Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191852
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
252 PM EDT TUE MAY 19 2015

.SYNOPSIS...
DRY HIGH PRESSURE WILL BUILD ACROSS THE REGION WEDNESDAY...WITH
BRIEFLY UNSETTLED WEATHER CROSSING THE FORECAST AREA ON THURSDAY.
DRIER CANADIAN HIGH PRESSURE WILL RETURN TO THE CAROLINAS AND
NORTHEAST GEORGIA FRIDAY AND REMAIN INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 245 PM EDT TUESDAY...BROAD/FLAT SUBTROPICAL RIDGE REMAINS IN
PLACE ACROSS THE SOUTHEAST WHILE A CLOSED UPPER LOW CONTINUES TO
ROTATE OVER THE FOUR CORNERS STATES.  AT THE SURFACE...A COLD FRONT
EXTENDING FROM A LOW PRESSURE SYSTEM OVER SOUTHEAST CANADA CONTINUES
TO MIGRATE THROUGH THE OHIO VALLEY INTO THE TENNESSEE VALLEY AIDED
BY AN UPPER SHORTWAVE MOVING THROUGH THE GREAT LAKES.  CLOSER TO
HOME...MODEST INSOLATION HAS ALLOWED FOR ABUNDANT DESTABILIZATION
ACROSS THE REGION.  IN RESPONSE...WEAK CIN CONTINUES TO BE OVERCOME
AS LIGHT SHOWERS AND A FEW THUNDERSTORMS ARE EVIDENT ON RADAR.
MODEST CU FIELD ON VISIBLE SAT BOLSTERS CONFIDENCE IN CONTINUED
INITIATION...AND PROPAGATION OF CURRENT CONVECTION.  THUS...CAMPOP
GUIDANCE WAS FAVORED TO PIN DOWN MOST LIKELY AREAS OF CONVECTION
WHICH YIELDED HIGH CHANCE TO LOW END LIKELY POPS ALONG THE I85
CORRIDOR...WITH THE HIGHEST POPS RESIDING OVER THE NC PIEDMONT.
BUFKIT SOUNDINGS ACROSS REGION DO INDICATE SOME MODESTLY DEEP
UPDRAFT POTENTIAL OVER THESE REGIONS WITH THE MOST LIKELY THREATS
ADJACENT TO ANY ROBUST CONVECTION BEING GUSTY WINDS.  POPS WILL
LOWER INTO THE EVENING AFTER SUNSET AHEAD OF THE APPROACHING FRONTAL
AXIS...WITH LOW END CHANCE TO SLIGHT CHANCE POPS FAVORED UNTIL
MIDNIGHT...BEFORE A DRY FCST PREVAILS.

FOR WEDNESDAY...THE FRONTAL AXIS IS PROGGED TO QUIETLY SLIDE
SOUTHEAST THROUGH THE REGION OVERNIGHT...WITH MODELS INDICATING SOME
POTENTIAL FOR THE FRONT TO STALL JUST TO THE SOUTH.  A WEAK SFC WAVE
LOOKS TO DEVELOP/MOVE ALONG THE QUASI-STATIONARY BOUNDARY ON
WEDNESDAY ENHANCING SOUTHERLY UPSLOPE POTENTIAL ACROSS THE SOUTHWEST
ESCARPMENT.  THUS THE FCST FEATURES SLIGHT TO LOW END CHANCE LEVEL
POPS OVER THE UPPER FRENCH BROAD VALLEY...WITH AN ADDITIONAL MENTION
ACROSS THE SOUTHERN TIER OF THE CWFA ADJACENT TO THE FRONTAL AXIS
ITSELF.  SOUNDINGS LOOK RATHER UNIMPRESSIVE FOR WEDNESDAY THEREFORE
NOTHING MORE THAN GARDEN VARIETY SHOWERS...WITH PERHAPS A FEW
RUMBLES OF THUNDER ARE FCST.  TEMPERATURES ON WEDNESDAY WILL REMAIN
ABOVE NORMAL DESPITE THE FROPA...ALBEIT LESS HUMID AS DEWPOINTS IN
THE LOWER TO MID 50S ARE FCST OVER THE PIEDMONT REGIONS WITH 40S
FCST OVER THE MTNS.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 2 PM TUESDAY...ANOTHER AREA OF HEIGHT FALLS WILL OVERSPREAD
THE EASTERN CONUS DURING THE EARLY PART OF THE SHORT TERM...WHICH
WILL ACT TO FINALLY SURGE THE COLD FRONT/CP AIR MASS THROUGH THE CWA
BY THE END OF THE WEEK. IN THE INTERIM...CHANCES FOR CONVECTION WILL
INCREASE AHEAD OF THIS SURGE BEGINNING LATE WED NIGHT/EARLY THU.
SHORT TERM MODELS INDICATE NO CLEAR CONSENSUS AS TO HOW HIGH THE
PROBABILITY OF CONVECTION WILL BE DURING THIS TIME...AS THE NAM
REMAINS QUITE A BIT MORE MOIST AND SOMEWHAT MORE UNSTABLE THAN OTHER
GUIDANCE. THE MAIN LIMITING FACTOR IN SUSTAINING GOOD COVERAGE OF
CONVECTION WILL BE TIMING...AS THE BEST LIFT AND MOISTURE MAY BE
EAST OF THE AREA BY THE TIME THE ATMOSPHERE REACHES PEAK
DESTABILIZATION THU AFTERNOON. POPS WILL THEREFORE BE KEPT IN THE
30-40 PERCENT RANGE.

