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Wintry February 19-21, 2020 Winter Storm

Bsud said:
The NAM doing what it does best in these setups, Picking up on the colder air.
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What’s yours thinking on upstate sc. I’m leaning towards a quick burst of snow before moisture is cut off. The coastal low will takeover giving ne sc and coastal nc a good snow


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Jessy89 said:
What’s yours thinking on upstate sc. I’m leaning towards a quick burst of snow before moisture is cut off. The coastal low will takeover giving ne sc and coastal nc a good snow


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I could see upstate getting an inch or 2 similar to the last storm. I think the upstate could see more CAD than what's being modeled and also colder Thermals as that's what I'm thinking the NAM is picking up on
 
Wakefield says... maybe?
90288815160a08d17f9e55e6898dd53f.jpg
 
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i know it is the kiss of death to say but temps don't really concern me atm (at least here in clt). i think the main inhibiting factor is precip and if we get the models to finally get sig precip northward i think we will see a run go from trace amounts to a 2-3" system in short order as the upper levels are plenty cold and the warm sfc layer is shallow. should be a fun week, especially watching to see if the NAM leads the way.
 
The thermals for the upstate actually look decent especially since the moisture will be coming in around 1-3 pm. The warm layer is VERY thin. There's normally more moisture with these setups and you can see the CAD starting to funnel in as well so places from Greenville east to around Rock Hill in the Upstate I think will have even more cold air than others. If this sucker can slow down and not come in until 3-6 pm and this is REALLY going to get interesting in the upstate.
 
iGRXY said:
The thermals for the upstate actually look decent especially since the moisture will be coming in around 1-3 pm. The warm layer is VERY thin. There's normally more moisture with these setups and you can see the CAD starting to funnel in as well so places from Greenville east to around Rock Hill in the Upstate I think will have even more cold air than others. If this sucker can slow down and not come in until 3-6 pm and this is REALLY going to get interesting in the upstate.
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I’d rather it come in after dark but that’s not happening


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Webberweather53 said:
Even though it's the long range NAM which isn't always exactly reliable & while there isn't any precip falling in the model (yet) over NC, when you see low-mid level warm advection (warm colors) like that with frontogenesis (contours) superimposed over the dendritic growth zone (locations where it's -10C to -20C), there's a pretty strong case to be made that we could see some significant moderate-heavy banded precipitation w/ this storm, the only hinderance to this being that the low-levels will initially be pretty dry. However, I think if this 700mb temp advection & frontogenesis forecast generally verified, there would be more than enough forcing for ascent to easily overcome it.

Now that we've started to settle in on a pattern that'll be generally conducive to overrunning, this is definitely the type of storm that usually overperforms and trends wetter & further north down to the very last second.

View attachment 34857
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While a somewhat extreme case, the big winter storm earlier this month in GA & SC is another great case study of an overperforming overrunning event.

Notice the warm advection (shading) over north Georgia around the time light precipitation was forecast by most global models, we obviously know how that panned out.

The big key takeaway I want everyone to notice in the huge bust earlier this month is that this warm advection and modest frontogenesis was modeled in the portion of the troposphere where snow growth occurs in clouds (the dendritic growth zone (DGZ)), which corresponds to where temperatures are between roughly -10C and -20C (pay attention to the blue contours and the corresponding labels).

EQRODYXX0AcWCrX.png



Now revisit this LR NAM forecast.

Notice not only that the warm air advection (warm colors) is stronger, but there's also a ton of frontogenesis (or the enhancement/creation of fronts in purple contours) that wasn't present in the setup earlier this month in GA & SC. This argues for even more forcing for ascent & thus the potential for even heavier precipitation to be realized around I-40 corridor in NC & TN (Nashville - Knoxville - Greensboro - Raleigh/Durham) where 700mb temps are around -10C to -20C.


Keep a close eye on these subtleties in this setup going forward because they could become quite meaningful if we play our cards right the next few days.


namconus_temp_adv_fgen_700_seus_53 (1).png
 
Haven’t been following much as this is not favorable for a winter storm out this way in terms of getting heavy rates or much moisture. With that said, if coastal low gets going then those down East could see a winter storm, mostly East of Raleigh but could clip that area too. Snow showers will be fun to see tho and remain poss here and for many across NC with little to no accumulation.
 
Webberweather53 said:
While a somewhat extreme case, the big winter storm earlier this month in GA & SC is another great case study of an overperforming overrunning event.

Notice the warm advection (shading) over north Georgia around the time light precipitation was forecast by most global models, we obviously know how that panned out.

