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Double trouble? Chance for snow Thursday morning and Saturday in D.C. area.

Neither snow threat looks particularly serious at the moment, but both are worth monitoring

European model shows some snow in the region leading up to sunrise Thursday. (WeatherBell)
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A snowy month in the D.C. area could get a little snowier over the next five days. Two periods of snow are possible, the first Thursday morning and the second Friday night into the weekend.

Thursday’s snow, which will start as rain, could produce slick roads for the morning commute, especially in colder areas north and west of the Capital Beltway. The weekend storm has a chance to be more significant, potentially tapping Atlantic moisture while drawing in very cold air.

However, neither of these snow chances are a lock to produce meaningful accumulation. Temperatures may not cool down fast enough before the snow ends Thursday for much to stick. Meanwhile, the weekend storm could miss us to the southeast.

D.C. has already seen double its typical January snowfall

In other words, both storm systems have the potential to be disruptive, but there’s also the possibility that neither delivers.

Snow timing and amounts

Thursday morning

Precipitation could begin as early as Wednesday after 10 or 11 p.m., probably starting as rain and with temperatures near 40. The rain could change to snow between predawn and sunrise Thursday from northwest to southeast across the region. Any snow should shut off between midmorning and midday.

This seems like the kind of event that could produce a coating to an inch or so in the immediate D.C. area and perhaps 1 to 2 inches in our colder areas to the north and west, but we will refine this outlook and produce a forecast accumulation map Wednesday.

Here is what we view as the chances for different amounts of snow in the District:

  • Chance of at least 1 inch: 40 percent (60 percent north and west of the Beltway, 30 percent south and east)
  • Chance of at least 3 inches: 20 percent (40 percent north and west of the Beltway, 10 percent south and east)

Here’s how much different models project: High-resolution NAM: 3 inches; American (GFS): 2 inches; SREF: 1-2 inches; NAM: 1-2 inches; UKMet: 1-2 inches; European: 1-inch; ICON and Canadian: coating.

Note that the model projections may be somewhat overdone, as they incorrectly assume all snow will stick. In reality, temperatures will be above freezing as rain changes to snow Thursday morning, so some accumulation will be lost.

Friday night into weekend

There is substantial uncertainty regarding the start time for any snow with this second system. Some modeling suggests snow could develop as early as Friday night, while others delay the onset until Saturday night. And as mentioned, it’s possible there’s no snow at all.

Given the wide range in start times, the end times also vary, ranging from Saturday to the first half of Sunday.

Here are our projected snow chances for the District:

  • Chance of at least 1 inch: 35 percent (25 percent north and west of the Beltway, 45 percent south and east)
  • Chance of at least 3 inches: 25 percent (15 percent north and west of the Beltway, 35 percent south and east)
  • Chance of at least 6 inches: 15 percent (10 percent north and west of the Beltway, 25 percent south and east)

Here’s how much different models project: European: 2 inches; American (GFS): 1 inch; UKMet: none; Canadian: none.

The large group of simulations in the American, Canadian and European modeling systems offer the following snowfall probabilities:

  • Chance of at least 1 inch: European, 55 percent; American, 50 percent; Canadian, 25 percent
  • Chance of at least 3 inches: European, 45 percent; American, 25 percent; Canadian, 15 percent
  • Chance of at least 6 inches: European, 35 percent; American, 15 percent; Canadian, 0 percent

Discussion

Thursday’s storm system

A strong cold front is the trigger for Thursday’s potential snow. The front will initially produce rain overnight Wednesday that should change to snow Thursday morning. The big question is whether temperatures will fall quickly enough to allow the snow to accumulate.

Temperatures in and around the city are likely to stay above freezing until (and unless) there is a burst of heavy snow to offer some cooling. Models vary on how heavy the snow will be and how fast temperatures will fall. Any accumulations should be light with the best chances for an inch or two in our typical colder locations west and north of the city.

After the snow ends Thursday afternoon, it will be very cold, with temperatures staying below freezing into the weekend. So any snow that falls will stick around.

Friday night into the weekend system

The Friday night into Saturday snow threat is the more interesting one, as it might have a strong high-altitude disturbance to potentially aid in the development of a storm to our south. However, models vary on exactly how strong the disturbance will be and its track and timing.

The big question mark concerning the system is where and when a storm forms and whether it tracks close enough to the coast to pull precipitation into our area. The models recently have varied from offering us a significant snowstorm to missing us to the south, trending more toward a miss.

Tuesday’s American model simulation keeps precipitation well to our south on Saturday but develops a storm along the coast close enough Saturday night and Sunday to offer light snow along and east of Interstate 95.

The European modeling system has generally been more bullish than the American (GFS) for snow prospects. But Tuesday’s European model has backed off on the idea of a significant snowstorm and now predicts only an inch or two Saturday.

On Monday, the UKMet model forecast clipped us with snow for Saturday, but its latest run Tuesday shifted the snow back to the south, keeping us dry. The Canadian model also keeps us dry.

We’re still far enough away from the storm onset that anything from a significant snowstorm to a miss is possible, though the former is looking less likely.

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