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000
FXUS62 KGSP 091503
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1003 AM EST MON DEC 9 2013

.SYNOPSIS...
AN AREA OF PERSISTENT CONVERGENCE WILL LINGER OVER THE REGION TODAY
AND WELL INTO TUESDAY BRINGING MORE SHOWERS TO THE AREA. RELATIVELY
COLD AND DRY HIGH PRESSURE IS THEN EXPECTED TO MOVE BACK INTO THE
CAROLINAS FROM THE WEST LATE TUESDAY AND INTO WEDNESDAY AND REMAIN
OVER THE REGION THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF MID MORNING...RADAR SHOWS A WIDE BAND OF PRECIP STREAMING NE
ACROSS THE HEART OF THE FCST AREA...BUT WITH LITTLE ON THE COASTAL
SIDE OF THE BAND. HAVE TIGHTENED THE POP GRADIENT CLOSER TO I-85
WHICH LOWERED THE PRECIP CHANCES ON THE SE FRINGE...ALBEIT
TEMPORARILY. THE BAND SHOULD SLOWLY TRANSLATE EAST THROUGH THE
DAY...SO THE PRECIP CHANCES GO BACK UP TO LIKELY. TEMPS ARE ALSO A
PROBLEM...WITH THE DRAINING/MODIFYING OF THE WEDGE AIR MASS THROUGH
THE DAY AROUND THE EDGES. THE TRENDS SHOW A SLOW START WHICH IMPLIES
THE WEDGE WILL HANG ON LONGER THAN EXPECTED. THIS MIGHT REQUIRE THE
MAX TEMP TO BE LOWERED E OF THE BLUE RIDGE...AND HAVE STARTED IN
THAT DIRECTION WITH THE MORNING UPDATE.

PREVIOUS DISCUSSION...
AS OF 630 AM EST...WATER VAPOR IMAGERY CONTINUES TO SHOW A PLUME OF
DEEP MOISTURE FEEDING FROM THE WRN GULF OF MEXICO INTO THE SRN
APPALACHIANS. REGIONAL RADARS PLACE THE HEAVIEST BAND OF SHOWERS IN
THE SWLY 850 MB JET ALONG THE ERN SLOPES OF THE MTNS AND THE
ADJACENT FOOTHILLS...WITH THE REST OF THE AREA CONTINUING TO SEE AT
LEAST LIGHT RAIN AND AREAS OF DRIZZLE. IR CLOUD TOPS ARE NOT AS COLD
AS PREVIOUSLY AND ANY ISOLD THUNDER SHOULD BE CONFINED TO FAR SW
SECTIONS IN THE STEEPEST MID LEVEL LAPSE RATE AIR. MEANWHILE...THE
MODIFYING COLD AIR DAMMING LAYER WILL GET INCREASINGLY PINCHED TODAY
AS SFC LOWS MOVE UP THE ERN SEABOARD AND ACROSS THE GREAT LAKES. IN
ADDITION TO THE PRECIPITATION...WIDESPREAD LOW CLOUDS AND FOG WILL
PERSIST...WITH TEMPS RUNNING BELOW GUIDANCE VALUES. THE OCNL HEAVIER
SHOWERS MIXING UP THE BL SHOULD KEEP DAYTIME FOG FROM GETTING TOO
DENSE.

THE UPSTREAM SRN STREAM WAVE OVER THE SW TODAY SHOULD SHEAR OUT AS
IT MOVES EAST TOWARD THE MS RIVER VALLEY TONIGHT. THE MAIN RESPONSE
WILL BE ANOTHER SURGE OF MOISTURE INTO THE SW MTNS OVERNIGHT.
PRELIMINARY QPF FOR THE SW MTNS THROUGH TONIGHT APPROACHES 1.75
INCHES. FFG GUIDANCE FOR THIS AREA IS GENERALLY AROUND 2.5 INCHES IN
THREE HOURS...SO NO SIGNIFICANT HYDRO PROBLEMS ARE EXPECTED.
HOWEVER...THE MAIN STEM RIVERS WILL CONTINUE TO RESPOND AND THIS
WILL NEED TO BE MONITORED. NO FLOOD WATCHES ARE CURRENTLY PLANNED.
PROFILES WILL COOL A BIT FROM THE TOP DOWN TOWARD DAYBREAK ACROSS
THE NRN/WRN MTNS...BUT WITH KEEP ALL PRECIPITATION LIQUID THROUGH
TONIGHT.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 215 AM SUNDAY...THE SHORT RANGE PERIOD INITIALIZES EARLY
TUESDAY MORNING AS DEEP SOUTHWEST FLOW MOISTURE AXIS CONTINUES TO
MIGRATE ACROSS THE FORECAST AREA AHEAD OF A COLD FRONT.  BY DAYBREAK
TUESDAY...THE FRONT SHOULD BE PUSHING THROUGH THE MOUNTAINS AND INTO
THE FOOTHILLS REGION WITH COLD ADVECTION AND HIGH PRESSURE BUILDING
FROM THE WEST.  LATEST GUIDANCE CONTINUES TO INDICATE WEAK FRONTAL
WAVE DEVELOPING TUESDAY MORNING THAT WILL ENHANCE WARM ADVECTION
AND LOW LEVEL SHEAR PROFILES ACROSS THE NC PIEDMONT AND THE
EASTERN UPSTATE.  SHOWERS ADJACENT TO THE BOUNDARY WILL CONTINUE
SPREADING EAST THROUGH THE DAY WITH SOME EMBEDDED CONVECTIVE
SEGMENTS POSSIBLE ALONG AND EAST OF THE I77 CORRIDOR WHICH WILL
ALLOW FOR INCREASED RAIN RATES AT TIMES.  THUS FOR THE
FCST...TAPERED CATEGORICAL POPS DOWN THROUGH TUESDAY MORNING ACROSS
THE NORTHEAST GA AND SOUTHWEST NC MOUNTAINS AS BETTER UPSLOPE
FORCING COMPONENT SHIFTS EAST AHEAD OF THE FRONT.  LIKELY POPS WILL
PREVAIL THROUGH THE MORNING AND INTO THE EARLY AFTERNOON FOR THE
REMAINDER OF THE FORECAST AREA WITH SOME CATEGORICAL POPS SPREAD
ACROSS THE PIEDMONT TO ACCOUNT FOR WEAK CONVECTIVE PROCESSES
YIELDING BETTER COVERAGE.

