Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 192358
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
758 PM EDT SAT APR 19 2014

.SYNOPSIS...
A MOIST LOW PRESSURE SYSTEM WILL CONTINUE MOVING OFF THE SOUTH
CAROLINA COAST THROUGH SUNDAY. HIGH PRESSURE WILL BRIEFLY BUILD IN
MONDAY...BEFORE A COLD FRONT PUSHES ACROSS THE REGION ON TUESDAY. A
BROAD AND DRY AREA OF HIGH PRESSURE WILL THEN BUILD IN FROM THE
NORTH WEDNESDAY AND LINGER THROUGH THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 750 PM SATURDAY...DEFORMATION ZONE RAIN SHIELD SHOWS NO SIGNS
OF RELENTING THIS EVENING. IN FACT...WE/VE SEEN RATES INCREASE QUITE
A BIT ACROSS WESTERN NC SINCE LATE AFTERNOON...WITH PERIODS OF HEAVY
RAIN BEING REPORTED AT SEVERAL METAR SITES. EXPECT THE WESTERN EDGE
OF THE PRECIP SHIELD TO GRADUALLY ERODE...AS THE PRECIP BAND
EXHIBITS A GRADUAL EAST/SOUTHEAST DRIFT. THE MAIN HYDRO THREAT AREA
WILL CONTINUE TO BE CHARLOTTE METRO...WHICH HAS SEEN WIDESPREAD 2+
INCH STORM TOTAL AMOUNTS...AND WHERE OCCL HEAVY RAINFALL WILL REMAIN
LIKELY THROUGH THE EVENING.

AS OF 445 PM SATURDAY...AS THE UPPER LOW CONTINUES TO WOBBLE EAST
AND OFF THE GA/SC COAST THROUGH THE REMAINDER OF THE AFTERNOON AND
EVENING...DEFORMATION ZONE PRECIP SHOULD GRADUALLY SHRINK IN
COVERAGE AND MOVE/SHIFT TOWARD THE SOUTHEAST. IN THE INTERIM...
CATEGORICAL POPS WILL CONTINUE THROUGH MID-EVENING OR SO ACROSS MUCH
OF THE NC ZONES...AS WELL AS PORTIONS OF THE EASTERN SC PIEDMONT.
ADDITIONAL RAINFALL AMOUNTS SHOULD GENERALLY AVERAGE LESS THAN A
HALF INCH...ALTHOUGH SOME ENHANCEMENT IS OCCURRING IN THE VICINITY
OF THE EASTERN ESCARPMENT...OWING TO AN IMPROVING EASTERLY UPSLOPE
COMPONENT TO THE FLOW...AND SOME LOCALLY HIGHER AMOUNTS COULD BE
SEEN THERE.

AS OF 240 PM EDT SATURDAY...THE 12 UTC RUNS OF THE NAM AND GFS BOTH
HAVE A POTENT UPPER TROPOSPHERIC JET STREAK ROUNDING THE EAST SIDE
OF THE UPPER LOW ATTM. STRONG UPPER DIVERGENCE HAS DEVELOPED IN THE
EXIT REGION OF THE JET STREAK...PRETTY MUCH OVER THE HEART OF THE
FORECAST AREA. I JUST SAW A PIREP ISSUED BY THE ZTL CWSU THAT
SEVERAL AIRCRAFT HAVE REPORTED MODERATE TURBULENCE IN THE VCNTY OF
KCLT WITH THIS AREA OF UPPER ASCENT. THE GFS 18 UTC AGEOSTROPHIC
VERTICAL CIRCULATION OVER WRN NC IS ABOUT AS STRONG AS IT GETS. ALL
OF THIS EXPLAINS THE INCREASE IN RAINFALL OVER WRN NC...ESP THE
FOOTHILLS AND PIEDMONT...AND THE NRN UPSTATE. WHILE THE PW/S ARE NOT
THAT IMPRESSIVE...THE ZONAL COMPONENT OF THE H8 FLOW ON THE GFS
CONTINUES TO RUN 3 TO 4 STANDARD DEVIATIONS ABOVE NORMAL. BASED ON
THE COOLING CLOUD TOPS ON THE REGIONAL IR IMAGERY...I SUSPECT THAT
WE WILL SEE MODERATE RAIN FALL ACROSS THESE ZONES FOR AT LEAST
ANOTHER 4 TO 6 HORUS. THIS SHOULD YIELD ADDITIONAL RAINFALL AMOUNTS
OF AROUND A HALF INCH...POSSIBLY UP TO THREE QUARTERS OF AN INCH.
THIS SHOULD NOT BE ENOUGH TO CAUSE ANY SIGNIFICANT FLOODING
CONCERNS...THOUGH A FEW LARGER STREAMS AND SMALLER RIVER MAY
APPROACH BANKFULL.

