The first storm, expected to come through between Monday afternoon and Tuesday morning, is most likely to bring a wintry mix of snow, sleet, freezing rain and rain to the region. The National Weather Service has placed the western part of the Washington region in an “enhanced” threat zone for a winter storm and a “slight” threat for the immediate area and places to the east.
It is too soon to project how much snow or frozen precipitation might fall, but this is likely to be the case where places north and west of the Beltway, especially toward the mountains, have a higher chance of an extended period of frozen precipitation and disruptive amounts. From the District and to the south and east, this may be more of a rainstorm.
The models have been waffling in their handling of the expected storm system. Sometimes they’ve shown the storm suppressed far enough to the south to keep any precipitation out of the area but most recently favor it tracking well to our north and west drawing in a surge of warm air aloft, which favors a wintry mix or even mostly rain rather than snow. Some model simulations have offered a third scenario, a storm tracking toward Kentucky before re-forming to our south, which would help pull cold air back across the area to give us accumulating snow.
The reasons the models have been jumping around is that there are two streams of flow, one across Canada and our northeastern states, and another coming from the west-southwest; exactly how they might interact is difficult for the models to resolve. To further complicate the situation, there is a strong zone of high pressure to our northeast, which can strongly affect what happens to the storms approaching from the west or southwest. The models have to accurately figure out how the two streams of flow will interact with the high pressure to get a solid handle on the forecast.
The European modeling system presents a lot of uncertainty about the evolution of the potential storm and its center of low pressure. Of its 50 simulations, most take the low center toward West Virginia or Ohio, then redevelop another south along the East Coast, as shown in the maps below.
Most of the predicted tracks argue for snow or mixed precipitation to change to rain in the immediate area, and ice in our colder areas, unless the low center transfers quickly to a new position along the coast south of our latitude, which would allow for more cold to infiltrate southward.
The big question mark is how far north and east the primary low center will track before a new low center develops. The farther north it gets, the more likely we’ll see a mostly rain scenario. But if the low tracks farther south, the chances for accumulating snow increase.
Unfortunately for snow lovers, most of the models aren’t simulating such a snowy track.
The main simulations of the American (GFS), Canadian, UKMet and European models suggest the low center will track to our west and north, favoring more sleet and freezing rain, especially north and northwest of the District, with more of a plain rain event to the south and southeast.
At this point, we would lean toward more of a wintry mix, with our colder areas seeing a brief period of snow changing to sleet and freezing rain and possibly plain rain, and the rest of the area seeing mixed precipitation that changes to plain rain, especially east and southeast of Interstate 95.
The storm appears to be one that would produce a moderate amount of precipitation (the equivalent of about 0.5 to one inch of rain), lasting 12 to 18 hours. It could certainly create slick travel on untreated surfaces, especially north and west of the Beltway on Monday into Tuesday morning. Precipitation would taper off by midday Tuesday.
If the immediate area doesn’t see much frozen precipitation from this first storm, the American and European models show the potential for more of a snow producer in about a week, around next Thursday.
However, forecasts that far into the future don’t have much reliability and could change. While the American and European models show a significant snow event, the Canadian model shows a much weaker system.