Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191851
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
251 PM EDT TUE AUG 19 2014

.SYNOPSIS...
A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL 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. A
WEAK COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST LATE
FRIDAY INTO SATURDAY AND BRING SOME MINOR RELIEF FROM THE HEAT.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
SCATTERED CONVECTION CONTINUES TO DEVELOP ALONG A NARROW AXIS FROM
THE SOUTHERN NC FOOTHILLS...ACROSS THE SOUTHWEST NC PIEDMONT AND
NORTHERN TIER OF COUNTIES IN SC...GENERALLY ALONG A WEAK
CONVERGENT/INSTABILITY AXIS. WITH CAPE EXCEEDING 2000 J/KG ACROSS
MUCH OF THE UPSTATE/EASTERN SC PIEDMONT...OUTFLOW BOUNDARIES SHOULD
SUPPORT SOLID COVERAGE INTO THE EASTERN UPSTATE/ERN SC PIEDMONT AND
SOUTHERN NC PIEDMONT THROUGH LATE AFTERNOON. ELSEWHERE...INSTABILITY
IS WEAKER...BUT STILL EXPECT WIDELY SCATTERED CONVECTION TO DEVELOP
OVER THE HIGH TERRAIN...ESP IN THE HIGH TERRAIN NEAR THE BLUE RIDGE.
CHANCES SHOULD ALSO INCREASE ACROSS THE WESTERN MTNS TOWARD
EVENING...AS CONVECTION OVER THE TENN VALLEY APPROACHES...SUPPORTED
BY A WEAK NW/UPSLOPE FLOW. MOIST PROFILES/HIGH FREEZING LEVELS
SHOULD RESULT IN A MINIMAL SEVERE WEATHER THREAT. BUT WHILE MEAN
CLOUD-BEARING FLOW SHOULD SUPPORT 10-20 KT CELL MOVEMENT TOWARD THE
SE...SOME SUBTLE BACK-BUILDING HAS BEEN OBSERVED IN SPOTS...SO THE
MAIN THREAT MAY BE LIMITED TO A LOW END/LOCALIZED FLASH FLOOD
CONCERN.

DEEP LAYER DRYING ASSOCIATED WITH EASTWARD SHIFT OF A MID-LEVEL
SHORT WAVE TROUGH SHOULD RESULT IN DIMINISHING OF CONVECTION FAIRLY
QUICKLY THIS EVENING. THE ONLY EXCEPTION MAY BE ALONG THE TENN
BORDER. LATE TONIGHT...ATTENTION TURNS TO SHORT WAVE TROUGH AND/OR
ASSOCIATED (POSSIBLY ORGANIZED) CONVECTION APPROACHING THE AREA IN
VEERING UPPER FLOW. THE SHORT TERM MODELS...DESPITE PICKING UP ON
THIS SHORT WAVE...DO NOT DEVELOP MUCH IN THE WAY OF CONVECTION
ACROSS THE AREA EARLY WEDNESDAY.

