high risk

Very concerned that if much of the snow falls during the daylight hours Sunday, it will really struggle to accumulate in very marginal low-level temperatures. Rates will be critical to our chances of a measurable snowfall.

Most of the 12Z mesoscale guidance today showed that the organized snow would have a really tough time making it into the DC Metro area, and that seems to be playing out.

Maybe? I haven't looked at the mechanics of why this band is way out ahead of the actual arctic boundary. Another possibility is a few scattered bursts of snow right on the late night front....

Looks like roughly 3AM(west)-5AM(east) timing for the passage of the arctic front.

I understand the skepticism, but those forecasts were relying on intense radiational cooling late at night, and clouds/wind seemed to wreck those opportunities. This will be pure advection of an intensely cold air mass, and it's legit arctic air. I think this has a much better chance (and I'd say it's very likely) of single digits.

Indeed. Looks like mid 20s at midnight. In fact, it stays in the mid 20s through around 4am, and we then drop at least 20 degrees in the 4-5 hours following.

I gave 1/2 of a laughing emoji for the concept of this comment and 1/2 for the utter butchery of Louis' name

VERY well stated. The HRRR is generally pretty good with warm season convection (minus some flaws and the inherent challenges with modeling weakly-forced storms) but has never proven itself as a winter weather model.

Saturday looks brutal, with temps in the mid to upper teens and sustained winds in the 20-30mph with higher gusts.

With how cold surfaces have been, even a half inch of snow at night would likely cause problems on some of the roads, with the ungodly amount of leftover salt possibly saving us from a complete mess. School systems will have a complicated decision.

Was not a total miss. It had a very modest amount of snow about 24 hours earlier than the map you showed, with some sort of lead wave.

AI models don't do particularly well with QPF. They get a general shape of the field but struggle to resolve amounts and detail. I'd focus far more on 500 heights and SLP.

The mean has very limited value at this range, because a few snowy ensemble members can skew it. The probabilistic output is far more useful, but I'm not sure how easy it is to find that on the web.

I'm looking forward to those 4 hours above freezing on Tuesday!

This is exhibit A for the problem with using mean values from a large ensemble. There are a handful of GEFS and ECMWFE members with huge snowfall totals, so the mean value ends up as a couple of inches. But the 50th percentile map shows 0 for our area, and the chance of 1" of snow at KDCA is under 30%.