2016-2017 Great Tennessee Valley Winter Discussion

[John1122]

12z GFES currently disagrees with the OP as far as the late run warming goes. It's BN for the Valley for every 5 day period all the way through day 16.

[Carvers Gap]

13 minutes ago, John1122 said:

12z GFES currently disagrees with the OP as far as the late run warming goes. It's BN for the Valley for every 5 day period all the way through day 16.

Yep. GEFS basically reloads the pattern.

[John1122]

18z eliminated the 20 degrees c above normal the 12z spit out and is now back to below normal and with miller A's swirling in the same time frame. Not as cold as the epic 6z run. I guess it's typical pattern change madness. Not clear how a math problem, which is sort of how computers models work, can have such widely varied outcomes in a 6 hour period.

[nrgjeff]

Good news from SPC. Monday night looks like tornadoes are even less likely in the Deep South. Appears ongoing convection on the coast and offshore should bury the warm front. Maybe a coastal front inches ashore early Tuesday? Diurnal min even in Dixie Alley. At any rate I agree with SPC punting tornado wording for Monday night. Sleep is good!

[Carvers Gap]

LR is interesting.  12z GEFS drops heights in GOA which is not great if you like winter.  12z Euro Op puts a ridge there, displaces cold south, has a Cahir's connection, and a bowl shaped trough which looks juicy.  Time to see what the EPS brings.

Hey Jeff, good to hear about the tornado probability going down.

[John1122]

EPS and GFES  build heights over Siberia and Alaska and move it poleward. This displaces the polar vortex and sends it down into Canada bringing frigid cold from Alaska down the Rockies and then to the Eastern side of the lower 48.

 

 

 

 

[John1122]

GFES look for the same period.

 

 

[ShawnEastTN]

Hopefully we get a bit of moisture around that time frame also, models show it then take it away then show it then take it away run to run...

[John1122]

There will be storms coming through but they're liable to cut because the NAO is neutral. 

The Euro/EPS has been trying to develop several lows along the Gulf. We'll see though. At worst we have cold no longer locked in Siberia and snow pack should really build to our north.

[JayCee]

Quote

FLOOD WATCH
NATIONAL WEATHER SERVICE MORRISTOWN TN
309 PM EST MON DEC 5 2016

...FLASH FLOOD WATCH IN EFFECT FOR SEVIER COUNTY BURN SCARS...

.AN UPPER LEVEL LOW PRESSURE SYSTEM WILL BRING PERIODS OF RAIN TO
THE AREA TONIGHT AND TUESDAY. ALTHOUGH RAINFAL TOTALS FOR THE
ENTIRE RAIN EVENT WILL GENERALLY NOT EXCEED 1.25 INCHES...THE BEST
RAINFALL ACCUMULATIONS IN THE GATLINBURG AREA ARE EXPECTED DURING
TUESDAY MORNING. REMEMBER THAT BURN SCARS PROVIDE AN ABOVE NORMAL
THREAT OF FLOODING...OR MUD AND DEBRIS SLIDES...WITH EVEN MODERATE
AMOUNTS OF RAINFALL.

TNZ073-074-061000-
/O.NEW.KMRX.FF.A.0003.161206T0900Z-161206T2100Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
NORTH SEVIER-SEVIER SMOKY MOUNTAINS-
INCLUDING THE CITIES OF...SEVIERVILLE...GATLINBURG
309 PM EST MON DEC 5 2016

...FLASH FLOOD WATCH IN EFFECT FROM LATE TONIGHT THROUGH TUESDAY
AFTERNOON...

THE NATIONAL WEATHER SERVICE IN MORRISTOWN HAS ISSUED A

* FLASH FLOOD WATCH FOR A PORTION OF EAST TENNESSEE...INCLUDING
  THE FOLLOWING AREAS...NORTH SEVIER AND SEVIER SMOKY MOUNTAINS.

* FROM LATE TONIGHT THROUGH TUESDAY AFTERNOON

* RAINFALL POSSIBLY EXCEEDING ONE INCH FALLING UPON THE BURN SCAR
  COULD LEAD TO FLASH FLOODING OR DANGEROUS MUD AND DEBRIS SLIDES.

* FLOODING OF LOW LYING AREAS...ROADWAYS...AND STREAMS WILL BE
  POSSIBLE. MOVE AWAY FROM RECENTLY BURNED AREAS. LIFE THREATENING
  FLOODING OF CREEKS...ROADS AND NORMALLY DRY ARROYOS IS POSSIBLE.
  THE RAINS COULD TRIGGER ROCKSLIDES...MUDSLIDES AND DEBRIS FLOWS
  IN STEEP TERRAIN...ESPECIALLY IN AND AROUND THE BURN AREAS.

 

 

[JayCee]

Copied this from James Spann's weather blog: 

 

Quote

On This Day In 1886
A big snowstorm in the southeastern U.S. produced 11 inches at Montgomery AL, 18.5 inches at Rome GA, and 22.5 inches at Knoxville TN.

