185
FXUS62 KGSP 130735
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
335 AM EDT TUE AUG 13 2013
.SYNOPSIS...
A COLD FRONT IS EXPECTED TO CROSS THE AREA TONIGHT AND EARLY
WEDNESDAY. A WEDGE OF COOL HIGH PRESSURE WILL BECOME ESTABLISHED
THROUGH THE WEEKEND. A MAJOR UPPER TROUGH DEVELOPING OVER THE
MISSISSIPPI VALLEY WILL BRING DEEP MOISTURE BACK OVER THE HIGH
PRESSURE WEDGE BY THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 325 AM...LATEST SFC ANALYSIS INDICATED A COLD FRONT ENTERING
THE NRN OHIO RIVER VALLEY...LEE TROUGH ACROSS THE EASTERN CAROLINAS.
REGIONAL RADAR IMAGES INDICATE THAT DEEP CONVECTION REMAINS ACTIVE
ALONG AND AHEAD OF THE UPSTREAM COLD FRONT AND WITHIN THE CAROLINA
LEE TROUGH. IN ADDITION...CONVECTION REMAINS ACROSS EASTERN
KY...LIKELY NEAR A WASHED OUT STATIONARY FRONT AND BELOW AN AREA OF
JET DIVERGENCE. AT THIS TIME...VERY LITTLE SHRA/TSRA COVERAGE EXIST
UPSTREAM OF THE FORECAST AREA.
THE AXIS OF A POSITIVELY TILTED H5 TROUGH WILL RIPPLE ACROSS THE MID
WEST DURING THE DAY. THE GFS INDICATES THAT THE ENTRANCE BRANCH OF A
NEW ENGLAND H3 JET WILL PIVOT SOUTHWARD AHEAD OF THE
TROUGH...SLIDING ACROSS THE CWA LATER THIS MORNING. LINGERING
INSTABILITY AND INCREASING UPPER SUPPORT SHOULD RESULT IN AN
INCREASE IN CONVECTION ACROSS EASTERN TN DURING THE PRE DAWN PERIOD.
STEERING FLOW AND THE ARRIVAL OF JET DIVERGENCE...WILL SUPPORT A
SHARP INCREASE IN DEEP CONVECTION ACROSS THE NC MTNS AFTER SUNRISE.
CLUSTERS OF SHRA/TSRA SHOULD INCREASE THROUGH THE REST OF THE
MORNING...FORMING A BROKEN SW TO NE LINE BY MID DAY. THIS LINE WILL
STEADILY TRACK EAST...LIKELY EXITING THE CWA AS EARLY AS MID
AFTERNOON. IN THE WAKE OF THE LINE AND AHEAD OF THE COLD FRONT...SCT
AIR MASS STORMS MAY CONTINUE ACROSS THE CWA UNTIL THE EARLY EVENING.
BASED ON EXPECTED STORM STRUCTURE AND MARGINAL OVERLAP OF
INSTABILITY AND SHEAR...A FEW DAMAGING WIND EVENTS ARE POSSIBLE THIS
AFTERNOON ACROSS THE FOOTHILLS AND PIEDMONT...ESPECIALLY NEAR THE
I-77 CORRIDOR. WE WILL HIGHLIGHT THE SEVERE POTENTIAL ALONG WITH
HEAVY DOWNPOURS IN THE HWO. HIGH TEMPERATURES SHOULD RANGE NEAR
NORMAL.
AFTER SUNSET...THE SW TO NE COLD FRONT IS EXPECTED TO SWEEP ACROSS
THE WESTERN CAROLINAS AND NE GA. THE FRONT SHOULD MOVE SOUTH AND
EAST OF THE FORECAST AREA BY LATE TONIGHT. SCT SHRA/TSRA MAY
CONTINUE TO DEVELOP ALONG AND AHEAD OF THE FRONT...BUT SEVERE
POTENTIAL APPEARS LIMITED. IN THE WAKE OF THE FRONT...NW WINDS WILL
DEVELOP AND LLVL THICKNESSES WILL SLOWLY DECREASE. HOWEVER...LATE
CAA AND LINGERING CLOUDS SHOULD KEEP MIN TEMPS CLOSE TO NORMAL.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 250 AM TUESDAY...THE MAJORITY OF MODEL GUIDANCE IS PAINTING A
CONSIDERABLY DRIER PICTURE FOR THE SHORT TERM PERIOD THAN IN
PREVIOUS RUNS...WITH STRONG SUGGESTIONS THAT THE SURFACE RIDGE
BUILDING DOWN THE EASTERN SEABOARD WILL PUSH A RELATIVELY DRY AND
COOL LOW-LEVEL AIR MASS THROUGH MUCH OF THE AREA...WITH VERY WEAK OR
NON-EXISTENT INSTABILITY. AS SUCH...THE GFS IN PARTICULAR FEATURES
VERY LITTLE QPF RESPONSE DURING THE PERIOD...EXCEPT ALONG THE BLUE
RIDGE...AS A E/SE FLOW BECOMES ESTABLISHED IN RESPONSE TO PRESSURE
FALLS WEST OF THE REGION.
