Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 212027
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
427 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 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 /21Z MONDAY THROUGH SATURDAY/...
AT KCLT... MOIST AND UNSTABLE AIR MASS WILL PROVIDE A VARIABLE
CEILING AND VISIBILITY CONDITION DURING THIS FORECAST PERIOD.
OUTSIDE OF LOW CEILING AND VISIBILITY IN SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS THROUGH THIS EVENING... CLOUD BASES WILL BE
NEAR 4K FT AND VISIBILITY UNRESTRICTED. AFTER 06Z... STRATUS NEAR 4
HND FT LIKELY TO FORM WITH OCCASIONAL VISIBILITY NEAR 5 MI IN FOG.
WIDELY SCATTERED SHOWERS AND AN ISOLATED THUNDERSTORM ARE POSSIBLE
OVERNIGHT. AFTER 13Z TUESDAY... CEILING WILL SLOWLY INCREASE TO 2K
TO 3K FT RANGE AND VISIBILITY UNRESTRICTED EXCEPT IN SCATTERED
SHOWERS. SURFACE WIND WILL BE FROM THE NORTHEAST LESS THAN 10 KT...
BECOMING LIGHT AND VARIABLE AT TIMES OVERNIGHT.

ELSEWHERE... MOIST AND UNSTABLE AIR MASS WILL PROVIDE A VARIABLE
CEILING AND VISIBILITY CONDITION DURING THIS FORECAST PERIOD.
OUTSIDE OF LOW CEILING AND VISIBILITY IN SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS THROUGH THIS EVENING... CLOUD BASES WILL BE
NEAR 4K FT AND VISIBILITY UNRESTRICTED. CONVECTIVE STORMS WILL BE
MOST LIKELY AT KAVL... KGMU... KGSP... AND KHKY. AFTER 06Z...
STRATUS NEAR 4 HND FT LIKELY TO FORM WITH OCCASIONAL VISIBILITY NEAR
5 MI IN FOG. WIDELY SCATTERED SHOWERS AND AN ISOLATED THUNDERSTORM
ARE POSSIBLE OVERNIGHT. AFTER 13Z TUESDAY... CEILING WILL SLOWLY
INCREASE TO 2K TO 3K FT RANGE AND VISIBILITY UNRESTRICTED EXCEPT IN
SCATTERED SHOWERS. KAVL WILL HAVE SOUTHERLY SURFACE WIND AT 10 KT OR
LESS. OTHERWISE... SURFACE WIND WILL BE FROM THE NORTHEAST LESS THAN
10 KT... BECOMING LIGHT AND VARIABLE AT TIMES OVERNIGHT.

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...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH  86%     MED   70%     HIGH  80%     MED   72%
KGSP       MED   72%     MED   78%     MED   75%     MED   60%
KAVL       MED   67%     MED   64%     MED   76%     LOW   51%
KHKY       HIGH  80%     MED   60%     MED   74%     MED   70%
KGMU       HIGH  89%     MED   76%     HIGH  84%     LOW   57%
KAND       HIGH  82%     MED   77%     HIGH  80%     MED   66%

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...LGL






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