Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 281838
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
238 PM EDT THU MAY 28 2015

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL PERSIST ACROSS THE REGION THROUGH THE
WEEKEND AND INTO EARLY NEXT WEEK. DEEPER MOISTURE WILL GRADUALLY
POOL ALONG THE SOUTHERN APPALACHIANS IN THE SOUTHERLY FLOW BETWEEN
LOW PRESSURE APPROACHING THE MID MISSISSIPPI VALLEY FROM THE WEST
AND THE OFFSHORE BERMUDA HIGH TO THE EAST. A COLD FRONT WILL PUSH
SOUTHWARD INTO THE REGION AROUND MID WEEK AND THEN LIKELY STALL
NEARBY.

&&

.NEAR TERM /THROUGH FRIDAY/...
SCATTERED/NUMEROUS CONVECTION CONTINUES TO FIRE ACROSS THE SOUTHERN
APPALACHIANS AND UPPER SAVANNAH RIVER VALLEY THIS AFTERNOON. CLOUD
COVER HAS SOMEWHAT LIMITED BUOYANCY ACROSS THE HIGH TERRAIN THUS
FAR...SO THE BEST COVERAGE IS CURRENTLY FOUND OVER THE USRV. POPS
HAVE BEEN INCREASED TO LIKELY THERE FOR THE NEXT COUPLE OF HOURS.
ELSEWHERE...COVERAGE IS MUCH MORE ISOLATED...AND OUTFLOW BOUNDARIES
ASSOCIATED WITH ONGOING CONVECTION APPEAR TO BE STRUGGLING TO
INITIATE NEW ACTIVITY AWAY FROM THE ONGOING CONVECTION.
NEVERTHELESS...STEERING CURRENTS AND PROPAGATING OUTFLOWS SHOULD
RESULT IN A GRADUAL INCREASE IN POPS FROM SW TO NE THROUGH THE
AFTERNOON..WITH MOST AREAS SEEING 30-40 POPS. CELL MOVEMENT WILL
REMAIN SLOW UNTIL/UNLESS OUTFLOWS GET A BIT OF MOMENTUM IN THEIR
WAKE. THUS...LOCALLY HEAVY RAINFALL WILL BE A CONCERN IN THE VERY
NEAR TERM....WHILE A BRIEF MICROBURST OR TWO CANNOT BE RULED OUT.

WHILE COVERAGE OF CONVECTION SHOULD DIMINISH THIS EVENING...A LIGHT
S/SE LOW LEVEL UPSLOPE FLOW AND THE LINGERING DEEP MOIST PLUME COULD
ALLOW AT LEAST ISOLATED CONVECTION COULD PERSIST FOR MUCH OF THE
OVERNIGHT NEAR THE BLUE RIDGE...AND 20-30 POPS WILL BE CARRIED IN
THESE AREAS THROUGH THE PERIOD.

FOR FRIDAY...SHORT TERM GUIDANCE INDICATES THE MOIST PLUME WILL LIFT
NORTH AND BECOME DIFFUSE THROUGH THE DAY...AS UPPER SHEAR ZONE/WEAK
TROUGH CONTINUES TO SHEAR OUT. AS SUCH...FORECAST SOUNDINGS ARE
QUITE DRY ACROSS THE FORECAST AREA BY AFTERNOON. IN FACT...SHORT
TERM MODEL QPF RESPONSE AND CONVECTION-ALLOWING MODELS SUGGEST
TOMORROW AFTERNOON WILL BE QUITE INACTIVE. POPS MAY THEREFORE
ACTUALLY PEAK IN THE MORNING HOURS. NEVERTHELESS...MODERATE
INSTABILITY SHOULD SUPPORT AT LEAST ISOLATED CONVECTION ACROSS MUCH
OF THE AREA THROUGH THE AFTERNOON...WHILE THE HIGHEST POPS (ABOUT 50
PERCENT) WILL BE RESERVED FOR THE TENN BORDER COUNTIES...NEARER THE
RETREATING MOIST PLUME.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AT 200 PM EDT THURSDAY...ON FRIDAY EVENING AN UPPER RIDGE WILL BE
ALONG THE EAST COAST...WHILE AN UPPER TROUGH WILL BE OVER THE
PLAINS. THE TROUGH AXIS SLOWLY PROGRESSES TO THE MS RIVER VALLEY BY
LATE SUNDAY...WHILE THE RIDGE PROGRESSES OFF THE EAST COAST.