THE RAIN AND DRIZZLE WILL GRADUALLY TAPER OFF LATER TONIGHT. CLOUDS
ARE EXPECTED TO LINGER THROUGH MID-MORNING SUNDAY OVER MOST OF THE
PIEDMONT...THOUGH THERE IS SOME HOPE OF CLEARING OVER THE MOUNTAINS
AND THE WESTERN MOST FOOTHILLS. STILL...SUNRISE SERVICES WILL
PROBABLY BE CLOUDY FOR THE MOST PART EAST OF THE MOUNTAINS.
OTHERWISE AFTERNOON TEMPERATURES WILL MODERATE A GOOD 10 TO 15
DEGREES FROM TODAY/S.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF MIDDAY SATURDAY...SHORT UPPER RIDGE REMAINS OVER THE FA SUNDAY
NIGHT AS DEEP LOW MOVES OFF THE SOUTHEAST COAST...MAINTAINING
NORTHERLY LLVL FLOW INTO MONDAY. WRAPAROUND MOISTURE FROM THE LOW
LINGERING OVER THE ERN HALF OF THE FA LATE SUNDAY THUS GETS SHUNTED
OFF TO THE SOUTH OVERNIGHT...WHILE SOME LLVL MOISTURE DOES ADVECT
INTO THE WRN FA AS THE FLOW BACKS. THIS MOIST LAYER IS SHALLOW ON
PROG SOUNDINGS. CONVECTION ACRS THE FA WILL LIKELY REMAIN CAPPED BY
SUBSIDENCE WITHIN THE RIDGE MON AFTN. HOWEVER...LATE MONDAY THE RIDGE
COLLAPSES AS TROUGH SWINGS INTO THE OHIO VALLEY. SOME OF THE 09Z SREF
MEMBERS INDICATED THE CAP WILL BREAK AS EARLY AS MON EVENING...AND
SOME SFC BASED INSTABILITY COULD BE REALIZED IF THAT SCENARIO
HAPPENED EARLY ENOUGH. MORE LIKELY THOUGH...THE INVERSION DISSOLVES
CLOSER TO TUE MRNG AS THE TROUGH DIGS IN AHEAD OF IMPENDING FROPA.
POPS WILL BE REINTRODUCED INTO THE MTNS EARLY TUE MRNG AS FRONTAL
MOISTURE SPREADS IN WITH WEAK UPSLOPING.

DECENT SFC BASED CAPE DOES DEVELOP OVER THE FA AHEAD OF THE FRONT ON
TUESDAY. NONE OF THE SHEAR PARAMETERS LOOK THREATENING FOR SEVERE
WX...AND WITH THE STRONGER FORCING BEING WELL TO OUR NORTH THE QPF IS
LIGHT ON ALL THE CONSULTED GUIDANCE. BEST INSTABILITY IS SHOWN OVER
THE NC PIEDMONT...WITH MODEL CONSENSUS SHOWING CAPE PEAKING AROUND
1000 J. DCAPE IS ALSO FAIRLY HIGH ON GFS WHICH HAS FAIRLY HIGH CLOUD
BASES...SO THERE MAY BE A LOW-END PULSE STORM WIND THREAT. POPS
DIMINISH LATE TUE FOLLOWING THE DIURNAL PEAK AND AS THE FRONT
DEPARTS. VERY SHALLOW MOISTURE ON NW FLOW TUE NIGHT MIGHT PRODUCE
SOME ADDITIONAL SHOWERS IN THE MTNS. WINDS MAY ALSO BE MODERATELY
GUSTY IN THE HIGHER TERRAIN TUE AND TUE NIGHT.