OTHERWISE...COLD ADVECTION REGIME WILL INITIATE BEHIND THE FROPA
WITH REMNANT LOW LEVEL MOISTURE POOLING ALONG THE NORTHERN
MOUNTAINS.  LATEST NAM/SREF CONTINUES TO INDICATE A PERIOD OF
NORTHWEST FLOW INDUCED SNOW SHOWERS ACROSS THESE ZONES EARLY ON
TUESDAY MORNING POSSIBLY LASTING THROUGH THE AFTERNOON HOURS WITH
LITTLE TO NO ACCUMULATIONS EXPECTED.  BEYOND THAT...CONDITIONS WILL
IMPROVE ACROSS THE REGION AS HIGH PRESSURE BUILDS IN FOR THE
REMAINDER OF THE SHORT RANGE PERIOD.  AS MENTIONED
ABOVE...TEMPERATURES WILL COOL TO BELOW NORMAL LEVELS BEHIND THE
FROPA ON TUESDAY FOR AREAS ALONG AND NORTH OF THE I40 CORRIDOR WITH
NEAR NORMAL TEMPERATURES ELSEWHERE.  FURTHER COOLING WILL OCCUR FOR
WEDNESDAY AND THURSDAY WITH BELOW NORMAL TEMPERATURES EXPECTED.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 2 AM EST MONDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
THURSDAY WITH THE AXIS OF A BROAD UPPER TROF TO OUR NORTH AND A
CLOSED H5 LOW SPINNING UP OVER THE FAR SW CONUS. AS WE MOVE INTO
FRIDAY...HEIGHTS WILL RISE AS THE UPPER TROF LIFTS NE AND THE CLOSED
H5 LOW OPENS BACK UP AND MORPHS INTO A HEALTHY LOOKING SHORTWAVE AS
IT MOVES EASTWARD OVER THE WEEKEND. AS WE MOVE INTO SUN AND
MON...THE CONSISTENCY AMONG THE LONG RANGE MODELS DIMINISHES QUITE A
BIT WRT TO THE UPPER SYNOPTIC PATTERN. THE LATEST 00Z RUN OF THE GFS
IS MORE PROGRESSIVE WITH THE ABOVE SHORTWAVE AND AMPLIFIES ANOTHER
BROAD UPPER TROF OVER EASTERN CANADA LATE SAT THRU SUN....WHILE THE
OLDER RUN OF THE ECMWF MOVES ANOTHER POTENT LOOKING SHORTWAVE RIGHT
OVER THE CAROLINAS ON SUN AND WITH HEIGHTS RISING SLIGHTLY IN ITS
WAKE.

