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NYC/PHL January 7-9 Potential Part Deux


NickD2011

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Here's DT's 1st guess Snowman.gif

Incredibly bold 1st guess. Isolated 16" totals in the hilltops for a 30hr event isn't crazy, but widespread 8"+ is ballsy.

Then again, minor modeled norlun events have dropped heavy accumulations on many occasions, and the signal for this event is way above minor. Even the GFS had several runs with a max area over .75 liquid. If people lowball their forecasts and then 1-2" per hour bands setup shop for 6 hours, everyone will look back and say we should have seen it coming.

As a counterpoint, the Euro doesn't usually miss so horrendously in the short term, and this would be a bad QPF underforecast. And nothing besides the NAM really supports this guess. Except intuition.

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Just because I'm cautious, I wouldn't go above 3-6" for anyone right now in the Tri-state until tomorrow. The setup and strength of that band will make forecasters insane until it's actually there. I'm happy though that models collectively seem to give us at least a couple or few inches. Also, Long Island might briefly torch on the easterly wind coming into the band. So 3-6" might be a reasonable call for the area. Plowable/shovelable but probably not more.

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Hurricane said 1-3" for Philly, 2-4" for Bucks and Trenton on N&E. NYC is included in 2-4" but remember he's just a Philly forecaster.

Very reasonable. If I were forecasting I wouldn't call for anything greater than 6" anywhere, with the higher range exclusively up towards the Catskills. I'd certainly wait for a better indication from the other globals, the SREFs, and the ensembles. Most likely I'd wait until viewing the upstream radar early Friday morning before making any increases to snowfall projections. 2-4 isn't peanuts.

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I think given the guidance and the fact that temps will be in the low-mid 30s on the easterly wind, 3-5 is a really good call for NYC/LI and coastal CT. The hudson Valley should do better because of the ratios being better, but yes, as someone said before, this is a marginal event for most.

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Just because I'm cautious, I wouldn't go above 3-6" for anyone right now in the Tri-state until tomorrow. The setup and strength of that band will make forecasters insane until it's actually there. I'm happy though that models collectively seem to give us at least a couple or few inches. Also, Long Island might briefly torch on the easterly wind coming into the band. So 3-6" might be a reasonable call for the area. Plowable/shovelable but probably not more.

I'm thinking similarly. Too early to say exactly where the hvy 6"+ band sets up and I do believe there will be one. We've still got 36 hrs of model trending ahead of us. I'm cool with letting the Hudson Valley take the jackpot w/ this one since I've still got snow cover here. All I ask for is a couple inches and then 2-3 feet next week, that's it.

My best guess at this point is the the NAM is overdone and the GFS underdone at the surface; probably go with a blend somewhere around 0.25-0.40" for most of the area.

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Like I said before, probably a general 1-3", but those who get within that heavier band will probably see 2-4/3-5". I don't see QPF higher than .5-.75 except on the Nam which is still inaccurate in this time range. I would split the gfs and nam and that's what we'll get. If the band does get going and in Norlun events, they tend to amp more up more than expected, than some local spots could get up to 8-9".

We won't know the exact details until probably late tomorrow, if not early Friday. In fact, I wouldn't be surprised if this ended up being a total now cast event either because of the complex and very rare setup.

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I'm thinking similarly. Too early to say exactly where the hvy 6"+ band sets up and I do believe there will be one. We've still got 36 hrs of model trending ahead of us. I'm cool with letting the Hudson Valley take the jackpot w/ this one since I've still got snow cover here. All I ask for is a couple inches and then 2-3 feet next week, that's it.

My best guess at this point is the the NAM is overdone and the GFS underdone at the surface; probably go with a blend somewhere around 0.25-0.40" for most of the area.

Hudson Valley will definitely be cooler than we'll be, and they seem to get as much banding as any of us. But there is quite a signal there for an inverted trough/norlun band developing, and those can defy all expectations if they really access the available instability. I'm pretty sure the Nam has to be overdone, but someone can certainly see an impressive snowfall max where the band sits. The 15" over western Suffolk on the NAM is insane, but maybe 8-10" isn't.

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Hudson Valley will definitely be cooler than we'll be, and they seem to get as much banding as any of us. But there is quite a signal there for an inverted trough/norlun band developing, and those can defy all expectations if they really access the available instability. I'm pretty sure the Nam has to be overdone, but someone can certainly see an impressive snowfall max where the band sits. The 15" over western Suffolk on the NAM is insane, but maybe 8-10" isn't.

12/13/88 was insane. Areas just to the west of the trough axis are going to get clocked. Ratios will not be a problem in those areas.

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Looks like it could be a mesoscales vs. globals battle shaping up for the impact and extent of this band's impact on the area. 0z RGEM looked wetter than 18z did and had the same impact area as the NAM generally. I wouldn't really buy the GGEM (performed atrociously on the last storm) but the GFS and Euro dragging the jackpot area to the north into SNE might be something to pay attention to.

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Looks like it could be a mesoscales vs. globals battle shaping up for the impact and extent of this band's impact on the area. 0z RGEM looked wetter than 18z did and had the same impact area as the NAM generally. I wouldn't really buy the GGEM (performed atrociously on the last storm) but the GFS and Euro dragging the jackpot area to the north into SNE might be something to pay attention to.

The mesoscale models will own this event. I'm not jumping head first for the NAM QPF from tonight, but if its still there at 12z, I'm onboard.

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The mesoscale models will own this event. I'm not jumping head first for the NAM QPF from tonight, but if its still there at 12z, I'm onboard.

The biggest problem for me personally is the SREF not agreeing with the NAM...they are mesoscale models too. As I replied to Yehuda, I do not envy the forecast there...it seems like there is high bust potential. Its actually not an easy forecast up here either, but I think the lower Hudson Valley forecast is harder in this setup. There is almost certainly going to be an inverted trough initially there, but the question is how quickly it shifts to the northeast.

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The biggest problem for me personally is the SREF not agreeing with the NAM...they are mesoscale models too. As I replied to Yehuda, I do not envy the forecast there...it seems like there is high bust potential. Its actually not an easy forecast up here either, but I think the lower Hudson Valley forecast is harder in this setup. There is almost certainly going to be an inverted trough initially there, but the question is how quickly it shifts to the northeast.

Yup, exactly. The associated snow band develops across parts of NJ and Pa initially (or even slightly SW of there) before shifting northeast and actually tilting counterclockwise a bit. Thereafter NAM holds it basically in place from LI through the western Catskills but the GFS, GGEM, and Euro shift it northeast. I can recall cases where the banding moved and cases where it was stubbornly anchored in place.

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Yup, exactly. The associated snow band develops across parts of NJ and Pa initially (or even slightly SW of there) before shifting northeast and actually tilting counterclockwise a bit. Thereafter NAM holds it basically in place from LI through the western Catskills but the GFS, GGEM, and Euro shift it northeast. I can recall cases where the banding moved and cases where it was stubbornly anchored in place.

I agree. The fact that the rest of the models want to shift the heavier QPF axis into SNE is something to be cautious about. That plus it's almost impossible for me to trust the NAM on anything more than 24 hours out. When the MM5 comes into its accurate range tomorrow, that'll be something to pay attention to also. It totally nailed the last storm to a tee in obliterating E NJ.

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