BY WED AFTERNOON...DRIER AIR ALOFT/STEEPER LAPSE RATES IS RESULTING
IN APPRECIABLY STRONGER BUOYANCY IN FORECAST SOUNDINGS ACROSS THE
AREA. NEVERTHELESS...THE SHORT TERM MODELS ARE RATHER MUTED IN THEIR
QPF RESPONSE WED AFTERNOON. NEVERTHELESS...BASED UPON THE DEGREE OF
INSTABILITY...AND THE POTENTIAL FOR WEAK WAVES RIPPLING THROUGH THE
NW FLOW...WILL FEATURE 30-50 POPS ACROSS MUCH OF THE AREA...WITH THE
HIGHEST FAVORED ACROSS THE WESTERN MTNS...IN LIGHT OF PERSISTENT LOW
LEVEL W/NW FLOW ACTING ON A POTENTIALLY VERY UNSTABLE AIR MASS
ACROSS THE TENN VALLEY. THE POTENTIAL FOR SEVERE CONVECTION SHOULD
BE A BIT HIGHER WED OWING TO THE DRIER AIR ALOFT/MORE UNSTABLE
SCENARIO.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 215 PM TUE...A STRONG UPPER RIDGE AXIS WILL BLOSSOM OVER THE
MIDDLE AND LOWER MS RIVER VALLEY WED NIGHT THROUGH THU...AND THEN
EXPAND EASTWARD TOWARD THE APPALACHIANS THROUGH FRI. A 90 KT 250 MB
JET STREAK RIDING OVER THE BUILDING RIDGE AXIS ON THU WILL PRODUCE
INCREASED UPPER DIVERGENCE SWD ALONG THE APPALACHIAN CHAIN...BUT
THERE IS CONSIDERABLE UNCERTAINTY WHETHER OR NOT THE BEST FORCING
WITH THIS WILL REACH FAR ENOUGH S TO AFFECT OUR AREA. WHAT IS MORE
CERTAIN IS THAT INSTABILITY IN THE DEEP LAYER NW FLOW SHOULD BE
SUFFICIENT FOR UPSTREAM MCS GENERATION THU...BUT WITH THE BULK OF
THE ACTIVITY LIKELY PASSSING N AND E OF OUR AREA. A GENERAL HIGHER
CHC N TO LOWER CHC S POP PATTERN WILL BE NEEDED FOR OUR FORECAST
AREA THU AFTN AND EVENING. TEMPS SHOULD WARM TO A COUPLE OF
CATEGORIES ABOVE NORMAL...BUT WILL KEEP MAX VALUES BELOW MOS AND
LEAN TOWARD THE BIAS CORRECTED MOS MAXES WHICH HAVE BEEN
CONSISTENTLY COOLER THIS SUMMER.

THE DEEP LAYER FLOW COMPONENT MAY BECOME MORE NRLY AROUND THE
STRENGTHENING RIDGE ON FRI...WHICH COULD DRIVE ANY UPSTREAM
CONVECTION FARTHER TO THE SOUTH FROM IT/S GENESIS REGION IN THE OH
VALLEY AND SRN GREAT LAKES. IN ADDITION...THE STEEPER LAPSE RATES
THAT DEVELOPED ON THE ERN PERIPHERY OF THE RIDGE THU WILL PERSIST
THROUGH FRI. A SIMILAR PATTERN OF DIURNAL...HIGHER N/LOWER S POPS
WILL BE FEATURED FOR FRI ALONG WITH CONTINUED ABOVE CLIMO/BELOW MOS
MAX TEMPS IN THE 90S.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 140 PM EDT TUESDAY...THE MEDIUM RANGE PICKS UP AT 00Z ON
SATURDAY WITH THE UPPER RIDGE AXIS NEARLY STATIONARY AND JUST TO OUR
WEST AND BROAD UPPER TROFFING JUST OFF THE ATLANTIC SEABOARD. FOR
THE REMAINDER OF THE PERIOD...THE RIDGE AXIS REMAINS LARGELY IN
PLACE WHILE THE UPPER TROF BECOMES NEARLY STATIONARY AND MORPHS INTO
A CLOSED H5 LOW OVER THE WEEKEND. THE LATEST MODEL GUIDANCE
CONTINUES TO SUGGEST THAT SOME FLATTENING OF THE UPPER RIDGE IS
LIKELY TOWARDS THE END OF THE PERIOD...YET THIS IS EXPECTED TO BE
MINIMAL.

