Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 162341
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
741 PM EDT THU APR 16 2015

.SYNOPSIS...
A COOL AND DAMP WEDGE OF HIGH PRESSURE WILL GIVE WAY TO PROGRESSIVELY
WARMER AND DRIER AIR FRIDAY INTO SATURDAY. A WARM FRONT WILL MOVE
INTO THE REGION FROM THE SOUTHWEST SATURDAY NIGHT INTO
SUNDAY...ACCOMPANIED BY ABUNDANT MOISTURE AND MORE RAINFALL. A COLD
FRONTAL PASSAGE EARLY NEXT WEEK WILL FINALLY RESTORE DRIER
CONDITIONS.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 730 PM EDT THURSDAY...STILL SEEING LINGERING LIGHT
RAIN/SHOWERS ACROSS THE MOUNTAINS...AND LIGHT RAIN/DRIZZLE ACROSS
THE UPSTATE AND PORTIONS OF THE NORTH CAROLINA PIEDMONT WITH
ISENTROPIC UPGLIDE CONTINUING. BUMPED POPS UP AGAIN ACROSS EXTREME
WESTERN ZONES TO ACCOUNT FOR CURRENT PRECIPITATION TRENDS. WINDS
CONTINUE TO DROP OFF AS FORECAST AND FOR THE MOST PART OTHER GRIDS
LOOK TO BE IN GOOD SHAPE. AS MENTIONED EARLIER THIS AFTERNOON...
WITH WINDS DECOUPLING OVERNIGHT...WILL HAVE TO MONITOR FOR POTENTIAL
AT LEAST PATCHY DENSE FOG FORMATION.

AS OF 430 PM EDT THURSDAY...HEAVIER RAIN ASSOCIATED WITH A WEAK
SHORTWAVE ALOFT IS PUSHING INTO THE SOUTHWEST MOUNTAINS...SO HAVE
INCREASED POPS IN THAT AREA OVER THE NEXT FEW HOURS. THIS IS ALSO
SUPPORTED BY HI-RES REFLECTIVITY GUIDANCE. OTHERWISE...ALL GRIDS
LOOK GOOD AND NO CHANGES MADE.

AS OF 245 PM EDT THURSDAY...THE UPPER PATTERN CONTINUES TO BE
HIGHLIGHTED BY MOIST SW FLOW CONVEYOR BELT AROUND ROTATING CLOSED
UPPER LOW ATOP THE SOUTHERN ROCKIES...WITH WEAK...NEARLY FLAT
SHORTWAVE RIDGING ACROSS THE SOUTHEAST.  AT THE SURFACE...
SPRINGTIME CAD REGIME CONTINUES TO PREVAIL ACROSS THE SOUTHERN APPS
PROVIDING AMPLE FOCUS FOR UPGLIDE INDUCED RA/DZ OVER THE NC/SC
PIEDMONT REGIONS.  FURTHER WEST A BAND OF SHOWERS ASSOCIATED WITH A
WEAK UPPER WAVE CONTINUE TO ADVECT EAST ACROSS THE CUMBERLAND PLATEAU
THIS AFTERNOON.  AS EXPECTED...LITTLE TO NO INSTABILITY IS PRESENT
ACROSS THE WESTERN NC MOUNTAINS THEREFORE INWARD MOVING CONVECTION
IS WEAKENING AS IT APPROACHES THE WEDGE BOUNDARY...AND SHOULD
CONTINUE TO DO SO.

FOR THE REMAINDER OF THE AFTERNOON AND OVERNIGHT...FCST FEATURES
CHANCE POPS ACROSS THE PIEDMONT/FOOTHILLS ZONES WHERE MODELS PROG
THE BEST UPGLIDE WILL RESIDE.  BY EARLY MORNING POPS WILL DECREASE
OVER THE NC/SC PIEDMONT TO NON-MENTIONABLE LEVELS WHILE AT LEAST LOW
END CHANCE POPS REMAIN IN PLACE ALONG THE BLUE RIDGE.  MOST GUIDANCE
FAVORS DECREASED UPGLIDE BY MID MORNING AMIDST CALMING FLOW AND SOME
WEAK MID LEVEL DRYING PER TIME HEIGHTS.  THUS...WOULD NOT BE
SURPRISED TO SEE PATCHY DENSE FOG BY MORNING ESPECIALLY ACROSS THE
NC PIEDMONT AND IN THE WESTERN NC MTN VALLEYS.

