Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 240308
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1008 PM EST TUE DEC 23 2014

.SYNOPSIS...
A MOIST AIRMASS WILL REMAIN OVER THE REGION TONIGHT BEFORE A COLD
FRONT CROSSES ON WEDNESDAY. HIGH PRESSURE WILL ARRIVE ON THURSDAY
AND LINGER INTO FRIDAY. ANOTHER FRONTAL SYSTEM WILL CROSS THE AREA
ON SATURDAY AND SUNDAY...FOLLOWED BY HIGH PRESSURE ON MONDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 950 PM...ONE BATCH OF RAIN IS EXITING OUR I-77 CORRIDOR
ZONES...JUST AS ANOTHER IS OVERSPREADING THE WESTERN MOUNTAINS. THIS
RAIN SHIELD WILL OVERSPREAD THE FORECAST AREA OVER THE NEXT 2-3
HOURS...AND LIKELY PERSIST FOR A GOOD CHUNK OF THE NIGHT...AS
FRONTAL ZONE WILL MOVE SLOWLY ACROSS THE TENN VALLEY THE REMAINDER
OF THE NIGHT. THEREFORE...EXPECT A GOOD 1-2 INCH SOAK OVERNIGHT
ACROSS THE MOUNTAINS OF SOUTHERN NC/NORTHEAST GA AND SC. LOCALLY
HIGHER AMOUNTS WILL BE POSSIBLE NEAR THE BLUE RIDGE. I STILL DONT
THINK THIS WILL BE ENOUGH TO CAUSE ANY SIGNIFICANT HYDRO ISSUES...
ESP SINCE WE HAVE YET TO SEE MUCH IN THE WAY OF RAINFALL. WHILE
LOCALIZED PROBLEMS CANNOT BE RULED OUT...STILL DON/T SEE THE NEED TO
ISSUE A WATCH...SO WILL LET THE HWO MENTION RIDE FOR NOW.

QLCS MOVING QUICKLY ACROSS WESTERN GA AT THIS TIME CERTAINLY RAISES
AN EYEBROW OR TWO. HOWEVER...IT/S STILL FEEDING OFF SOME SOMEWHAT
RESPECTABLE NEAR-SURFACE AIR. MEANWHILE...TEMPS ARE STILL IN THE 40S
ACROSS THE WESTERN CAROLINAS AND NORTHEAST GEORGIA WITHIN ENTRENCHED
CAD REGIME. IN FACT...THE NORTHERN EDGE OF THE QLCS IS BECOMING
CONSPICUOUSLY LESS REFLECTIVE. THEREFORE...WHILE WE WILL ADVERTISE A
MENTION OF THUNDER OVERNIGHT (OF THE ELEVATED VARIETY)...THE SEVERE
WEATHER THREAT APPEARS TO BE VERY SMALL IN OUR FORECAST AREA.

TEMPS ARE EXPECTED TO SLOWLY RISE OVERNIGHT AS THE CAD PARENT HIGH
MOVES INTO AN INCREASINGLY UNFAVORABLE POSITION...AND THE WEDGE
FEELS THE SQUEEZE FROM ALL SIDES. IN FACT...SOUTHERN PIEDMONT AREAS
MAY WELL SEE A COMPLETE SCOURING BY DAYBREAK.

AS OF 655 PM...NOT MUCH TO DO WITH THE FORECAST AT THIS POINT BUT
SIT BACK AND WATCH...AS WIDESPREAD RAIN CONTINUES TO OVERSPREAD THE
AREA FROM GEORGIA/TENN VALLEY. QPF WAS SCALED BACK JUST A BIT
THROUGH 06Z IN LIGHT OF THE LATEST RADAR TRENDS...WHICH SUGGESTS THE
BETTER PRECIP RATES WILL REMAIN WEST AND SOUTHWEST OF THE FORECAST
AREA FOR THE NEXT FEW HOURS. OTHERWISE...TEMPS WILL REMAIN STEADY OR
SLOWLY RISE IN MOST AREAS...AS THE SURFACE WEDGE LAYER SLOWLY
BECOMES SHALLOWER.

