FXUS62 KGSP 090540
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1240 AM EST WED DEC 9 2009
.SYNOPSIS...
A STORM SYSTEM MOVING FROM THE PLAINS TO THE MIDWEST TONIGHT WILL
PULL DEEP MOISTURE AND PRECIPITATION ACROSS THE WESTERN CAROLINAS
AND NORTHEAST GEORGIA. A COLD FRONT WILL SWEEP THROUGH EARLY
WEDNESDAY WHICH WILL USHER IN STRONG WINDS AND COOLER TEMPERATURES.
A LARGE AREA OF HIGH PRESSURE WILL BUILD IN FROM THE WEST ON
THURSDAY AND WILL MOVE OVERHEAD ON FRIDAY. ANOTHER LOW PRESSURE
SYSTEM WILL ORGANIZE OVER THE GULF OF MEXICO FRIDAY NIGHT AND SHOULD
PASS BY JUST TO OUR SOUTH ON SATURDAY. THE LOW WILL MOVE AWAY SUNDAY
AS ANOTHER ARCTIC HIGH BUILDS IN FOR EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
FIRST THINGS FIRST...A CALL TO AVERY COUNTY COMMS HAS UNVEILED AN
ONGOING FZRA EVENT...WITH ICE ACCRETION OCCURRING ON ELEVATED
SURFACES. FORTUNATELY...TEMPS WILL BE TOO WARM FOR SIGNIFICANT ICING
TO OCCUR ON ROADWAYS...AND TEMPS WILL GRADUALLY WARM OVERNIGHT AS THE
COLD DOME GRADUALLY ERODES FROM THE TOP DOWN. A WINTER WX ADVISORY
FOR FZRA HAS ALREADY BEEN ISSUED THRU 3 AM.
OTHERWISE...WIDESPREAD LIGHT TO MODERATE RAIN CONTINUES WITHIN WARM
CONVEYOR BELT REGION OF MAJOR PLAINS CYCLONE. THE BACK EDGE OF THE
UPGLIDE PRECIP IS ALREADY CROSSING THE UPPER SAVANNAH RIVER VALLEY
AS OF 0230Z. HOWEVER...FORCING/MOISTURE REMAINS MORE THAN ADEQUATE
TO SUPPORT NUMEROUS COVERAGE OF SHOWERS ACROSS THE CWFA PRIOR TO THE
ARRIVAL OF FRONTAL FORCING LATER TONIGHT. PRECIP TOTALS HAVE BEEN
RESPECTABLE THIS EVENING...BUT HARDLY ANYTHING TO GET TOO CONCERNED
ABOUT...GENERALLY IN THE .75-1.0 RANGE. ADDITIONAL AMOUNTS OF .5-1.0
INCH ARE EXPECTED OVERNIGHT...ESP ACROSS THE MTNS OF NE GEORGIA AND
SW NC. IF THERE IS A FLOODING CONCERN OVERNIGHT...THIS IS WHERE IT
WILL BE. HOWEVER...DO NOT EXPECT QPF TO BE SIGNIFICANT ENOUGH FOR AN
ORGANIZED FLOODING THREAT...BUT CANNOT ALTOGETHER RULE OUT LOCALIZED
FLOODING IN ASSOCIATION WITH CONVECTIVE ELEMENTS WITHIN THE FRONTAL
BAND.
FINALLY...THE WIND CONCERN. GIVEN THE WARM ADVECTION/SOUTHERLY
NATURE OF THE SITUATION...STRONG WINDS OVERNIGHT SHOULD BE RELEGATED
TO THE RIDGES/PEAKS OF THE NC MTNS. HOWEVER...CONVECTIVE ELEMENTS
WITHIN THE FRONTAL BAND MAY MIX POCKETS OF STRONGER WINDS DOWN TO
THE VALLEY FLOORS. FORTUNATELY...IT APPEARS THAT THE STRONGEST CORE
OF THE LLJ WILL BE SLIGHTLY DOWNSTREAM OF THE FRONTAL FORCING...SO
DEVELOPMENT OF WIDESPREAD WIND PROBLEMS IN THE MTNS SHOULD REMAIN
LOW PRIOR TO SUNRISE.
