Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 280515
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1215 AM EST SAT FEB 28 2015

.SYNOPSIS...
COLD CANADIAN HIGH PRESSURE WILL REMAIN ACROSS THE AREA THROUGH THE
WEEKEND. THE ATMOSPHERE WILL MOISTEN CONSIDERABLY AHEAD OF AN
APPROACHING COLD FRONT THAT IS EXPECTED TO CROSS THE AREA ON MONDAY.
ANOTHER HIGH WILL SLIDE OVER THE REGION IN THE FRONTS WAKE. THE HIGH
WILL BE SHORT LIVED...HOWEVER...AS A MORE SUBSTANTIAL COLD FRONT
CROSSES THE REGION BY LATE WEDNESDAY OR EARLY THURSDAY.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...WINDS WERE UPDATED WITH A BLEND OF THE LATEST NAM
AND ADJMAV. SKY COVER WAS UPDATED FROM SATLLITE IMAGERY.

930 PM UPDATE...CLOUDS HAVE YET TO FORM OVER THE CWFA OR EVEN
IMMEDIATELY UPSTREAM WITHIN THE BUILDING WEDGE. NEWEST GUIDANCE
/00Z NAM/ STILL SHOWS DEVELOPMENT OF A LOW CLOUD LAYER AFTER
MIDNIGHT...SO THOUGH SKIES HAVE BEEN KEPT CLEARER THIS EVENING...AN
INCREASING TREND LATER STILL IS APPROPRIATE. DRIER AIR IS FILTERING
INTO THE PIEDMONT ON THE WEDGE FLOW AS DEWPOINTS ARE GENERALLY
TRENDING DOWNWARD. DEPRESSIONS ARE STILL PRETTY LARGE AND PROFILES
NOT CONDUCIVE TO WIDESPREAD FOG DEVELOPMENT...BUT IF ANYWHERE THE
SRN END OF THE CWFA COULD SEE SOME LIGHT FOG DEVELOP IN A FEW SPOTS.
THIS AREA IS STILL SEEING THE LIGHTER WINDS AND HIGHER
DEWPOINTS...THAT IS...THE WEDGE HAS NOT YET MOVED IN THERE. REVISED
TEMPS THRU MRNG BASED ON LATEST OBS AND SHORT-TERM CONSENSUS
PRODUCT...BUT VALUES ARE NOT MUCH DIFFERENT FROM THE PREVIOUS
EXPECTATIONS.

AT 200 PM...HIGH PRESSURE WILL MOVE FROM THE MIDWEST INTO THE MID-
ATLANTIC STATES OVERNIGHT. BY SATURDAY SUNRISE...THE HIGH WILL HAVE
WEDGED SW ALONG THE EAST SLOPES OF THE MOUNTAINS. THIS WILL PRODUCE
INCREASING NE FLOW AND COLD ADVECTION. ALSO...MODEL TIME HEIGHTS
SHOW PLENTY OF MOISTURE BELOW H850...SO EXPECT CLOUDS TO DEVELOP
OVERNIGHT AS BOUNDARY LATER TEMPS COOL.

