Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201504
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1104 AM EDT SUN JUL 20 2014

.SYNOPSIS...
THE COMBINATION OF WEAK LOW PRESSURE ACROSS THE DEEP SOUTH AND HIGH
PRESSURE ACROSS THE MID ATLANTIC STATES WILL PUMP DEEP MOISTURE
ACROSS THE REGION THROUGH TUESDAY. A WEAK COLD FRONT AND MID LEVEL
TROUGH WILL PUSH OVER AND STALL OVER THE REGION DURING THE LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1040 AM EDT UPDATE...A COMPLICATED SITUATION UNFOLDING WRT TO
SENSIBLE WX ACROSS THE AREA AND UPDATES MAY NEED TO BE ADJ MORE
FREQUENTLY THROUGH THE TODAY PERIOD. THE LATEST VIS IS SHOWING A
GOOD AMOUNT OF MLVL DRYING WEST WITH THE LLVLS REMAINING IN A WEDGE
CONFIG ANCHORING IN LOW STCU MOAT LOCALES. MEANWHILE...H85 FLOW
REMAINS SSE/LY AND MOIST IN RESPONSE TO A DEVELOPING LLVL LOW AND
ULVL S/W MOVING ACROSS MIDDLE TN. THUS...MAX TEMPS STILL HAVE A HIGH
BUST POTENTIAL...BUT FOR NOW WILL COUNT ON SOME MEASURE OF THINNING
AND BREAKOUT OF CLOUDS TO ALLOW TEMPS TO REACH ARND 80 NON/MTNS AND
M70S MTN VALLEYS. THIS IS INLINE WITH THE LOW END OF GUIDANCE...BUT
THEN AGAIN GUIDANCE HAS BEEN OVERLY OPTIMISTIC LATELY WITH TEMP
RISES. THE CONVEC POTENTIAL WILL BE EVALUATED AS WE PROGRESS IN THE
AFTERNOON...BUT FOR NOW WILL KEEP THE THUNDER MENTION...WHICH COULD
DEVELOP LATE AS THE LLVLS ARE SLOW TO MODIFY. NO GREAT PRECIP THREAT
THIS AFTERNOON...BUT AN AREA OF WIDESPREAD LIGHT TO MODERATE RAIN
SHOULD CONTINUE TO AFFECT THE SRN AND FAR ERN ZONES THROUGH THE
MORNING...BEFORE RAINING ITSELF OUT.


AS OF DAYBREAK...A BAND OF LIGHT TO MODERATE RAIN EXTENDING FROM NE
GEORGIA ACROSS THE UPSTATE TO THE S OF I-85 WILL MOVE SLOWLY N
THROUGH MID MORNING BASED ON RADAR TREND. WILL BUMP PRECIP CHANCE
INTO THE LIKELY RANGE ACROSS THE I-85 CORRIDOR TO HANDLE THIS.
EXPECT IT TO WEAKEN BY 14Z OR SO.

