The second significant snowstorm in one week blanketed the Washington region Friday, icing over roads and shutting down schools. Widespread amounts of 2 to 5 inches fell on top of similar totals from the storm on Monday and Tuesday. The combination of the two storms left behind more than half a foot in many areas.
Reagan National Airport, Washington’s official observing location, posted 3.7 inches on top of the 4.1 inches from the early-week storm. This week’s 7.8 inches has pushed the seasonal total above the average of 4.4 inches.
The airport has now seen almost 20 times the snow that accumulated all of last winter.
The snowfall, which piled up quickly early in the day before easing around noon, exceeded predictions of 1 to 4 inches.
How much fell and where
Although 3 to 5 inches was most common, amounts ranged from 1 to 6 inches across the region, highest in the north and lowest in the south.
Through early evening, here are some of the preliminary snow totals:
- Gaithersburg, Germantown, Clarksburg, Darnestown and Damascus: Around 6 inches.
- Ellicott City: 5.8 inches.
- Ashburn: 5 inches.
- Dulles Airport: 4.9 inches.
- Poolesville and Rockville: 4.5 inches.
- Crofton: 4.3 inches.
- Fairfax, Reston and Vienna: 4.3 inches
- Baltimore-Washington International Marshall Airport: 4.2 inches.
- Manassas and Centreville: 4 inches.
- Laurel, Bowie, Bethesda and Silver Spring: 4 inches.
- National Airport: 3.7 inches.
- Lorton: 2.6 inches.
- Waldorf: 2 inches.
- Dale City: 2 inches
- Prince Frederick: 1.2 inches.
- Fredericksburg: 1.0 inches
- Leonardtown: 0.8 inches.
Several aspects of this week’s snowfall have been notable:
- Days with snow cover are becoming increasingly less common around the District because of climate warming. But, due to the two storms this week, we’ll have five or six such days this week. That’s the most since January 2019 when there were six following a 10-inch snowstorm. In 2016, there were nine following the January “Snowzilla” blizzard.
- This is the first time we’ve had two plowable snowfalls in such short succession since February 2010, when there were back-to-back blizzards. In February 2015, there were two snowfalls with similar spacing, but the second one turned to rain and overall amounts were lower.
- January snowfall has been mainly feast or famine over the last decade. 2016, 2019, 2022 and now 2024 all featured well above average amounts. But the other years in this span produced little or no snow.
How this storm came together
Friday’s storm was known as a clipper. Such storms approach from the west-northwest, and while they’re efficient at lifting the air, they tend to be “starved” for moisture. Plus, they are usually embedded in a fast-moving jet stream, meaning a quick hit and limited time for accumulation. As a result, the Mid-Atlantic typically only experiences up to a few inches of dry, powdery snow from such systems.
Friday’s clipper took an ideal track to maximize snowfall across the region, as shown in the image below. The core of the clipper’s surface low pressure is shown by the red “L” while the blue and green tones are weather radar returns, showing the intensity of precipitation.
In the upper atmosphere, the disturbance associated with the clipper was supercharged with spin, as shown in the image below. In the early morning hours, especially from 4 a.m. to 8 a.m., the amount of spin aloft was rapidly increasing over the area. This sharply increased the upward motion in the lower and middle atmosphere. The result was cooling and freezing of moisture into thick clouds and moderately heavy snow.
Why predicted amounts were too low in some places
In a number of places, snow amounts exceeded the 1 to 4 inches predicted by the Capital Weather Gang. Why did we underestimate amounts? In short, the track of the clipper shifted far enough south in the 24 hours leading up to the event that we needed to scramble to increase our predictions. And even then, the adjustments made weren’t quite enough for the areas that got the most.
On Wednesday evening, most computer models suggested the clipper would track far enough north that we’d see a coating to a couple of inches, at best. Our area was at the very southern fringe of the region expected to see snow.
Whenever the area you forecast for is on the edge of a snowstorm, predicting amounts is particularly challenging. If the storm shifts slightly, you can end up with either significant snowfall or next to nothing. In this case, it was the former.
On Thursday, as it became apparent the clipper would take a more southerly track, we increased our snowfall forecast, calling for 1 to 3 inches from downtown Washington and to the south and 2 to 4 inches to the north. In quite a few areas, that was an accurate forecast. But, in other areas, it was 1 to 2 inches too low, but it was reflected in the “boom” scenario shown in our forecast map.
Some folks claim we forecast snow too conservatively. It’s true that we underestimated amounts in some areas for both of this week’s storms. But, in the past, we’ve overestimated snow amounts sometimes, too. The bottom line is that forecasting snowfall is very challenging and it’s hard to nail it every time.
For both storms this week, even if we underestimated amounts in some areas, we correctly predicted the storms would cause slick roads and be disruptive. From the standpoint of preparing people for the impacts of the storm: mission accomplished.