high risk

To be clear, this isn't a big deal in any way, but it's not a TT issue. They're using the p-type information directly out of the GFS (and do that for all of the models) and not are computing it on their own. In lighter precip, the GFS can sometimes overmix the lower levels and warm them up a bit too much, and that appears to be what is happening in that example.

I've been bullish on this event, but I can't argue with what everyone else has observed in the guidance this afternoon and evening: while I think it's unwise to completely dismiss the threat further south, the highest chances of seeing precip tomorrow morning are going to be well north of DC.

The big takeaway from the morning model runs is that a lot of the guidance delays the arrival of the precip and allows an opportunity to warm up before arrival. That said: 1) The HRRR still has a lead band of precip (out ahead of the main frontal band) moving through the northern half of the area around 12-13Z. As said previously, even a few hundredths would create huge problems with temperatures likely still in the upper 20s then 2) Even if you consider a solution like the NAM Nest which delays precip until 16Z or so, it's about 32 or 33 degrees when it arrives. Given how cold surfaces will be after a very cold day and night, you can absolutely still get icing on roads and sidewalks in that scenario. The biggest threat is certainly for areas a good distance north and northwest of DC, but I do believe that there is a still a decent threat for everyone along and north of I-66 in VA and Rt 50 in MD, and a slight threat likely extends a little bit south of there if the HRRR solution is correct.

Spot on. It's pretty clearly going to be well down into the 20s Saturday night before the temperature rises later at late. All road surfaces will be super cold, so just getting to 32 or 33 Sunday morning won't end the icing threat. It's also worth noting that the NAM Nest appears to be doing its usual thing of being slow with precip arrival, and the earlier start shown by some of the other guidance certainly suggests a fairly disruptive (and likely a high-impact) icing event. The only thing keeping it from being an extreme high-impact event will be that it's on a Sunday morning.

Correct. It's initialized with the previous GFS cycle and has a fairly similar overall configuration (with higher resolution).

One quick note: maps like these for any models except RAP/HRRR are completely derived by the site that displays them, and they involve a lot of estimating and interpolating. Only the RAP/HRRR have explicit totals by type. That said, most of the guidance now shows at most a very brief period of rain at the start.

one hell of a band in the NAM3. Looks like a freakin' squall line.... edit: Ninja'ed by @Deck Pic

While I don't get too worked up over HRRR snow details 36 hours out, the 18z forecast is consistent with the idea that has been discussed about good amounts to the west with the shortwave dynamics and then a secondary max to the southeast as the coastal low spins up. Unpleasant screw zone in between, although its totals there would be acceptable, at least to me. And the band of heavier totals with the coastal low isn't far southeast of I-95 at all....

True, although temps should rise quickly later tonight as the southerly winds and clouds increase. But you make a good point that temps here in the early evening have plummeted, so all surfaces will be really cold in the early morning, and any very light rain will freeze on the cold surfaces even if the air temp warms to near 32.

I think that what is happening is that the MAG site where you got this image displays "snow depth change" and not "positive snow depth change" like Tropical Tidbits does. The distinction is that the snow depth change is going to tally snow on the ground today that melts before Thursday night as a negative. So, if an area has 4" melt and then gets 4" of new snow, that map will show a 0. (Even negative values are possible, but that map starts at 0.) The positive snow depth map on Tropical Tidbits looks way different and shows several inches of new snow across VA/MD/DE.

Sneaky freezing drizzle potential early Wednesday? Several CAMs show some spotty light precip early Wednesday generally on the east side of the Potomac. Some of it is shown as rain, but some of it is freezing rain. Air temperatures are progged to be right around freezing, but the surface temperatures will likely be colder than that.

I-95 in central Virginia still a complete mess. People stuck in their cars for many hours and running out of gas now.

Superstorm '22 is a lock. Got it!

5.8" in southern Howard County. Feeling fortunate to have stayed just south of the northwestern edge of the snow for several hours.

This traffic map does an incredible job showing which areas have been crushed and where the northern edge of the snow has resided.

Will be retired. NAM (parent and nest), RAP/HRRR, and Hi-Res Windows will be turned off when the RRFS is implemented (or very soon after).

Sort of. Yes, the NAM (and RAP/HRRR and Hi-Res Windows) will be subsumed by a hi-res, hourly FV3 ensemble (called the RRFS), but the configuration of that hi-res FV3 is not what the configuration of the RRFS members will be (different physics, different initialization....). Think of this run that you showed as sort of a hi-res GFS for now.

My standard word of caution that the 10:1 maps should not be used verbatim in many events, but especially in one with warm ground and marginal temps (at least at the start). We're not going to see 10:1 for most of the event, and while I am a believer in rates overcoming warm ground (especially when it's not the middle of the day), some accumulation could initially be lost. The accumulated snow depth maps tend to cut amounts a bit too much in these scenarios, but a compromise between the 10:1 and snow depth maps can work.

I'm rooting hard for this, not just because I want snow, but also because it will be even more difficult to retire the NAM if it scores a huge win on this event.

great sunset pics! it was definitely a pretty evening:

There is definitely some sneaky wind potential Saturday with a forced line of convection on the front later in the day. I'm tossing the NAM Nest solution which has the line fall apart - it tends to run cool, and I'm not buying its idea that we only get into the low 60s Saturday with the temp dropping as the sun sets. I think we have a good shot to hit 70 and get a dew point up around 60, and it will stay warm until the line arrives. With really strong winds just above the ground, it won't take much to mix down that momentum - that said, we won't have "much". Even at 70/60, instability will be really limited due to warm mid-level temperatures. So I think that we'll get a gusty line of showers, but it seems like little chance of lightning and a low chance of gusts close to SVR. The strongest winds might be later in the evening right behind the front.

Even if we got a dusting, which seems unlikely now, the need for pre-treatment is really, really questionable. You'd have light snow falling during the daylight hours with marginal air temperatures and road temperatures clearly well above freezing.

We already do, for the RAP/HRRR.

You're correct that it's a mesoscale version of the GFS (it's not as simple as just saying it's the GFS run at 3 km). The FV3 is now one of the Hi-Res Windows, along with the ARW and ARW2. (The FV3 replaced the NMMB in the last HiResWindow upgrade.) All 3 of those models, along with the NAM Nest and HRRR, make up the HREF. The hi-res version of the FV3 is an initial step towards replacing all of the hi-res models (the Hi-Res Windows, HRRR, NAM Nest, and the HREF products) with an hourly, high-res FV3 ensemble in a few years.

70! It's glorious.