National Weather Service Weather Forecast Office

Area Forecast Discussion

996
FXUS62 KGSP 030218
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1018 PM EDT WED OCT 2 2013

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST ACROSS THE REGION THROUGH THE REST OF
THE WORK WEEK. A COLD FRONT...POSSIBLY ENHANCED WITH TROPICAL
MOISTURE...WILL APPROACH FROM THE WEST ON SUNDAY AND BRING UNSETTLED
AND RAINY WEATHER TO THE AREA FOR SUNDAY NIGHT THROUGH MONDAY.  HIGH
PRESSURE WILL RETURN BEHIND THE PASSING DISTURBANCE ON TUESDAY.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1015 PM EDT WEDNESDAY...DEWPOINTS CONTINUE TO RUN HIGHER THAN
EXPECTED OVER THE REGION THIS EVENING. EVEN WITH THE HIGH CLOUD
COVER THIS SHOULD SET THE STAGE FOR MOUNTAIN VALLEY FOG LATER
TONIGHT.

AS OF 735 PM EDT WEDNESDAY...HIGH CLOUD COVER CONTINUES TO EXPAND
ACROSS THE WRN CAROLINAS AND NE GA AS AN UPPER LOW LIFTS WELL WEST
OF THE FA. MODEL SOUNDINGS ONLY BECOME MORE SATURATED ALOFT
OVERNIGHT...AND I PLAN TO INCREASE CLOUD COVER A LITTLE DURING THE
OVERNIGHT HOURS. THIS COULD AFFECT THE AMOUNT OF MOUNTAIN VALLEY FOG
AND STRATUS THAT DEVELOPS OVERNIGHT. HOWEVER...DEWPOINTS HAVE ALSO
BEEN RUNNING A LITTLE OVER WHAT WAS EXPECTED SO I/LL HOLD ON THAT
VALLEY FOG FOR NOW.

AS OF 525 PM EDT WEDNESDAY...FORECAST GOING INTO THE EVENING HOURS
IS IN EXCELLENT SHAPE. INCREASED SKY COVER TO ACCOUNT FOR INCREASING
HIGH CLOUD COVER...BUT THAT/S ABOUT IT.

AS OF MID AFTERNOON...THE FCST LOOKS LIKE IT IS IN GOOD SHAPE.
SOME ENHANCED CU OVER THE MTN RIDGETOPS...BUT OTHERWISE FAIR. ONLY
MINOR CHANGES WERE MADE TO TEMPS.

OVER THE NEXT 24 HOURS...CHANGES ARE IN STORE TO THE OVERALL PATTERN
THAT MAY NOT BE READILY APPARENT...BUT WILL SET THE STAGE FOR EVENTS
SEVERAL DAYS OUT. THE AXIS OF AN UPPER RIDGE WILL MOVE EAST OF THE
FCST AREA TONIGHT WHICH WILL RESULT IN A SW FLOW AT MID AND UPPER
LEVELS ACROSS THE WRN CAROLINAS. MOISTURE WILL RETURN ALOFT...BUT
NOT YET TO ANY GREAT DEGREE. MEANWHILE...AT LOW LEVELS...THE CENTER
OF THE ANTICYCLONE AT THE SURFACE AND 850MB WILL NOT MOVE EAST UNTIL
THURSDAY...THUS THE APPARENT LACK OF CHANGE. IN FACT...TONIGHT AND
THURSDAY MORNING ARE EXPECTED TO BE VERY SIMILAR TO THE LAST FEW
NIGHTS WITH DENSE VALLEY FOG DEVELOPING IN THE PRE-DAWN HOURS AND
LASTING PAST DAYBREAK. A SHORT WAVE WILL LIFT NORTHWARD AND WILL
MOVE PAST TO THE WEST OVERNIGHT WHICH WILL BRUSH SOME MID LEVEL
FORCING ACROSS THE MTNS...BUT THE MOISTURE WILL NOT HAVE RETURNED
YET...SO TONIGHT SHOULD BE DRY. LOW END PRECIP CHANCES WERE CUT
BACK. ON THURSDAY...THERE IS SOME SMALL CHANCE THAT BUOYANCY WILL BE
IMPROVED RELATIVE TO RECENT DAYS...BUT THINK THE NAM IS OVERDONE.
THE NAM APPEARS TO ELIMINATE THE LOW LEVEL INVERSION TOO QUICKLY AND
DEVELOPS TOO MUCH INSTABILITY...WHICH IT RELIEVES WITH CONVECTIVE
PRECIP ALL ACROSS THE NC MTNS STARTING EARLY IN THE DAY.
MEANWHILE...THE OTHER MODELS REMAIN DRY. THINK A COMPROMISE IS IN
ORDER AND WILL KEEP A SLIGHT CHANCE POP IN THE AFTERNOON. HIGH TEMPS
MIGHT BE ANOTHER DEGREE OR TWO WARMER THAN TODAY.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
AS OF 230 PM EDT WEDNESDAY...MODELS CONTINUE TO INDICATE THAT AN
UPPER RIDGE WILL BUILD IN FROM THE WEST THU NIGHT INTO FRI AND
REMAIN IN PLACE AT LEAST THRU SAT. MEANWHILE...A NORTHERN STREAM
UPPER LOW PRESSURE TROUGH OVER THE GREAT BASIN FRI IS EXPECTED TO
PROGRESS INTO THE WESTERN GREAT LAKES REGION BY SAT NIGHT...PUSHING
AN UPPER RIDGE AXIS OFF THE ATLANTIC COAST THRU THIS PERIOD.

