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Area Forecast Discussion

406
FXUS62 KGSP 170006
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
806 PM EDT TUE SEP 16 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA TODAY...ENHANCING CHANCES FOR
SHOWERS AND THUNDERSTORMS THROUGH TONIGHT. IN ITS WAKE...SEASONABLY
COOL AIR WILL SPILL INTO THE REGION WEDNESDAY. THE COOL CONDITIONS
AND MOSTLY DRY WEATHER WILL LAST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
745 PM EDT UPDATE...SCATTERED CONVECTION WILL CONTINUE TO AFFECT
PARTS OF THE WESTERN NC PIEDMONT AND SOUTHERN UPSTATE SC OVER THE
NEXT SEVERAL HOURS. LATEST CONVECTION ALLOWING MODELS SUGGEST THAT
THE CONVECTION SHOULD DIMINISH AFTER MIDNIGHT...SO POPS WERE UPDATED
TO RAMP DOWN ACCORDINGLY. OTHERWISE...EXPECT A COOL AIR WEDGE TO SET
UP ACROSS THE FORECAST AREA OVERNIGHT...LEADING TO CONSIDERABLE LOW
CLOUDS WITH PATCHY FOG. HENCE...HAVE INCREASED THE SKY COVER AND
MENTIONED PATCHY FOG FOR MOST LOCATIONS THRU SUNRISE.

AS OF 845 AM...VERY SPOTTY SHOWERS CONTINUE ACROSS THE REGION...WITH
SLIGHTLY BETTER COVERAGE NOW DEVELOPING CLOSER TO THE FRONT OVER
EXTREME NW NC. WILL MAINTAIN MAINLY ISOLATED LATE MORNING POPS AND
RAMP UP TO MORE SOLID SCATTERED COVERAGE WITH THE FRONT THIS
AFTERNOON. HAVE ALSO TRIMMED MAXES A DEGREE OR SO IN MOST AREAS IN
LINE WITH THE 06Z BIAS CORRECTED MOS AND IN LIGHT OF PREVIOUS DAYS.
OTHERWISE... THE FOG AND LOW STRATUS SHOULD IMPROVE RAPIDLY GIVEN
THE LIGHT DOWNSLOPE FLOW.

A SERIES OF SUBTLE SHORT WAVES IS EXPECTED TO RIPPLE THROUGH THE
DEVELOPING EASTERN TROUGH OVER THE NEXT 24 HOURS...WITH A MODEL
CONSENSUS SUGGESTING THE FIRST ONE WILL APPROACH OUR AREA BY EARLY
THIS EVENING...ALONG WITH AN ACCOMPANYING COLD FRONT. THESE FEATURES
WILL FIND AN AIR MASS WITH LESS DEEP-LAYER MOISTURE CONTENT THAN
WE/VE BEEN SEEING IN RECENT DAYS. HOWEVER...THE ADDITIONAL HEATING
(WITH MAXES EXPECTED TO PEAK NEAR CLIMO) WILL RESULT IN MODERATE
DESTABILIZATION ACROSS THE REGION THIS AFTERNOON. THUS...EXPECT SCT
CONVECTION TO DEVELOP ACROSS THE MTNS BY LATE AFTERNOON...WITH
ACTIVITY TRUCKING EASTWARD FAIRLY QUICKLY IN MODERATELY FAST W/NW
FLOW. SPEAKING OF WHICH...DEEP LAYER SHEAR IS EXPECTED TO BE RATHER
RESPECTABLE TODAY...WITH FORECAST SOUNDINGS DEPICTING BULK 0-6KM
SHEAR OF AROUND 30 KTS. HOWEVER...INSTABILITY IS NOT EXPECTED TO BE
VERY ROBUST (SBCAPE 1500-2000 J/KG)...BUT SOME DEGREE OF MESOSCALE
ORGANIZATION AND A BRIEF SEVERE WIND GUST OR TWO CANNOT BE RULED
OUT.

