Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 220221
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1021 PM EDT THU AUG 21 2014

.SYNOPSIS...
A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL CONTINUE TO PROVIDE
VERY WARM TEMPERATURES ACROSS THE REGION INTO SATURDAY. A BACK DOOR
COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST USHERING IN
COOLER TEMPERATURES STARTING SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 1020 PM...CONVECTION HAS DISSIPATED NEARLY ON SCHEDULE WITH NO
SIGNIFICANT REDEVELOPMENT EXPECTED BEFORE DAYBREAK. HOWEVER...
DEVELOPING MCS CURRENTLY OVER ERN IN COULD MAKE A RUN AT THE MTNS
NEAR OR SHORTLY AFTER DAYBREAK. LATEST CAM AND SYNOPTIC GUIDANCE
SHOWS SOME CONVECTION REACHING THE TN BORDER AROUND 12Z...EVEN IF
THE CENTER OF THE MCS MOVES TO OUR NORTH. THEREFORE...HAVE DROPPED
POP FOR MOST OF THE NITE...BUT ALLOW IT TO COME BACK TO SLIGHT CHC
ALONG THE TN BORDER BY 12Z. OTHERWISE...CONVECTIVE DEBRIS IS MUCH
THINNER AND LESS COVERAGE THAN LAST NITE. THIS COULD ALLOW MORE FOG
TO FORM IN THE NORMALLY MORE FOGGY AREAS. HAVE UPDATED FOR THESE
FEATURES...AND LEFT LOWS AS IS.

AS OF 750 PM...BLUE RIDGE CONVECTION HAS DISSIPATED AS EXPECTED.
HOWEVER...CONVECTION TO THE NORTH CONTINUES TO MOVE SOUTHEAST TOWARD
THE AREA WITH ISOLATED CONVECTION DEVELOPING AHEAD OF THE LINE. THAT
SAID...THE CONVECTION IS DIMINISHING AS IT MOVES SE. LATEST CAM AND
SYNOPTIC GUIDANCE ALSO SHOW THESE TRENDS. THEREFORE...HAVE REMOVED
POP SOUTH OF THE TN BORDER AND I-40 CORRIDOR...BUT LEFT POP IN FOR
THOSE AREAS THIS EVENING. TAPER POP OFF TO NON-MENTIONABLE CHC AFTER
MIDNIGHT AS THE CONVECTION SHUD DISSIPATE. CANNOT RULE OUT AND
ADDITIONAL STRONG OR SEVERE STORM BEFORE MIDNIGHT...BUT CHC WILL
RAPIDLY DIMINISH AFTER SUNSET. HAD TO MAKE SOME SIGNIFICANT
ADJUSTMENTS TO DEW POINTS AS READINGS WERE NOT FOLLOWING THE USUAL
DIURNAL PATTERN. OTHERWISE...UPDATES MAINLY FOR CURRENT CONDITIONS.

AS OF 430 PM...LATEST CAM AND SYNOPTIC GUIDANCE NOT VERY BULLISH ON
CONVECTIVE CHANCES THIS AFTERNOON. ALL THE GUIDANCE SHOWS THE
CURRENT CONVECTION OVER THE BLUE RIDGE DISSIPATING IN THE MORE
STABLE AIR OVER THE FOOTHILLS AND PIEDMONT AS THE CONVECTION MOVES
SE. IN FACT...THEY ARE EVEN SUGGESTING THE CONVECTION OVER THE KY
AND WV WILL DISSIPATE AS IT MOVES SE TOWARD THE AREA. WILL NOT GO
THAT FAR...BUT WILL KEEP THE CURRENT POP TREND OF DIMINISHING THE
BLUE RIDGE POP AND INCREASING POP ACROSS THE NRN TIER FOR THE
CONVECTION TO OUR NW. THAT SAID...WOULD NOT BE SURPRISED IF POP IS
TRIMMED EVEN FURTHER AT THE 730 PM UPDATE IF THESE TRENDS CONTINUE.
OTHERWISE...UPDATES WERE FOR CURRENT CONDITIONS.