AT THE SURFACE...ATLANTIC HIGH PRESSURE REMAINS OVER THE CAROLINAS
AND GA INTO SATURDAY...BUT WITH A WEAKENING TREND AS THE CENTER OF
THE HIGH DRIFTS FARTHER OFFSHORE...AND A COLD FRONT APPROACHES FROM
THE NW. THE MODELS INDICATE A MODEST DECREASE IN LOW LEVEL MOISTURE
OVER MUCH OF OUR AREA FRIDAY NIGHT AND SATURDAY...AS A LEE TROUGH
DEVELOPS IN THE PIEDMONT. AS THE TROUGH APPEARS TO SHIFT EAST ON
SUNDAY...MOISTURE SPREADS ACROSS OUR AREA FROM THE WEST IN ADVANCE
OF THE SLOW MOVING AND WEAKENING COLD FRONT.

THE GREATEST INSTABILITY WILL BE ALONG THE LEE TROUGH IN THE
PIEDMONT...BUT SHEAR APPEARS TO BE QUITE LIMITED. WITH ONLY WEAK
ISENTROPIC UPGLIDE AND UPSLOPE FLOW...PRECIPITATION SHOULD NOT BE
EXCESSIVE OUTSIDE OF LOCALLY ROBUST CONVECTION. TEMPERATURES WILL
RUN SLIGHTLY ABOVE NORMAL.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM THURSDAY...MODELS ARE IN GOOD AGREEMENT AT THE START OF
THE EXTENDED PERIOD. A FRONTAL BOUNDARY WILL HAVE SLOWED ITS
SOUTHEASTWARD MOTION CONSIDERABLY AND BECOME ALMOST STATIONARY OVER
THE SOUTHERN APPALACHIANS BY SUNDAY NIGHT...LEADING TO A HEALTHY
INCREASE IN POPS. THE BOUNDARY WASHES OUT SOMEWHAT BUT REMAINS IN
PLACE MONDAY AND TUESDAY...KEEPING POPS ELEVATED THROUGH TUESDAY
NIGHT. A LACK OF SIGNIFICANT UPPER LEVEL FORCING AND SHEAR SHOULD
KEEP THE PROBABILITY OF ORGANIZED SEVERE STORMS RELATIVELY
LOW...THOUGH ISOLATED PULSE-TYPE STRONG TO SEVERE STORMS CAN`T BE
RULED OUT DUE TO MARGINAL INSTABILITY EACH AFTERNOON. WEAK MEAN FLOW
AND POSSIBLE WEAK MECHANICAL UPSLOPE FORCING WILL MAKE LOCALLY HEAVY
RAINFALL THE MAIN THREAT FOR THE EXTENDED PERIOD.

GUIDANCE DIVERGES SOMEWHAT IN THE SECOND HALF OF THE PERIOD...WITH A
SURFACE HIGH EXPANDING OVER THE NORTHEAST AND PUSHING THE NOW
BACKDOOR FRONTAL BOUNDARY OUT OF THE AREA. DUE TO DIFFERENCES IN
MODEL POSITION AND STRENGTH OF A POTENTIAL CUT-OFF UPPER LEVEL LOW
OVER MS/LA...THE 12Z GFS SWEEPS THE BACKDOOR FRONT IN MORE QUICKLY
THAN THE 00Z ECMWF. CONSEQUENTLY THE GFS DISPLAYS A DRIER SOLUTION
FOR WEDNESDAY AND THURSDAY THAN THE WET ECMWF...RESULTING IN POPS
JUST SLIGHTLY ABOVE CLIMO. THE  FORECAST IS CLOSER TO A GFS
SOLUTION WITH THE FASTER FRONTAL PASSAGE...BUT THE WETTER/SLOWER
ECMWF BEARS WATCHING UNTIL THE GUIDANCE COMES INTO BETTER
AGREEMENT.