ON SAT...THE WEDGE LOOKS LIKE IT WILL REMAIN IN PLACE. HENCE...IT
LOOKS LIKE A CHILLY DAY EAST OF THE MOUNTAINS ALONG WITH
CONSIDERABLE CLOUDINESS. MAX TEMPS WILL RANGE FROM THE MID 30S OVER
PORTIONS OF THE NORTHERN NC PIEDMONT AND FOOTHILLS TO THE MID 40S
OVER PARTS OF NE GA AND THE WESTERN UPSTATE. THE MOUNTAINS WILL ALSO
REMAIN CHILLY WITH THE WARMEST TEMPS OCCURRING IN THE SW MOUNTAIN
VALLEYS OUTSIDE THE WEDGE WHERE HIGHS WILL REACH INTO THE 40S.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
AS OF 235 PM FRIDAY...GUIDANCE IN GOOD AGREEMENT THAT A HYBRID COLD
AIR DAMMING EVENT WILL BE ONGOING AT THE BEGINNING OF THE PERIOD.
THE GUIDANCE ALSO AGREES THAT LOW LEVEL ISENTROPIC LIFT WILL DEVELOP
SAT NITE AND CONTINUE INTO SUNDAY AS SLY FLOW DEVELOPS ABOVE THE
COLD DOME. HOWEVER...THERE STILL REMAINS A SPLIT IN THE TIMING OF
PRECIP DEVELOPMENT AS THIS LIFT GETS GOING. THE ECMWF AND GFS ARE
SLOWER...WITH THE ECMWF THE SLOWEST...WHILE THE NAM AND SREF ARE
FASTER...WITH THE NAM THE FASTEST. AGAIN...HAVE USED A MDL BLEND FOR
TIMING AS EVEN THE SLOWER GUIDANCE SHOWS A SIGNIFICANT INCREASE IN
MOISTURE AND ISENTROPIC LIFT SAT NITE. THEREFORE...END UP WITH CHC
POP BY DAYBREAK SUNDAY ACROSS NE GA...MUCH OF THE UPSTATE AND THE
SRN NC MTNS AND FOOTHILLS...WITH SLIGHT CHC ELSEWHERE. NOW FOR
TEMPS...THE NAM HAS WARMED...BUT STILL HAS BELOW FREEZING WET BULB
TEMPS FOR MUCH OF THE AREA AT ONSET. THE GFS IS COLDER EVEN WITH THE
SLOWER ONSET...SHOWING FREEZING RAIN/DRIZZLE DEVELOPING BEFORE
QUICKLY WARMING AFTER ONSET. ONCE AGAIN USED A BLEND TO DEVELOP THE
TEMP FORECAST WHICH INDICATES FREEZING PRECIPITATION AT ONSET THEN
QUICKLY WARMING WITH ALL LIQUID BY NOON SUNDAY. HAVE ALSO INCLUDED
DRIZZLE OR FREEZING DRIZZLE ALL AREAS AS THAT COULD BE THE
PREDOMINANT PRECIP CHARACTER EARLY ON. THE GOOD NEWS IS THAT QPF
WILL BE VERY LIGHT LEADING TO ONLY A VERY LIGHT ACCRETION...MAINLY
ACROSS THE MTNS AND FOOTHILLS AT ONSET. THAT SAID...COLD TEMPS COULD
BECOME LOCKED IN ACROSS PORTIONS OF THE AREA AND HIGHER ACCRETIONS
COULD DEVELOP. LOWS SAT NITE WILL BE 5 TO 10 DEGREES BELOW NORMAL
WHILE HIGHS SUNDAY WILL BE 10 DEGREES BELOW NORMAL ACROSS THE MTNS
AND UP TO 20 DEGREES BELOW NORMAL ELSEWHERE IN THE CAD REGION.

PRECIP TAPERS OFF OUTSIDE OF THE MTNS SUN NITE AS THE BEST
ISENTROPIC LIFT MOVES NORTHEAST OF THE AREA. STILL EXPECT RAIN AND
DRIZZLE TO CONTINUE THRU THE NITE HOWEVER. THE CAD ERODES MONDAY AS
A COLD FRONT MOVES IN FROM THE WEST. PRECIP CHC TAPERS OFF EVEN
FURTHER TO SLIGHT CHC OUTSIDE OF THE MTNS. THAT SAID...PRECIP CHC
REMAINS HIGH ACROSS THE MTNS SUN NITE AND EARLY MONDAY WITH THE
FRONT. TEMPS REMAIN WARM ENUF ALL AREAS FOR PRECIP TO REMAIN LIQUID
THRU THE PERIOD. LOWS SUN NITE WILL RANGE FROM NEAR NORMAL TO AS
MUCH AS 10 DEGREES ABOVE...WHILE HIGHS MONDAY WARM TO NEAR NORMAL
LEVELS.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 230 PM FRIDAY...AN ACTIVE PATTERN EXPECTED IN THE MEDIUM
RANGE. UPPER RIDGE WILL BUILD OVER THE EASTERN STATES TUE-WED...AS A
TROF DEEPENS OVER THE WEST. THE TROF WILL BEGIN TO CONSOLIDATE AND
PROGRESS OUT INTO THE PLAINS ON WEDNESDAY. AT THE SFC...A 1032 MB
HIGH WILL QUICKLY TRANSLATE EAST FROM THE GREAT LAKES TO OFF THE
EAST COAST BY TUESDAY EVENING. THE GUIDANCE SEEMS TO BE IN GOOD
AGREEMENT ON INCREASING ISENT LIFT THRUT THE LLVLS...WITH MOISTURE
SPREADING IN FROM THE SW ATOP A DEVELOPING WEDGE. THE MID-UPR LVLS
LOOK FAIRLY NEUTRAL FOR SUPPORTING UVM. HOWEVER...GIVEN THE STRONG
850 MB WAA...AND PLENTY OF MOISTURE...I THINK HIGH-END CHC TO LIKELY
POPS LOOKS GOOD BY DAYBREAK TUESDAY...CONTINUING THRU THE DAY. ANY
AMOUNT OF PRECIP/DRIZZLE SHUD HELP LOCK IN AN IN SITU COLD AIR
DAMMING WEDGE...KEEPING TEMPS ABOUT 10 DEG BELOW NORMAL.

