Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 252052
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
452 PM EDT MON MAY 25 2015

.SYNOPSIS...
HIGH PRESSURE WILL SLIDE FARTHER EAST INTO THE ATLANTIC...TAKE ON A
MORE SUMMER-LIKE BERMUDA HIGH PATTERN...AND REMAIN THERE THROUGH THE
WEEK. THIS WILL PRODUCE A MOIST SOUTHERLY FLOW WITH INCREASED
CHANCES FOR WIDESPREAD SHOWERS AND THUNDERSTORMS EACH DAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
430 PM UPDATE...WITH ONLY ISOLD SHOWERS PRESENT OVER NORTH GA AND
LAPS ANALYSIS STILL SHOWING ONLY LOW CAPE VALUES IN THE UPPER
SAVANNAH RIVER VALLEY...BACKED OFF POPS LATE THIS AFTN. MESO MODELS
AND NEW NAM STILL KEY ON CONVECTION DEVELOPING THIS EVENING...SO
RETAINED EVENING POPS AS IS.

AS OF 230 PM EDT...AN INCREASINGLY MOIST BOUNDARY LAYER IS PROVIDING
PLENTY OF LOWER LEVEL CONVECTIVE CLOUD COVER OVER THE WRN CAROLINAS
AND NE GA LATE THIS AFTN...BUT REGIONAL RADARS REMAIN QUIET GIVEN
THE WEAK CAPPING ALOFT AND LIMITED TRIGGERS. THE CAP WILL FURTHER
DIMINISH OVER WRN SECTIONS THROUGH EARLY EVENING AND SRLY UPSLOPE
SHOULD GENERATE SOME SCATTERED CONVECTION IN SW SECTIONS THROUGH THE
EVENING HOURS. ANTICIPATE SLIGHTLY IMPROVING UPPER LEVEL DIVERGENCE
OVER THE REGION OVERNIGHT AS AN UPPER LEVEL JETLET LIFTS NWD ALONG
THE APPALACHIANS. IN ADDITION...WEAK SHORTWAVES WILL RIDE NORTHWARD
ALONG THE SRN APPALACHIANS IN THE DEEP LAYER S/SW FLOW EAST OF THE
MAIN TROUGH AXIS OVER THE PLAINS. ALSO...MOIST LOW LEVEL SRLY
UPSLOPE FLOW INTO THE HIGHER TERRAIN WILL INCREASE OVERNIGHT. THIS
SHOULD COME TOGETHER TO YIELD BETTER COVERAGE OVERNIGHT ACROSS THE
WESTERN HALF OF THE AREA. INSTABILITY SHOULD BE FAIRLY WEAK OVER THE
MTNS WHERE COVERAGE WILL BE BEST. ANTICIPATE MILD MINS ON THE WARM
SIDE OF GUIDANCE GIVEN THE EXPECTED CLOUDS AND LIGHT SRLY MIXING.

