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Area Forecast Discussion

406
FXUS62 KGSP 182100
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
500 PM EDT THU SEP 18 2014

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE WILL LINGER ATOP THE REGION INTO
SATURDAY. COOL TEMPERATURES WILL RETURN TO NORMAL READINGS ON SUNDAY
AHEAD OF A COLD FRONT WHICH IS FORECAST TO PASS THROUGH ON MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 430 PM...KGSP RADAR SHOWS A FEW SMALL SHOWERS MAINLY NEAR THE
SC BLUE RIDGE. SATELLITE IMAGERY SHOWS THAT A VEIL OF CIRRUS HAS
SPREAD OVER TOP OF THE DEEP CONVECTION...WHICH APPEARS TO HAVE
STUNTED ITS GROWTH. THE CIRRUS ALSO APPEARS TO HAVE PUT THE BRAKES
ON DESTABILIZATION...NETTING ONLY ABOUT 1500 J/KG OF CAPE...NOT ENUF
TO REALLY DO A WHOLE LOT WITHOUT SOME DECENT LOW LEVEL FORCING TO
HELP IT ALONG. SOME MINOR ADJUSTMENTS WILL BE MADE TO THE POP AND
SOME DOWNWARD ADJUSTMENTS TO TEMPS AS WELL. WILL CONTINUE TO MONITOR
FOR POSSIBLE STRONGER STORMS IN THE SAVANNAH RIVER BASIN.

PREVIOUS DISCUSSION...

AS OF 245 PM...RADAR SHOWING ISOLATED CONVECTION BEGINNING TO
DEVELOP ACROSS THE UPSTATE. DESPITE THE EARLY CLOUDS...SKIES HAVE
SCATTERED ALLOWING HEATING TO HELP DEVELOP MODERATE INSTABILITY
ALONG AND SOUTH OF I-85 WITH WEAK INSTABILITY ELSEWHERE. GIVEN THE
VERY MOIST LOW LEVELS...EXPECT ISOLATED CONVECTION TO CONTINUE TO
DEVELOP THRU THE AFTERNOON INTO THE EARLY EVENING. COVERAGE COULD
REACH SCT LEVELS ALONG THE BLUE RIDGE WHERE DIFFERENTIAL HEATING AND
WEAK UPSLOPE FLOW MAY LEAD TO BETTER COVERAGE. ALTHOUGH CHC OF SVR
STORMS IS LOW...BEST CHC WILL BE ACROSS THE UPPER SAV RIVER VALLEY
WHERE INSTABILITY...SHEAR AND DCAPE ARE HIGHEST.

HIGH PRESSURE CONTINUES TO BUILD INTO THE AREA FROM THE NORTH
OVERNIGHT. THIS WILL LEAD TO AN INCREASE LOW LEVEL ELY TO SELY FLOW.
COPIOUS LOW LEVEL MOISTURE WILL REMAIN ACROSS THE AREA AS WELL.
THEREFORE...EXPECT A RETURN OF LOW CLOUDS ACROSS THE AREA. ALTHOUGH
OVERALL PRECIP COVERAGE WILL DECREASE AFTER MIDNIGHT...THE INCREASED
UPSLOPE FLOW AND WEAK ISENTROPIC LIFT...WILL KEEP AT LEAST ISOLATED
SHRA ALONG THE BLUE RIDGE...ALONG WITH PATCHY DRIZZLE ACROSS MUCH OF
THE AREA. PATCHY FOG...WITH ISOLATED DENSE FOG...WILL DEVELOP AGAIN
AS WELL. LOWS WILL BE A LITTLE ABOVE NORMAL.

