Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191856
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
256 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 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 /19Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...RAINFALL INTENSITY AND COVERAGE IS
INCREASING OVER WESTERN NC...THOUGH THE HEAVIER RAIN IS LOCATED A
LITTLE WAYS TO THE NORTH AND WEST OF THE KCLT AIRFIELD. AS LONG AS
THE UPSTREAM AIRMASS CONTINUES TO BE SATURATED BY PCPN...IFR CIGS
SHOULD CONTINUE TO AFFECT THE AIRFIELDS...ESPECIALLY AT KCLT AND THE
UPSTATE SITES. IFR CIGS WERE KEPT AT KCLT THROUGH 21 UTC WITH MVFR
DEVELOPING THEREAFTER. HOWEVER...I SUSPECT THAT IFR COULD CONTINUE
LONGER THAN THIS AT KCLT. GUSTY NORTHEAST WINDS WILL CONTINUE
THROUGH THE NIGHT FROM KCLT DOWN TO KAND. WIND GUSTS OF 25 KTS
SHOULD BE COMMON. CIGS SHOULD BEGIN TO LIFT BY LATE EVENING ONCE THE
PCPN STARTS TO DIMINISH.

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

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-19Z
KCLT       MED   70%     HIGH  82%     HIGH  96%     HIGH 100%
KGSP       LOW   59%     HIGH  82%     HIGH  96%     HIGH 100%
KAVL       MED   69%     HIGH  85%     HIGH 100%     HIGH 100%
KHKY       HIGH  86%     MED   74%     HIGH 100%     HIGH 100%
KGMU       LOW   56%     HIGH  84%     HIGH  94%     HIGH 100%
KAND       MED   70%     HIGH  83%     HIGH  97%     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...MCAVOY
SHORT TERM...WIMBERLEY
LONG TERM...SBK
AVIATION...MCAVOY





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