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Pattern The Great December Dump

I definitely think western areas (**focus on foothills**) from the upstate through central VA should keep an eye on this one. Weak CADS / CADs with retreating strong highs / in-situ CADs have gotten the job done for those folks in the past. Especially with the cold/dry air mass initially in place.

For RDU folks, don't get your hopes up. These setups don't historically do well for us (as currently modeled). I would see this as a win if we get a little bit of sleet.
 
FallsLake said:
I definitely think western areas (**focus on foothills**) from the upstate through central VA should keep an eye on this one. Weak CADS / CADs with retreating strong highs / in-situ CADs have gotten the job done for those folks in the past. Especially with the cold/dry air mass initially in place.

For RDU folks, don't get your hopes up. These setups don't historically do well for us (as currently modeled). I would see this as a win if we get a little bit of sleet.
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Agreed...definitely foothills looks interesting.
 
It would be really nice if we could get the AO to go back negative. Looks like we may have a chance going into the end of the month. NAO dips back down to perhaps neutralish... Can't complain about that. The problem is the PNA goes way negative and that's an issue. We lose our western ridge. One of these days both the Atlantic and Pacific will play nice and we'll have some fun.

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Blue_Ridge_Escarpment said:
Another thing to watch is if a meso high starts to pop up in VA like the 6Z EPS just showed.
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FallsLake said:
I definitely think western areas (**focus on foothills**) from the upstate through central VA should keep an eye on this one. Weak CADS / CADs with retreating strong highs / in-situ CADs have gotten the job done for those folks in the past. Especially with the cold/dry air mass initially in place.

For RDU folks, don't get your hopes up. These setups don't historically do well for us (as currently modeled). I would see this as a win if we get a little bit of sleet.
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Aside from the stereotypical NWP biases w/ CAD, having snow on the ground all the way down into central & southwestern Virginia before this event unfolds definitely is a reason to be concerned about this busting cold for parts of the western piedmont & would raise the possibility of a meso high forming over VA.

I certainly agree areas like RDU are on the outside looking in, could be a close call for places like GSP, CLT, & GSO however.

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Last panel of the NAM...
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Ethan80963! said:
FWIW NAM looks better for the second system
View attachment 27568
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Yes. That trailing energy was much stronger and better oriented compared to 6z. You could see it very early in the run which gives it some more weight. If that can trend more over the next 24 hours, there would be an increase with the onset of precip and more of an icing threat for the CAD favored areas.
 
packfan98 said:
Yes. That trailing energy was much stronger and better oriented compared to 6z. You could see it very early in the run which gives it some more weight. If that can trend more over the next 24 hours, there would be an increase with the onset of precip and more of an icing threat for the CAD favored areas.
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I think it goes without even saying that the NAM is going to show a huge ice storm for the CAD areas in the next 24 hours then likely fade back to reality as we get to the short term NAM range. Seems like it does this every time. When it got in range of the early December storm last year, the first couple runs showed a major ice storm even down into the Midlands, then adjusted in the coming days.
 
The 12km NAM is really close to producing ice down in NE GA & SC at the end of the run w/ 33F & 32F rain at Atlanta and Augusta respectively.

namconus_T2m_eus_53.png

Dews in the mid-upper 10s over NC are far from ideal but could be just enough to get the job done for a little while esp with nearly optimal the diurnal timing being depicted here.



namconus_Td2m_eus_53.png







I don't think we're far from pulling the trigger on a thread for this, very curious to see what the RGEM shows.
 
packfan98 said:
Yes. That trailing energy was much stronger and better oriented compared to 6z. You could see it very early in the run which gives it some more weight. If that can trend more over the next 24 hours, there would be an increase with the onset of precip and more of an icing threat for the CAD favored areas.
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Looking on the NAM vorticity map. would you call that second wave a positive tilted storm?
 
Robert West said:
I think it goes without even saying that the NAM is going to show a huge ice storm for the CAD areas in the next 24 hours then likely fade back to reality as we get to the short term NAM range. Seems like it does this every time. When it got in range of the early December storm last year, the first couple runs showed a major ice storm even down into the Midlands, then adjusted in the coming days.
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I definitely never trust any model that is on an island by itself. At this lead time, I'm looking for trends at the 500mb levels and with the push of cold air from all models to glean any insights. It's a fun hobby...most of the time...
 
CADEffect said:
Looking on the NAM vorticity map. would you call that second wave a positive tilted storm?
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I would say that the energy is still slightly positive, but much better than the 6z run. However, the energy doesn't represent an entire trough axis like we usually associate with longwave patterns and Miller A storms. @Webberweather53 please jump in here if you want. I'm very much an amateur enthusiast.
 
I know @Myfrotho704_ did a excellent breakdown on skew-t plots and helped me out with some homework. It would be cool if someone could work and explain the vorticity maps as well.
 
Webberweather53 said:
The 12km NAM is really close to producing ice down in NE GA & SC at the end of the run w/ 33F & 32F rain at Atlanta and Augusta respectively.

View attachment 27573

Dews in the mid-upper 10s over NC are far from ideal but could be just enough to get the job done for a little while esp with nearly optimal the diurnal timing being depicted here.



View attachment 27571







I don't think we're far from pulling the trigger on a thread for this, very curious to see what the RGEM shows.
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The key is how long the high can push the cold and dry air south, and if it'll be enough. Direction seems to remain out of the NE for quite awhile so there isn't much of an issue there. It really can come down to just a degree or two. Last year seemed to be more up a degree or two here at least, but it's different every time. That is a strong high, but that's what it was last time. I'm sure 33 and rain will happen here again unless I see numerous models showing ZR for a bit.
 
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