EXPECT THE LOW CLOUDS TO ONLY SLOWLY LIFT AND/OR SCATTER OUT FRIDAY
GIVEN THE CONTINUED E TO SE LOW LEVEL FLOW. THE ISOLATED SHRA AND
PATCHY DRIZZLE SHUD END BE MID MORNING...BEFORE PRECIP CHC INCREASES
FOR THE AFTERNOON. THERE WILL BE QUITE A BIT OF ELEVATED INSTABILITY
AS MID LEVELS COOL WITH THE DEVELOPING TROF OVER THE SE. HOWEVER...
ANY FORCING WILL BE WEAKER AS WILL THE INSTABILITY. THEREFORE...
EXPECT PRECIP COVERAGE TO BE ISOLATED OUTSIDE OF THE MTNS AND SCT
OVER THE MTNS WHERE DIFFERENTIAL HEATING AND SE FLOW WILL BE
STRONGER. HIGHS WILL BE A FEW DEGREES BELOW NORMAL...UNLESS CLOUDS
SCATTER OUT SOONER...WHICH WILL MAKE HIGHS CLOSER TO NORMAL.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 230 PM EDT THURSDAY...THE SHORT TERM FORECAST PERIOD
INITIALIZES FRIDAY EVENING WITH THE MEAN UPPER PATTERN FEATURING A
TROF EJECTING OUT TO SEA OVER NOVA SCOTIA WHILE NEARLY ZONAL FLOW
PREVAILS WESTWARD INTO THE GREAT LAKES REGION.  A SECOND UPPER TROF
WILL BE AMPLIFYING AS IT EJECTS OUT OF SOUTH CENTRAL CANADA WITH A
COLD FRONT EXTENDING SOUTHWARD INTO THE NORTHERN PLAINS STATES.
CLOSER TO HOME...SURFACE RIDGING CENTERED OVER NEW ENGLAND WILL HAVE
WEDGED SOUTHWARD INTO NORTHEAST GA AND THE WESTERN CAROLINAS IN AN
EARLY FALL CAD REGIME.  EASTERLY UPSLOPE FLOW ALONG THE BLUE RIDGE
COMBINED WITH RATHER UNIMPRESSIVE ISENTROPIC UPGLIDE WILL WARRANT
MENTIONABLE POPS AT FORECAST INITIALIZATION.  THUS FOR FRIDAY
EVENING THE FORECAST FEATURES CHANCE LEVEL POPS ACROSS THE BLUE
RIDGE WITH ONLY SLIGHT CHANCE LEVELS RESIDING JUST EAST OF THE
FOOTHILLS.

POPS TAPER THROUGH THE OVERNIGHT LEADING TO A MOSTLY DRY FORECAST
FOR SATURDAY AS ABOVE MENTIONED CAD WEDGE BEGINS TO RETREAT YIELDING
ONLY SLIGHT CHANCE POPS ACROSS THE SOUTHERN TIER OF THE FORECAST
AREA WHERE BEST MOISTURE WILL RESIDE.  EXPECTING FORECAST TO REMAIN
DRY THROUGH THE OVERNIGHT INTO SUNDAY BEFORE POPS RAMP UP AHEAD OF
APPROACHING ABOVE MENTIONED UPPER TROF AND ASSOCIATED COLD FRONT.
SOUTHERLY MOISTURE ADVECTION WILL GRADUALLY RESUME ON SUNDAY HOWEVER
SHOULD NOT BE SUFFICIENT ENOUGH TO WARRANT EVEN ISOLATED/SCATTERED
PREFRONTAL CONVECTION.  THERE REMAINS SOME MODEL DISCONTINUITY
REGARDING THE TIMING OF THE INITIAL FRONTAL INTRUSION ON SUNDAY
EVENING WITH THE SLOWER NAM BEING THE OUTLIER.  THE GLOBAL GFS/ECMWF
ARE APPROX 6 HOURS FASTER WITH THE FRONTAL CONVECTION SLIDING INTO
THE NC MOUNTAINS BY THE END OF THE FORECAST CYCLE.  THEREFORE CHANCE
LEVEL POPS ARE FEATURED ALONG THE TN LINE WITH ONLY SLIGHT CHANCE
POPS RESIDING ACROSS THE REMAINDER OF THE WESTERN NC MOUNTAINS.  AS
FOR THE PIEDMONT REGIONS OF NC/SC...EXPECTING A DRY AND FAIRLY NICE
SUNDAY.  TEMPERATURES THROUGH THE SHORT TERM PERIOD WILL GRADUALLY
MODERATE TO AT OR JUST ABOVE NORMAL LEVELS AS THE LOW LEVEL FLOW
VEERS SOUTHERLY BY SUNDAY.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 1240 PM THU...LESS WARM AIR WILL ADVECT INTO THE REGION ON
MONDAY COINCIDENT WITH THE PASSAGE OF A MOISTURE LACKING COLD FRONT.
THERE REMAINS THE POSSIBILITY OF A ROUND OF MAINLY NC MTN SHOWERS
SUNDAY NIGHT AND MAYBE A FEW SHOWERS EAST OF THE BLUE SOMETIME ON
MONDAY. THE INFLUX OF POST FRONTAL DRIER AIR AND ENCROACHING SFC
RIDGE WILL RESULT IN DRY AND COOLER WX MONDAY NIGHT AND TUE AM MINS
ARE PROGGED TO BE ABT 5 DEG F BELOW CLIMO.

