Special Weather Statement, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
243 PM EDT FRI SEP 28 2012

.SYNOPSIS...
HIGH PRESSURE ATOP THE REGION WILL GIVE WAY TO AN APPROACHING COLD
FRONT OVERNIGHT. THE FRONT WILL STALL OUT OVER THE CAROLINAS
BRINGING UNSETTLED WEATHER TO THE REGION AS A LOW RIDES UP ALONG THE
FRONT SATURDAY INTO THE FIRST PART OF THE WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 230 PM...AXIS OF A SHORTWAVE TROF WAS ANALYZED ENTERING THE
SRN APPALACHIANS...HELPING AID IN DEVELOPING CONVECTION ALONG THE
BLUE RIDGE FROM THE NRN MTNS NORTH INTO VA. THE HIGH RES MODELS AND
OP MODELS AGREE ON SCATTERED STORMS SURVIVING AS THEY TRACK EAST
INTO THE NC PIEDMONT. SPC MESOANALYSIS SHOWS 1000-1500 J/KG OF
SBCAPE FROM THE BLUE RIDGE EAST. LAPS SNDGS SHOW SOME MID LVL DRY
AIR AND DECENT LLVL LAPSE RATES. SO A FEW STORMS MAY BECOME SEVERE
PRODUCING GUSTY WINDS AND HAIL. MORE ISOLD COVERAGE EXPECTED TO THE
SOUTH LATER THIS AFTN INTO EARLY EVENING.

TONIGHT...A ZONALLY-ORIENTED SFC FNT WILL PUSH INTO THE AREA WITH
MOISTURE. MEANWHILE...HEIGHTS WILL FALL ALOFT...AS A POLAR VORTEX
CENTERED OVER NRN ONTARIO DROPS SOUTH TOWARD THE GREAT LAKES.
Q-VECTOR CONVERGENCE WILL BE ON THE INCREASE...HELPING SUPPORT LIFT
ACRS THE CWFA. SO ISOLD TO SCATTERED SHWRS AND A FEW TSTMS WILL BE
POSSIBLE THRU THE NIGHT...ESPECIALLY ALONG THE I-40 CORRIDOR. TEMPS
WILL BE IN THE 50S MTNS AND LWR-MID 60S PIEDMONT.

SATURDAY...FORCING LOOKS TO MAXIMIZE IN THE 12-18Z TIME FRAME...AS
AN UPPER TROF AXIS SWINGS THRU THE OH VLY TO THE APPALACHIANS. WHILE
THE SFC FRONT IS PROGGED TO SETTLE ACRS THE LWR PIEDMONT...THE
DRIER/COOLER AIR WILL REMAIN BACK TO THE NORTH...ALLOWING FOR SOME
INSTBY ACRS THE ENTIRE AREA. FCST SNDGS SHOW MOIST SOUNDINGS WITH
INCREASING SHEAR. SO WHILE COVERAGE OF SHWRS LOOKS GREATER THAN
TODAY...SEVERE THREAT SHUD BE LOW GIVEN THE MOIST SNDGS. GOING WITH
LIKLY POPS FOR PRETTY MUCH THE ENTIRE NC PORTION OF THE CWFA WITH
CHC TO THE SOUTH. TEMPS WILL BE ABOUT A CATEGORY BELOW NORMAL UNDER
THE CLOUDS AND PRECIP.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 135 PM FRIDAY...A RATHER LOW CONFIDENCE FORECAST EVOLVES
DURING THE SHORT TERM IN DEVELOPING SPLIT FLOW REGIME...AND IN LIGHT
OF LIKELY UPPER LOW DEVELOPMENT IN THE SOUTHERN STREAM. SATURDAY
NIGHT...THE MODELS ARE CONVERGING TOWARD A CONSENSUS OF DRIVING THE
FRONTAL ZONE/DRIER AIR THROUGH THE AREA BY 06Z SUNDAY. AS SUCH...WE
WILL BEGIN DIALING DOWN POPS SUCH THAT THEY WILL BE NO GREATER THAN
SLIGHT CHANCE BY 00Z...AND LESS THAN 20 PERCENT BY 12Z. MODEL
SOLUTIONS THEN BEGIN TO DIVERGE QUITE SUBSTANTIALLY ON SUNDAY. IT IS
CERTAIN THAT WARM CONVEYOR BELT MOISTURE/PRECIP WILL OVERSPREAD THE
REGION EARLY NEXT WEEK...AS AFOREMENTIONED UPPER LOW OPENS UP AND
PROGRESSES EAST. HOWEVER...WHILE THE GFS SUGGESTS THIS EVENT WILL
BEGIN SUNDAY MORNING...THE ECMWF HOLDS OFF PRECIP UNTIL 24 HOURS
LATER. TIMING IN OTHER MODEL SOLUTIONS DEPICTS JUST ABOUT EVERYTHING
IN BETWEEN THESE TWO EXTREMES. THERE IS ALSO TREMENDOUS SPREAD IN
THE ENSEMBLE GUIDANCE. WITH THIS IN MIND...HAVE OPTED FOR A
CONSERVATIVE ROUTE AT THIS POINT...BRINGING A LOW CHANCE POP INTO
OUR WESTERN ZONES BY SUNDAY AFTERNOON...GRADUALLY RAMPING UP TO
SOLID CHANCE ACROSS THE SOUTHERN HALF OF THE AREA BY THE END OF
SUNDAY NIGHT...WITH HIGH CHANCE/LIKELY POPS IN ALL AREAS MONDAY.

