eduggs

That's why we have meteorologists to interpret model output. Otherwise we wouldn't need people to forecast the weather. The GFS was actually showing something very similar to other guidance once you took the dry air into consideration.

The GFS might be a great model with a very minor glitch in the algorithm used to model surface precipitation.

The obvious answer is the near saturated lower levels. But that seems too simple to be right. I don't recall the GFS having this problem to this degree in previous years. And this is not the first time it's been observed this winter.

That's not the GFS. That's a 3rd party interpretation of the GFS output. Plus the GFS is showing -38C at 750mb at the peak of the "precipitation" near NYC. I think we should look more at the model forecast soundings and mid-level charts and less at 3rd party snow maps.

The GFS was right a few days ago when it started strengthening and sharpening the southern stream wave and signaling a greater separation and storm threat. The model caught this feature earlier than other guidance. But the GFS also appears to have a problem with its QPF parameter that has been observed several times this winter season, and notably today. It shows precipitation at the surface that would actually sublimate or evaporate before reaching the ground. Simulated radar reflectivity maps look pretty good, but QPF is way off. The dry lower-mid level air was very well modeled with this storm. In fact it appears that, outside of the QPF parameter, the GFS did very well.

For radar reflectivity it's not bad.

It's 45/35 now and dropping off pretty quickly, especially the dew point. Plenty of time to cool down.

We have a threat tomorrow. A small change in the height field would have delivered us a major snowstorm. Correlations with indices are meaningful but weak. Weather at the local level is primarily dependent on random chance even though many correlations exist.

I suspect the sharp gradient in 700mb humidity represents approximately how far north the accumulating snow should actually be getting on the 18z GFS.

We're not necessarily going to see storms like tomorrow in the long-range anomaly charts. Averaging also skews and masks the details. But the details are everything with local weather.

Big difference between 1 and 3 inches. My guess is you'd be happy with 3 and a little disappointed with 1. I won't be satisfied with anything less than 4, but I would still be excited by a dusting. I expect nothing.

Watching the precipitation spreading into KY... So far it looks roughly well-modeled. I'd love to see the incipient shield punch right into Ohio. And ideally into southwest PA. The further north the initial SLP pushes, the further north along the coast it is likely to shift or redevelop to. Just wishcasting... Shift the entire synoptic setup 20 miles north and all of I-95 is likely looking at a moderate snowstorm.

Gradient! The EC goes from 1"-10" in 40 miles across NJ. Ouch!

If you just looked at the Euro at 18hr you'd assume we were all going to get crushed. Such a shame that the SLP is sliding ENE.

If you're a person in, say, Asbury Park, NJ, with an average interest in the weather... how are you supposed to interpret: 20% chance of <1" 50% chance >2" 30% chance of 6"+ (in 8 hours) 10% chance of 10"+ I guess you go with the Watch. But the public doesn't read forecast discussions. I guess people just check their weather apps nowadays.

If you loop the past 2 days of GFS runs, you see our system at H5 shift steadily south and west and become increasingly deep and negatively tilted. However, modeled heights off New England and the Canadian Maritimes have not really risen. As a result, we've seen the surface reflection really tuck up into western NC and push a lot of moisture further north into the mid-Atlantic. But regardless of this early northward push, the entire system inevitably gets shunted eastward, which prevents the precipitation shield from expanding NW up the coast. At some point, the main system could gain enough latitude that even with an eastward shunt most of the area is into plowable snow. But that would mean most of CPA is already in the game.

But we're still looking at SNJ, maybe coastal CNJ, and the Islands off MA for any appreciable snow. Maybe now we're also looking at LI possibly back to NYC as well as the SE coast of MA for an inch or two. That's not fundamentally different than where we were at yesterday. We need to see significant snow getting into northern MD, SEPA before we can start thinking about accumulating snow in and around NYC.

Those plumes are amazingly well distributed. Tiny bit of clustering 0-2" and then good spacing from 2 -20". Right now I would go with some light snow, dusting to an inch for NYC. Still tons of dry air near 700mb. But big bust potential on the high end. I like WS watch to Monmouth Co. NJ. But what's the criteria there?

A lot of the members are tucked, but none really gaining latitude. We need this off DE and for it to move NE and not E or ENE. The GFS does look pretty interesting in the mid- and upper levels though. And I'm glad to see precipitation moving into southern OH - that's been a milepost for me in getting precip. to NYC. Right now tomorrow is shaping up to be a painful day of radar watching and wishing.

That's radar reflectivity, not precipitation at the ground. A lot of that NW of Delaware is virga.

For the past day, there has been a significant north trend (precipitation coverage and amounts) on most guidance in VA, MD, DE and SNJ associated with the southern stream wave. But this trend has been muted further up the coast. It continues to look unlikely that anything meaningful with get north of SNJ. But convection in the South or a further deepening of the southern stream wave shifts could still shift everything further north. I could see CNJ and SEPA getting into the game. But the northern stream height field is really preventing the SLP from moving NE up the coast and expanding the precipitation shield to inland areas.

I only counted 3 out of 30 GEFS members that were good hits for NYC. And the GEFS are by far the most favorable ensemble for snow. But then again the ensemble clusters tend to shift with the operational model in the short term.

Soundings are still really dry in EPA, NJ, CT etc on the GFS. I don't trust the northern edge at all. I love the trends and the GFS looks pretty good at H5 at 30 hours. But the RGEM looks much more reasonable IMO. Same with the 18z EC. Remember when people were calling this wave anafrontal I really really hope this keeps on trending, but I think expectations should remain low north of the Delmarva.

The 0z RGEM trimmed the northern edge just slightly. Just a brush for the Cape. The significant trends over the past day have been in VA, MD, and DE as the southern stream is modeled increasingly robust. But there's not much room for this wave to bend the flow further up the coast due to the northern stream height field, so the precipitation bump doesn't translate much northeast up the coast. We still need a major change aloft to get precipitation NW of coastal NJ and the eastern Cape and Islands.

Recent runs have pushed snow a little further north into NVA, and I could see that continue a little bit. But it may not translate up the coast for the reason you mention. The precipitation edge seems to be running more east-west instead of northeast up the coast.