AS OF 230 PM...KGSP RADAR CONTINUES TO SHOW AN AREA OF LIGHT TO
MODERATE RAIN...WITH EMBEDDED HEAVY RAIN AND THUNDER...MOVING NWD
OVER THE PIEDMONT OF THE CAROLINAS. THIS AREA OF PRECIP WILL
GRADUALLY WEAKEN OVER NC AS IT MOVES FARTHER N AND DEEPER OVER THE
WEDGE...BUT WILL STILL REQUIRE ALTERING THE PRECIP PROBABILITY TO
ACCT FOR VERY HIGH PROBABILITY RIGHT AWAY OVER THE NC FOOTHILLS AND
WRN PIEDMONT. WILL ALSO NOT RULE OUT AN OCCASIONAL LIGHTNING STRIKE.
MEANWHILE...OVER PORTIONS OF THE TN VALLEY AND SRN APPALACHIANS
OUTSIDE THE WEDGE...SOME TSTM ACTIVITY MAY SKIRT THE SW MTNS OF NC
THROUGH LATE AFTERNOON. BRIEFLY LOWERED THE POP IN BETWEEN THESE TWO
AREAS...BUT EXPECT THAT INCREASING FORCING SHOULD HELP MORE STORMS
TO DEVELOP...AND THE ATMOSPHERE WILL CATCH UP WITH THE FCST. TEMPS
ARE STILL IN GOOD SHAPE.

LOOKS LIKE AN ACTIVE 18-24 HRS ACROSS THE WESTERN CAROLINAS AND NE
GEORGIA. A MULTITUDE OF FORCING WILL CONVERGE UPON THE FCST AREA
THROUGH TONIGHT...WITH PLENTY OF DEEP MOISTURE. IT IS GOOD BET THAT
THE ENTIRE FCST AREA WILL SEE RAIN AT SOME POINT...THOUGH PERHAPS
NOT CONTINUOUSLY AS A 100 PCT POP MIGHT SUGGEST TO SOME. THE MAIN
ISSUES OVERNIGHT CONCERN RAINFALL AMTS AND WIND ON THE RIDGETOPS. A
45-55KT LOW LEVEL JET WILL TRANSLATE E ACROSS THE MTNS IN THE 06Z TO
12Z WED TIME FRAME. THIS COULD RESULT IN SOME STRONG WIND GUSTS ON
THE RIDGETOPS...BUT USUALLY THIS DOES NOT RESULT IN HIGH WINDS DOWN
IN THE VALLEYS DURING NIGHTTIME WARM ADVECTION FLOWS. WILL NOT ISSUE
ANY ADVISORIES FOR WIND. AS FOR HEAVY RAIN...EXPECT THE PASSAGE OF
SEVERAL SHOWERS THAT COULD CONTAIN FAIRLY HIGH RAINFALL RATES.
HOWEVER...THE TREND IN QPF IN THE MODELS AND OTHER GUIDANCE HAS BEEN
DOWNWARD...AND ANTECEDENT CONDITIONS ARE RELATIVELY DRY IN SPITE OF
RECENT LIGHT RAIN. THIS DOES NOT EXACTLY LOOK LIKE THE CASE WHERE
CONVECTION WILL RACE AHEAD OF THE FRONT AND MOVE ALONG THE GULF
COAST TO DISRUPT THE MOISTURE TRANSPORT TO THE CAROLINAS. IF
ANYTHING...IT LOOKS A BIT MORE LIKE THE CASE WHERE MOISTURE
TRANSPORT COULD BE ENHANCED A BIT BY A SLOW MOVING SYSTEM. AT ANY
RATE...CONFIDENCE IS STILL NOT HIGH ENOUGH THAT WE WILL HAVE ANY
SORT OF FLOODING WHERE THE RAIN IS LIKELY TO BE THE HEAVIEST...NEAR
THE BLUE RIDGE IN GEORGIA AND ALONG THE SC/NC BORDER. SO...A WATCH
WILL NOT BE ISSUED AT THIS TIME. EXPECT THE WEDGE TO HOLD ACROSS THE
REGION OVERNIGHT...MEANING TEMPS WILL BE NEARLY STEADY...PERHAPS
RISING A DEGREE OR TWO IN THE EARLY MORNING HOURS.

