Severe Thunderstorm Warning 278, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
436 PM EDT THU AUG 21 2014

.SYNOPSIS...
A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL CONTINUE TO PROVIDE
VERY WARM TEMPERATURES ACROSS THE REGION INTO SATURDAY. A BACK DOOR
COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST USHERING IN
COOLER TEMPERATURES STARTING SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 430 PM...LATEST CAM AND SYNOPTIC GUIDANCE NOT VERY BULLISH ON
CONVECTIVE CHANCES THIS AFTERNOON. ALL THE GUIDANCE SHOWS THE
CURRENT CONVECTION OVER THE BLUE RIDGE DISSIPATING IN THE MORE
STABLE AIR OVER THE FOOTHILLS AND PIEDMONT AS THE CONVECTION MOVES
SE. IN FACT...THEY ARE EVEN SUGGESTING THE CONVECTION OVER THE KY
AND WV WILL DISSIPATE AS IT MOVES SE TOWARD THE AREA. WILL NOT GO
THAT FAR...BUT WILL KEEP THE CURRENT POP TREND OF DIMINISHING THE
BLUE RIDGE POP AND INCREASING POP ACROSS THE NRN TIER FOR THE
CONVECTION TO OUR NW. THAT SAID...WOULD NOT BE SURPRISED IF POP IS
TRIMMED EVEN FURTHER AT THE 730 PM UPDATE IF THESE TRENDS CONTINUE.
OTHERWISE...UPDATES WERE FOR CURRENT CONDITIONS.

AS OF 215 PM EDT...A PROMINENT 500 MB RIDGE AXIS WILL PERSIST OVER
THE LENGTH OF THE MS RIVER VALLEY TONIGHT THROUGH FRI. CONVECTION
ARISING FROM IMPULSES RIDING OVER THE UPPER RIDGE HAS ALREADY FILLED
IN ON REGIONAL RADARS FROM SE KY TO WV THIS AFTN. HOWEVER...THE
CONVECTION ALLOWING MODELS STILL SHOW THE BEST AFTN TSTM TRIGGERING
OVER THE SRN MTNS WHERE LAPS SFC BASED CAPE VALUES ARE RUNNING 3000
TO 4000 J/KG. THEN...THE MESOSCALE MODELS DEPICT THE WEAK CONVECTIVE
SYSTEM TO THE N PASSING MAINLY NORTH OF THE AREA THIS EVENING. SOME
TRAILING CONVECTION FROM THIS NRN SYSTEM MAY BRUSH THE NRN TIER FROM
21Z TO 03Z. MAINLY MID AND HIGH DEBRIS CLOUDS SHOULD LINGER THROUGH
THE NIGHTTIME HOURS...WITH ANY FOG AND LOW CLOUD ISSUES CONFINED TO
THE SW MTN VALLEYS. EXPECT ANOTHER NIGHT OF MILD MINS...WITH MAINLY
LOW TO MID 60S IN THE MTNS AND AROUND 70 ELSEWHERE.