ONCE PRECIP BEGINS...THE PRESENCE OF BROAD SURFACE HIGH PRESSURE
OVER THE MID-ATLANTIC SUGGESTS IN-SITU COLD AIR DAMMING WOULD LIKELY
DEVELOP. SINCE WE ARE REASONABLY CONFIDENT THAT PRECIP WILL DEVELOP
BY MONDAY...MAX TEMPS AS MUCH AS 10 DEGREES BELOW CLIMO WILL BE
ADVERTISED.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AT 200 PM EDT FRIDAY...BROAD UPPER TROUGH WILL EXIST ACROSS CANADA
FROM TUESDAY THROUGH FRIDAY...WHILE A SOUTHERN STREAM TROUGH WEAKENS
OVER THE OH...TN AND LOWER MS RIVER VALLEYS. A SURFACE WAVE WILL
MOVE FROM FROM THE GULF STATES MONDAY NIGHT TO THE SOUTHERN
APPALACHIANS BY TUESDAY MORNING. UPGLIDE OVER A WARM FRONT TO THE
EAST...AND UPSLOPE FLOW INTO THE BLUE RIDGE ESCARPMENT...WILL SERVE
TO FOCUS SUBSTANTIAL RAINFALL ACROSS OUR AREA. THE WAVE AND ITS
TRAILING COLD FRONT WILL MOVE EAST OF THE AREA BY WEDNESDAY
MORNING...HOWEVER SLOW MOVEMENT OF THE WAVE AND WRAP AROUND MOISTURE
WARRANT SMALL POPS INTO THURSDAY...EVEN AS HIGH PRESSURE BUILDS IN
FROM THE WEST. A COLD FRONT WILL CROSS OUR AREA FROM THE NW ON
FRIDAY...BUT CONFIDENCE IS LOW THAT THIS SYSTEM WILL HAVE MUCH
MOISTURE TO WORK WITH...AND ONLY MINIMAL POPS WILL BE CARRIED WITH
THIS SYSTEM. THE DIURNAL TEMPERATURE RANGE WILL BE LIMITED BY CLOUDS
AND MOISTURE INITIALLY...FOLLOWED BY COOLING.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...BKN TO OVC CIRRUS THIS AFTN WITH A LIGHT VARIABLE
WIND...GENERALLY FAVORING WSW UNTIL SUNSET THEN WNW. CONVECTION IS
EXPECTED TO CONTINUE DEVELOPING ACRS THE NC MTNS AND NW PIEDMONT
THRU THE AFTN INTO EARLY EVENING...GENERALLY ISOLD TO SCATTERED IN
COVERAGE. GUIDANCE KEEPS MOST OF THIS ACTIVITY NORTH OF THE
TERMINAL...BUT A FEW CELLS MAY GET CLOSE. HAVE VCSH WITH A TEMPO FOR
TS FOR THE 21-24Z TIME FRAME. CONVECTION MAY LINGER INTO THE
OVERNIGHT...AS A FNTL BNDRY SAGS SOUTH INTO THE AREA. FOR NOW...WILL
KEEP OUT MENTION OF CONVECTION FOR NOW. GUIDANCE GENERALLY VFR
OVERNIGHT...BUT SOME MODELS ARE HINTING AT SOME STRATUS AND PATCHY
FOG ACRS THE NC PIEDMONT TOWARD DAYBREAK. CONFIDENCE STILL LOW...BUT
HAVE 6SM BR AND A SCT MVFR CLOUD MENTION. CONVECTIVE CHCS LOOK
BETTER SATURDAY...BUT EXPECTING MOST OF THAT ACTIVITY AFTER 18Z.

