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Area Forecast Discussion

499
FXUS62 KGSP 171848
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
248 PM EDT FRI APR 17 2015

.SYNOPSIS...
DRIER AND WARMER AIR WILL SPREAD INTO THE REGION THROUGH SATURDAY. A
WARM FRONT WILL LIFT NORTHEAST ACROSS THE AREA SATURDAY NIGHT INTO
SUNDAY...ACCOMPANIED BY ABUNDANT MOISTURE AND MORE RAINFALL. A COLD
FRONT WILL CROSS THE AREA ON MONDAY...USHERING IN SEASONABLE
TEMPERATURES AND DRY CONDITIONS.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 245 PM EDT FRIDAY...THE SYNOPTIC PATTERN HAS NOT CHANGED ALL
THAT MUCH FROM YESTERDAY...OR DAYS PAST FOR THAT MATTER.  IT STILL
FEATURES ROTATING CLOSE UPPER LOW OVER THE FOUR CORNERS WHILE DEEP
SOUTHWEST WAA PREVAILS ACROSS THE SOUTHEAST UNITED STATES.  AT
THE SURFACE...SPRINGTIME WEDGE STARTING TO ERODE AS EXPECTED THIS
AFTERNOON AS WINDS HAVE VEERED SOUTHERLY ACROSS NORTHEAST GA AND THE
UPSTATE...ALONG WITH A FEW LOCATIONS OVER THE NC PIEDMONT.
FURTHERMORE...H5 SHORT WAVE AND ASSOCIATED VORTICITY MAXIMA
CONTINUES TO SLIDE EAST ACROSS THE DEEP SOUTH WITH A BROAD AREA OF
PRECIPITATION ACCOMPANYING.  LATEST SPC MESO ANALYSIS NOT ALL THAT
IMPRESSIVE AS INSTABILITY REMAINS NEARLY NONEXISTENT ACROSS THE FCST
AREA.  MODELS FAVOR IMPROVING LAPSE RATES WITH HEATING THIS
AFTERNOON...HOWEVER STILL SKEPTICAL AS PRECIP SHIELD AND ASSOCIATED
LOW OVERCAST SKY COVER WILL LIMIT HEATING.  NEVERTHELESS...THE FCST
DOES FEATURE INCREASING POPS THROUGH THE AFTERNOON/EVENING HOURS
WITH CHANCES FOR THUNDER MENTIONED...AND WILL CONTINUE WITH SUCH IN
THE HWO.  POPS WILL LOWER AFTER MIDNIGHT AS THE PRIMARY UPPER WAVE
EJECTS TO THE EAST...AND A WEAK/DRY BACK DOOR FRONT SLIDES SOUTHWARD
ACROSS THE REGION.  HELD ON TO TOKEN SLIGHT/CHANCE POPS THROUGH
MORNING TO ACCOUNT FOR ANY RESIDUAL SHRA ALONG THE BOUNDARY.  LATEST
SOUNDINGS DO NOT SUGGEST AS MUCH MID DRYING AS THE PREVIOUS
RUN...THEREFORE NOT ALL THAT CONFIDENT IN AREAS OF DENSE FOG
OVERNIGHT.  THAT SAID...WOULDNT BE SURPRISED TO SEE ISOLATED CASES OF
SUCH ACROSS THE NC PIEDMONT/FOOTHILLS JUST AHEAD OF THE INTRUDING
BOUNDARY WHEN WINDS ARE CALMEST AND THE PBL IS DECOUPLED.

