Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 041757
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
157 PM EDT MON MAY 4 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH THE MIDDLE OF
THE WEEK. A WEAK COLD FRONT IS EXPECTED TO DRIFT DOWN FROM THE NORTH
ON THURSDAY. FOR THE LATE PART OF THE WEEK...UNCERTAINTY IS HIGH AS
LOW PRESSURE MAY MOVE UP THE SOUTHEAST COAST AND OVER THE CAROLINAS.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 2 PM...SFC HIGH PRESSURE WILL RIDGE EAST TO WEST ACROSS THE
REGION. FORECAST SOUNDINGS INDICATE THAT FOOTHILL AND PIEDMONT AREAS
WILL REMAIN WEAKLY CAPPED. HOWEVER...THINNER LLVL CIN SHOULD FAVOR
THE DEVELOPMENT OF RIDGETOP SHRA/TSRA THIS AFTERNOON. CAMS INDICATE
THE DEEP CONVECTION WILL QUICKLY DISSIPATE EARLY THIS EVENING. STORM
MOTIONS APPEAR LIMITED TO 10 KTS OR SO...LIMITING COVERAGE OF THE
CONVECTION. AREAS THAT DO SEE RAINFALL THIS AFTERNOON AND EVENING
WOULD LIKELY SEE MORNING FOG. I WILL UPDATE THE FORECAST TO UPDATE
SKY...POPS...AND TEMPS.

AS OF 10 AM...CONDITIONS ACROSS THE REGION REMAIN CLEAR WITH LIGHT
SOUTHWEST WINDS. I WILL UPDATE THE FORECAST TO REDUCE SKY COVER AND
POPULATE TEMPS/DWPTS WITH OBSERVATIONS. THE TEMPERATURES HEADING
INTO THIS AFTERNOON APPEAR ON TRACK. I WILL DELAY RIDGETOP
CONVECTION BY ONE TO TWO HOURS BASED ON 12 FFC SOUNDING AND LATEST
RUNS OF CAMS.

AS OF 630 AM EDT MONDAY...CURRENT FCST REMAINS ON TRACK THEREFORE NO
SIGNIFICANT CHANGES MADE/NEEDED TO THE FCST.  DID ADJUST
TEMPS/DEWS OVER THE NEXT FEW HOURS TO ACCOUNT FOR RECENT TRENDS.
EXPECTING MID LEVEL CLOUDINESS TO DISSIPATE THIS MORNING AS PRIMARY
H5 WAVE EXITS EAST.  HOWEVER...LOW LEVEL CU WILL PREVAIL BY LATE
MORNING AS LAPSE RATES STEEPEN IN THE MOIST PBL.

PREVIOUS DISCUSSION...

AS OF 315 AM EDT MONDAY...THE PATTERN ALOFT CONTINUES TO FEATURE A
BROAD FLAT RIDGE OVER THE SOUTHEAST CONUS...WHILE A WEAK H5 IMPULSE
SLIDES THROUGH THE MEAN FLOW OVER THE SOUTHERN APPS AS EVIDENT ON
RECENT WV IMAGERY.  AT THE SURFACE...HIGH PRESSURE CENTERED OFF THE
NC COASTLINE CONTINUES TO ROTATE LEADING TO WEAK SSE FLOW OVER FCST
AREA.  THIS PATTERN WILL PREVAIL THROUGH THE PERIOD WITH ONLY SLIGHT
MODIFICATION TO THE SURFACE HIGH EXPECTED AS IT SLOWLY SLIDES
FURTHER OUT TO SEA.  GUIDANCE CONTINUES TO FAVOR CONVECTION ACROSS
THE HIGH TERRAIN OF WESTERN NC THIS AFTERNOON/EVENING WITH THE
NAM12/CAMS BEING THE MOST AGGRESSIVE.  IN ADDITION...00Z ARW/NMM
PRODUCTS INDICATE SOME CONVECTION OVER THE NC/SC PIEDMONT...INTO
PORTIONS OF NORTHEAST GA.  SOUNDINGS DUE INDICATE SOME INSTABILITY IN
THE LOW/MID LEVELS...HOWEVER WITHIN VERY SHALLOW MOIST LAYER BENEATH
MID/UPPER WARM NOSE.

