eduggs

People like the rip the NAM. But it looks like the GFS was wrong about keeping heavy snow out of ENY (ALB) and most of SNE. It's been shifting steadily for two days. The GFS was also too snowy in EPA (PHL) and SNJ. The NAM looks to have been much faster to pick up on these trends.

UK held or slight improvement. The trend towards shifting the lows northeast and delaying their decay/shunt south is leading to a more north-south oriented snow accumulation distribution as it pushes moisture into the damned cold air. There will likely be a snowfall max now in ENY with excellent ratios. But if we can hold off mixing, our QPF might get a boost leading to a 2nd max further south near NYC or the HV but with lower (still decent) ratios.

The 9z RAP also shifted heavy snow into C/ENY and SVT (like the HRRR/NAM) and brought mixing into the southern tier of NY. A surface low in WNY is not ideal. We still do great locally, but I don't like seeing more snow in ALB than BGM.

The 8z HRRR directs the best snow into the Catskills and ENY through the end of its run. There is still locally a few-hour burst of mod-heavy snow and probably a little more to come beyond its 18 hour range, but the northeast shift continues. That's pushing a bit of a dryslot into SNY and PA. I don't like seeing the HRRR seemingly shift towards the NAM. Can't wait to see that trend reverse. Most other guidance looks solid however.

ICON looks slightly better than 0z. GFS and RRFS look very similar to their previous runs. All solid for most of the area! Gotta watch the radar, obs, and HRRR today to see if the northeast shift is real or not.

The 6z HRRR and esp NAM should concern snow lovers from NYC south and west. The surface and mid-level low centers continue to tick further northeast. That's getting heavy snow into SVT now, and even BOS on the NAM. That's a yellow caution flag at minimum. On the other hand, the 6z RGEM held steady or even ticked a hair south and wetter locally.

Main overrunning band reaches ELI through NW CT to ALB NY. That continues the multi-cycle trend of pushing this band further north and east into New England.

I actually think BGM is more likely to mix with sleet than western LI as crazy as that sounds... because of the track of the 700mb low. Otherwise I agree, good map.

The RRFS has snowfall rates of 2-3" per hour tomorrow night (assuming 10:1). The heavy snow only lasts an hour or two on the model, but it would be fun. Other models have a burst of heavy snow as well though mostly 1-2" per hour max.

Real early (probably premature) radar hallucination... but to my eye the radar looks pretty good tonight. Returns are turning sharply southward over Lake Huron and there's already a finger of reflectivity oriented NW to SE situated pretty far west relative to model guidance. Probably doesn't mean much at this point.

On the GFS, PHL and EPA has been losing snow and CT, MA, and ENY have been gaining snow.

GFS still looks good locally as depicted in terms of QPF. But it definitely shifted northeast with the mid-level lows. It now gets significant snow to ALB and HFD. A day ago they were both on the fringe of the forecasted precip. shield. The HRRR (1z, 2z) also appears to be slowly ticking northeast aloft too. Need that to stop.

Those are some hellacious snowfall rates just after 0z on the RGEM. Looks like 2"+ per hour for an hour or two. That would cause some serious problems on the roadways for holiday travelers.

The 0z HRRR and NAM had pretty well defined 700mb lows NORTH of Lake Ontario. They keep the circulation alive almost to Ottawa. That's why they push sleet past Binghamton and briefly to Monticello, NY. The GFS has a weaker 700mb low that dissipates more quickly. Hence warm air near 700mb doesn't surge as far northeast, keeping the mixing line much further southwest. We can't know for sure what will happen, but the NAM has a track record with mid-level lows.

For what it's worth, the RRFS gets sleet the NJ-NY border, including NYC, after a really good thump. QPF is higher this run, however, and there's likely a little more snow to end.

You implied the NAM was wrong regarding snowfall last Tue... Not that posters who misinterpret its output were wrong. But you can't hold misinterpretation against the NAM. I agree with you about this event. The 18z NAM was at or past the outer envelope of ensemble solutions. It also has a tendency to make larger run-to-run changes than other models. That makes its outlier depictions unlikely.

I don't think there has been much model flip flopping over the past 48 hours. A few mesos were really suppressed at the end of their ranges initially and the 18z NAM jumped pretty far north. Other than that, most models, esp globals and ensembles, have been pretty consistent. That should lend confidence. And in fact it does. The problem is there have been plenty of cases in the past where a late shift in a model (often the NAM) heralded a true shift in outcome despite model consensus. These cases being memorable probably biases the memory and skews perceptions of likelihood, but it has and can happen.

Don, I think you know that's not NAM output. That looks like Pivotal 10:1 "clown" map. NAM produces liquid precipitation output and a vertical temperature profile. I believe it also generates a ptype. I recall it did pretty well on all three. Just because you get 0.2" liquid with mostly snowflakes doesn't mean they will accumulate. That's not the NAM's fault. That's user error.

That was a huge snowstorm and the NYC area was clearly on the fringe.

On the HRRR, at 0z Sat (tomorrow), Orange County is at 2-4" while NYC metro is < 1". It's not the best angle of approach locally and there's still some concern there that the best banding could slide north and east into CT. On the plus side, the HRRR still manages respectable QPF locally and the low level convergence (inv trof) overnight Sat occasionally manifests as undermodeled localized banding.

Nice run from the 0z HRRR for NYC north and east. It even keeps light snow going into Saturday morning. Sleet mixes in briefly to the NY border. But... major snow to ALB, plowable to ORH, and accumulating to BOS is a bit of a red flag for us. The 700mb low is getting pretty far northeast before getting shunted south... For now we're all still very much in the game but still feeling nervous.

Playing catch-up with the afternoon's models and noticing that the 18z GFS is the best short range (24hr - 36hr) run for the ENTIRE NYC metro that we've seen in a while. An outcome like that would really spread the love. It's probably a bit optimistic, but still fun to see!

Probably gonna be some big parachute flakes as the sleet line approaches with flakes sticking together in the near freezing 700mb layer.. especially if winds aren't too strong.

It's cool to see solidly subfreezing temperatures in place for an event for a change. It looks downright cold in the lower Hudson valley tomorrow. It should transform the landscape no matter what wintry precip. falls.

The heaviest precipitation will probably fall after sunset... but it would be nice to get an hour or two of accumulating snow during daylight... we'll see.