Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 212359
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
659 PM EST FRI NOV 21 2014

.SYNOPSIS...
HIGH PRESSURE ATOP THE REGION THROUGH SATURDAY WILL GIVE
WAY TO A VERY MOIST SOUTHERLY FLOW ON SUNDAY. DRIER AND LESS MILD
AIR WILL THEN OVERSPREAD THE AREA IN THE WAKE OF A COLD FRONT BY
TUESDAY.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 645 PM...NO SIGNIFICANT CHANGES WITH THE 2330 UTC UPDATE. I
ADJUSTED TEMPS AND DEWPTS TO LINE UP WITH LATEST METAR TRENDS.
WINDS/SKY WERE UPDATED WITH THE LATEST GUIDANCE FOR THE 00Z TAFS.
OTHERWISE...FCST IS ON TRACK.

AS OF 200 PM EST FRIDAY...A WEAK UPPER RIDGE AXIS WILL CROSS THE
REGION TONIGHT AND OFF THE ATLANTIC COAST BY SAT MORNING. NEARLY
ZONAL UPPER FLOW BECOMES SWLY BY SAT EVENING IN RESPONSE TO AN
APPROACHING SOUTHERN STREAM UPPER SHORTWAVE FROM THE SOUTHERN
PLAINS. THIS WILL ALLOW CP SURFACE HIGH CENTERED OVER THE CENTRAL
APPALACHIANS TO SLIDE SOUTHEASTWARD INTO THE CAROLINAS COASTAL
PLAINS BY SAT MORNING...AND OFF THE COAST BY LATE SAT
AFTERNOON/EVENING. AS FOR OUR SENSIBLE WEATHER...WE WILL SEE
CONTINUED DRY CONDITIONS TONIGHT THROUGH SAT UNDER THE SURFACE
RIDGE. HIGH CLOUDS WILL OVERSPREAD THE REGION FROM THE SOUTHWEST BY
TOMORROW AFTERNOON AS A SURFACE LOW PRESSURE SYSTEM APPROACHES FROM
THE SOUTHERN PLAINS. TEMPERATURES WILL CONTINUE TO RUN 7-10 DEGREES
BELOW NORMAL.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 215 PM FRIDAY...SOME MIXED SIGNALS AS TO THE SEVERE WEATHER
POTENTIAL EAST OF THE MTNS ON SUNDAY/SUNDAY NIGHT...WHICH IS THE
MAIN FOCUS OF THE SHORT RANGE PERIOD. ON THE ONE HAND...THE 12Z RUNS
OF THE GFS AND NAM SHOW THE VORTICITY CENTER ASSOCIATED WITH THE
NEGATIVELY TILTED SHORT WAVE LIFTING NE ON A TRACK THAT IS FURTHER E
THAN PREVIOUS RUNS. IT HAS BEEN MY EXPERIENCE THAT OUR BEST SEVERE
WEATHER POTENTIAL IN HIGH SHEAR LOW CAPE SCENARIOS TENDS TO HAPPEN
WITH A STRONGER...MORE ADVECTIVE SHORT WAVE TRACKING FARTHER S SO AS
TO PROVIDE SOME STRONG SYNOPTIC SCALE ORGANIZATION THAT FAVORS
LINEAR CONVECTION. THE TREND IN THE GFS/NAM SUGGESTS THIS MIGHT BE
MORE OF A POSSIBILITY...ALTHO THE 12Z RUN OF THE ECMWF HAS THIS
FEATURE STILL MOVING ON A TRACK WELL TO OUR NW. ON THE OTHER HAND...
ALL THE MODELS AGREE THAT OUR POTENTIAL LOW CAPE ENVIRONMENT HAS
EVEN LESS POTENTIAL ON SUNDAY AFTERNOON/EVE...NOW WITH NONE OF THE
SOLUTIONS BRINGING A COASTAL FRONT/WEDGE BOUNDARY FAR ENOUGH INLAND
SO AS TO BRING THE WEAK CAPE INTO THE S/SE FRINGE OF THE FCST AREA.
THAT WILL NOT SUPPORT SEVERE POTENTIAL. SO...AS IT STANDS NOW...IT
