By Wes Junker February 3 at 2:25 PM  Forecast models have recently been kicking around the idea of a coastal storm that may provide some wintry precipitation for the Washington region early next week. The evolution of this storm is one that rarely delivers big snow but occasionally blasts the Mid-Atlantic with a sloppy snowstorm. Even if this storm doesn’t deliver a large amount of snow, just a couple of inches — or a few hours of wintry mix — could be enough to have an impact on the D.C. region.  It’s far too early to nail down what kind of precipitation we’ll see or how many inches of it will fall, but it’s something we will be monitoring over the coming days. However, we can say that a coastal storm will likely develop somewhere along the East Coast Monday night or Tuesday and that it could bring us some kind of precipitation, and it may be of the wintry variety. How much of it will fall is certainly still a question mark.  This storm does not have nearly the same kind of model agreement like we saw leading up to Snowzilla. Models have really been jumping around on how the system might evolve. And we see a few flags that indicate this storm may not be too worrisome for the Washington area.  First, this storm is a Miller B-type storm. Yes, it’s the same kind of storm as Snowzilla, but it has one significant difference. The models have it forming too far to the north to deliver much snow to the Mid-Atlantic, with the original storm tracking across the Great Lakes instead of across the Tennessee Valley or Southeast.  This track almost always guarantees low-level temperature issues — they’re usually too warm for much accumulating snow in the Washington region. Even last night’s run of the European model, which was bullish for snow because of its very cold high-level temperatures, still had surface temperatures between 33 and 35 degrees during the bulk of the storm.  Second, where the coastal low actually develops is still very much unknown. This factor often determines how much and what type of precipitation we’ll end up with. Last night’s European model had an almost ideal location to give us snow. Today’s GFS offered light snow because it developed the low a little too far east to offer us a significant snowstorm.  The D.C.-Baltimore National Weather Service has put out a slight winter storm threat for the entire region, which is just a notch above having no risk at all. They note that the outlook is both low confidence and the storm itself appears to be low impact, which when combined leads to a slight winter storm risk. A slight risk means that “if a threat materializes, it may cause travel disruptions.”  Let’s first look at last night’s European model forecast for Tuesday afternoon. It has the low developing off the coast in the same location where most of our heavier snowstorms typically have one, but because the original storm tracks down from the Great Lakes, we don’t get enough cold air and temperatures are still above freezing at this point on Tuesday.  This scenario would offer some snow accumulation west of the city, providing the snow fell heavily enough, but might only accumulate on the grass and trees elsewhere around the region. Road temperatures would likely be too warm to accumulate snow.  Today’s European model tracks the low much farther east than last night’s run and only offers a little light snow.  Today’s GFS (see below) brings the storm in faster and develops the low farther to the north and east than last night’s European model. The map below shows the GFS forecast for Tuesday morning (as opposed to the European forecast above, which is for Tuesday afternoon). The low is east of the eastern edge of the map below.  Even though the low is farther east than we’d like to see for snow in Washington, today’s GFS forecast would offer an inch or two of snow for the western suburbs, where driving in the morning might end up tricky. But it would probably only produce light conversational snow for the Beltway and points east.  The European model ensemble forecasts of the low positions on Tuesday morning illustrate how much uncertainty there is in the forecast (below). Note that a number of the lows are located well off the coast — way too far east to support much snow, and some are too far east to give us any precipitation at all. Some already have the low to our north. That almost always means we dry slot after a period of light precipitation.  However, there also are a few members that develop the low inland, which would argue for a rain storm. The ensembles argue that there is a chance of precipitation on Tuesday and that it could bring some snow but also could end up missing us or leaving us wet rather than white.  Over the next week we’ll be monitoring the system and hopefully will be able to home in on whether the system will pose a threat of giving someone in the area a messy wet snowstorm. However, this is one of those situations where we might not know exactly how it will unfold until 24 to 48 hours ahead of time.
The storm could develop Monday or Tuesday, though there's still a large amount of uncertainty about what kind of precipitation will fall.