Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 021318
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
818 AM EST MON MAR 2 2015

.SYNOPSIS...
A COLD FRONT WILL CROSS THE FORECAST AREA ON TODAY WITH ANOTHER
ROUND OF CANADIAN HIGH PRESSURE ARRIVING IN ITS WAKE. YET ANOTHER
MOIST COLD FRONT IS EXPECTED TO CROSS THE REGION WEDNESDAY AND
THURSDAY...FOLLOWED BY DRY HIGH PRESSRUE LATE IN THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 800 AM...DO NOT LIKE THE TREND OF VISIBILITY ACROSS THE
WESTERN UPSTATE...SO THINK IT BEST TO PAINT IN A DENSE FOG ADVISORY
FOR THE REMAINING AREA ALONG/S OF I-85...WHICH HAS THE BENEFIT OF
FILLING IN A GAP BETWEEN ADVISORIES ISSUED BY NEIGHBORING OFFICES.
HAVE NOT CHANGED THE EXPIRATION TIME.

PREVIOUS DISCUSSION...

AS OF 645 AM...AREAS OF DENSE FOG CONTINUE TO PLAGUE MUCH OF THE
PIEDMONT AND FOOTHILLS...AND A DENSE FOG ADVISORY CONTINUES THERE
THROUGH 15Z. MEANWHILE...ONE LAST BAND OF LIGHT SHOWERS IS IN THE
PROCESS OF DISSIPATING ALONG THE TENN BORDER...SUPPORTING A DOWNWARD
TREND IN MOUNTAIN POPS THROUGH THE REMAINDER OF THE MORNING.

AS OF 305 AM...THE MOST IMMEDIATE CONCERN WILL BE THE ONGOING FOG
SITUATION...IN WHICH WE ARE SEEING WIDESPREAD 1/2-1/4 MILE VISBY
ACROSS MUCH OF THE PIEDMONT AND FOOTHILLS. A DENSE FOG ADVISORY WILL
BE ISSUED SHORTLY ROUGHLY ALONG/EAST OF HIGHWAY 25...AS VISBY WAS
IMPROVING ACROSS THE UPPER SAVANNAH RIVER VALLEY/THE WESTERN
UPSTATE...WHERE THE SURFACE GRADIENT IS A BIT MORE PRONOUNCED IN
VICINITY OF A COLD FRONT...AND THERE IS ALSO SOME INCREASING
DOWNSLOPE FLOW OFF THE HIGH TERRAIN OF NORTH GA.

OTHERWISE...PATCHY RAIN WILL CONTINUE TO PASS NEAR THE NC AND GA
MTNS EARLY THIS MORNING...BUT A DIMINISHING TREND IS EXPECTED
THROUGHOUT THE MORNING...AND POPS WILL BE MAINTAINED AT CHANCE OR
LESS THROUGH THIS TIME. OTHERWISE...WITH THE QUASI-ZONAL STATE OF
THE MID-LEVEL FLOW...COLD ADVECTION WILL BE DELAYED ACROSS MOST
AREAS OUTSIDE THE MTNS...UNTIL SURFACE HIGH PRESSURE EXPANDS ACROSS
THE CENTRAL APPALACHIANS AND MID-ATLANTIC LATER TODAY. THIS WILL
RESULT IN A BACKDOOR COLD FRONT/COLD AIR DAMMING REGIME DEVELOPING
GRADUALLY FROM NORTHEAST TO SOUTHWEST ACROSS THE CWA THIS AFTERNOON
THROUGH TONIGHT. AS SUCH...THERE WILL BE QUITE THE TEMP GRADIENT
ACROSS THE AREA THIS AFTERNOON...WITH HIGHS RANGING FROM THE LOWER
TO MID-40S ACROSS THE MTN VALLEYS OF NORTHWEST NC...TO THE LOWER 50S
ACROSS THE NORTHWEST PIEDMONT...TO 65-70 ACROSS THE LOWER SC
PIEDMONT.

