* Winter storm watch for entire area Sunday afternoon through Monday afternoon *

In short, yes it looks like it will snow Sunday night into early Monday. Yes, it looks like it will accumulate at least in some parts of the area. And yes, it will likely impact the morning commute, with possible delays and cancellations. At least 1-2″ seems likely from D.C. to the south. Up to several inches is possible, even north of D.C., but far from a sure bet. March storms are notorious for busted forecasts, so be sure to read through the end of this post to understand where the uncertainty lies…

Timeline

Precipitation is on track to arrive from the southwest late Sunday afternoon, probably starting as a wintry mix before changing to all snow during the evening. Here is our best guess on the overall timeline…

4-7 p.m Sunday: Wintry mix arrives from southwest to northeast. Temps in the upper 30s to low 40s too warm for road accumulation.

7-10 p.m. Sunday: Wintry mix changes to all snow from northwest to southeast. Light accumulation possible on untreated roads mainly in the colder suburbs, as temps drop into the mid-30s.

10 p.m.-5 a.m. Sunday night: Snow, moderate at times especially from around D.C./I-66/Rt. 50 and to the south. Accumulation likely, even on treated roads inside the Beltway, as lows bottom in the upper 20s.

5 a.m.-9 a.m. Monday: Snow tapers in intensity from west to east, but lighter snow may still add additional accumulation with temps near 30.

9 a.m.-1 p.m. Monday: Occasional light snow may linger, with little or no additional accumulation. Road conditions improve with the help of the warm March sun shining through clouds, despite temps in the low 30s.

How much snow in total? The upper-level energy doesn’t seem to exist to support amounts more than our last storm on March 3, when most places saw around 4-6″. But since some models show a bit more than that, we need to keep 6″+ in play as a “boom” scenario, even though we’re leaning closer to 2-3″ (on average) in the immediate metro area. The wildcard is always whether and where a locally heavier band of snow might develop. For this event we think the best chance is west and southwest of D.C., but this is always difficult to pin down.



CWG snowfall forecast, issued Saturday at 2:55 p.m.

Will it be cold enough and snow hard enough to accumulate on roads? The thinking for now is yes. As we get later in the evening and into the overnight, falling snow should help push temperatures to near or below 30. And without the aid of the warm March sun, snow should accumulate even on pavement. That said, accumulations may very well be lower in the urban core of downtown D.C./Arlington/Alexandria were temperatures and pavement temperatures should be a touch warmer than elsewhere.

Will there be a cutoff in accumulating snow northern of D.C.? Like the last storm, some models show the northern suburbs to be on the northern fringe of the heavier precipitation, due to the storm trying to shift south a bit and dry air intruding from the north. This could result in a sharp cutoff in accumulating snow somewhere in the northern suburbs, making the forecast even more uncertain north of D.C.



Some models, like the European and North American Model (NAM) above, show storm total precipitation tapering around and north of D.C. (StormVistaWxModels)

What does CWG winter weather expert Wes Junker have to say?

Today’s NAM folded and now has the same look as the other models, in that it finally lost the elevated warm layer. All the models are now suggesting that we see accumulating snow. However, the upper system has a sheared look which rarely nets a major snowstorm and unless an intense precipitation band forms, such troughs rarely deliver really intense snowfall rates. For that reason, we’ve chosen to be conservative with our forecast accumulations. The sharp northern cut-off of precipitation now being forecast by some of the models also complicates the forecast for areas north of the city. In many respects, this storm is similar to the March 3rd event except the air mass feeding into the region is not quite as cold.