Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 200246
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1046 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/...
AS OF 1030 PM...ONE FINAL UPDATE THIS EVENING BASED ON RADAR TRENDS.
AREA OF THUNDERSTORMS THAT MOVED DOWN FROM SW VA INTO THE NRN
FOOTHILLS AND NW PIEDMONT SHOULD RAIN ITSELF OUT NEAR KHKY THROUGH
04Z. A FEW OTHER ISOLATED SHOWERS NOTED OVER UPSTATE SC AND THE
UPPER FR BROAD VALLEY SHOULD ALSO DISSIPATE...ALTHO ONE OR TWO MORE
STRAYS CANNOT BE RULED OUT OVER THE SAVANNAH RIVER BASIN OWING TO
RESIDUAL CAPE AROUND 1000 J/KG. BACKED OFF ON POP ALONG TN BORDER
BASED ON LACK OF UPSTREAM CONVECTION. TEMPS LOOK OK.

REMAINDER OF PREVIOUS DISCUSSION...

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 /03Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...VFR FOR AWHILE THIS EVENING...BUT A GREATER CHANCE OF
RESTRICTIONS OVERNIGHT COMPARED TO OTHER DAYS. THE KEY IS THE LIGHT
PRECIP THAT FELL LATE THIS AFTERNOON. THE GUIDANCE IS CONSISTENT
WITH BRINGING VSBY DOWN TO MVFR NO LATER THAN 08Z. DEWPT DEPRESSION
IS ALREADY LESS THAN 10. THINK MOST PLACES AROUND THE CLT METRO AREA
WILL HAVE MVFR VISIBILITY EVEN IF IT DOES NOT HAPPEN AT KCLT UNTIL
CLOSER TO DAYBREAK. THE FOG SHOULD BURN OFF BY 13Z AT THE LATEST.
FOR WEDNESDAY...INDICATIONS ARE THAT ORGANIZED CONVECTION COULD MOVE
DOWN FROM THE NW IN THE AFTERNOON...ALTHO AREAS TO THE N AND NE HAVE
THE BETTER PROBABILITY. CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE ANY
THUNDERSTORM CHANCE BUT THIS MAY IMPROVE WITH LATER ISSUANCES. A
WEST WIND DIRECTION IS FAVORED WITH THE GRADUALLY VEERING FLOW
ALOFT. HAVE BENT THIS AROUND TO A WNW PREVAILING CONDITION...BUT A
LEE TROF NEARBY COULD BRING THIS BACK AROUND TO WSW.

ELSEWHERE...INITIAL CONCERN IS SCATTERED CONVECTION OVER THE UPSTATE
THAT COULD IMPACT KGMU AND KAND THROUGH MID EVENING. KGMU IS IN THE
GREATEST IMMINENT DANGER SO A TEMPO WAS USED. THIS ACTIVITY HAS
EJECTED AN OUTFLOW BOUNDARY THAT SIGNALS ITS SLOW DEMISE...SO IT
MIGHT NOT AFFECT KAND WITH ANYTHING MORE THAN A TEMPORARY CHANGE IN
WIND DIRECTION TO NE OR E. EXPECT CONVECTIVE DEBRIS FROM MID EVE
ONWARD AND THEN THE FORMATION OF FOG AT MOST PLACES...PARTICULARLY
WHERE RAIN FELL. KAVL ONCE AGAIN HAS A CHANCE FOR FOG THAT THE MODEL
GUIDANCE HAS PROBABLY OVERDONE...BUT LOW LEVEL MOISTURE IS ALSO THE
BEST IT HAS BEEN LATELY...SO IT MIGHT JUST WORK OUT. ANY FOG SHOULD
BURN OFF BY MID MORNING WEDNESDAY...AFTER WHICH THE MTNS HAVE THE
BEST CHANCE FOR DEEP CONVECTION. ONLY KAVL GETS A TOKEN PROB30 FOR
NOW BUT THIS COULD EASILY BE MUCH HIGHER IF ORGANIZED CONVECTION
MOVES IN FROM THE NW.

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...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH  81%     MED   78%     HIGH  86%     HIGH 100%
KGSP       HIGH 100%     HIGH  95%     HIGH 100%     HIGH 100%
KAVL       HIGH  91%     HIGH  97%     HIGH  95%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH  95%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH  95%     HIGH 100%     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...HG
LONG TERM...JPT
AVIATION...PM





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