AT THE SFC...A STRONG HIGH CENTERED OVER FAR EASTERN QUEBEC AND A
DEEPENING LOW MOVING INTO THE NORTH ATLANTIC WILL ESTABLISH A COOLER
AIR WEDGE PATTERN JUST TO OUR NORTH ON SAT. THIS PROVIDES FOR MORE
PERSISTENT NELY LOW LVL FLOW OVER THE FCST REGION AS THE HIGH IS
SLOW TO MOVE EASTWARD AND THE LOW REMAINS OFF THE NORTHEAST COAST
THRU EARLY NEXT WEEK. PREVIOUS MODEL RUNS HAD THE WEDGE PATTERN
BREAKING DOWN BY EARLY NEXT WEEK...HOWEVER THE LATEST RUNS SUGGEST
THAT THE CANADIAN SFC HIGH WILL ACTUALLY MOVE SOUTHWARD EARLY NEXT
WEEK AND MAINTAIN THE WEDGE THRU THE END OF THE MEDIUM RANGE. THIS
SOLUTION IS BETTER SUPPORTED BY THE 00Z ECMWF...WITH THE LATEST 12Z
GFS ACTUALLY SPINNING UP A TROPICAL CYCLONE AND MOVING IT INTO THE
GULF OF MEX BY NEW DAY 7. THIS CAUSES THE FLOW TO BECOME MORE SELY
OVER THE CAROLINAS BY THAT TIME. AS FOR THE SENSIBLE WX...I KEPT A
SOLID CHANCE POP FOR MOST OF THE ZONES ON SAT AND SUN WITH THE
DEEPER MOISTURE EXPECTED TO REMAIN OVER THE AREA AND SOME WEAK
SHORTWAVE ACTIVITY PROVIDING SOME DEGREE OF UPPER SUPPORT EACH
AFTERNOON/EVENING. THE DEEPER MOISTURE IS EXPECTED TO SHIFT EASTWARD
ON MON AND TUES AND THE WEDGE WEAKENS AND THUS WIDESPREAD SHOWER AND TS
ACTIVITY IS NOT AS LIKELY OVER THE WESTERN CAROLINAS. TEMPS START
OUT ABOVE NORMAL ON SAT AND COOL THRU THE WEEKEND...WITH VALUES
EXPECTED TO REBOUND A FEW DEGREES BY EARLY NEXT WEEK.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE...SCATTERED CONVECTION IS DEVELOPING GENERALLY
ALONG/EAST OF A LINE FROM KAVL TO KGSP...AND SOUTH OF A LINE FROM
KAVL TO KHKY. AS SUCH...THE MOST LIKELY TERMINALS TO SEE CONVECTION
IN THE VERY NEAR TERM WILL BE KCLT AND KGSP...MAINLY AFTER 19Z.
ALTHOUGH THERE HAVE BEEN OCCL LIGHTNING STRIKES WITH THIS
ACTIVITY...BASED UPON THE MAGNITUDE OF INSTABILITY...FEEL THAT
COVERAGE OF TS IS SUCH THAT TEMPOS CAN BE LIMITED TO -SHRA AT THESE
TWO TERMINALS (ALONG WITH VCTS AT KGSP)...WHILE THE MENTION WILL BE
LIMITED TO VCTS/VCSH ELSEWHERE. CONVECTION SHOULD DIMINISH TO
ISOLATED COVERAGE OR LESS THIS EVENING. THE MAIN CONCERN THEN WILL
SHIFT TO THE LATE NIGHT/EARLY MORNING FOG DEVELOPMENT. MVFR BR HAS
BEEN INCLUDED AT MOST TERMINALS PRIOR TO 12Z. WHILE KAVL STANDS A
REASONABLE CHANCE TO SEE IFR OR LOWER CONDITIONS...CONFIDENCE IS
RATHER LOW ATTM.

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

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-19Z
KCLT       HIGH  92%     HIGH 100%     HIGH  88%     HIGH  96%
KGSP       HIGH 100%     HIGH 100%     HIGH  97%     HIGH 100%
KAVL       HIGH  92%     HIGH  94%     HIGH  95%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  94%     HIGH  93%

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
SHORT TERM...HG
LONG TERM...JPT
AVIATION...JDL






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