WEDNESDAY...NEAR TERM MODELS INDICATE THAT A COLD FRONT WILL SWEEP
ACROSS THE REGION BETWEEN 10Z-18Z. WEAK INSTABILITY ALONG AND AHEAD
OF THE FRONT MAY SUPPORT A FEW TSRA DURING THE MORNING. FORECAST
SOUNDINGS INDICATE THAT THE ATMOSPHERE WILL FEATURE VERY HIGH SHEAR
WITH WEAK ELEVATED CAPE. I BELIEVE THAT A MINIMAL RISK FOR SEVERE
TSRA EXISTS...WE WILL CONTINUE TO MENTION IN THE HWO. RAINFALL WILL
GRADUALLY DIMINISH ACROSS THE CWA WITH THE PASSAGE OF THE FRONT.
STORM TOTAL RAINFALL IS FORECAST TO RANGE FROM 2 INCHES ACROSS THE
RIDGES TO 1-1.25 ACROSS THE NC PIEDMONT. FLOODING BEYOND POOR
DRAINAGE AND SMALL CREEKS IS NOT EXPECTED AT THIS POINT...WE WILL
CONTINUE TO HIGHLIGHT IN THE HWO. HIGH TEMPERATURES ARE FORECAST TO
RANGE FROM THE 50S ACROSS THE MTNS TO MID 60S EAST.
WINDS WILL BE THE HEADLINE TO WEDNESDAY/S FORECAST. NEAR TERM MODELS
INDICATE A LARGE H7 80-100 KTS JET WILL STREAK ACROSS THE CWA
TOMORROW AFTERNOON. FORECAST SOUNDINGS SHOW THE POTENTIAL FOR MIXING
TO INCREASE TO 5 KFT IN THE WAKE OF THE COLD FRONT. THIS WOULD ALLOW
SIGNIFICANT MOMENTUM TRANSFER TO OCCUR WITH THE PASSAGE OF THE
AFTERNOON LLVL JET. I WILL FORECAST WIDESPREAD AND PERSISTENT GUSTS
INTO THE 30-35 KT RANGE. HOWEVER...PEAK AFTERNOON GUSTS WILL LIKELY
FALL IN THE 40-50 KTS RANGE ACROSS THE CWA...ESPECIALLY ACROSS THE MTNS.
THIS FORECAST SUPPORTS ADVISORY LEVEL WINDS...BUT REMAINS MARGINAL
FOR A HIGH WIND WARNING. HOWEVER...THE RECENT MODERATE RAIN WILL
SATURATE THE SOIL AND COULD RESULT IN WIDESPREAD TREE AND POWER LINE
DAMAGE. THIS WOULD BE VERY SIMILAR TO THE NOVEMBER 10TH-11TH EVENT. WE
WILL ISSUE A HIGH WIND WARNING FOR THE MTNS AND A HIGH WIND WATCH
FOR THE FOOTHILLS AND PIEDMONT FROM 6 AM UNTIL 7 PM TOMORROW.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY/...
AS OF 105 PM TUESDAY...THE BALANCE OF THE SHORT RANGE THROUGH THE
END OF THE DAY FRIDAY LOOKS QUIET. WE BEGIN WITH A SMALL POSSIBILITY
OF SOME UPSLOPE PRECIP OVER THE NRN MTNS OF NC ON WEDNESDAY EVENING.
HOWEVER...THE FLOW AT 850MB IS ACTUALLY SOUTH OF WEST...WHICH IS NOT
AS FAVORABLE FOR PRECIP GENERATION. THE COLD AIR WILL MOVE IN AFTER
SUNSET WHICH SHOULD CHANGE THE PRECIP OVER FROM LIQUID TO SOLID
BEFORE IT COMES TO END AROUND MIDNIGHT. NO MORE THAN A DUSTING IS
EXPECTED AT HIGH ELEVATIONS.