MAX TEMPS WILL REMAIN ABOVE CLIMO MONDAY...WITH MIN TEMPS REMAINING
A CATEGORY OR TWO ABOVE AVERAGE. A VERY MOIST AIRMASS AND HEFTY
CLOUD COVER DURING THE SECOND HALF OF THE PERIOD WILL KEEP HIGHS
RIGHT AROUND NORMAL WHILE LIMITING THE DIURNAL TEMPERATURE RANGE
CONSIDERABLY.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
AT KCLT...MAIN CONCERN THIS PERIOD IS CONVECTIVE POTENTIAL DURING
THE REMAINDER OF THE PM. ALTHOUGH THE BEST COVERAGE DURING THIS TIME
WILL BE ACROSS THE FAR WESTERN CAROLINAS...ONE LONE CELL HAS DEVELOPED
RECENTLY JUST SOUTH OF THE TERMINAL...THUS THE TEMPO FOR TSRA HAS
BEEN MOVED TO 18-22Z. OTHERWISE...WINDS WILL GENERALLY REMAIN
SOUTHERLY...WITH SOME GUSTS POSSIBLE NEAR SHOWERS AND STORMS.
SUFFICIENT MOISTURE WILL REMAIN IN PLACE THROUGH THE PERIOD SUCH
THAT THERE WILL BE A POTENTIAL FOR CIG AND/OR VISBY RESTRICTIONS
LATE TONIGHT/EARLY FRI. HOWEVER...CONFIDENCE IS QUITE LOW ATTM...AND
IN FACT...LOW CIGS AND/OR FOG MAY BE CONFINED TO AREAS CLOSER TO THE
HIGH TERRAIN.

ELSEWHERE...SCATTERED CELLS ARE DEVELOPING ALONG AN AXIS FROM
ROUGHLY KAND TO KAVL. TEMPOS FOR TSRA WILL PERSIST AT THESE
TERMINALS THROUGH 22Z. STEERING WINDS AND PROPAGATING OUTFLOW
BOUNDARY SHOULD TAKE THIS ACTIVITY OFF TO THE E/NE RATHER GRADUALLY.
THUS...TEMPOS HAVE ALSO BEEN INTRODUCED AT KGSP/KGMU AFTER 19Z. VCTS
WILL BE RETAINED AT KHKY FOR NOW...BUT WILL HAVE TO WATCH THAT SITE
CLOSELY FOR A POTENTIAL TEMPO AS WELL. SUFFICIENT MOISTURE WILL
REMAIN IN PLACE THROUGH THE PERIOD SUCH THAT THERE WILL BE A
POTENTIAL FOR CIG AND/OR VISBY RESTRICTIONS LATE TONIGHT/EARLY FRI.
VISBY RESTRICTIONS WILL BE CARRIED AT MOST TERMINALS DURING THIS
TIME...WITH LOW CIGS LIMITED TO KAVL. LOW CIGS CAN BY NO MEANS BE
RULED OUT ELSEWHERE...BUT CONFIDENCE IS QUITE LOW ATTM.

OUTLOOK...MOIST SW FLOW WILL CONTINUE TO AFFECT THE TERMINAL
FORECAST AREA THROUGH THE UPCOMING WEEKEND...AS A COLD FRONT LAYS
OVER TO THE NORTH OF THE AREA. EXPECT POCKETS OF MORNING FOG AND/OR
STRATUS MOST DAYS...WITH CONTINUED CHANCES OF AFTN/EVENING SHRA/TSRA
EACH DAY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  97%     HIGH  97%
KGSP       HIGH 100%     HIGH 100%     HIGH  97%     HIGH  94%
KAVL       HIGH  99%     MED   78%     HIGH  94%     MED   76%
KHKY       HIGH  92%     HIGH  85%     HIGH 100%     HIGH  94%
KGMU       HIGH 100%     HIGH 100%     HIGH  90%     HIGH  83%
KAND       HIGH 100%     HIGH 100%     HIGH  94%     HIGH  94%

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...HG
NEAR TERM...JDL
SHORT TERM...JAT
LONG TERM...LEV
AVIATION...JDL



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