The latest reliable computer models favor a snowier scenario, with snow Wednesday night into Thursday morning, a pause on Thursday afternoon into the evening, and then another potential period of snow Thursday night into Friday morning. This would mark the third winter weather event in the past 10 days.
The National Weather Service has placed the entire region in an “enhanced” (level 3 out of 5) threat zone for a winter storm.
While several models have us in the sweet spot for snow, shifts in where the front is located could lead to very different outcomes as the two waves pass by. If one or both waves pass to our north, we would see more sleet and freezing rain or even rain, while northern Maryland and Pennsylvania would get most of the snow. But if one or both waves pass to the south, we might end up with little precipitation, while central Virginia sees more substantial snow.
For the District
Chance of at least one inch of snow: 70 percent
Chance of at least three inches of snow: 50 percent
Chance of at least six inches of snow: 25 percent
Wednesday night to Friday storm scenarios
1) Snowy scenario — at least three to six inches
The Arctic front pushes south of the D.C. area Tuesday with cold air firmly in place by Wednesday evening. Then snow is generated as winds from the southwest aloft send comparatively mild air flowing across the frontal zone.
The snow would continue through Wednesday night before possibly pausing as the first wave of low pressure shifts off the coast. The snow would then probably redevelop later Thursday and keep going into the early morning on Friday as the next wave comes through.
The European modeling system, the UKMet model and the Canadian model support this scenario and suggest a high likelihood it would produce at least three inches and possibly more than six inches in the District.
2) The wintry mix scenario — one to three inches of snow and some sleet/freezing rain
The precipitation would begin as light snow around Wednesday evening, with the snow giving way to mix of sleet and or freezing rain around the city and south and east due to milder air moving in at high altitudes. Temperatures near the ground would remain below freezing Thursday except over Southern Maryland.
As the first wave exits off the coast, the front would probably sink a little farther to the south, putting the area deeper in the cold air. That push of colder air would allow the next round of light precipitation to fall as snow Thursday night into Friday morning.
The American model has been suggesting this scenario, although its most recent run shifted toward the colder and snowier European camp.
3) The big-miss scenario — little or no snow and ice accumulation
In this scenario, the heaviest precipitation with the first wave would mostly miss us to the north. Areas near the Pennsylvania border might see snow, but the rest of the area probably would see a light mix to rain event as mild air is drawn into the region at low levels.
Then the second wave would come through far enough south that its precipitation would mostly miss us, although we might get brushed with some light snow.
This scenario is favored by the NAM model and some of the individual simulations in the American modeling system.
We also could see a blend of these scenarios. Right now, we would lean toward a blend of the first two scenarios. We’ll do our best to narrow down the possibilities Tuesday.
Reviewing Sunday’s forecast
On Sunday, our prediction of one to four inches, mostly on grassy areas, worked out for large parts of the region. That’s apparent in the map above, where all the observed amounts shaded in blue on the left-hand panel fell within that range.
However, the observations in purple exceeded four inches and launched into our boom scenario. They were mainly well west and northwest into the mountains. Because temperatures were so marginal for accumulation, between 31 and 35 degrees, amounts tended to be elevation-dependent. Hilly and mountainous locations where the temperatures dipped to 31 or 32 degrees saw snow accumulate much more readily than those that were above 33.
Our forecast for snow was too high in the zone around downtown Washington and Alexandria and to the east and northeast. These locations saw just a coating or so. While it snowed here, air and ground temperatures proved too warm for it to stick much, and it didn’t snow intensely enough to overcome that. Sometimes the snow mixed with rain. In parts of Southern Maryland, however, where the snow was heavier, amounts were as high as two to four inches despite similar temperatures.
Overall, compared with forecasts from the National Weather Service and other outlets, our forecast performed well. We accurately described the timeline for the event and when rain would change to snow. We correctly conveyed that the storm would not have a major impact on the area, rating it a Category 1 on our five-point scale.
The possibility that the snow might have trouble sticking in lower elevations near the city was mentioned in our discussion. In hindsight, we should’ve communicated this in our snowfall map, something we’ll try to do next time when temperatures are marginal for accumulation.
Another Sunday storm coming?
The fourth winter storm in two weeks is possible Saturday night into Sunday. Computer models differ on how it may evolve and whether it will produce significant precipitation, but there is some potential for additional snow, ice and/or rain. We’ll focus more on that as it draws nearer.