11:30 p.m. update: Putting final tweaks on map…hang tight – it will be up within 10 minutes.
11:05 p.m. update: Most of the model output is now in and I am going to draw up a snowfall map forecast for posting around 11:30 p.m. and will then wrap things up for the night. So hang tight for the next 25 minutes and check back around 11:30 p.m. for our first call snowfall map.
11:00 p.m. update: Here’s a graphic showing snowfall totals from the GFS model across the region:
The colors mesh together some, but it’s showing 6-10 inches or so. A little of the snow shown may initially melt, so I’d shave an inch or two off what you see for more of a realistic simulation.
10:50 p.m. update: My read of the GFS model is that it would suggest about 6 inches of snow in D.C., very similar amounts to the other models. Although it changes the rain to snow earlier than the NAM model, it doesn’t forecast the snow to be quite as heavy.
10:45 p.m. update: The GFS model – the one which has consistently simulated a significant snowstorm for the D.C. area since yesterday – is streaming in. And it’s rock solid in telling the same story: a major snowstorm for the D.C. area – with rain transitioning to sleet and then snow between 1 and 4 a.m. early Thursday morning (about 5 hours faster than the NAM) and snow throughout the day Thursday. More details in a moment.
10:30 p.m. update: The regional version of the Canadian model (another one of the half dozen or so models we look at) is very similar to the NAM in terms of the amount of snow it forecasts for D.C. and the changeover time from sleet to snow. It predicts around 6 inches of snow for D.C. and the changeover from sleet to snow to occur between 7 and 10 a.m. Thursday. Here’s an animation:
10:15 p.m. update: The National Weather Service in Sterling, Va. is forecasting 6-8 inches from this storm in the immediate metro area, and 8-10 inches in our far northern suburbs, and 4-6 inches in the southern suburbs.
If you visit its winter weather page, you can see that it shows a minimum and maximum snow scenarios (similar to our bust and boom scenarios). On the low-end, it sees 1-3 inches (10 percent chance) and on the high end 10-12 inches (10 percent chance).
10:00 p.m. update: The high resolution version of the NAM model suggests about 9 hours of frozen precipitation, moderate to heavy at times, Thursday in the immediate D.C. area. Here’s its simulated radar from 7 a.m. to 7 p.m.:
Between 7 a.m and 10 a.m. Thursday – from the first to second frame – the precipitation is changing over from sleet to snow. In all of the other frames, the precipitation shown would be moderate to heavy snow until between 4 and 7 p.m., when the precipitation tapers off.
9:35 p.m. update: Here’s a look at the total snowfall simulated by the NAM model:
We would subtract a few inches off the totals you see here as it’s assuming every flakes sticks and some of the snow initially will not accumulate due to the rain preceding it.
9:30 p.m. update: For snow lovers, the NAM has definitely taken a step in the right direction. After 7 a.m. Thursday, which is around the time it forecasts a changeover from mixed precipitation to accumulating snow, it forecasts falling temperatures and snow continuing for much of the day. From 7 a.m. Thursday through the late afternoon hours, it forecasts 0.68 inches of liquid equivalent which would (assuming 10 inches of snow for every inch of liquid equivalent) imply 6 or 7 inches of snow for D.C. proper. It would suggest 7-10 inches for our colder suburbs to the north and west.
Update at 10:05 p.m.: Our winter weather expert Wes Junker says, taking the NAM model literally, it would still be sleeting in D.C. at 7 a.m. (due to a warm layer around 8,000 feet high) and changing over to snow closer to 9 a.m.. So the model probably suggests more like 5 inches for D.C. proper, but on top of some accumulating sleet.
9:20 p.m. update: The NAM model is coming in and it seems to be bringing in the cold air slightly sooner than earlier runs. Below see how, in the last three model runs, the position of the freezing line at 7 a.m. Thursday – shown in dark blue – has crept southeast towards Washington.
Note that the other models tend to drop temperatures below freezing at least a few hours sooner than the NAM, but the NAM has made a slight move towards dropping to freezing sooner and an earlier changeover.
9:10 p.m. update: The latest suite of model simulations from SREF model shows a wide range of solutions, ranging from half an inch to 13 inches. The average simulation forecasts 5 inches. The variability in the forecasts relates to differences in the timing of the changeover of the precipitation from rain to snow. Generally, the simulations with the later changeover times forecast a lot less snow, as more of the precipitation falls as rain.
Introduction from 9 p.m.: As an Arctic front sinks south Wednesday night into Thursday morning, rain will change to sleet and then snow. Depending on how fast the transition from rain to snow occurs, snow totals could be on the light side to possibly moderate or even heavy. The best chance of heavy amounts will be in our colder northwest suburbs. Right now, we believe the most likely snowfall in the immediate metro area is in the 3-6 inches range. But less or more is certainly possible.
Follow along (above) as we track tonight’s latest model data and try to get a handle on the timing of the transition from rain to snow late Wednesday night into Thursday and the ultimate snow amounts.