Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
710 PM EST Wed Mar 1 2017

.SYNOPSIS...
A cold front will cross the area tonight, followed by cool high
pressure that gradually builds in from the northwest through the end
of the week. The high will slide east of the area late in the
weekend, allowing return flow to bring above normal temperatures
back in for early next week. Another cold front approaches from the
west midweek.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 700 PM EST: Quite a night across the GSP forecast area. The
HRRR had it spot-on with the discrete cells ahead of the line, and
with plentiful low-level shear, most have been supercells with much
larger hail than originally expected. Wind damage reports trickling
in now as well. So far no reported tornadoes, just might not be
enough low-level instability to get them to the ground, but at least
a couple of reports of wall clouds. The convective line has moved
east and so with this update have cleared several counties in NC from
the Severe Thunderstorm Watch. Adjusted pops/wx accordingly.

Otherwise, the approaching strong cold front has reached a line from
Nashville, TN to Jackson, MS this afternoon. Deep convection ahead
of this front has developed in the rich, mid 60s dewpoint air from
far northern AL to southeast TN, with increasing support from upper
divergence associated with a 140+ kt jetlet at 300 mb. The plume of
abundant low level theta e will stretch toward the southwest part of
our forecast area through mid to late afternoon. In addition, the
more northern parts of the line advancing across TN will likely pose
a severe wind threat to the TN/NC border counties this afternoon as
well. Gusty southwest winds will continue throughout the forecast
area through late afternoon as deep mixing from the warm
temperatures will reach closer to the 40 to 50 kt low level jet
moving overhead. Warm advection gusts should be sub-advisory, but an
SPS has been issued for gusts in the 30 to 40 mph range.

The convective threat will them ramp up from the west and southwest
after 20Z for all of our area. Convection-allowing models indicate
discrete cellular development firing well southeast of the main
activity through the late afternoon hours. Still anticipate the best
mountain timing from the mainly frontal band mainly 19Z to 23Z, with
foothills timing generally 22Z to 01Z, and lower piedmont mainly 00Z
to 03Z. A pocket of fairly steep lapse rates will cross the region
with the deeper convection, permitting the capping inversion to
dissipate. It appears that best overlap of instability and shear
will affect northeast GA, the extreme southern NC mountains, and the
western SC Upstate around 21z and this is where the tornado threat
will be highest. Consensus SBCAPE values should reach 1000+ J/kg
during the peak. Sfc to 3 km bulk shear is expected to exceed 50 kt,
with sfc to 6 km values 70+ kt. A damaging wind threat will be
supported throughout the entire area through early evening as these
convective features translate east.

Cold advection winds behind the front should pick up with the
arrival of an embedded 50 kt jet from 06Z onward. A wind advisory
will be posted for the higher terrain from the French Broad Valley
northward along the Blue Ridge. The gradient will slowly relax
through Thursday as dry high pressure stretches from the southern
plains to southern Appalachians. Max temps will be some 15 to 20
degrees cooler than today in most areas, more in the higher terrain.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 200 PM EST Wednesday: The ulvl pattern remains broadly
cyclonic through the period...with a strong s/w swinging by north of
the area early Fri. This wave will have little if any effect on the
FA as the sfc trof reflection is weak and very limited wrt to
moisture. The GFS does produce weak upslope -shra arnd daybreak
Fri...however all other op models remain quite dry during this time.
So...little change will be made to the PoP grids thru the
period...meaning dry conds thru Sat evening.

