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NorthGeorgiaWX

Monday, February 17

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7 minutes ago, KingOfTheMountains said:

I suspect, much like with our last storm, Euro may be a bit too warm at the surface. I think as far as surface ptype/temps go we are gonna have to wait til hi-res guidance gets into range. While the globals right now can be used on bigger picture stuff like the handling of the vort at H5 and trough alignment. 

We are starting to get into that time frame where medium range guidance is not as useful. Like you said, big picture wise, we can still gain some things from it but this is such a borderline setup, hi-res guidance is going to have to have the final call. The mountains are certainly going to be favored in a borderline temp setup, just a matter of moisture.
 

My local experience here in Sky Valley says this is going to be simply a moisture issue, with temps in guidance the way they are, we will get to around freezing if moisture will cooperate. 

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3 minutes ago, Preston said:

We are starting to get into that time frame where medium range guidance is not as useful. Like you said, big picture wise, we can still gain some things from it but this is such a borderline setup, hi-res guidance is going to have to have the final call. The mountains are certainly going to be favored in a borderline temp setup, just a matter of moisture.
 

My local experience here in Sky Valley says this is going to be simply a moisture issue, with temps in guidance the way they are, we will get to around freezing if moisture will cooperate. 

Yep, at least as modeled now, the column is prepped to deliver snow. We just need the moisture to cooperate. As long as the surface isn't any warmer than 38 or so I'd be confident in our area seeing at least a trace of accumulating snow if the moisture is there. 

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2138105140_98ewbg(2).gif.3f2cc4fd720a616e409e4bbe67d91524.gif

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Mon Feb 17 2020
 
Day 2
Valid 12Z Tue Feb 18 2020 - 12Z Wed Feb 19 2020 

...There is a Marginal Risk of Excessive Rainfall over parts of 
the Gulf Coast Region and Southeast U.S. from Tuesday into early 
Wednesday...

...Louisiana to Mississippi and Georgia...
A Marginal Risk area remains in place across Mississippi eastward 
into Georgia from Tuesday into early Wednesday.
The only real 
change in this forecast cycle was to pull the Marginal Risk area 
into Louisiana in response to a fairly consistent signal from the 
operational and ensemble mean model QPF.  Once again, the driving 
force in the mid-levels will be a low amplitude wave to the north 
and ridging to the south and west.  Another player will be a 
surface low with a trailing cold front extending back into the 
Southern Plains that moves south and east with time. 

Ahead of the main cold front, the leading edge of greater low 
level moisture with surface dewpoints in the low to mid 60s will 
gradually make its way northward in advance of the main cold 
front. Precipitable water values of 1.5 to 1.8 inches (some 
standardized anomalies of +2 to +3 for the Gulf Coast states for 
mid-February) will creep into the southern tier of states from the 
Gulf of Mexico.
 Given favorable low to mid level wind speeds and 
directions, flow will be supportive of training axes of heavy 
rainfall from WSW to ENE with potential for rainfall rates between 
1-2 in/hr. Instability looks to be marginal...with MUCAPE values 
generally under 1000 J/kg.  So there are a few signals supporting 
the potential for locally heavy rainfall amounts but there are 
others which will be offsetting the potential.

As mentioned in the previous outlook, the Marginal Risk areas 
attempt to span the area which has a better chance of seeing 
higher rainfall rates in the south...but where antecedent 
conditions are not as wet and the associated Flash Flood Guidance 
values are higher (which includes parts of Louisiana as shown by 
the 17/00Z model runs)...and areas to the north where 7-14 day 
percent of normal rainfall is 300+ percent with above average soil 
moisture, high streamflow anomalies, and lower Flash Flood 
Guidance values. 

Bann

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It appears the Canadians recent investments in their model have been well spent. GFS continues to embarrass on the global scale, and now the British are about to put a ton of money into their models as well. 

 

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2 minutes ago, Dahlonegadawg said:

Things seem to be looking better as i take breaks today? Yalls thoughts?

I would say slowly increasing likelihood of snow, at least falling, somewhere in the SE US. Where that could be is still highly undecided, and will likely take a while to pin down. 

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NWS GSP starting to at least entertain the idea of snow. 

