eduggs

Glad the GFS joined the party. It actually looks a lot like the NAM. Still a late developer for everyone except maybe eastern Maine and the Maritimes. Still really good to see a semblance of consensus this far out.

Kind of immature and late developing mid-levels on the RGEM. Even on the much sharper NAM, the mid-levels haven't taken off by the end of the run. They look like they would really get going thereafter, but mostly for the benefit of eastern NE. The quick forward motion also limits the potential somewhat. Plowable would be more than acceptable.

The NAM has the vortmax further south than 18z at the end of the run and it's sharper. Nice run. That would lead to a snow event for most of the area. The limiting factors are the quick motion and the relatively undeveloped or late developing mid-levels. If the trof digs further south and matures sooner, the chances of significant snow increase, along with the possibility of mix, or even rain. Overall I think the guidance right now looks promising for snow on Friday - maybe even plowable.

I would maybe put the odds of a 3-6" storm somewhere in the NE at 50%. But the odds that our region will get that range is probably less. Most snow events don't work out from 4 days out. That doesn't mean it's not a decent snow threat... just that the likelihoods are always low until the short range.

Not great wave spacing on the 18z GFS. The best baroclinicity is offshore. That's not a great look. But the trof axis is nice as things stand, so it wouldn't take much of a sharpening of the trof to kickstart a more tucked surface system. Inter-model ensembles are still supportive of something. Unfortunately everyone is eager for a slam dunk biggie.

Maybe over 12"? Should be lots of 1 foot+ totals in SNJ.

Can you squeak out another .1" to get to 9"?

Interesting post. By their very nature, ensemble means will be more expansive at the edges than reality. One or two outliers can blur and mask the true sharpness of the gradient. That's probably part of the issue. But I wouldn't expect that to be so noticable at 12hrs. I think the handling of mid-level dry air may be an issue on the EC as well as the GFS (and maybe others?).

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.