Winter storm warning extended southeast
11:45 a.m. update: The National Weather Service has extended the Winter Storm Warning over the immediate metro area and now includes the District as well as Fairfax, Prince William, southern Fauquier, and Stafford counties in Va. and Anne Arundel and Prince George's county in Maryland. Calvert, Charles, and St. Mary's county remain under a Winter Weather Advisory. The Warning is in effect through 4 a.m. for the potential for 5-10 inches of snow.
In an earlier Special Weather Statement (bold emphasis added), the NWS cautioned:
"...RAPIDLY DETERIORATING CONDITIONS FOR THE MID TO LATE AFTERNOON AND EVENING RUSH HOUR COMMUTE...
After a break in precipitation this morning ... Accumulating snow will overspread the area this afternoon and evening. A mix of rain and snow will quickly change to all snow during the afternoon as it becomes heavy. The period of heavy snow will coincide with the late afternoon and evening rush hour commute across most of the region ... Including the Washington DC and Baltimore metropolitan areas. Conditions in southern Maryland will deteriorate around sunset as precipitation changes to snow.
The heavy snow will reduce visibilities below a quarter mile with snowfall accumulation rates at times of 2 inches per hour. This will produce dangerous travel conditions during rush hour. Snow will move out of the area by midnight."
I endorse this message and would not advise being on the roads after 4 p.m. You may risk getting caught in horrendous backups and/or getting stuck somewhere.
The model output this morning (from the GFS and NAM) support snowfall rates of at least 1-2" per hour from 4 to 7 p.m. - then gradually winding down around 9 or 10 p.m. Again, do not be surprised if thunder accompanies the snow. It has already been reported with precipitation in West Virginia.
Wes Junker, our winter weather expert has written in to say:
"The radar over West Virginia is looking impressive this morning and the models continue to advertise a big thump this afternoon. The model soundings this morning continue to suggest the potential convection (i.e thunder) embedded within the band of heaviest snow which could lead to intense snowfall rates of an inch or two an hour."
"The NAM predicts 1.00" of liquid equivalent in a 6 hr period and the GFS .75". That would translate to 7 to 10 inches of snow if we had a 10-1 snow to liquid ratio. The actual ratios probably will be lower than that in the city but such intense snowfall would still accumulate rapidly. The heavy precipitation rates should lead to temperatures falling rapidly this afternoon when the next shot of heavy precipitation occurs which should lead to most of the precipitation falling in the form of snow."