Ah--the good ole days. 

[Carvers Gap]

The 12z EPS, after several runs of improvement over the GOA, reverts back to low heights over the GOA.  As DT stated, we need those to be gone or it just bottles the cold up in western Canada.  Also, he mentioned the omega ridge in west Alaska is stubborn to move and is forming the low heights over the eastern GOA.  The GEFS looked decent at 12z.  Personally, I think this cold air (that is modeled as -65 BN in some places over the northern plains and Canada) is wrecking havoc on model consistency.  Not sure I would trust any cold or heat outside of day 10.   As long as that extreme cold exists to our north, there is the risk it could be discharged south.

[John1122]

The 12z EPS continues with the below normal look in the extended. The +EPO keeps the true bone rattling cold from moving into the area though.  It tries to build a -epo but it quickly fades and neutral to below normal heights approach the GoA.

[Carvers Gap]

52 minutes ago, JayCee said:

 

That is a long term worry.  I fish that river drainage.  I am sure it is going to receive a ton of silt.  If Gatlinburg decides to replace those burned areas with new trees, I will be first in line to help.  Just one of many problems created by that fire...with human suffering at the top of the list.

 

 

 

 

 

[John1122]

1 minute ago, Carvers Gap said:

The 12z EPS, after several runs of improvement over the GOA, reverts back to low heights over the GOA.  As DT stated, we need those to be gone or it just bottles the cold up in western Canada.  Also, he mentioned the omega ridge in west Alaska is stubborn to move and is forming the low heights over the eastern GOA.  The GEFS looked decent at 12z.  Personally, I think this cold air (that is modeled as -65 BN in some places over the northern plains and Canada) is wrecking havoc on model consistency.  Not sure I would trust any cold or heat outside of day 10.   As long as that extreme cold exists to our north, there is the risk it could be discharged south.

I was just posting about the same thing. The one thing about the +EPO is that it splits the flow. We're in a decent position with the cold to possibly take advantage of a well timed slider. If the -EPO were in place with that level of PV displacement we'd be cold and dry for the most part, hoping for clippers or NW flow events. I can't see past 240 on the EPS but it appears to be trying to build a ridge on the west coast by 240. Not sure if it just progresses or tries to lock in on that run.

[Carvers Gap]

15 minutes ago, John1122 said:

I was just posting about the same thing. The one thing about the +EPO is that it splits the flow. We're in a decent position with the cold to possibly take advantage of a well timed slider. If the -EPO were in place with that level of PV displacement we'd be cold and dry for the most part, hoping for clippers or NW flow events. I can't see past 240 on the EPS but it appears to be trying to build a ridge on the west coast by 240. Not sure if it just progresses or tries to lock in on that run.

We must have posted almost at the same time.  The EPS gets wonky at d13 with an almost perfect oval around the NH at 500mb(edit).  Very few kinks.  It looks overly smoothed.  When that happens, we go zonal at d14 speaking of the mean.  The control reloads the pattern for cold.  Though I am biased towards cold, I have to say it looked like a more reasonable option vs the smoothing.  Weeklies come out soon, so that will give us another perspective.  I don't consider it a bad run FWIW.  

[BNAwx]

25 minutes ago, Carvers Gap said:

The 12z EPS, after several runs of improvement over the GOA, reverts back to low heights over the GOA.  As DT stated, we need those to be gone or it just bottles the cold up in western Canada.  Also, he mentioned the omega ridge in west Alaska is stubborn to move and is forming the low heights over the eastern GOA.  The GEFS looked decent at 12z.  Personally, I think this cold air (that is modeled as -65 BN in some places over the northern plains and Canada) is wrecking havoc on model consistency.  Not sure I would trust any cold or heat outside of day 10.   As long as that extreme cold exists to our north, there is the risk it could be discharged south.

With the cold relatively close by and somewhat of a split flow, you have to think they'll be some s/w's plowing through that the models can't lock in on until we get closer in time.  Whether it does us any good remains to be seen.  Personally, I don't mind a "little" SE ridging either as long as it isn't on roids...

[Carvers Gap]

There has been a ton of variability in the LR.  I think the extreme cold in Canada is causing problems w modeling.  The GOA situation is something to watch.  It has been a somewhat consistent feature but varies in strength.  I am definitely watching for a slider along the Arctic boundary.  I don't see one yet, but something to watch for w these systems not slowing down much and rounding the base of that cold air.

[Coach B]

26 minutes ago, John1122 said:

The one thing about the +EPO is that it splits the flow. We're in a decent position with the cold to possibly take advantage of a well timed slider. If the -EPO were in place with that level of PV displacement we'd be cold and dry for the most part, hoping for clippers or NW flow events.

