FXUS62 KGSP 111142
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
642 AM EST FRI DEC 11 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL CROSS EAST OVER THE REGION THROUGH EARLY
SATURDAY. AN AREA OF LOW PRESSURE WILL THEN MOVE UP THE EAST COAST
INTO SUNDAY. HIGH PRESSURE BRIEFLY BUILDS BACK OVER THE AREA MONDAY
BEFORE A COLD FRONT APPROACHES THE REGION FROM THE WEST TUESDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
ARCTIC HIGH PRESSURE WILL CONTINUE SETTLING OVER THE AREA DURING THE
NEAR TERM...RESULTING IN MAX TEMPS TODAY A COUPLE OF CATEGORIES
BELOW CLIMO. PROGGED THICKNESS VALUES AND FORECAST SOUNDINGS SUPPORT
COOLER MET MOS...AND WILL STICK VERY CLOSE TO THOSE NUMBERS. THE MAIN
CONCERN FOR THE DAY WILL BE THE VERY DRY AIR MASS...SEE THE FIRE WX
DISCUSSION BELOW FOR DETAILS.
COLD WEATHER PERSISTS INTO TONIGHT...BUT SHOULD BE TEMPERED BY
INCREASING HIGH CLOUDS...AT LEAST ACROSS THE SOUTHERN HALF OF THE
AREA. AREAS ALONG THE I-40 WILL BE LESS AFFECTED BY THE HIGH
CLOUDS...SO ANOTHER NIGHT OF BELOW NORMAL LOWS CAN BE EXPECTED.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 220 AM FRIDAY...UPPER FLOW REMAINS FAIRLY ZONAL SAT-SUN WITH A
SERIES OF WEAK SHORTWAVES MOVG OVER THE REGION. LOW LEVEL MOISTURE
SURGES OUT OF THE GULF AND NE OVER THE AREA BRINGING PRECIP TO THE
CWA SAT-SAT NIGHT. AT THE SAME TIME...SFC HIGH PRES OVER THE MID
ATLANTIC WILL RIDGE SW OVER THE CWA WITH LOWER THKNS VALUES IN THE
WEDGE THAT DEVELOPS. EXPECT SOME IN-SITU REINFORCEMENT OF CAD AS
PRECIP BEGINS. USING NAM-GFS BLEND WITH TOP DOWN METHOD BROUGHT
SLIGHT CHC SLEET INTO THE SW CWA EARLY SAT MRNG...INCRSNG TO LIKELY
THERE IN THE AFTN WHILE WARMING AND TURNING TO RAIN. INCRSNG POPS
WILL SLOWLY SURGE NE ACROSS THE CWA DURING SAT AFTN-EVE WITH A
WINTRY MIX OF SLEET...SOME SNOW AND RAIN...TRANSITIONING TO RAIN
FROM THE SW THRU THE AFTN...EXCEPT PART OF THE NC N MTNS...
FOOTHILLS AND NW PIEDMONT WHERE IT COULD REMAIN MOSTLY SLEET. NOT
LOOKING AT SIG ACCUMS ATTM BUT WILL HAVE TO WATCH CLOSELY. TOP DOWN
METHOD ALSO SHOWS MOST OF AREA TURNING TO RAIN SAT NIGHT BUT N MTNS
AND NC FOOTHILLS COULD ALSO SEE SOME -FZRA AFTER MIDNIGHT UNTIL
AFTER DAYBREAK. THEN AS THKNS WARMS EXPECT RAIN SUN MRNG UNTIL
PRECIP TAPERS OFF IN THE AFTN WHEN SYSTEM MOVES OUT. TEMPS SUN AFTN
SHOULD THEN WARM INTO THE M40S.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 205 AM FRIDAY...THE OP MODELS ARE AGREEING BETTER WITH THE
OVERALL SYNOPTIC PATTERN...WITH THE GFS MAINTAINING A MORE DYNAMIC
AND DEEPER ULVL TROF OVER THE E COAST BY 12Z WED. WITH RELATIVELY
LOW GEFS SPREAD ASSOCIATED WITH THE S/RN STREAM AND THE LATE ECMWF
CUT OFF LOW NOT REALLY AFFECTING THE SENSIBLE WX OVER THE SE
REGION...AVERAGE OR A LITTLE ABOVE AVERAGE CONFIDENCE IS HAD IN
MAINTAINING GOOD CONTINUITY WITH THE PREVIOUS FORECAST.
A LOW AMPLITUDE RIDGE WILL BE QUICK TO BREAK DOWN AND MOVE EAST OF
THE AREA MON AS THE PATTERN REMAINS HIGHLY PROGRESSIVE. THERE SHOULD
STILL BE ENOUGH DRY AIR THROUGH A DEEP LAYER AND INSOLATION TO ALLOW
ALLOW MAX TEMPS RIGHT AROUND NORMAL...YET A FEW DEGREES LOWER THAN
THE OPTIMISTIC MEXMOS.