OTHERWISE...WE REMAIN AT THE BASE OF A LONG WAVE UPPER TROF THROUGH
THE PERIOD...WHICH ESSENTIALLY KEEPS OUR FLOW ALOFT FAST AND NEARLY
ZONAL. THE CORE OF THE UPPER JET WILL REMAIN TO OUR N SO EXPECT TO
SEE PATCHES OF MID/HIGH CLOUDS MOVING THROUGH WITH JET STREAKS. THE
TEMPS ARE THE MAIN CONCERN. WENT WITH THE COOLER GUIDANCE WEDNESDAY
NIGHT WITH THE HIGH BUILDING IN. THE NEW GUIDANCE IS RIGHT IN LINE
WITH THE OLD FORECAST FOR THURSDAY AND THURSDAY NIGHT SO ONLY MINOR
CHANGES WERE MADE. ON FRIDAY...A SURFACE HIGH OF ARCTIC ORIGIN WILL
MOVE OVERHEAD. THE AIR MASS WILL BE HIGHLY MODIFIED BY THEN...BUT
STILL UNDERCUT THE GUIDANCE WHICH KEEPS TEMPS IN THE LOW/MID 40S FOR
HIGHS. EXPECT TO SEE IT CLOUD UP IN THE AFTERNOON AS WELL.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 315 PM TUESDAY...THE MEDIUM RANGE WILL REMAIN ACTIVE WITH A
SIGNIFICANT SYSTEM AT BOTH ENDS. THE PERIOD BEINGS FRIDAY NIGHT WITH
BROADLY CONFLUENT AND NEARLY ZONAL FLOW ALOFT WHICH WILL PERSIST
THROUGH THE WEEKEND. THE PATTERN BEGINS TO AMPLIFY TUESDAY INTO
WEDNESDAY AS A SHARP MID AND UPPER LEVEL TROF MOVES ACROSS THE
SOUTHERN PLAINS. SIGNIFICANT DIFFERENCES BETWEEN THE MODELS ARE
PRESENT MAINLY IN THE FORM OF TIMING THE TWO SYSTEMS. THE GFS AND
GEM AND ARE DEFINITELY THE FAST SOLUTIONS COMPARED TO THE 12Z ECMWF
AND GENERALLY RUN 12 TO 24 HOURS AHEAD. I HAVE GENERALLY FOLLOWED
THE ECMWF FOR THE DETAILS OF THE FORECAST.
THE FIRST SYSTEM WILL AFFECT THE FA ON SATURDAY. IT BEGINS WITH A
SURFACE HIGH CENTERED JUST TO THE EAST WITH A LOW DEVELOPING OVER
THE NW GULF. MOISTURE BEGINS TO SPREAD OVER THE TOP OF THE WEDGE ON
SATURDAY BUT THE ECMWF ONLY BRINGS MEASURABLE PRECIP AS FAR NORTH AS
THE NC/SC STATE LINE. THIS IS DEFINITELY SLOWER THAN ITS PREVIOUS
RUN AND I HAVE KEPT THINGS DRY THROUGH 12Z SATURDAY. AN AREA OF
UPPER DIVERGENCE IN THE ENTRANCE REGION OF A STRONG JET STREAK OVER
THE MID ATLANTIC...COMBINED WITH GOOD ISENTROPIC LIFT OVER THE TOP
OF THE WEDGE WILL BE THE MAIN COMPONENTS OF FORCING. LOW LEVEL
THICKNESS VALUES WILL SUPPORT SOME DEGREE OF MIXED PRECIP DURING THE
ONSET ACROSS MUCH OF THE AREA. I HAVE GENERALLY WARMED MIN TEMPS
FRIDAY NIGHT FROM THE PREVIOUS FORECAST EXPECTING CONSIDERABLE HIGH
CLOUDINESS AND THIS RESULTS IN TEMPS NEAR FREEZING DURING THE ONSET.
VIGOROUS WAA AT H85 WILL CREATE A DEFINITIVE WARM NOSE MAKING THE
PTYPE SOME MIX OF FREEZING RAIN AND SLEET. THIS SHOULD BE FAIRLY
SHORT LIVED AND DO NOT...AT THIS POINT...EXPECT MUCH MORE THAN A
NUISANCE EVENT FOR A FEW HOURS. POPS WILL FAVOR THE SOUTHEASTERN TWO
THIRDS OF THE FA AS THE BULK OF THE PRECIP WILL REMAIN CONFINED
CLOSER TO THE SURFACE LOW NEAR THE COAST. SOME LINGERING LIGHT
PRECIP SATURDAY NIGHT BEFORE THE LOW PULLS AWAY TO THE NORTHEAST SO
WILL CARRY A BLANKET CHANCE POP.