AT THE SFC...THE MODELS APPEAR TO BE IN BETTER OVERALL AGREEMENT WRT
THE SYNOPTIC PATTERN FOR THE FIRST HALF OR SO OF THE MEDIUM
RANGE...BUT BEYOND THAT MAJOR DIFFERENCES REMAIN. ON THURSDAY
CANADIAN HIGH PRESSURE IS EXPECTED TO BE CENTERED TO OUR NW OVER THE
CENTRAL MISS RIVER VALLEY WITH COOL AND DRY NLY LOW LVL FLOW OVER
THE CWFA. THIS HIGH WILL SLIDE NE OF THE FCST AREA BY EARLY
SAT...AND BEYOND THIS POINT MODEL SOLUTIONS CONTINUE TO DIVERGE
QUITE A BIT. THE GFS MOVES A COLD FRONT OVER THE CWFA SAT NIGHT WITH
ANOTHER ROUND OF CANADIAN HIGH PRESSURE SLIDING IN BEHIND THE FROPA
ON SUN AND MON. THE ECMWF...HOWEVER TRIES TO SPIN UP A LOW JUST OFF
THE SE COAST ON SUNDAY AND MOVE IT UP THE CAROLINA COAST ON SUN AND
EARLY MON. THE DEVELOPMENT AND MOVEMENT OF THE LOW ON THIS MODEL RUN
IS CONSIDERABLY SLOWER COMPARED TO 12Z RUN OF THE ECMWF THE PREVIOUS
DAY. B/C OF THESE DISCREPANCIES...I DID NOT MAKE ANY MAJOR CHANGES
TO THE SENSIBLE FCST AND STILL HAVE POPS RAMPING UP LATE FRI AND
INTO SAT FROM SLIGHT CHANCE TO HIGH END SOLID CHANCE BY SAT
AFTERNOON. I KEEP THEM AT SOLID CHANCE THRU SUN AND BEGIN TO TAPER
THEM BACK OFF ON MON. FROZEN PRECIP REMAINS A POSSIBILITY OVER THE
WEEKEND...HOWEVER IT IS STILL TOO EARLY TO TRY AND PREDICT SPECIFIC
TYPES AND AMOUNTS. TEMPS WERE NOT CHANGED SIGNIFICANTLY WITH VALUES
STARTING OUT WELL BELOW NORMAL AND WARMING TOWARDS THE END OF THE
PERIOD.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
AT KCLT...LIGHT RAIN AND DRIZZLE WILL BE INTERRUPTED BY OCCASIONALLY
MODERATE RAIN SHOWERS TODAY. EXPECT MAINLY LIFR CONDITIONS GIVEN THE
CONTINUED WARM ADVECTION OVER THE SLOWLY MODIFYING CAD
LAYER...HOWEVER...THE SHOWERS SHOULD PROVIDE JUST ENOUGH MIXING FROM
TIME TO TIME TO KEEP CIGS/VSBY FROM CRASHING TO VLIFR. TCLT RADAR
SHOWS 40 TO 45 KT OF SW FLOW NEAR 2 KFT TO PROVIDE SOME LLWS THROUGH
THE MORNING HOURS. OTHERWISE...EXPECT SFC WINDS TO REMAIN LIGHT OR
VARIABLE...BUT SHOW SOME OCCASIONAL SRLY DIRECTIONS AS THE SFC CAD
LAYER GETS PINCHED OFF. LITTLE TO NO IMPROVEMENT IN CIG/VSBY IS
EXPECTED THROUGH THE AFTN/EVENING HOURS...WITH CONDITIONS
DETERIORATING AGAIN TONIGHT.

ELSEWHERE...THE DEEP SW FLOW OF MOISTURE OVER THE SHALLOWING CAD
LAYER WILL CONTINUE TO PRODUCE WIDESPREAD LIGHT RAIN AND
DRIZZLE...WITH OCCASIONAL MODERATE RAIN SHOWERS. THE CAD APPEARS
JUST DEEP ENOUGH OVER THE FOOTHILL TAFS TO PRECLUDE A LLWS MENTION
AT PRESENT...BUT WILL INCLUDE AT KAVL WITH AROUND 40 KT NEAR 2000
FT. EXPECT CIG/VSBY TO GENERALLY LOCK INTO THE LIFR RANGE...WITH
ONLY OCCASIONAL IMPROVEMENT LATE THIS AFTN...BEFORE CONDITIONS
DETERIORATE AGAIN TONIGHT. EXPECT SFC WINDS TO COME UP FROM THE S
TODAY AND THEN BECOME VARIABLE AGAIN TONIGHT.

OUTLOOK...LOW RESTRICTIONS WILL CONTINUE INTO TUE MORNING BEFORE
DRYING OCCURS FROM THE WEST WITH A FRONTAL PASSAGE STARTING TUE
AFTERNOON THROUGH TUE NIGHT. DRY HIGH PRESSURE WILL SET UP THROUGH
WED AND CONTINUE THROUGH LATE WEEK.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-15Z
KCLT       MED   69%     MED   73%     MED   78%     HIGH  95%
KGSP       MED   68%     MED   66%     MED   63%     MED   65%
KAVL       MED   69%     MED   65%     MED   76%     MED   75%
KHKY       MED   69%     MED   75%     MED   69%     HIGH  82%
KGMU       MED   76%     MED   73%     MED   75%     MED   77%
KAND       MED   71%     MED   70%     MED   76%     HIGH  95%

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...JPT
NEAR TERM...HG/PM
SHORT TERM...CDG
LONG TERM...JPT
AVIATION...HG