There’s only one word we have to describe the outlook for the weekend storm as of Wednesday: messy. There are plenty of signs that the storm will be mostly rain, if not entirely rain, in the immediate Washington area. But there are also indications it could be cold enough, particularly for our neighbors west and north, for a dangerous ice storm.
It’s also going to take us on a wild temperature roller coaster. Depending on the storm track, temperatures could start in the 30s, rise into the 40s or 50s and then plummet to the coldest weather we’ve seen so far this year by Monday morning ― single digits at Dulles International Airport and teens in Washington with subzero wind chills. That alone is enough weather for one weekend, but we still have a winter storm to analyze.
The following comes with the standard caveat that even though it feels as if it should be Friday, it is only Wednesday, and there is still time for things to change before this storm arrives. That being said, we see two potential scenarios. In both cases, precipitation would begin Saturday afternoon, and be over Sunday morning at the earliest and Sunday evening at the latest.
Scenario 1: Mostly rain
When precipitation begins Saturday, there could be sleet or wet snowflakes mixed in, but the track of the storm is too far north and west for Washington to get any significant snow. There is a slight chance for snow on the back end of the storm, as Arctic air pours in behind the cold front, but that could be limited.
This scenario is supported by the GFS. Pennsylvania, Upstate New York and New England would get hammered with snow in this scenario, but south of the Tri-State area, it’s mostly rain. It would still be significant for travelers on the road and we would be facing local flooding issues with melting snow. In this scenario, the impacts won’t be icy roads, but there will be impacts, nonetheless.
Scenario 2: Wintry mix ending as snow, highest risk in colder areas
This one is tricky, as it’s only half-explained by what’s in the forecast models.
If temperatures are low enough, there’s a chance that parts of the Washington region could get accumulating snow, and more significantly, the coldest areas could face an ice storm that would cause dangerous travel conditions. In this scenario, the Washington region gets it all: rain, snow, freezing rain and sleet. The immediate metro would probably start off with snow, switch to rain and then end with snow. Areas far north and west — Frederick, Loudoun and especially Maryland and West Virginia panhandles — could have multiple hours of freezing rain and ice accumulation.
The European and NAM models support this idea as of Wednesday, but there’s another reason we’re taking this scenario seriously (beyond that it’s the one the European model is suggesting).
Global forecast models, even the European, have shown relatively low skill in predicting how cold it will be in our region before a winter storm. We’ve talked about “the wedge” before, cold-air damming that happens when there’s cold high pressure over the Northeast. Light winds from the north cause cold air to filter down into the Washington region and are trapped here by the mountains to the west. When storms come through, temperatures can be several degrees below what the global models predicted, and we’re seeing hints that might be the case this weekend.
To circle all the way back to the original caveat, this is still a really low-confidence forecast. Sometimes the models come together, and we know well in advance what a storm will do. Other times, it takes until the day or two before to get a good picture. It looks as if that will be the case this weekend.