FOR FRIDAY...ANOTHER H5 IMPULSE IS PROGGED TO EJECT FROM THE PARENT
CYCLONE TO THE WEST.  EXPECTING THIS FEATURE TO PROVIDE AT LEAST
WEAK UPPER SUPPORT DURING THE AFTERNOON AS RETURNING SOUTHERLY WAA
PREVAILS AT THE SFC.  A WEAK COLD FRONT WILL ALSO BE APPROACHING
FROM THE WEST...IMPACTING THE HIGH TERRAIN LATE IN THE DAY.  BOTH
NAM/GFS GUID INDICATE LOW LEVELS OF INSTABILITY...BUT CANT RULE OUT
A FEW SHOWERS AND OR THUNDERSTORMS.  OTHERWISE...INCREASING
DOWNSLOPING FLOW WILL ALLOW FOR MODEST DRYING BEHIND THE CAD
EROSION.  THUS THE FCST FEATURES DECREASING CLOUDINESS...WITH ONLY
SLIGHT CHANCE POPS OUTSIDE THE HIGH TERRAIN WHERE CHANCE LEVELS ARE
FAVORED.  TEMPERATURES ON FRIDAY WILL RECOVER SOMEWHAT...BUT SHOULD
REMAIN AT OR JUST BELOW NORMAL LEVELS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
AS OF 2 PM THURSDAY...ANY LINGERING SCT/ISLD DIURNAL CONVECTION IS
EXPECTED TO DIMINISH FRI EVENING...GIVING WAY TO AN UNSEASONABLY
WARM AND MOIST FRI NIGHT/SAT MORNING...WITH MIN TEMPS EXPECTED TO
AVERAGE AROUND 10 DEGREES ABOVE CLIMO. THERE ARE MIXED SIGNALS AS TO
THE EXTENT OF CONVECTIVE CHANCES SAT AFTERNOON/EVENING...AS TEMPS
ARE EXPECTED TO WARM TO 76-81 WITHIN A STILL-MOIST LOW LEVEL REGIME.
A SHORT TERM MODEL CONSENSUS DEPICTS CAPE MAXIMIZING AT AROUND 1000
J/KG DURING THE AFTERNOON...PERHAPS A LITTLE MORE UNSTABLE THAN
FRIDAY. THERE WILL ALSO BE AN INCREASING...ALBEIT WEAK SE UPSLOPE
FLOW. MEANWHILE...THE UPPER RIDGE AXIS IS EXPECTED TO BUILD OVER THE
REGION BY AFTERNOON. NEVERTHELESS...MOST OF THE SHORT TERM MODELS
PRODUCE A CONVECTIVE QPF RESPONSE DURING THE AFTERNOON...AND POPS IN
THE 20-30 PERCENT RANGE APPEAR WARRANTED ACROSS MUCH OF THE AREA...
WITH THE HIGHEST POPS FAVORED ACROSS WESTERN AREAS.