AS OF 215 PM EDT...A PROMINENT 500 MB RIDGE AXIS WILL PERSIST OVER
THE LENGTH OF THE MS RIVER VALLEY TONIGHT THROUGH FRI. CONVECTION
ARISING FROM IMPULSES RIDING OVER THE UPPER RIDGE HAS ALREADY FILLED
IN ON REGIONAL RADARS FROM SE KY TO WV THIS AFTN. HOWEVER...THE
CONVECTION ALLOWING MODELS STILL SHOW THE BEST AFTN TSTM TRIGGERING
OVER THE SRN MTNS WHERE LAPS SFC BASED CAPE VALUES ARE RUNNING 3000
TO 4000 J/KG. THEN...THE MESOSCALE MODELS DEPICT THE WEAK CONVECTIVE
SYSTEM TO THE N PASSING MAINLY NORTH OF THE AREA THIS EVENING. SOME
TRAILING CONVECTION FROM THIS NRN SYSTEM MAY BRUSH THE NRN TIER FROM
21Z TO 03Z. MAINLY MID AND HIGH DEBRIS CLOUDS SHOULD LINGER THROUGH
THE NIGHTTIME HOURS...WITH ANY FOG AND LOW CLOUD ISSUES CONFINED TO
THE SW MTN VALLEYS. EXPECT ANOTHER NIGHT OF MILD MINS...WITH MAINLY
LOW TO MID 60S IN THE MTNS AND AROUND 70 ELSEWHERE.

THE FLOW PATTERN BETWEEN THE RIDGE AND A NEW ENGLAND LOW PRES SYSTEM
WILL AMPLIFY ON FRI...WITH MORE NNW FLOW DEVELOPING ALONG THE
APPALACHIANS BETWEEN THESE FEATURES. THIS SHOULD BRING THE NRN TIER
OF THE FORECAST AREA A BIT MORE INTO THE PATH OF ANY UPSTREAM MCS
ACTIVITY FROM THE OH VALLEY LATE FRI. IN ADDITION...SFC BASED
INSTABILITY AND LAPSE RATES LOOK JUST A TOUCH MORE ROBUST FOR FRI
AFTN...BUT STILL RELATIVELY UNIMPRESSIVE FOR SEVERE WX COMPARED TO
UPSTREAM AREAS. OTHERWISE...WESTERLY DOWNSLOPING 850 MB FLOW THROUGH
THE PERIOD WILL MAKE IT A STRUGGLE TO GET MUCH CONVECTION GOING FROM
OTHER SOURCES...AND MAX TEMPS WILL LIKELY GAIN A DEGREE OR SO OVER
THU VALUES. SRN PIEDMONT HEAT INDEX VALUES COULD SURPASS 100 FRI
AFTN IF WE SEE SLIGHTLY LESS DEWPOINT MIXING.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 210 PM THURSDAY...STRONG UPPER RIDGE WILL PERSIST OVER THE
MISS VALLEY THROUGH THE PERIOD...PLACING MUCH OF THE SOUTHEAST AND
MID-ATLANTIC WITHIN MODERATE N/NW UPPER FLOW. OUR AREA WILL
THEREFORE REMAIN SUSCEPTIBLE TO /RING OF FIRE/ CONVECTION DEVELOPING
NEAR QUASI-STATIONARY FRONTAL ZONE ACROSS THE OHIO VALLEY/CTRL
APPALACHIANS REGION...WHICH COULD DROP INTO THE CAROLINAS IN
SOMEWHAT ORGANIZED FASHION DURING THE AFTERNOON AND EVENING.
THERMODYNAMIC PROFILES WILL REMAIN SUFFICIENT TO SUPPORT ISOLATED
SEVERE WEATHER SATURDAY AFTERNOON/EVENING.