DRIER/CONVECTION-FREE WEATHER AND MORE SEASONAL TEMPS ARE EXPECTED
BY FRIDAY...AS SURFACE RIDGE EXTENDS TO THE SOUTHEAST COAST BY
12Z.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM EDT TUESDAY...A BROAD ULVL TROF WILL PUSH OFF THE EAST
COAST SAT AND MAKE WAY FOR A SIGFNT PATTERN CHANGE OVER THE WEEKEND.
WITH THE HUDSON BAY LOW MAINTAINING AREAS OF LOW PRESSURE OVER ERN
CAN...A STRONG UPPER RIDGE WILL BUILD ACROSS THE CENTRAL PLAINS AND
SHIFT EAST OVER THE ERN CONUS THROUGH THE PERIOD. GOOD CONFIDENCE IS
HAD IN THE FCST WITH THE OP MODELS SHOWING SIMILAR TIMING AND
STRENGTH WITH THIS RIDGE THRU MON. SOME VARIANCES ARE NOTED WITH 12Z
GFS BREAKING DOWN THE RIDGE SEVERAL HRS BEFORE THE 00Z ECMWF...BUT
ALL IN ALL...THE SENSIBLE WX WILL BE RATHER PLEASANT AND
NON/THREATENING WITH INCREASING WARMTH.