ELSEWHERE...SHOWERS AND TSTMS DEVELOPING NORTH OF KAVL AND
KHKY...WITH MORE DEVELOPMENT EXPECTED THRU THE AFTN HOURS. HAVE VCTS
AT BOTH SITES. IN THE UPSTATE...CHCS ARE LOWER SUCH THAT NO MENTION
OF TS WILL BE CARRIED WITH THESE TAFS. THERE IS ABOUT A 20% CHC...SO
NOT OUT OF THE QUESTION A FEW CELLS DEVELOP IN THE UPSTATE.
OTHERWISE...VFR CONDITIONS ARE EXPECTED THRU THIS EVENING WITH WEST
WINDS. OVERNIGHT...GUIDANCE SHOWS SIMILAR FOG POTENTIAL TO LAST
NIGHT...SO TRENDS WILL BE SIMILAR IN THE TAFS. KAVL WILL LIKELY HAVE
SOME FOG OVERNIGHT...AND KHKY HAS THE NEXT BEST CHC BASED ON
POTENTIAL FOR RAINFALL THIS AFTN/EVE. FOR SATURDAY...CONVECTIVE CHCS
INCREASE AS A COLD FRONT SAGS SOUTH INTO THE AREA. HAVE PROB30 AT
ALL SITES FOR END OF 18Z TAF PERIOD.

OUTLOOK...A SLOW-MOVING FRONT WILL STALL ACROSS THE AREA THRU THE
WEEKEND...BRINGING MORE WIDESPREAD RESTRICTIONS IN CLOUDS/PRECIP
EXPECTED AS WEEKEND WEARS ON. AN AMPLIFIED SYSTEM WILL DEVELOP
ACROSS THE DEEP SOUTH EARLY NEXT WEEK. THIS SYSTEM WILL LIKELY
SUPPORT LOW CEILINGS AND RAINFALL ACROSS THE REGION AT LEAST THROUGH
MID WEEK.

AN EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLE SHOWING THE
PERCENTAGE OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED ISSUANCE
CATEGORY IS AVAILABLE AT FOLLOWING LINK (USE LOWER CASE)...

WWW.WEATHER.GOV/GSP/AVIATION/TABLES.HTM

&&

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

&&

SYNOPSIS...JAT
NEAR TERM...ARK
SHORT TERM...JDL
LONG TERM...JAT
AVIATION...ARK

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
311 PM EDT FRI SEP 28 2012

NCZ035-036-056-502-504-282000-
ALEXANDER-CATAWBA-GREATER BURKE-GREATER CALDWELL-IREDELL-
311 PM EDT FRI SEP 28 2012

...STRONG THUNDERSTORMS WILL AFFECT CENTRAL IREDELL...NORTHERN
CATAWBA...SOUTHEASTERN CALDWELL...SOUTHERN ALEXANDER AND SOUTHERN
BURKE COUNTIES THROUGH 400 PM EDT...

AT 311 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM MILLERSVILLE TO 3
MILES EAST OF GRANITE FALLS TO DREXEL...MOVING SOUTHEAST AT 15 MPH.

THESE STORMS WILL IMPACT LOCATIONS NEAR...
  RUTHERFORD COLLEGE...
  ST. STEPHENS...
  ICARD...
  STONY POINT...
  LOOKOUT SHOALS LAKE...

PEA SIZE HAIL...WIND GUSTS UP TO 40 MPH...AND TORRENTIAL RAIN ARE
EXPECTED WITH THESE STORMS. IN ADDITION...HEAVY RAINFALL MAY FLOOD
AREAS WITH POOR DRAINAGE...SUCH AS DITCHES AND UNDERPASSES. AVOID
THESE AREAS AND DO NOT CROSS FLOODED ROADS.

LAT...LON 3593 8110 3589 8080 3578 8082 3566 8107
      3560 8152 3564 8176 3576 8183 3583 8145
      3592 8120

HG

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
317 PM EDT FRI SEP 28 2012

NCZ036-037-057-281945-
DAVIE-IREDELL-ROWAN-
317 PM EDT FRI SEP 28 2012

...STRONG THUNDERSTORMS WILL AFFECT DAVIE...IREDELL AND NORTHWESTERN
ROWAN COUNTIES THROUGH 345 PM EDT...

AT 317 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 3 MILES EAST OF
HUNTSVILLE TO HARMONY TO 4 MILES NORTH OF LOOKOUT SHOALS LAKE...
MOVING SOUTHEAST AT 25 MPH.

THESE STORMS WILL IMPACT LOCATIONS NEAR...
  FARMINGTON...
  BERMUDA RUN...
  STATESVILLE...
  ADVANCE...
  COOLEEMEE...

PEA SIZE HAIL...WIND GUSTS UP TO 40 MPH...AND TORRENTIAL RAIN ARE
EXPECTED WITH THESE STORMS.

LAT...LON 3588 8041 3585 8038 3582 8047 3576 8045
      3554 8090 3558 8095 3562 8093 3570 8099
      3571 8105 3578 8111 3590 8102 3596 8082
      3606 8064 3605 8049 3607 8046 3596 8037
      3589 8036

HG

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