Before discussing it in any more detail, it’s worth remembering that forecasting winter storms more than two to three days in advance is a very low-confidence endeavor; we need only look at the storm earlier this week as a fresh reminder of that. Recall how what looked to be a major winter storm at different points in time ultimately resulted in a snow hole over Washington.
The European model does indeed show heavy amounts of snow and mixed precipitation falling over the region. A storm system cuts across Tennessee on Monday night, into Tuesday, and redevelops into a coastal storm near Cape Hatteras, off the coast of North Carolina, by Tuesday night. It is very slow-moving, crawling to a position east of the Delmarva Peninsula on Wednesday morning before slowly drifting out to sea.
The storm draws down enough cold air for a long-duration, heavy snowstorm in our western and northern suburbs, with a sloppy mix of precipitation near the Interstate 95 corridor, including rain, heavy, wet snow and possibly sleet. If the model is right, this would be a very elevation-dependent snow event with amounts tending to increase as you head north and west of the city.
Above, I am describing what the model is showing; in reality, it’s way too early to try to forecast specifics such as where the rain-snow line might set up, and how much precipitation will fall and where.
The UKMet and Canadian models do not show the kind of extreme winter solution forecast by the European model. They tend to suggest that the storm will track far enough north that it is more of rain event, although significant snow could fall in the mountains and a little wet snow work its way down to lower elevations as the storm exits.
The American model presents this weird (and unlikely) scenario in which two storms come through back-to-back Tuesday and Wednesday, the first bringing rain, and the second bringing snow. Seldom, in reality, do two storms follow in such close succession. They are more likely to be one entity.
The European model forecast, which implies a very high-impact storm, is a possible but not likely outcome. But because the model is the highest performing model, it warrants mention. For the storm earlier this week that largely missed Washington, it never once forecast a big snow event and turned out to be right.
But the European modeling system shows how much uncertainty there is with next week’s forecast. While its primary simulation shows a big winter storm in the Mid-Atlantic region, about a third of its 50 alternative simulations with small tweaks present a nonevent, and another third a moderate event.
Note, in the image below, its forecast position for the storm Tuesday night. You can see there is a big range of where it may be centered based on where the red L’s are placed, which is an indication in the uncertainty in the forecast.
The L’s near the Outer Banks of North Carolina are in a good position for the storm to supply snow to the Washington area, but the ones farther north less so.
As I wrote Wednesday, the fact that we’re into late March would tend to favor a more northern track which would draw up enough warm air for more rain than snow. Also, the negative phase of the North Atlantic Oscillation, which tends to force storms to take a more southern track, will be weakening and returning to neutral levels. That said, in the past, sometimes the Washington area has been socked by major winter storms when the oscillation went through this transition phase.
One other attribute this storm has going for it as a potential snow producer is cold high pressure to the north, which can feed cold air south. It’s a little farther north than ideal for a big snow event in Washington and not all that strong, but is at least present whereas it was absent for the storm earlier this week.
The bottom line is that the pattern seems to offer at least one more small chance for a winter storm before we turn to spring. More likely than not, it will not materialize into a blockbuster, but the European model suggests that we should pay close attention.