Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 212344
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
744 PM EDT MON JUL 21 2014

.SYNOPSIS...
THE COMBINATION OF WEAK LOW PRESSURE ACROSS THE DEEP SOUTH AND HIGH
PRESSURE ACROSS THE MID ATLANTIC STATES WILL PUMP DEEP MOISTURE
ACROSS THE REGION THROUGH TUESDAY. A COLD FRONT WILL APPROACH FROM
THE NORTH DURING MID WEEK AND THEN STALL OVER THE REGION DURING THE
LATE WEEK. THIS BOUNDARY SHOULD WASH OUT EARLY IN THE WEEKEND.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 740 PM...CONVECTION DISSIPATED AS INSTABILITY DIMINISHED AND
THE SFC BOUNDARY MOVED SOUTH OF THE CWFA. HOWEVER...SHRA ARE BACK ON
THE INCREASE IN THE DEVELOPING MOIST UPSLOPE FLOW. EXPECT SHRA TO
CONTINUE OFF AND ON MOST OF THE NITE. ANYTHING MORE THAN SCT
COVERAGE WILL BE HARD TO PIN DOWN...BUT BEST COVERAGE WILL MOST
LIKELY BE ALONG THE BLUE RIDGE. PREVIOUS UPDATE FOR TEMPS IS
GENERALLY ON TRACK...WITH ONLY MINOR UPDATES NEEDED FOR CURRENT
CONDITIONS AND LATEST GUIDANCE.

AS OF 425 PM...CONVECTION DISSIPATING ACROSS THE ERN CWFA AND
DEVELOPING ALONG THE SRN FRINGE WHERE SFC BOUNDARY IS REACTIVATING
IN AN AREA OF HIGH INSTABILITY. EXPECT THE MAIN AREA OF TSRA WILL
REMAIN ALONG THE BOUNDARY...AND SLOWLY MOVE SOUTH OF THE AREA WITH
THE BOUNDARY...WHILE SCT SHRA AND ISOLATED TSRA DEVELOP ELSEHWERE.
HAVE RETAINED THE EARLY EVENING LIKELY POP ALONG THE BLUE RIDGE FOR
THE DEVELOPING UPSLOPE FLOW...WITH SCT POP ELSEWHERE. HAVE GREATLY
TRIMMED TEMPS OVER THE EAST WHERE RAIN WAS MORE WIDESPREAD...BUT
KEPT TEMPS WARM ACROSS THE WEST WHERE RAIN IS MORE ISOLATED.

