Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 290610
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
210 AM EDT WED JUL 29 2015

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST OVER THE REGION THROUGH WEDNESDAY...WITH
TEMPERATURES REMAINING ABOVE NORMAL. A WEAK COLD FRONT WILL APPROACH
THE AREA FROM THE NORTHWEST ON THURSDAY AND SETTLE JUST SOUTH OF THE
REGION ON FRIDAY. THE FRONT WILL LIKELY REMAIN STALLED JUST SOUTH OF
THE AREA THROUGH THE WEEKEND...WITH COOLER TEMPERATURES EXPECTED.
MOISTURE SHOULD INCREASINGLY RETURN NORTHWARD OVER THE FRONT THE
LATTER HALF OF THE WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 2 AM...I WILL RECONFIGURE THE FOG MENTION TO LATEST GUIDANCE
AND OBSERVATIONS. OTHERWISE...THE CURRENT FORECAST REMAINS ON TRACK.

AS OF 1215 AM...LATEST REGIONAL RADAR COMPOSITE INDICATES THAT
SHOWERS HAVE DISSIPATED ACROSS THE CWA. LATEST GUIDANCE SHOWS LITTLE
POTENTIAL FOR SHOWERS TO DEVELOP THROUGH THE REST OF THE NIGHT. I
WILL UPDATE THE FORECAST TO REDUCE POPS BELOW SCHC AND DELAY MENTION
OF FOG.

0200 UTC UPDATE...POPS HAVE BEEN REDUCED OVER MOST OF THE AREA PER
RADAR TRENDS...WITH THE EXCEPTION OF THE NW NC PIEDMONT WHERE
ACTIVITY IS MOST PRONOUNCED. ONLY MINOR CHANGES WERE MADE TO
TEMPERATURES AND DEW POINTS OVERNIGHT. SKY COVER WAS UPDATED FROM
INFRARED SATELLITE IMAGERY.

0000 UTC UPDATE...POPS HAVE BEEN ADJUSTED TO ACCOUNT FOR MORE
CONVECTION MOVING TOWARD THE NW NC PIEDMONT...AND ACTIVITY OVER THE
SC PIEDMONT. QPF WAS ADJUSTED ACCORDINGLY.

2315 UTC UPDATE...POPS HAVE BEEN INCREASED IN THE NW NC
PIEDMONT...THE SOUTHERN INTERSTATE 77 CORRIDOR...AND THE SW NC
MOUNTAINS PER RADAR TRENDS. QPF HAS BEEN ADJUSTED ACCORDINGLY. SKY
COVER WAS UPDATED FROM VISIBLE SATELLITE IMAGERY...WITH INCREASES IN
THE PIEDMONT AND MOUNTAINS...AND DECREASES IN BETWEEN.

2100 UTC UPDATE...POPS HAVE BEEN RAISED ALONG THE SOUTHERN
INTERSTATE 77 CORRIDOR PER RADAR TRENDS...AND LOWERED IN THE SC
INTERSTATES 85 CORRIDOR.

1940 UTC UPDATE...POPS AND QPF HAVE BEEN ADJUSTED TO FAVOR THE
INTERSTATE 85 CORRIDOR PER RADAR TRENDS. SKY COVER WAS UPDATED FROM
VISIBLE SATELLITE IMAGERY.

AS OF 230 PM...CONVECTION WILL CONTINUE TO DEVELOP AND DRIFT TOWARD
THE S-SE THIS AFTN...AS SUBTLE SHORTWAVE ENERGY ROUNDS THE EASTERN
PERIPHERY OF A LARGE UPPER LEVEL HIGH. THE LATEST HRRR AND THE 12Z
HIGH-RES WINDOWS ARE IN REALLY GOOD AGREEMENT ON THE TRENDS...SO I
THINK THE POP GRIDS ARE ON TRACK...SINCE THEY WERE BLENDED WITH
THOSE CAM POPS EARLIER. AS FOR SEVERE THREAT...WHILE THE STORMS HAVE
BEEN GETTING FAIRLY TALL...THE FREEZING LEVEL ABOVE 15 KFT...AND
LOW-MOD DCAPE OF 600-800 J/KG IS KEEPING THE MICROBURST THREAT IN
CHECK. THERE IS ALSO A HEAVY RAIN THREAT...AS PWATS ARE 1.8-2.0"
ACRS THE PIEDMONT...WITH SLOW STORM MOTIONS.