ON WEDNESDAY...AS OUR FLOOD THREAT GOES DOWN...OUR SEVERE WEATHER
THREAT CREEPS UP A BIT. SHEAR WILL BE PLENTIFUL AND THE LATEST
GUIDANCE SHOWS SUFFICIENT INSTABILITY TO GIVE PAUSE ABOUT A HIGH
SHEAR/LOW CAPE QLCS SCENARIO. HOWEVER...THE INGREDIENTS APPEAR TO
FAIL TO COME TOGETHER AT THE SAME TIME AND PLACE.  THE BEST SHEAR
WILL LIKELY RACE OFF TO THE EAST WITH THE LOW LEVEL JET EARLY IN THE
MORNING. MEANWHILE...IT WILL TAKE SOME TIME TO DESTROY THE REMNANT
OF THE WEDGE...PERHAPS NOT UNTIL MIDDAY OR EARLY AFTERNOON FROM THE
SOUTH. THAT DOES PROVIDE FOR SOME SUFFICIENT OVERLAP DURING THAT
TIME...BUT THE STRONG FORCING REMAINS TO THE WEST. EVEN AT THAT...
THE UPPER TROF SHOULD BE DEAMPLIFYING THROUGH THE DAY WITH THE SHORT
WAVE STEADILY SHEARING OUT. MOST OF OUR GOOD SEVERE QLCS CASES
FEATURE A STRONGLY ADVECTIVE SRN STREAM WAVE THAT ORGANIZES THE
CONVECTION INTO A LINE...BUT THIS ONE APPEARS TO NOT HAVE THAT KIND
OF FORCING...AND IT ONLY WEAKENS WITH TIME AS THE WAVE FINALLY MOVES
IN FROM THE WEST IN THE EVENING. WILL HAVE TO KEEP AN EYE ON
IT...BUT FOR NOW AGREE WITH DAY2 OUTLOOK IN KEEPING THE MARGINAL
RISK TO THE S AND E. TEMPS WILL BE TRICKY DEPENDING ON WEDGE
DESTRUCTION.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AT 200 PM EST TUESDAY...THE COLD FRONT SHOULD BE MAKING ITS WAY
ACROSS THE EASTERN PORTION OF THE FORECAST AREA CIRCA 00Z THU. THE
12Z NAM AND SREF ARE STILL SLOWER WITH THE FRONT THAN THE GLOBAL
MODELS...BUT THE GAP HAS CLOSED TO MORE LIKE 3 OR SO HOURS SLOWER.
HENCE...EXPECT NUMEROUS SHOWERS AND PERHAPS SOME EMBEDDED
THUNDERSTORMS TO BE ONGOING WED EVENING ESSENTIALLY ALONG AND EAST
OF THE I-77 CORRIDOR. THE FRONT AND ASSOCIATED SHOWERS SHOULD THEN
MOVE WELL EAST OF THE AREA BY MIDNIGHT. THE EXCEPTION WILL BE IN THE
MOUNTAIN NW FLOW UPSLOPE AREAS WHERE SCATTERED RAIN/SNOW SHOWERS
WILL PERSIST INTO THE EARLY CHRISTMAS. IN FACT...THE UPPER TROUGH
AXIS WILL TRAIL THE FRONT BY ABOUT 6 HOURS OR SO AND THE ADDED UPPER
SUPPORT MAY LEND TO AN UPTICK IN UPSLOPE PRECIP AFTER MIDNIGHT FOR A
WHILE EVEN LOW LEVEL WIND FIELDS ARE NOT IDEAL FOR UPSLOPE PRECIP.
ALSO...SOME MID LEVEL CLOUDS ASSOCIATED WITH TROUGH WILL SLOW
CLEARING EAST OF THE MOUNTAINS.

