Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 042312
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
712 PM EDT MON MAY 4 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH THE MIDDLE OF
THE WORK WEEK. A WEAK COLD FRONT IS EXPECTED TO DRIFT DOWN FROM THE
NORTH ON THURSDAY. THE REMAINDER OF THE WEEK AND WEEKEND IS STILL
FAIRLY UNCERTAIN AS LOW PRESSURE MAY MOVE UP THE SOUTHEAST COAST AND
OVER THE CAROLINAS OR REMAIN JUST OFFSHORE.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
2315 UTC UPDATE...POPS AND QPF WERE UPDATED BASED ON RADAR
TRENDS...WITH A AN INCREASE IN IN THE NORTHERN NC MOUNTAINS
BORDERING TN. SKY COVER WAS UPDATED FROM VISIBLE SATELLITE
IMAGERY. WINDS WERE UPDATED TO INCORPORATE THE LATEST NAM
GUIDANCE...WITH MODEST GUSTS PRESERVED OVERNIGTH IN THE HIGH NC
MOUNTAINS.

AS OF 245 PM...LATEST VISIBLE SATELLITE IMAGES INDICATED CU
CONGESTUS ACROSS THE MTNS WITH FAIR WEATHER CU ACROSS THE FOOTHILLS
AND PIEDMONT. MESOSCALE ANALYSIS CONTINUED TO SHOW AN AREA OF SBCIN
ACROSS THE WESTERN NC MTNS AND ADJACENT FOOTHILLS.
OTHERWISE...SBCAPE WAS LIMITED TO AROUND 250 J/KG. LATEST VCP32 SCAN
FROM KGSP INDICATED A FEW SMALL SHOWERS ACROSS THE NRN MTNS AND
ACROSS THE SOUTHERN MTNS. IT APPEARS THAT CONVECTIVE POTENTIAL WILL
EXCEED ACTIVITY OBSERVED THIS WEEKEND...BUT NOT REACH THE LEVEL
INDICATED IN THE LATEST CAMS. ANY STORMS THAT DO DEVELOP WILL BE
VERY SLOW MOVING...POSSIBLY AS SLOW AS 10 KTS. BASED ON THE
INSTABILITY PROFILES AND SLOW STORM MOTIONS I WILL INDICATE POPS
HIGHLY DEPENDENT ON ELEVATION...WITH SCHC ACROSS THE VALLEY AND
LIKELY ABOVE 6 KFT. CONVECTION SHOULD DISSIPATE EARLY THIS
EVENING...FOLLOWED BY GRADUAL CLEARING. THIN SKY COVER...LIGHT TO
CALM WINDS...AND POCKETS OF WET GROUND COULD RESULT IN FOG DURING
THE PRE DAWN HOURS.

