Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 242107
AFDGSP

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

.SYNOPSIS...
A COLD FRONT WILL THE CROSS AREA THROUGH THIS EVENING AND MOVE
SOUTHEAST OF THE REGION OVERNIGHT. HIGH PRESSURE WILL BUILD IN
BEHIND THE FRONT FOR FRIDAY AND THE WEEKEND. ANOTHER FRONT IS
EXPECTED TO REACH THE AREA ON MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 435 PM EDT...THE BEST CONVECTIVE COVERAGE AHEAD OF THE SLOWLY
MOVING COLD FRONT OVER THE MTNS IS DEVELOPING FROM THE EASTERN EDGE
OF THE MOUNTAINS OUT ACROSS THE FOOTHILLS AND PIEDMONT AS ADDITIONAL
UPPER SUPPORT ARRIVES FROM THE W IN THE TROUGH AXIS. A FAIRLY DECENT
COLD POOL MAY DEVELOP OVER THE FOOTHILLS AND LEAD TO WIDESPREAD
COVERAGE FOR A FEW HOURS AS THE ACTIVITY MOVES EASTWARD. OTHER THAN
IN TRAINING AREAS...MOVEMENT SHOULD SUFFICIENT TO LARGELY PRECLUDE
HYDRO PROBLEMS. IT WILL TAKE VERY TALL CELLS TO PRODUCE SEVERE
WEATHER IN THE WARM AND MOIST AIRMASS...BUT MARGINAL QUARTER HAIL
AND 50+ WINDS APPEAR MOST POSSIBLE ALONG AND EAST OF INTERSTATE 77
AS THE CONVECTIVE COLD POOLS BUILD.

STILL ANTICIPATE A STEADY DECLINE IN COVERAGE FROM LATE EVENING
THROUGH THE OVERNIGHT AS THE COLD FRONT MOVES EAST OF THE AREA AND
HIGH PRESSURE THEN BUILDS SOUTHWARD TO BRING A SOMEWHAT DRIER
AIRMASS INTO THE AREA. HOWEVER...LOW LEVEL MOISTURE WILL REMAIN
ELEVATED OVERNIGHT AND LIGHT WINDS SHOULD ALLOW FOG TO DEVELOP
THROUGHOUT THE MOUNTAIN VALLEYS...AND PERHAPS ALSO ACROSS PARTS OF
THE PIEDMONT.

ON FRI...EVEN WITH THE REMNANTS OF THE FRONT REMAINING SOUTH OF THE
AREA...WINDS ARE FORECAST TO VEER TO THE SE DURING THE AFTERNOON.
THE LIGHT UPSLOPE COMPONENT AND WEAKENING CAP MAY ALLOW FOR A FEW
ISOLATED MOUNTAIN SHOWERS FRIDAY AFTERNOON. 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 /21Z THURSDAY THROUGH TUESDAY/...
AT KCLT...THUNDERSTORMS WILL BE NUMEROUS AT THE AIRFIELD THROUGH
EARLY EVENING AS SEVERAL ROUNDS OF ACTIVITY AHEAD OF THE COLD FRONT
MOVE SWIFTLY FROM THE WSW AHEAD OF THE APPROACHING TROUGH. TEMPO
GUSTS OF 25 KT ALONG WITH MVFR RESTRICTIONS SEEM A GOOD BET BASED ON
OBSERVED IMPACTS ELSEWHERE. CONDITIONS WILL CALM DOWN BY LATE
EVENING AS THE BOUNDARY MOVES THROUGH. WINDS WILL BECOME LIGHT AND
THEN TURN OUT OF THE NE LATE TONIGHT. GIVEN THE LINGERING LOW LEVEL
MOISTURE...MOST GUIDANCE SUGGESTS THAT MVFR CLOUDS WILL DEVELOP
TOWARD SUNRISE WITH SOME LIGHT FOG. THIS SHOULD DISSIPATE BY 14Z.

ELSEWHERE...THUNDERSTORMS WILL REMAIN FAIRLY NUMEROUS NEAR ALL THE
MTN AND FOOTHILL TAF SITES THROUGH EARLY EVENING. ANY TSTMS SHOULD
PRODUCE LOCAL MVFR RESTRICTIONS AND SOME LOW END GUSTS. THE STORMS
WILL MOVE EAST OF THE AREA AS A COLD FRONT MOVES THROUGH MID TO LATE
EVENING. THE OVERNIGHT SHOULD BE QUIET BUT SOME IFR FOG IS A GOOD
BET AT KAVL WHERE CROSSOVER OVER TEMPS WILL BE MET. ANTICIPATE SW
FLOW EARLY TURNING NRLY THEN NE OVERNIGHT...EXCEPT CONTINUED NW
WINDS AT KAVL.

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

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       HIGH  85%     HIGH  94%     MED   64%     HIGH  80%
KGSP       HIGH  93%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   78%     MED   64%     MED   79%     HIGH 100%
KHKY       HIGH  86%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  93%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  87%     HIGH  80%

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/LG
SHORT TERM...WIMBERLEY
LONG TERM...JDL
AVIATION...HG/LG






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