MORNING LOW CLOUDS WILL ALLOW SFC HEATING AND INSTABILITY TO GET OFF
TO A VERY SLOW START ON TUE. TEMPERATURES SHOULD ONCE AGAIN STRUGGLE
INTO THE 80S EAST OF THE MTNS AND UPPER 70S IN THE MTN VALLEYS...AS
CUMULUS FILLS IN AS THE LOWER CLOUDS LIFT AND SCATTER. ANOTHER SHOT
OF DEEPER MOISTURE AND LIFT WILL MOVE OVER THE FAR SW MTNS ON
TUESDAY AFTN...WHERE LOW LEVEL SW UPSLOPE FLOW WILL BE ENHANCED. IN
ADDITION...CONVECTION GENERATING AHEAD OF THE LIFTING WAVE ACROSS
THE CENTRAL/LOWER MS RIVER VALLEY WILL MAKE A RUN EASTWARD THROUGH
THE DAY...POSSIBLY TRIGGERING ADDITIONAL CONVECTION ACROSS THE DEEP
SOUTH...AND PERHAPS APPROACHING THE SRN APPALACHIANS LATE. A SHARP W
TO E GRADIENT IN LATE DAY POPS WILL BE ADVERTISED.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 145 PM MONDAY...NOT MUCH CHANGE IN EARLIER THINKING AS THE
LATEST MODEL GUIDANCE SHOWS A MOIST FLOW OUT OF THE GULF PERSISTING
AS AN UPPER RIDGE/ANTICYCLONE REMAINS NEARLY STATIONARY OFF THE
SOUTHEAST COAST AND AN UPPER TROF DEAMPLIFIES AND LIFTS NE ACROSS
THE MIDWEST THRU THE MIDDLE PART OF THE WEEK. THUS...ONCE AN AXIS OF
HIGHER PW AIR MOVES OVER THE WRN CAROLINAS AND NE GEORGIA...IT WILL
REMAIN THERE...PROVIDING THE FUEL FOR SHOWERS/TSTMS. THE MODELS
SUGGEST THAT WEAK IMPULSES WILL LIFT NE ACROSS THE REGION THAT WILL
ENHANCE CONVECTIVE POTENTIAL. WHAT IS LESS CERTAIN IS TIMING OF
THESE FEATURES. WHILE DIURNAL ENHANCEMENT IS EXPECTED...THE PRECIP
SHOULD NOT ENTIRELY DIE OFF EACH NIGHT. THAT MIGHT BE ESPECIALLY
TRUE TUESDAY NIGHT. THE CONVECTION ALLOWING MODEL GUIDANCE RUNS THAT
END RIGHT AROUND 00Z WEDNESDAY SHOW A CONVECTIVE BAND MOVING IN FROM
THE W AT THAT TIME...SO EXTRAPOLATION OF THAT FEATURE WOULD BRING A
BETTER CHANCE OF SHOWERS/STORMS ACROSS THE FCST AREA ON TUESDAY
EVENING COMPARED TO THE DAYTIME PERIOD. THE ORGANIZATION OF THE
CONVECTION ALSO SUGGESTS SOME NON-ZERO THREAT FOR SEVERE TSTMS THRU
THE TUESDAY EVENING HOURS. WE ARE LEFT WITH A FCST THAT FAVORS
LIKELY POP OVER THE MTNS AND CHANCE POP OVER THE PIEDMONT FOR MOST
OF THE PERIOD...WHICH IS A BIT DECEPTIVE IN THAT IT MIGHT IMPLY A
CONTINUAL THREAT. IN REALITY...THERE WILL BE LONG STRETCHES WHEN
NOTHING HAPPENS...IT IS JUST NOT POSSIBLE RIGHT NOW TO PIN DOWN WHEN
THE SHOWERS/STORMS WILL PASS. THE BEST THREAT FOR SEVERE WEATHER
AFTER TUESDAY EVENING STILL LOOKS LIKE LOCALLY HEAVY RAIN OWING TO
THE HIGH MOISTURE CONTENT OF THE AIR MASS. TEMPS WILL BE A CATEGORY
OR SO ABOVE NORMAL EACH DAY...BUT WELL ABOVE NORMAL AT NIGHT BECAUSE
OF THE MOIST AIR MASS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 150 PM EDT MONDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
FRIDAY WITH BROAD UPPER RIDGING OVER THE REGION WITH VARIOUS LOBES
OF EMBEDDED UPPER SHORTWAVE ENERGY TO OUR NORTH AND NW. THE OVERALL
SYNOPTIC PATTERN DOES NOT CHANGE APPRECIABLY OVER THE SE REGION THRU
THE REMAINDER OF THE MEDIUM RANGE WITH UPPER RIDGING WEAKEN A BIT ON
DAYS 6 AND 7. THIS COINCIDES WITH THE APPROACH OF A CENTRAL PLAINS
UPPER SHORTWAVE BY THE END OF THE PERIOD NEXT MONDAY. THE ECMWF IS A
BIT FASTER WITH ITS APPROACH COMPARED TO THE NEWER RUN OF THE
GFS...HOWEVER THE TIMING DIFFERENCES ARE LESS THAN 24HRS.

AT THE SFC...WE WILL BE UNDER THE INFLUENCE OF THE BERMUDA HIGH THRU
MOST OF THE PERIOD. THIS WILL ALLOW MOIST SLY LOW LVL FLOW OVER THE
REGION WITH SOME MINOR LOW TO MID LVL DRYING EXPECTED ON SAT AND
SUN. THE MODELS GENERATE AN ELONGATED COLD FRONT TO OUR NW ON SAT.
THIS FRONT IS ASSOCIATED WITH A SFC LOW THAT DEEPENS AS IT MOVES NE
OF THE GREAT LAKES. THE PROGRESSION OF THE FRONTAL ZONE SLOWS AS IT
PUSHES FARTHER SOUTH AND APPEARS TO ESSENTIALLY LAY UP JUST TO OUR
NORTH ON SUN AND MON AS THE BERMUDA HIGH PREVENTS IT FROM MOVING
FARTHER SOUTH. THE GFS TRIES TO SPIN UP ANOTHER LOW OVER THE CENTRAL
MISS RIVER VALLEY ON SUN...YET IT BECOMES REABSORBED BACK INTO THE
BERMUDA HIGH OVER THE NEXT 48 HRS OR SO. AT PRESENT...THE ECMWF IS
LESS BULLISH WITH THE LOW DEVELOPMENT. AS FOR THE SENSIBLE FCST...NO
MAJOR CHANGES WERE NEEDED. WE CAN EXPECT A TYPICAL SUMMERTIME
DIURNALLY DRIVEN CONVECTION PATTERN WITH GOOD CHANCES FOR WIDESPREAD
SHOWERS AND TS EACH DAY WITH SOMEWHAT REDUCED CHANCES ON SAT AND SUN
OVER THE SOUTHEASTERN ZONES. WELL ORGANIZED CONVECTION STILL LOOKS
UNLIKELY WITH WEAK SHEAR/HELICITY VALUES ANTICIPATED.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
21Z KCLT UPDATE...THOUGH WIND OBS HAVE BEEN VRB OCCASIONALLY DUE TO
INFLUENCE OF WEAK SFC LOW PASSING OVER ERN KY...S TO SSW WINDS WILL
PREVAIL. THUS WILL RETAIN THIS MENTION IN TAF. BASED ON LATEST HRLY
GUIDANCE...NOT AS CONFIDENT THAT CIGS WILL ARRIVE BY 06Z. BUT WILL
AWAIT MORE GUIDANCE BEFORE DELAYING THE RESTRICTIONS...AND GIVE FULL
TREATMENT FOR 00Z.