HIGH PRESSURE CENTERED ALONG THE GULF COAST WILL RIDGE NORTHWARD
OVER THE REGION DURING CHRISTMAS. HENCE...EXPECT PLENTY OF SUNSHINE
AND TEMPS A LITTLE ABOVE CLIMO. THE MODELS FORECAST THE CENTER OF
THE HIGH TO MIGRATE DIRECTLY OVER THE WESTERN CAROLINAS AND NE GA
THU NIGHT AND THEN MOVE EAST OF THE AREA ON FRIDAY. GENERALLY CLEAR
CONDITIONS WILL PREVAIL UNTIL LATE IN THE DAY FRIDAY WHERE TIME
HEIGHTS INDICATE THAT MID AND HIGH CLOUDINESS WILL BE ON THE
INCREASE. TEMPS WILL BE CONTINUE A LITTLE ABOVE CLIMO THU NIGHT AND
FRI AS AIRMASS IS NON POLAR IN ORIGIN.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 130 PM TUESDAY...HIGH PRESSURE WILL DRIFT OFF THE SOUTHEAST
COAST EARLY SATURDAY AS HEIGHTS FALL GENTLY OVER THE ERN STATES IN
RESPONSE TO TWO SEPARATE SHORTWAVES. THE LEADING NRN STREAM WAVE WILL
CROSS ONTARIO SATURDAY INDUCING SFC CYCLOGENESIS. LATEST GFS/EC/GEM
HAVE TRENDED SLOWER WITH THE ASSOCIATED FRONT...CONTINUING TO SHOW IT
EXTENDING TO THE GULF COAST...BUT NOW DELAYING ITS WEAK PUSH ACRS THE
SRN APPALACHIANS UNTIL SAT NIGHT.

THE SRN STREAM WAVE COMES INTO PLAY SAT NIGHT/SUNDAY AS IT DIGS INTO
TEXAS AND A SFC LOW FORMS ALONG THE FRONT INVOF THE GULF COAST. THIS
GENERAL EVOLUTION IS DEPICTED ON ALL THREE MODELS THOUGH THE DETAILS
AND TIMING ARE NOT CONSISTENT. CONSENSUS DOES SUPPORT INCREASING POPS
BEGINNING LATE SAT...THEN TAPERING OFF MONDAY. THE GEM PROGRESSION OF
THE SHORTWAVE IS FASTEST...MAKING THE LOW SPIN UP OVER LA/MS...BEFORE
THE FRONT REACHES THE MTNS. SAID LOW REMAINS AN OPEN FRONTAL WAVE.
THE EC IS CLOSE TO THE GEM WITH THE GENESIS OF THE LOW /BUT CLOSES IT
OFF/ AND IS MUCH SLOWER IN BRINGING IT THRU OUR CWFA. THE GFS IS
SLOWER WITH THE WAVE SUCH THAT IT FORMS TO OUR SOUTH AND KEEPS US ON
THE COOL SIDE OF THE SYSTEM. THUS THE GFS IS THE ONLY MODEL
SUGGESTING A SIGNIFICANT WINTRY PRECIP THREAT WITH THE EVENT...THAT
BEING SUN NIGHT INTO MON OVER THE NC MTNS. NONE OF THE CONSULTED
GUIDANCE INDICATES QPF WILL BE ENOUGH TO CAUSE NOTABLE HYDRO
CONCERNS.