CONVECTIVE CHANCES WILL LIKELY REACH A NADIR DURING EARLY EVENING...
THEN GRADUALLY DIMINISH TOWARD THE OVERNIGHT HOURS. WITH PLENTY OF
LOW LEVEL JUICE LINGERING...MIN TEMPS SHOULD AVERAGE A LITTLE ABOVE
CLIMO FOR ONE MORE NIGHT BEFORE THE COOLER AIR ARRIVES.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUE...AN AMPLIFIED UPPER PATTERN WILL BE SEEN OVER THE
CONUS DURING THE PERIOD...KEEPING MOST OF THE ERN STATES UNDER A
LONGWAVE TROUGH. HOWEVER THE PATTERN DOES KEEP MOVING AS THE RIDGE
MOVES FROM THE INTERMOUNTAIN WEST INTO THE PLAINS...WITH A WEAK SFC
HIGH BUILDING INTO THE ERN CONUS DOWNSTREAM OF IT. OUR AREA WILL BE
UNDER THE INFLUENCE OF THE WEAK HIGH WEDNESDAY BEFORE A LARGER
CANADIAN HIGH SLIDES IN FOR THURSDAY. A COUPLE OF WEAK SHORTWAVES
BURIED IN THE UPPER FLOW ARE ALSO SHOWN ON THE NAM/GFS/EC...RESOLVED
MORE DISTINCTLY ON THE NAM ON ACCOUNT OF ITS HIGHER RESOLUTION.
MOISTURE PROFILES APPEAR INSUFFICIENT FOR THESE WAVES TO PRODUCE ANY
PRECIP ON THEIR OWN...AND THEY ARE POORLY TIMED TO ENHANCE DIURNAL
CONVECTION WITHIN THE CWFA. IN FACT ON THU THE SUBSIDENCE IN THE WAKE
OF A WAVE APPEARS TO BE ITS BIGGEST IMPACT. THOUGH LAPSE RATES ARE
NOT THAT BAD EITHER DAY...MODELS SUPPORT SCHC POPS ACRS MUCH OF THE
AREA WED. THE GREATER SUBSIDENCE THU LENDS CONFIDENCE TO A DRY FCST.
TEMPS WILL BE A COUPLE CATEGORIES BELOW CLIMO BOTH DAYS THOUGH
CLEARER SKIES THU WARRANT SLIGHTLY WARMER MAXES. THE SFC HIGH AND
TIGHTENING HEIGHT GRADIENT WITHIN THE DOWNSTREAM UPPER TROUGH LINE UP
THU NIGHT TO ALLOW CAD TO FORM WHICH PERSISTS INTO THE WEEKEND.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 200 AM TUE...AS UPPER TROUGH PROGRESSES EWD THRU THE CANADIAN
MARITIMES...EARNEST COLD AIR DAMMING CONTINUES OVER OUR REGION
REINFORCING SEASONABLY COOL TEMPS FRI-SAT. EASTERLY FLOW MAY PRODUCE
SOME CLOUD COVER BUT PRECIP IS NOT EXPECTED. PARENT HIGH MOVES
OFFSHORE FAIRLY QUICKLY BUT THE WEDGE HOLDS ON THRU SATURDAY.
FALLING UPPER HEIGHTS TAKE THEIR TOLL ON IT BY SUNDAY
MORNING...BRINGING RETURN FLOW AHEAD OF A LOW PRESSURE SYSTEM
CROSSING THE GREAT LAKES.  16/00Z GFS AND 15/12Z EC CONTINUE TO
DEPICT THIS SYSTEM DIFFERENTLY BUT BOTH FEATURE A COLD FRONT MOVING
OUT OF THE TENN VALLEY AND INTO OUR AREA EARLY IN THE WEEK. EACH
MODEL AGREES WITH THE PATTERN SEEN ON THEIR OWN PREVIOUS RUNS.
BEYOND THAT THE GENERAL CONSENSUS IS FOR AN AMPLIFYING UPPER
PATTERN...WITH A DEEP ERN CONUS TROUGH CARVING OUT BY NEXT TUESDAY.
TEMPS TREND UPWARD THRU THE PERIOD AS THE WEDGE GIVES WAY AND THE
FROPA OCCURS...BUT AT THEIR WARMEST ARE AROUND CLIMO.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...SCATTERED CONVECTION OVER THE WESTERN NC PIEDMONT WILL
AFFECT THE TERMINAL AT LEAST THROUGH 02Z PER LATEST RADAR TRENDS AND
CONVECTION ALLOWING MODELS. HENCE...HAVE MENTIONED TEMPO FOR TSRA
BETWEEN 00Z AND 02Z. LATEST GUIDANCE CONTINUES TO SUGGEST MVFR
CIGS/VISBY OVERNIGHT AS A COOL AIR WEDGE SETS UP OVER THE AREA. THE
CONDITIONS WILL THEN IMPROVE TO VFR AFTER SUNRISE. THE WEDGE WILL
REMAIN IN PLACE THRU WED NIGHT...LEADING TO CONSIDERABLE LMVFR
CLOUDINESS WITH PERSISTENT NE WINDS.

ELSEWHERE...SCATTERED CONVECTION WILL CONTINUE TO AFFECT PARTS OF
THE WESTERN NC FOOTHILLS/PIEDMONT AND SOUTHERN UPSTATE SC OVER THE
NEXT SEVERAL HOURS PER LATEST RADAR TRENDS AND CONVECTION ALLOWING
MODELS. LATEST GUIDANCE CONTINUES TO SUGGEST THAT A COOL AIR WEDGE
WILL DEVELOP OVERNIGHT...YIELDING MVFR CIGS/VISBY ACROSS MUCH OF THE
REGION WITH POSSIBLE IFR CIGS/VISBY IN PARTS OF THE NC MTNS/VALLEYS.
HENCE...HAVE GONE WITH TEMPO FOR IFR CIGS/VISBY AT KAVL BETWEEN
08Z-12Z. OTHERWISE...CONDITIONS SHOULD IMPROVE TO IFR AFTER SUNRISE.
WITH THE WEDGE REMAINING IN PLACE...EXPECT CONSIDERABLE LVFR CLOUDS
AND LIGHT NE WINDS TO PERSIST AT LEAST THRU WED AFTERNOON.

OUTLOOK...ALTHOUGH THE CHANCES FOR DIURNAL CONVECTION WILL GREATLY
DIMINISH AFTER WEDNESDAY...THE POTENTIAL FOR LATE NIGHT/MORNING
FOG/STRATUS WILL PERSIST INTO LATE WEEK...ESP IN THE MTN VALLEYS.
CONDITIONS MAY FINALLY DRY OUT FOR THE WEEKEND.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       HIGH  88%     MED   69%     HIGH  86%     HIGH  97%
KGSP       HIGH  82%     MED   70%     HIGH  94%     HIGH 100%
KAVL       HIGH  86%     HIGH  84%     MED   71%     MED   62%
KHKY       HIGH  86%     LOW   59%     MED   76%     MED   64%
KGMU       HIGH  82%     LOW   55%     HIGH  88%     HIGH 100%
KAND       HIGH  82%     MED   61%     HIGH  84%     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...CDG
NEAR TERM...CDG/JOH
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JOH






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