568
FXUS62 KGSP 202329
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
629 PM EST FRI NOV 20 2009
SYNOPSIS
HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH SATURDAY. A LOW
PRESSURE SYSTEM FROM THE GULF OF MEXICO WILL THEN APPROACH THE
CAROLINAS LATE SATURDAY NIGHT THROUGH SUNDAY AND MOVE ALONG THE
CAROLINA COAST EARLY MONDAY. THIS LOW IS EXPECTED TO REACH THE NEW
ENGLAND COAST BY TUESDAY AS HIGH PRESSURE SETTLES BRIEFLY BACK OVER
THE SOUTHEAST STATES.
NEAR TERM /THROUGH SATURDAY/
HIGH CLOUDS WILL THICKEN AND LOWER OVER THE FA TONIGHT AND SATURDAY
AS LOW PRESSURE DEVELOPS ALONG THE NRN GULF COAST. THERE IS
CONSIDERABLE MODEL DIFFERENCE IN THE EVOLUTION OF THE LOW AND THE
PCPN PATTERN THAT RESULTS. THE GFS IS MUCH FASTER WITH THE AREA OF
RAIN THAN IS THE NAM. THE OLD EC AND THE SREF STRONGLY SUPPORT THE
SLOWER NAM. IN ADDITION...THE AIRMASS OVER THE REGION IS QUITE
DRY...AND WHILE HIGH CLOUDS WILL BE ON THE INCREASE...IT WILL BE
HARD FOR US TO SEE ANY RAINFALL THROUGH THE DAYTIME HOURS ON
SATURDAY UNDER THE DRY WEDGE OF HIGH PRESSURE THAT BUILDS DOWN THE
THE EAST COAST. THE GFS SHOOTS A COUPLE LLVL POT VORT MAXES OUT OF
THE NRN GULF TONIGHT. WHILE THERE IS AN MCS WELL SOUTH OF LA COAST
ATTM...IT IS MOVING OFF TO THE ESE. PCPN IS HAVING A HARD TIME
MAKING IT ONTO THE SRN LA AND NE TX COASTS ATTM...AND THE AREA OF
PCPN THAT DEVELOPS ACROSS THIS AREA ON THE GFS ALREADY SEEMS
OVERDONE. THIS ALSO GIVES ME CONFIDENCE IN GOING SLOWER THAN THE
GFS. THEREFORE...I/VE ONLY GOT A SMALL AREA OF SLIGHT CHANCE POPS
ALONG THE SW FRINGE OF THE FA LATE IN THE DAY ON SAT...MAINLY ACROSS
NE GA.
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
AS OF 110 PM FRIDAY...THE 12 UTC OP GFS FCST OF MASSIVE RESPONSE
DEVELOPING INTO THE WEDGE...ASSOCIATED WITH LARGE SCALE FORCING WELL
REMOVED FROM UNDER THE MAIN S/WV WILL BE DISCOUNTED FOR SATURDAY
NIGHT. WILL PLAN TO TAKE THE MORE CONSERVATIVE NAM/SREF/ECMWF
APPROACH STILL FEATURING THE INFLUX OF DEEPER RH FROM THE SW
OVERNIGHT...ALTHOUGH ACCOMPANIED BY WEAKER FORCING THAN EARLIER
EXPECTED. SO...THE SATURDAY NIGHT SENSIBLE WX WILL BE THICKENING
CLOUDS...AND INCREASING RAIN CVRG...BECOMING WIDESPREAD ACRS THE SW
CWFA AND UPSLOPE AREAS HEADING TOWARD SUNDAY MORNING.
