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Wintry Potential Dec 13-14 Ice Threat

Webberweather53

Webberweather53

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Sleet City USA said:
God almighty CMC
zr_acc.us_ma.png
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Despite showing absurd ZR totals, I think the area affected by ZR on this CMC is a realistic threat zone for this event, at least for now. The US 1 corridor is probably on the outside looking in, towards Charlotte, Greenville-Spartanburg, & Greensboro this might be a close call, oth for the blue ridge escarpment and extreme W piedmont (Hickory, Wilkesboro, Mt Airy, etc), I’d feel halfway decent about my chances for some glaze Friday morning
 
Webberweather53 said:
Isentropic upglide over the CAD dome is usually hard for the globals to capture (& typically underdone on the models), don’t be shocked to see greater coverage of freezing drizzle or light ZR and perhaps some IP vs what’s currently being shown near the onset of this event.
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Can definitely see that signal on the gfs, obviously some frontogenesis on the mountains with WAA around the western piedmont/foothills with winds coming out of the SE at 850mb, those ingredients should allow spotty precip before the main stuff moves in like you said 1575914310776.png
 
euro is gonna probably barely show anything, but it did take a step towards more wintry by strengthening wave number 2 which speeds up precip and showing a stronger vortex, which acts as better confluence, this run is gonna be close tho
 
Myfrotho704_ said:
Can definitely see that signal on the gfs, obviously some frontogenesis on the mountains with WAA around the western piedmont/foothills with winds coming out of the SE at 850mb, those ingredients should allow spotty precip before the main stuff moves in like you said View attachment 27588
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Exactly. The key here with the earlier onset of even light precip driven by isentropic upglide and WAA vs what’s being modeled is that it establishes and reinforces the CAD dome sooner and generates corresponding low-level NEly flow that increases cold air advection over CAD favored areas faster than forecast. Processes like these are often overlooked but can mean the difference between mid 30s and rain vs near 30-upper 20s & ZR
 
SimeonNC said:
One thing I am noticing is a somewhat of a southern trend of the CAD high, all three globals now have it getting down to around the Mason-Dixon line before starting to move out, I am not sure but I think this could lead to a deeper CAD.
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Most likely it would lead to a stronger CAD and personally I am looking for models to trend the CAD stronger as we get closer.
 
don't really know why the models are trending to a high further south ? GFS does show a stronger trough in NE Canada, which would help, but the euro shows the trough more north, altho it was stronger, maybe @Webberweather53 can chime in ? gfs_z500a_namer_fh78_trend.gif
 
Ethan80963! said:
Most likely it would lead to a stronger CAD and personally I am looking for models to trend the CAD stronger as we get closer.
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The idea of a ~1040 HP being so far south despite it moving out quickly is what makes me think that the CMC isn't completely out to lunch with its p-type distribution.
 
CMC is believable if it's right about getting the precip in as quick as it's showing. It's the quickest model by far with getting precip into GSP/NC.

Euro - GFS - CMC valid 1am Friday morning

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Mods feel free to delete this but since all major models are now calling for at least some ZR in Western NC around 4-5 days out, I thought it would be appropriate to start the thread.

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In my opinion, I think with a strong high being so far south before moving out that the frozen precip field could be a bit wider, and with more areas close to VA seeing more in the way of IP than ZR. I do not expect nothing more than a minor glaze at the moment.
 
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SimeonNC said:
Mods feel free to delete this but since all major models are now calling for at least some ZR in Western NC around 4-5 days out, I thought it would be appropriate to start the thread.
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We can roll with it. I've just moved the relevant posts from the last page of the December thread over here.
 
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Myfrotho704_ said:
don't really know why the models are trending to a high further south ? GFS does show a stronger trough in NE Canada, which would help, but the euro shows the trough more north, altho it was stronger, maybe @Webberweather53 can chime in ? View attachment 27595
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The stronger trough over eastern/Atlantic Canada certainly doesn't hurt. I think some of the models are probably beginning to pick up on the meso high that develops in VA nearly superimposed onto fresh snow cover that'll be deposited earlier in the week from the anafrontal event to our north & west.
 
