Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 260004
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
804 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/...
730 PM UPDATE...A FEW SHOWERS HAVE MOVED INTO THE WRN UPSTATE FROM
GEORGIA...BUT HAVE APPEARED TO STRUGGLE. MESOANALYSIS SHOWS MUCAPE
VALUES SUBSTANTIALLY LOWER OVER OUR CWFA COMPARED TO AREAS SOUTH AND
WEST WHERE ACTIVITY IS ONGOING. THE SEMI-ORGANIZED LINES OF ACTIVITY
PROPAGATING EWD OUT OF TN AND GA ARE EXPECTED TO ALSO STRUGGLE AS
THEY CROSS INTO OUR CWFA. THOUGH MOISTURE FLUX OVERNIGHT SHOULD
OFFSET NOCTURNAL STABILIZATION TO SOME DEGREE...CHANCES FOR
SHOWERS/TSTMS LATER TONIGHT WITH SHORTWAVES APPEAR TO BE LOWER THAN
PREVIOUSLY THOUGHT...SO I BACKED OFF POPS EXCEPT NEAR THE SRN FACING
BLUE RIDGE...WHICH IS STILL FAVORED FOR DEVELOPMENT BY CNVCTN
ALLOWING MODELS. REMNANT OUTFLOW BOUNDARIES FROM ANY CELLS
ASSOCIATED WITH THIS EVENING/S ACTIVITY MIGHT SERVE TO FOCUS
DEVELOPMENT LATER WHEN THE ENVIRONMENT BECOMES MORE FAVORABLE.

AS OF 230 PM EDT...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 /00Z TUESDAY THROUGH SATURDAY/...
AT KCLT...MOIST SOUTHERLY FLOW WILL RAMP UP OVERNIGHT ON W SIDE OF
BERMUDA HIGH. MOST GUIDANCE PROGS LOW STRATUS FORMING AFTER
MIDNIGHT...WITH CONSENSUS NOW SUGGESTING IT WILL BOTTOM OUT AT THE
LOW END OF MVFR. THIS IS PLAUSIBLE AS A STEADY SOUTH WIND SHOULD
KEEP THE SFC LAYER MIXED ENOUGH TO KEEP IFR AT BAY. THE STRATUS WILL
SLOWLY LIFT TO VFR BY MIDDAY...WITH A HEALTHY CU FIELD QUICKLY
REPLACING IT. PRECIP CHANCES INCREASE THRU THE AFTERNOON AS DIURNAL
INSTABILITY DEVELOPS...WITH BEST CHANCES AFTER 00Z WHEN SHORTWAVES
ARE EXPECTED TO PASS OVERHEAD. PROB30 THUS SHIFTED A BIT TOWARD THE
END OF THE PERIOD.

ELSEWHERE... A CHALLENGE FOR THE TAFS THIS PERIOD IS HOW BEST TO
REPRESENT THE RATHER PERSISTENT PRECIP CHANCES AT THE SC SITES AND
KAVL. LOOSELY ORGANIZED CONVECTIVE ACTIVITY MOVING OUT OF EAST TN
AND NRN GA IS EXPECTED TO WEAKEN AS IT MOVES INTO THE WRN CAROLINAS
AND ENCOUNTERS MORE STABLE AIR. BY LATE EVENING A FEW SHRA OR EVEN
TSRA COULD ENCROACH ON THE WRN SITES. USED MAINLY VCSH/VCTS TO
HIGHLIGHT THIS POSSIBILITY. ALSO...WITH MOISTURE INCREASING ON
SOUTHERLY FLOW AND WEAK SHORTWAVES PASSING OVER THE MTNS/FOOTHILLS
LATER IN THE NIGHT...ADDITIONAL SHRA/TSRA DEVELOPMENT IS EXPECTED.
HOWEVER WITH CHANCES STILL BEING LOW AT THE TAF SITES JUST A VC
MENTION HAS BEEN MADE...EXCEPT AT KAVL WHERE THE CHC WAS GOOD ENOUGH
FOR A TEMPO. THE SAME MOIST LLVL FLOW SHOULD BRING IN LOW MVFR TO
IFR CIGS AT ALL SITES BETWEEN MIDNIGHT AND SUNRISE. A RELATIVE LULL
IN PRECIP CHANCES SHOULD OCCUR FROM AROUND DAYBREAK UNTIL MIDDAY
TUE. CIGS COULD EVEN DROP SLIGHTLY LOWER AFTER DAYBREAK. THE LOW
CIGS SHOULD HAVE MIXED OUT ENOUGH BY 16-17Z TO ALLOW SFC HEATING AND
DESTABILIZATION. PROB30 USED TO HIGHLIGHT THE BETTER PRECIP CHANCES
DURING THIS TIME.

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
AFTN/EVENING SHRA/TSRA EACH DAY. HOWEVER...PASSING UPPER LEVEL
DISTURBANCES COULD GENERATE A FEW TSTMS AT OTHER TIMES OF THE DAY.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH  89%     HIGH  89%     HIGH 100%
KGSP       HIGH  97%     HIGH  90%     HIGH  80%     HIGH  98%
KAVL       HIGH  96%     HIGH  90%     HIGH  84%     HIGH  98%
KHKY       HIGH 100%     HIGH  92%     MED   75%     HIGH 100%
KGMU       HIGH  97%     HIGH  95%     HIGH  81%     HIGH  94%
KAND       HIGH  95%     HIGH  88%     HIGH  94%     HIGH  92%

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...WIMBERLEY


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