Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191806
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
106 PM EST FRI DEC 19 2014

.SYNOPSIS...
A PLUME OF MOISTURE WILL ROTATE ACROSS THE REGION TONIGHT INTO
SATURDAY WITH DRY HIGH PRESSURE RETURNING ON SUNDAY. AN AREA OF LOW
PRESSURE WILL BRING RAIN CHANCES BACK BY MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 100 PM...FOR THE 1730 UTC UPDATE...I UPDATED THE NEAR TERM
GRIDS THRU SATURDAY MORNING FOR THE 18Z TAFS. SOME CHANGES TO THE
DEPICTION OF WINTRY MIX OF PRECIP LATE TONIGHT IN THE NC MTNS.
MODELS ARE CONTINUING TO TREND VERY LIGHT AND SPOTTY ON QPF WITH
THIS SYSTEM. SO NO BIG CHANGES WITH THIS UPDATE. I WILL FINALIZE
TEMPS/POPS/WX WITH THE NEXT UPDATE (2030 UTC).

AS OF 930 AM...FOR THE 1430 UTC UPDATE...FCST LOOKS PRETTY MUCH ON
TRACK. I TWEAKED SKY COVER THRU NOON TO REFLECT MORE SUNSHINE PER
SAT TRENDS. OTHERWISE...EXPECT AN INCREASE IN HIGH CLOUDS THIS AFTN
WITH TEMPS NEAR NORMAL IN THE MTNS AND A CATEGORY OR TWO ABOVE
NORMAL ACRS THE PIEDMONT...THANKS TO A DOWNSLOPE WNWLY FLOW.

PREVIOUS DISCUSSION...
A SURFACE RIDGE NOW EXTENDING FROM THE GREAT LAKES TO THE MID MS
RIVER VALLEY WILL MOVES SLOWLY EAST AND OVER THE APPALACHIANS BY
TONIGHT. WITH LIMITED CLOUD COVER TODAY IN THE WAKE OF THE DEPARTING
MID LEVEL ENERGY...AND SLIGHTLY ABOVE NORMAL HEIGHTS ALOFT...MAXIMUM
TEMPERATURES SHOULD RUN NEAR NORMAL...DESPITE WEAK COLD ADVECTION IN
NE SURFACE WINDS. THE MODELS SHOW ONLY WEAK ISENTROPIC UPGLIDE
SETTING UP OVER THE SURFACE RIDGE LATE TONIGHT...SUPPORTIVE OF ONLY
LIGHT PRECIPITATION DESPITE SUBSTANTIAL CLOUD COVER. MINIMUM
TEMPERATURES WILL RUN SLIGHTLY ABOVE NORMAL UNDER THE CLOUDS...BUT
STILL NEAR OR BELOW FREEZING IN MUCH OF THE MOUNTAINS.

MODEL SOUNDINGS...WHILE COLD ENOUGH FOR ICE NUCLEATION AT THE UPPER
END OF THE MOIST LAYER...HAVE EITHER A WARM NOSE ALOFT OR WARM
SURFACE TEMPERATURES BY LATE TONIGHT...DEPENDING ON THE MODEL AND
THE LOCATION. EXAMINING BOTH A TOP DOWN APPROACH AND THE BOURGOIUN
METHOD...AND BLENDING THE NAM AND GFS...WOULD YIELD A LIGHT FREEZING
RAIN EVENT IN MUCH OF THE NC MOUNTAINS...BEFORE A TRANSITION TO
SLEET AND SNOW...AND THEN SNOW.

