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Central PA - March 2013


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GEFS tighten up the northern edge a bit, so if you were north of the .75 line you might of lost some precip, if you were south of it you probably gained some, but the axis is the same from 18z and definitely better then 12z, especially along the mason dixon line.  Again GFS starting to hone in on the edge and tighten it up some , thats all

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Just watched the weather forecast from "up home" WTAJ with Steve Newton. Dude has 8-12 for southern parts of Blair, Huntingdon, Mifflin, Juniata and 12-18 for the southern tier. Seems like a bit of a ballsy call...

 

Wow, I just watched the forecast on the website. I don't remember the last time I saw WTAJ throw up numbers that big, they look SREF heavy..thats for sure. The accum zones in this part of central PA look similar to my map (WTAJ viewing area) in terms of placement, except my ranges are 1-3, 3-6, 6-10, and 10-15. I'm not really too worried about western areas in my map as I am about the eastern areas, and how much the precip manages to round the corner toward New England. I'm waiting for most of the rest of 0z guidance to make those tweaks in my map. 

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Yep. But definitely a step down from the 18z ensemble mean.

 

Yes, and also smooths out the northern feature...it won't be that broad with the gradient. The means do that because, well, they're means....and they broad stroke a tight gradient. Also keep in mind that this snow will fall on likely 8:1 ratios so 1" QPF means 8", .5" means 4" and so on.

 

Been a crazy day...and tomorrow will be crazier.

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Yes, and also smooths out the northern feature...it won't be that broad with the gradient. The means do that because, well, they're means....and they broad stroke a tight gradient. Also keep in mind that this snow will fall on likely 8:1 ratios so 1" QPF means 8", .5" means 4" and so on.

 

Been a crazy day...and tomorrow will be crazier.

 

I doubt ratios will be that poor up here in State College. We have elevation and cooler air aloft. As long as we aren't stuck with very light snow the whole time, we should be good for 10:1 up here, I would think.

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I doubt ratios will be that poor up here in State College. We have elevation and cooler air aloft. As long as we aren't stuck with very light snow the whole time, we should be good for 10:1 up here, I would think.

 

You're right...that far north. Sorry my brain is still stuck at work and focusing on the SQV from Selinsgrove south. 8:1 ratios near the M-D line. Better ratios farther north, but less precip. Catch 22.

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GFS shows .75 liquid for MDT been consistent.

 

And the SREFs were even higher than that. None of the guys are sold on the SREFS, but those members correlating above the mean (for THV, MDT, LNS) on the 21z via the SREF plumes are definitely grabbing my attention. The numbers we had tonight will likely be upped tomorrow. Today, I would rather have started low instead of jumping the gun and being too high. People understand if you increase your totals (and it adds some level of excitement as well) up to the event, but if you drop the totals, disappointment sets in and people react like the folks in the MA forum that live near Richmond

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And the SREFs were even higher than that. None of the guys are sold on the SREFS, but those members correlating above the mean (for THV, MDT, LNS) on the 21z via the SREF plumes are definitely grabbing my attention. The numbers we had tonight will likely be upped tomorrow. Today, I would rather have started low instead of jumping the gun and being too high. People understand if you increase your totals (and it adds some level of excitement as well) up to the event, but if you drop the totals, disappointment sets in and people react like the folks in the MA forum that live near Richmond

 

Yea that's the thing about the plumes in the southern Penn sites... the distribution is fairly even and there's not really anything outlying on the high side that would warrant eliminating to temper the mean. In fact THV's plumes have like 13 members at or ABOVE the mean of 15".. and only about 5 members with any kind of significant separation below that (ranging from 2-8"). It remains to be seen how they evolve the next couple runs and how they ultimately pan out, but man that is a strong signal from them for big snow. 

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What, no NAM map verbatim??  :snowing:

 

Well played on the conservative call.  You have lots more data to use by the time tomorrow evening rolls around.  What are your thoughts on banding across the southern tier?

