For a week, we’ve been talking about the colder-than-normal weather set to arrive by Thursday. The cold is a necessary ingredient for snow, and it appears reasonably likely that the D.C. area will see its first flakes late this week or over the weekend. But the moisture necessary for a significant snow event seems to be missing — at least in the next seven days.
Any snow we see between Thursday and the weekend is likely to result from clippers, fast-moving disturbances from the northwest limited in moisture. We may experience back-to-back such clippers late Friday and late Saturday.
Some model forecasts had teased the possibility of a coastal storm throwing back some more substantial snow into the cold air late Thursday into Friday, but we’ve never really bought into that idea. For one, temperatures are likely to be above freezing, which would limit how much snow could stick and, more importantly, we expect most of the precipitation to remain well to our east because of the shape of the jet stream. Since Sunday, even the models that were predicting snow from the coastal storm have backed off.
So could the clippers Friday into the weekend, even if starved of moisture, offer any chance for accumulation? There’s a small chance.
Clippers offer the most snow potential when they pass just to our south. This does two things: 1) It allows cold air to flow into the region from the north. 2) It places our region in a zone of rising air where narrow bands of accumulating snow can develop.
The American (GFS) model run Monday morning shows two clippers passing to our south in succession Friday night and Saturday night. If the model is right, that could mean two brief periods of light snow or snow showers. However, even with its favorable track for these clippers, the model’s predicted temperatures would just be marginally cold enough for accumulation — right around freezing near Washington. Our colder suburbs would have a better chance of a dusting or light coating.
The European model is much weaker than the American model with the first clipper and predicts that second clipper to pass so far south that we’d completely miss it. So there is the chance we don’t see any snow at all this week.
Models have a hard time predicting the exact path and timing of these fast-moving systems more than a few days in advance, so we won’t really have a good idea as to whether one or both will produce snow in our area for another couple of days.
The bottom line here is that the general pattern appears favorable for the chance of some scattered light snow or flurries between Friday and Sunday as these little impulses in the atmosphere zip by. But accumulating snow, while a possibility, is more of a long shot.
If we don’t see much snow this week, the overall pattern is expected to remain cold the following week, so we will have more opportunities. The average date of the first measurable snow in Washington is about Dec. 15, so if it happens next week, it will be right on time.