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Wintry January 3rd-6th, 2018 Winter Storm The ARCC/Xtreme Weather Special

I’m a bit concerned that we continue to get these favorable trends at H5 but the models continue to show the surface low east of where we expect it should be. They either need to get a clue or we do...are we missing something or are they really out to lunch? I mean, looking at the upper level pattern depicted on the Nam, I would expect the low and precipitation to be farther west.
 
Shawn said:
Haha the 3KM nam has NO idea what to do with the low. It bounces all over the place cause it cant figure out where to place it with that crud out in front. No worries. It's close to a coastal hugger this run, in reality.
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The reason the 12km NAM is doing this is related to its convective parmeterization, the Betts-Miller-Janic scheme which I discussed in detail on this forum several weeks ago. The net result of the BMJ scheme in the NAM is it creates spurious low-level vortices in the midst of very intense convective heating because the BMJ scheme was not intended for use in the extratropics (but is cost effective for the modeling community) and doesn't account for entrainment and downdrafts (which are important for extratropical convection), and fails to explicitly model convective feedback processes at each grid point like the Kain-Fritsch scheme does w/ a 1-D cloud model all of which are important for properly resolving extratropical convection. The 3-km NAM has boundary layer issues and the non-linear feedbacks between diabatic heating and potential vorticity generation are too strong and practically runaway in situations like this where deep convection is possible over a large geographic area. In some ways, what we're seeing in the large-scale in advance of this storm does remind me a little of what occurred preceding January 2000 but not everything is the same and our NWP models have come quite a ways since then. That doesn't mean the same adjustments can't occur (as we've seen time & time again in the short-medium range), perhaps we just see them a little sooner this time around instead of practically the night before...
 
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Rain Cold said:
I’m a bit concerned that we continue to get these favorable trends at H5 but the models continue to show the surface low east of where we expect it should be. They either need to get a clue or we do...are we missing something or are they really out to lunch? I mean, looking at the upper level pattern depicted on the Nam, I would expect the low and precipitation to be farther west.
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There is a lot of vorticity crap out in front on various modeling. Some say convective feedback, but its becoming apparent there could be some junk out there that screws us.
 
Nice moisture getting back to RDU. Nam is so wonky with it's precip on the NW side
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I'm 65 miles Inland from the Atlantic in Florence County. Have not seen a true coastal storm like what is being depicted in a long time or for that fact, in my lifetime. Was too young to remember the lead up and aftermath of the 89' storm.

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Rain Cold said:
I’m a bit concerned that we continue to get these favorable trends at H5 but the models continue to show the surface low east of where we expect it should be. They either need to get a clue or we do...are we missing something or are they really out to lunch? I mean, looking at the upper level pattern depicted on the Nam, I would expect the low and precipitation to be farther west.
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Yeah that’s why I said RDU to I-95 the sweet spot (based on what I was seeing at 500mb) and I was actually surprised at the behavior of the low after phase, would expect more over the coastal plain of NC than what’s depicted. It’s still the nam...ha


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Jon said:
Yeah that’s why I said RDU to I-95 the sweet spot (based on what I was seeing at 500mb) and I was actually surprised at the behavior of the low after phase, would expect more over the coastal plain of NC than what’s depicted. It’s still the nam...ha


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If you remove the likely spurious low-level vortices in the NAM offshore which interfere w/ low-level moisture transport, you end up w/ precip expanding (verbatim) well past the I-95 corridor into the eastern piedmont of NC
 
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Xtreme Weather said:
Yup this NAM done gone got carazzy... just have to wonder if the northern stream continues to come down quicker and catch the SW before it rounds the base and then phases. Oh wait this is the NAM we talking about LoL
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Most other guidance has trended towards this solution aside from the DWD-ICON & NAVGEM which were way NW of other NWP to begin with
 
As a kid in the late 90's eary 2000's I can remember several suprise lows come out of the gulf and crush my neck of the woods. Any analogs Webber?
 
With regards to Georgia, I conceivably could see the system trending enough NW to support snow from Forsyth south and Americus east. I don't think that Atlanta is completely out of the game yet, but this will most likely be confined to the Southern suburbs if it even makes it to the general area.
 
1300m said:
The way this is trending, I am not entirely sure this thing doesn't cutoff over GA before it's over. There is another trailing piece that is racing in like crazy at the end, and it too has been trending faster and faster. If that happens, we are looking at a Jan 2000 redux into an Arctic air mass.

namconus_z500_vort_us_fh69_trend.gif
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I agree it's still jumping the low. Maybe it's right, but for now, I doubt it. I could see this closing overnGA as well. Imho there should be more qpf inland as well over GA SC and NC
 
The more I look at old charts from Jan 2000's carolina crusher, the more the 00z NAM looks like it. Hm. THe ETA missed the precip shield inland, but could that have been because the extra vorticity out in front was there (just not modeled well in 2000) that threw it off?
 
As long as the vortices are bull I definitely think precip should be even further inland, but not sure how much there would be.
 
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