Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201801
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
201 PM 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 SOUTH IN MID WEEK THEN STALL OVER THE REGION DURING
THE LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
130 PM EDT UPDATE...MADE SIGFNT CHANGES TO THE WX GRIDS...BASICALLY
LOWERING POPS NRN ZONES AND TAKING OUT THUNDER MENTION ALL BUT SRN
MOST ZONES THIS AFTERNOON INTO THE EVENING. MAX TEMPS WERE ALSO
BROUGHT DOWN A COUPLE DEGREES...WIDESPREAD BREAKS IN CLOUD COVER ARE
SEEN ACROSS THE WRN ZONES...SO MAX TEMPS WERE LEFT MOSTLY UNTOUCHED
THERE.

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 WEDNESDAY/...
AS OF 2 PM EDT SUNDAY...A WEAK 500 MB LOW PRESSURE CENTER SPINNING
OVER THE DEEP SOUTH MON NIGHT WILL RETROGRADE WWD THROUGH TUE. LIGHT
EASTERLY FLOW EAST OF THIS FEATURE IN THE SFC TO 850 MB LAYER WILL
CONTINUE TO PROVIDE SOME WEAK UPSLOPE FORCING THROUGH TUE AFTN.
MOISTURE REMAINS RELATIVELY DEEP...AND PERSISTENT SFC HIGH PRES
ALONG AND JUST EAST OF THE SRN APPALACHIANS WILL LIKELY LEAD TO
CLOUDIER AND COOLER THAN MOS CONDITIONS.

A WEAK COL REGION WILL DEVELOP OVER THE SRN APPALACHIANS TUE NIGHT
INTO EARLY WED...WITH LIGHT WINDS UP THE COLUMN. HEIGHTS WILL START
TO FALL AGAIN FROM THE NW LATER IN THE DAY AS THE NEXT H5 SHORTWAVE
DIVES SE THROUGH THE OH VALLEY. SOME VERY WEAK WESTERLY DOWNSLOPE
COULD SET UP EAST OF THE MTNS ON WED...BUT WITH CONTINUED LOW LEVEL
MOISTURE...WILL TRIM TEMPS SLIGHTLY UNDER GUIDANCE. CONSIDERABLE
PIEDMONT INSTABILITY WILL BE POSSIBLE WED AFTN IF ENOUGH BREAKS IN
THE CLOUDS OCCUR...AND STEEPER 850 TO 500 MB LAPSE RATES SHOULD
ARRIVE FROM THE W ACROSS THE MTNS THROUGH THE AFTN. GIVEN THAT LOW
LEVEL WIND CONVERGENCE WILL BE BEST OVER THE MTNS...WILL FEATURE THE
HIGHEST CHC POPS THERE LATE IN THE DAY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 210 PM SUNDAY...THE GFS AND ECMWF ARE IN GOOD AGREEMENT ON THE
DAY 4 AND 5 PERIOD THEN THE GFS BECOMES MORE PROGRESSIVE WITH A
DEEPER TROUGH AT THE END OF THE CURRENT FORECAST. THERE IS AGREEMENT
THERE WILL BE SOME DEGREE OF AN UPPER LEVEL TROUGH OVER THE EASTERN
STATES WHILE AN UPPER RIDGE DOMINATES WEATHER FOR THE WEST.

STARTING THIS MEDIUM RANGE PERIOD AT 00Z THURSDAY...THE UPPER TROUGH
STARTS TO DESCEND OVER THE EAST WITH THE WEAK SURFACE COLD FRONT
CROSSING THE OHIO RIVER AT 00Z THURSDAY. PREFRONTAL INSTABILITY WILL
BE POOLED AHEAD OF THE FRONT WITH 3000 TO 3400 CAPE VALUES ALONG THE
OHIO RIVER AT 00Z THURSDAY ON THE GFS. AT 00Z THURSDAY...THE GFS HAS
NEAR 2500 CAPE VALUES OVER CLT AND THE FAR SW NC MTNS WITH AROUND
1600 ALONG I-26 IN BETWEEN THE HIGHER VALUES. SOME LIGHT SHEAR FROM
925MB TO 700MB IN DIRECTION WITH NOT MUCH CHANGE IN WIND SPEED OVER
OUR REGION. THIS WIND SHEAR WILL BE GREATER THURSDAY AFTERNOON WITH
700MB WIND 25 TO 30KTS AND 925MB WIND FROM VERY LIGHT TO 20KTS.
INSTABILITY WILL NOT BE SO STRONG LATE THURSDAY FOR OUR AREA...BUT
STILL WITH A HIGH VALUE OF 2300 NEAR HARTWELL GA TO AROUND 1600 FOR
CLT. WITH THE FOCUS OF THE FRONT...INSTABILITY AHEAD OF THE FRONT
AND SOME SHEAR...EXPECT AT LEAST A FEW SEVERE STORMS LATE THURSDAY.
THESE SEVERE STORMS MOST LIKELY WILL BE MOST NUMEROUS FROM NE GA TO
ALONG AND SOUTH OF I-85. THE FRONT IS FORECAST TO STALL OUT ROUGHLY
WEST TO EAST ACROSS OUR AREA LATE FRIDAY INTO THE WEEKEND AS THE
FRONT WEAKENS AND DISSIPATES. THE PROXIMITY OF THE FRONT WOULD
SUPPORT AN INCREASE IN POPS LATE FRI OVER WHAT WE HAD IN FORECAST
FOR THE PIEDMONT.