THE CWFA LOOKS TO BE WITHIN THE COOL CYCLONIC FLOW CLOSE TO THE
PERIPHERY OF THE EASTERN CONUS L/WV TROUGH ON TUESDAY WITH MODERATELY
STRONG SFC RIDGING BUILDING DOWN THE EASTERN SLOPES WEDNESDAY INTO
THURSDAY. WITHIN THIS DRY AND COOL PATTERN...TEMPERATURES SHOULD
AVERAGE 5 TO 8 DEG F BELOW CLIMO EACH DAY.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
AT KCLT...CIGS HAVE FINALLY LIFTED...BUT SCT TO BKN LOW VFR WILL
CONTINUE THRU THE AFTERNOON. EXPECT BKN TO OVC LOW VFR TO DEVELOP
THIS EVENING WITH CONTINUED LOW LEVEL MOISTURE AND DEVELOPING SELY
FLOW. CIGS SHUD DETERIORATE TO MVFR OVERNIGHT AND IFR TOWARD
MORNING. VSBY SHUD BOTTOM OUT AT MVFR. HOWEVER...CANNOT RULE OUT
LIFR CIGS AND IFR VSBY AROUND DAYBREAK. SHUD AGAIN BE A SLOW
INCREASE TO MVFR CIGS/VFR VSBY TOWARD MID MORNING...THEN LOW VFR BY
EARLY AFTERNOON. LIGHT WIND THIS AFTERNOON BECOMES LIGHT ESE FOR
LATE AFTERNOON INTO EARLY EVENING. WINDS RETURN TO ENE OVERNIGHT
INTO FRI MORN WITH SOME INCREASE IN SPEED. THERE IS A SMALL CHC OF
CONVECTION THIS AFTERNOON...BUT TOO LOW FOR TAFS. COULD BE SOME
LIGHT SHRA ANYTIME OVERNIGHT OR FRI MORNING...AGAIN CHC LOW.

ELSEWHERE...SIMILAR CONDITIONS AS KCLT...ESPECIALLY KHKY. THE SC
SITES SHUD SEE LOW VFR FOR THE BULK OF THE AFTERNOON BEFORE FALLING
TO IFR OVERNIGHT. KAVL HAS THE BEST CHC OF SEEING LIFR OR VLIFR
TOWARD MORNING. HOWEVER...CHC STILL TO LOW TO INCLUDE FOR NOW.
ANOTHER MORNING WITH A SLOW RISE TO LOW VFR THRU CIG RESTRICTIONS.
THERE IS A SMALL CHC OF CONVECTION THIS AFTERNOON...BUT TOO LOW FOR
TAFS. COULD BE SOME LIGHT SHRA ANYTIME OVERNIGHT OR FRI MORNING...
AGAIN CHC LOW. WINDS WILL BE VARIABLE THIS AFTERNOON AND EVENING...
LIGHT NE TO SE. HOWEVER...STRONGER NELY WINDS DEVELOP OVERNIGHT AND
CONTINUE THRU FRI MORN. KAVL WILL SEE LIGHT SLY WIND DEVELOP FRI.

OUTLOOK...THE POTENTIAL FOR LATE NIGHT/MORNING FOG/STRATUS WILL
PERSIST INTO THE EARLY PART OF THE WEEKEND...ESPECIALLY IN THE MTN
VALLEYS. CONDITIONS MAY FINALLY DRY OUT FOR THE LATTER PART OF THE
WEEKEND. A COLD FRONT MAY BRING INCREASING CHANCES FOR SHOWERS/TSTMS
EARLY NEXT WEEK.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       HIGH 100%     HIGH  82%     MED   73%     HIGH  87%
KGSP       HIGH 100%     HIGH  84%     MED   79%     HIGH  87%
KAVL       HIGH 100%     HIGH  93%     HIGH  80%     HIGH  91%
KHKY       HIGH 100%     HIGH  91%     MED   77%     HIGH  89%
KGMU       HIGH 100%     MED   78%     LOW   57%     HIGH  91%
KAND       HIGH 100%     HIGH  85%     MED   64%     HIGH  91%

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...PM/RWH
SHORT TERM...CDG
LONG TERM...CSH
AVIATION...RWH






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