THE FLOW PATTERN BETWEEN THE RIDGE AND A NEW ENGLAND LOW PRES SYSTEM
WILL AMPLIFY ON FRI...WITH MORE NNW FLOW DEVELOPING ALONG THE
APPALACHIANS BETWEEN THESE FEATURES. THIS SHOULD BRING THE NRN TIER
OF THE FORECAST AREA A BIT MORE INTO THE PATH OF ANY UPSTREAM MCS
ACTIVITY FROM THE OH VALLEY LATE FRI. IN ADDITION...SFC BASED
INSTABILITY AND LAPSE RATES LOOK JUST A TOUCH MORE ROBUST FOR FRI
AFTN...BUT STILL RELATIVELY UNIMPRESSIVE FOR SEVERE WX COMPARED TO
UPSTREAM AREAS. OTHERWISE...WESTERLY DOWNSLOPING 850 MB FLOW THROUGH
THE PERIOD WILL MAKE IT A STRUGGLE TO GET MUCH CONVECTION GOING FROM
OTHER SOURCES...AND MAX TEMPS WILL LIKELY GAIN A DEGREE OR SO OVER
THU VALUES. SRN PIEDMONT HEAT INDEX VALUES COULD SURPASS 100 FRI
AFTN IF WE SEE SLIGHTLY LESS DEWPOINT MIXING.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 210 PM THURSDAY...STRONG UPPER RIDGE WILL PERSIST OVER THE
MISS VALLEY THROUGH THE PERIOD...PLACING MUCH OF THE SOUTHEAST AND
MID-ATLANTIC WITHIN MODERATE N/NW UPPER FLOW. OUR AREA WILL
THEREFORE REMAIN SUSCEPTIBLE TO /RING OF FIRE/ CONVECTION DEVELOPING
NEAR QUASI-STATIONARY FRONTAL ZONE ACROSS THE OHIO VALLEY/CTRL
APPALACHIANS REGION...WHICH COULD DROP INTO THE CAROLINAS IN
SOMEWHAT ORGANIZED FASHION DURING THE AFTERNOON AND EVENING.
THERMODYNAMIC PROFILES WILL REMAIN SUFFICIENT TO SUPPORT ISOLATED
SEVERE WEATHER SATURDAY AFTERNOON/EVENING.

BY THE END OF THE PERIOD...THE FRONTAL ZONE MAY BEGIN TO BACK DOOR
ITS WAY INTO THE AREA BY EARLY SUNDAY...AS THE STILL-BUILDING UPPER
RIDGE BEGINS TO SQUEEZE THE DOWNSTREAM UPPER LOW OFF THE EAST
COAST...ALLOWING WEAK SURFACE RIDGING TO BUILD DOWN THE EASTERN
SEABOARD. THEREFORE...IN ADDITION TO THE CONTINUED THREAT OF
MIGRATION OF UPSTREAM CONVECTION INTO THE AREA...THE BACKDOOR FRONT
MAY PROVIDE AN ADDITIONAL FOCUS FOR CONVECTION ON SUNDAY. HOWEVER...
EXACTLY WHERE THE BEST CHANCES WILL OCCUR IS STILL SUBJECT OF
DEBATE...AS THE AIR NORTH OF THE BOUNDARY MAY BE TOO STABLE TO
SUPPORT MUCH IN THE WAY OF PRECIP CHANCES. THE HIGHEST POPS WILL BE
FAVORED ACROSS THE SOUTHWEST ZONES...WHERE CONFIDENCE IN ADEQUATE
INSTABILITY IS HIGHEST...AND A WEAK EASTERLY FLOW MAY PROVIDE AN
ADDITIONAL SOURCE OF LIFT NEAR THE BLUE RIDGE. TEMPS WILL REMAIN
ABOVE NORMAL UNTIL SUNDAY...WHEN MAXES WILL LIKELY BE BELOW NORMAL
UNDER MORE EXTENSIVE CLOUD COVER AND E/NE FLOW.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 1230 PM THURSDAY...THE MEDIUM RANGE MODEL CONSENSUS PROVIDES
GOOD CONTINUITY FROM INHERITED FCST TO START OFF THE WORKWEEK. STILL
EXPECTING SFC RIDGING TO BE NOSED SSWD INTO THE CWFA WHILE UPPER
RIDGE AXIS BUILDS INTO THE EASTERN CONUS. SENSIBLE WX WILL FEATURE
MAX TEMPERATURES ABOUT 5 DEG F BELOW CLIMO WITH POSSIBLY A FEW
SHOWERS FORCED BY THE EASTERLY LLVL FLOW. SUPPRESSED ORIENTATION TO
AMOPSHERE LOOKS TO CONTINUE INTO TUESDAY WITH EFFECTIVELY MINIMAL
SHOWER CHANCES AND TEMPERATURES PERHAPS WARMING A FEW DEG F.
DEEPER LAYERED RIDGING IS PROGGED TO BREAK DOWN DURING THE LATTER
HALF OF THE PERIOD...ALLOWING TEMPERATURES TO CLIMB BACK TO NORMAL
AND PERHAPS THUNDERSTORM CHANCES RETURNING BY THURSDAY.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
AT KCLT...THE MIXING OUT OF DEWPOINTS HAS LED TO A FAIRLY PALTRY
CUMULUS FIELD THIS AFTN. LATEST CAM AND SYNOPTIC GUIDANCE SHOWS NO
CONVECTION REACHING OR EVEN APPROACHING THE AIRFIELD THIS AFTERNOON
AND EVENING. THEREFORE...WILL KEEP JUST A LITTLE INCREASE IN VFR
CLOUDS THROUGH THE EVENING HOURS...TRANSITIONING TO MID AND HIGH
DEBRIS CLOUDS FOR THE OVERNIGHT. NW SFC WINDS EARLY ARE EXPECTED TO
TOGGLE TO WSW THIS EVENING AND THEN RETURN TO NW THROUGH FRIDAY
MORNING WITH SLOWLY IMPROVING MIXING. ANY CONVECTIVE CHANCES FOR NW
NC LOOK RELEGATED TO THE AFTN PERIOD FRI AND WILL NOT BE MENTIONED
IN THE CURRENT KCLT TAF THROUGH 18Z.

