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Nov. 27th - Nov. 29th Upper Level Low


LithiaWx

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18Z NAM closes off 540DM at 5H over border of AL/TN. Precip wraps around nicely. Possible snow over N AL/MS into Central TN. 5H low rotates into Central TN. Western TN getting highest QPF rates and deformation band could be setting up. Hr72 ULL moving into Eastern TN nice deformation band in Western TN. Snow/flurries over Central TN/N MS. N AL/GA should be seeing snow, with light sn-shrs/flurries down in BHM-ATL metros, maybe mixing with rain. By Hr 78 the heaviest of snow is too our north for the Ohio Valley guys. Still plenty of wrap around moisture, again depending on BL temps either a mix or light snow showers/flurries down to BHM-ATL metros. Light Snow/flurries over most of TN into the Western sections of the Carolinas. By 84 still light snow over TN far N AL/GA and along the Apps. BL temps on soundings will have to be carefully checked to verify some of these locations.

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After reading this, I am wondering a bit about the severe threat in the Carolinas with this system. Any other opinions?

SEVERE THREAT:ALTHOUGH FORCING WILL LARGELY BE ABSENT THROUGH MONDAY AFTERNOON(PARTICULARLY EAST OF HWY 1)...IF THERE ARE BREAKS IN CLOUD COVERAND DIURNAL INSTABILITY DEVELOPS...LOW LEVEL WARM ADVECTION MAY BESUFFICIENT TO RESULT IN THE DEVELOPMENT OF ISOLD CONVECTION...ORDIURNAL INSTABILITY COULD SUSTAIN ANY CONVECTION THAT MAY MOVEONSHORE IN LOW-LEVEL SOUTHEAST FLOW. WITH THIS IN MIND...IF AN ISOLDCONVECTION DEVELOPS MON AFTERNOON...LOW/DEEP LAYER SHEAR WOULD BEMORE THAN SUFFICIENT FOR SUPERCELLS.A VERY CLOSE ANALOG TO THIS SYSTEM (W/REGARD TO THE SYNOPTICPATTERN) IS THE NOVEMBER 16 2006 EVENT THAT RESULTED IN FAIRLYWIDESPREAD WIND DAMAGE IN ASSOC/W A STRONGLY FORCED LINE OFCONVECTION ALONG THE FRONT IN ADDITION TO ISOLATED TORNADICSUPERCELLS (ONE OF WHICH SPAWNED A DEADLY EF3 TORNADO IN COLUMBUSCOUNTY) MOVING INLAND AHEAD OF THE FRONT IN ASSOC/W SOUTHEASTERLYLOW LEVEL FLOW OFF THE ATLANTIC. THE KINEMATIC ENVIRONMENTALONG/AHEAD OF THE FRONT MON NIGHT WILL BE CHARACTERIZED BY EXTREMELOW/DEEP LAYER SHEAR...WITH A 50-60 KT SOUTHEASTERLY LLJ AT 925-850MB AND A 75-100 KT SOUTHERLY JET AT 500 MB. UPPER AND LOWER LEVELFORCING IS ALSO PROGGED TO BE IMPRESSIVE...WITH STRONG HEIGHT FALLS(100-180 METERS BETWEEN 00-12Z TUE) COINCIDENT WITH THE COLD FRONTALPASSAGE MON NIGHT. THE PRIMARY LIMITING FACTOR WILL OF COURSE BEINSTABILITY...IN PART DUE TO POOR DIURNAL TIMING. HOWEVER...GIVEN ANATYPICALLY LONG PERIOD (18-24 HRS) OF STRONG SOUTH/SE FLOW OFF THEATLANTIC AHEAD OF THE FRONT... ANTICIPATE DEWPOINTS TO RISE INTO THELOWER 60S...PARTICULARLY IN THE SANDHILLS/COASTAL PLAIN. THIS...INADDITION TO GOOD LAYER-LIFTING ASSOC/W STRONG HEIGHT FALLS INADVANCE OF THE UPPER LOW MAY BE SUFFICIENT TO RESULT IN MARGINALSURFACE-BASED INSTABILITY OVER ALL OR PORTIONS OF THE AREA...DESPITEPOOR DIURNAL TIMING. AS A RESULT...SEVERE STORMS /DAMAGING WINDS/WILL CERTAINLY BE POSSIBLE ALONG AND AHEAD OF THE FRONT MONDAYEVE/NIGHT...IN ADDITION TO ISOLATED TORNADOES. -VINCENT

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1322344941[/url]' post='1144478']

I'm in the bullseye here in Glenville, NC. Just checked to make sure there weren't any spider webs in my Vantage Vue rain gauge.

Ready for the deluge. I sure hope the northwest flow is strong enough to lay some accumulations here.

I doubt nw flow will provide anything more than just flurries or perhaps a rogue light snow shower. Even during our (jackson county) more robust and even intense nw flow events the southern section of the county rarely gets accumulations. Now, our best chance for accumulating snow will be Monday night or tuesday night. I'd say up to an inch is possible for you.

