As a complex storm system oozes into the region Sunday-Monday, just enough cold air should be in place to make forecasting the location of the rain-snow line challenging. But we lean against a significant late season snow event, though elevated locations well west of the city have a decent chance of light accumulations.
As discussed yesterday, in late March you need both heavy precipitation and much colder than normal air for accumulating snow in the Washington, D.C. area. We see both quantities lacking somewhat.
Lack of sufficiently cold air
The NAM and the GFS models actually simulate temperatures cold enough for accumulating snow Sunday night all the way to I-95 but we’re a bit skeptical they are right as the primary low will be passing to our west, which can allow temperatures to warm more than these models indicate.
The latest European model never moves the freezing line east of a line from Winchester to Hagerstown which may be more realistic.
“This would be a slam dunk for getting accumulating snow in the city if it were January or February instead of late March,” says Wes Junker, Capital Weather Gang’s winter weather expert. But alas…
Lack of heavy precipitation
The setup for this storm may involve a “dry slot” affecting D.C. Junker explains:
Having a storm track to the Ohio Valley and then transfer its energy to a coastal low is always dicey as the initial slug of moisture and snow tracks northward into the Ohio Valley and moisture associated with the new low often misses us to the south and east. We usually get some precipitation but often don’t get the intense precipitation rates needed to get any meaningful accumulating snow in the city this late in the season.
Scenario 1, light accumulations: The NAM and GFS models are right, and a mix of rain and snow that begins Sunday afternoon transitions to all snow from west to east Sunday night. With snow falling at night (and not having to fight the March sun), an inch or so could fall inside the Beltway, with up to a few inches in our colder suburbs to the west and northwest. (40 percent chance)
Scenario 2, little or no accumulation, except towards the mountains: The European model is most accurate and we get mostly rain or a mix of rain and snow. Accumulations range from maybe a coating to an inch west of the beltway to nothing in town. A few inches of snow could fall in the Blue Ridge mountains in this scenario. (60 percent chance)
Storm timing: The timing of the storm probably spans from Sunday afternoon through around Monday midday.
Like our other March storms and winter storms dating back to last winter, this is probably just a nuisance event in the immediate D.C. area while perhaps an inconvenience farther west and northwest. But the margin for error with this event is small, so we will keep you posted on inevitable changes required to the forecast.