ELSEWHERE...LATEST CAM AND SYNOPTIC GUIDANCE SHOWS THE BLUE RIDGE
CONVECTION DIMINISHING AS IT MOVES SE INTO THE MORE STABLE FOOTHILLS
AND PIEDMONT THIS AFTERNOON AND EVENING. IN FACT...THE GUIDANCE ALSO
SHOWS THE CONVECTION TO THE NW OF THE AREA DISSIPATING BEFORE
REACHING THE AREA. FOR NOW...WILL KEEP THE VCTS AT KAVL/KHKY BASED
ON RADAR TRENDS...BUT THIS COULD BE OVERDONE. IF CURRENT TRENDS
HOLD...NO AMD WILL BE NEEDED FOR THE SC SITES AS CONVECTION
DISSIPATES. EXPECT MAINLY FEW TO SCT CUMULUS SOUTH...WITH LITTLE
MORE THEN BRIEF VFR CIGS ACROSS THE NRN TIER THROUGH EVENING...WITH
LINGERING MID AND HIGH DEBRIS CLOUDS OVERNIGHT. THE HIGH CLOUDS MAY
HELP TO CURTAIL FOG FORMATION...AND THE RELATIVELY DRY MIXING OF
DEWPOINTS THIS AFTN ALSO SUGGESTS THAT ANY IFR FOG WOULD BE CONFINED
TO JUST THE SW MTN RIVER VALLEYS NEAR DAYBREAK. WILL KEEP ALL TAFS
DRY ON FRI THROUGH 18Z. EXPECT MAINLY LIGHT W TO NW WINDS...BRIEFLY
GUSTY AT KAVL THIS AFTN...TOGGLING SW IN SC OVERNIGHT. WINDS WILL
COME UP FROM THE NW WITH MIXING THROUGHOUT ON FRI MORNING.

OUTLOOK...A SIMILAR PATTERN TO LATE THU IS EXPECTED FRI AFTN AND FRI
NIGHT...WITH MAINLY FAR NRN TIER SCT CONVECTION POSSIBLE. A BACKDOOR
COLD FRONT WILL SAG INTO THE REGION THROUGH THE WEEKEND...WITH
CHANCES OF RESTRICTIONS INCREASING AT KHKY AND KAVL. A MORE DIURNAL
PATTERN OF EARLY MORNING LOW CLOUDS/FOG AND SCATTERED AFTN TSTMS MAY
RETURN EARLY NEXT WEEK.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   72%     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: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

SYNOPSIS...CSH
NEAR TERM...HG/RWH
SHORT TERM...JDL
LONG TERM...CSH
AVIATION...HG/RWH

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