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000
FXUS62 KGSP 120615
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
215 AM EDT WED MAR 12 2014

.SYNOPSIS...
A COLD FRONT WILL PUSH THROUGH THE FORECAST AREA TODAY WITH COOL
HIGH PRESSURE BUILDING IN ON THURSDAY. THE AIRMASS WILL SLOWLY
MODERATE WARMER INTO SATURDAY...BEFORE A BROAD AND COLDER UPPER
LEVEL TROF BUILDS IN SUNDAY THROUGH MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 210 PM...THE LATEST RADAR IMAGES INDICATED WIDESPREAD LIGHT
RAIN PUSHING ACROSS THE NORTHERN SAVANNAH RIVER VALLEY. I WILL
UPDATE POPS TO INDICATE THE ARRIVAL OF THE RAINFALL.

AS OF 1015 PM...FCST STILL ON TRACK. CLOUDS A BIT SLOW TO WORK INTO
THE NRN TIER/I-40 CORRIDOR...SO TEMPS HAVE DROPPED FASTER THAN FCST
TRENDS...WHILE THE SRN TIER WITH THICKER CIRRUS ARE DROPPING SLOWER.
SO THE MAIN CHANGE WITH THIS UPDATE WAS TO TEMP TRENDS INTO THE
OVERNIGHT. OTHERWISE...STILL EXPECT GRADUAL RAMP UP OF POPS FROM SW
TO NE THRU THE NIGHT.

AS OF 800 PM...NO MAJOR CHANGES TO THE FCST WITH THIS UPDATE. A FEW
TWEAKS TO THE AVIATION GRIDS FOR THE 00Z TAFS...BUT OTHERWISE NO
CHANGES.

AS OF 215 PM EDT...SHORTWAVE TROUGH CURRENTLY OVER SERN TX IN THE SRN
STREAM WILL SLIDE ALONG THE GULF COAST TONIGHT. THE TROUGH WILL
CONTINUE TO PRODUCE ABUNDANT CIRRUS ACRS THE CENTRAL GULF STATES THIS
AFTN...EVENTUALLY SPREADING INTO OUR CWFA FROM THE SOUTHWEST BY
EVENING. OTHERWISE THIS AFTN SKIES WILL REMAIN MOSTLY CLEAR AND
TEMPERATURES IN THE UPPER 60S TO MID 70S. DEWPOINTS APPEAR TO HAVE
MIXED OUT BUT STABILIZED...MITIGATING ANY FURTHER DROP IN RH THOUGH
KEEPING IT IN THE NEAR CRITICAL 25-30 PERCENT RANGE.

MEANWHILE A DEEPENING SFC LOW ASSOCIATED WITH A STRONG UPPER WAVE
WILL MOVE INTO THE OH/TN VALLEYS BY TMRW MRNG. MODEST LLVL SW FLOW
WILL PRECEDE THIS SYSTEM ACRS THE SOUTHEAST. ABUNDANT MIDLEVEL
MOISTURE WILL ADVECT INTO THE REGION BEGINNING LATE EVENING...QUICKLY
FOLLOWED WITH ADDITIONAL MOISTURE IN THE LLVLS. A KEY INGREDIENT IS
MISSING IN ISENTROPIC UPGLIDE...WITH BOTH ISENTROPIC CHARTS AND
TRADITIONAL ISOBARIC FIELDS SHOWING NEUTRAL OR EVEN COLD ADVECTION.
HOWEVER DPVA WITH THE SRN STREAM WAVE LOOKS MORE THAN CAPABLE OF
DRIVING PRECIP ON ITS OWN. THE CAA NEARER THE SFC COULD BE DUE TO A
COLD POOL ASSOCIATED WITH THE PRECIP SHIELD. AT ANY RATE...SOME
UPSLOPE WILL COME INTO PLAY THOUGH THIS IS MAINLY THOUGHT TO BE IN
THE SW MTNS GIVEN THE DEEP SW TO WSW FLOW. QPF IS PRETTY LIGHT ON
MOST GUIDANCE WHICH COULD BE DUE TO THE LACK OF GOOD LLVL FORCING.

