Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 190009
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
809 PM EDT MON AUG 18 2014

.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM WILL LINGER OVER THE AREA TONIGHT AND
THEN SLOWLY MOVE OFF THE COAST ON TUESDAY. A BROAD UPPER LEVEL RIDGE
OF HIGH PRESSURE WILL THEN BUILD ACROSS THE MISSISSIPPI RIVER VALLEY
OVER THE NEXT FEW DAYS AND LINGER FOR THE REST OF THE WORK
WEEK...RESULTING IN ABOVE NORMAL TEMPERATURES AND DRIER WEATHER.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 730 PM...THE THUNDERSTORMS OVER THE WRN PIEDMONT HAVE EXITED
THE GSP COUNTY WARNING AREA...SO THE PRECIP CHANCES OVER THE
PIEDMONT WILL BE RAMPED DOWN FOR THE NEXT FEW HOURS. AT THE SAME
TIME...SCT/NUMEROUS SHOWERS AND STORMS HAVE INVADED THE WRN PART OF
THE NC MTNS...SO AN UPWARD ADJUSTMENT WILL BE MADE TO HANDLE THE
EASTWARD PROGRESS OF THIS ACTIVITY. THE BOUNDARY LAYER WAS
STABILIZING E OF THE MTNS SO THE EWD EXTENT MIGHT NOT BE THAT GREAT.
THE BEST INSTABILITY WILL REMAIN OVER NE GEORGIA AND THE LAKELANDS
WHERE THE AIRMASS REMAINS UNUSED. THIS SHOULD ALLOW CONVECTION OVER
N GEORGIA TO REACH INTO THE LAKELANDS THROUGH MID EVE. WILL INCREASE
POP DOWN IN THAT AREA AS WELL. TEMPS ARE IN DECENT SHAPE.

REMAINDER OF PREVIOUS DISCUSSION...

A LULL IS EXPECTED IN ANY CONVECTIVE ACTIVITY LATER THIS EVENING.
HOWEVER...CHANCES WILL INCREASE AGAIN DURING THE EARLY MORNING AS
A SHORT WAVE APPROACHES FROM GA/AL. DESPITE THE RATHER POTENT
APPEARANCE OF THIS WAVE...THE MODELS ARE NOT EXACTLY ROBUST WITH
THEIR QPF RESPONSE IN OUR AREA. CERTAINLY THE TIMING REFLECTS AN
ABSENCE OF ROBUST INSTABILITY WITH WHICH TO INTERACT. MEANWHILE...
THERE APPEARS TO BE A CONSENSUS THAT THE BETTER LOW LEVEL SHEAR WILL
PASS SOUTH OF OUR AREA. THUS THE POTENTIAL FOR ORGANIZED CONVECTION
APPEARS TO BE HIGHER SOUTH OF OUR AREA. NEVERTHELESS...POPS WILL
INCREASE TO 30-50 PERCENT ACROSS THE WESTERN HALF OF THE AREA
BETWEEN 06Z AND 12Z.

BY TUE AFTERNOON...THE WAVE IS EXPECTED TO BE PUSHING EAST OF THE
AREA...LIKELY PLACING THE AREA WITHIN WEAK SYNOPTIC SCALE SUBSIDENCE
THAT COULD LIMIT COVERAGE OF CONVECTION DURING THE AFTERNOON.
OVERALL...THERE IS QUITE A BIT OF UNCERTAINTY REGARDING THE
EVOLUTION OF CONVECTION TUE MORNING...SO WE WILL ESSENTIALLY FEATURE
TOKEN 30/40 POPS ACROSS THE AREA DURING THE AFTERNOON.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM MONDAY...AN ENDLESS PARADE OF S/W`S WILL BE IMPACTING
OUR FORECAST AREA DURING THIS CYCLE. THE FIRST WILL BE EXITING OUR
REGION TUESDAY. I LEFT A SLIGHT CHANCE IN THE FAR EASTERN FA OF NC
DURING THE EARLY EVENING... AND ALSO ACROSS THE WEST FACING SLOPES
OF THE NC MOUNTAINS (ALSO IN THE EVENING )...WHERE WEAK UPSLOPE
PERSISTS.