THE FORECAST FOR THE NEXT 24 HOURS REMAINS FROUGHT WITH BUST
POTENTIAL...PROBABLY MORE SO THAN THE LAST TWO DAYS...BECAUSE OF THE
WEAKENED COLD AIR DAMMING SIGNAL IN THE MODEL GUIDANCE. THE
MODELS...AND ESPECIALLY THE NAM...SUGGEST A PERIOD DURING THE
AFTERNOON WHEN LOW CLOUDS WILL BREAK UP AND ALLOW FOR SOME WARMUP AS
SFC WINDS COME AROUND TO SE. HOWEVER...UPSLOPE FLOW AND VERY WEAK
WARM ADVECTION AT 850 MB COULD KEEP CLOUDS AND A REMNANT COOL POOL
ANCHORED OVER THE NC FOOTHILLS AND NRN UPSTATE. HAVE LEANED TOWARD
THIS SCENARIO AND BLENDED THE COOLER GUIDANCE INTO THE FCST WHICH
LOWERED THE TEMP A FEW DEGREES...MAYBE NOT ENOUGH. AT ANY
RATE...THINK THE NAM IS WAY TOO OPTIMISTIC WITH SCATTERING THE
CLOUDS AND DEVELOPING INSTABILITY. BY LATE IN THE DAY...THE NEXT
UPPER SYSTEM WILL START TO BREAK OFF A WEAK CLOSED 500 MB OVER THE
SOUTHEAST...AND A SFC LOW SHOULD FORM TO OUR SW IN RESPONSE. THIS
WILL STRENGTHEN THE SE FLOW AT LOW LEVELS AND FORCE THE
REDEVELOPMENT OF SHOWERS...MOST LIKELY OVER THE AREA S AND E OF I-85
CLOSE TO THE OLD WEDGE BOUNDARY...TONIGHT. TEMPS WILL REMAIN MILD.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
AT 315 AM SUNDAY...ON MONDAY...SHORT RANGE MODELS CONTINUE TO
INDICATE THAT THE REGION WILL REMAIN UNDER A WEAK MID LEVEL TROF AS
RIDGING PERSISTS OVER THE WESTERN ATLANTIC AND ROCKIES. AT THE
SFC...BROAD HIGH PRESSURE IS FORECAST TO REMAIN RIDGED ACROSS THE
MID ATLANTIC STATES AS SHALLOW LOW PRESSURE MEANDERS ACROSS THE DEEP
SOUTH. THE COMBINATION OF SOUTHEAST LLVL UPSLOPE WINDS...A WEAK
FIELD OF INSTABILITY..AND DEEP MOISTURE SHOULD SUPPORT AT LEAST 40
TO 60 POPS FROM WEST TO EAST ON MONDAY. GFS INDICATE QUITE A BIT OF
DEEP CONVECTION ACROSS THE MIDLANDS EARLY MONDAY MORNING...APPEARING
WITH SIGNIFICANT CONVECTIVE FEEDBACK. HOWEVER...A REALISTIC
APPEARING S/W MAY RIPPLE NORTH ACROSS THE REGION BY MON
AFTERNOON...SUPPORTING THE HIGHEST POPS ACROSS THE PIEDMONT. CLOUDS
AND RAINFALL SHOULD LIMIT HIGHS TO 7 TO 9 DEGREES BELOW NORMAL.

ON TUESDAY...THE MID LEVEL WEAKNESS WILL FILL IN THROUGH THE DAY AS
A 590 DM RIDGE CENTERS OVER THE DEEP SOUTH. FORECAST SOUNDINGS
INDICATE A TALL AND SKINNY LAYER OF INSTABILITY...WITHOUT A
SIGNIFICANT SUBSIDENCE INVERSION. IT IS POSSIBLE THAT A PORTION OF A
WEAK MID LEVEL DISTURBANCE COULD RIPPLE ACROSS NRN GA DURING THE
AFTERNOON. HOWEVER...IT APPEARS THAT COVERAGE WILL BE GENERALLY
ASSOCIATED WITH DIURNAL INSTABILITY AND WEAK UPSLOPE FLOW. THE
ARRIVAL OF WARMER LLVL THICKNESSES AND LESS CONVECTION SHOULD FAVOR
HIGH TEMPERATURES 3 TO 4 DEGREES WARMER THAT MONDAY/S VALUES.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 330 AM SUNDAY...I WILL USE A BLEND OF THE GFS AND ECMWF
THROUGH THE EXTENDED RANGE. GENERALLY...DIURNAL CONVECTION IS
EXPECTED ACROSS THE FORECAST AREA ON WEDNESDAY. MID LEVEL HEIGHTS
INDICATE RIDGE CENTERS ACROSS THE ROCKIES AND WESTERN ATLANTIC...AS
A TROF DIGS ACROSS THE GREAT LAKES REGION. TEMPERATURES SHOULD WARM
TO WITHIN 5 DEGREES OF NORMAL.