SATURDAY WILL BE HIGHLIGHTED BY DECREASING CLOUDINESS AS DOWNSLOPING
FLOW PREVAILS AMONGST INCREASING HEIGHTS ALOFT AS AXIS OF SHORTWAVE
RIDGE SHIFTS OVERHEAD.  POPS WILL INCREASE YET AGAIN THROUGH THE DAY
AS FCST SOUNDINGS INDICATE MODEST DESTABILIZATION WITH HEATING.
HOWEVER EXPECTING UPPER RIDGING TO PROVIDE SOME SUBSIDENCE THEREFORE
KEPT POPS AT OR BELOW CHANCE LEVELS THROUGH THE DAY.  TEMPERATURES
ON SATURDAY WILL DEPEND HIGHLY ON HOW SOON THE SKY COVER SCT OUT.
TOOK A MIDDLE OF THE ROAD APPROACH AS IT PERTAINS TO GUIDANCE...WITH
THE FCST FEATURING HIGHS 3-5 DEGREES ABOVE NORMAL.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 200 PM FRIDAY...TWO AREAS OF CONCERN TO DEAL WITH IN THE SHORT
TERM. THE FIRST WILL BE A PERIOD OF HEAVY RAIN ON SUNDAY AND THEN A
RISK OF SEVERE STORMS ON MONDAY.

THE UPPER RIDGE OVER THE SOUTHEAST U.S. WILL TRANSLATE EASTWARD
SATURDAY NIGHT AS THE UPPER LOW THAT HAS BEEN OVER THE 4-CORNERS
BEGINS TO MOVE EAST THANKS TO A DIGGING TROUGH MOVING SE OUT OF THE
CANADIAN PRAIRE. A SHORT WAVE OUT AHEAD OF THE UPPER LOW WILL MOVE
NE FROM THE GULF COAST AND ACROSS THE WESTERN CAROLIANS AND NE GA ON
SUNDAY. AT THE SURFACE...A WARM FRONT WILL APPROACH FROM THE SW ON
SUNDAY. ALL OF THIS WILL RESULT IN ALL TYPES OF FORCING ACROSS THE
REGION ON SUNDAY. PWATS WILL BE IN THE 1.5-1.7" RANGE WITH A 35-45
KT SELY 850 MB JET INTO THE BLUE RIDGE. WILL RAMP POPS UP QUICKLY TO
CATEGORICAL FROM WEST TO EAST BY MIDDAY SUNDAY...THEN DECREASE
RAPIDLY FROM WEST TO EAST LATE SUNDAY AS THE AXIS OF DEEP MOISTURE
AND FORCING SHIFT EAST. HEAVY RAIN LOOKS TO BE A GOOD BET...BUT THE
RELATIVELY QUICK MOVEMENT OF THE SYSTEM SHOULD PRECLUDE ANY SERIOUS
HYDRO ISSUES. BLENDING THE MODEL CONSENSUS AND WPC QPF GUIDANCE...
RESULTS IN GENERALLY 1.5"-2.0" FROM LATE SATURDAY NIGHT INTO SUNDAY
NIGHT. THE HIGHEST AMOUNTS AS USUAL ARE EXPECTED TO BE NEAR THE BLUE
RIDGE ESCARPMENT WHERE 2-3" OF RAIN CAN BE EXPECTED. THESE VALUES
ARE UNDER THE 12 TO 24 HOUR FFG. THERE MAY BE SOME LOCALIZED
FLOODING BUT WIDESPREAD FLOODING IS UNLIKELY. HOWEVER...WILL
CONTINUE TO MENTION HEAVY RAIN IN THE HWO. AN IN SITU WEDGE WILL
RESULT IN COOL TEMPS ON SUNDAY AND WILL THEREFORE TREND TOWARD
CONSRAW GUIDANCE TEMPS.