THUS GIVEN RECENT DAYS LACK OF VERIFICATION OF THE HIGHER RES
GUID...LEANED ON THE LOW END OF GUIDANCE AS IT PERTAINS TO POPS THIS
AFTERNOON.  THIS YIELDED ISOLATED/SCATTERED SHRA AND OR TSRA OVER
THE MOUNTAINS...WITH POPS SHARPLY TAPERING TO NON MENTIONABLE LEVELS
OVER THE PIEDMONT AND NORTHEAST GA.  LACK OF PRESENT TRIGGERING
MECHANISMS WAS THE LEADING FACTOR IN KEEPING POPS OUT OF THE LOWER
TERRAIN LOCATIONS...WHILE DEEPER MOISTURE AND POSSIBLE UPSLOPE
FORCING COULD PROMOTE INITIATION OVER THE MTNS.  THINK ANY TSRA THAT
DOES OCCUR WILL FEATURE PRIMARY THREATS OF CLOUD TO GROUND LIGHTNING
AND BRIEF HEAVY RAINFALL.  OTHERWISE...PARTLY/MOSTLY CLOUDY SKIES
WILL PREVAIL AS CU DEVELOPS WITH PEAK HEATING THIS AFTERNOON.  HIGHS
WILL TOP OUT IN THE LOWER 80S OUTSIDE OF THE MTNS...WHILE THE HIGHER
TERRAIN REACHES INTO THE 70S FOR MOST LOCATIONS.  CONDITIONS WILL
IMPROVE THROUGH THE EVENING WITH HEATING LOSS...THUS ALL POPS ARE
REMOVED AROUND MIDNIGHT.  PATCHY FOG COULD OCCUR ON TUESDAY MORNING
IN AND AROUND THE MTN VALLEYS...ESPECIALLY IF/WHERE ANY DAYTIME
PRECIPITATION HAS OCCURRED.  LOWS OVERNIGHT WILL REMAIN AT OR JUST
ABOVE NORMAL REGIONWIDE.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 215 AM MONDAY...THE SHORT RANGE STILL LOOKS RELATIVELY
UNEVENTFUL...AS AN UPPER RIDGE SLOWLY AMPLIFIES OVER THE REGION ON
TUESDAY AND WEDNESDAY EVEN AS AN UPPER LOW ORGANIZES AND MOVES N
ALONG THE FL/GA COAST. THE PATTERN SUPPORTS WEAK SURFACE HIGH
PRESSURE ACROSS THE REGION THRU THE PERIOD. A WEAK SFC BOUNDARY GETS
STRUNG OUT TO THE N AND PROBABLY WILL NOT BE ABLE TO MAKE IT THIS
FAR S THRU WEDNESDAY NIGHT. THE MODELS HAVE LATCHED ONTO THIS IDEA
THAT MAINLY DIURNAL SHOWERS/THUNDERSTORMS WILL FORM ACROSS THE
HIGHER TERRAIN BOTH DAYS. WHILE THE FCST GENERALLY FOLLOWS THAT
PLAN...WITH A SLIGHT CHC/CHC EACH AFTERNOON/EVENING...MY CONFIDENCE
IS PROBABLY NOT AS HIGH AS THE FCST MIGHT SUGGEST. THUS FAR...THE
MODELS HAVE BEEN OVERDEVELOPING THE AFTERNOON CONVECTION OVER THE
MTNS THE LAST FEW DAYS. ON TUESDAY AND WEDNESDAY...BUOYANCY IS NOT
REALLY ALL THAT GREAT. LOW LEVEL MOISTURE CONVERGENCE IS NOT
IMPRESSIVE. BACKWARD TRAJECTORIES EACH AFTERNOON SUGGEST THAT THE
MTNS REMAIN ISOLATED FROM ANY REAL MOISTURE SOURCE. THIS SUGGESTS
THAT THE AMT/EXTENT OF PRECIP IN THE MODELS OVER THE MTNS MIGHT BE
OVERDONE. TEMPS WERE GENERALLY NUDGED A BIT WARMER THRU THE PERIOD