THE GFS CONTINUES TO BE MOST AGGRESSIVE WITH THE ESTABLISHMENT OF
THE 500MB TROUGH WHILE MOVING A 500MB CUT OFF LOW FROM NE NORTH
DAKOTA AT 12Z SAT TO LAKE MICHIGAN 12Z MON AS A DEEP TROUGH EXTENDS
TO THE GULF. SOME LOW LEVEL SE UPSLOPE COULD SUPPORT SHOWERS SAT PM
ALONG THE BLUE RIDGE. THE SURFACE COLD FRONT WOULD ARRIVE AT THE
VERY END OF THE CURRENT FORECAST...PERHAPS MONDAY MORNING FROM TN.
IF THE GFS SOLUTION WERE TO OCCUR NEXT WEEK...TEMPS COULD BE SEVERAL
DEGREES BELOW NORMAL. PERHAPS NOT AS COOL AS WHAT WE JUST
EXPERIENCED AS I DO NOT SEE ANY SURFACE HIGH MOVING TO A PLACE TO
SUPPORT A CAD EVENT.

TEMPS ARE FORECAST TO BE NEAR NORMAL THURSDAY WITH STORMS MOVING IN
THEN 3 TO 4 DEGREES BELOW NORMAL FRI AND A COUPLE DEGREES BELOW OVER
THE WEEKEND.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AT KCLT...CIGS WILL REMAIN MVFR OVER THE NEXT FEW HRS WITH SOME
POSSIBLE IMPROVEMENT TO VFR WITH DRY AIR WESY BUILDING IN. NO GOOD
CHANCEL FOR THUNDER WITH LOW INSTABILITY AND WEDGE HANGING ON. THERE
WILL BE VCSH AND POSSIBLY SOME -SHRA AFT 03Z AS AN MCS MOVES WELL
TO THE SOUTH OF THE TERMINAL. A GOOD CASE FOR IFR CIGS/VSBY BEFORE
DAYBREAK AS LLVL MOISTURE IS MAINTAINED IN WEDGE PATTERN WHILE DRY
AIR ALOFT IS MAINTAINED.

ELSEWHERE...GENERALLY MVFR CONDS ARE EXPECTED AT ALL SITES THIS
EVENING WITH NO GOOD CHANCE OF THUNDER. TEMPORARY VCSH IS POSSIBLE AS
MOIST FLOW PERSIST AT THE SURFACE AND A FEW POCKETS OF WEAK VORT
ENERGY PASS EAST IF DEFINED SW/LY FLOW ALOFT. EXPECT FIGHT CONDS TO
DETERIORATE OVERNIGHT ACROSS MOST SITES PERHAPS INTO THE IFR RANGE
BEFORE SUNRISE...WITH GENERAL IMPROVEMENT THROUGH MID AFTERNOON AS
WEDGE CONTINUES.

OUTLOOK...A GRADUAL RETURN TO A MORE TYPICAL PATTERN WITH DIURNAL
SHOWERS AND STORMS IS EXPECTED STARTING ON MONDAY...AND CONTINUING
THROUGH MID WEEK. A FRONTAL SYSTEM IS EXPECTED TO CROSS THE REGION
THURSDAY NIGHT...BRINGING STRONGER CONVECTION AND POSSIBLE FLIGHT
RESTRICTIONS INTO MID MORNING FRIDAY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH  85%     HIGH 100%     HIGH  90%     HIGH  87%
KGSP       LOW   54%     HIGH  89%     HIGH  95%     HIGH  86%
KAVL       HIGH 100%     HIGH  89%     HIGH  87%     HIGH  84%
KHKY       HIGH  98%     HIGH  94%     HIGH  83%     HIGH  83%
KGMU       HIGH  85%     HIGH 100%     HIGH  98%     HIGH  86%
KAND       MED   75%     HIGH  97%     MED   74%     MED   66%

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...DEO
NEAR TERM...PM/SBK
SHORT TERM...HG
LONG TERM...DEO
AVIATION...SBK





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