SOME DEGREE OF CLEARING SHOULD OCCUR SUNDAY NIGHT AS THE AXIS OF
DEEP MOISTURE SHIFTS NE AND A DOWNSLOPE WIND COMPONENT THROUGH THE
COLUMN DEVLOPS. ON MONDAY...A COLD FRONT WILL MOVE ACROSS THE REGION
FROM WEST TO EAST. BOTH THE NAM AND GFS INDICATE THAT THE ATMOSPHERE
WILL DESTABLIZE BY AFTERNOON WITH CAPES MOST LIKELY INCREASING TO
BETWEEN 1000 AND 1500 J/KG PER GFS AND ECM. ALSO...0-6KM SHEAR
INCREASES TO ABOUT 40KT. THIS MAY SUPPORT SOME ORGANIZION TO THE
CONVECTION AS THE COLD FRONT MOVES THROUGH. THE 12Z NAM MODEL
REFLECTIVY SUGGESTS THAT A BROKEN LINE OF CONVECTION WILL ACCOMPANY
THE FRONT ACROSS THE AREA ON MONDAY WITH A FEW SEVERE STORMS
POSSIBLE. WITH THE AREA SOLIDLY IN THE WARM SECTOR ON MONDAY...MAX
TEMPS ARE EXPECTED TO BE ABOUT 5 DEGREES ABOVE CLIMO.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 245 PM FRIDAY...MONDAY NIGHT...SFC HIGH PRESSURE WILL BUILD
OVER THE FORECAST AREA IN THE WAKE OF A PASSING COLD FRONT. 12Z GFS
INDICATES THAT H85 TEMPERATURES WILL COOL BY 5 C FROM 0Z TO 12Z
TUESDAY...A LITTLE LESS COOLING ON THE ECMWF. USING A BLEND OF
GUIDANCE...I WILL FORECAST LOW TEMPERATURES FROM THE UPPER 40S
WITHIN THE MTN VALLEYS TO MID 50S EAST. ON TUESDAY...BROAD HIGH
PRESSURE WILL REMAIN ACROSS THE CWA. THE REGION SHOULD SEE MOSTLY
SUNNY CONDITIONS WITH A LIGHT SOUTHWEST WIND. TEMPERATURES SHOULD
RESPOND TO THE LATE APRIL SUN AND WEAK DOWNSLOPING...FORECAST TUES
HIGHS SLIGHTLY ABOVE NORMAL.

WEDNESDAY THROUGH FRIDAY...THE GFS AND ECMWF GENERALLY AGREE THAT A
LARGE CLOSED MID LEVEL LOW WILL REMAIN ACROSS THE NORTHEAST AND
EASTERN CANADA...AS A RIDGE LINGERS OVER THE SOUTHERN PLAINS. THE
HEIGHTS ACROSS THE CWA WILL LIKELY REMAIN NW TO SE THROUGH THE
PERIOD. THE MODELS ARE IN LESS AGREEMENT WITH THE PLACEMENT AND
TIMING OF SFC FEATURES...PRIMARILY WEAK FRONTS AND PRESSURE CENTERS.
I AM MORE CONFIDENT TIMING MID LEVEL FEATURES WITHIN THE NW FLOW
ACROSS THE SOUTHERN APPALACHIANS...I WILL FAVOR THE ECMWF.
OVERALL...I WILL KEEP CONDITIONS DRY ON WED...BUT MOISTURE WILL
INCREASE THROUGH THE DAY. A SHORT SERIES OF MID LEVEL S/W ARE
FORECAST TO RIPPLE ACROSS THE CWA THURSDAY THROUGH FRIDAY.
TEMPERATURES SHOULD RANGE CLOSE TO NORMAL WITH AFTERNOON DEWPOINTS
ONLY IN THE 40S. GIVEN THE TRACK OF THE MID LEVEL DISTURBANCES AND
WEAK DIURNAL INSTABILITY...I WILL INDICATE ONLY SCHC POPS ACROSS THE
MTNS ON THURSDAY. FORECAST SOUNDINGS SHOW GREATER INSTABILITY FRIDAY
AFTERNOON...FROM THE MTNS TO THE PIEDMONT. THE COMBINATION OF THE
PASSING DISTURBANCE AND INSTABILITY SHOULD SUPPORT SCT COVERAGE
ACROSS THE MTNS AND ISO EAST.