THINKING THAT WE WILL BE DRIER THAN INDICATED.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 315 AM MONDAY...THE MEDIUM RANGE LOOKS MORE INTERESTING AND
MORE UNCERTAIN IN LIGHT OF THE 00Z RUN OF THE GFS...WHICH WANTS TO
TAKE LOW PRESSURE OF SUB-TROPICAL ORIGIN ONSHORE OF SC ON THURSDAY
AND THEN WESTWARD THURSDAY NIGHT BEFORE STALLING INLAND ON FRIDAY.
IF THIS DEVELOPMENT WERE TO PAN OUT...WE WOULD CERTAINLY NEED TO
RAISE PRECIP CHANCES CONSIDERABLY LATE IN THE WEEK. FORTUNATELY...A
PEEK AT THE 00Z RUN OF THE ECMWF WILL KEEP US FROM MAKING THOSE
CHANGES JUST YET...AS THAT MODEL KEEPS THE UPPER/SFC LOW OFFSHORE
THRU THE PERIOD. FEW CHANGES WERE MADE AS A RESULT. PRECIP CHANCES
WERE RAISED SLIGHTLY ON THURSDAY...WHICH SHOWS THE MOST PROMISE FOR
SOME CONVECTIVE ACTIVITY WITH A WEAK FRONT DRIFTING INTO THE
VICINITY...BUT MAINLY TO COME MORE IN LINE WITH NEIGHBORS AND THE
LATEST GUIDANCE FROM HPC. AFTER THAT...THE ECMWF SUGGESTS MORE OF
THE SAME...WITH WEAK HIGH PRESSURE AND AN UPPER RIDGE...AND THE
REGION STILL CUT OFF FROM ANY MOISTURE TRANSPORT FROM THE GULF OR
ATLANTIC. TEMPS SHOULD BE SLIGHTLY ABOVE NORMAL.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AT KCLT AND ELSEWHERE...VFR CLOUD BASES AND VISIBILITY WILL CONTINUE
THROUGH THE 18Z TAF PERIOD. SFC HIGH PRESSURE WILL RIDGE EAST TO
WEST ACROSS THE REGION. FORECAST SOUNDINGS INDICATE THAT FOOTHILL
AND PIEDMONT AREAS WILL REMAIN WEAKLY CAPPED. HOWEVER...THINNER LLVL
CIN SHOULD FAVOR THE DEVELOPMENT OF RIDGETOP SHRA/TSRA THIS
AFTERNOON. CAMS INDICATE THE DEEP CONVECTION WILL QUICKLY DISSIPATE
EARLY THIS EVENING. STORM MOTIONS APPEAR LIMITED TO 10 KTS OR
SO...LIMITING COVERAGE OF THE CONVECTION. AREAS THAT DO SEE RAINFALL
THIS AFTERNOON AND EVENING WOULD LIKELY SEE MORNING FOG.
HOWEVER...THE COVERAGE APPEARS TOO LOW TO MENTION IN ANY OF THE
TAFS. A REPEAT OF MTN CONVECTION IS EXPECTED ON TUESDAY. WINDS WILL
REMAIN LIGHT FROM THE SW...LIKELY SEEING A PERIOD OF CALM WINDS
DURING THE PREDAWN HOURS.

OUTLOOK...ISOLATED TO SCATTERED DIURNAL MOUNTAIN CONVECTION IS
EXPECTED THROUGH THURSDAY...AS MOIST SOUTHERLY FLOW PERSISTS.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  97%     HIGH 100%
KHKY       HIGH 100%     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...PM
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...NED


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