There will be a couple non/precip concerns however. As high pressure
builds in Fri afternoon....the p/grad will increase and a measure of
llvl CCA will enable gusty high elev mtn winds likely reaching adv
levels into the early evening. Dry cP air mixing in will also make
for low RH values Fri/Sat afternoons creating possible fire-wx
concerns. Winds should not be an issue...yet a FDS may be needed
across NE GA and the Upstate depending on fuel moisture levels.
Another concern will be for frost/freeze outside the mtns. Thu night
looks okay...even with mins reaching frost temps...as sfc winds look
to remain mixed keeping td/s rather low. Mins on Fri night should
easily reach freezing or below across the majority of the non/mtns
as the cP sfc high settles in. A freeze watch may be issued on Thu
if the cold guidance trend continues. With the expected airmass
mix...max temps will remain arnd or a bit below normal thru the
period in mostly sunny skies.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 145 PM EST Wednesday: Models are in pretty good agreement on
the overall pattern to start out the medium range. An upper trough
will exit off the East Coast Saturday night thru Sunday, then a
large ridge builds in late Sunday thru Tuesday, becoming fairly
amplified. Models begin to diverge with the next trough that will
cross the Rockies and reach the Great Lakes by Tuesday night. The
12z GFS is much deeper than the 12z EC/CAN. This results in a slower
timing of the next cold front. But the 12z EC has come in a little
slower than the previous run, closer to the GFS on the front's
arrival late Tuesday. However, the EC has the upper trough quickly
dampening into zonal flow, it hangs the front up across the area
Wed-Thu. I opted to stay close to the WPC, which has PoPs ramp up a
little quicker than the GFS, but not as slow as the EC. And the
stalled front on the 12z EC is a new development, so I have PoPs
taper off by early Wednesday for now. Temps will start out seasonably
cool early Sunday, but warm back up to about 10-15 deg above normal,
with highs in the lower 70s expected across most of the Piedmont by
Monday.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Strong cold front moving across the area with
discrete +TSRA moving across the area. KAVL/KHKY behind the
convective line but other TAFs still carry TEMPO TSRA with winds G35-
45kt. Any restrictions would be temporary in nature and associated
with the TSRA themselves. Good news is that behind the convective
line, conditions should improve rapidly as the front is moving very
quickly. Have winds shifting NW at KCLT by 06z, with clearing behind
it. Some gusty winds may still be possible tomorrow especially at
KAVL where wind advisory remains in effect.

Outlook: Drier conditions will set up behind the front from Thursday
through the weekend into early next week. A reinforcing front will
cross the region Friday, but with very limited moisture.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Wind Advisory until noon EST Thursday for NCZ033-049-050-053-
     065-501-503-505-507-509.
SC...None.

&&

SYNOPSIS...ARK
NEAR TERM...HG/TDP
SHORT TERM...SBK
LONG TERM...ARK
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
317 PM EST Wed Mar 1 2017

GAZ010-017-NCZ048-051-052-058-059-062>064-SCZ001>003-022030-
Rabun-Habersham-Madison-Swain-Haywood-Graham-Northern Jackson-Macon-
Southern Jackson-Transylvania-Oconee Mountains-Pickens Mountains-
Greenville Mountains-
317 PM EST Wed Mar 1 2017

...SEVERE THUNDERSTORM WATCH 59 IN EFFECT UNTIL 10 PM EST THIS
EVENING...

This Hazardous Weather Outlook is for northeast Georgia, western
North Carolina and upstate South Carolina.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

..Thursday...High winds possible. Gusty northwest winds will
continue across the mountains into Thursday morning.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time..
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.
..Tuesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of large
hail...damaging winds...tornadoes or flash flooding to our office.

NCZ033-049-050-053-065-501-503-505-507-509-022030-
Avery-Yancey-Mitchell-Buncombe-Henderson-Caldwell Mountains-
Burke Mountains-McDowell Mountains-Rutherford Mountains-
Polk Mountains-
317 PM EST Wed Mar 1 2017

...SEVERE THUNDERSTORM WATCH 59 IN EFFECT UNTIL 10 PM EST THIS
EVENING...
...WIND ADVISORY IN EFFECT FROM 8 PM THIS EVENING TO NOON EST
THURSDAY...

This Hazardous Weather Outlook is for western North Carolina.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Severe Thunderstorm Watch.
   Wind Advisory.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

..Thursday...High winds possible. Gusty northwest winds will
continue across the mountains into Thursday morning.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time..
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.
..Tuesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of large
hail...damaging winds...tornadoes or flash flooding to our office.

GAZ018-026-028-029-NCZ035>037-056-057-068>072-082-502-504-506-508-
510-SCZ004>014-019-022030-
Stephens-Franklin-Hart-Elbert-Alexander-Iredell-Davie-Catawba-Rowan-
Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-Greater Caldwell-
Greater Burke-Eastern McDowell-Greater Rutherford-Eastern Polk-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Chester-Greenwood-
317 PM EST Wed Mar 1 2017

...SEVERE THUNDERSTORM WATCH 59 IN EFFECT UNTIL 10 PM EST THIS
EVENING...

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...Frost/freeze possible. Temperatures are expected to
drop to near or below freezing early Saturday morning. With the
early start to the growing season, a Freeze Warning may be needed.
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.
..Tuesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of large
hail...damaging winds...tornadoes or flash flooding to our office.

Krentz

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