Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 250013
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
813 PM EDT THU JUL 24 2014

.SYNOPSIS...
A COLD FRONT WILL MOVE EAST OF THE AREA OVERNIGHT. HIGH PRESSURE
WILL BUILD IN BEHIND THE FRONT FOR FRIDAY AND THE WEEKEND. ANOTHER
COLD FRONT IS EXPECTED TO REACH THE AREA FROM THE NORTHWEST ON
MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 740 PM EDT...SFC OBS PLACE THE SLOWLY ADVANCING COLD FRONT
ALONG THE ERN SLOPES OF THE MTNS...WITH STEADY PROGRESS EWD EXPECTED
THROUGH THE LATE EVENING AND OVERNIGHT HOURS. THE FINAL ROUND OF
CONVECTIVE TRIGGERING SHOULD DRIVE A SERIES OF COLD POOL INDUCED
THUNDERSTORMS EWD ACROSS THE NC PIEDMONT THROUGH 10 PM THIS
EVENING...WITH ONLY RESIDUAL LINGERING SHOWERS IN THE NW FLOW INTO
THE HIGH TERRAIN THROUGH MIDNIGHT. ALTHOUGH SOME DEGREE OF DRYING IS
EXPECTED ON DEVELOPING N TO NE FLOW OVERNIGHT...THE BOUNDARY LAYER
WILL LIKELY SEE THE SLOWEST DRYING...LEADING TO LOW CLOUD FORMATION
AND AT LEAST PATCHY FOG. THE AREAS THAT RECEIVED APPRECIABLE
RAINFALL AND THE MTN VALLEYS WILL STAND THE BEST CHANCE OF FOG
DEVELOPMENT.

LIGHT WINDS ARE EXPECTED TO VEER AROUND TO SE OR PERHAPS EVEN SRLY
IN SRN SECTION THROUGH THE DAY ON FRIDAY. THE LIGHT UPSLOPE
COMPONENT AND WEAKENING CAP MAY ALLOW FOR A FEW ISOLATED MOUNTAIN
SHOWERS FRIDAY AFTERNOON BUT MOST LOCATIONS SHOULD BE DRY. MAX TEMPS
WILL TOP OUT A COUPLE DEGREES BELOW CLIMO.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 130 PM THU...UPPER HEIGHTS INITIALLY RISE FRI NIGHT AS A TROUGH
LIFTS AWAY FROM THE EAST COAST...BUT REMAIN NEARLY STEADY THEREAFTER
LEAVING OUR REGION UNDER SLIGHTLY CYCLONIC FLOW OVER THE WEEKEND. BY
LATE SUNDAY HOWEVER HEIGHTS BEGIN TO FALL AGAIN AS ANOTHER SHORTWAVE
DIGS INTO THE MIDWEST. AT THE SFC WEAK HIGH PRESSURE WILL PERSIST
OVER THE SERN CONUS ALONG WITH LIGHT SWLY TO WLY FLOW.

FOR SATURDAY THE MAIN DIFFICULTY IS TO DETERMINE WHETHER THE SFC HIGH
WILL PROVIDE ENOUGH SUBSIDENCE TO STIFLE DIURNAL CONVECTION. MODELS
DIFFER RATHER WIDELY IN THEIR DEPICTION OF THE CAP. 09Z SREF MEMBER
SOUNDINGS MOSTLY SHOW A SIGNIFICANT MIDLEVEL INVERSION...BUT THE
MEMBERS WHICH ARE UNCAPPED SHOW CAPE VALUES A BIT HIGHER THAN CLIMO
GIVEN THE LACK OF RIDGING ALOFT. DRY MID-UPPER LEVELS AND LACK OF
SHEAR IMPLY PULSE-MODE THREATS IF ANY CELLS ARE TO FIRE. ON THE OTHER
HAND...GFS/GEFS IMPLY CAPPING AND ACCORDINGLY HAVE NO QPF RESPONSE.
OVERALL SUPPORT SEEMS TO BE BETTER FOR A DRY FCST...THUS I HAVE
MAINTAINED IT. HIGH TEMPS WILL BE ABOUT NORMAL FOR SATURDAY.

THE POTENTIAL CAPPING IS A CRITICAL QUESTION FOR SUNDAY...BUT AT THAT
TIME THERE IS THE ADDED ISSUE OF WHETHER THE COLD FRONT PLOWING ACRS
THE OH/TN VALLEYS WILL HAVE ANY IMPACT DURING PEAK HEATING.  EARLIER
MODEL RUNS SUGGESTED THE FRONT WOULD BE NEAR ENOUGH TO PUT OUR AREA
IN A MORE FAVORABLE ENVIRONMENT FOR STRONG STORMS SUNDAY AFTN...BUT
LATEST GUIDANCE HAS DELAYED IT AND A FAIR NUMBER OF THE LATEST RUNS
AGAIN KEEP CONVECTION TO A MINIMUM OVER THE CWFA. ENSEMBLE SOLUTIONS
LEND SOME SUPPORT THOUGH...AND IN LIGHT OF THE UNCERTAIN MODEL TRENDS
AND CONTINUED EXPECTATION THAT THE FRONT WILL BE NEARBY...LOW POPS
HAVE BEEN KEPT SUNDAY AFTN...RAMPING UP INTO SUNDAY NIGHT. TEMPS WILL
INCH UP SLIGHTLY FURTHER SUNDAY UNDER HIGHER THICKNESSES IN THE SWLY
FLOW.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 150 PM THURSDAY...SUBSTANTIAL/ANOMALOUSLY STRONG UPPER HEIGHT
FALLS WILL BE INTRODUCED TO THE EASTERN CONUS EARLY IN THE MEDIUM
RANGE PERIOD...ALLOWING A COLD FRONT TO PUSH TOWARD THE REGION. THE
LATEST GLOBAL MODEL RUNS HAVE CONTINUED A RECENT TREND OF DRIER
PRE-FRONTAL AIR AND A WEAKER QPF RESPONSE WITH THE FRONT IN THE LATE
SUNDAY NIGHT/EARLY MONDAY TIME FRAME. IN FACT...A CONSENSUS SEEMS TO
BE DEVELOPING THAT PROBABILITIES FOR SHOWERS WILL BE VERY LOW...
EXCEPT PERHAPS ACROSS THE SOUTHERN AND EASTERN FRINGE OF OUR
PIEDMONT AREAS MON AFTERNOON...WHEN THE FRONT WILL HAVE A LITTLE
MORE IN THE WAY OF BUOYANCY TO WORK WITH. NEVERTHELESS...EARLY NEXT
WEEK IS STILL TOO FAR IN THE FUTURE FOR US TO GET TOO CUTE WITH
TIMING THE POSITION OF THE FRONT...AND THESE SCENARIOS TYPICALLY
EVOLVE MORE SLOWLY THAN ADVERTISED BY THE MODELS THIS TIME OF YEAR.
THEREFORE...WILL GENERALLY FEATURE A SHOTGUNNED CHANCE POP ACROSS
THE CWFA THROUGHOUT MONDAY...DIMINISHING TO SLIGHT CHANCE OR LESS BY
EVENING.