AFTER DAYBREAK...SRN SHORTWAVE WILL MOVE TO THE ATLANTIC COAST AND
SUPPORT DIMINISHES FOR PRECIP OVER THE PIEDMONT. HOWEVER...BY THIS
TIME THE SFC LOW WILL BEGIN TO CROSS THE CENTRAL APPALACHIANS AND
LLVL WIND FIELDS RAMP UP. SFC FRONT WILL NOT CROSS UNTIL LATE
AFTERNOON KEEPING THE FA IN THE WARM SECTOR THRU DIURNAL PEAK TEMPS.
INSTABILITY DIFFERS SOMEWHAT BETWEEN NAM/GFS AS ONE MIGHT
EXPECT...WITH THE SREF MEMBERS BASICALLY SUPPORTING A BLEND OF ALL
THREE MODELS. MODEST CAPE OF 100-200 J LOOKS LIKELY IN PARTS OF THE
AREA. SHEAR IS NO PROBLEM WITH CONSENSUS SUPPORTIVE OF A LOW END
SEVERE /HSLC/ THREAT...IF THE INSTABILITY IS REALIZED. FREQUENT GUSTS
OF 25-30 KT ARE LIKELY FROM MID MORNING THRU THE END OF THE DAY. AT
LEAST A FEW WIND GUSTS OF 35-40 KT ARE POSSIBLE IN ALL AREAS...MAYBE
A BIT HIGHER. A WIND ADVY MAY BE NEEDED AND ISSUED OVERNIGHT TONIGHT.

MODEL CONSENSUS IS FOR A CRASH IN TEMPS BEHIND THE FRONT...WITH THE
TENN BORDER ZONES SEEING TEMPS FALL ENOUGH FOR A SNOW MENTION VERY
LATE IN THE AFTN...THOUGH THIS IS UNLIKELY TO BE ASSOCIATED WITH CAPE
AND ANY ACCUMULATION WOULD NOT OCCUR UNTIL LATER.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AS OF 230 PM TUESDAY...THE MAIN FOCUS FOR THE SHORT RANGE WILL BE
THE POST-FRONTAL AIR MASS WEDNESDAY NIGHT. THICKNESSES DROP RAPIDLY
SUCH THAT ANY REMAINING PRECIP OVER THE MTNS SHOULD QUICKLY CHANGE
TO SNOW FROM HIGH ELEVATIONS TO THE VALLEY FLOORS BY MID EVENING.
THE MODELS ARE IN GOOD AGREEMENT WITH A NW FLOW OF LOW LEVEL
MOISTURE GENERATING SNOW SHOWERS IN THE UPSLOPE AREAS NEAR THE TN
BORDER THROUGH THE EARLY MORNING HOURS ON THURSDAY. THE NEW GUIDANCE
SUGGESTS THAT SOME SNOW SHOWER ACTIVITY COULD PERSIST BEYOND
SUNRISE. PRECIP AMTS HAVE TRENDED SLIGHTLY HIGHER AS WELL...WITH
SOME SUPPORT FROM THE PASSAGE OF ANOTHER SHORT WAVE EARLY THURSDAY
MORNING. A CONSENSUS QPF BETWEEN THE PREVIOUS FCST AND A BLEND OF
THE HPC/SREF/GFS/NAM YIELDS ADVISORY LEVEL SNOW AMOUNTS. IF THE FCST
DOES NOT CHANGE...A WINTER WX ADVISORY MAY BE ISSUED FOR THE ZONES
THAT BORDER TENNESSEE FOR WEDNESDAY NIGHT. WINDS WILL REMAIN STRONG
BEHIND THE FRONT WEDNESDAY EVENING...PERHAPS WITH ADVISORY LEVEL
GUSTS AT ELEVATIONS ABOVE 3500 FEET. A WIND ADVISORY MIGHT BE ISSUED
FOR HIGH ELEVATIONS IF THE FCST DOES NOT CHANGE. EAST OF THE
MTNS...IT SHOULD BE BRISK AND COLD WITH TEMPS DROPPING BELOW
FREEZING.

THE REST OF THE FORECAST IS QUIET IN COMPARISON. THE UPPER TROF AXIS
SHOULD MOVE OFF THE EAST COAST ON THURSDAY FOLLOWED BY AN UPPER TROF
BUILDING IN FROM THE WEST THURSDAY NIGHT AND DAMPENING ON FRIDAY.
THIS WILL SUPPORT ANOTHER DRY HIGH PRESSURE AIR MASS MOVING ACROSS
THE FCST AREA THROUGH THE REMAINDER OF THE PERIOD. THERE IS SOME
CONCERN ON THURSDAY THAT PORTIONS OF THE FCST AREA WILL FLIRT WITH
RED FLAG FIRE CONDITIONS BECAUSE OF A VERY LOW RH IN THE AFTERNOON
AND SOME LINGERING WIND GUSTS OVER THE MTNS. OTHERWISE...TEMPS WILL
BE WELL BELOW NORMAL ON THURSDAY BUT SHOULD MODERATE FOR THURSDAY
NIGHT AND THEN BACK TO NEAR NORMAL ON FRIDAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 145 AM EDT WED...THERE IS STILL MUCH UNCERTAINTY IN THE EXT
RANGE FCST. THE ULVL PATTERN/ENERGY AND MASS FIELDS ARE NOT WELL
AGREED UPON WHICH LEADS TO VARYING SFC SENSIBLE WX SOLNS BTW THE
MAIN OP MODELS. THE INCOMING COLD FRONT SAT IS MORE PRONOUNCED AND
HAS GREATER GOM MOISTURE FLUX THAN THE CWC/ECMWF. HOWEVER...THERE IS
DECENT AGREEMENT WITH THE LLVL THERMAL FIELDS AND WILL COUNT ON
MAINLY ALL RAIN IN ISENT WARM SECTOR LIFT. THERE COULD BE BRIEF
-SNSH ACROSS THE HIGHEST NC MTN TERRAIN WITH NO SIGFNT ACCUMS
THROUGH 14Z SAT.

