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January 7th/8th Storm Discussion


TauntonBlizzard2013

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Just now, ORH_wxman said:

The 12z models overall have been a little more bullish, so I'm sure they'll bring the higher amounts a bit west. Plus, the synoptics in general argue for good snows along the QPF gradient.

Just seems like they hastily threw out that graphic to get the word out to the public.

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i wonder how they generate those snow charts. 

experience with this sort of thing is that you get higher totals closer to the absolute cut-off to nil.   yet that product smears it out over some 80 mi of gradually diminishing totals. 

i suspect it's like 4-6" then down to 1" along a 10 mile wide axis along the nw arc - where that aligns, who knows.  but these parallel bands that drop of so neatly and orderly doesn't seem to happen in these types of 'needle thread' scenarios.  

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I mentioned this to Will last night ... when the 500 mb evolution of the 00z UKMET showed something similar (though back many naut miles SW).  We speculated then that although the 00z UMKET looked really tasty as the trough was turning form neutral to slightly negatively tilted over the longitude of the Tennessee Valley, that the small 'blob' of vorticity it was depicting off the Carolina coasts might get exaggerated as the primary mechanical forcing for surface low development.  

Below is the 12z RGEM panels for hour 36.  I have annotated it to help elucidate those concerns... I tend to like the RGEM model, but this depiction below really ... I hate to say but it smacks as though it is picking the wrong perturbation(s) in the atmosphere as it's impetus for its surface development. 

RGEM.jpg

 

I could see one of two things happening here... One, sometimes the convection does "rob" and whisks things prematurely seaward, but often those are proven false in the guidance. That could correct a short (like < 24 hours to almost having to now-cast) the surface evolution farther west to where there is a truck load of better forcing associated with strong DPVA moving west of the perceived center.  

In simpled terms, the surface wave looks too far separated from the main jet dynamics; the reason, may be in part what's called convective feedback. 

The other thing that may happen is that the baroclinic axis really is way out there and this thing really is riding up that far west of the lower level boundary... That would cause a very vertically tilted sheared system, and you would see the W side of the activity expand (oblong) associated with IVT. 

I would also enter that if a solution like that above took place, you'd almost have to have some sort of Norlun expression while that mlv sucker roared through just SE of SNE.

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1 minute ago, Typhoon Tip said:

I mentioned this to Will last night ... when the 500 mb evolution of the 00z UKMET showed something similar (though back man naut miles SW).  We speculated then that although the 00z UMKET looked really tasty as the trough was turning form neutral to slightly negatively tilted over the longitude of the Tennessee Valley, that the small 'blob' of vorticity it was depicting off the Carolina coasts might get exaggerated as the primary mechanical forcing for surface low development.  

Below is the 12z RGEM panels for hour 36.  I have annotated it to help elucidate those concerns... I tend to like the RGEM model, but this depiction below really ... I hate to say but it smacks as though it is picking the wrong perturbation(s) in the atmosphere as it's impetus for its surface development. 

RGEM.jpg

 

I could see one of two things happening here... One, sometimes the convection does "rob" and whisks things prematurely seaward, but often those are proven false in the guidance. That could correct a short (like < 24 hours to almost having to now-cast) the surface evolution farther west to where there is a truck load of better forcing associated with strong DPVA moving west of the perceived center.  

In simpled terms, the surface wave looks too far separated from the main jet dynamics; the reason, may be in part what's called convective feedback. 

The other thing that may happen is that the baroclinic axis really is way out there and this thing really is riding up that far west of the lower level boundary... That would cause a very vertically tilted sheared system, and you would see the W side of the activity expand (oblong) associated with IVT. 

I would also enter that if a solution like that above took place, you'd almost have to have some sort of Norlun expression while that mlv sucker roared through just SE of SNE.

Well, the there has been evidence of an IVT, so perhaps the latter is correct

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7 minutes ago, #NoPoles said:

Well, the there has been evidence of an IVT, so perhaps the latter is correct

Possibly ... 

Brian mentioned a couple days ago in some post .. how usually an IVT in a middle range turns out to either be closer to where the low turns out to be, or... it just doesn't verify too well. 

This is similar... perhaps.  I've noticed that about middle range guidance tendencies as well...they tend to develop IVT as an artifact for having the wrong track for the low in the first place; model has all this dynamic forcing west of the low so it develops (mechanically) an IVT there instead.  ...it's that sort of ordeal.  But then as it comes into nearer term focus the model sans the east track and just develops it where it should have in the first place.   Boom - west correction in near terms. 

Could happen here...not sure.. .But, there are valid reasons to question some of those tracks that are way out at sea like that. 

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