Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 202341
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
741 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 MONDAY/...
AS OF 740 PM...CONVECTION DID NOT DEVELOP AS EXPECTED THIS
AFTERNOON. HOWEVER...SHRA AND ISOLATED TSRA WILL MOVE NORTH ACROSS
THE YADKIN RIVER VALLY AND THE NC/TN BORDER THRU THE EVENING.
CONVECTION IS TRYING OT MOVE NORTH INTO THE SRN CWFA...BUT
DISSIPATING AS IT DOES. HAVE KEPT BEST POP CHC ACROSS THE SRN CWFA
THRU THE NITE AS THE GUIDANCE SHOWS THIS CONVECTION MOVING INTO THE
AREA. OTHERWISE...ONLY SMALL CHANCES NORTH OF THIS AREA. LOOKS LIKE
AT LEAST PATCHY LIGHT FOG A GOOD BET AGAIN...WITH PATCHY DENSE FOG
OVER THE MTN VALLEYS. LOW TEMPS LOOK ON TRACK WITH ONLY MINOR
CHANGES.

AS OF 425 PM...CONVECTION REMAINS LIMITED ACROSS THE CWFA...WITH
ISOLATED CELLS OVER THE MTNS AND UNION NC. STILL EXPECT CONVECTION
TO INCREASE INTO EARLY EVENING AS WEAK INSTABILITY DEVELOPS AND
CONVECTION FROM GA MOVES INTO THE SRN UPSTATE. HAVE UPDATED FOR
THESE TRENDS AND CURRENT CONDITIONS FOR OTHER FIELDS.

PREVIOUS DISCUSSION...LIGHT SHOWERS CONTINUE TO MOVE NORTHEAST
ACROSS THE PIEDMONT ATTM AND WILL COUNT ON A SLOW DISSIPATION OVER
THE NEXT COUPLE HRS. SBCIN VALUES REMAIN RATHER HIGH IN A
SHALLOW...BUT CONTINUOUS NE/LY WEDGE FLOW...SO THUNDER CHANCES ARE
NIL. SOME BETTER SBCAPE IS MATERIALIZING TO THE SOUTH...BUT THIS
AREA OF DEEP CONVECT WILL REMAIN SOUTH OF THE CWFA THROUGH THE
EVENING. THERE IS AN AREA OF TSTMS OVER CENT GA WHICH WILL LIKELY
AFFECT THE SRN ZONES AFT 00Z OR SO...BUT DONT EXPECT STRONG
DEVELOPMENT OR A HYDRO ISSUE AS THEY WILL CONTINUE MOVING EAST AND
INSTABILITY WILL BE LOW END.

THE WEDGE REMAINS IN PLACE OVERNIGHT WITH PRETTY GOOD DRY AIR ADV
OCCURRING OVERHEAD. THIS WILL ENABLE LOW CLOUDS AND VSBYS...BUT LIMIT
THE CHANCES FOR PRECIP...THUS THE POP GRIDS HAVE BEEN REDUCE
OVERNIGHT TO ISOL/SCT. ANOTHER TRICKY TEMP DAY IS IN STORE MON. THE
MODELS AGREE WITH KEEPING THE NE/LY LVL FLOW WHILE THE H92-H85 FLOW
BRINGS IN A GOOD AMOUNT OF ATL MOISTURE...BUT THEN THEY THIN CLOUDS
OUT A BIT IN THE AFTERNOON. TOO EARLY TO TELL HOW MUCH INSOL WILL BE
MATERIALIZED...SO WENT WITH LOW END GUIDANCE ONCE AGAIN. WITH GOOD
UPSLOPE FLOW AND A DEEPENING H5 CLOSED LOW OVER AL...PRECIP CHANCE
WILL REMAIN LIKELY..ESP SOUTH. INSTABILITY LOOKS MORE LIKELY LOW END
THAN TODAY...SO THE THUNDER GRIDS WERE CAPPED AT ISOL NORTH AND SCT
SOUTH BEGINNING LATE AFTERNOON. THESE THUNDER CHANCES COULD ACTUALLY
NOT PAN OUT AT ALL...HOWEVER...DEPENDING ON THE AMOUNT OF DRYING AND
AVAILABLE INSOL.

&&

.SHORT TERM /MONDAY NIGHT 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 /00Z MONDAY THROUGH FRIDAY/...
AT KCLT...EARLY EVENING CONVECTION SHUD REMAIN EAST OF THE AIRFIELD.
HOWEVER...ADDITIONAL SHRA WILL BE POSSIBLE OVERNIGHT BUT CHC OF TSRA
IS LOW. THE BIGGER CONCERN WILL BE DEVELOPING MVFR CIGS AFTER
MIDNIGHT THEN IFR CIGS AND MVFR VSBY BEFORE DAYBREAK. CONDITIONS
WILL BE SLOW TO IMPROVE THRU THE MORNING WITH COPIOUS LOW LEVEL
MOISTURE AND SELY LOW LEVEL FLOW. MAY SEE SOME BREAKS AGAIN BY
AFTERNOON WITH INCREASING INSTABILITY LEADING TO THE CHC OF SCT
CONVECTION. NLY WIND BECOMES NELY THIS EVENING THEN TURNS ENE
OVERNIGHT AND REMAINS THERE THRU THE PERIOD.

ELSEWHERE...SIMILAR CONDITIONS TO KCLT...BUT BETTER CHC OF OVERNIGHT
SHRA ACROSS THE SC TAFS. OTHERWISE...DEVELOPING IFR CIGS AND MVFR
VSBY OVERNIGHT...VSBY AND CIGS IFR AT KAVL. SLOW IMPROVEMENT THRU
THE DAY. AGAIN...MAY BE ENUF BREAKS FORE INCREASED CONVECTIVE
COVERAGE DURING THE AFTERNOON. WINDS BECOME ELY OVERNIGHT AND REMAIN
THERE THRU THE DAY. KAVL WILL SEE LIGHT WINDS BECOMING SLY FOR THE
AFTERNOON.

OUTLOOK...A GRADUAL RETURN TO A MORE TYPICAL PATTERN WITH DIURNAL
SHOWERS AND STORMS IS EXPECTED STARTING 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...

            23-05Z        05-11Z        11-17Z        17-23Z
KCLT       HIGH  93%     HIGH  84%     HIGH  84%     MED   75%
KGSP       HIGH  81%     MED   78%     HIGH  90%     HIGH  91%
KAVL       HIGH  92%     MED   76%     HIGH  82%     HIGH  83%
KHKY       HIGH  92%     MED   72%     HIGH  86%     HIGH  83%
KGMU       HIGH  93%     HIGH  83%     HIGH  88%     HIGH  91%
KAND       HIGH  93%     MED   77%     MED   65%     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...DEO
NEAR TERM...RWH/SBK
SHORT TERM...HG
LONG TERM...DEO
AVIATION...RWH






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