A GOOD PHASING IS ADVERTISED BY THE MODELS...ESP THE GFS...BETWEEN
THE S/RN AND N/RN SYSTEMS BY 06Z TUE. THIS SHOULD ALLOW PLENTY OF
GOOD GOM MOISTURE FLUX AND ISENTROPIC LIFT AHEAD OF THE SFC FRONT
AND A STRONG ULVL JET TO WORK WITH. THUS...THE HIGHEST QPF TOTALS
WILL BE EXPECTED BETWEEN 06Z-18Z TUE. THERE IS THE SUGGESTION OF A
MESO/LOW CROSSING THE NC MTNS EARLY TUE AND THE GFS CROSS SECTIONS
INDICATE A MODERATE AMOUNT OF ELCAPE THROUGH 18Z...SO THE INCLUSION
OF ISOL THUNDER WAS ADDED TO THE S/RN HALF OF THE CWFA THROUGH 18Z.
THE WRAP AROUND SN FEATURE IS STILL DEPICTED BY THE GFS AND LOOSELY
SUPPORTED BY THE ECMWF...SO CHC SN POPS ACROSS THE NRN MTNS
CONTINUES TO LOOK A GOOD BET...HOWEVER WITH THE FAST DYNAMIC
FLOW...LITTLE ACCUMULATION IS EXPECTED WITH MOST LIKELY A HIGHER
ELEVATION AC CUM OF AN INCH OR TWO.
BY WED MORN...ANOTHER ARCTIC HIGH MAKES ITS WAY TO THE EAST COAST
AND SLOWLY PUSHES EAST THROUGH THE REMAINDER OF THE EXT PERIOD. THIS
IS AGREEING WITH HPC/S ASSESSMENT OF THE GREENLAND BLOCK
TELECONNECTION THEORY AND BOTH OF THE OP MODELS ARE PICKING UP ON
THIS. SO...WILL EXPECT DRY CONDITIONS WED THROUGH THU WITH MAX TEMPS
A CAT OR TWO BELOW NORMAL.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AT KCLT/KHKY...WINDS SHOULD REMAIN LIGHT OUT OF THE NW FOR MUCH OF
THE DAY...BEFORE BECOMING CALM BY EVENING. OTHERWISE...EXPECT LITTLE
MORE THAN HIGH/THIN CLOUDS OVER THE AREA DURING THE NEXT 24 HOURS.
ELSEWHERE...NOCTURNAL WIND MAX DID INDEED DEVELOP AT KGSP/KGMU THIS
MORNING...WITH GUSTS AS HIGH AS 27 KT REPORTED EARLY THIS MORNING AT
KGSP. THESE WINDS TYPICALLY DIE DOWN MID-LATE MORNING AS DOWNSLOPE
DRAINAGE FROM THE MTNS SLOWS. BY EARLY AFTERNOON...WINDS SHOULD
BECOME LGT/VRBL IN THE SC FOOTHILLS IN RESPONSE TO LEE TROUGH. N/NW
WINDS SHOULD BE MORE PERSISTENT AT KAVL...BUT SHOULD GO CALM SHORTLY
AFTER SUNSET THIS EVENING.
OUTLOOK...VFR EXPECTED EARLY SATURDAY. A GULF COAST STORM SYSTEM
COULD SPREAD LIGHT MIXED PRECIP INTO THE REGION SATURDAY AFTERNOON
INTO THE NIGHT...WITH FLT RESTRICTIONS POSSIBLE INTO EARLY SUNDAY.
VFR CONDITIONS RETURN BY EARLY MONDAY BEFORE ANOTHER GULF COAST
SYSTEM AFFECTS THE AREA DURING MID-WEEK.
&&
.FIRE WEATHER...
RFW CONTINUES FOR NORTHEAST GA. TEMPS HAVE BEEN COOLED SLIGHTLY FROM
PREVIOUS FORECAST...BUT THIS IS HAVING VERY LITTLE EFFECT ON THE RH
FORECAST. IN FACT...RH SHOULD BOTTOM OUT IN THE 15-20 PERCENT RANGE
IN ALL AREAS THIS AFTERNOON. SOME LOCATIONS MAY EVEN DIP BELOW 15
PERCENT BRIEFLY. THE GOOD NEWS IS WIND SHOULDN/T BE MUCH OF AN ISSUE
THIS AFTERNOON.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...RED FLAG WARNING FROM 10 AM THIS MORNING TO 6 PM EST THIS
EVENING FOR GAZ010-017-018-026-028-029.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...SBK
NEAR TERM...JDL
SHORT TERM...RB
LONG TERM...SBK
AVIATION...JDL
FIRE WEATHER...JDL