THURSDAY THROUGH SATURDAY...ANOTHER MID LEVEL TROF WILL SETTLE OVER
THE SOUTHERN APPALACHIAN REGION. SYNOPTIC SCALE FORCING SHOULD PEAK
ACROSS THE REGION AS THE TROF ARRIVES THURSDAY NIGHT INTO EARLY
FRIDAY. WPC INDICATES A MUCH SLOWER APPROACH OF THE SFC COLD FRONT
DURING THE LATE WEEK. MODELS AND NATIONAL GUIDANCE INDICATES THAT
THE FRONT MAY NOT REACH THE MTNS UNTIL EARLY FRIDAY...THEN
REMAINING STATIONARY THROUGH SATURDAY. BASED ON THIS SLOWER
SOLUTION...I WILL KEEP CHC TO SCHC POPS DAY AND NIGHT THROUGH
SATURDAY. DAYTIME TEMPERATURES WILL RANGE 3 TO 5 DEGREES BELOW
NORMAL.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
AT KCLT...EXPECT A CEILING IN THE MVFR RANGE TO PREVAIL THROUGH THE
MORNING HOURS. CANNOT RULE OUT A BRIEF IFR CONDITION IF A MODERATE
SHOWER MOVES OVERHEAD...BUT THIS WAS LEFT OUT FOR LACK OF
CONFIDENCE. CONDITIONS SHOULD IMPROVE TO VFR IN THE EARLY AFTERNOON
AS FLOW VEERS A BIT AT LOW LEVELS...WHICH SHOULD ALLOW FOR SOME
DESTABILIZATION INTO THE PIEDMONT. WENT FOR SCATTERED THUNDERSTORMS
IN THE EVENING HOURS BUT THIS COULD DEVELOP ANY TIME FROM MID
AFTERNOON ONWARD. IF WE BREAK OUT...EXPECT SFC WIND TO COME AROUND
TO SOMETHING MORE EASTERLY. UPSLOPE WILL IMPROVE AGAIN AFTER
MIDNIGHT. THIS SHOULD BRING MVFR CEILING BACK IN THE EARLY MORNING
HOURS. IFR IS A DISTINCT POSSIBILITY...BUT HAD TO LEAVE THIS OUT OF
THE TAF FOR NOW AS THE FCST WAS ALREADY TOO LONG.

ELSEWHERE...MVFR CONDITIONS ARE EXPECTED TO PREVAIL BUT MIGHT
DETERIORATE AS LOWER CLOUDS OVER N GEORGIA ATTEMPT TO MOVE IN. ANY
IFR CONDITION SHOULD IMPROVE TO MVFR DURING MID MORNING...AND THEN
VFR IN THE MID/LATE AFTERNOON. WIND SHOULD BE NNE FOR THE BETTER
PART OF THE DAY...UNTIL CLOUDS LIFT AND BREAK UP A BIT ALLOWING SFC
WINDS TO VEER AROUND TO SE. WILL INCLUDE A PROB30 FOR THUNDERSTORMS
IN THE MID AFTERNOON TO EARLY EVENING. AFTER SUNSET...BEST CHANCE
FOR PRECIP WILL BE S OF I-85 SO THIS WAS LEFT OUT OF THE FCST.

OUTLOOK...IFR CONDITIONS ARE POSSIBLE EARLY MONDAY MORNING WITH
INCREASING UPSLOPE FLOW. A RETURN TO A MORE TYPICAL PATTERN WITH
DIURNAL SHOWERS AND STORMS IS EXPECTED STARTING ON MONDAY...AND
CONTINUING THROUGH MID WEEK.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-15Z
KCLT       HIGH  82%     MED   71%     LOW   59%     MED   70%
KGSP       HIGH  80%     HIGH  92%     LOW   57%     MED   68%
KAVL       MED   72%     MED   60%     MED   71%     HIGH 100%
KHKY       MED   74%     MED   73%     MED   67%     HIGH  82%
KGMU       HIGH  81%     HIGH  92%     MED   61%     MED   64%
KAND       HIGH  84%     HIGH  99%     MED   68%     MED   65%

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...NED
NEAR TERM...PM/SBK
SHORT TERM...NED
LONG TERM...NED
AVIATION...PM





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