LOOKS LIKE A SITUATION WHERE WE WILL HAVE A HIGHLY SHEARED
ENVIRONMENT AND WE WILL BE GEARED UP FOR SEVERE POTENTIAL...THAT
WILL REMAIN UNREALIZED FOR LACK OF BOUYANCY AND ORGANIZATION. I
WOULD SUGGEST KEEPING AN EYE ON THIS...PARTICULARLY IF FUTURE MODEL
TRENDS SUGGEST STRONGER FORCING OR BETTER LOW LEVEL ADVECTION THAT
COULD BRING WEAK BOUYANCY INTO THE REGION. WILL NOT MENTION SEVERE
POTENTIAL IN THE HWO FOR NOW. THE MODELS ALSO CONTINUE TO KEEP THE
DEEPER CONVECTION AND PRECIP RATES ALONG THE COASTAL FRONT THROUGH
SUNDAY EVENING. PRESENT THINKING IS THAT EVERYONE WILL GET A DECENT
RAIN...BUT WITH DRY ANTECEDENT CONDITIONS AND LOWER RATES... FLOOD
POTENTIAL LOOKS TOO LOW TO MENTION FOR THE TIME BEING. EXPECT SOME
STRONG WINDS AT RIDGETOPS SUNDAY AND SUNDAY EVENING...BUT IT IS TOO
EARLY TO MENTION POSSIBLE ADVISORY LEVEL WINDS AT RIDGETOPS AS WELL.
THAT LEAVES US FOR THE TIME BEING WITH A DECENT RAIN EVENT. WARM
ADVECTION SHOULD RAISE TEMPS HIGH ENOUGH BEFORE PRECIP ONSET THAT
ONLY RAIN IS INCLUDED IN THE FCST. THE MODELS SHOW A TREND TOWARD
DELAYING THE ONSET UNTIL CLOSER TO 06Z ON THE SC BLUE RIDGE...WITH
PRECIP POTENTIAL INCREASING/EMANATING FROM THERE. IF THIS TIMING
SLIPS FURTHER...WITH ONSET MORE TOWARD DAYBREAK SUNDAY...WE COULD
HAVE A SITUATION WITH TRAPPED COLD AIR IN THE MTN VALLEYS THAT COULD
PROVIDE FOR SOME P-TYPE ISSUES AT ONSET...SO KEEP THAT IN MIND AS
WELL. THE TIMING ON THE BACK END HAS SLIPPED AS WELL...SO THE VERY
HIGH POP WAS KEPT LONGER INTO THE SUNDAY NIGHT TIME FRAME ACROSS A
LARGER AREA. THE BULK OF THE PRECIP SHOULD LEAVE TO THE NE BY
SUNRISE MONDAY. THE UPPER TROF WILL REMAIN WELL TO THE WEST AND THE
IN SITU WEDGE SHOULD BE DESTROYED BY THEN...WHICH MEANS THAT MONDAY
COULD BE RELATIVELY WARM WITH HIGH TEMPS MAKING IT INTO THE LOWER
70S ACROSS THE PIEDMONT. THIS MIGHT LEAD TO SOME INSTABILITY BY THE
AFTERNOON WHILE WE RETAIN SOME STRONG BUT UNIDIRECTIONAL SHEAR. HAVE
KEPT A CHANCE POP ACROSS THE REGION WITH A SMALL CHANCE OF THUNDER
MAINLY OVER THE AREA S/E OF I-85. A LACK OF A TRIGGER MAY PREVENT
MUCH FROM HAPPENING AS THERE IS LITTLE FORCING SEEN IN THE MODEL
GUIDANCE.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 340 PM FRIDAY...ON TUESDAY...BOTH THE GFS AND ECMWF INDICATE
THAT THE FORECAST AREA WILL REMAIN ON THE EAST SIDE OF MID LEVEL L/W
TROF. A DRY SLOT IS EXPECTED TO INCREASE THROUGH THE DAYLIGHT HOURS
ACROSS THE SOUTHERN APPALACHIAN REGION. I WILL FORECAST DRY
CONDITIONS...WITH CLOUDS BEGINNING TO INCREASE FROM THE WEST DURING
THE EARLY EVENING. TEMPERATURES ARE FORECAST TO RANGE FROM 3 TO 5
DEGREES BELOW NORMAL.