AT THE SURFACE...SURFACE HIGH PRESSURE CENTERED OFF THE ATLANTIC
COAST WILL CONTINUE TO RIDGE INTO THE REGION THU NIGHT INTO SAT.
THIS WILL RESULT IN CONTINUED DRY CONDITIONS ACROSS MUCH OF THE CWA
EXCEPT RIDGE TOPS OF THE NC MTNS WHERE SLIGHT CHANCE OF CONVECTION
CAN BE SEEN ON EACH DAY DUE TO THE LESSER DEGREE OF CAPPING
INVERSION ALOFT. BY SAT NIGHT...A TRAILING COLD FRONT WILL APPROACH
FROM THE MISSISSIPPI VALLEY AS THE SURFACE RIDGE WEAKENS AND MOVE
EAST OF THE AREA. WITH BETTER INSTABILITY AND INCREASING MOISTURE
AHEAD OF THE FRONT...HAVE MENTIONED 20/30 POPS OVER THE WESTERN HALF
OF THE CWA THRU EARLY SUN MORNING. TEMPS WILL REMAIN AROUND 3-5
DEGREES ABOVE NORMAL THRU THE PERIOD.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 145 PM WEDNESDAY...STILL PLENTY OF UNCERTAINTY IN THE MEDIUM
RANGE ON THE DETAILS ASSOCIATED WITH A TROPICAL DISTURBANCE AND ITS
INTERACTION WITH A FRONTAL ZONE SUNDAY THRU TUESDAY. TIMING AND
TRACK DIFFERENCES AMONG THE MODEL SOLNS ARE SIMILAR TO WHAT THEY
WERE YESTERDAY. THE MAIN REASON FOR THIS IS THAT THERE IS STILL A
LOT OF MODEL SPREAD IN THE MID LATITUDE SYSTEM...AND THE TROPICAL
DISTURBANCE IS STILL WEAK (SO OP MODELS ARE TASKED TO FORECAST
TROPICAL CYCLOGENESIS RATHER THAN BEING INITIALIZED WITH A BOGUS
CIRCULATION). SO I/M FAIRLY CONFIDENT THINGS SHUD START CONVERGING
ONCE THE SYSTEM GETS A BIT BETTER ORGANIZED. SPEAKING OF...THE 2 PM
TROPICAL OUTLOOK FROM THE NHC HAS BUMPED UP THE PROBABILITY OF THE
SYSTEM BECOMING AT LEAST A TD TO 70 PCT WITHIN THE NEXT 48 HOURS. IT
CERTAINLY IS LOOKING BETTER ON SAT IMAGERY...AS IT APPROACHES THE
TIP OF THE YUCATAN. HOWEVER...ONCE IT ENTERS THE GULF OF MEXICO...IT
IS EXPECTED TO REMAIN IN MARGINAL...IF NOT UNFAVORABLE...
ENVIRONMENT FOR FURTHER STRENGTHENING.

