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NYC/PHL: January 25-27 Potential Bomb Part 4


earthlight

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I'd say the best critical thickness value we may need to be looking at is the1000-700mb 2840 line with this storm. 850 zero line well displaced SE on the GFS run, while 1000-500mb ...540 line NW. Either way, surface temps may still only be marginal along the NJ coast to support mostly snow...even if GFS verified (which still may be biased slightly SE).

1000-850mb thicknesses look fine.The problem's at 850mb-700mb. In fact if the GFS was further west, that would be a raging sleet storm. I suspect the ensembles are similar in this respect but I dont have access to their upper level thickness values.

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One last thing. Most of the models a few days ago had the low running up the apps or atleast onshore....they 'locked' on for a few runs. Then they all had their solutions off the coast, except for the Canadian, which hasn't flopped. This has happened a few times this year and I expect the models try to get back to that 'locked' in position over the next few days. Odds are it won't make it all the way back, but far enough for what I called for in my previous post.

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1000-850mb thicknesses look fine.The problem's at 850mb-700mb. In fact if the GFS was further west, that would be a raging sleet storm. I suspect the ensembles are similar in this respect but I dont have access to their upper level thickness values.

Here is the GFS out to 84 hours at 700mb (red dashed line)...

post-3568-0-29372400-1295802627.gif

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1000-850mb thicknesses look fine.The problem's at 850mb-700mb. In fact if the GFS was further west, that would be a raging sleet storm. I suspect the ensembles are similar in this respect but I dont have access to their upper level thickness values.

BUFKIT sounding for 12z GFS at PHL looks fine. Starts as light rain due to a thin warm layer but quickly changes to snow with some wriggle room. Temps from surface to 850 are -1 to -3 colder above that.

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Spag. plots show many deep members NW of the OP but do not see any inland solutions. Close to the coast yes, but no apps runners so to speak. Can't wait for the individuals

925 temp charts show ne wind down the coast, which is good. Temps are at or below 0c on the blended mean. The only thing that looks a little warm is the thicknesses but its snow verbatum along the I-95.

12z ens mean looking more robust like the 0z from last night. Mean 300mb and 500mb trof slightly deeper, more amplified, and neg titled. The spread isn't huge, which gives moderate confidence. I think this comes in on the western end of the current range. Maybe halfway between 12z GFS and Euro. Probably a great track for places just inland with a elevation over 400ft.

Yeah temps are below 0 everywhere except briefly above at the surface. But it's warm above 850mb, hence the high thickness values, especially 850mb-700mb. Hard to complain about current GFS, GEFS, NAM positions.

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12z ens mean looking more robust like the 0z from last night. Mean 300mb and 500mb trof slightly deeper, more amplified, and neg titled. The spread isn't huge, which gives moderate confidence. I think this comes in on the western end of the current range. Maybe halfway between 12z GFS and Euro. Probably a great track for places just inland with a elevation over 400ft.

Yeah temps are below 0 everywhere except briefly above at the surface. But it's warm above 850mb, hence the high thickness values, especially 850mb-700mb. Hard to complain about current GFS, GEFS, NAM positions.

The 1000-700mb thickness, coupled with the marginal surface temperatures are problematic south and east of Philly.

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12z ens mean looking more robust like the 0z from last night. Mean 300mb and 500mb trof slightly deeper, more amplified, and neg titled. The spread isn't huge, which gives moderate confidence. I think this comes in on the western end of the current range. Maybe halfway between 12z GFS and Euro. Probably a great track for places just inland with a elevation over 400ft.

Yeah temps are below 0 everywhere except briefly above at the surface. But it's warm above 850mb, hence the high thickness values, especially 850mb-700mb. Hard to complain about current GFS, GEFS, NAM positions.

Well, with the deepening low and favorable wind positions, i think even the coastal plain will survive but accumulate is differnent. However, its January, its cold, we have snow pack, and snow begets snow.

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I think this storm ends up like storms that were typical in the 70's and 80's. A Gulf low that eventually tracks from Hatteras to the B/M but without HP in an ideal spot. The coast back to NE Jersey sees 2-4" followed by a 6 hour period of moderate rain that ends in a brief period of non accumulating snow. Further inland sees more in the way of snow but eventually mixes with or changes over to sleet and rain. Then the jackpot area of 6-12 encompasses extreme NW Jersey, the Poconos, northeastward on an arc toward the Tappan Zee including the Catskills. We haven't seen one of these in quite a while.

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Well, with the deepening low and favorable wind positions, i think even the coastal plain will survive but accumulate is differnent. However, its January, its cold, we have snow pack, and snow begets snow.

I agree. I think the boundary layer can stay near freezing with a nearly isothermal column even with a lot of low level WAA. It might depend on the precip intensity for coastal areas. With a weakening, southern stream wave and only modestly deepening surface low I definitely favor elevated areas. Stronger, closer surface low track could actually help produce snow IMO if low-mid levels don't get too warm. 800mb doesn't care it's January.

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I think this storm ends up like storms that were typical in the 70's and 80's. A Gulf low that eventually tracks from Hatteras to the B/M but without HP in an ideal spot. The coast back to NE Jersey sees 2-4" followed by a 6 hour period of moderate rain that ends in a brief period of non accumulating snow. Further inland sees more in the way of snow but eventually mixes with or changes over to sleet and rain. Then the jackpot area of 6-12 encompasses extreme NW Jersey, the Poconos, northeastward on an arc toward the Tappan Zee including the Catskills. We haven't seen one of these in quite a while.

Looking at the latest runs...I would definitely agree with this- makes sense right now.

Still could be a few surprise wrinkles though over the next couple days as the models resolve the shortwave interactions, which remail really complex at this point.

Frankly, I was pleasantly surprised the last 24 hours when the lead Nrn stream shortwave actually outraced the Srn wave to reintroduce a cold air source into the picture- definitely a pleasant change, and hopefully a good trend!

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I agree. I think the boundary layer can stay near freezing with a nearly isothermal column even with a lot of low level WAA. It might depend on the precip intensity for coastal areas. With a weakening, southern stream wave and only modestly deepening surface low I definitely favor elevated areas. Stronger, closer surface low track could actually help produce snow IMO if low-mid levels don't get too warm. 800mb doesn't care it's January.

no, 800 doesnt care, but the surface does, and 850 looks fine on the gfs, gefs, and nam. Its all speculation. so much time.

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I agree. I think the boundary layer can stay near freezing with a nearly isothermal column even with a lot of low level WAA. It might depend on the precip intensity for coastal areas. With a weakening, southern stream wave and only modestly deepening surface low I definitely favor elevated areas. Stronger, closer surface low track could actually help produce snow IMO if low-mid levels don't get too warm. 800mb doesn't care it's January.

This may be true many times, but 800 definitely comes into play in cases with marginal surface temps...

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This is def going to be the biggest thread the needle event this season, at least so far. At least we have the potential to see snow from this. A couple days ago everyone was so sure it would be a definite rainstorm over here, but now we could see some snow. Things are marginal at best though but the incoming high from the Great Lakes could really save us from a snow pack killer.

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no, 800 doesnt care, but the surface does, and 850 looks fine on the gfs, gefs, and nam. Its all speculation. so much time.

Right. That's why I worry about right at the surface for SE coastal areas and then between 800-900mb. If the mid-levels back around to the SE, things could warm up really fast. GFS is cold now because the surface track is way offshore.

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