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NYC/PHL Potential Jan 11-14 Event Discussion Part Two


NickD2011

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He'd do better than 10-1 dude...GFS shows sub 528 thicknesses over eastern PA and he's got a ton of elevation. He's probably looking at 4-8" easily on this run, potentially more. I'd imagine ratios would be around 12:1 here in Westchester County with 15:1 in the mountains of eastern PA.

The Norlun event Friday had nearly 20:1 ratios in CT.

The only problem for Hazelton will be if the low shifts east a little bit and they end up on the outskirts of the main banding, where snow is not as steady.

Its not valid to assume greater than 10:1 ratios based simply on temperature and elevation. Dynamics are much more important. During 12/26 ratios under the superband were 14:1 or so, but just west in the screw zone of west-central and NW Jersey, it was only 10:1. Wind and poor dynamics killed our ratios.

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No one knows the exact QPF for the storm yet, obviously....but there's a big difference in coastal climatology regarding ratios and climatology in the Poconos. My family has a house in extreme NE PA at 1500' elevation where I've spent a ton of time, and snowstorms are often much fluffier there with surface temperatures being colder than NYC by about 10F in winter, as well as elevation enhancement on most wind directions from the start of the Allegheny Plateau. You can't use 10:1 ratios for the Poconos as they often bang out way more. This looks like a fairly cold storm to me, just a shade warmer than 12/26, with NYC probably in the mid 20s and the Poconos in the upper teens to low 20s.

To reiterate: Surface temps have little to nothing to do with ratios.

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To reiterate: Surface temps have little to nothing to do with ratios.

I was really surprised at the orientation of the snow on the clown maps from tonights 00z GFS run. I was definitely expecting more snow back towards the Island and shore. Probably struggling w/ the boundary layer.

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03z SREF's are still concerning to me. They are driving the primary very far north so that the CCB is going to have serious trouble developing fast enough for our area..it then becomes an issue for the more heavy snowfall amounts.

Remember last nights 06z NAM and DGEX were developing the CCB as the primary strengthened off the M/A coast. This is now occurring much further north because the primary is stronger on today's models.

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To reiterate: Surface temps have little to nothing to do with ratios.

It's not just about surface temps...he's going to have colder 850s, some elevation enhancement too. Obviously the ratios are dependent on the dynamics of what banding reaches him, but it's certainly fair to assume he's going to receive a higher ratio at 1500' in PA than at JFK.

And a warm BL can certainly affect the ratios because then you tend to get a lot of aggregate flakes and wet snow that melts easily and doesn't really accumulate...particularly when we're talking about a city with tons of pavement versus the rural mountains.

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I was really surprised at the orientation of the snow on the clown maps from tonights 00z GFS run. I was definitely expecting more snow back towards the Island and shore. Probably struggling w/ the boundary layer.

The clown maps always have the boundary layer cut-off near the coast so seems sort of irrelevant what they show. They seem to think I'm going to mix on an event that's clearly 100% snow.

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00z Euro ensembles are still a nice hit..but initially a bit less amplified than 12z. The surface low still tucks in underneath the Cape at 84 hours. They are developing a good CCB signal back as far west as TTN, hooking southeast towards the Central NJ coast..and then northeast towards New England, encompassing NYC..SE NY..LI..CT..etc.

They look pretty similar to the GFS but the CCB signal stretches back a bit further southwest. Nothing really dramatic, just noticeable since it affects our specific area.

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00z Euro ensembles are still a nice hit..but initially a bit less amplified than 12z. The surface low still tucks in underneath the Cape at 84 hours. They are developing a good CCB signal back as far west as TTN, hooking southeast towards the Central NJ coast..and then northeast towards New England, encompassing NYC..SE NY..LI..CT..etc.

They look pretty similar to the GFS but the CCB signal stretches back a bit further southwest. Nothing really dramatic, just noticeable since it affects our specific area.

Do you know what the QPF is for NYC metro?

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Yes, the best picture describes a thousand words is see what happened at Belmar on 12/5/03 and compare it to what occurred at JFK or Staten Island....that epitomizes these sort of systems.

Crazy gradient where the mix line stayed south of us by about 5 miles for the first day of the storm and being so close to the mix line gave us enhanced snowfall rates. When it got colder for the second day of the storm, the snowfall rate actually got lighter!

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Looping through the last few runs of the SREF, there are definitely some poor trends there to keep the primary strong and develop the CCB later as a result. I would definitely watch out for this on tomorrows guidance suite. We will see how it unfolds tomorrow!

It might just be the NAM members screwing up the mean, since the GFS wasn't anywhere near as bad as the NAM in that regard. Who knows, but IMO the primary holding on too long is the biggest possible downside to this event right now for us. It not only keeps the coastal from taking over, but it also roars warm air in aloft. Other models aren't really showing this trend and the Euro actually weakened the primary, so it might just be the NAM hiccupping like it usually does.

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It might just be the NAM members screwing up the mean, since the GFS wasn't anywhere near as bad as the NAM in that regard. Who knows, but IMO the primary holding on too long is the biggest possible downside to this event right now for us. It not only keeps the coastal from taking over, but it also roars warm air in aloft. Other models aren't really showing this trend and the Euro actually weakened the primary, so it might just be the NAM hiccupping like it usually does.

NAM is not a medium-range synoptic model and thus shouldn't be used for this storm right now.

That being said, I am watching the 6z NAM roll out arrowheadsmiley.png

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It might just be the NAM members screwing up the mean, since the GFS wasn't anywhere near as bad as the NAM in that regard. Who knows, but IMO the primary holding on too long is the biggest possible downside to this event right now for us. It not only keeps the coastal from taking over, but it also roars warm air in aloft. Other models aren't really showing this trend and the Euro actually weakened the primary, so it might just be the NAM hiccupping like it usually does.

Looking back over the posts from last night, I see there was an absurd amount of panic that ranged the full spectrum-- from p type issues to dry slot to people getting upset if we got "only" 4-8 inches.... crazy stuff lol.

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NAM is not a medium-range synoptic model and thus shouldn't be used for this storm right now.

That being said, I am watching the 6z NAM roll out arrowheadsmiley.png

LOL-I know it's barely worth the bandwidth used to make it, but it's still cool to watch, and hopefully win from.

I'm glad the Euro and ensembles held firm-that's what I really stayed on for. The GFS and Euro ensembles have really been rock solid with the event for days now.

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LOL-I know it's barely worth the bandwidth used to make it, but it's still cool to watch, and hopefully win from.

I'm glad the Euro and ensembles held firm-that's what I really stayed on for. The GFS and Euro ensembles have really been rock solid with the event for days now.

Im still worried about dryslot issues (not as much about p-type), but not enough to lose sleep over it.... 1 inch of qpf would be a pretty big deal for us, and it looks like both show about that much.

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Im still worried about dryslot issues (not as much about p-type), but not enough to lose sleep over it.... 1 inch of qpf would be a pretty big deal for us, and it looks like both show about that much.

Heh, losing sleep's already a done deal for me bud. :lol:

You must be p'oed that this event looks to almost entirely be at night?

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Heh, losing sleep's already a done deal for me bud. :lol:

You must be p'oed that this event looks to almost entirely be at night?

Yea a little lol, although our local news guys are still saying "heavy snow persists thru wednesday afternoon" :whistle: They always say stuff like that though-- and the next thing you know, the sun comes out early.

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