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Dec 15-18 Arctic Front/Snow Thump/Meltdown to the Border


HoarfrostHubb

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3 minutes ago, Baroclinic Zone said:

Also could be something that keeps totals pretty uniform across the southern areas as opposed to the typical gradient.

It's almost like the initial stages of a weak coastal front. It's convergence there. It happened the other night in RI and adjacent SE MA. And then pretty good wedgy inland in the aftn.

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the FRH grid shows for BOS how lacking a blocking high pressure N really f*'s up a solid cold air mass...

what a fantastic turn-around that is... good lord! -17 C at T1 all the way to + 5 C in 30 hours, with less than .1" liq equiv during that transition.  Meanwhile, the middle boundary layer wind is all the way around to 150 degs at some 24 kts sustained... just fire-hoses the coastal plain..  

whatever snow falls in the meme-"thump" expectation would be very fleeting there, if the implication of what those numbers above are doing verifies.

as for the interior, ...different story between hours 48 and 54;  i see ALB's numbers being more typically playing out right up to I-495 or even I-95 over inland areas in this circumstance. the whole geographic region succumbs to southerly gradient so we sort of suffer the same fate there. as such... even though the wind will unilaterally turn around the dial (initially) and be south-ish, it seems there is enough isentropic differential between the air mass over the lower OV and what is in the interior up this way ...to force sufficient/proficient ascent.

in fact, the nam is the most robust of all models i've seen re the secondary/inverted trough closure beyond 54 hours. but, it appears to be doing so without more obvious known mechanics for Miller B in general..  i was wondering if it may have some convective feed-back going on with the initial pulse of elevated lift down over the m/a.  seems the mid/deeper layer flow is so fast over all that it's outpacing the the ability for the llv's to catch up. even though the air mass is moving S-N at low levels ... it's still dense and viscous. the nam seems to resolve that by spinning up the new low because the wind over the water immediately east of the coast is obviously less resistant... it's more like a purer mechanical circulation more so than having baroclinic thermodynamics involved. 

either way... should the nam succeed and that does close off as it move over or just se of the region, it will definitely delay the warm air arrival - after that it becomes a matter of how long. ...6 hours ...12... for ever... I don't think it would be forever, because eventually the pressure disontinuity moves off and there's really nothing to prevent the ageostrophic flow from just dying.. that would leave the area exposed and naked...defenseless against the onslaught of SSW flow fisting up the coast from the m/a. 

 

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Snowing again here in St. Johnsbury.  At 10 am I drove through a squall just south of town on 191.  Visibility was 1/10th of a mile at best for a couple of miles and there were a few spots visibility was 1/20 of a mile based on the mile markers which in that stretch are every .05 miles.

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1 hour ago, CoastalWx said:

4KM NAM also shows cold tuck potential in ern/NA MA after temps try to creep into U30s. Another hazard to watch.

Puts most of E MA from I-90 northward back below freezing late afternoon and early evening. That would be really nasty...you'd prob get a flash freeze with all the low level moisture hanging around....it could end up as 33-34F instead, but that is something that could be really dangerous actually if its like 28-30F like the 4km NAM shows.

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16 minutes ago, ORH_wxman said:

Puts most of E MA from I-90 northward back below freezing late afternoon and early evening. That would be really nasty...you'd prob get a flash freeze with all the low level moisture hanging around....it could end up as 33-34F instead, but that is something that could be really dangerous actually if its like 28-30F like the 4km NAM shows.

seems like it's been a while since we've seen a straight up BL resistance scenario... 

i was writing about that a little while ago .. .how this whole ordeal is like the mid level rage is out-pacing the ability for the llv to move in lock-step, so you end up with enhancing isentropic lift ... and hygroscopic feed-back... and viscous terminating seaward-related coastal 'fake' low but real enough to impart drain... all of it

all that is taking place amid the east striations of a straight S-N 'look' in the atmosphere.  very interesting scenario - 

Euro doesn't seem to be as 'on the same page' as these other meso tools which is a wonder too 

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