ICE ACCUMULATIONS WOULD BE QUITE LIGHT...BUT WOULD STILL WARRANT A
WINTER WEATHER ADVISORY SHOULD CONFIDENCE BE GREAT ENOUGH. WITH
MODEL SOUNDINGS SO MARGINAL FOR ICE VERSUS SNOW...CONFIDENCE IS TOO
LIMITED FOR A SECOND PERIOD ADVISORY AT THIS TIME. A MENTION OF A
WINTRY MIX WILL BE MADE IN THE HAZARDOUS WEATHER OUTLOOK HOWEVER.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 320 AM EST FRIDAY...THE LATEST 00Z SHORT RANGE MODELS HAVE
TRENDED DRIER AND A BIT COLDER WITH THE PASSAGE OF UPPER SHORTWAVE
ON SAT. THEREFORE...HAVE MADE REASONABLE CHANGES TO THE POPS/P-TYPE
ACCORDINGLY.

A WEAK SOUTHERN STREAM UPPER SHORTWAVE IS FORECAST TO PASS OVERHEAD
ON SAT...SHEARING OUT AS IT PUSHES OFF THE CAROLINAS COAST BY SAT
NIGHT. H5 HEIGHTS WILL RISE OVER THE SE BY SUN AS WEAK UPPER RIDGE
BUILDS IN FROM THE WEST.

SURFACE PATTERN AND SENSIBLE WEATHER...A WEAK CAD WILL SET UP OVER
THE CWA ON SAT AS HIGH PRESSURE CENTERED OVER THE OHIO VALLEY SHIFTS
EAST. MEANWHILE...A CYCLOGENESIS WILL OCCUR OFF THE SC COAST AND
THIS WILL AID IN MOISTURE ADVECTION TO OUR SE ZONES OF THE CWA. THE
LATEST NAM AND GFS HAVE BACKED OFF ON THE QPF RESPONSE...ESPECIALLY
OVER THE SC PIEDMONT AS DEEPER MOISTURE WILL REMAIN SOUTH WHILE
BETTER UPPER FORCING PASSES NORTH OF THE AREA. THIS UPPER FORCING
WILL PROVIDE BETTER LIFT OVER THE NORTHERN HALF OF THE CWA...WITH
MODELS SHOWING LIGHT QPF RESPONSE LESS THAN A TENTH OF AN INCH.
THERMAL PROFILE IS SUPPORTIVE OF A BRIEF PERIOD OF SNOW OVER THE NC
MTNS/VALLEYS AND PORTIONS OF THE NORTHERN NC PIEDMONT ON SAT
MORNING...TRANSITIONING TO RAIN BY LATE SAT MORNING. ARAS OVER THE
NOTHERN NC MTNS WILL SEE A SLIGHT CHANCE OF FREEZING RAIN ON SAT
NIGHT AS SURFACE TEMPS DIPS INTO THE FREEZING LEVEL WHILE MID-LAYER
WARM NOSE ALOFT DEVELOPS. AFTER COORDINATING WITH NEIGHBORING
OFFICES...HAVE MENTIONED LOW END LIKELY POPS OVER THE NC MTNS AND
PORTIONS OF THE NC PIEDMONT WITH 40/50S ELSEWHERE ON SAT
MORNING...RAMPING DOWN INTO THE CHANCE RANGE BY SAT 18Z. CONDITIONS
SHOULD DRY OUT BY SAT EVENING AS THE SHORTWAVE PUSHES OFFSHORE AND
MOISTURE ASSOCIATED WITH THE LOW OFF THE CAROLINAS COAST PULLS
FARTHER NE.

SUN...NE FLOW WILL CONTINUE IN WEAK CAD REGIME OVER THE REGION AS
1028 MB HIGH BECOMES CENTERED OVER THE NEW ENGLAND. HAVE GONE WITH
MOSTLY DRY FORECAST (SLIGHT CHANCE POPS AT BEST) UNDER THE WEAK
RIDGING ALOFT DURING THE DAY ON SUN...WITH POPS RAMPING UP FROM WEST
TO EAST INTO THE SOLID CHANCE/LIKLEY RANGE BY LATE SUN NIGHT AS
MOIST ISENTROPIC LIFT INCREASES AND BETTER UPPER DIFFLUENT SWLY FLOW
SETS UP. NO FROZEN PRECIP IS EXPECTED ON SUN NIGHT GIVEN WARMER
THERMALPROFILE. TEMPS ON SAT WILL RUN 5-7 DEGREES BELOW
NORMAL...WITH A FEW DEGREES BELOW NORMAL ON SUN.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
AS OF 230 AM EST FRIDAY...THE LATEST 00Z GLOBAL MODELS ARE IN GOOD
AGREEMENT WITH REGARD TO THE OVERALL SYNOPTIC PATTERN AND THERMAL
THROUGH THE MEDIUM RANGE PERIOD.