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After reading this, I am wondering a bit about the severe threat in the Carolinas with this system. Any other opinions?

SEVERE THREAT:ALTHOUGH FORCING WILL LARGELY BE ABSENT THROUGH MONDAY AFTERNOON(PARTICULARLY EAST OF HWY 1)...IF THERE ARE BREAKS IN CLOUD COVERAND DIURNAL INSTABILITY DEVELOPS...LOW LEVEL WARM ADVECTION MAY BESUFFICIENT TO RESULT IN THE DEVELOPMENT OF ISOLD CONVECTION...ORDIURNAL INSTABILITY COULD SUSTAIN ANY CONVECTION THAT MAY MOVEONSHORE IN LOW-LEVEL SOUTHEAST FLOW. WITH THIS IN MIND...IF AN ISOLDCONVECTION DEVELOPS MON AFTERNOON...LOW/DEEP LAYER SHEAR WOULD BEMORE THAN SUFFICIENT FOR SUPERCELLS.A VERY CLOSE ANALOG TO THIS SYSTEM (W/REGARD TO THE SYNOPTICPATTERN) IS THE NOVEMBER 16 2006 EVENT THAT RESULTED IN FAIRLYWIDESPREAD WIND DAMAGE IN ASSOC/W A STRONGLY FORCED LINE OFCONVECTION ALONG THE FRONT IN ADDITION TO ISOLATED TORNADICSUPERCELLS (ONE OF WHICH SPAWNED A DEADLY EF3 TORNADO IN COLUMBUSCOUNTY) MOVING INLAND AHEAD OF THE FRONT IN ASSOC/W SOUTHEASTERLYLOW LEVEL FLOW OFF THE ATLANTIC. THE KINEMATIC ENVIRONMENTALONG/AHEAD OF THE FRONT MON NIGHT WILL BE CHARACTERIZED BY EXTREMELOW/DEEP LAYER SHEAR...WITH A 50-60 KT SOUTHEASTERLY LLJ AT 925-850MB AND A 75-100 KT SOUTHERLY JET AT 500 MB. UPPER AND LOWER LEVELFORCING IS ALSO PROGGED TO BE IMPRESSIVE...WITH STRONG HEIGHT FALLS(100-180 METERS BETWEEN 00-12Z TUE) COINCIDENT WITH THE COLD FRONTALPASSAGE MON NIGHT. THE PRIMARY LIMITING FACTOR WILL OF COURSE BEINSTABILITY...IN PART DUE TO POOR DIURNAL TIMING. HOWEVER...GIVEN ANATYPICALLY LONG PERIOD (18-24 HRS) OF STRONG SOUTH/SE FLOW OFF THEATLANTIC AHEAD OF THE FRONT... ANTICIPATE DEWPOINTS TO RISE INTO THELOWER 60S...PARTICULARLY IN THE SANDHILLS/COASTAL PLAIN. THIS...INADDITION TO GOOD LAYER-LIFTING ASSOC/W STRONG HEIGHT FALLS INADVANCE OF THE UPPER LOW MAY BE SUFFICIENT TO RESULT IN MARGINALSURFACE-BASED INSTABILITY OVER ALL OR PORTIONS OF THE AREA...DESPITEPOOR DIURNAL TIMING. AS A RESULT...SEVERE STORMS /DAMAGING WINDS/WILL CERTAINLY BE POSSIBLE ALONG AND AHEAD OF THE FRONT MONDAYEVE/NIGHT...IN ADDITION TO ISOLATED TORNADOES. -VINCENT

SPC says....

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0134 AM CST SAT NOV 26 2011

VALID 281200Z - 291200Z

...SOUTHEAST...

ALTHOUGH GUIDANCE HAS BECOME MORE CONSISTENT WITH THE TRANSITION TO

A CUTOFF UPPER-LEVEL LOW CENTERED INVOF LOWER MS VALLEY AT

12Z/MON...SPREAD BETWEEN ECMWF/SREF ENSEMBLE MEMBERS AND

DETERMINISTIC ECMWF/GFS/NAM/CMC RUNS IS VERY LARGE WITH THE DETAILED

EVOLUTION OF THIS LOW IN THE SOUTHEAST ON D3. THIS BREEDS RATHER LOW

CONFIDENCE IN THE PLACEMENT OF ATTENDANT KINEMATIC FEATURES AS WELL

AS THE ASSOCIATED SURFACE COLD FRONT THAT SHOULD SERVE AS A FOCUS

FOR CONVECTIVE DEVELOPMENT. AMBIENT INSTABILITY APPEARS TO REMAIN

QUITE LIMITED...BUT A NARROW CORRIDOR OF WEAK BUOYANCY COULD DEVELOP

SOMEWHERE ALONG THE FRONT FROM THE COASTAL PLAINS OF GA TO NC. GIVEN

THESE FACTORS /ESPECIALLY CONSIDERING THE LOW CONFIDENCE OVER THE

SYNOPTIC PATTERN EVOLUTION/...WILL DEFER TO LATER OUTLOOKS FOR

POSSIBLE INCLUSION OF SEVERE PROBABILITIES.