AT KCLT...CCL HEIGHTS AND IMPROVING LOW LEVEL MOISTURE CONTINUE TO
SUPPORT MAINLY BROKEN CUMULUS AT 4500 TO 5 KFT THROUGH THE LATE
AFTERNOON HOURS. AS THE CUMULUS FIELD WEAKENS LATE THIS
EVENING...LOWER LEVEL MOISTURE WILL ALLOW MVFR CIGS TO FILL IN
THROUGH THE EARLY OVERNIGHT HOURS...WITH IFR QUITE POSSIBLE LEADING
UP TO DAYBREAK. THE GFS/LAMP ARE MORE BULLISH ON THE IFR
CLOUDS...WHILE THE NAM HAS MORE SRLY FLOW MIXING AND CONTINUED
MVFR...BUT THE SFC WINDS ON THE NAM MAY BE TOO ROBUST. WILL THUS
CONTINUE THE PREVIOUS FORECAST OF DEVELOPING OVERNIGHT IFR TOWARD
09Z. ANY CONVECTION SHOULD STAY WELL WEST OF THE AIRFIELD AS A WEAK
MID LEVEL CAP REMAINS THROUGH THE PERIOD. ANTICIPATE FAIRLY STEADY
SRLY SFC WINDS THROUGHOUT...SLIGHTLY HIGHER DURING PERIODS OF DEEPER
MIXING...BUT GENERALLY 10 KT OR LESS WITH ONLY INFREQUENT LOW END
GUSTS.

ELSEWHERE...EXPECT MAINLY LOWER VFR CIGS WITH CUMULUS FROM HEATING
THIS AFTN AND EVENING. MOIST SRLY UPSLOPE FLOW WILL ALLOW MVFR CIGS
TO FILL BACK IN LATE THIS EVENING AND OVERNIGHT...WITH A PERIOD OF
IFR LIKELY BEFORE DAYBREAK. ANY UPSLOPE INDUCED SHOWERS WILL BE
GENERALLY ISOLD TO SCATTERED LATE THIS AFTN...BUT COVERAGE COULD
ACTUALLY INCREASE OVERNIGHT AS BETTER UPPER SUPPORT SWINGS OVER THE
MTN CHAIN. WILL CONTINUE THE MENTION OF VCSH AND TARGETED PROB30 FOR
THE BEST CHANCE NIGHTTIME PERIODS. THE LOW CLOUDS WILL BE SLOW TO
IMPROVE...WITH RESTRICTIONS LIKELY THROUGH THE LATE MORNING HOURS.
EXPECT SRLY FLOW AROUND 10 KT OR LESS THROUGHOUT...WITH OCNL LOW END
GUSTS THIS AFTN AT KAVL.

OUTLOOK...S TO SW FLOW MOISTURE WILL CONTINUE TO STREAM ACROSS THE
TERMINAL FORECAST AREA THROUGH THE WEEK. EXPECT INCREASED MORNING
STRATUS TO RESULT...WITH BETTER THAN CLIMATOLOGICAL CHANCES OF
MAINLY AFTN/EVENING SHRA/TSRA EACH DAY. HOWEVER...PASSING UPPER
LEVEL DISTURBANCES COULD GENERATE A FEW TSTMS AT NIGHT.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-18Z
KCLT       HIGH 100%     HIGH 100%     MED   73%     HIGH  85%
KGSP       HIGH 100%     HIGH  98%     MED   77%     HIGH 100%
KAVL       HIGH 100%     HIGH  94%     HIGH 100%     HIGH  85%
KHKY       HIGH 100%     HIGH 100%     MED   75%     HIGH 100%
KGMU       HIGH 100%     HIGH  94%     MED   77%     HIGH 100%
KAND       HIGH 100%     HIGH  96%     MED   70%     HIGH  91%

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...JPT
NEAR TERM...HG/WIMBERLEY
SHORT TERM...PM
LONG TERM...JPT
AVIATION...HG/WIMBERLEY



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