THE SECOND SYSTEM IS PROGGED TO AFFECT THE FA AT THE END OF THE
FORECAST PERIOD...BUT THIS IS ALSO WHERE THE GREATEST TIMING
DIFFERENCES ARE PRESENT IN THE MODEL SOLUTIONS. AT ANY RATE...THIS
EVENT APPEARS TO BE MUCH MORE DYNAMIC THAN THE SATURDAY EVENT. THERE
IS A MUCH MORE PRONOUNCED MID AND UPPER LEVEL SHORTWAVE...AS WELL AS
A MUCH MORE CLASSIC POSITIONING OF THE DAMMING HIGH TO THE NORTHEAST.
THICKNESSES ON BOTH THE ECMWF AND THE GFS WOULD SUPPORT WINTRY
PTYPES BUT AT THIS POINT WILL LEAVE AS RA/SN. ANOTHER SIGNIFICANT
DIFFERENCE REVOLVES AROUND THE STRENGTH OF THE PARENT HIGH WHICH IS
1036MB ON THE GFS AND 1023MB ON THE ECMWF. WILL CARRY A SHOTGUN
CHANCE POP FOR NOW...WAITING FOR MORE MODEL CONSISTENCY TO NAIL DOWN
THE DETAILS.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...NE WINDS AND IFR CIGS EXPECTED TO CONTINUE INTO
THE LATE NIGHT HOURS WITH AT LEAST OCNL VSBY RESTRICTIONS DUE TO
AREAS OF RAIN CONTINUING TO DEVELOP AND MOVE NE ACRS THE PIEDMONT.
STRONG LLVL JET TRANSLATING EAST ACRS THE FA WILL RESULT IN VERY
STRONG WIND GUSTS JUST ABOVE THE SFC. SFC FRONTAL BAND TO APPROACH
DURING THE PRE-DAWN HOURS AND WINDS EXPECTED TO SHIFT TO SW IN
RESPONSE. DRYING BEHIND THE COLD FRONT TO RAPIDLY DIMINISH RAINFALL
CVRG BY MID-MORNING...AS STRONG SW WIND GUSTS MIX DOWN TO THE SFC AND
LINGER INTO THE AFTERNOON.
ELSEWHERE ACRS THE FA...WIDESPREAD RAIN WILL LINGER ACRS THE
MOUNTAINS AND FTHLS INTO THE LATE HOURS BEFORE A PRE-DAWN COLD
FRONTAL APPROACH AND SUBSEQUENT PASSAGE CAUSES RAIN TO DIMINISH.
STRONG LLVL JET TRANSLATING EAST ACRS THE FA WILL RESULT IN VERY
STRONG WIND GUSTS JUST ABOVE THE SFC...WHICH WILL WORK DOWN TO THE
SFC LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON.
OUTLOOK...VFR EXPECTED TONIGHT THROUGH FRIDAY...ALTHOUGH GUSTY WINDS
MAY LINGER MUCH OF TUE NIGHT...ESPECIALLY ACRS THE MOUNTAINS. A GULF
COAST STORM SYSTEM COULD SPREAD LIGHT MIXED PRECIP INTO THE REGION
ON SATURDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...HIGH WIND WARNING FROM 6 AM THIS MORNING TO 7 PM EST THIS
EVENING FOR GAZ010-017.
WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR GAZ010-017.
HIGH WIND WATCH FROM 6 AM EST THIS MORNING THROUGH THIS
EVENING FOR GAZ018-026-028-029.
NC...HIGH WIND WARNING FROM 6 AM THIS MORNING TO 7 PM EST THIS
EVENING FOR NCZ033-048>053-058-059-062>065-501-503-505-
507-509.
WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR NCZ033-
048>053-058-059-062>065-501-503-505-507-509.
FREEZING RAIN ADVISORY UNTIL 3 AM EST EARLY THIS MORNING FOR
NCZ033-501-503.
HIGH WIND WATCH FROM 6 AM EST THIS MORNING THROUGH THIS
EVENING FOR NCZ035>037-056-057-068>072-082-502-504-506-
508-510.
SC...HIGH WIND WATCH FROM 6 AM EST THIS MORNING THROUGH THIS
EVENING FOR SCZ001>014-019.
&&
$$
SYNOPSIS...PM
NEAR TERM...JDL/NED
SHORT TERM...PM
LONG TERM...BSH
AVIATION...CSH/JDL
