eduggs

If the beaches and eastern sections are going to accumulate a coating to an inch, it starts now. The bands have finally aligned SW to NE.

Agreed. Except the irony is the GFS was probably the best model with this from 5 days out. At least the best for all parameters except the only one that anybody looks at, QPF. I hope that minor issue gets fixed. It's unfortunate that so many people will learn the wrong lesson from this. People have to stop looking at QPF maps and especially 3rd party snow maps. Anybody who looked at the GFS 700mb charts was not surprised by the northward extent of the snow.

If that area gets nothing than it's a slight bust. Forecast there calls for 1-3." Yesterday's CMC, RGEM, EC etc gave that area a few inches. But the modeled cutoff has been very sharp and plenty of individual runs over the past few days (CMC, ICON, NAM, HRRR) gave nothing.

I expect flakes in the air in places like Sandy Hook, NJ and along the south shore of LI etc over the next few hours. Whether they accumulate is still unclear.

The issue is not surface dry air. It's 850mb - 700mb.

The SREFs were way too far NW yesterday, which they often are with coastal events. I don't recall the EPS showing an 8" mean and PHL. Maybe for one run with an extremely sharp cutoff? The EC did end up a little too far NW with precipitation... but I don't have access to the soundings to determine if the placement of features was too far NW or just the surface QPF.

Only the QPF parameter was off on the GFS. And that is the least accurate model parameter. If you simply used the 50% humidity at 700mb to mark the precipitation shield, it lined up very well with the EC and CMC/RGEM. In fact the EC might have been even further NW than the GFS. My appreciation for the GFS model has increased after this event, with the major caveat that its QPF parameter along the boundary with a cold, dry airmass cannot be trusted.

Doesn't really seem like an overachiever relative to modeling. Guidance was locked and loaded for that area (once it caught on) almost 2 days ago. But I guess it seems like an overachiever relative to expectations considering recent warmth and recent history.

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.