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January 6th-7th Potential Storm

SimeonNC said:
Yeah I've noticed that the models are really quick to erode the CAD, even the RGEM.

Also, you know more than me but I feel like the HP in Canada makes this more of a hybrid thab in-situ
Click to expand...
This is from GSP
Meanwhile, the remnant high
pressure to the east sets up an in-situ wedge of colder air ahead of
the precip. How much cold air remains in place at the onset of
precip is not entirely certain, but should be enough to allow for
near freezing temps well before daybreak.

Im not a good teacher but here's a rundown. In-Situ CAD setup is one in which little or no cold air advection is occurring because the high pressure center which we relied on in the classic setup is too far to the south. Cold air is established through evaporational cooling caused by a pool of dry air east of the Appalachians.
 
SNOWMANN said:
This is from GSP
Meanwhile, the remnant high
pressure to the east sets up an in-situ wedge of colder air ahead of
the precip. How much cold air remains in place at the onset of
precip is not entirely certain, but should be enough to allow for
near freezing temps well before daybreak.

Im not a good teacher but here's a rundown. In-Situ CAD setup is one in which little or no cold air advection is occurring because the high pressure center which we relied on in the classic setup is too far to the south. Cold air is established through evaporational cooling caused by a pool of dry air east of the Appalachians.
Click to expand...
Thanks
 
GSP gets that typically models tend to underestimate the CAD and relying on the cold biased ones. Can’t say I’m surprised tbh. East Flat Rock, Chimney Rock, and especially Saluda, Tryon, and Landrum do exceptionally well in these setups. I’ve seen plenty of times these last 3 years where I get a Trace to a tenth of inch and 10 minutes up the road in Tryon they’re sitting at a qtr to a third of inch. And Saluda will be sitting at half an inch plus.
 
zr_acc-imp.us_ma.png
 
Cad Wedge NC said:
Dews will only tell part of the story, You have to look at wet-bulbs if you want a true comparison.
Click to expand...
I'm going to pay very close attention to not only where DPs bottom out during the evening but also do they rise as fast as the NAM is showing as precip approaches. If in reality we are sitting in the mid to upper teens for dews that evening vs the low 20's and generally hold to the low 20's as precip arrives, I think there's a solid chance at some icing. Also paying attention to where the temps are sitting around 10pm. Are we sitting around 33-35 with Dews in the low 20's or are we sitting in th mid to upper 30's range? Noway to know until tomorrow night.
 
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First call Map. I went with something closer to GSP's thinking. Feel confident that Brevard, Hendersonville, Saluda, Tryon/Landrum, Chimney Rock get a pretty significant icing event. Saluda takes the cake for holding onto low level cold air. I think the high country gets close to 0.25" and the French Broad River Valley ends up with a solid 0.1"+. The escarpment probably gets a legit ice event out of this. Areas to the west and south are the question marks. The foothills I think have a good shot for as much as 0.25" but at least 0.1". The northern upstate (especially along and north of 85 and east of highway 25) get some icing, but how much is really up in the air. Could be a trace, could be enough to cover the tops of tree, could be more. Just south of 85 through the piedmont probably end up with a trace with areas further north getting up to a tenth of an inch.

Like I said above areas along the border and the piedmont it's really a nowcasting type of thing. If the CAD is being underdone and you get a footprint and higher icing like the CMC/RGEM/CAMS. If we're sitting around 10pm with DP in the upper 20's and temps in the mid 30's similar to the NAM/3K/HRRR, then yeah don't expect much if any ZR. Really is a waiting game around this way.
 
Ice forecast. This looks mainly like a foothill/escarpment deal. Cities in the Piedmont/upstate could get a quick glaze for a hour or so then a quick flip to cold rain, areas like hickory will probably stay ZR for a bit longer as usual, and the escarpment might struggle to get above freezing until late morning/lunchtime B5766308-5F6B-43F0-95C5-DA134E302418.jpeg
 
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