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I doubt nw flow will provide anything more than just flurries or perhaps a rogue light snow shower. Even during our (jackson county) more robust and even intense nw flow events the southern section of the county rarely gets accumulations. Now, our best chance for accumulating snow will be Monday night or tuesday night. I'd say up to an inch is possible for you.

During the stronger events MBY is within range but near the furthest reaches it seems whereas Cashiers will have blue skies.

Hoping my five month old daughter can see her first flakes. A wishcast for sure.

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1322345575[/url]' post='1144490']

During the stronger events MBY is within range but near the furthest reaches it seems whereas Cashiers will have blue skies.

Hoping my five month old daughter can see her first flakes. A wishcast for sure.

You live near big ridge which makes sense. I keep generalizing southern Jackson too much. I think she will see flakes fly if not stick.

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I've been interested in the one around the 1st, or so. 18z is closing it over Ga. looks like, and it's pretty far south. Cheez mentioned this one the other day, then I think it was gone 'til the 5th.....and now there it is. Haven't checked how cold it is, but if it happens, and finds it's own cold air.....

I still have problems getting too enthused about the 18z :) But this is sure an odd looking fall so far...lots of excitement and still no real cold. T

Edit: Huh....guess I was looking at a stored map :) Never mind, lol. Sorry...but it did look good. T

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NWS Blacksburg

Precipitation type still a tough call Tuesday evening. With the cutoff low...pockets and layers of warm and cold air will have some places seeing snow...others seeing rain and may be isolated areas of freezing drizzle. Best snow chances will be in the higher elevations with possible freezing drizzle on western slopes. As the low moves north...a deeper layer of cold air will bring mostly snow to the mountains late Tuesday night into the day Wednesday. Accumulations on Wednesday best on western slopes with flurries toward the Blue Ridge. Pressure rises also increasing Wednesday for windy and gusty conditions. These winds may be strong enough to push flurries into the foothills and Roanoke valley.

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Comparing 00z NAM to this morning's 12z run thru 36hr, upper low is not quite as deep (very small difference), but the vort maxes are stronger....I would take the stronger vort maxes....also, the upper low is not going toward negative tilt quite as fast....so, both of these are good in my view from an overall strength standpoint of the upper low.

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I am reasonably impressed w/ the 0z NAM's handling of the low. Though easily entertained...When I animated the maps, it's pretty impressive that a computer can model a low just wandering around. If you think about it, computer modeling has come light years during the past two decades.

(edit) Looks like the NAM is running on Foothills' top secret model he has stored in his basement.:whistle:

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The trough extends down into the Central Gulf on this cutoff, no wonder its being calculated as 4 to 5 Standard deviations below normal. Its actually tapping moisture from past Campeche well down toward Central America.

This run looks similar maybe a little south. Has the moisture rotate through ATL by Tuesday morning associated with pretty cold air aloft (-6).

The surprise snow in def. band should still occur around Memphis to Tupelo well before this time period though. This run still gives northern Miss. and west TN the best chance at snow. It even brings precip to western SC and the western piedmont of NC during the day Tuesday as the cold core passes over the Mtns of NC.

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The wave entering the Pacific NW flattens the ridge behind our upper low, and that throws the upper low more NNE instead of NE...best snows look to be in N MS/AL, and most of western TN.

The NAM still has the vort and associated moisture running through ATL Tuesday morning with the -6 air...pretty sure that should be snow, if thats real. Normally spokes do rotate around very much like this under a Cutoff, so I'm still expecting atleast a period or maybe 2 periods of snow bands to pass across northern third to 1/2 of GA. The lions share does look to stay put in n. Miss and probably around MEM or just east of there.

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The NAM still has the vort and associated moisture running through ATL Tuesday morning with the -6 air...pretty sure that should be snow, if thats real. Normally spokes do rotate around very much like this under a Cutoff, so I'm still expecting atleast a period or maybe 2 periods of snow bands to pass across northern third to 1/2 of GA. The lions share does look to stay put in n. Miss and probably around MEM or just east of there.

do you think 'thunder snow' is possible given the dynamics of this system?

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The NAM still has the vort and associated moisture running through ATL Tuesday morning with the -6 air...pretty sure that should be snow, if thats real. Normally spokes do rotate around very much like this under a Cutoff, so I'm still expecting atleast a period or maybe 2 periods of snow bands to pass across northern third to 1/2 of GA. The lions share does look to stay put in n. Miss and probably around MEM or just east of there.

Thanks for the update! I really hope we see some snow fly... ugh I'm such a weenie. :lol:

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