&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...IFR/MVFR AND EVENTUALLY VFR CONDITIONS ARE FAVORED THROUGH
THIS TAF CYCLE.  WEDGE CONTINUES TO HOLD ACROSS THE REGION...HOWEVER
NOT FOR MUCH LONGER AS H5 VORT MAX APPROACHES FROM THE WEST AND
PARENT WEDGE HIGH RETREATS.  NOT EXPECTING MUCH IMPROVEMENT AS FAR
AS RESTRICTIONS THIS AFTERNOON HOWEVER...ESPECIALLY WITH POSSIBLE
SHRA/TSRA.  THUS...INITIALIZED TAF AT IFR WITH LIGHT SOUTHERLY WINDS
AHEAD OF VCSH ADDITION AND MVFR CIGS THIS AFTERNOON.  ALSO ADDED
TEMPO TO ACCOUNT FOR ANY THUNDER WITH THE DEEPER
CONVECTION...ALTHOUGH NOT THAT CONFIDENT.  BEYOND THAT LOWERED CIGS
BACK TO IFR PER GUIDANCE AS LLV MOISTURE REMAINS PLENTIFUL AMONGST A
DECOUPLING PBL.  DID FEATURE BRIEF MENTION FOR MVFR FOG BY MORNING
AS WINDS REMAIN CALM AHEAD OF WEAK BACK DOOR FRONTAL INTRUSION.
FINALLY...TAF RECOVERS TO LOW VFR BY MID MORNING AS BKN CU PREVAILS
AMONGST LIGHT NORTHERLY WINDS.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE AS WEDGE SLOWLY ERODES INTO
THE AFTERNOON/EVENING ONLY TO BE FOLLOWED BY SHRA/TSRA ASSOCIATED
WITH PRIMARY H5 VORT MAX SLIDING THROUGH THE SOUTHEAST.  THUS...ALL
TAFS INITIALIZE EITHER MVFR/IFR WITH THE EXCEPTION OF KHKY WHERE LOW
CLOUDS HAVE SCATTERED BRIEFLY...BUT SHOULD FILL BACK IN LATER THIS
AFTERNOON.  TAFS FEATURE WX MENTION AT ALL SITES IN THE FORM OF
VCTS/VCSH OR TSRA TEMPOS WITH SLIGHT ADJUSTMENTS TO TIMING BASED ON
LOCATION.  EXPECTING THE BULK OF THE ACTIVITY TO REMAIN SOUTH OF
INTERSTATE 40...THUS KHKY WILL SEE THE LEAST AMOUNT OF IMPACT.  IFR
RESTRICTIONS PREVAIL THROUGH THE OVERNIGHT AS LOW CIGS/VISB SETTLE
IN AS PBL DECOUPLES BEHIND EXITING PRECIP...AND AHEAD OF INTRUDING
WEAK BACK DOOR FRONT.  EXPECTING SOME PATCHY FOG OVERNIGHT...WITH
THE BEST CHANCES BEING AT THE NC SITES...AND ALSO AT KAND.  BEYOND
THAT CONDITIONS WILL GRADUALLY IMPROVE AS DOWNSLOPE FLOW PREVAILS
THROUGH THE END OF THE PERIOD.

OUTLOOK...DRIER WEATHER IS FAVORED SATURDAY AFTERNOON. DEEPER
MOISTURE WILL RETURN ALONG A WARM FRONT SAT NIGHT THROUGH
SUNDAY...WITH HEAVY RAINFALL AND WIDESPREAD RESTRICTIONS LIKELY ONCE
AGAIN. THUNDERSTORMS WILL THEN BE POSSIBLE THROUGH MONDAY AS A COLD
FRONT REACHES THE AREA FROM THE WEST.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       MED   61%     MED   63%     LOW   49%     MED   75%
KGSP       MED   73%     MED   60%     MED   69%     MED   75%
KAVL       HIGH  99%     HIGH  84%     HIGH  80%     HIGH 100%
KHKY       LOW   59%     HIGH 100%     HIGH  81%     MED   70%
KGMU       MED   75%     LOW   59%     MED   66%     HIGH  85%
KAND       MED   74%     MED   67%     LOW   58%     HIGH  80%

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...CDG
SHORT TERM...LG
LONG TERM...NED
AVIATION...CDG



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