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The Big One - Forecast & Discussion


Wow

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The good news for atlanta and athens is I think a lot of that would in fact be sleet with the boundary layer so cold...especially considering the precip would be coming down so fast and hard it wouldn't stay in the warm layer long at all. In fact, with that type of convection/heavy precip..there would likely be some dynamical cooling at play and some areas might see that heavy precip go over to snow as the lift in that east to west band would be tremendous. Again though, I think it has to be over done. But hell even half this is a massive hit so either way it's big.

 

But here is the 925mb temps in the heart of that heavy precip

 

namUS_925_temp_063.gif

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Probably not, I just looked at it for ATL and its usless, does not show anything but rain til 06Z Wed AM...noy buying that at all....its still slow wedging alot of places in.

Yeah I was gonna say. When the precip is over ATL, the 2m freezing line is up in Virginia, at least until +60hr.

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The nam would result in about 6inches of concrete. You'd get a quick several inches of snow, then probably 2-3 inches of sleet with some snow 1inch to cap it off on top for triad

 

With temperatures in the low 20s for most of the storm.  Don't get me wrong; I'm rooting for snow, but that would be epic.

 

We'd get a fresh batch of snow at the end of the storm, too.

 

 

Actually, it does matter and nice catch -- with an 850 low that strong -- going to be some wraparound snow.

 

 

Oh, yes, I agree.  I just don't know if analysis of what the NAM is showing at hr 84 is wise, haha.

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I'm having a hard time believing this to be quite honest. But fwiw..and this is just through hour 66

 

Wow, cut that in half and it's still a really bad deal!  NAM takes the southern wave neg over eastern TX which increases heights ahead of it sig, unsure if I buy it at this point but something to keep an eye on.  The model appears to be catching on to something similar to the 2/9 0Z Euro, which given the range, arrow is pointed towards the 12z Euro, NAM is playing ketchup.  The northern stream may be coming in late, that is why we have this double barrel solution, with the primary not getting cranked to off the VA Capes.  Could be a two wave setup for the SE, but with the source of cold exiting stage right, many are going to need t rely on heights crashing on the backside.

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That is an odd map.  It is very unlikely that the higher snow totals will be in the lower part of the Upstate.  I suspect that map treats all frozen precip as snow like the Euro snow maps do.

Agree completely, I can't buy that Greenwood will get triple what Asheville gets. I am quite amazed by the models today, actually too much so. I just can't buy into the solutions they are showing. My head won't let my heart buy into the idea of 6-10 inches or more for the upstate (some showing 12 inches plus). I would love it of course, but to be realistic, I think the smaller amounts the TV mets are showing may be closer to reality, even if they are being conservative. A couple of things to remember here, the solutions we are seeing is based on a phase. If that doesn't happen (and it may not) then this is a totally different game. The Jan 88 analog mentioned is fine, but surface temps were much colder for many areas in that storm. Also, someone mentioned ground temps - I think that could be a real problem, as temps have soared into the 60s all weekend over much of the area, and will be pushing 50 or more tomorrow. Cold surface temps or not, it will take a while (and lots of frozen precip) to get the ground cold enough for accums. And I am still concerned about surface temps. Virtually all local mets have highs Tues and Wed in the mid 30's, even for many mtn locations. I look to March 09 and Christmas 2010 to show how temps a couple degrees above freezing can destroy accums. We'll see, I hope it truly is epic!  :snowing: 

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Soundings say this is mostly all freezing rain and some sleet for RDU. Brief period of rain as well and snow at the end.

 

NAM goes bonkers closes off the 500mb s/w at 84 hours, wraps in the surface low bringing a big surge of warm air aloft.

 

This is probalby another extreme solution. Holy cow the model waffles/confusion is amazing.

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Soundings say this is mostly all freezing rain and some sleet for RDU. Brief period of rain as well and snow at the end.

 

NAM goes bonkers closes off the 500mb s/w at 84 hours, wraps in the surface low bringing a big surge of warm air aloft.

 

This is probalby another extreme solution. Holy cow the model waffles/confusion is amazing.

Yep, not going to buy into this one. It would be the most devastating ice storm ever to hit the southeast. NAM is too amped up IMO.

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That run is just ominous for the Atlanta area. Ice storm of epic proportions. It would look like The Day After Tomorrow with a storm like that. You'd need an insane amount of shelters opened for people. Nearly region wide, power would be out. City would be shut down for quite possibly a week or more. The damage would be indescribable. Please let that not happen.

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The good news for atlanta and athens is I think a lot of that would in fact be sleet with the boundary layer so cold...especially considering the precip would be coming down so fast and hard it wouldn't stay in the warm layer long at all. In fact, with that type of convection/heavy precip..there would likely be some dynamical cooling at play and some areas might see that heavy precip go over to snow as the lift in that east to west band would be tremendous. Again though, I think it has to be over done. But hell even half this is a massive hit so either way it's big.