WARM FRONT ACTIVATION IS EXPECTED TO OCCUR QUICKLY ACROSS THE
SOUTHEAST LATER TODAY INTO TONIGHT...AS A CYCLONE CROSSES THE
CENTRAL CONUS. UPGLIDE PRECIPITATION IS EXPECTED TO EXPAND INTO THE
FORECAST AREA THIS EVENING...WITH LIKELY POPS WARRANTED ACROSS
ROUGHLY THE SOUTHWEST HALF OF THE AREA TONIGHT. WITH TEMPS EXPECTED
TO FALL BELOW FREEZING ACROSS PORTIONS OF THE NORTHERN BLUE RIDGE...
SOME FREEZING RAIN WILL BE POSSIBLE TOWARD DAYBREAK ACROSS PORTIONS
OF THE NORTHERN NC MTNS AND FOOTHILLS. HOWEVER...IT IS NO SURE THING
THAT PRECIP WILL EXPAND THAT FAR NORTH...AND IF IT DOES QPF WILL BE
VERY LIGHT...WITH THE BULK OF RAINFALL EXPECTED TO FOCUS CLOSER TO
THE CAD FRONT ACROSS SOUTHERN PIEDMONT AREAS AND THE SC MIDLANDS.
THEREFORE...NO HEADLINES FOR FREEZING RAIN WILL BE ENTERTAINED ATTM.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AT 300 AM EST MONDAY...ON TUESDAY MORNING A POSITIVELY TILTED UPPER
TROUGH WILL EXTEND FROM HUDSON BAY TO NW MEXICO. THE TROUGHS TILT
BECOMES MORE POSITIVELY BY THURSDAY AS THE NORTHERN PORTION PROGRESSES
INTO EASTERN CANADA...WHILE THE SOUTHERN PORTION REMAINS OVER NW
MEXICO AND THE SW USA.

AT THE SURFACE...COOL HIGH PRESSURE WILL BE LODGED ALONG THE EASTERN
SEABOARD ON TUESDAY...WITH MOISTURE ISENTROPIC UPGLIDE OVER A FRONT IN
S GA PRODUCING WIDESPREAD PRECIPITATION OVER NE GA AND THE WESTERN
CAROLINAS. AT THIS POINT IT APPEAR THAT THIS WILL BE MOSTLY A RAIN
EVENT...AS THE COLDEST PART OF THE RIDGE WILL BE WELL N OF OUT AREA.
AN EXCEPTION MIGHT BE IN THE NORTHERN NC MOUNTAINS EARLY IN THE DAY.
THE SURFACE RIDGE MOVES OFFSHORE LATE TUESDAY WHILE A COLD FRONT
CROSSES THE OH AND MID MS RIVER VALLEY. THIS FRONT SLOWLY CROSSES
OUR AREA ON WEDNESDAY...FINALLY MOVING SW OF THE AREA ON WEDNESDAY
NIGHT. INSTABILITY WILL BE PRESENT AHEAD OF THE FRONT...POSSIBLE
SUPPORTING A FEW THUNDERSTORMS ON WEDNESDAY. CAPE AND SHEAR DO NOT
APPEAR TO COME INTO GOOD ALIGNMENT AT THIS TIME. BEHIND THE
FRONT...COLD ADVECTION WILL SUPPORT A CHANGEOVER TO SNOW IN THE NC
MOUNTAINS WEDNESDAY NIGHT.

THE HIGH TEMPERATURE TUESDAY WILL RUN AROUND 17 DEGREES BELOW NORMAL
IN COLD AIR DAMMING ON TUESDAY...AND THE MINIMUM TEMPERATURE AROUND
5 DEGREE ABOVE NORMAL UNDER CLOUD COVER WITH ARM ADVECTION SETTING UP
AHEAD OF THE FRONT. TEMPERATURES WEDNESDAY AND WEDNESDAY NIGHT WILL
BE AROUND 5 DEGREE ABOVE NORMAL...IN WARM ADVECTION AHEAD OF THE
FRONT...AND LINGERING CLOUD COVER ITS WAKE.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AT 300 AM EST MONDAY...ON THURSDAY MORNING A POSITIVELY TILTED UPPER
TROUGH WILL EXTEND FROM EASTERN CANADA TO NW MEXICO...WHILE A FLAT
RIDGE WILL BE CENTERED OVER THE BAHAMAS. BY FRIDAY MORNING THE
NORTHERN STREAM TROUGH PROGRESSES...ORPHANING AN UPPER LOW OVER NW
MEXICO AND THE SW USA. THE EASTERN TROUGH AMPLIFIES INTO SATURDAY...
THOUGH STILL REMAINING BROAD...WHILE THE UPPER LOW REMAINS IN NW
MEXICO. BY SUNDAY THE UPPER LOW FILLS AND THE REMAINING TROUGH
PROGRESSES OVER THE SOUTHERN PLAINS. SHORTWAVES ROUNDING THE EASTERN
TROUGH RESULTING IN SOME AMPLIFICATION EARLY MONDAY...THOUGH THE
MODELS DIVERGE ON THE TIMING OF THESE FEATURES.

