A powerful storm is forecast to form off the Mid-Atlantic coast Sunday into Monday and has the potential to produce substantial amounts of precipitation, including snow, in the D.C. area. But it’s far from certain whether the storm will meet this higher-end potential.
The storm’s impact locally boils down to the following: If it strengthens fast enough and close enough to the coast, drawing cold air southward, it could wallop parts of the area with heavy, windblown snow. But if it strengthens more slowly and farther offshore, the resulting precipitation — probably a mix of rain and lighter snow — will be rather modest.
We lean toward a compromise between these scenarios. This means periods of rain and wet snow on Sunday probably changing to all snow at night, with light accumulations of around 1 to 3 inches. This could lead to some delays and closures Monday morning.
However, we cannot completely dismiss the outside chance that the storm develops explosively nearer the coast, potentially pasting parts of the area with 6 inches or more of snow by Monday morning. In this scenario, the heft of snow, combined with gusty winds, would bring the risk of power outages as well as likely widespread school closures. Blizzard conditions could develop near the Chesapeake Bay and over the Delmarva Peninsula.
What’s the potential timing of any snow, and how could the storm evolve?
Here’s how we see the timing and details of the storm in the D.C. area (still subject to change):
Sunday morning into afternoon: Rain, or a mix of rain and snow, is likely to develop during the morning and continue through afternoon. We lean toward any snow being fairly light with temperatures in the mid-30s or higher, which would limit accumulation potential during the daylight hours. But we can’t rule out snow becoming heavy enough to drop temperatures closer to freezing and start accumulating, especially on grassy areas, by late afternoon.
Sunday evening and overnight: Precipitation should change to primarily snow, and accumulating snow becomes more likely as temperatures drop into the low 30s. A period of heavier snow is possible, but if snow remains on the lighter side, then accumulation could be at higher amounts on grass than roads.
Monday: Snow may continue at times during the morning but should trend lighter and probably won’t produce much additional accumulation. Temperatures rise to the upper 30s to near 40 for afternoon highs.
What are the range of snowfall possibilities?
Models have not come to a consensus on how the storm will play out. That makes predicting snowfall amounts more challenging than usual.
It’s not just uncertainties in the storm track that make predicting snow amounts difficult. It’s also temperatures that will be barely low enough to support snow accumulation. If the storm develops too far to the east, the precipitation will not be heavy enough to tap the cold air necessary for the snow to stick. If this turns out to be just a light snow (or mix of rain and snow), little will accumulate because temperatures will not fall enough.
Taking everything together, our best estimate is for 1 to 3 inches to fall, mostly Sunday night into the predawn hours Monday, but this is a low-confidence forecast subject to change. We’d lean toward lower-end amounts near downtown D.C. where temperatures are usually slower to cool, and higher amounts in our normally colder suburbs north and northwest of the Beltway, and particularly toward the mountains.
Here’s our current thinking for the odds of different amounts in the Beltway area:
- Chance of at least 1 inch: 50 percent.
- Chance of at least 3 inches: 35 percent.
- Chance of at least 6 inches: 20 percent.
- Chance of 10 inches or more: 10 percent.
Because of the temperatures hovering near or above freezing during the storm, more accumulation will occur on grass than roads, especially during the day. The most likely period for slick roads to develop will be Sunday night into Monday morning.
Here’s how much snow the different models are projecting (we are counting only snow that accumulates with temperatures 33 degrees or lower):
- American (GFS): 10 to 15 inches.
- American AI and NAM: 4 to 8 inches.
- European: 2 to 5 inches.
- European AI: 2 to 4 inches.
- Canadian: 1 to 4 inches.
- German: 1 to 3 inches.
- UK Met: 0 to 2 inches.
The American model, which predicted up to 3 feet of snow in D.C. on Thursday, has backed off some in its predictions, but remains an outlier on the high end. We lean more toward the European and UK Met models, which have higher accuracy ratings. Much of the snow that falls probably won’t fall from the ocean storm itself but rather from a zone of converging air, known as an inverted trough, in its wake.
The National Weather Service is predicting 1 inch of snow for the area as most probable but points to a high-end possibility (10 percent chance) of up to 8 inches.
The post D.C. area could see pasty snow Sunday into Monday. How much could fall? appeared first on Washington Post.