BY THE END OF THE PERIOD...THE FRONTAL ZONE MAY BEGIN TO BACK DOOR
ITS WAY INTO THE AREA BY EARLY SUNDAY...AS THE STILL-BUILDING UPPER
RIDGE BEGINS TO SQUEEZE THE DOWNSTREAM UPPER LOW OFF THE EAST
COAST...ALLOWING WEAK SURFACE RIDGING TO BUILD DOWN THE EASTERN
SEABOARD. THEREFORE...IN ADDITION TO THE CONTINUED THREAT OF
MIGRATION OF UPSTREAM CONVECTION INTO THE AREA...THE BACKDOOR FRONT
MAY PROVIDE AN ADDITIONAL FOCUS FOR CONVECTION ON SUNDAY. HOWEVER...
EXACTLY WHERE THE BEST CHANCES WILL OCCUR IS STILL SUBJECT OF
DEBATE...AS THE AIR NORTH OF THE BOUNDARY MAY BE TOO STABLE TO
SUPPORT MUCH IN THE WAY OF PRECIP CHANCES. THE HIGHEST POPS WILL BE
FAVORED ACROSS THE SOUTHWEST ZONES...WHERE CONFIDENCE IN ADEQUATE
INSTABILITY IS HIGHEST...AND A WEAK EASTERLY FLOW MAY PROVIDE AN
ADDITIONAL SOURCE OF LIFT NEAR THE BLUE RIDGE. TEMPS WILL REMAIN
ABOVE NORMAL UNTIL SUNDAY...WHEN MAXES WILL LIKELY BE BELOW NORMAL
UNDER MORE EXTENSIVE CLOUD COVER AND E/NE FLOW.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 1230 PM THURSDAY...THE MEDIUM RANGE MODEL CONSENSUS PROVIDES
GOOD CONTINUITY FROM INHERITED FCST TO START OFF THE WORKWEEK. STILL
EXPECTING SFC RIDGING TO BE NOSED SSWD INTO THE CWFA WHILE UPPER
RIDGE AXIS BUILDS INTO THE EASTERN CONUS. SENSIBLE WX WILL FEATURE
MAX TEMPERATURES ABOUT 5 DEG F BELOW CLIMO WITH POSSIBLY A FEW
SHOWERS FORCED BY THE EASTERLY LLVL FLOW. SUPPRESSED ORIENTATION TO
AMOPSHERE LOOKS TO CONTINUE INTO TUESDAY WITH EFFECTIVELY MINIMAL
SHOWER CHANCES AND TEMPERATURES PERHAPS WARMING A FEW DEG F.
DEEPER LAYERED RIDGING IS PROGGED TO BREAK DOWN DURING THE LATTER
HALF OF THE PERIOD...ALLOWING TEMPERATURES TO CLIMB BACK TO NORMAL
AND PERHAPS THUNDERSTORM CHANCES RETURNING BY THURSDAY.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
AT KCLT...EXPECT CONVECTION TO REMAIN WELL NORTH OF THE AIRFIELD THEN
DISSIPATE THIS EVENING...IN LINE WITH CAM AND SYNOPTIC GUIDANCE.
THAT SAID...A BRIEF TURN TO NLY WIND IS POSSIBLE IF ANY OUTFLOW
BOUNDARY CAN MAKE IT THAT FAR SOUTH. OTHERWISE...EXPECT VFR
CONDITIONS THRU THE PERIOD AS GUIDANCE HAS BEEN OVER-FORECASTING ANY
FOG FORMATION. SHUD SEE LIGHT NLY WIND WITH MIXING FRI MORNING THEN
A TURN SWLY FOR THE AFTERNOON. MAIN AREA OF CONVECTION SHUD REMAIN
NORTH AND WEST OF THE AIRFIELD ONCE AGAIN.

ELSEWHERE...KHKY HAS THE BEST CHC OF SEEING ANY TSRA THIS EVENING
WITH A SMALL CHC AT KAVL. OTHERWISE...EXPECT CONVECTION TO DISSIPATE
THIS EVENING...IN LINE WITH CAM AND SYNOPTIC GUIDANCE. SHUD SEE VFR
CLOUDS THRU THE PERIOD. GUIDANCE HAS BEEN OVER-FORECASTING FOG AND
EXPECT THEY ARE AGAIN...BUT DID KEEP KAVL WITH A PERIOD OF MVFR VSBY
AS THEY ARE THE ONLY TAF SITE THAT HAS A DECENT CHC OF FOG. THAT
SAID...THE NORMALLY MORE FOGGY NON-TAF SITES COULD SEE RESTRICTIONS.
EXPECT LIGHT NLY WIND WITH MIXING FRI MORNING THEN A TURN TO W OR SW
FOR THE AFTERNOON...NW AT KAVL. ONCE AGAIN...KAVL/KHKY HAVE THE BEST
CHC OF SEEING ANY CONVECTION...SO PROB30 INCLUDED THERE.

OUTLOOK...A SIMILAR PATTERN IS EXPECTED FRI NIGHT...WITH MAINLY FAR
NRN TIER SCT CONVECTION POSSIBLE. A BACKDOOR COLD FRONT WILL SAG
INTO THE REGION THROUGH THE WEEKEND...WITH CHANCES OF RESTRICTIONS
INCREASING AT KHKY AND KAVL. A MORE DIURNAL PATTERN OF EARLY MORNING
LOW CLOUDS/FOG AND SCATTERED AFTN TSTMS MAY RETURN EARLY NEXT WEEK.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  91%     HIGH  88%     HIGH  97%     HIGH 100%
KHKY       HIGH 100%     HIGH  86%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     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...CSH
NEAR TERM...HG/RWH
SHORT TERM...JDL
LONG TERM...CSH
AVIATION...RWH





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