There now looks to be a brief break in the precip Wednesday night as
the first wave of forcing moves east and some drier air moves in. Of
course, this sets the stage for the potential for some wintry precip
as moisture moves back in Thursday ahead of the surface wave moving
along the front and some upper divergence associated with a coupled
jet streak. The guidance still doesn`t agree on how far north the
moisture moves or just how cold the air will be. That said, it is
now looking like there will be precip at least as far north as the I-
85 corridor and likely the NC mountains. Precip tapers off quickly
Thursday night as the wave moves east of the area. The thermal
profiles and partial thickness progs show the precip to be rain or
snow with no significant warm nose. I`m beginning to become wary of
the snowfall potential given the previous 2 snow events where the
thermal profile and thickness values were quite similar. I suspect
this event could be similar where precip begins as snow over the
western CWFA along and north of the I-85 corridor with accumulations
developing where precip can fall for the longest period of time.
That said, have followed the national guidance for now which keeps
the accumulating snow across the higher elevations and mainly rain
outside of the mountains. Of course, this forecast could go either
way, so interested parties will need to stay abreast of the latest
updates.
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Just now, KingOfTheMountains said:

Yeah that was a great run! Sign me up lol

Yeah it looks nice and juicy on that run. Can't wait for my 35 degree rain NE of Atlanta haha. 

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Geez I was joking about the 35 degree rain but I was right. Outside of the mountains where it depicts snow, its a cold 33-35 degree from  I-20 north on the 18z NAM

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nam_2020021718_066_34.91--83_36.thumb.png.5f9536d9fd2127344dc79080f4daec8e.pngThis is a sounding for Clayton at onset. This would very quickly transition from rain/wintry mix to all snow, and the surface temp would go below freezing. Would stay snow from then on, possibly even high ratio snow towards the end as the upper air thermals crash. 

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23 minutes ago, Shannon said:

Geez I was joking about the 35 degree rain but I was right. Outside of the mountains where it depicts snow, its a cold 33-35 degree from  I-20 north on the 18z NAM

Yeah, I pulled up some soundings for that area too just to check and it is definitely mostly rain unfortunately. The unfortunate truth to our climatology that snow most often favors the further north and higher terrain. Might transition to a mix in the latter half of the event. Just one run though, still time for things to change. 

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2 minutes ago, KingOfTheMountains said:

nam_2020021718_066_34.91--83_36.thumb.png.5f9536d9fd2127344dc79080f4daec8e.pngThis is a sounding for Clayton at onset. This would very quickly transition from rain/wintry mix to all snow, and the surface temp would go below freezing. Would stay snow from then on, possibly even high ratio snow towards the end as the upper air thermals crash. 

NAM has me intrigued with a strengthening Low Pressure off the Carolina coast. That sort of setup could keep the snow going and give wrap around precip to NE GA. 

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1 minute ago, Preston said:

NAM has me intrigued with a strengthening Low Pressure off the Carolina coast. That sort of setup could keep the snow going and give wrap around precip to NE GA. 

Yeah if that were to happen verbatim we would probably be on the light fringes of the coastal storm bombing out. Very light QPF but potentially very high ratios. Nearly a perfect run for our area. Slightly colder onset, and the coastal development being a little closer to the coast is the only improvements we could possibly have over that. Unfortunately it's days away and almost certain to change lol

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5 minutes ago, KingOfTheMountains said:

Yeah if that were to happen verbatim we would probably be on the light fringes of the coastal storm bombing out. Very light QPF but potentially very high ratios. Nearly a perfect run for our area. Slightly colder onset, and the coastal development being a little closer to the coast is the only improvements we could possibly have over that. Unfortunately it's days away and almost certain to change lol

Agreed, I would be much more excited about that if it were mid day Wednesday and we were seeing that. 

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I would be a little wary of the NAM 12km though. It's usually over amped. Not to say it's wrong but I would like some other model support. 

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5 minutes ago, NorthGeorgiaWX said:

I would be a little wary of the NAM 12km though. It's usually over amped. Not to say it's wrong but I would like some other model support. 

Oh no doubt. Only reason I'm even entertaining it at this lead time is because of how well it did a little over a week ago. 

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And I'm only treating the coastal as a potential bonus. All I'm looking for is better QPF during the over running portion of the event. Which, according to the experts, the globals almost always underestimate QPF on the northern fringe during. If not for that fact I wouldn't feel very good about the setup. 

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GFS is actually a little colder at onset than the NAM. 35 in Clayton, and soundings indicate all snow despite some of the ptype maps showing a change to rain. If these temps verify, we just need QPF. Even GFS isn't bad with probably an inch or so in accumulation. 

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Do you think if this ends up being able to produce snow it’ll be more than a dusting in this area? Just in your honest opinion, i know there’s still a lot 

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5 minutes ago, Dahlonegadawg said:

King, how do readings look for Dahlonega?

Borderline right now. Could go either way. NAM and GFS have that area being right on the rain/snow line for the majority of the event. Verbatim it's showing a situation where northern Lumpkin would be mostly snow, southern Lumpkin mostly rain, and a sloppy wintry mix in between. But we're nowhere near ready for that level of detail yet, that line is gonna move all over the place over the next couple days. 

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