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Feb 12-13 Sleet/Snow/ZR Event


JoshM

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The 12z nam is different from the 0z Euro in that 1) It has warmer for GA with sig wintry precip only far north as wedging not yet established in time south of there for a big hit of IP/ZR. There's more like. 0.25-0.50 ATL-AHN and AGS, .50 CAE, and under 0.25 MCN. The different angle is in play as per Lookout 6z nam comment . 2) The 2nd wave looks like it may be weaker, much further south, and may end up not amounting to much at all. So, overall 12z nam would be big hit nc/far n ga/nwcorner sc from 1st wave, but much less wintry ATL-CAE and south of there for 2 waves combined. Lookout and others, agree or disagree? Of course this is unreliable 54-84 Nam vs Euro.

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I'm not saying it will trend south, just stating the differences between the nam and euro. If this wave is as amped up as the nam, the euro and gfs are likely too cold aloft and would spell more rain or ice for areas further south. If you are in georgia or south carolina, you don't want this first wave as strong or as far north as the nam.

Oh, I agree...The energy this strong would take us out for sure for the first wave.  My guess is the nam is too far north at this point.

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Hasn't every storm this winter pretty much been colder aloft than models predicted? I would worry about that for you guys. Gonna be hard to get 850's to sink much lower in the set up for sleet the further south you go but I would guess 2m temps on the maps start getting colder especially with it speeding up on that first wave.  GFS may finally catch on today. 

I think they have been about right as far as temps aloft go. I can't think of any situation where they were really off.

 

As far as surface temps go, the nam has the system coming in so fast that the wedge sets up well after the rain/precip has started. So this isn't like one of those situations where the models fail to grasp on to the dry air in place and evaporational cooling. Instead, things will already be saturated when the wedge starts to move south so I'm hesitant to say the surface temps are too warm since it's that initial evaporational cooling that often makes the difference and that's when you can say the models are probably a few degrees too warm. In this case though, i don't know.

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This run is still well north of the euro with it's precip shield. It's also still warmer aloft across north ga/sc than the euro. Taken verbatum though, it's rain over to sleet and/or freezing rain between hours 66 and 72 for much of northeast ga.  It's surface temps are a little misleading because actual soundings show temps right at freezing, with subfreezing wetbulbs, by around hour 69.. 

 

Still a significant sleet/freezing rain event for many in northeast ga and a hell of a snow storm for the mountains but the rain at the start sucks for the athens/gainesville areas.

 

Yes, there are differences obviously wrt precip shield and r/s line.. but the overall process of delivering the precip earlier as primarily an overrunning event and pulling off the southern wave energy.

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The 12z nam is different from the 0z Euro in that 1) It has warmer for GA with sig wintry precip only far north as wedging not yet established in time south of there for a big hit of IP/ZR. There's more like. 0.25-0.50 ATL-AHN and AGS, .50 CAE, and under 0.25 MCN. The different angle is in play as per Lookout 6z nam comment . 2) The 2nd wave looks like it may be weaker, much further south, and may end up not amounting to much at all. So, overall 12z nam would be big hit nc/far n ga/nwcorner sc from 1st wave, but much less wintry ATL-CAE and south of there for 2 waves combined. Lookout and others, agree or disagree? Of course this is unreliable 54-84 Nam vs Euro.

Agreed larry. Those areas would stand to get a fair amount of rain before any changeover...and any snow accumulations would be completely wiped out for much of south carolina and areas just outside the mountains/far northeast ga.

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From WXsouth facebook:

Another view of the final snowfall graphics through 84 hours (Tuesday night). WxBell graphics shows this as a big 9" to 12" snowstorm in much of NC. One of the better snowfalls affecting much of mid South region in a few years. Use this map only as a TREND, not the final forecast. The European Model also had major amounts but was more in Georgia and northwest SC than the NAM is showing. Right now, a blend of NAM and Euro is the best overall way to go, since mesoscale features are better captured on the NAM not European. But we will compare all the model runs here in a few hours.
Bottom line, this event starts Monday in Tennessee Valley and northern MS, AL, GA then spreads into Carolinas overnight and Va , Carolinas Tuesday. The High Pressure is in an excellent spot with plenty of cold air coming in, in fact for North Carolina and northeast Georgia and northern SC, the temps will fall into the middle and upper 20's by early Tuesday and hold there through the storm Tuesday. A strong damming event and a wild (and rare) Winter storm is shaping up.

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Correct. This is the type of setup where the winners will be on the battle line during the heart of the storm. Best rates with heavy wet flakes.

The sleet line is perilously close to MBY. Although, if you can be just north of that transition, that's almost always the best snow rates.

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Yes, there are differences obviously wrt precip shield and r/s line.. but the overall process of delivering the precip earlier as primarily an overrunning event and pulling off the southern wave energy.

The thing is though for areas in ga/sc, we don't want the precip to come in so fast so the cad can set up. The timing is great..perfect in fact, for north carolina but not so much for ga and sc.

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The thing is though for areas in ga/sc, we don't want the precip to come in so fast so the cad can set up. The timing is great..perfect in fact, for north carolina but not so much for ga and sc.

 

Yeah I suppose you guys need the CAD fully in place to get in on the fun.  With such an extended fetch of moisture to work with, hopefully we all can cash in on something here.

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The thing is though for areas in ga/sc, we don't want the precip to come in so fast so the cad can set up. The timing is great..perfect in fact, for north carolina but not so much for ga and sc.

 

Also, though not definite, the 2nd wave setting up to be weak/far south (very little in W GOM at hour 84) as per very unreliable 84 12Z NAM vs. Euro. So, to me the 2 models have big diff.'s and NC gets a lot from either but much of SC/Ga get far less from two waves, combined. But it is NAM 54-84, which is often bad.

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The sounding for KRDU for the 12z NAM is just beautiful...3 or so hours of heavy rates and almost all liquid is a textbook all snow sounding. A county or so south at KFAY not so pritty, heavy IP, etc.

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Yeah I suppose you guys need the CAD fully in place to get in on the fun.  With such an extended fetch of moisture to work with, hopefully we all can cash in on something here.

I hope so too. It would really..and I mean really hurt for a lot of georgia/sc folks see nc get hammered with that much snow while we miss something really special here by 1 or 2 degrees.

Also, though not definite, the 2nd wave setting up to be weak/far south (very little in W GOM at hour 84) as per very unreliable 84 12Z NAM vs. Euro. So, to me the 2 models have big diff.'s and NC gets a lot from either but much of SC/Ga get far less from two waves, combined.

Exactly.

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I'm going All in if the euro comes in the same on the 12z run

Although the 00z run was a bit of a different evolution then the previous several runs, the consistency of it showing a major winter storm for man in the SE is very noteworthy and carries weight.

 

As much as I love the NAM solution, it is likely too amped up and too far NW, a typical bias. Euro solution makes pretty good sense. GGEM is also a reasonalbe setup. The American models are both sides of the extreme.

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Such extreme differences for as little as 48 to 60 hours (the differences start out very early) out is nuts. Nam has a million inches of snow for nc while the gfs has essentially nothing.

 

Whenever these situations arise with a dry GFS and amped up Euro/NAM, I turn to the old Gary Gray archives leading up the 96 blizzard.  I've saved them: http://wow.americanwx.com/gg/

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