IN ANY CASE...IT IS LOOKING MORE LIKELY THE TC OR WAVE WILL LIFT N
TO THE GULF COAST...THEN MERGE/INTERACT WITH A BAROCLINIC ZONE INVOF
THE SOUTHEAST STATES. THE 12Z GFS HAS COME IN RATHER STRONG WITH THE
LOW AND DEEPER WITH THE UPR TROF...RESULTING IN AN EXTRATROPICAL
TRANSITION SIGNATURE IN THE QPF SWATH. THE TRANSITION PLACES THE
HEAVY QPF RIGHT ACRS THE I-85 CORRIDOR SUNDAY NIGHT THRU MONDAY
(GENERALLY 2-4 INCHES)...AS THE LOW TRACKS NC ACRS THE MIDLANDS.
THIS OF COURSE IS STILL ONE OF MANY POSSIBLE SCENARIOS. I STILL
THINK THE HEAVY RAIN MENTION IN THE HWO LOOKS GOOD. AS FOR ANY
SEVERE THREAT...THAT IS STILL LESS CERTAIN THAN THE HEAVY RAIN
THREAT...AS EVEN THE STRONGER GFS KEEPS THE BEST INSTBY AND SHEAR
COUPLED TOGETHER TO OUR SOUTH AND EAST.

I BLENDED THE 12Z WPC GRIDS FOR THIS PACKAGE. TEMPS WILL BE ABOVE
NORMAL SUNDAY AHEAD OF THE SYSTEM...WITH JUST A SLGT CHC TO LOW-END
CHC POP CREEPING IN FROM THE SW LATE IN THE DAY. THEN BELOW NORMAL
HIGHS AND NEAR NORMAL LOWS MONDAY AND BEYOND. POPS WERE STILL CAPPED
AT LIKELY GIVEN THE LINGERING UNCERTAINTY ON TIMING.

TUESDAY AND WEDNESDAY...MODELS DIVERGE FURTHER AS A WRN ATLANTIC
RIDGE MAY BLOCK PROGRESSION OF THE FRONT AND RESULT IN LINGERING
UNSETTLED WX THRU MIDWEEK. WILL KEEP A SLGT CHC TO LOW-END CHC POP
IN FOR THESE PERIODS.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
AT KCLT...LIGHT OR CALM WINDS OVERNIGHT WITH INCREASING HIGH CLOUD
COVER. WINDS WILL EVENTUALLY COME UP OUT OF THE SOUTH DURING THE
LATE MORNING HOURS THURSDAY AT SPEEDS OF 4 TO 6 KTS.

ELSEWHERE...AS THE DAY SHIFT OBSERVED...THE MAIN ISSUE WILL BE FOG
DEVELOPMENT AROUND DAYBREAK THURSDAY. MID AND HIGH LEVEL CLOUD COVER
WILL CONTINUE TO INCREASE ACROSS THE REGION...BUT ANOTHER ROUND OF
DENSE MTN VALLEY FOG LOOKS LIKE ANOTHER GOOD BET ESPECIALLY AS
DEWPOINTS ARE RUNNING HIGHER THAN PREDICTED. I DID NOT TAKE
ASHEVILLE DOWN ANY LOWER THAN THE DAY SHIFT DID AS A NOD TO THE
INCREASING CLOUD COVER...BUT KEPT A MIN VSBY OF 1 SM AND CIG OF 005.
THERE IS ALSO THE POSSIBILITY OF IFR FOG AT KAND/KHKY...BUT NOT ENUF
CERTAINTY FOR ANYTHING OTHER THAN AN MVFR VISIBILITY. ONCE
AGAIN...THE FOG SHOULD BURN OFF AROUND 13Z TO 14Z. MORE FAIR WEATHER
STRATOCU EXPECTED ON THURSDAY...WITH A SW WIND.

.OUTLOOK...HIGH PRESSURE WILL LINGER THROUGH SATURDAY. MOISTURE WILL
INCREASE AHEAD OF AN APPROACHING COLD FRONT ON SUNDAY...WITH A
TROPICAL WEATHER FEATURE POSSIBLY MOVING NWD FROM THE GULF OF MEXICO
INTO THE FRONTAL ZONE TOWARD THE END OF THE PERIOD.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH 100%     HIGH  94%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH  86%     HIGH 100%     HIGH 100%
KAVL       HIGH  97%     HIGH  80%     HIGH  86%     HIGH 100%
KHKY       HIGH 100%     HIGH  83%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH  94%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     MED   77%     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...JOH
NEAR TERM...MCAVOY/PM
SHORT TERM...JOH
LONG TERM...ARK
AVIATION...MCAVOY