TEMPS WILL REMAIN SEVERAL DEGREES ABOVE CLIMO THRU SATURDAY...WITH
THE DIURNAL RANGE BEING LIMITED SUNDAY BY CLOUDS/PRECIP. ONCE THE
FRONT/WAVE MOVE THROUGH TEMPS WILL RETURN TO NEAR CLIMO.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...VERY POOR FLT CONDITIONS WILL PERSIST THROUGH THE PERIOD.
AN AREA OF MODERATE RAIN WILL MOVE OVER THE TERMINAL BY THE START OF
THE PERIOD...AND CONTINUE FOR A COUPLE OF HOURS. THIS ACTIVITY HAS
SHOWN A TENDENCY TO BRIEFLY SCATTER OUT THE LIFR CIGS OVER UPSTATE
SC AND FAR WESTERN NC. THUS...BRIEF PERIODS OF IFR OR EVEN MVFR
CONDITIONS WILL BE POSSIBLE THROUGH 03Z OR SO. HOWEVER...LIFR CIGS
SHOULD QUICKLY FILL IN ONCE THIS AREA OF RAIN LIFTS NORTHEAST OF THE
TERMINAL. OCCASIONAL LULLS IN RAIN SHOULD OCCUR OVER THROUGH MUCH OF
THE TAF PERIOD...BUT THE BULK OF THE PERIOD SHOULD SEE AT LEAST -DZ.
VISBY IS EXPECTED TO GRADUALLY DETERIORATE INTO THE OVERNIGHT...WITH
NO BETTER THAN 2SM EXPECTED AFTER MIDNIGHT. LLWS WILL INCREASE AFTER
MIDNIGHT...AS VERY STRONG WINDS TRANSLATE ACROSS THE AREA ABOVE
SHALLOW COOL WEDGE. CHANCES FOR SCATTERED THUNDERSTORMS WILL
INCREASE ON WED MORNING...WARRANTING A PROB30 DURING THIS TIME. VERY
SLOW IMPROVEMENT IN CIGS IS EXPECTED DURING THE DAYLIGHT HOURS WED.

ELSEWHERE...BRIEF PERIOD OF IMPROVEMENT TO IFR/MVFR CONDITIONS IS
NOT EXPECTED TO LAST AT THE MTN AND FOOTHILLS TERMINALS...AND LIFR
CONDITIONS SHOULD RETURN (OR PERSIST) AT ALL TERMINALS BY NO LATER
THAN 02Z. ONCE THIS OCCURS...LIFR CIGS SHOULD SETTLE IN FOR THE LONG
HAUL. OCCASIONAL LULLS IN RAIN SHOULD OCCUR OVER THROUGH MUCH OF THE
TAF PERIOD...BUT THE BULK OF THE PERIOD SHOULD SEE AT LEAST -DZ.
VISBY IS EXPECTED TO GRADUALLY DETERIORATE INTO THE OVERNIGHT...WITH
NO BETTER THAN 2SM EXPECTED AT ALL TERMINALS AFTER MIDNIGHT. LLWS
WILL INCREASE AFTER MIDNIGHT...AS VERY STRONG WINDS TRANSLATE ACROSS
THE AREA ABOVE SHALLOW COOL WEDGE. CHANCES FOR SCATTERED
THUNDERSTORMS WILL INCREASE ON WED MORNING...WARRANTING A PROB30
DURING THIS TIME.VERY SLOW IMPROVEMENT IN CIGS IS EXPECTED DURING
THE DAYLIGHT HOURS WED. DRY AIR MAY BEGIN TO FILTER INTO THE FAR
WESTERN CAROLINAS BY THE END OF THE PERIOD...RESULTING IN QUICKLY
IMPROVING CONDITIONS.

OUTLOOK...IMPROVING FLT CONDITIONS ARE EXPECTED WED NIGHT...AS DRY
HIGH PRESSURE BUILDS INTO THE AREA AND PERSISTS THROUGH LATE WEEK.

CONFIDENCE TABLE...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       HIGH  85%     HIGH  85%     MED   77%     HIGH 100%
KGSP       HIGH  80%     HIGH  85%     HIGH  88%     HIGH  85%
KAVL       MED   77%     HIGH  85%     HIGH  83%     HIGH  85%
KHKY       HIGH  85%     MED   78%     HIGH  88%     HIGH  96%
KGMU       HIGH  80%     HIGH  85%     HIGH  88%     HIGH  85%
KAND       HIGH  80%     HIGH  80%     HIGH  89%     HIGH  84%

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...RWH
NEAR TERM...JDL/PM
SHORT TERM...LG
LONG TERM...WIMBERLEY
AVIATION...JDL



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