THE BIGGER DIFFERENCE IN THE MODELS OCCURS SUN THROUGH TUE WITH THE
EVOLUTION OF THE AFOREMENTIONED SFC BOUNDARY. WHILE THE GFS IS
MAINTAINING NEARLY UNIFORM FLOW THROUGH A DEEP LAYER AND THUS A
NEARLY STATIONARY COASTAL SFC FRONT...THE ECMWF AND CMC DEVELOP A
STRONG ULVL TROF AND COASTAL MILLER/A CYCLOGENESIS SUN NIGHT. THIS
LATTER SCENARIO WOULD BRING IN MUCH GREATER MOISTURE AND ALONG WITH
SOME MEASURE OF LOWERING PARTIAL THICKNESSES AND DIURNAL
COOLING...SN OR A RA/SN MIX SUN AND MON NIGHTS. THIS IDEA WAS GIVEN
A LITTLE MORE WEIGHT THAN THE TOTALLY SUPPRESSED AND DRY GFS SOLN.
THE GOING MID CHANCE POPS STILL LOOK GOOD SUN NIGHT THROUGH MON
NIGHT WITH SNOW ACCUMS ACROSS THE NC MTNS EARLY MON AND PERHAPS LOW
END ACCUMULATING SNOW INTO THE NC FOOTHILLS AND PIEDMONT MON NIGHT.
TEMPS WILL BEGIN THE PERIOD RIGHT AROUND NORMAL AND LIKELY DROP TO
8-10 DEGREES BELOW NORMAL BY MON WITH WINDS SHIFTING NE/LY AS A
CANADIAN HIGH BUILDS TO THE NORTH AND A BROAD ULVL TROF DEVELOPS
OVER THE ERN CONUS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...THE CENTER OF 990 MB LOW WILL TRACK FROM THE OHIO RIVER VALLEY
TO THE NEW ENGLAND COAST THROUGH THE TAF PERIOD. LLVL LIFT AND DEEP
MOISTURE WILL SWEEP NORTH AHEAD OF APPROACHING COLD FRONT THIS
MORNING AND AFTERNOON. -SHRA WITH AT LEAST MVFR CEILINGS IS EXPECTED
DURING MORNING DAYLIGHT HOURS. FROPA IS EXPECTED BETWEEN 22-02Z
ACROSS THE TERMINAL. AS THE FRONT APPROACHES...SW WILL STRENGTHEN
THROUGH THE AFTERNOON...WITH GUSTS NEAR 40 KTS. IN THE WAKE OF THE
FRONT...WIND WILL VEER FROM THE NW WITH GUSTS IN THE MID TO UPPER 30
KTS.

ELSEWHERE...MVFR CEILINGS AND -SHRA WILL INCREASE AHEAD OF AN
APPROACHING COLD FRONT THIS MORNING. BY MID DAY...SW WINDS WILL
STRENGTHEN SIGNIFICANTLY...WITH GUSTS IN THE MID TO UPPER 30 KTS. IN
THE WAKE OF THE FRONT...WIND WILL VEER FROM THE NW WITH GUSTS IN THE
MID TO UPPER 30 KTS.

OUTLOOK...DRY HIGH PRESSURE WILL REMAIN OVER THE WESTERN CAROLINAS
THROUGH THE REMAINDER OF THE WORK WEEK.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  99%     HIGH  81%     HIGH  90%     HIGH 100%
KGSP       HIGH  97%     HIGH  84%     HIGH 100%     HIGH 100%
KAVL       HIGH  97%     MED   71%     HIGH  99%     HIGH  98%
KHKY       HIGH 100%     MED   75%     HIGH  95%     HIGH 100%
KGMU       HIGH  98%     MED   72%     HIGH 100%     HIGH 100%
KAND       HIGH  94%     MED   73%     HIGH  96%     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...JOH
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...HG
AVIATION...NED