MAJOR HEIGHT FALLS ARE FORECAST ACROSS THE CENTRAL CONUS BY LATE IN
THE WEEKEND...WITH PHASING OF THE NORTHERN AND SOUTHERN STREAMS
EXPECTED...RESULTING IN A BROAD/FULL-LATITUDE TROUGH THAT WILL COVER
MUCH OF THE EASTERN HALF OF THE COUNTRY BY EARLY NEXT WEEK. AHEAD OF
ATTENDANT CYCLONE AND SURFACE COLD FRONT...A BROAD AND VERY MOIST
WARM CONVEYOR BELT AXIS IS EXPECTED TO OVERSPREAD THE SOUTHEAST SAT
NIGHT INTO SUNDAY...WARRANTING 80-90 POPS ACROSS OUR AREA DURING
THIS TIME FRAME. PWATS INCREASE TO 2-3 STANDARD DEVS ABOVE
CLIMATOLOGY DURING THIS TIME...WHILE A FAIRLY STRONG S/SE FLOW COULD
ENHANCE RAINFALL RATES NEAR THE BLUE RIDGE. MODEL FORECASTS OF
BUOYANCY AND SHEAR SUGGEST A NON-ZERO SEVERE THUNDERSTORM THREAT
DURING THIS TIME...ALTHOUGH SURFACE HIGH PRESSURE MOVING ACROSS
SOUTHEAST CANADA WILL SEND A BACK DOOR COLD FRONT THROUGH THE MID-
ATLANTIC...AND TOWARD THE CAROLINAS BY EARLY SUNDAY...POSSIBLY
SETTING THE STAGE FOR IN-SITU COLD AIR DAMMING. HOWEVER...IT REMAINS
HIGHLY UNCERTAIN AS TO HOW FAR SOUTH THE BOUNDARY WILL PUSH. EVEN IF
A LOW-END SEVERE THREAT DOES MATERIALIZE...HEAVY RAIN SHOULD BE THE
PRIMARY THREAT...ESP NEAR THE BLUE RIDGE.

THE WARM CONVEYOR BELT IS EXPECTED TO SHIFT GRADUALLY NORTHEAST OF
THE AREA SUNDAY NIGHT...AS CYCLONE BEGINS TO OCCLUDE IN THE VICINITY
OF THE GREAT LAKES. THIS SUPPORTS GRADUALLY DECREASING POPS SUNDAY
NIGHT...WITH SOLID WARM SECTOR CONDITIONS EXPECTED BY MONDAY MORNING
IN ADVANCE OF APPROACHING FRONTAL ZONE.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...ON MONDAY...BOTH THE GFS AND ECMWF INDICATED
A STRONG LOW PRESSURE SYSTEM CENTERED OVER THE INTERNATIONAL BORDER
NEAR THE GREAT LAKES. DURING THE MORNING HOURS...THE ASSOCIATED WARM
FRONT IS FORECAST TO RUN SOUTH ALONG THE APPALACHIAN
MOUNTAINS...AROUND A WEAK CAD...EAST TOWARD THE NC OUTER BANKS. A
NORTH TO SOUTH ORIENTED COLD FRONT SHOULD BE PUSHING EAST ACROSS
MIDDLE KY/TN BY 12Z MON. THIS PATTERN WILL PLACE MOST OF THE
FORECAST AREA WITHIN THE WARM SECTOR...WITH AN AREA OF ERODING CAD
ACROSS THE NC PIEDMONT. THE SFC COLD FRONT IS EXPECTED TO CROSS THE
FORECAST AREA DURING THE AFTERNOON AND EVENING. THE TIMING OF THE
FRONT WILL FAVOR TEMPERATURE RANGING ABOVE NORMAL...RANGING FROM THE
MID 70S WITHIN THE MTN VALLEYS TO AROUND 80 EAST. FORECAST SOUNDINGS
FROM THE GFS AND ECMWF ARE A LITTLE INTERESTING...FEATURING CAPE
VALUES AROUND 1000 J/KG...WBZ LESS THAN 8KFT...AND SRH AROUND 70
M2/S2. GIVEN THE FRONTAL TIMING...INSTABILITY...AND SHEAR...THIS
WILL BE A CASE OF LINEAR CONVECTION CROSSING THE SOUTHERN
APPALACHIANS. I WILL FORECAST LIKELY POPS ACROSS THE MTNS TO SOLID
CHC POPS EAST OF THE MTNS. ORGANIZED SEVERE WEATHER IS
QUESTIONABLE...BUT SEVERAL HAIL EVENTS COULD OCCUR DURING THE
AFTERNOON.