COOL WEDGY TEMPS CONTINUE ACRS THE AREA SUNDAY NIGHT...BUT TEMPS
REBOUND TO SLIGHTLY ABV CLIMO FOR MON AND TUE.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 145 PM SATURDAY...STRONG LATITUDINAL UPPER RIDGING WILL
DEVELOP TO THE WEST EARLY WED AND PUSH EAST OVER THE FCST AREA
THROUGH THU. THIS WILL BRING DOWN A STRONG CANADIAN SFC HIGH AND
ALLOW FOR DEEP LAYERED DRYING WHILE THE HIGH SETTLES INTO AN ATL
RIDGE CONFIG THU. THERE WILL BE SOME MEASURE OF AN AIRMASS MIX WED
MAINLY ACROSS THE ERN ZONES WHERE MAX TEMPS WILL PROBABLY BE HELD A
COUPLE DEGREES BELOW NORMAL ACROSS THE NW PIEDMONT. DOWNSLOPE FLOW
WILL AIDE IN WARMER THAN NORMAL TEMPS ACROSS THE REST OF THE
NON/MTNS...WHILE THE MTNS VALLEYS REACH RIGHT AROUND NORMAL. THE
LLVL FLOW VEERS S/LY THU AND ALLOWS A BETTER MODIFICATION OF SFC
BASED THETA/E AND TEMPS/TDS WILL RESPOND A COUPLE DEGREES WARMER.
ALL IN ALL...BOTH DAYS SHOULD MOSTLY SUNNY AND PLEASANT WITH TD/S
REMAINING BELOW 50 F MOST LOCALES.