AT THE SURFACE...ON THURSDAY A COLD FRONT WILL BE DEPARTING THE
AREA....WITH A TIGHT PRESSURE GRADIENT IN ITS WAKE KEEPING MOIST
UPSLOPE FLOW GOING INTO THE NC MOUNTAINS BORDERING TN. BY FRIDAY
HIGH PRESSURE SETTLE OVER THE CENTRAL APPALACHIANS...AND THE
PRESSURE GRADIENT RELAXES OVER OUR AREA. ON SATURDAY THE HIGH
SETTLES SOUTH OVER THE CAROLINAS AND GA. ANOTHER COLD FRONT RAPIDLY
CROSSES THE AREA SATURDAY NIGHT....FOLLOWED BY ANOTHER ROUND OF HIGH
PRESSURE ON SUNDAY. THERE ARE SOME INDICATIONS THAT MOISTURE MAY
SPREAD NORTH OVER THIS HIGH ON SUNDAY...BUT CONFIDENCE IS LACKING.

TEMPERATURES WILL RUN AROUND 15 DEGREES BELOW NORMAL IN COLD
ADVECTION BEHIND THE FIRST FRONT ON THURSDAY AND FRIDAY...WARMING TO
AROUND 5 DEGREES BELOW NORMAL AHEAD OF AND IMMEDIATELY BEHIND THE
SECOND FRONT ON SATURDAY AND SUNDAY.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
AT KCLT AND ELSEWHERE...CLT HAS STILL YET TO FALL BELOW THE TERMINAL
MINIMUM THIS MORNING...BUT THEY ARE SITTING RIGHT ON THE FENCE ATTM.
WILL CONTINUE TO TAKE THE OPTIMISTIC ROUTE AND LEAVE CONDITIONS AT
1/2SM/VV002...BUT VLIFR CONDITIONS ARE VERY MUCH IN THE REALM OF
POSSIBILITY. OTHERWISE...THE MAIN CHALLENGE FOR THIS PERIOD IS (OF
COURSE) TIMING IMPROVEMENT OF THE WIDESPREAD LIFR/VLIFR CONDITIONS
THIS MORNING. CURRENT THINKING IS THAT IN LIGHT OF THE LIGHT MIXING
ACROSS THE AREA...AND AN INCREASING DOWNSLOPE FLOW ABOVE THE
SURFACE...THAT WE SHOULD SEE STEADY IMPROVEMENT IN FLT CONDITIONS
AFTER 14Z OR SO...WITH MVFR/VFR EXPECTED AT MOST TERMINALS BY 16Z...
AND PROBABLY A LITTLE LATER AT KCLT. SW WINDS WILL GRADUALLY TURN
TOWARD THE NW THROUGHOUT THE DAY...AND GENERALLY REMAIN AROUND 5 KTS
GIVE OR TAKE. NE WINDS AT AROUND 10 KTS WILL THEN BECOME ESTABLISHED
TONIGHT...AS ANOTHER COLD AIR DAMMING EVENT COMMENCES. PRECIP AND
LOW CIG CHANCES WILL THEN INCREASE AGAIN FROM THE SOUTHWEST BY LATE
THIS EVENING...WITH NO BETTER THAN MVFR CONDITIONS EXPECTED BY THE
END OF THE PERIOD.

AT KAVL...IT/S A DIFFERENT WORLD AT KAVL THIS MORNING...AS OTHER
THAN A VERY BRIEF PERIOD OF RESTRICTIONS EARLIER THIS MORNING...VFR
HAS PREDOMINATED. MEANWHILE...WINDS HAVE COME ROARING UP THE
VALLEY...CURRENTLY REPORTING SUSTAINED AT 19 KTS. PRESSURE GRADIENT
WILL SUPPORT GUSTY NW WINDS THROUGH MUCH OF THE MORNING. BUT THIS
SHOULD ALSO ACT TO LIMIT ANY FOG AND LOW CIG CONCERNS...ALTHOUGH I
STILL WOULD NOT RULE OUT A BRIEF MVFR CIG THIS MORNING. WINDS WILL
BEGIN TO DIMINISH THIS AFTERNOON...MAKING THE TURN TOWARD THE SE BY
THIS EVENING.

OUTLOOK...LOW CIGS AND LIGHT PRECIP/DRIZZLE WILL BE LIKELY ACROSS
MUCH OF THE AREA THROUGH AT LEAST TUE. A COLD FRONT WILL MOVE SLOWLY
THROUGH THE REGION WED THROUGH THURSDAY...BRINGING CHANCES FOR
HEAVIER RAINFALL TO THE AREA.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     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...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR GAZ018-026-
     028-029.
NC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ035>037-
     056-057-068>072-082-502-504-506-508-510.
SC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR SCZ004>014-
     019.

&&

$$
SYNOPSIS...JAT
NEAR TERM...JDL/PM
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...JDL


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