Excellent points! The cold being depicted in Canada and the N Plains is really amazing. That kind of cold when it penetrates this far south usually results in cold and dry as you pointed out. Correct me if I'm wrong, but the +EPO keeps the Pac Jet pointed in our direction and should throw a number of disturbances at us in the flow. Just need something to slide under or hook up with the serious cold just to our north.

[Carvers Gap]

11 minutes ago, BNAwx said:

With the cold relatively close by and somewhat of a split flow, you have to think they'll be some s/w's plowing through that the models can't lock in on until we get closer in time.  Whether it does us any good remains to be seen.  Personally, I don't mind a "little" SE ridging either as long as it isn't on roids...

Yep.  Agree.  I must have been writing while you were posting.  A little ridging might turn a system just enough to slow it down and bend it slightly northeast.  This run of the EPS just doesn't have enough blocking over the Atlantic in the d10-15 range.  Still a lot of room for changes as that is a ways out there.  Someone on the MA mentioned that they didn't like the spacing right now.  I might tend to agree.  But that much cold in Canada makes things very interesting.

[Carvers Gap]

DT put this out last night.  Pretty good summation of where we are.  Has a good EPO explanation.

 

[Carvers Gap]

I am not a huge fan of the CFS2 as sometimes it seems like it uses voodoo.  However, it has grown colder for January over the past week.  Also, its most recent runs spit-out a cold February.  I have low confidence in that model, but there are some trends there.

[John1122]

The positive to the NAO situation is that on this side of the Apps we need it less than the other side of the Apps. We had a few pretty snowy years in parts of the Valley with a +NAO prevailing recently.  That said, I'd generally prefer and -NAO. More help from the Pacific is what really matters for most of the Valley, especially the western areas. 

[Snowless in Carrollton]

2 minutes ago, John1122 said:

The positive to the NAO situation is that on this side of the Apps we need it less than the other side of the Apps. We had a few pretty snowy years in parts of the Valley with a +NAO prevailing recently.  That said, I'd generally prefer and -NAO. More help from the Pacific is what really matters for most of the Valley, especially the western areas. 

Is there a reason why areas on the other side of the Apps need a -NAO more so than on the west side of the Apps ?

 

[John1122]

One of the big functions of a -NAO is that it blocks storms from cutting west of the Apps and it blocks cold air from scooting out of the way of approaching storms on the east coast. But this side of the Apps, especially western areas of the Tennessee Valley can do well when storms cut the Apps or even across East Tennessee, especially if the Pacific is cooperating and there's a good cold source in the upper Midwest. 

[Carvers Gap]

11 minutes ago, Snowless in Carrollton said:

Is there a reason why areas on the other side of the Apps need a -NAO more so than on the west side of the Apps ?

 

Good question.  We have done decently well with +PNA during some recent years when the unicorn (-NAO) has been absent.  We actually like sliders here as much as Nor'easters.  Seems like for those east of the Apps, sliders get disrupted by the Apps and that is a less favorable set-up.  Being on the lee side does not work most times with sliders.  We can get sliders without a -NAO.  You all need a system to turn the corner which is why a -NAO helps you all more.  That said, we rarely get CAD.  Though sometimes cold gets banked on this side of the Apps and gets trapped if return flow moves into quickly.

[John1122]

We tend to get front end thumped occasionally in retreating cold situations that are similar to CAD situations. It happened a couple of times the last two years.  If a -NAO had been in place the cold would have locked in, the storm would have stayed south and east of of the Apps and the eastern valley would have gotten  15+ inches from the big storm last year that went right up the spine of the Apps. It would have spread heavy snow anywhere NW of it's track east of the Apps too. That situation would have hurt the impressive middle Tennessee totals though.  Sliders are usually good for the whole valley but sometimes less so over the Apps. -NAO Carolina cutters are usually good for the Eastern half of the valley and over the Apps. Apps runners are good for the Western side of the Valley. It's tough to get a set up where snow runs from Say North Miss, to Myrtle Beach and points north. That can happen with sliders and some Miller A's but usually someone is getting left out. 

[Carvers Gap]

Weeklies are a mixed bag. 2M temps look decent through week 5 either at or BN.  Week 6-7 warm for most of NA.  I think until this new blocking pattern takes hold and the cold is established...things are going to be all over the place.  Great thing...precip above normal for time frame over the entire valley.  The 500mb pattern is sketchy after week 3.

[Stovepipe]

Great discussion today friends!  Does DT regularly put out those kind of videos?  That was the best I've seen from him outside of an amwx call in show, very informative.  I hope to see more of those this winter.  Glad to see you local folks getting fired up, time to stock up on popcorn!  

 

[Carvers Gap]

CAPE over in the MA described the weeklies as chaotic.  I concur.  The control was full of wild swings and almost looked like it was "guessing."  I would add...nothing overly exciting on the mean.  As always, it is the details that matter and we understandably don't see those on a broad brush LR model.  The phrase "flip a coin" was also used by someone...pretty much sums it up.