AT 230 PM EDT MONDAY... CUTOFF LOW ALOFT TO OUR SOUTHWEST WILL
PERSIST THROUGH TONIGHT HELPING TO MAINTAIN MOIST SOUTHEAST FLOW
ACROSS THE CWA. AT THE SURFACE... HIGH TO THE NORTHEAST WILL
CONTINUE TO RIDGE SOUTHWARD EAST OF THE APPALACHIANS. BOUNDARY ALONG
THE EAST SIDE OF THE SURFACE RIDGE SEPARATING CLOUDY AND MOIST AIR
MASS FROM AIR TO OUR EAST AND SOUTH WHERE DAYTIME HEATING OCCURRED
HELPED A NICE THERMAL AND STABILITY GRADIENT DEVELOP. HIGH
PRECIPITABLE WATER AND CAPE IN THE 1000 TO 2000 J/KG PROMOTED THE
FORMATION OF AN AREA OF SHOWERS AND THUNDERSTORMS FROM UPSTATE SC
EASTWARD TO THE CHARLOTTE METRO AREA. LATEST MESO ANALYSES INDICATE
SOME OF THE CAPE HAS BEEN CONSUMED BY CONVECTION AND LOSS OF DAYTIME
HEATING THIS EVENING SHOULD WEAKEN BOUNDARY A BIT MORE. HOWEVER...
DEEP MOISTURE AND A MORE UPSLOPE BOUNDARY LAYER WIND COMPONENT THIS
EVENING ARE LIKELY TO PROVIDE INCREASED CHANCE OF SHOWERS AND
ISOLATED THUNDERSTORMS ALONG THE BLUE RIDGE ESCARPMENT. THUS... POPS
WILL REFLECT A SLIGHT DECREASING TREND WHERE AFTERNOON CONVECTION
WAS MAXIMIZED BUT INCREASE POPS ALONG THE ESCARPMENT BEFORE
DECREASING TOWARD MORNING. LARGE SCALE PATTERN DURING TUESDAY WILL
BE SIMILAR TO TODAY SO EXPECT COMBINATION OF MOISTURE AND AT LEAST
MODEST INSTABILITY WILL PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS.
EASTERLY WIND COMPONENT ONCE AGAIN IS LIKELY TO PROMOTE SHOWERS
ALONG THE EAST SLOPES... BUT UNDETECTABLE MESOSCALE FEATURES COULD
RESULT IN LOCAL ENHANCEMENTS. NIGHTTIME AND DAYTIME TEMPERATURES
WILL BE SIMILAR TO THOSE OF THE PAST COUPLE OF DAYS.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 215 PM EDT MONDAY...12Z NUMERICAL GUIDANCE STILL INDICATES
THAT A SLOW TRANSITION WILL OCCUR IN THE SE U.S. BETWEEN A WEAK
UPPER LOW AND A DEVELOPING UPPER TROF OVER THE EASTERN U.S. BY THE
END OF THE WEEK. THE FLOW AT 850 MB IS FCST TO VEER SUBSTANTIALLY
TUESDAY NIGHT. THEREFORE ANY ONGOING SHOWERS TUESDAY EVENING SHOULD
END WITH NO ADDITIONAL NOCTURNAL SHOWERS EXPECTED.  THIS WILL ALSO
BRING THE DEMISE OF THE WEDGE LIKE PATTERN AND A RETURN TO MORE OF A
DIURNAL/CLIMO TREND IN THE PRECIP ON WED AS THE WIND FIELD IS
FORECAST TO BE SW-W THROUGH THE COLUMN. THE 12Z NAM AND GFS BOTH
INDICATE THAT A COLD FRONT WILL REACH THE AREA ON THU AND WITH THE
FRONT PERHAPS REACHING THE PIEDMONT BY EVENING. MODEL SOUNDINGS
INDICATE THAT THE FLOW WILL HAVE A DECIDELY WESTERLY COMPONENT
THROUGH THE COLUNM ON THU WHICH WILL LIMIT CONVECTIVE COVERAGE
OUTSIDE THE MOUNTAINS. HENCE...WILL SHOW LIKELY POPS MOUNTAINS AND
CHANCE OTHER AREAS ON THU. A FEW SEVERE STORMS ARE NOT OUT OF THE
QUESTION ON THU AS CAPES SHOULD EASILY POOL TO 1500-2000J AHEAD OF
THE FRONT. MAX TEMPS SHOULD INCREASE TO JUST SHY OF CLIMO ON WED AND
NEAR CLIMO ON THU.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 220 PM MONDAY...MEDIUM RANGE MODELS IN AGREEMENT THAT A COLD
FRONT WILL BE IN THE AREA THURSDAY EVENING AS AN EASTERN UPPER
TROUGH IS ESTABLISHED. HOWEVER...GUIDANCE IS UNCLEAR AS TO WHETHER
FRONT WILL CLEAR THE FORECAST AREA ENTIRELY OR STALL SOMEWHERE OVER
THE REGION. THE ECM IS SLOWER WITH THE ARRIVAL OF THE FRONT AND
STALLS THE BOUNDARY ACROSS THE AREA ON FRI. ON THE OTHER HAND THE
GFS/NAM ARE INDICATING THAT A CLEAN FROPA WILL OCCUR WHICH WILL
ALLOW A DRYER AIRMASS TO TEMPORARILY OVERSPREAD THE AREA FRI. AT
THIS POINT...WILL LEAN TOWARD THE SOLUTION OF A CLEAN FROPA AS THE
STRENGTH OF THE UPPER EASTERN UPPER TROUGH WOULD SEEM TO SUPPORT A
MORE ROBUST FRONT REACHING THE SE U.S. HENCE...WILL INDICATE
LOWERING POPS FOR FRI. HOWEVER...12Z GFS INDICATES THAT BOUNDARY
LAYER FLOW WILL QUICKLY TURN TO THE SE ON SAT AS FRONT BEGINS TO
WASH TO THE SOUTH AND HIGH PRESSURE MOVES OFF THE COAST TO THE NE.
THIS WARRANTS POPS IN THE UPSLOPE AREAS. CLIMO POPS SEEM WARRANTED
ON SUNDAY AS THE BERMUDA HIGH PATTERN DEVELOPS OVER THE SE U.S. AND
A LEE TROUGH DEVELOPS OVER THE PIEDMONT. ON MONDAY...AN APPROACH OF
ANOTHER COLD FRONT DICTATES HIGHER POPS. A GUIDANCE CONSENSUS
INDICATES THAT TEMPS SHOULD BE WITHIN A COUPLE DEGREES OF CLIMO
THROUGH THE PERIOD.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AT KCLT... MVFR RETURNS THIS EVENING WITH IFR BEFORE MIDNIGHT. LIFR
DEVELOPS OVERNIGHT WITH ONLY A SLOW IMPROVEMENT THRU THE DAY TUE. IN
FACT...THE BULK OF THE DAY COULD BE MVFR. INCLUDED A VCSH OVERNIGHT
AS SHRA WILL RETURN TO THE AREA BUT REMAIN SCT. PROB30 INCLUDED FOR
THE AFTERNOON AS SCT CONVECTION WILL DEVELOP ONCE AGAIN. WINDS WILL
BE NE TO ENE THRU THE PERIOD.

ELSEWHERE... SIMILAR CONDITIONS TO KCLT...EXCEPT IFR FOG AND AND
CIGS AT KAVL. KAVL WILL ALSO SEE VERY LIGHT TO CALM WINDS UNTIL
AFTERNOON WHEN A LIGHT SLY WIND DEVELOPS.

OUTLOOK...A GRADUAL RETURN TO A MORE TYPICAL PATTERN WITH DIURNAL
SHOWERS AND STORMS IS EXPECTED WEDNESDAY. A FRONTAL SYSTEM
APPROACHING FROM THE NORTHWEST WILL CROSS THE REGION THURSDAY
NIGHT...BRINGING STRONGER CONVECTION AND POSSIBLE FLIGHT
RESTRICTIONS THROUGH FRIDAY.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-23Z
KCLT       MED   71%     MED   75%     MED   78%     MED   70%
KGSP       MED   70%     HIGH  90%     MED   62%     MED   70%
KAVL       LOW   55%     MED   68%     LOW   57%     LOW   58%
KHKY       MED   69%     HIGH  81%     HIGH  83%     MED   70%
KGMU       MED   76%     HIGH  84%     MED   69%     MED   70%
KAND       HIGH  87%     MED   76%     MED   67%     MED   62%

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...DEO
NEAR TERM...LGL/RWH
SHORT TERM...LG
LONG TERM...LG
AVIATION...RWH





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