TUESDAY NIGHT THRU THURSDAY...THE 12Z RUNS OF THE GFS AND ECMWF
STILL DIFFER ON THE TIMING OF A SLOW-MOVING ANAFRONT FROM THE NW.
THE GFS CONTINUES TO BE ON THE FAST SIDE OF GUIDANCE...WHILE THE
ECMWF IS CATCHING UP BUT STILL SLOWER. GOING WITH THE WPC PREFERENCE
(SLOWER THAN GFS)...WEDNESDAY LOOKS WARM (UP TO 15-20 DEG JUMP FROM
TUESDAY/S TEMPS) UNDER DECENT SWLY FLOW. PRECIP WILL MOVE IN FROM NW
TO SE DURING THE DAY (OR EVENING IF ECMWF IS RIGHT)...WITH POTENTIAL
FOR A SOAKING RAIN. CANNOT RULE OUT SOME THUNDER ALONG THE FRONT
ACRS THE PIEDMONT...AS BOTH THE GFS AND ECMWF SHOW INSTBY IN THE
WARM SECTOR. BUT SEVERE THREAT SHUD BE MINIMAL. THE BIGGER CONCERN
MAY BE HEAVY RAIN. ALTHO...THE GUIDANCE HAS BACKED OFF THE QPF
SOMEWHAT FROM PREV RUNS. STILL PLAN TO LEAVE ANY MENTION OUT OF THE
HWO. TEMPS WILL BE ABOVE NORMAL OVERNIGHT THEN ONLY RISE A FEW DEG
ON THURSDAY...AS CLOUDS/PRECIP GIVE WAY TO NWLY CAA FLOW. THE 850 MB
TEMPS WILL FALL SUCH THAT THE HIGHEST ELEVATIONS MAY SEE SOME SNOW
ON BACK EDGE OF THE THE PRECIP SHIELD. SOME MINOR ACCUMS MAY BE
POSSIBLE.

THURSDAY NIGHT THRU FRIDAY NIGHT...BOTH THE GFS AND ECMWF SHOW DRY
POLAR HIGH PRES BUILD IN FROM THE NW...RETURNING OUR AREA TO BELOW
NORMAL TEMPS AND DRY CONDITIONS. HIGHS IN THE 40S TO LWR 50S FRIDAY
WITH LOWS BACK BELOW FREEZING FOR MOST AREAS.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...HIGH CLOUDS WILL SPREAD IN FROM THE WEST OVERNIGHT...
     BUT BEFORE DAYBREAK A MODEL BLEND WOULD BRING AN MVFR CIG TO THE
FIELD. THE CIG WOULD RISE TO LOW VFR BY MIDDAY...REMAINING THERE
THROUGH THIS EVENING. GUIDANCE DOES NOT SUPPORT A VSBY RESTRICTION.
WINDS WILL FAVOR THE NE THROUGH THE FORECAST AS COOL HIGH PRESSURE
REMAINS ALONG THE EASTERN SEABOARD.

ELSEWHERE...INCREASING HIGH CLOUD COVER FROM WEST WILL OCCUR EARLY
IN THE FORECAST. GUIDANCE BRING MVFR CIGS TO KAVL AND THE SC SITES
BEFORE DAWN...WITH LOW VFR AT KHKY. BY MIDDAY THE SC SITES AND KAVL
RISE TO LOW VFR...WHILE KHKY FALLS TO MVFR. THE KHKY CIG RISES TO
LOW VFR THIS EVENING...WHILE KAVL AND KAND FALL TO MVFR. MOIST FLOW
FROM THE SOUTH OVER COOL HIGH PRESSURE WILL SPREAD PRECIPITATION
OVER THE SAVANNAH RIVER VALLEY LATE THIS EVENING...BUT THE CHANCE OF
RAIN AT KAND IS TOO LOW TO MENTION. GUIDANCE DOES NOT FAVOR VSBY
RESTRICTIONS. WINDS WILL FAVOR THE NE AT FOOTHILLS SITES AS HIGH
PRESSURE REMAINS ALONG THE EAST COAST. KAVL WINDS WILL FAVOR THE SE.

OUTLOOK...COLD AIR DAMMING STRENGTHENS INTO SUNDAY. FLIGHT
RESTRICTIONS WILL BE POSSIBLE DURING THIS TIMEFRAME...PARTICULARLY
LATE SAT NIGHT AND SUN DUE TO INCREASING MOISTURE AND LIFT OVER THE
WEDGE. RAIN CHANCES LINGER INTO WEDNESDAY AS SEVERAL FRONTS CROSS
THE AREA...BUT CONFIDENCE IS LIMITED ON RESTRICTIONS.

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...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JAT/LG/WIMBERLEY
SHORT TERM...RWH
LONG TERM...ARK
AVIATION...JAT



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