 

In a situation like this, you can get a few interesting things happening...especially with a bombing surface low. A few things of note: watch where that 700mb low tracks. Generally speaking, the best VV's tend to be about 100km north of center with decent VV's about 50km on either side (I confirmed this with Dr. Scala tonight). In a CCB, there are usually several different deformation bands that set up and propagate away from the center of circulation. Much like ripples if you dropped a rock in a calm pond. You'll get these deform bands set up and where it's a crest in the ripple (pond analogy), that's where your best VV's are going to be. In the trough of the ripple, you get downward motion and can be detrimental to big snows. It's where these bands set up once they push away from the surface low that's the best bet. As the surface low deepens, more of these ripples will get pushed out until eventually it may form into one larger "ripple" which will likely set up as the main deformation band. That band will likely set up to our south (south of the M-D line or very close to it), but remember that there are sub-bands as well which can also put down good rates of snow. 

 

From what I can tell you from experience, it seems as though the QPF shield is usually larger than modeled, and that band can actually be farther N or NW of what is expected as well. Not saying it will happen here, but just saying what I've seen from experience..Anyone remember the blizzard last month in New England? Not much guidance suggested a deformation zone that far NW of the surface low. Just an example of a storm that developed completely differently than this storm will. Just something to watch out for.

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Euro has backed off on precip up here in central PA a bit. Still better than last night's 00z, but not quite as robust as today's 12z (which wasn't that robust anyway).

 

Yes, it's a bit further north with the coastal low, but that doesn't actually translate to higher precip up here on this run, unfortunately.

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Euro has backed off on precip up here in central PA a bit. Still better than last night's 00z, but not quite as robust as today's 12z (which wasn't that robust anyway).

 

Yes, it's a bit further north with the coastal low, but that doesn't actually translate to higher precip up here on this run, unfortunately.

 

Any qpf totals? Thanks for the clarification.

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About .4 for MDT and LNS, around half an inch for York and Philly. Precip isn't overly heavy in these locations, but kinda spread out a bit.

 

Hagerstown a little over 0.7. PIT,JST, and AOO are about 0.6", Latrobe closer to 0.7". The extremely sharp cutoff remains, with Clearfield and SEG around 0.1" and UNV around 0.16"

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About .4 for MDT and LNS, around half an inch for York and Philly. Precip isn't overly heavy in these locations, but kinda spread out a bit.

 

Hagerstown a little over 0.7. PIT,JST, and AOO are about 0.6", Latrobe closer to 0.7". The extremely sharp cutoff remains, with Clearfield and SEG around 0.1" and UNV around 0.16"

 

I guess then maybe I am .3. I am sticking with my 2 to 4. But the massive cutoff that developed north of 22 has me nervous.  

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Ok, here we go. My first call map.

post-1507-0-83360600-1362470676_thumb.pn

I will probably not be around until after the 12z suite is completely out later today, and I will get an update on this thing before it arrives.

Anyways, just saw the 03 SREFs.. and they have tightened a bit with near I-80 being literally the dividing line between low probs for 1+ to the north and likely to near certainty probs to the south. Also noteworthy was 4+ and 8+ prob bullseyes were just a bit further south. That could be significant in CTP's decision to upgrade watch products later this morning. I kept my 6 inch line infringing into the second tier of watch counties.. but model blend plus this slightly further south SREF probs lead me to think that CTP will be going advisory or holding watches til 12z for Cambria, Blair, Huntingdon, Juniata, and Mifflin counties at least. Perry and Dauphin are near that line too. Stuck with a general 6-10" for the southern tier counties and ran a 10-15" range in the southern Laurels and adjacent southern tier.

Eastern Pa remains very uncertain and I stayed pretty liberal with the 1-3 line getting to about AVP but didn't go crazy with any higher categories. SREFs supportive a high probability of 1+ but still look a little weak on higher probs. Couple that with how dry the Euro was up there and the GFS being drier and I think thats a pretty safe call at this point for that side of PA. That could easily change though and thus I will likely be making final adjustments late today.

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