SOUTHWESTERLY UPPER DIFFLUENT FLOW WILL SET UP BY MON AS A LOW
AMPLITUDE UPPER RIDGE AXIS PUSHES OFF THE EAST COAST WHILE AN UPPER
TROUGH DIGS INTO THE UPPER MID-WEST. A LOW IN THIS UPPER TROUGH WILL
CLOSE OFF AS IT DIGS INTO THE LOWER MISSISSIPPI VALLEY THROUGH TUE
NIGHT...BECOMING NEGATIVELY TILED AS IT SWINGS ACROSS THE SOUTHEAST
BY WED. NWLY FLOW ALOFT WILL SET UP BY THU AS THE UPPER TROUGH
PUSHES OFF THE ATLANTIC COAST.

AT THE SURFACE...1030MB HIGH CENTERED OVER THE NE WILL BE
RESPONSIBLE FOR CAD OVER THE CWA ON MONDAY...WITH A CYCLOGENESIS
OCCURRING OFF THE CAROLINAS COAST AT THE SAME TIME. GIVEN THE
COMBINATION OF STRONG MOIST ISENTROPIC LIFT...UPPER DIFFLUENT FLOW
AND GOOD MOISTURE ADVECTION IN THE WAKE OF THE CYCLOGENESIS...PRECIP
WILL BE ONGOING ACROSS THE CWA ON MONDAY. DESPITE THE CAD WITH
DECENT WARM NOSE ALOFT...SURFACE TEMPS WILL RUN ABOVE FREEZING
LVL...SUGGESTING ALL LIQUID PRECIP FOR MOST LOCATIONS ATT. WITH
DECENT QPF RESPONSE (0.25-0.75")PER 00Z GFS AND ECMWF...HAVE RAISED
POPS INTO THE LOW LIKELY RANGE DURING THE DAY ON MONDAY...RAMPING
DOWN INTO THE LOW END CHANCE RANGE THRU MON NIGHT AS THE LOW OFF THE
NC COAST PULLS FARTHER NE AWAY AND THE CAD WEAKENS.