MONDAY NIGHT THROUGH THURSDAY...MEDIUM RANGE MODELS INDICATE THAT
THE CENTER OF A LARGE HIGH PRESSURE AREA WILL SLIDE ACROSS THE
REGION. AT THE MID LEVELS...HEIGHTS SHOULD REMAIN GENERALLY ZONAL
ACROSS THE WESTERN CAROLINAS AND NE GA. OVERALL...TEMPERATURES
SHOULD AVERAGE VERY CLOSE TO CLIMO. ALSO...POPS WILL REMAIN LIMITED
TO LESS THAN A SCHC TUESDAY AND WEDNESDAY. WEAK RETURN FLOW IS
FORECAST TO DEVELOP ON THURSDAY...ALLOWING MOISTURE TO INCREASE
ACROSS THE CWA. I WILL FORECAST TEMPERATURES SLIGHT ABOVE NORMAL
WITH DIURNAL POPS. POP VALUES WILL RANGE FROM A CHC ACROSS THE MTNS
TO SCHC EAST.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AT KCLT...EXPECT IFR /OR LOWER/ CIGS THROUGH THE PERIOD WITH -RADZ
TO START OFF AS ISENTROPIC UPGLIDE CONTINUES ACROSS THE REGION. RADZ
WILL TAPER OFF OVER THE NEXT FEW HOURS WITH WINDS DECREASING AS
WELL...AND EXPECT VSBYS AND CIGS BOTH TO DROP OVERNIGHT. CONTINUED
TREND OF TEMPO 1/2SM FG OVC001 AROUND SUNRISE AS WINDS SHOULD JUST
ABOUT COMPLETELY DECOUPLE...ALLOWING FOR AT LEAST A BRIEF PERIOD OF
MORE SIGNIFICANT RESTRICTIONS. SLOW IMPROVING TREND ON FRIDAY WITH
MVFR CIGS NOT EXPECTED UNTIL AROUND NOON/16Z AND CIGS ONLY LIFTING
TO VFR TOWARD THE END OF THE PERIOD. WINDS WILL BE LIGHT WITH HIGH
PRESSURE AXIS FIRMLY IN CONTROL BUT SHOULD FAVOR THE NORTH SIDE
UNTIL TOWARD THE END OF THE PERIOD AS THE RIDGE AXIS SHIFTS SLIGHTLY
AND WINGS THE /CONTINUED LIGHT/ WINDS AROUND TO THE SOUTHWEST.

ELSEWHERE...-RADZ CHANCES BEST AT KHKY/KGSP/KGMU WITH -RA OR -SHRA
POSSIBLE FOR KAVL/KAND.  AS WITH KCLT...EXPECT WIDESPREAD IFR CIGS
AND VSBYS OVERNIGHT WITH THE POSSIBILITY OF LOWER CONDITIONS AS
WINDS DECOUPLE TOWARD SUNRISE. CONDITIONS WILL GRADUALLY IMPROVE TO
MVFR AT ALL SITES DURING THE EARLY AFTERNOON AS THE WEDGE
ERODES...WITH THE EXCEPTION OF KAND CLOSER TO THE DEEPER MOISTURE
WITH AN APPROACHING WEAK FRONT AND UPPER DISTURBANCE. FOR THAT SAME
REASON...INCLUDED VCSH FOR KAVL/KAND AT THE END OF THE PERIOD.

OUTLOOK...DRIER WEATHER IS FAVORED INTO SATURDAY. DEEPER MOISTURE
WILL RETURN ALONG A WARM FRONT SAT NIGHT THROUGH SUNDAY...WITH HEAVY
RAINFALL AND WIDESPREAD RESTRICTIONS LIKELY ONCE AGAIN.
THUNDERSTORMS WILL THEN BE POSSIBLE THROUGH MONDAY AS A COLD FRONT
REACHES THE AREA FROM THE WEST.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       MED   64%     MED   69%     LOW   38%     MED   60%
KGSP       HIGH 100%     LOW   52%     LOW   55%     MED   60%
KAVL       HIGH  93%     LOW   58%     LOW   38%     HIGH 100%
KHKY       LOW   39%     MED   62%     LOW   55%     HIGH  80%
KGMU       HIGH 100%     LOW   35%     LOW   38%     MED   60%
KAND       HIGH 100%     LOW   52%     LOW   55%     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...CSH
NEAR TERM...CDG/TDP
SHORT TERM...JDL
LONG TERM...NED
AVIATION...TDP


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