomorrow.
11:10 p.m. update: This close to the onset of the snow event, we cannot ignore the latest model trends which suggest less snow. We are not changing our accumulation outlook, but believe totals are more likely to be near the low end than the high end west of the Chesapeake Bay. As we've said all along, the uncertainty with this storm is higher than with others so further adjustments - either upward or downward may be necessary even as the event is underway tomorrow.
One thing the latest models do not tend to show is heavy snow banding occurring tomorrow afternoon and evening. Instead, they suggest a light, intermittent snow stretched out over a long period spanning the morning into the evening. If they are right, the risk of snow that accumulates quickly and causes serious impacts may be reduced, especially as you head west.
10:40 p.m. update: The latest GFS is coming in and is EAST of earlier runs indicating less snow. Both the NAM and GFS would now suggest totals would on the low end of our estimates. Need to digest this and look at some other model data coming in before drawing any conclusions.
10:35 p.m. update: One thing we haven't discussed much is the wind, which will increase throughout the day tomorrow. By late afternoon, winds will probably be up to 15-20 mph and 20-25 mph tomorrow night with gusts to 30 mph. The windiest weather comes Monday, when gusts could reach 30 to 40 mph.
10:20 p.m. update: This is the kind of storm where we might see big differences in snow totals between BWI and Dulles, with BWI much more likely to see significant snow than Dulles because it's further to the north and east, closer to the storm center. Also, the storm will get stronger as it moves north hence the blizzard warnings for New York City (forecast for 10-16" of snow) and Boston (forecast for 15-20" of snow). Accuweather is cautioning that the Philadelphia Eagles game tomorrow night against the Vikings (at 8:20 p.m.) may be played in some of the worst conditions ever there for a football game.
10:00 p.m. update: Looking at the latest radar, it appears most of the snow remains south of the metro region - mainly south and southeast of Fairfax, Prince William and Fauquier counties. Light snow has been reported around Fredericksburg, While some of this light snow may gradually make its way into the metro region overnight, the main action is likely to be from mid-to-late tomorrow morning into early tomorrow evening when the coastal low gets going.
Model watchers have probably seen that the latest NAM model simulates not a lot of precip with this storm. Taken literally, it would suggest just a couple inches of snow for D.C. metro, with a little less in the western suburbs and a little more east. However, the SRES model that came out just a few hours early indicated a 80-90% chance of more than 0.5" melted liquid - which would equate to more than 5" of snow. The bottom line is that there is likely to be a sharp gradient with this storm's precipitation field that's very sensitive to the exact track and strength of the low. So it wouldn't take much for us to get more or less than our 3-6" forecast. We're sticking with that 3-6" forecast for the time being.