ON TUESDAY...VERY LITTLE CHANGE FROM TODAY. ONCE AGAIN...HIGH
TEMPERATURES ARE FORECAST TO RANGE FROM THE MID TO UPPER 70S WITHIN
THE MTN VALLEYS TO THE LOW 80S TO THE EAST. FORECAST SOUNDINGS
INDICATE A GREATER TEMPERATURE INVERSION AROUND 15 KFT...REMAINING
UNDER MID LEVEL RIDGE. I WILL KEEP POPS A LITTLE LOWER THAN
INDICATED FOR MON AFTERNOON AND EVENING. I WILL FAVOR THE EAST
FACING SLOPES WITH CHC POPS...SCHC ACROSS THE VALLEYS...WITH LITTLE
TO NO COVERAGE EXPECTED EAST.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 315 PM MONDAY...THE SHORT TERM CONTINUES TO BE FAIRLY
UNEVENTFUL...DOMINATED BY HIGH PRESSURE OFF THE ATLANTIC RIDGING
WESTWARD TOWARD THE SOUTHEAST AND MID-ATLANTIC STATE...AND WEAK
RIDGING ALOFT. EXPECT A TYPICAL DIURNAL PATTERN IN SHOWER AND
THUNDERSTORMS ACTIVITY...MAINLY CONCENTRATED OVER THE MOUNTAINS
WHERE SOME SBCAPE MAY BE REALIZED...SO CONTINUED TREND OF SLIGHT TO
LOW CHANCE POPS IN THOSE AREAS. THE OTHER FORECAST ISSUE...NOT
REALLY MUCH OF AN ISSUE FOR THE SHORT TERM BUT REALLY FOR THE
EXTENDED...IS PROGRESSION OF A NON-TROPICAL LOW PRESSURE DEVELOPING
OVER THE BAHAMAS. THROUGH THE END OF THE SHORT TERM...STILL NOT
REALLY EXPECTING ANY IMPACTS FROM THIS LOW...BUT FORECAST
DIFFERENCES IN THE SYNOPTIC MODELS MAY MEAN SOME LARGE RESULTING
DIFFERENCES IN SENSIBLE WEATHER. ALL GUIDANCE IS TRENDING TOWARD
TURNING THIS LOW A LITTLE MORE TO THE RIGHT...BUT GFS/NAM/SREF STILL
HAVE THE CENTER OF THE LOW APPROACHING THE SOUTH CAROLINA COAST AT
THE END OF THE SHORT TERM...WITH SOME PRECIPITATION SPREADING TOWARD
OUR SOUTHERN ZONES. ECMWF ON THE OTHER HAND KEEPS THE SURFACE LOW
WELL OFFSHORE WITH NO REAL IMPACTS TO OUR FORECAST AREA AT ALL. FOR
NOW...HAVE TRENDED A LITTLE HIGHER WITH SKY COVER ACROSS EASTERN
ZONES WHICH MAY KEEP HIGH TEMPERATURES A LITTLE LOWER THURSDAY
AFTERNOON...BUT KEPT POPS WITH MORE OF A DIURNAL TREND WITH HIGHEST
CHANCES OVER THE MOUNTAINS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 320 PM MONDAY...AS WE WORK INTO THE EXTENDED/MEDIUM RANGE...
ALL EYES WILL BE ON THE NON-TROPICAL LOW IN THE ATLANTIC. NHC DOES
HAVE A 30 PERCENT CHANCE OF THIS LOW DEVELOPING SUBTROPICAL
CHARACTERISTICS OVER THE NEXT 5 DAYS SO WE WILL CONTINUE TO MONITOR.
AS FOR THE FORECAST HOWEVER...DEFINITELY SOME CONCERNS WITH
DIFFERENCES IN THE MAJOR SYNOPTIC MODELS WITH ECMWF KEEPING THE LOW
OFFSHORE AND THE GFS BRINGING THE LOW INLAND OVER SOUTH CAROLINA AND
SPREADING PRECIPITATION INTO OUR AREA LATE IN THE WEEKEND. WITH
THIS...THE GFS IS BRINGING A BULLSEYE OF OVER 4 INCHES QPF TO
CENTRAL SOUTH CAROLINA...WITH WIDESPREAD 1-2 INCHES ACROSS OUR
EXTREME SOUTHEAST ZONES. THIS IS LIKELY OVERDONE WITH CONVECTIVE
FEEDBACK BUT DOES GO TO SHOW THE RANGE OF POSSIBILITIES...BETWEEN
NOTHING ON THE ECMWF TO THE HEFTY QPF VALUES ON THE GFS. WPC AND NHC
GUIDANCE SUGGESTS...AT LEAST FOR NOW...FAVORING THE WESTWARD
PROGRESSION OF THE LOW BUT CONFIDENCE IS NOT PARTICULARLY HIGH AT
THIS POINT. SO FOR NOW...HAVE BEGUN BRINGING IN MID-RANGE CHANCE
POPS ACROSS EASTERN ZONES OVER THE WEEKEND.

BEYOND ALL THIS...A STRONG TROUGH PUSHING THROUGH THE PLAINS OVER
THE WEEKEND WILL ALLOW A COLD FRONT TO APPROACH THE APPALACHIANS
EARLY NEXT WEEK. GFS IS FASTER WITH THIS...ABSORBING WHAT IS
LEFTOVER OF THE FORMER COASTAL LOW BY THE END OF THE PERIOD...
WHEREAS THE ECMWF HOLDS OFF ON PHASING THESE TWO SYSTEMS TILL AFTER
THE END OF THE PERIOD. EITHER WAY...THE APPROACH OF THE COLD FRONT
WILL PUSH ANY EFFECTS FROM THE COASTAL LOW OFFSHORE AS THE FRONT
PUSHES EASTWARD. CONFIDENCE FOR THE END OF THE PERIOD IS
PARTICULARLY LOW DUE TO THE TIMING DIFFERENCES IN THE FRONT AND
UNCERTAINTY REGARDING THE POSITION/TIMING/PROGRESSION OF THE COASTAL
LOW.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
AT KCLT...VFR. LOW VFR CIGS ARE NOT AS LIKELY AS OVER THE MOUNTAINS
TO THE WEST. MODEL SOUNDINGS DO NOT LOOK MOIST ENOUGH FOR DAYBREAK
FOG. DAYTIME PRECIPITATION SHOULD REMAIN TO THE WEST NEAR THE
MOUNTAINS WHERE BETTER INSTABILITY WILL EXIST. LIGHT WINDS WILL
FAVOR THE S.

ELSEWHERE...VFR. A SMALL CHANCE OF SHOWERS WILL DWINDLE THIS
EVENING OVER THE NC MOUNTAINS AS HEATING ABATES...BUT A LOW VFR
CIGS REMAINS POSSIBLE AT KAVL THIS EVENING. MODEL GUIDANCE WAS NOT
OVERLY SUPPORTIVE OF DAYBREAK FOG...BUT AS SOME DID OCCUR IN THE SW
NC MOUNTAINS...AND THE LOWER ATMOSPHERE IS TRENDING MORE MOIST WITH
TIME...GREATER FOG COVERAGE WILL BE ALLOWED BY DAWN...PRODUCING ONLY
LOW IFR AT KAVL ONLY. LIGHT WINDS WILL FAVOR THE S.

OUTLOOK...ISOLATED TO SCATTERED DIURNAL MOUNTAIN CONVECTION IS
EXPECTED THROUGH FRIDAY...AS MOIST SOUTHERLY FLOW PERSISTS.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     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...JPT
NEAR TERM...NED
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JAT


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