TONIGHT...WEAK LOW PRES OVER SOUTHERN GA...AND HIGH PRES TO THE
NORTH OF THE AREA WILL KEEP A LIGHT S/SE FLOW ACRS THE CWFA. THIS
MAY BE ENUF TO ALLOW FOR LINGERING SHRA AND A FEW EMBEDDED TSTMS
WELL PAST SUNSET. I HAVE POPS ON A SLOW DIMINISHING TREND FOR THE
TONIGHT PERIOD...TO SLGT CHC BY DAYBREAK WED. LOWS IN THE MID-UPR
60S IN THE MTNS AND LWR-MID 70S PIEDMONT.

ON WEDNESDAY...THE SYNOPTIC PATTERN WILL NOT CHANGE MUCH FROM
TODAY...WITH 500 MB HIGH PRES CONTINUING TO NOSE N AND E INTO THE
AREA FROM THE SOUTHERN PLAINS. HOWEVER...THE OP MODELS ALL RESOLVE
ANOTHER VORT MAX DRIFTING SOUTH AROUND THE RIDGE ACRS THE OHIO
VALLEY. THIS MAY HELP TRIGGER CONVECTION. THE LLVLS WILL BE
SIMILAR...WITH ELEVATED DEWPTS IN THE 70S ACRS THE PIEDMONT. CAPE
SHUD BE BACK ABOVE 1500 J/KG OR SO WITH VERY WEAK SHEAR. THE CAMS
THAT GO OUT THRU TOMORROW SHOW SIMILAR CONVECTIVE TRENDS AS TODAY.
SO WILL GO WITH HIGH-END CHC TO LIKELY POPS. SEVERE THREAT WILL
REMAIN LOW WITH MOIST MID LVLS. A SMALL EXCESSIVE RAIN THREAT WILL
CONTINUE. HIGHS AROUND PERSISTENCE IN THE 80S MTNS AND LWR-MID 90S
PIEDMONT.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AS OF 140 PM TUESDAY...RETROGRESSION OF THE SUBTROPICAL HIGH INTO
THE SOUTHERN ROCKIES/HIGH PLAINS WILL OCCUR THROUGHOUT THE SHORT
TERM PERIOD...AS A SERIES OF SHORT WAVES CARVE OUT A LONG WAVE
TROUGH ACROSS MUCH OF EASTERN NORTH AMERICA BY THE END OF THE
PERIOD. THIS WILL INTRODUCE A (RATHER WEAK) FRONTAL BOUNDARY INTO
OUR AREA BY THURSDAY. MEANWHILE...SLIGHT COOLING OF THE MID-LEVEL
TEMPS AND CONTINUED HIGH DEWPOINT TEMPERATURES...ALONG WITH THE
APPEARANCE OF THE BOUNDARY SHOULD SUPPORT CONTINUED GOOD CHANCES OF
CONVECTION THURSDAY AFTERNOON...WITH PERHAPS A BETTER CHANCE FOR A
FEW PULSE-SEVERE STORMS WITHIN A MORE UNSTABLE ENVIRONMENT.