TUE...MODELS AGREE THAT IN SITU CAD AND MOIST ISENTROPIC
LIFT REGIME WILL SUPPORT LOW END CHANCE FOR PRECIP THROUGH THE
AFTERNOON BEFORE POPS RAMP UP FROM WEST TO EAST INTO THE LIKELY
RANGE AS A SURFACE LOW AND ASSOCIATED COLD FRONT APPROACH FROM THE
WEST. THE LOW IS EXPECTED TO LIFT NE ACROSS THE TN VALLEY AND INTO
KY TUE NIGHT INTO WED MORNING...PUSHING A STRONG COLD FRONT THROUGH
THE FORECAST AREA. ALTHOUGH THERE WILL BE STRONG LLVL WIND
SHEAR/UPPER FORCING...SEVERE WEATHER CHANCES LOOK MINIMAL GIVEN ZERO
SBCAPE. THE MAIN ISSUE WILL BE STRONG CAA FLOW BEHIND THE
FRONT...SUPPORTING RAIN SHOWERS TRANSITIONING TO SNOW BY TUE NIGHT
OVER THE NC MTNS. WITH WRAP AROUND MOISTURE AND PREVAILING CAA NW
FLOW...SNOW WILL BE ONGOING OVER THE TN BORDER COUNTIES THROUGH WED
NIGHT. SNOW ACCUMS WILL BE LIMITED TO THE HIGHER PEAKS OF THE MTNS.
ELSEWHERE...CONDITIONS SHOULD DRY OUT BY WED AFTERNOON AS THE FRONT
AND ASSOCIATED MOISTURE MOVE OFF TO THE EAST AND DRY HIGH PRESSURE
BUILDS IN FROM THE WEST. TEMPS WILL BE 5-7 DEGREES BELOW NORMAL ON
MON...NEAR NORMAL TUE...AND 2-5 DEGREES BELOW NORMAL WED/THU.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...VFR CONDITIONS ARE EXPECTED THRU THE PERIOD. A MID LVL
DISTURBANCE WILL RIPPLE ACRS THE AREA LATE TONIGHT THRU SATURDAY
WITHIN ZONAL WESTERLY FLOW. THIS FEATURE WILL SPREAD PLENTY OF MID
AND HIGH CLOUDS THIS AFTN THRU THE EVENING. SOME LLVL MOISTURE WILL
APPROACH FROM THE SW AROUND DAYBREAK SATURDAY...LOWERING CIGS TO
SOMEWHERE AROUND 3500-5000 FT. CANNOT RULE OUT A BRIEF PERIOD OF
MVFR CIGS...BUT CONFIDENCE IS LOW. ALSO...THERE IS A CHC FOR SPOTTY -
RA AND SPRINKLES SATURDAY MORNING. WILL ADD A PROB30 FOR -RA...BUT
KEEPING IT VFR. WINDS WILL BE LIGHT THRU THE PERIOD...GENERALLY NE
THRU THE AFTN...THEN E/SE OVERNIGHT...THEN BACK TO NE BY DAYBREAK
SATURDAY...HOWEVER...WILL BE VARIABLE THRU THE PERIOD.

ELSEWHERE...GRADUALLY THICKENING AND LOWERING CIRRUS WILL PREVAIL
UNTIL THIS EVENING...WHEN LOW LEVEL MOISTURE ARRIVES IN ADVANCE OF A
MID LVL DISTURBANCE FROM THE WEST. LOW VFR CIGS ARE EXPECTED LATE
THIS EVENING AT KAVL AND THE SC SITES...WITH LIGHT PRECIPITATION AS
WELL. A WINTRY MIX OF RA/SN/FZRA MAY FALL AT KAVL LATE TONIGHT...
BEFORE A CHANGE TO LIGHT SNOW BY DAYBREAK. OTHER THAN POSSIBLE VSBY
RESTRICTIONS IN PRECIP AT KAVL...THE MAIN CONCERN FOR RESTRICTIONS
WILL BE MVFR CIGS CREEPING IN FROM THE SW TOWARD THE UPSTATE AROUND
DAYBREAK SATURDAY. A CONSENSUS OF THE GUIDANCE DOES PREVAIL MVFR AT
KAND FOR SATURDAY MORNING. FOR NOW...I KEPT ALL THE OTHER SITES VFR.
THE LOW CLOUDS WILL LIKELY PERSIST THRU 18Z.

OUTLOOK...LINGERING LOW LVL MOISTURE MAY KEEP SOME FOG AND LOW
STRATUS AROUND SATURDAY NIGHT THRU SUNDAY. A WETTER SYSTEM WILL THEN
TRACK INTO THE AREA FOR MONDAY LIKELY BRINGING WIDESPREAD CLOUDS AND
PRECIP RESTRICTIONS. YET ANOTHER STORM SYSTEM IS EXPECTED TO CROSS
THE AREA LATE TUESDAY OR EARLY WEDNESDAY...BRINGING ANOTHER ROUND
OF PRECIP.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
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  95%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  94%
KAND       HIGH 100%     HIGH 100%     HIGH  94%     MED   79%

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...ARK/JAT
SHORT TERM...JOH
LONG TERM...JOH
AVIATION...ARK



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