MODELS DIFFER ON TIMING AND DEGREE OF NWLY FLOW DEVELOPING OVER THE
CAROLINAS AND NE GA WEDNESDAY AND THURSDAY...AS AN UPPER LEVEL RIDGE
BUILDS FROM THE WESTERN GULF OF MEXICO INTO THE NRN PLAINS. THIS
EVOLUTION...COMBINED WITH A PERSISTENT CUTOFF UPPER LOW MEANDERING
OVER THE GREAT LAKES...WILL SET UP A NWLY FLOW PATTERN ACROSS THE
ERN CONUS...AND ALMOST A RING OF FIRE (ROF) LOOK. ALTHOUGH OUR SHORT
TERM SUITE OF GUIDE VARY IN DETAIL...THE OVERALL PHILOSOPHY / OR BIG
PICTURE / SEEM TO COINCIDE. AS A RESULT THE STAGE WILL BE SET FOR
CLUSTERS OF SHOWERS/TSTMS TO RIDE THE NWLY FLOW DOWN INTO/TOWARD OUR
REGION. IT APPEARS THE FIRST SUCH WOULD BE ASSOCIATED WITH THE
ENERGY IN THE WESTERN OHIO VALLEY TUESDAY...REACHING OUR NC
MOUNTAINS IN THE WEE HOURS WEDNESDAY. CORFIDI VECTORS SUGGEST THAT
ACTION WOULD SPREAD E-SE...POTENTIALLY REACHING PARTS OF NE GA AND
UPSTATE OF SC. STEEP LOW LEVEL LAPSE RATES AND FAT CAPE (ESPECIALLY
WHERE LACK OF DEBRIS CLOUDS MOVE) COULD PROVE FOR AN INTERESTING
WEATHER DAY.

YET ANOTHER S/W WILL FOLLOW ON THURSDAY. FLOW ALOFT SUBTLY SHIFTS
MORE NWLY...THEREFORE I HAVE BROUGHT POPS A BIT DEEPER (SOUTHWARD)
IN OUR CWA IN THE AFTERNOON. ALTHOUGH POPS WITH EACH OF THE
AFOREMENTIONED EPISODES REMAIN ON THE LOW SIDE...THE CONDITIONAL
PROBABILITIES REMAIN ELEVATED. WE ARE NEAR GUIDE POPS OVERALL...OR
SLIGHTLY HIGHER ON OUR SOUTHERN FORECAST FRINGES. ONCE WE GET A
BETTER HANDLE IF/WHERE THESE CLUSTERS WILL FOCUS...POPS CAN BE
ADJUSTED ACCORDINGLY.

ON THE TEMPERATURE END OF THE SPECTRUM...POTENTIAL DEBRIS CLOUDS AND
SHOWERS AND THUNDERSTORMS WOULD SUGGEST LOWERING GUIDE. HOWEVER LOW
LEVEL THERMAL PROFILE IS SOLIDLY ON THE RISE AND WOULD SUGGEST
TEMPERATURE VALUES REACHING NEAR MAXES...WITH DIFFERENTIAL HEATING
EVEN OF WIDESPREAD CONVECTION DEVELOP.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 210 PM EDT MONDAY...THE MEDIUM RANGE PICKS UP AT 00Z ON FRIDAY
WITH THE UPPER RIDGE AMPLIFYING OVER THE MISS RIVER VALLEY WHILE
ANOTHER BROAD UPPER TROF DIGS DOWN JUST OFF THE ATLANTIC SEABOARD.
FOR THE REMAINDER OF THE PERIOD...THE RIDGE AXIS REMAINS LARGELY IN
PLACE TO OUR WEST WHILE THE UPPER TROF BECOMES NEARLY STATIONARY AND
MORPHS INTO A CLOSED H5 LOW OVER THE WEEKEND. THE LATEST LONG RANGE
MODEL GUIDANCE SUGGESTS THAT WE WILL PROBABLY SEE SOME FLATTENING OF
THE UPPER RIDGE BY THE END OF THE PERIOD...BUT IT WONT BE TOO
SIGNIFICANT.

