* Winter storm watch late Saturday night to late Sunday night *

11:15 p.m. update: After reviewing the evening models, our forecast thoughts have not changed from what’s below. We still expect several inches of snow on Sunday and lean toward some more on Monday. However, we still have low confidence in projecting how much or how little may fall on Monday.

Models may be converging on the best chance for a heavy band of snow to develop in northern Maryland toward the Mason Dixon line on Monday. This may mean areas farther south end up on the low side of snow projections. This is something we’ll look at closely on Saturday and revise our forecast as needed.

Original article

Washington’s long snow drought is about to end.

Confidence is high that the Washington region will see several inches of snow on Sunday and possibly more Sunday night through late Monday or early Tuesday. The expected snow will stick to roads, making travel hazardous, but it will bring joy to snow lovers deprived of any significant accumulation for about two years.

The storm that will bring the snow is the same one that brought epic snowfall to the mountains in California and will race east over the next few days.

In the Washington region, snow will begin between about 4 a.m. and 10 a.m. Sunday and continue for a good part of the day. Freezing temperatures mean the snow will stick and quickly coat untreated roads and sidewalks. There is some chance the snow will mix with or change to sleet and rain late Sunday afternoon or evening, especially southeast of the Beltway.

The National Weather Service has issued a winter storm watch for much of the area for the potential for 5 or more inches of snow through late Sunday night.

The wild card is what happens Sunday night into Monday night or Tuesday morning, as a coastal storm gets going near the Carolinas. There is some chance that snow, possibly heavy at times, will continue with at least several more inches of accumulation. The latest computer model guidance on Friday morning was favoring more snowfall during that period, bumping up totals.

Alternatively, meaningful snowfall could taper off late Sunday, with just spotty, intermittent precipitation that doesn’t amount to much afterward.

Forecast totals

If the storm’s second wave materializes, which is dependent on a new coastal storm developing quickly near the North Carolina coast, snow will continue to fall into Monday or even Monday night and early Tuesday. Totals could exceed half a foot, possibly reaching double-digits in inches in some areas.

But, if the coastal storm forms either too far north, or too far off the coast, the additional accumulations will be limited to the few inches from the initial wave on Sunday.

  • Based on all of the model information and our forecast experience, we believe a moderate 4-to 8-inch snowstorm is the most likely scenario in D.C. area for this event, although we cannot rule out 8 to 12-plus inches if the second wave materializes or just 2 to 4 inches if it does not and the first batch of snow turns out to be lackluster.
  • In summary, the floor for this event is about two 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 precipitation.

Chance of at least one inch: 90 percent

Chance of at least three inches: 65 percent

Chance of at least six inches: 45 percent

Chance of at least 12 inches: 10 percent

The storm promises to produce the most snow in Washington since at least Feb. 20, 2019 when 2.6 inches fell, and could even outperform the Jan. 12 to 14 storm of that year, which laid down 10.3 inches. If ingredients align perfectly for snowfall with this storm, that more significant amount could be topped.

However, it is unlikely the storm will rival the January 2016 blizzard, the biggest snowstorm of the past decade, which unloaded 15 to 30 inches across the area.

The map below, from the National Weather Service, shows expected snowfall through 7 p.m. Monday. We think it’s a reasonable assessment at this point although we believe snow amounts will tend to increase from south to north rather than set up so uniformly.

Our snow map (at the top of this section) shows predicted amounts for the entire storm through Tuesday, if precipitation continues that long. It will likely require some adjustment, upward or downward as the storm draws closer.

Storm impacts

Considering the combination of snow and freezing temperatures on Sunday, we expect untreated roads to quickly become snow-covered and slick. Occasional bursts of moderate to heavy snow are possible, which will reduce visibility. Major, well-traveled roads, especially those that are treated, should be passable but could still become slick when snow falls steadily. Expect airport delays and possibly some flight cancellations.

Depending on how the storm evolves Sunday night into Monday, schools open for in-person learning may delay or close, or switch to distance learning for the day on Monday.

What we know and what we’re less confident about

This is still a complicated forecast as the computer models used to inform weather forecasts still haven’t come into agreement on a number of important details that will affect how much snow we will end up with.

What we know:

  1. A storm, originating in the Pacific Ocean, will track from the Central Plains to the Ohio Valley region.
  2. Temperatures across the area Sunday morning at the onset of the storm will be in the 20s — plenty cold enough to support accumulating snow and result in slick roads and walkways.
  3. The circulation of the Ohio Valley storm will spread warm air that will be lifted over a cold dome of air over our region, leading to overrunning snow across the region Sunday.
  4. The snow on Sunday should produce at least a couple of inches.
  5. A new coastal storm will develop somewhere to our south which will help hold the low-level temperatures near freezing into Monday.

What we’re less confident about:

  1. How quickly and how far offshore the new coastal storm will form.
  2. Whether enough warm air moves into the area to change the snow to a wintry mix late Sunday and, if so, how much the mixing will cut down on snowfall amounts, continuing into Monday.
  3. How long the snow might continue. If the coastal storm develops too far offshore, total snowfall amounts would be limited to what falls in the initial wave, which could end Sunday evening. Precipitation after that would be light and spotty.
  4. Whether a zone of heavy snow will develop on Monday. If the coastal storm cranks up, it could generate an area of heavy snow that would greatly increase storm totals.
  5. Where the band of heaviest snow will set up. The farther south the coastal storm forms, the better the chances will be for the snowfall jackpot to be in the immediate Washington area. If it forms farther north (i.e. northeast of the Virginia Tidewater), areas north of Washington will see the heaviest snow.