In the Washington region, snow will begin between 4 and 10 a.m. on Sunday and continue well into the day. Freezing temperatures mean that the snow gets stuck and quickly covers untreated roads and sidewalks. There is a chance that the snow will mix with or change to snow and rain late on Sunday afternoon or evening, especially southeast of the Beltway.
The wild card is what happens Sunday night to Monday night or Tuesday morning, when a coastal storm starts near the Carolinas. There is a certain chance that snow, possibly heavy at times, will continue with at least several centimeters of accumulation. The latest computer model guide on Friday morning favored more snowfall during that period and totally supported it.
Alternatively, meaningful snowfall may subside late on Sunday, with only spotty, intermittent precipitation that does not amount to much afterwards.
If the second wave of the storm is realized, which is due to a new coastal storm developing rapidly near the North Carolina coast, the snow will continue to fall until Monday or even Monday evening and early Tuesday. The total can exceed half a foot and possibly reach double digits in inches in some areas.
But if the coastal storm is formed either too far north or too far off the coast, further accumulations will be limited to a few centimeters from the first wave on Sunday.
- Based on all model information and our forecast experience, we believe that a moderate 4 to 8 inch snowstorm is the most likely scenario in the DC range for this event, although we can not rule out 8 to 12 inches if the second wave materializes or only 2 more 4 inches if it does not and the first batch of snow turns out to be weak.
- In summary, the floor for this event is about 2 inches and the ceiling is a little over a foot. Areas southeast of the district may see lower snow totals due to periods of mixed rainfall.
Risk of at least one inch: 90 percent
Risk of at least three inches: 65 percent
Risk of at least six inches: 45 percent
Risk of at least 12 inches: 10 percent
However, it is unlikely that the storm will compete with Snowstorm in January 2016, the largest snowstorm in the last decade, which loosened 15 to 30 inches over the area.
The map below, from the National Weather Service (below), shows expected snowfall until 19.00 on Sunday. We think this is a reasonable assessment right now and will issue our own snow map later today.
Given the combination of snow and freezing temperatures on Sunday, we expect untreated roads to quickly become snow-covered and slippery. Occasional stretching of moderate to heavy snow is possible, which reduces visibility. Large, well-traveled roads, especially those being treated, should be passable but can still become slippery when the snow falls steadily. Expect delays at the airport and possible cancellations.
Depending on how the storm develops Sunday evening to Monday, schools that are open for personal learning may delay or close, or switch to distance learning for the day on Monday.
What we know and what we are less sure about
This is still a complicated forecast because the computer models used to inform weather forecasts have still not agreed on a number of important details that will affect how much snow we will end up with.
- A storm originating in the Pacific Ocean will trace from the Central Plains to the Ohio Valley region.
- Temperatures over the area Sunday morning at the beginning of the storm will be in the 20s – cold enough to support accumulating snow and result in slippery roads and walkways.
- The circulation of the storm in the Ohio Valley will disperse hot air that will be lifted over a cold dome of air over our region, leading to excess snow over the region Sunday.
- The snow on Sunday should produce at least a few inches.
- A new coastal storm will develop somewhere in the south that will help keep the low temperatures close to freezing until Monday.
What we are less sure of:
- How fast and how far offshore the new coastal storm will form.
- Whether enough warm air moves into the area to change snow to a winter mix late on Sunday and, if so, how much the mix will reduce the amount of snowfall, continues until Monday.
- How long the snow can continue. If the coastal storm develops too far at sea, the total amounts of snowfall would be limited to what falls in the initial wave, which may end on Sunday evening. The precipitation after that would be light and spotty.
- Whether a zone with heavy snow will develop on Monday. If the coastal storm turns up, it can generate an area with heavy snow that would greatly increase the storm total.
- Where the band with the heaviest snow will be set up. The further south the coastal storm is formed, the better the chance of the snowfall jackpot being in the immediate Washington area. If it forms further north (ie northeast of Virginia Tidewater), areas north of Washington will see the heaviest snow.
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