ON WEDNESDAY...MODEL AGREEMENT ACROSS THE REGION REMAINS FAIRLY
CLOSE. BY 12Z WED...THE CENTER OF A COASTAL LOW IS EXPECTED TO PUSH
OFF THE COAST OF THE CAROLINAS. THE WESTERN EDGE OF THE ASSOCIATED
CLOUD SHIELD AND MODEL QPF SPREAD ACROSS THE CLT METRO AREA WED
AM...REACHING THE NC FOOTHILLS DURING THE AFTERNOON. I WILL FORECAST
CHC TO SCHC POPS FOR RA...A FEW PATCHES OF SN IS POSSIBLE ACROSS THE
HIGH TERRAIN. TEMPERATURES SHOULD COOL TO 10 DEGREES BELOW NORMAL.

WEDNESDAY NIGHT INTO THANKSGIVING...BOTH MODELS HAVE WAVERED IN
PREVIOUS RUNS WITH THE POTENTIAL PASSAGE OF A SHARP MID LEVEL
TROF. HOWEVER...THE 12Z RUNS HAS YIELDED FAIRLY CLOSE AGREEMENT.
BASED ON THE GUIDANCE IT APPEARS THAT SIGNIFICANT FORCING AND
MOISTURE WILL DIVE ACROSS THE REGION WEDNESDAY NIGHT...REMAINING
WELL INTO THANKSGIVING DAY. GIVEN THE CURRENT MODEL AGREEMENT...I
WILL INCREASE POPS ACROSS THE MTNS INTO NE GA. HOWEVER...PROVIDED
THE UNCERTAIN EVOLUTION OF THIS ENERGY...I WILL KEEP POPS LOWER THAN
SCHC EAST. DURING THE MORNING...PRECIP SHOULD BE ASSOCIATED WITH THE
APPROACH OF THE MID LEVEL VORT...DURING THE DAY...COOL AND MOIST NWF
SHOULD SUPPORT UPSLOPE SHOWERS ALONG THE TN LINE. I WILL MENTION
BOTH SNOW AND RA FOR PRECIP TYPES. THANKSGIVING LOWS ARE FORECAST TO
RANGE FROM THE 20S ACROSS THE MTNS TO LOW 30S EAST. HIGH
TEMPERATURES SHOULD RANGE FROM THE 40S ACROSS THE MTNS TO AROUND 50
EAST.

ON FRIDAY...THE CLOSED MID LEVEL LOW SHOULD BEGIN TO TRACK NORTHEAST
OFF THE MID ATLANTIC COAST. LINGERING NWFS MAY CONTINUE ACROSS THE
MTNS INTO FRIDAY MORNING. OTHERWISE...CONDITIONS WILL REMAIN DRY TO
THE EAST. TEMPERATURES ARE FORECAST TO RANGE 10 TO 15 DEGREES BELOW
NORMAL.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS WILL PERSIST THROUGH 00Z
SUNDAY. LIGHT WINDS OF ENE TO ESE OVERNIGHT THRU SATURDAY MORNING...
AS DRY HIGH PRESSURE CENTERED OVER THE MID ATLANTIC SATES GRADUALLY
MIGRATES OFF THE EAST COAST. THE EXCEPTION WILL BE AT KAVL WHERE
NORTHERLY WINDS WILL BECOME SOUTHERLY BY THIS EVENING AND STAY THAT
WAY THRU THE TAF PERIOD. WE SHOULD SEE MOSTLY CLEAR SKIES OVERNIGHT
WITH INCREASING HIGH CLOUDINESS EXPECTED BY DURING THE DAY ON
SATURDAY...AHEAD OF AN APPROACHING LOW PRES SYSTEM.

OUTLOOK...DRY HIGH PRESSURE WILL GIVE WAY TO INCREASING RETURN FLOW
AND MOISTURE SATURDAY NIGHT. CLOUDS AND PRECIPITATION RETURN TO THE
AREA ON SUNDAY...AS A WARM FRONT CROSSES THE REGION FROM THE SOUTH.
BRIEF DRYING FOLLOWS THE FRONT ON MONDAY INTO TUESDAY.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     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...CSH
NEAR TERM...ARK/JOH
SHORT TERM...PM
LONG TERM...NED
AVIATION...ARK



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