NO MAJOR CHANGE WERE MADE TO THE FCST GRIDS WITH THE BIGGEST CHANGE
RESULTING IN LOWERING SKY/POP SUN INTO MON. THE LATEST GUIDANCE
TRENDS HAVE EXTENDED THE WRN PORTION OF THE SFC RIDGE WHILE STRONG
SUBSIDENCE DOMINATES THE REGION. THIS WILL FORCE SIGFNT GOM MOISTURE
FLUX WEST OVER THE DEEP SOUTH THROUGH MOST OF THE PERIOD AND ALSO
MAINTAIN A STABLE AIRMASS OVER THE CWFA. SOME AFTERNOON -SHRA ARE
POSSIBLE WITH MTN TOP CONVERGENCE SAT THRU MON...BUT ALL IN ALL THE
ATMOS WILL REMAIN STRONGLY CAPPED AND ALLOW ONLY FAIR WX CU AND
PASSING CI. THINGS CHANGE LATE MON INTO TUE AS THE BERMUDA HIGH
BREAKS DOWN AND ALLOWS INCREASING UPSLOPE FLOW AND ADDED ATL
MOISTURE IN A MORE UNSTABLE ENVIRONMENT. THUS...POPS FOR NEW DAY 7
WERE INTRODUCED AT LOW/MID CHANCE MTNS/FTHILLS AND SW/RN
ZONES...WITH ISOL ACTIVITY PROBABLE EAST. THUNDER INITIATION SHOULD
BE LATE DAY FOCUSING ON THE HIGHER TERRAIN. MAX TEMPS WILL INCREASE
THROUGH THE PERIOD IN GOOD INSOL EACH DAY. STARTING AT AROUND NORMAL
SAT AND INCREASING BY 8-10 DEGREES BY TUE.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
AT KCLT...PRIMARILY VFR THROUGH THE PERIOD WITH THE EXCEPTION OF
AFTERNOON CONVECTION...WHICH IS ALREADY STARTING TO INITIATE ACROSS
THE REGION.  WITH MODEST INSTABILITY AROUND THE AREA...AND GIVEN CURRENT
RADAR RETURNS...OPTED TO INITIALIZE TAF WITH VCSH UNDER LOW VFR CIGS
WITH A TEMPO FROM 19Z-23Z FOR 4SM TSRA.  SOME CONVECTION COULD BE
ORGANIZED WITH GUSTY WINDS BEING THE PRIMARY THREATS THUS INCLUDED
VRB G20KT WINDS.  OTHERWISE...EXPECTING THE COLD FRONT TO WORK
THROUGH THE REGION OVERNIGHT ALLOWING FOR DRIER AIR TO ADVECT IN
AMONGST LIGHT NORTHERLY FLOW.  THEREFORE TAF FEATURES LIGHT/CALM
WINDS JUST AHEAD OF THE FRONT WITH WINDS INCREASING SLIGHTLY OUT OF
THE NORTH AFTER MIDNIGHT.  EXPECTING LOW CLOUDS TO SCT BEHIND THE
FRONT WITH ONLY FEW HIGH LEVEL CIRRUS PREVAILING THROUGH PERIODS
END.  LASTLY...WINDS ARE EXPECTED TO VEER SOUTHERLY LATE IN THE
PERIOD AS A WAVE DEVELOPS ALONG THE OLD FRONTAL AXIS...THUS ADDED IN
AT 17Z HOWEVER CONFIDENCE IN TIMING IS RATHER LOW AT THIS TIME.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH ALL SITES ASIDE FOR
KAVL FEATURE TEMPO MENTION FOR AFTERNOON TSRA WITH MVFR VISB/CIG
RESTRICTIONS.  CONFIDENCE IN PRECIP REMAINS LOWER AT KAVL AS REGION
OF BEST INSTABILITY REMAINS OVER THE LOW TERRAIN WHERE ABUNDANT
DIFFERENTIAL HEATING HAS OCCURRED...THEREFORE OPTED TO CARRY VCTS.
OTHERWISE...ALL WX IS REMOVED FROM THE TAF IN THE 00Z-01Z TIMEFRAME
AS DIURNAL INDUCED INSTABILITY FALLS OFF AHEAD OF THE FRONT.  SOME
CONVECTION COULD REINITIATE ALONG THE BOUNDARY AS IT SLIDES THROUGH
OVERNIGHT...HOWEVER AT THIS TIME CONFIDENCE IN TIMING AND OR
LOCATION IS LOW.  WINDS WILL REMAIN NORTHERLY BEHIND THE FRONT UNDER
SCT HIGH LEVEL CLOUDS...WITH THE EXCEPTION OF KAVL WHERE GUIDANCE
FAVORS A FEW LOW...POSSIBLY IFR CLOUDS WITH A TEMPO FOR SUCH TO ALSO
INCLUDE IFR FOG IN THE VALLEY.  LASTLY...AS NOTED AT KCLT
ABOVE...WINDS WILL VEER SOUTHERLY AT ALL SITES ASIDE FOR KAVL AS A
WEAK WAVE SLIDES ALONG THE OLD FRONTAL AXIS ON WEDNESDAY.

OUTLOOK...THE PASSAGE OF A WEAK COLD FRONT SHOULD BRING BACK
SOMEWHAT DRIER CONDITIONS FOR WEDNESDAY. A WEAK WAVE SLIDING ALONG
THE OLD FRONTAL AXIS WILL CROSS THE AREA WED NIGHT AND
THURSDAY...WITH CHANCES OF SHRA AND AFTN TSRA RETURNING. DRY WX
RETURNS FOR THE UPCOMING WEEKEND.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  96%     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...SBK
NEAR TERM...CDG
SHORT TERM...JDL
LONG TERM...SBK
AVIATION...CDG


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