The big key takeaway I want everyone to notice in the huge bust earlier this month is that this warm advection and modest frontogenesis was modeled in the portion of the troposphere where snow growth occurs in clouds (the dendritic growth zone (DGZ)), which corresponds to where temperatures are between roughly -10C and -20C (pay attention to the blue contours and the corresponding labels).

View attachment 34862



Now revisit this LR NAM forecast.

Notice not only that the warm air advection (warm colors) is stronger, but there's also a ton of frontogenesis (or the enhancement/creation of fronts in purple contours) that wasn't present in the setup earlier this month in GA & SC. This argues for even more forcing for ascent & thus the potential for even heavier precipitation to be realized around I-40 corridor in NC & TN (Nashville - Knoxville - Greensboro - Raleigh/Durham) where 700mb temps are around -10C to -20C.


Keep a close eye on these subtleties in this setup going forward because they could become quite meaningful if we play our cards right the next few days.


View attachment 34863
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How about the 850 fgen? The nam last time looked intense for us down here and is insane looking at 6Z further south. However now that I look at the models and compare, does it haveto do with DGZ location?
 
ForsythSnow said:
How about the 850 fgen? The nam last time looked intense for us down here and is insane looking at 6Z further south. However now that I look at the models and compare, does it haveto do with DGZ location?
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The key to maximizing your chances for heavy precip and overperformance with an overrunning event is to have the sloped frontogenesis intersect the DGZ. Intense 850mb frontogenesis below the DGZ increases the frequency of “warm rain” processes/collision-coalescence in clouds that’s both less effective at generating hydrometeors (and thus precipitation) & snow compared to the Bergeron process in mixed phase clouds.

It honestly still doesn’t technically hurt you to have intense FROGEN and significant warm advection 850mb, but you would much rather see that higher up in the troposphere over your locale.
 
Webberweather53 said:
The key to maximizing your chances for heavy precip and overperformance with an overrunning event is to have the sloped frontogenesis intersect the DGZ. Intense 850mb frontogenesis below the DGZ increases the frequency of “warm rain” processes/collision-coalescence in clouds that’s both less effective at generating hydrometeors (and thus precipitation) & snow compared to the Bergeron process in mixed phase clouds.

It honestly still doesn’t technically hurt you to have intense FROGEN and significant warm advection 850mb, but you would much rather see that higher up in the troposphere over your locale.
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For those learning the "DGZ" area Eric is speaking of is where the snowflakes form in the atmosphere. Think of it as a cold area in the upper atmosphere that allows the formation of snowflakes. If you are adequately saturated with moisture in that zone, and get enough heavy snowflakes falling out of that zone, the rest of the atmosphere to the surface can cool down quickly in a heavy burst.
 
I know it may be a taboo thing to do but I like to pinpoint unfavorable locations vs favorable locations that many can use nearby in storm events. My unfavorable spots would be Morganton, Lenoir, Shelby and Mount Airy. My favorable would be Rocky Mount and Roanoke Rapids.
 
Until we actually see it otherwise, I would not bet against having the precip here in central NC. We have had rain every week here since November. The precip hasn't been the problem. Until we actually see that wet pattern broken, then I would count on plenty of precip around.
 
even if we see the 84hr nam look anemic with moisture i wouldn't get too worked up or throw in the towel, nam will likely have some sig shifts in precip even inside 36hrs.
 
Webberweather53 said:
While a somewhat extreme case, the big winter storm earlier this month in GA & SC is another great case study of an overperforming overrunning event.

Notice the warm advection (shading) over north Georgia around the time light precipitation was forecast by most global models, we obviously know how that panned out.

The big key takeaway I want everyone to notice in the huge bust earlier this month is that this warm advection and modest frontogenesis was modeled in the portion of the troposphere where snow growth occurs in clouds (the dendritic growth zone (DGZ)), which corresponds to where temperatures are between roughly -10C and -20C (pay attention to the blue contours and the corresponding labels).

View attachment 34862



Now revisit this LR NAM forecast.

Notice not only that the warm air advection (warm colors) is stronger, but there's also a ton of frontogenesis (or the enhancement/creation of fronts in purple contours) that wasn't present in the setup earlier this month in GA & SC. This argues for even more forcing for ascent & thus the potential for even heavier precipitation to be realized around I-40 corridor in NC & TN (Nashville - Knoxville - Greensboro - Raleigh/Durham) where 700mb temps are around -10C to -20C.


Keep a close eye on these subtleties in this setup going forward because they could become quite meaningful if we play our cards right the next few days.


View attachment 34863
Click to expand...

Thanks Eric! Where do the heaviest snow bands set up in the photo above? is it right under the FGEN contours or is it just North or South of them?
 
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