A DEVELOPING CONSENSUS IN SHORT TERM MODEL GUIDANCE INDICATES THE
UPPER TROUGH AXIS WILL BE EAST OF THE FORECAST AREA BY FRI
MORNING...TAKING THE FRONTAL BOUNDARY ALONG WITH IT. ALTHOUGH
THICKNESS VALUES WILL NOT SUPPORT AN APPRECIABLE COOL DOWN (REALLY
ONLY TAKING MAXES BACK TO NEAR-NORMAL LEVELS)...THERE WILL BE A
NOTICEABLE CHANGE IN RELATIVE HUMIDITY ACROSS MUCH OF THE AREA FRI
AFTERNOON...AS DEWPOINTS COULD MIX OUT INTO THE 50S. THE RESULT WILL
BE SMALL (AT BEST) CHANCES FOR CONVECTION FRI AFTERNOON. ALTHOUGH
SMALL POPS WILL BE ADVERTISED...MAINLY HIGHLIGHTING SOUTHERN AREAS
NEARER THE BOUNDARY...EVEN THESE MAY PROVE TO BE ON THE HIGH
SIDE.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 210 PM TUESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SATURDAY WITH A BROAD UPPER TROF CENTERED OVER ONTARIO AND QUEBEC
AND VERY BROAD UPPER RIDGING IN PLACE OVER THE WESTERN CONUS. THIS
GENERAL PATTERN IS EXPECTED TO REMAIN IN PLACE THROUGH THE PERIOD
WITH SOME DEAMPLIFICATION OF THE UPPER TROF POSSIBLE TOWARDS THE END
OF THE PERIOD. AT THE SFC...RIDGING WILL SPREAD BACK OVER THE CWFA
FROM THE NW BY THE START OF THE PERIOD AND LINGER INTO EARLY NEXT
WEEK...GRADUALLY GETTING WEAKER. THE ECMWF STILL TRIES TO SPIN UP
SOME SORT OF SFC LOW TO OUR SOUTH BY THE END OF THE PERIOD...HOWEVER
THE GFS APPEARS LESS BULLISH ON LOW DEVELOPMENT NOW THAN IT HAS OVER
THE PAST COUPLE OF DAYS. ALSO OF NOTE...THE LONG RANGE MODEL
GUIDANCE IS NOW KEEPING THE PLUME OF DEEPER LYR MOISTURE FARTHER
SOUTH AND EAST COMPARED TO PREVIOUS GUIDANCE. THIS WILL ALLOW FOR
LOWER OVERALL POPS FOR MOST OF THE PERIOD. AS FOR THE SENSIBLE
FCST...WE CAN EXPECT MOSTLY DIURNAL CHANCES FOR SCT CONVECTION EACH
DAY/EVENING WITH THE BEST CHANCES OVER THE SE ZONES. TEMPS WILL
START OUT RIGHT AROUND NORMAL AND REMAIN NEAR NORMAL THROUGH THE
PERIOD.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...WET GROUND AND HUMID BL CONDITIONS ARE WIDESPREAD ACROSS
THE NC PIEDMONT THIS MORNING. BASED ON LATEST MOS GUIDANCE AND
FORECAST SOUNDING...IT APPEARS CONDITIONS WILL BECOME SUPPORTIVE FOR
MVFR FOG DURING THE PRE DAWN HOURS. THE TAF WILL INCLUDE A TEMPO FOR
8Z TO 12Z FOR 5SM BR. SIMILAR TO TUESDAY...EARLY MORNING HEATING
MAY SUPPORT MVFR CEILINGS THROUGH MID MORNING. A SWEEPING MID LEVEL
SHORTWAVE WILL APPROACH THE REGION THIS AFTERNOON...LIKELY
TRIGGERING CLUSTERS OF TSRA. USING THE EXAMPLE FROM TUESDAY...I WILL
INCLUDE A PROB30 FOR TSRA FROM 19Z THROUGH 23Z. WINDS SHOULD FAVOR A
SOUTH DIRECTION...LIKELY REMAINING LESS THAN 5 KTS.

ELSEWHERE...OVERALL CONDITIONS SHOULD FOLLOW THE TIMING OF CLT. KAVL
AND KHKY SHOULD SEE THE GREATEST POTENTIAL FOR FOG AND LOW CLOUDS
EARLY THIS MORNING. OTHERWISE...THE ENVIRONMENT SHOULD YIELD MORNING
MVFR STRATUS...MIXING TO VFR CU BY MID DAY.  A SWEEPING MID LEVEL
SHORTWAVE WILL APPROACH THE REGION THIS AFTERNOON...LIKELY
TRIGGERING CLUSTERS OF TSRA. USING THE EXAMPLE FROM TUESDAY...I WILL
INCLUDE A PROB30 FOR TSRA FROM 19Z THROUGH 23Z.

OUTLOOK...AN UPPER LEVEL TROUGH WILL AMPLIFY ACROSS THE ATLANTIC
STATES LATE IN THE WEEK...WITH THE LIKELY PASSAGE OF A COLD FRONT ON
FRIDAY. THE POTENTIAL FOR CONVECTION WILL INCREASE THROUGH
FRIDAY...THEN DECREASE BEHIND THE FRONT ON SATURDAY.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  93%     MED   67%     HIGH 100%     HIGH 100%
KGSP       LOW   56%     MED   65%     HIGH 100%     HIGH 100%
KAVL       MED   75%     MED   70%     HIGH 100%     HIGH 100%
KHKY       MED   74%     MED   76%     HIGH 100%     HIGH 100%
KGMU       MED   74%     MED   63%     HIGH 100%     HIGH 100%
KAND       HIGH  81%     MED   63%     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...NED
SHORT TERM...JDL
LONG TERM...JPT
AVIATION...NED


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