 

But here is the 925mb temps in the heart of that heavy precip

 

namUS_925_temp_063.gif

I like that map, thank you for posting that.  I just ran the 00z through bufkit, and vs the 18z run its much more cold in the 900mb layer down to right above the deck where it keeps me at 1.2-1.5c  I have a feeling SFC temps are a bit to warm given that much depth of cold layer.  What do you think?  We are below freezing from about 900 to 980mb then just above 0c at 2m

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Ran a sounding for me at 72 on the NAM.. It's >0C between 750 and 850mb level.  

I just looked and although I'm hoping this would be sleet if it came down that hard, that warm layer is awfully stout. It's max is actually centered around 825mb with a max temp of 3 to 4c through hour 63 and up to 5c at hour 66. And it  runs from 775mb to 875mb. That is really deep. So unless there is a lot of dynamical cooling (and even if there was it's hard to picture it over coming that big and hot warm nose) and it's really hauling ass down with a butt load of it's buddies, it's going to melt.

 

Boundary layer temps are coldest at 925mb..and get as cold as -4c or there abouts a hours 60 to 63 and -6c at hour 66. That is pretty cold. So  a snow flake will go through temps as warm as 41 to  as cold as 21. Pretty amazing. Sure makes it hard to figure out what the dominate precip type would be and where if such an extreme scenerio played out but it's clear there would be a LOT of freezing rain

 

btw, it should be noted the gfs is no where near this warm with it's mid level warm nose and for obvious reasons.

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Just finished watching his video; some sound reasoning, but I think there is something to be said about how much uncertainty he expresses overall. I would think that it is just as likely for this system to generate more snow in the piedmont than ice. Wouldn't the position of the low bring down more cold air? What if it phases?

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Chris, whats funny is the SFC low is a little further N moving through GA and a touch stronger (than the 18z run) but yet its actually colder at 2m for you and me...hmmmmm

 

i have no clue whether this is possible (havent heard or seen it to my recollection) if the wedge is there and building in, a stronger low whipping winds off the atl brings in warmer air aloft, but can also serve as a boost or fan of sorts to really drive that wedge in on the winds counterclockwise around the low

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I think the 850 freezing line is going to be much closer to the sfc freezing line as the storm bombs along the coast.  Miller A storms at this stage usually will have only a generally narrow ice band when in a n-s configuation from NC northward as the 850 low strengthens.  Basically saying the GSO-CLT-GSP corridor is going to be mostly snow with this low track.

 

Hgn5g6f.jpg

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i have no clue whether this is possible (havent heard or seen it to my recollection) if the wedge is there and building in, a stronger low whipping winds off the atl brings in warmer air aloft, but can also serve as a boost or fan of sorts to really drive that wedge in on the winds counterclockwise around the low

They stay around 050-070 at 10m 

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f

 

 

Chris, whats funny is the SFC low is a little further N moving through GA and a touch stronger (than the 18z run) but yet its actually colder at 2m for you and me...hmmmmm

Ironic considering that at first it's warmer because the nam doesn't get any precipitation up into north carolina with the first wave. in earlier runs that precip cooled the surface/boundary layer off upstream of us and then it headed our way. It still gets us there of course, just a little delayed.

 

Tough cookie to crack though since although we know there will be a lot of precip, how much is still up in the air to me. It's pretty unimaginable that much falls but again even if its half you are talking a hell of a lot and historical event. I'd hate to have to try and convey this to the public because it's such a potentially massive event but you can't scare the hell out of people and go nuts.  Just hope folks are prepared enough.

 

 

 

Soundings say this is mostly all freezing rain and some sleet for RDU. Brief period of rain as well and snow at the end.

 

NAM goes bonkers closes off the 500mb s/w at 84 hours, wraps in the surface low bringing a big surge of warm air aloft.

 

This is probalby another extreme solution. Holy cow the model waffles/confusion is amazing.

I don't think I've ever seen the models go so back and forth so much  with the specifics of a system(well two) and doing it with every run. In terms of the real world, sometimes it's big changes but other times they are minor but those minor changes wildly effect  the outcome.  It's nuts.

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Verbatim, that was a great NAM run for the NC mountains (for snow).  Strengthening closed 850mb low tracks from N MS, to extreme NW SC, to just east of Asheville.  For a 850mb low of that strength, it's pretty much a must to be NW of its track to get all snow (12z Euro and Euro Ensemble tracked the 850mb low more through central NC).  For the mtns, the NAM has strong warm advection lift combined with upslope flow out of the SE.  Also, a nice 500mb vort max track from central AL to central NC.  Heavy snow for the mtns on this NAM run.

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