BAND OF DEEP RH IS STILL EXPECTED TO TRANSLATE NE ACRS THE CWFA
SUNDAY ACCOMPANIED BY AN UNCERTAIN DEGREE OF FORCING...ALTHOUGH I
SUSPECT IT WILL BE MODERATE AT BEST. LATER DAY ENCROACHMENT OF
DRY SLOT REMAINS PROBABLE...BUT CONTINUED LLVL WAA FLOW ATOP
THE CHILLY DAMMED AIRMASS SHOULD CONTINUE TO PROMOTE WIDESPREAD
RAIN/DRIZZLE INTO THE EVENING. FOR SUNDAY NIGHT...DESPITE DEPARTURE
OF DEEPER RH...BROAD WEAK TO MODERATE SSE LLVL FLOW SHOULD CONTINUE
AID IN DEVELOPMENT OF AREAS OF LIGHT RAIN AND DRIZZLE WITHIN
LINGERING WEDGE CONDITIONS INTO MONDAY MORNING. WILL PLAN ON MAKING
PESSIMISTIC ADJUSTMENTS TO THE INHERITED FCST FOR MONDAY AS IT IS
QUESTIONABLE ON JUST HOW MUCH SFC PRESSURES RISE WITHIN WEAKENING
WEDGE...AND TO WHAT DEGREE THE SOUTHERLY FLOW JUST ABV THE SFC
DIMINISHES AND VEERS. EXPECTING TO MAKE A DOWNWARD TWEAK TO MAX
TEMPS AND EXTEND LINGERING LIGHT PCPN CHANCES.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
AS OF 220 PM FRIDAY...THE ECMWF REMAINS THE MODEL OF CHOICE THROUGH
THE EARLY MEDIUM RANGE. ON TUESDAY...H5 RIDGE AXIS WILL PIVOT ACROSS
THE CWA AS A CLOSED LOW SWINGS OVER THE HEARTLAND. WEAK SFC HIGH
PRESSURE WILL LIKELY PROVIDE PARTLY SUNNY SKY COVER. SIGNIFICANT
INSOLATION COMBINED WITH MILD THICKNESSES WILL SUPPORT HIGH
TEMPERATURES 5-8 DEGREES ABOVE NORMAL.
POOR MODEL CONSISTENCY AND AGREEMENT WILL YIELD A BELOW AVERAGE
CONFIDENCE FORECAST FOR WED AND THANKSGIVING. 00Z ECMWF WAS KEEPING
THE PERIOD DRY AND MILD...HOWEVER...THE NEW 12Z/20 RUN HAS A
SOUTHERN STREAM SYSTEM SURGING NORTHWARD WEDS NIGHT AND
THANKSGIVING. IF THE 12Z ECMWF SYSTEM VERIFIES...THEN THE FORECAST
SHOULD REFLECT DAMP AND COOL CAD CONDITIONS. HOWEVER...FOLLOWING
NATIONAL GUIDANCE AND THE GFS/ECMWF/GEM/ENSEMBLE MODEL CONSENSUS...I
WILL INDICATE SCHC POPS DEVELOPING OVER THE CWA WEDS NIGHT AND
REMAINING INTO THANKSGIVING EVENING. TEMPERATURE FORECAST WILL REMAIN
VERY CLOSE TO NORMAL.
ON FRIDAY...MEDIUM RANGE GUIDANCE FAVORS A DRY FORECAST.
CONSIDERABLE MODEL SPREAD WITH THE MID LEVEL PATTERN WILL MAKE
TEMPERATURE AND WIND FORECASTS UNCERTAIN. I WILL FAVOR VALUES 1-3
DEGREES BELOW NORMAL...WITH LIGHT NORTHWEST WINDS.
AVIATION /00Z SATURDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE...WINDS WILL FAVOR NORTHEAST THIS EVENING...
BUT WILL PROBABLY GO LIGHT AND VARIABLE BY LATE EVENING. SOME CIRRUS
IS NOTED ON IR SATELLITE IMAGERY AND THIS SHOULD STREAM OVERHEAD
LATE TONIGHT. THE HIGH CLOUDS ARE EXPECTED TO THICKEN ON SATURDAY AS
MOISTURE MOVES IN ALOFT. AT THIS POINT...CEILINGS SHOULD REMAIN
ABOVE 15K FT SO THE TAFS WERE LEFT WITH A NEW FM GROUP AFTER SUNRISE
TO BRING WIND BACK UP FROM THE NE AND THE HIGH CLOUD DETAILS WERE
LEFT OUT.
OUTLOOK...CLOUD CEILINGS WILL GRADUALLY LOWER SATURDAY EVENING WITH
MVFR CONDITIONS EXPECTED AFTER MIDNIGHT SATURDAY NIGHT. RAIN WILL
DEVELOP OVER THE REGION EARLY SUNDAY MORNING. WIDESPREAD IFR CIGS
AND MVFR FOG ARE EXPECTED SUNDAY AND MOST OF MONDAY. FAIR AND DRY
WEATHER IS THEN EXPECTED TUE AND WED.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...SBK
NEAR TERM...MCAVOY
SHORT TERM...CSH
LONG TERM...NED
AVIATION...MCAVOY/PM
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