Snow accumulation simulation from NOAA’s Rapid Refresh model through 1 am. - seems like a reasonable estimate of the distribution, but amounts may be a little too high north of Baltimore.

Late this afternoon, another clipper sweeps into the D.C. area, with areas of snow, starting right around the P.M. rush hour.

Here are some key points:

* Timing: snow starts between 4:00 and 8 p.m. from west (Loudoun/Frederick counties) to east (Anne Arundel, Calvert counties) and ends between 11 p.m. and 2 a.m. tonight. (note- this timing has been amended a bit from 3:30-5:30 p.m. start window stated earlier)

* Accumulations: we’re thinking a dusting to half an inch in the immediate D.C. area. However, if you live from Martinsburg to Baltimore and especially to the north, you could see an inch or a little more. Some spots in the higher elevations of western Maryland and southern Pennsylvania could see up to 3-6 inches. Areas south of Fairfax county may see just light snow showers and/or flurries and little/no accumulation.

* Coverage: Following from the accumulation potential, the steadiest/heaviest snow will tend to be in northern Maryland towards the Mason Dixon line. From D.C. and points south, snow may be spottier/lighter and fall more intermittently.

* Impacts: Although snow may begin during the P.M. rush, it probably will be light/spotty enough in the immediate D.C. area to cause only minor delays. After 6 or 7 p.m., a few slicks spots could develop as temperatures fall to 32 or a bit below.

More widespread slick travel may occur in Loudoun and Frederick counties, where the snow will arrive first and fall more heavily and temperatures are colder. Be prepared for some more significant delays although this is not a crippling storm.

D.C. = Dusting central

Snowfall amounts on days with the snow the last two winters in Washington, D.C.

Amazingly, the winter of 2012-2013 has seen snow fall on six different days in the Washington, D.C. area for a grand total of 1.5 inches. By tomorrow, we’re likely to be up to 7 days with the total still less than 2 inches.

What’s even more remarkable is that last winter (2011-2012) we had snow on 5 days for a total of just 2 inches.

If you combine the two winters, that’s 12 days with snow in D.C. producing 3.5 inches - or slightly less than 0.3 inches per events.

We will have to check the records, but I’m pretty confident these past two years are on their own in terms of snow-producing futility.

Capital Weather Gang winter weather expert Wes Junker offers this rationale for the frankly embarrassing snow output:

Last year was a La Nina year and this year has acted like a La Nina. More often than not, the storm track has been to our north putting us on the warm side of storms. Neither year has had much of a southern stream and the few times when there was a southern stream system there has been no interaction between the northern and southern streams in a way that would bring a low up the coast. This year when we have had cold, we have not had a southern stream so the only snow we’ve gotten is from clippers. We need a southern stream to get the moisture needed to get a big storm.