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NYC/PHL Jan 11-14 Threat Potential Part 3


am19psu

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03z SREFs are not as wrapped up or deep with the surface low. Definitely not further "east" per se...but less amplified for sure. Surface low was sub 996 on 21z...around ~1000 or maybe a bit below on 03z.

its going to be interesting to see what the indiv runs look like. I wonder if there is some really wet solutions that skew it that way towards higher. Also, if there are some that give little and skew it that way while the vast are hits....

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I don't think anyone honestly believes the NAM's QPF forecast is correct, but it may have the general idea right in tucking the low closer to the coast with H5 closing off....the H7 low also has a beautiful track just south of LI which guarantees that everyone in the metro would see fairly heavy snow, although I do think locations like JFK and the immediate Jersey shore might be dryslotted slightly as the heaviest banding occurs over SW Connecticut through Westchester into the Bronx and N NJ. GFS seems to pull the H7 low away more quickly, which would be a negative for NYC and its NW suburbs but might actually help people in Long Island. I do believe the NAM's QPF is on crack, though; there's just not much precedent for such a wide area receiving nearly 1" liquid in 6 hours, especially with the surface low only deepening to around 990mb. So far, I like a compromise between the NAM and ECM where the heaviest banding yields 12-15" snowfall with most places in the 8-12" category, perhaps 6-10" a bit further SW.

These bands are always the wild card in dynamic systems like this, and numerous times the models smooth the QPF too much without maxing the areas with the heaviest bands enough. I was supposed to get more snow from most models on 12/26, but parts of eastern NJ beat me by up to 10" from the dynamic band that sat overhead. Same for 2/12/06 (although I wasn't here at the time).

When the low isn't bombing and it's mostly just overrunning, the banding signatures aren't as prevalent and it's more of a widespread mod-heavy snow that isn't as heavy as the bands present in a bombing low, but also without the mins surrounding the band. The models are coming closer to making it a dynamic system here and are moving away from a heavier overrunning storm that doesn't develop the banding until New England. The question is the track of the coastal and how much influence the primary holds. Again, we should get an idea soon, hopefully by 12z and the eastern models come back west to an extent. The NAM is likely overdone to be sure and is hard to trust given its wildly changing solutions yesterday. I just can't see the low crossing E LI and there being such a ridiculous band the way the NAM has it for so long. Verbatim we would rival 12/26's amounts for some of us and with such a fast moving low, it seems unlikely. But the available energy and also baroclinicity is definitely a possible reason to believe the globals are too flat and resolving something incorrectly. I think the "blended" solution, or a slightly west version of most globals sounds like the best way to go now. The models certainly blew their collective top very quickly when the Gulf energy and heat was taken into account and went from a suppressed nothing to a monster in a matter of 2 runs.

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does anyone think isentropic lifting/overunning precip is being underestimated by the models?

Not so much in this case, there is not enough of a high to the north, that occurs more frequently with SW flow type storms or can occur with coastals in the case where you have a 1030+ high over Maine or SE Canada...once again though in this storm VIRGA is not likely to be a factor with GFS/NAM showing 32/25 33/23 when precip arrives near 00Z Tue evening.

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it did the same at 18z then came back with the 0z...

The off hour NAM runs the last few years have been frequently putrid, it had a horrific 06Z run with yesterday's storm where it missed S NJ and E LI entirely with the snow only 12-18 hours out....both places got 4-7 inches in the end...I used to sort of put some faith in the NAM's 06 and 18 runs but now only the GFS ones do I really look at much.

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Euro ensembles essentially in agreement with the OP.

I don't usually make these posts..but my hunch is that this is going to end up nearer to the ECMWF or GFS solution. The NAM is absolutely notorious for doing things like this with these type of storms---I don't have the greatest feeling about the fact that it's going to pull off the coup here.

I like a more moderate solution similar to the Euro or Euro ensembles..which unfortunately for us means less dynamic snow..and more .5-.75" QPF amounts with higher on the island. The rapid cyclogenesis and CCB development will take place over Southern New England.

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Already some pretty large de-amplification differences on the NAM through 21 hours. Frustrating early morning if you want big snow :yikes:

Gotta give the gfs credit between this and the blizzard two weeks ago it's looking good.

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Euro ensembles essentially in agreement with the OP.

I don't usually make these posts..but my hunch is that this is going to end up nearer to the ECMWF or GFS solution. The NAM is absolutely notorious for doing things like this with these type of storms---I don't have the greatest feeling about the fact that it's going to pull off the coup here.

I like a more moderate solution similar to the Euro or Euro ensembles..which unfortunately for us means less dynamic snow..and more .5-.75" QPF amounts with higher on the island. The rapid cyclogenesis and CCB development will take place over Southern New England.

I'm thinking maybe a slightly more wrapped up solution than the GFS, maybe about what the Euro has now. Something just seems "off" to me with these weak models like the GGEM and maybe GFS in keeping it so flat despite the strong upper air support, and I think they have some catchup left. But that's still nothing like the ridiculously amped NAM from 0z.

A good range may be 6-12 for most of the area, maybe 8-14 out on Long Island. Still a borderline major snow event and definitely an awesome birthday gift from Mother Nature (my birthday is on Wednesday, should be another long day shoveling!!). :snowman:

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