ONE HOLD OUT TO THE DRYING TREND IS THE NAM...WHICH BLOWS UP A
CONVECTIVE BLOB OVER THE FORECAST AREA WED NIGHT...AND SLOWLY
ADVANCES IT ACROSS THE CWA. WHILE I HAVE LITTLE DOUBT THERE WILL BE
SOME CONVECTION ALONG/NEAR THE FRONTAL BOUNDARY ACROSS OUR SOUTHERN
ZONES DURING THIS TIME...THE IDEA THAT SOMETHING WILL ORGANIZE (IN
RELATIVELY WEAKLY SHEARED ENVIRONS) AND PROPAGATE NORTHEAST INTO A
STABLE AIR MASS JUST DOESN/T JIVE. IN FACT...EXAMINATION OF ENSEMBLE
GUIDANCE INDICATES THE OPERATIONAL NAM IS AN EXTREME OUTLIER WITHIN
THE SREF SYSTEM AS WELL. AS SUCH...THE NAM/S MASS FIELDS ARE HIGHLY
SUSPECT WED NIGHT THROUGH THURSDAY...AND THE MODEL HAS LARGELY BEEN
DISREGARDED DURING THIS PERIOD. WE HAVE OPTED TO ADVERTISE CHANCE
POPS ALONG THE SOUTHERN ZONES...WITH SOLID CHANCES AND EVEN BRIEF
PERIODS OF LIKELY ALONG THE SOUTHERN BLUE RIDGE. MEANWHILE...IT
SEEMS FAIRLY CERTAIN THAT DRY AIR WILL PENETRATE AT LEAST INTO THE
NORTHERN ZONES...AND A DRY FORECAST WILL BE CARRIED THERE THROUGH
THE PERIOD. TEMPS WILL BE ABOUT 5 DEGREES BELOW NORMAL WED...AND
ABOUT 10 DEGREES BELOW NORMAL BY THURSDAY.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 315 AM...THE GLOBAL MODELS...WHILE MAINTAINING A PROMINENT
RIDGE DOWN THE EASTERN SEABOARD...ALSO SUGGEST A RETURN TO A WETTER
PATTERN DURING THE MEDIUM RANGE. THE ECMWF AND GFS AGREE IN CARVING
OUT A MAJOR LONG WAVE TROUGH ACROSS THE MISS VALLEY BY THE WEEKEND.
THIS HAS THE EFFECT OF DRAWING THE DEEP MOISTURE PLUME ASSOCIATED
WITH THE REMNANT BAROCLINIC ZONE BACK INTO OUR AREA BY FRIDAY. AS
SUCH...POPS RAMP UP TO SOLID CHANCE AND LIKELY ACROSS MUCH OF THE
AREA BY THE WEEKEND. THE GFS CONTINUES TO DEPICT THE POTENTIAL FOR
PERIODS OF HEAVY RAIN DURING THIS TIME...ESP AS A WEAK SUBTROPICAL
WAVE LIFTS OUT OF THE CENTRAL GULF OF MEXICO SATURDAY AND SAT NIGHT.
THE ECMWF IS MORE MUTED WITH THIS WAVE...AS WELL AS ITS QPF
RESPONSE...BUT NEVERTHELESS SUGGESTS A RELATIVELY WET WEEKEND.
ALTHOUGH THE SURFACE WEDGE WILL GRADUALLY WEAKEN DURING THE
PERIOD...THE INCREASING CLOUD COVER AND PRECIP COVERAGE WILL
MAINTAIN DAYTIME TEMPS WELL BELOW NORMAL...WITH MINS CREEPING CLOSER
TO NORMAL WITH INCREASING MOISTURE LEVELS.