THE REMAINDER OF THE FORECAST PERIODS LOOKS VERY SIMILAR TO WHAT WAS
EXPERIENCED ABOUT A WEEK AGO...WHEN AN UNUSUALLY COOL/DRY AIR MASS
BECAME ESTABLISHED OVER THE REGION UNDERNEATH AN ANOMALOUSLY STRONG
EASTERN TROUGH. IF ANYTHING...THIS AIR MASS PAY PROVE TO BE A LITTLE
MORE PERSISTENT THAN LAST WEEK/S. TEMPS ARE EXPECTED TO BE 5-10
DEGREES BELOW CLIMO THROUGH THE PERIOD...WHILE A HALT IN DIURNAL
CONVECTION IS EXPECTED THROUGH AT LEAST WED.

BY THE END OF THE PERIOD...THERE ARE SIGNS THAT...AGAIN SIMILAR TO
LAST WEEK/S EVENTS...THE TROUGH WILL EFFECTIVELY RETROGRADE...
ALLOWING MOISTURE TO RETURN WITHIN A DEVELOPING WEDGE-LIKE SCENARIO.
POPS AND CLOUDS WILL THEREFORE BEGIN TO INCREASE BY THE END OF THE
PERIOD...WITH TEMPS REMAINING COOL WITHIN A DEVELOPING EASTERLY LOW
LEVEL FLOW REGIME.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AT KCLT...ONE LAST ROUND OF THUNDERSTORMS SHOULD MOVE EAST OF THE
AIRFIELD BY 01Z. WINDS TURNING NRLY THROUGH THE LATE EVENING HOURS
WILL THEN TURN NE POST FROPA OVERNIGHT. THE BL STAYS MOIST AND
RECENT RAINFALL WILL CONTRIBUTE TO LOW STRATUS AND FOG DEVELOPMENT
IN THE PIEDMONT. THERE IS GROWING CONSENSUS FOR IFR CIGS DURING THE
EARLY MORNING HOURS...BUT IT MAY BATTLE WEAK NRLY WIND AND DRYING.
WILL COMPROMISE BY EDGING THE FORECAST CLOSER TO IFR WITH BKN010
LATE TONIGHT. EXPECT QUICK IMPROVEMENT BY 14Z...WITH VFR CONDITIONS
AND LIGHT ENE WINDS...POSSIBLY TOGGLING SE LATE DAY.

ELSEWHERE...PRECIPITATION HAS ENDED ACROSS THE MTN AND FOOTHILL TAF
SITES THIS EVENING. ANY RESIDUAL UPSLOPE INDUCED SHOWERS ALONG THE
SPINE OF THE MOUNTAINS SHOULD DISSIPATE BEFORE REACHING KAVL. THE
MOIST BOUNDARY LAYER COULD WELL LEAD TO LOW CLOUD AND FOG FORMATION
DURING THE EARLY MORNING HOURS. THE BEST CHANCE OF THIS WILL BE AT
KAVL...BUT WILL HINT AT SOME FEW TO SCT010 AT THE FOOTHILL
SITES...AND FORECAST IFR VSBY AT KHKY OVERNIGHT. THE LOW
RESTRICTIONS SHOULD DISSIPATE QUICKLY BY 14Z FRI MORNING...WITH
MAINLY SCT VFR CLOUDS THROUGH THE DAY ALONG WITH E TO SE
WINDS...EXCEPT SW FROM KAND TO KAVL DURING THE AFTN.

OUTLOOK...FRI NIGHT THROUGH SUNDAY MORNING SHOULD BE QUIET AND
VFR...EXCEPT FOR THE MTN VALLEYS WHERE EARLY MORNING FOG MAY OCCUR.
SCT THUNDERSTORMS MAY RETURN TO THE FORECAST AREA FOR SUNDAY
AFTERNOON...THOUGH MORE LIKELY MON...AS ANOTHER COLD FRONT
APPROACHES AND THEN MOVES THROUGH THE AREA BY MON NIGHT.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       HIGH 100%     HIGH  89%     HIGH  89%     HIGH 100%
KGSP       HIGH 100%     HIGH  95%     HIGH 100%     HIGH 100%
KAVL       HIGH  92%     MED   76%     HIGH  95%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH  94%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH  91%     HIGH  95%     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...LG
NEAR TERM...HG
SHORT TERM...WIMBERLEY
LONG TERM...JDL
AVIATION...HG





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