Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KGSP 182222
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
622 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 6 PM...WILL UPDATE THE FCST TO ACCOUNT FOR THE THUNDERSTORM
COVERAGE OVER THE NC PIEDMONT. PRECIP PROBABILITY WAS BUMPED UP TO
LIKELY ACROSS AREA E OF I-77. WILL ALSO NUDGE POP UPWARD OVER THE
CENTRAL AND SRN MOUNTAINS TO ACCT FOR CONVECTION MOVING IN FROM SE
TN. TEMPS ARE IN DECENT SHAPE.

PREVIOUS DISCUSSION...

A RATHER CLOUDY AND STABLE AIR MASS LINGERS OVER THIS NORTHWEST
THIRD OR SO OF THE FORECAST AREA...HAVING BEEN OVERWORKED BY MORNING
CONVECTION AND/OR ASSOCIATED OUTFLOW. THIS OUTFLOW BOUNDARY HAS
SURGED INTO THE SC LOWER PIEDMONT/MIDLANDS...AND SCATTERED
CONVECTIVE ACTIVITY IS NOW DEVELOPING ALONG THIS FEATURE...BUT
PRIMARILY SOUTH OF THE FORECAST AREA. MEANWHILE...SHOWER ACTIVITY
ASSOCIATED WITH CENTRAL APPALACHIAN SHORT WAVE TROUGH IS PASSING TO
OUR NORTH. THE UPSHOT IS...OTHER THAN A COUPLE OF HIGH TERRAIN
SHOWERS...THERE/S NO CONVECTION ACROSS THE FORECAST AREA AS OF
1830Z. CONSIDERING CURRENT OBSERVATIONAL/RADAR TRENDS...THIS MAY NOT
CHANGE MUCH OVER THE NEXT COUPLE OF HOURS. MEANWHILE...WE SHOULD SEE
AN INCREASE IN WEAK SYNOPTIC-SCALE SUBSIDENCE AS THE SHORT WAVE
SHIFTS TOWARD CENTRAL VA/NC. NEVERTHELESS...CAPE IS EXCEEDING 2000
J/KG (PER THE LATEST SPC MESOANALYSIS) ACROSS MUCH OF THE
PIEDMONT...SO STILL EXPECTING SCT CONVECTION TO DEVELOP THIS
AFTERNOON ACROSS MUCH OF THIS AREA. ADDITIONAL CONVECTION CONTINUES
TO DEVELOP AHEAD OF ANOTHER SHORT WAVE TROUGH WITHIN A VERY UNSTABLE
AIR MASS ACROSS ALA/MISS...AND THIS WILL LIKELY APPROACH OUR WESTERN
ZONES BY THIS EVENING. OVERALL...A GRADUAL UPTICK TO 30-50 POPS
(WITH THE HIGHEST IN THE WEST) WILL OCCUR THROUGH THE AFTERNOON INTO
EARLY EVENING.

A LULL IS EXPECTED IN ANY CONVECTIVE ACTIVITY LATER THIS EVENING.
HOWEVER...CHANCES WILL INCREASE AGAIN DURING THE EARLY MORNING AS
THE 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 BECOME QUITE UNSTABLE ACROSS THE PIEDMONT
THIS AFTERNOON...WHILE AN OUTFLOW BOUNDARY IS BEGINNING TO FOCUS
DEEP CONVECTION ACROSS THE CAROLINA PIEDMONT. HOWEVER...IT/S
BEGINNING TO APPEAR THAT THE BEST CHANCES ARE BEGINNING TO SHIFT TO
THE EAST AND SOUTH OF THE TERMINAL. NEVERTHELESS...HAVE OPTED TO
CONTINUE A TEMPO FOR -SHRA THROUGH THE AFTERNOON. OTHERWISE...THERE
SHOULD BE A GENERAL LULL IN CONVECTIVE CHANCES IN THE EVENING...WITH
CHANCES RETURNING BY MID-MORNING TUE...AS AN UPPER AIR DISTURBANCE
APPROACHES FROM THE WEST. OTHERWISE...VFR CONDITIONS WILL CONTINUE
ALONG WITH W/SW WINDS.

ELSEWHERE...SCT CONVECTION IS STILL ANTICIPATED THIS AFTERNOON
ACROSS THE REGION...BUT COVERAGE IS EXPECTED TO BE SOMEWHAT LIMITED
OVER THE FIRST 6 HOURS OF THE PERIOD. THEREFORE...WILL GENERALLY
ADVERTISE VCSH AT MOST TERMINALS INTO THE EVENING. CHANCES MAY
INCREASE JUST AFTER 00Z...AS SCT CONVECTION APPROACHES FROM THE
WEST...BUT THIS IS STILL SOMEWHAT UNCERTAIN ATTM. CHANCES FOR
CONVECTION WILL INCREASE AGAIN TOWARD DAYBREAK...AS AN UPPER AIR
DISTURBANCE APPROACHES FROM THE WEST. FOR NOW...THIS WILL BE HANDLED
IN THE TAFS WITH A RETURN OF VCSH BY DAYBREAK OR SO. OTHERWISE...
AREAS OF BR ARE EXPECTED LATE TONIGHT...ESP IN THE MTN VALLEYS.

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...

            22-04Z        04-10Z        10-16Z        16-22Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  93%     HIGH  87%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH  97%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  97%     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...JDL





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.