&&
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
AT KCLT...LIGHT SW WINDS AND SCT TO FEW MID AND HIGH CLOUDS EXPECTED
THROUGH MID MORNING. AT 545Z...REGIONAL RADAR INDICATED A CLUSTER OF
SHRA/TSRA OVER EASTERN KY. THE CONVECTION IS LIKELY SUPPORTED BY THE
COMBINATION OF A REGION OF JET DIVERGENCE WITH LINGERING
INSTABILITY. MODELS INDICATE THAT A BAND OF DIVERGENCE WILL PIVOT
EAST AS THE L/W TROUGH AXIS RIPPLES ACROSS THE MID WEST. CONVECTION
ALLOWING MODELS INDICATE THAT A SW TO NE BAND OF SHRA/TSRA IS
EXPECTED TO PUSH ACROSS THE CLT TERMINAL BETWEEN 17Z- TO 19Z...I
WILL HIGHLIGHT WITH A TEMPO. OTHERWISE...DAYTIME CONDITIONS WILL
FEATURE A WSW WIND BETWEEN 6 TO 10 KTS AND CU BASED BETWEEN 040 TO
050. FROPA SHOULD OCCUR BETWEEN 01Z TO 03Z...I WILL INDICATE A NW
WIND BY 3Z.
ELSEWHERE...KAVL CIGS AND VIS WILL REMAIN VERY UNCERTAIN THROUGH THE
REST OF THE PRE DAWN. RECENT OBS HAVE INDICATED VIS FLUCTUATIONS
FROM VLIFR TO VFR SINCE 4Z. THE PASSAGE OF THICK HIGH CLOUDS THROUGH
SUNRISE WILL LIKELY PRODUCE ADDITIONAL SWINGS IN VIS AND LOW CLOUDS
EARLY THIS MORNING. I EXPECT THAT CEILINGS WILL CONTINUE TO RANGE
FROM IFR TO LIFR...BUT VIS WILL REMAIN MORE VOLATILE...HIGHLIGHTED
WITH FM AND TEMPO GROUPS. EAST OF THE MTNS...KHKY WILL LIKELY FAVOR
MVFR VIS UNDER MOSTLY CLEAR CLOUD COVER. ELSEWHERE...CONDITIONS
SHOULD REMAIN VFR THROUGH SUNRISE...POSSIBLY SOME GROUND FOG. AT
545Z...REGIONAL RADAR INDICATED A CLUSTER OF SHRA/TSRA OVER EASTERN
KY. THE CONVECTION IS LIKELY SUPPORTED BY THE COMBINATION OF A
REGION OF JET DIVERGENCE WITH LINGERING INSTABILITY. MODELS INDICATE
THAT A BAND OF DIVERGENCE WILL PIVOT EAST AS THE L/W TROUGH AXIS
RIPPLES ACROSS THE MID WEST. CONVECTION ALLOWING MODELS INDICATE
THAT A SW TO NE BAND OF SHRA/TSRA IS EXPECTED TO PUSH ACROSS THE
TERMINALS BETWEEN 13Z TO 17Z...I WILL HIGHLIGHT WITH A TEMPO.
OTHERWISE...DAYTIME CONDITIONS WILL FEATURE A WSW WIND BETWEEN 6 TO
10 KTS AND CU BASED BETWEEN 040 TO 050. FROPA SHOULD OCCUR BETWEEN
01Z TO 03Z...I WILL INDICATE A NW WIND THIS EVENING.
OUTLOOK...A COLD FRONT WILL STALL TO THE SOUTH OF THE AREA ON
WEDNESDAY AND REMAIN FOR THE REST OF THE WORKWEEK. RESTRICTIVE
CEILINGS AND VISIBILITY MAY BECOME A COMMON OCCURRENCE EACH NIGHT
FROM WEDNESDAY THROUGH THE WEEKEND AS THE STALLED FRONT INTERACTS
WITH GULF AND ATLANTIC MOISTURE.
CONFIDENCE TABLE...
07-13Z 13-19Z 19-01Z 01-07Z
KCLT HIGH 95% HIGH 100% HIGH 100% HIGH 100%
KGSP HIGH 98% HIGH 95% HIGH 100% HIGH 100%
KAVL LOW 33% MED 72% HIGH 85% HIGH 90%
KHKY HIGH 100% HIGH 95% HIGH 100% HIGH 100%
KGMU HIGH 95% HIGH 98% HIGH 100% HIGH 100%
KAND HIGH 92% MED 73% 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...JDL
NEAR TERM...NED
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...NED