AT THE SFC...OUR AREA IS EXPECTED TO REMAIN UNDER A WARM AND MOIST
AIR MASS DURING THE FIRST PART OF THE PERIOD WITH WEAK HIGH PRESSURE
IN PLACE AND A SERIES OF WEAK MESO LOWS THAT TRY TO SPIN UP TO OUR
NORTH AND EAST. AS WE GO INTO THE WEEKEND...THE LONG RANGE MODELS
ARE LEANING TOWARDS A MORE ROBUST WEDGE DEVELOPING ON SAT AND
ESPECIALLY ON SUN. THIS PATTERN DEVELOPS FROM THE COMBINATION OF A
STRONG HIGH CENTERED OVER NOVA SCOTIA AND A LOW SPINNING UP AS IT
MOVES OFF THE NC COAST. THIS PROVIDES FOR STRONGER NELY LOW LVL FLOW
OVER THE FCST REGION AS THE HIGH IS SLOW TO PROGRESS EASTWARD AND
THE LOW REMAINS OFF THE NORTHEAST COAST THRU NEW DAY 7. THE WEDGE PATTERN
APPEARS TO BREAK DOWN BY THE END OF THE PERIOD EARLY NEXT
WEEK...HOWEVER MANY TIMES THESE FEATURES LINGER LONGER THAN THE
MODELS DEPICT. AS FOR THE SENSIBLE WX...NO MAJOR CHANGES WERE MADE
TO THE POP FCST WITH CHANCE COVERAGE INCREASED ON BOTH SAT AND SUN
AND ONLY SLIGHT CHANCE FOR MON AS THE DEEPER MOISTURE SHIFTS
EASTWARD AND THE WEDGE WEAKENS. TEMPS START OUT ABOUT A CATEGORY
ABOVE NORMAL ON FRI AND STEADILY COOL THRU EARLY NEXT WEEK WITH
VALUES ENDING RIGHT AROUND CLIMO IF NOT JUST BELOW.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AT KCLT...THE AIR MASS HAS BEEN STEADILY LOSING INSTABILITY OVER THE
LAST FEW HOURS NOW THAT DEEP CONVECTION HAS MOVED OFF TO THE EAST.
UPSTREAM CONVECTION OVER THE NC MOUNTAINS LOOKS TO BE A FEW HOURS
OUT AND SHOULD NOT ARRIVE BEFORE THE LAST EVENING PUSH. SO...WILL
NOT INCLUDE ANY PRECIP WITH THIS ISSUANCE THROUGH TUESDAY MORNING.
CLOUDS SHOULD BE MOSTLY OF THE MID/HIGH LEVEL DEBRIS VARIETY INTO
THE EARLY MORNING HOURS...WITH A LIGHT SW WIND. WILL AMEND THE TAF
IF THE DEEPER CONVECTION SURVIVES INTO THE NC FOOTHILLS. THERE
SHOULD BE A LULL DURING THE EARLY MORNING HOURS...BUT CHANCES FOR
THUNDERSTORMS WILL RAMP BACK UP AS ANOTHER UPPER WAVE APPROACHES
FROM THE WEST ON TUESDAY MORNING. THIS WILL BE HANDLED WITH A PROB30
THROUGH THE LATE AFTERNOON. THE PASSAGE OF THE WAVE SHOULD BRING
WINDS AROUND TO WNW IN THE AFTERNOON.

ELSEWHERE...DEEP CONVECTION MOVING IN FROM THE W THIS EVE WILL ONCE
AGAIN FIGHT ITS WAY INTO A PROGRESSIVELY LESS FAVORABLE AIR MASS
WITH NO GUARANTEE IT WILL SURVIVE TO REACH ANY TAF SITES. FOR THAT
REASON...WILL HANDLE IT WITH A VICINITY SHOWER/TSTM UNTIL IT BECOMES
MORE CLEAR THAT A THREAT EXISTS...AT WHICH TIME AMENDMENTS WILL BE
MADE. THIS IS MOST LIKELY AT KAND BASED ON PROXIMITY TO BETTER
SURFACE BASED INSTABILITY. WIND SHOULD BE SW. EXPECT A LULL THROUGH
THE EARLY MORNING HOURS. THE GUIDANCE YET AGAIN BRINGS KAVL DOWN TO
MVFR FOR LOW VISIBILITY THROUGH DAYBREAK...AND CONFIDENCE IS LOW FOR
NOW...UNTIL OR UNLESS THEY EXPERIENCE SOME PRECIP. IF THAT
HAPPENS...THEN PERIODS OF IFR ARE NOT A BAD BET. WILL RE-EVALUATE.
OTHERWISE...THE APPROACH AND PASSAGE OF ANOTHER WAVE WILL BRING
ANOTHER CHANCE OF THUNDERSTORMS ON TUESDAY. THE SOMEWHAT EARLY AND
LESS FAVORABLE TIMING OF THE WAVE MAY LIMIT COVERAGE...SO THIS IS
HANDLED WITH A PROB30. WIND SHOULD BE WSW.

OUTLOOK...SCT AFTERNOON CONVECTION AND PATCHY EARLY MORNING FOG WILL
REMAIN IN THE FORECAST THROUGH THE WEEK. THERE WILL ALSO BE
INCREASING CHANCES FOR ORGANIZED CONVECTION APPROACHING THE AREA
FROM THE NW DURING THE LATE NIGHT/EARLY MORNING HOURS.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  99%     HIGH  92%     HIGH  86%
KHKY       HIGH 100%     HIGH 100%     HIGH  95%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH  95%     HIGH  95%     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...JPT
NEAR TERM...JDL/PM
SHORT TERM...TS
LONG TERM...JPT
AVIATION...PM





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