Our setup at day 3-4 is pretty much what you'd expect to see for a cold air damming/Miller B winter storm in NC with a minor, but very important caveats. This second s/w timing-wise is pretty close to ideal however the trough near Atlantic Canada is displaced further north & coupled to a +NAO. This suggests a more progressive pattern overall and favors "in-situ damming" & a transient surface high, which is basically what we're seeing in guidance lately.

If we had a deeper trough that dug equatorward more off Atlantic Canada, we'd be looking at a much bigger event.

North America NCEPR1 z500a NC Miller B Winter Storms (1948-2019).png
gfs_z500a_namer_15.png
 
Has the EPS ran yet? I wonder how many more members show an ice event now compared to the last run.
 
Just finished reading RAH’s afternoon disco. They sound pretty low key about the whole thing. They did note the faster arrival of precip depicted by the latest Euro, but still only mentioning “brief” freezing rain possibilities. I will say that they seem to have underestimated the strength of today’s wedge (not that it is directly relevant to Thursday-Friday). I hope the model trends continue in our favor because nothing’s better than watching RAH play catch up in the AFDs.
 
Lowtown said:
Just finished reading RAH’s afternoon disco. They sound pretty low key about the whole thing. They did note the faster arrival of precip depicted by the latest Euro, but still only mentioning “brief” freezing rain possibilities. I will say that they seem to have underestimated the strength of today’s wedge (not that it is directly relevant to Thursday-Friday). I hope the model trends continue in our favor because nothing’s better than watching RAH play catch up in the AFDs.
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Yeah I'm in Charlotte this week and it was supposed to get up to 58 degrees.. it's only 53 currently.. I think there will be ice as far south as Charlotte as long as it rains hard enough to drop the temperature. CADs are always forecasted too warm 8 outa 10 times.
 
GSP
As of 130 pm Monday: Thanks to the broadening and increasing upglide
flow atop the SE CONUS to start off the period, the influx of deeper
rh will give rise to developing widespread pcpn Thursday night. With
cold and dry conditions in place before pcpn onset, a period of
light freezing rain is still possible along and north of I-40. While
a light ice accretion is possible by daybreak Friday, and pronounced
in-situ/hybrid cold air damming will likely develop in response to
any falling precip, current guidance indicates that parent surface
high pressure will be in an unfavorable location to lock in sub-
freezing temps for any significant length of time. Thus, a quick
transition to rain is forecast by Fri afternoon.
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Sleet City USA said:
Looks a lot more widespread/futher south to me.
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NAM has a lot of looks like that last year, only not to pan out. Let’s see what other models keep showing with timing ( if they speed up any)
 
I’m a little confused about the QPF on some of the models. Maybe one of y’all can help me understand.... The storm looks to be fairly weak, right? Is it legitimately possible for us to get over 1” QPF with such a weak storm? The precip field on the NAM looks anemic. Do we have any factors that suggest this will be a “wet” storm relative to what would be expected for such a weak system? Thanks!
 
The ICON has more moisture this run and a better wedge with some places 3-4+ degrees colder than last run. Still needs some work though
 
Nam obviously has a cold bias. No way it’s that cold with that much ice. That would cause some problems


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Myfrotho704_ said:
Can definitely see that signal on the gfs, obviously some frontogenesis on the mountains with WAA around the western piedmont/foothills with winds coming out of the SE at 850mb, those ingredients should allow spotty precip before the main stuff moves in like you said View attachment 27588
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To add to this (as I mentioned on twitter) we also have orographic lift & the isentropic upglide is virtually perpendicular to the orientation of the CAD dome, basically all favoring an earlier onset of at least light precipitation. The lighter precipitation is usually what causes the most problems in these kinds of setups & is the hardest to predict.
 
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