THE UPPER RIDGE AXIS SHIFTS EAST THU NIGHT AS AN H5 LOW DEEPENS
ACROSS THE UPPER MIDWEST. THE OP MODELS DISAGREE ON THE TIMING AND
NATURE OF THIS LOW WITH THE 12Z GFS CLOSING IT OFF AND PRODUCING A
SLOWER SYNOPTIC PATTERN BY ABOUT 12 HRS THAN THE 00Z ECMWF. THE GEFS
MEAN HEIGHTS/MSLP ARE A PRETTY GOOD COMPROMISE AS FAR AS TIMING AND
THIS WAS GIVEN THE MOST WEIGHT IN THE FCST. THERE ARE ALSO NOTABLE
DIFFERENCES WITH THE AMOUNT OF THE GOM RIDGING AND AVAILABLE MOIST
FLUX AHEAD OF THE SFC FRONT FRI. THE ECMWF SETS UP A STRONGER LLVL
RIDGE AND THUS DISRUPTS THE MOIST GOM FLOW MORESO THAN THE
GFS...LEAVING A DRY FROPA BY FRI NIGHT. IN ANY CASE THERE SHOULD BE
ENOUGH ISEN LIFT MOISTURE TO PRODUCE ISOL PREFRONTAL SHOWERS
BEGINNING EARLY FRI WITH AN INCREASE TO SCT COVERAGE ACROSS THE NC
MTNS BY THE AFTERNOON. MODEL SOUNDINGS SHOW THE PRESENCE OF ELCAPE
ON THE ORDER OF A COUPLE HUNDRED JOULES FRI AFTERNOON...SO THUNDER
MENTION WILL BE MAINTAINED THROUGH THE EVENING PERIOD. DONT SEE
ENOUGH IN THE DYNAMICS TO SUSPECT A SEVERE POTENTIAL ATTM AS UPPER
FORCING REMAINS WEAK AND SHEAR LEVELS ARE MODERATE AT BEST. MAX
TEMPS WILL CONTINUE TO INCREASE A COUPLE DEGREES EACH DAY.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
AT KCLT...DRIER LOW LEVEL AIR FILTERING IN ON NE WINDS HAS RESULTED
IN CIGS LIFTING TO VFR...AND THIS IS EXPECTED TO CONTINUE THROUGH
THE DURATION OF THE FORECAST PERIOD...ALTHOUGH WOULD NOT RULE OUT A
STRAY MVFR CIG THIS EVENING. HOWEVER...PERIODS OF IFR VISBY IN
MOD/HEAVY RAIN ARE EXPECTED TO CONTINUE THROUGH AT LEAST 03Z. RAIN
WILL GRADUALLY TAPER OFF LATE THIS EVENING INTO THE EARLY PART OF
THE OVERNIGHT...OCCL VISBY RESTRICTIONS WILL REMAIN POSSIBLE THROUGH
ABOUT 09Z. N/NE WINDS ARE EXPECTED TO REMAIN AT AROUND 10 KTS
THROUGH MUCH OF THE PERIOD. SOME GUSTS NEAR 20 KTS WILL BE POSSIBLE
THIS EVENING...BUT MORE LIKELY AFTER SUNRISE SUNDAY. VFR CIGS
(050-080 RANGE) SHOULD PERSIST THROUGH AT LEAST THE MORNING
HOURS...GRADUALLY SCATTERING OUT DURING THE AFTERNOON.

ELSEWHERE...MODERATE TO OCCASIONALLY HEAVY RAIN IS WIDESPREAD FROM
ROUGHLY THE NORTH/SOUTH CAROLINA BORDER NORTH TO THE I-40 CORRIDOR
IN NC. ALL TERMINALS EXCEPT PERHAPS KAND WILL SEE PERIODS OF RAIN
PERSIST THROUGH MUCH OF THE EVENING...WITH OCCL VISBY RESTRICTIONS
LIKELY...ESP AT KAVL. OTHERWISE...WE ARE NOT ANTICIPATING MUCH IN
THE WAY OF CIG ISSUES...AS CIGS HAVE LIFTED TO VFR AT MOST
TERMINALS...AND WITH NE WINDS GRADUALLY INTRODUCING DRIER LOW LEVEL
AIR TO THE REGION...CIGS ARE EXPECTED TO GENERALLY REMAIN VFR
THROUGH THE PERIOD...ALTHOUGH CHANCES WILL INCREASE FARTHER SOUTH
(ESP AT KAND). N/NE WINDS ARE EXPECTED TO REMAIN AT AROUND 10-15
KTS ACROSS THE PIEDMONT/FHILLS (MUCH LIGHTER AT KAVL) THROUGH MUCH
OF THE PERIOD. SOME GUSTS NEAR 20 KTS WILL BE POSSIBLE OUTSIDE THE
MTN VALLEYS THIS EVENING...BUT MORE LIKELY AFTER SUNRISE SUNDAY.

OUTLOOK...DRY HIGH PRES WILL THEN DEVELOP MONDAY...WITH A FAIRLY WET
FRONTAL SYSTEM EXPECTED ON TUE.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       MED   76%     HIGH  88%     HIGH 100%     HIGH 100%
KGSP       HIGH  81%     HIGH  98%     HIGH 100%     HIGH 100%
KAVL       HIGH  98%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  81%     HIGH  98%     HIGH 100%     HIGH 100%
KAND       HIGH  81%     HIGH  90%     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...SBK
NEAR TERM...JDL/MCAVOY
SHORT TERM...WIMBERLEY
LONG TERM...SBK
AVIATION...JDL






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