high risk

Ok, 3 things going on here: 1) The winter suite in the NBM is only updated at 01, 07, 13, and 19Z. So, if you're showing an 18Z cycle for this medium range case, it's as "stale" as you can have it. 2) In the medium range, the only inputs are the 50 ECMWF ensemble members, the 30 GEFS members, and the GFS. It doesn't even include the deterministic ECMWF run (don't ask). Some of the CMC members are now included in the parallel. Here is what you're going to hate: the NBM does not yet receive the 06/18Z ECWMF data. And at 19Z, the ECMWF ensemble has not yet arrived. So, the 18z cycle in question is still using the very snowy 00Z ECMWF ensemble. That's what's driving the big numbers. 3) One additional factor: bias correction is performed for QPF for the global model inputs, and the bias-corrected QPF is used by the NBM winter suite. The bias correction, based on the based 90 days of forecasted and observed QPF in this case is bumping up the QPF for the event, as it believes that the ECMWF ensemble has been running dry. So, you have some inputs with high raw precip values that are being further adjusted up. That's why the 18Z NBM looks so snowy. The 01Z cycle coming out soon will use the 12Z ECMWF ensemble and the 18Z GEFS; based on what I see in the QPF of those systems, my guess is the NBM snowfall will be a fair amount lower, although the bias correction might boost it a bit more than I expect.

Always like seeing NBM images here, but 1) this cycle reflects the 00Z Euro ensembles and not the less snowy 12Z 2) The NBM mean, like any ensemble mean, can be skewed by a handful of very snowy members. FWIW, the latest NBM cycle still keeps the probability of an inch or greater of snow this weekend at under 50%.

The NBM at this range gives heavy weight to the 00Z EPS, so this is exactly what I'd expect to see.

I'd like to take credit for a call, but I rode the NAM Nest. If I had a dollar for every "LOL NAM" and "the NAM sux" posts in the past 3 days, I could have retired early. I completely understand the skepticism back on Thursday and Friday, but once we got inside of 36 hours and it didn't budge, I thought it had a high likelihood of verifying with p-type, even if it did a poor job with QPF prior to the flip.

I'm not a huge fan of FV3, so I would hope so. One big thing is that a fully-coupled GFS will be implemented later this year, which should be very helpful. That means a lot of things, but it means that the atmosphere, water, land-surface, and sea ice will all "talk" to each other.

I would love if it takes that long, but I'm mentally prepared for 13-14z.

You are spot on. MPAS is going to replace FV3 in RRFS Version 2, and it will probably be used across the board eventually in the NWS models.

The GFS does use the FV3 core now. That has been the case since 2019.

With apologies, what do you mean by the "FV3 GFS replacement"?

It's pretty clear that the NAM is slow with the leading edge of the precip. It definitely has a bias of being too slow to advance precipitation into very dry air. The 18Z cycle doesn't bring snow into DC until 6Z, and I doubt it will take that long. It's probably good reason to ignore its QPF for the front end thump and go with wetter models. That said, none of that means that it must be off with the timing of the transition to sleet. It might very well be too fast with that, but I wouldn't base that off of not getting snow to the ground quickly enough at the leading edge.

Not true: HRRR and the three HiResWindows are all 3km. That said, I don't trust any of those for thermal profiles.

The reason that the NAM and Hires Windows are being retired is because it's impossible to maintain a model suite with so many different cores. That said, I need to figure out why I'm spending time defending the NAM....

The fact that it's one of the driest solutions is absolutely odd, and I don't mind treating it as a massive outlier. But I'm not sure that missing how significant the initial thump is will matter with how quickly we changeover, and I also don't think that it makes sense to compare radar to model forecast 400 miles away to determine what will happen here. Anyhow, you'll change over way later than we will no matter what......

The blanket "the NAM sucks" stuff is wild to me when the strength of the NAM Nest is nailing thermal profiles inside of Day 2. Maybe it's going to be too fast with the changeover, but complete dismissing of it makes no sense.

Agree fully. The wet content of what's on the ground followed by the deep freeze means that it will take a long time to get sidewalks and side streets back in order

So, the problem is that the NAM Nest is part of the HREF....... That means, though, that the other members (HRRR and HiRes Windows) are much snowier. They're all less icy than the RRFS and ECMWF.

The FV3 RRFS is also going bonkers with the freezing rain. I *think* it's way, way overdone and favor the sleet bomb idea of the NAM, but this will have to watched closely tomorrow.

There are plenty of valid arguments against the NAM, but making that point by showing changes across cycles of an forecast of what the lowest level radar reflectivity will look like at one particular moment, and then comparing that to a 6h-averaged precip rate from a different model doesn't make your case.

God, I really hope you meant "rimed".

Love that you showed the para! Friendly reminder that the NBM winter fields update at 01, 07, 13, and 19Z, so instead of showing the 12Z, it's best to wait one hour and use a version that incorporates more recent guidance.

The arctic front doesn't come through until Friday evening, but when it does, the freeze is on. Multiple models show upper 30s at 4pm falling to low teens by 1am.

Yes, but we're still going to get 2 years of the FV3-based RRFS in operations.

Big warm layers can easily reside in between those two levels. Some of the forecast soundings I have seen for this event show that exact scenario. The NAM precip type code is rock solid, based on the forecasted temperature profile.

Are you looking at the actual sounding, or just the temperatures at those levels??

They differ in more than just resolution, so they effectively are two different models (even though they have obvious commonalities). As you said, though, the 3 km is a far superior model, except for when it deepens hurricanes down to 850 mb.