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January Medium-Long Range Discussion


Holston_River_Rambler
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For those new to the hobby, and not quite familiar with the topo and how it greatly impacts the Great Valley hopefully this will help...(and yes there is some truth to the Cattanooga Snowdome lol).

This generally applies to anafrontal and Northwest Snow Flow Events. Surface LP has a ton of other variables. 

Think of the atmosphere as a liquid with differing viscosity. Warm is less dense and rises, cold undercuts the warm as if it has a thicker viscosity.

The Plateau acts like a dam for the denser cold air (Blue Arrows over Middle TN). Just west of Knoxville near Kingston, the Plateau has a natural spillway/funnel that allows as small area for the cold to funnel into the valley (if you watch fronts pass over, you can actually see this occur live on PWS's in the area). There is a much smaller spillway west of Chattanooga, but due to the nature/design of the Plateau, cold must slowly fill the Sequatchie Valley first before trying to continue advancing toward Chattanooga (leaving that area to primarily rely on the Kingston "spillway" to supply it with the cold. As lift generally pulls away from the valley from SW to NE, the column dries the quickest at Chatt. Add in the distance from Kingston to Chatt the slow moving cold air arrives almost too late...hence the Chattanooga Snowdome.

Other areas of interest due to topo..

1) Green Box Areas - as the cold naturally pushes SE, it sometimes can force moisture to pool up in these areas, enhancing snowfall output. This is what occurs 9/10x when East of Hwy 411 ends up with greater totals than west side.

2) Red Boxe Area - The downsloping winds of the Plateau speeds up the drying process further...making the Dome that much stronger.

962_g_1200x1200.png

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Looks like this coming weekend is going to be several degrees warmer the forecast shows plus by end of next week back up to mid 40’s.  Looks like a 3-4 day cold shot & it retreats.  The MJO is king. 

That’s weird…. When I go below freezing on Sunday afternoon, I don’t go back above freezing for a week and I’m in the valley.


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7 minutes ago, PowellVolz said:


That’s weird…. When I go below freezing on Sunday afternoon, I don’t go back above freezing for a week and I’m in the valley.


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A lot of different forecast out there.  I was just looking at several.  It’s funny. I know most are crap shoots.  Majority has it cold but very little snow. 

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2 minutes ago, Matthew70 said:

Is the tri cities really getting left out?

I hope not,but having lived up there for several years, it can definitely get the short end in these scenarios. On the flip side, they can sometimes score when no one else can. They are overdue for that honestly. 

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24-hour ratio map. I don't believe the barren spot down toward the southern valley. But great map otherwise and up for every from 12 and 18z. 
 
J7rmHDF.md.png
 
I don't either, usually those occur for warm nose, this setup just won't have one that pronounced I believe. 0z definitely has better looking QPF overall.

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Almost carbon copy anafrontal setup for the valley. While I don't believe Chatt Dome would be that strong as the accum map shows, it would be less (downslope cuts it). The Tri hole I have 0 belief in.

 

You can see the downslope (Red Circle), as well as the low level moisture getting banked up (Red Lines) on the 925 RH maps

 

Screenshot_20240109_232349_Chrome.jpg

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Hard to believe we are now 5 days & less especially for the west part of the state till this storm hits.  We still have the Friday storm though.  It could throw a wrench in the whole system.  Glad we are all getting some good rains. They were much needed to put a dent in the drought.  

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You can see errors in both the GFS and CMC on the 925 at 132hr

GFS inexplicably doesn't fill in the Tri hole, even tho the moisture transport/banking is there.

 

While CMC setup would create a hole toward Tri (due South to North wind would create downslope there off the Smokies). Chatt accum doesn't add up due to 0 downslope on it.

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1 minute ago, TellicoWx said:

You can see errors in both the GFS and CMC on the 925 at 132hr

GFS inexplicably doesn't fill in the Tri hole, even tho the moisture transport/banking is there.

 

While CMC setup would create a hole toward Tri (due South to North wind would create downslope there off the Smokies). Chatt accum doesn't add up due to 0 downslope on it.

I think models tend to over exaggerate both upslope and downslope as a rule, especially hi-res models. 

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3 hours ago, John1122 said:

Weird turn on the Euro as it just keeps light snow over the area for 12 hours longer than the other models and we get a couple inches that way in the eastern half of the area. Nashville and west still do okay there. 

Looked like it was trying to transfer the energy over south middle and east TN to the coastal bomb. Is that the first time we've seen that look with this storm? Strange

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For people East of the Plateau you want the EURO to keep trended for a negative tilt.  The only way we score is if we get a low to form and fire convection. If not then yes. The moisture will go poof.
 

the good news is the gfs is ticking that way but still not enough. That's the only way this brings much of anything to Eastern areas.

IMG_1134.thumb.png.9bf63f09b2a5de23feae9e7110bfd4b8.png
 

Need this to continue. We don't need an 1" of precip with this. Its so cold just need a few hours of good rates.IMG_1135.thumb.gif.fa4d8489f32358aa8a2af260f2b6461a.gif

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