FXUS62 KGSP 251812
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
112 PM EST FRI DEC 25 2009
.SYNOPSIS...
WEAK HIGH PRESSURE WILL BUILD ACROSS THE SOUTHEAST STATES THROUGH
THE WEEKEND WHILE A LARGE UPPER LEVEL TROUGH CROSSES OVERHEAD. A
STRONG UPPER LEVEL RIDGE WILL THEN BRING IN MUCH COOLER HIGH
PRESSURE MONDAY AND DROP TEMPERATURES BLOW NORMAL THROUGH THE MIDDLE
OF NEXT WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
JUST TO KEEP ALL INTERESTED PARTIES IN THE LOOP...HAVE CANCELLED FZRA
ADVISORY WHERE TEMPS HAVE WARMED SUFFICIENTLY AND PARED BACK ICE
STORM WARNING AREA TO ACCOUNT FOR LINGERING AREAS OF WARNING LEVEL
ACCRETION ALONG THE BLUE RIDGE AND WILL ALLOW TO EXPIRE ON SCHEDULE.
STOUT SSE LLVL 85H JET TO TRANSLATE DOWNSTREAM OF THE AREA THIS
AFTERNOON AND LOOSENING/VARYING SFC PRES GRADIENT TO ALLOW ALL
WIND PRODUCTS TO EXPIRE ON SCHEDULE AS WELL. HAVE ISSUED SHORT
FUSED FLASH FLOOD WATCH TO ACCOUNT FOR WIDESPREAD HEAVY RAIN
AND EMBEDDED DEEP CONVECTION ALONG THE I-77 CORRIDOR UNTIL 4 PM. NEW
12 UTC NAM SBCAPE FCSTS POS VALUES SKIRTING BY JUST TO THE SE OF THE
CWFA THIS AFTERNOON...SO WILL PLAN ON KEEPING JUST ELEVATED TSTM
THREAT ACRS THE SE CWFA.
&&
.SHORT TERM /SATURDAY THROUGH MONDAY/...
AS OF 325 AM FRI...AN INTENSE UPPER LOW WILL ROTATE ACROSS THE
WESTERN GREAT LAKES STATES SAT AND SAT NITE. THE CWFA WILL BE UNDER
A STRONG SOUTHWESTERLY UPPER LEVEL FLOW...THOUGH THE AIRMASS WILL BE
QUITE DRY OVERALL. HIGHS SAT WILL BE ABOVE NORMAL WITH HIGHER
THICKNESSES AND MOSTLY SUNNY SKIES. LOWS SHOULD BE NEAR OR SLIGHTLY
BELOW NORMAL.
BY SUNDAY THE UPPER LOW WILL WILL BEGIN TO BE PICKED BACK UP BY THE
WESTERLIES...MOVING BRIEFLY TO THE SOUTH BEFORE LIFTING OFF TO THE
NORTH. AS THIS HAPPENS...SOME UPPER DIVERGENCE DEVELOPS OVER THE
AREA AS A SHORT WAVE SHOOTS ACROSS THE REGION. A WEAK GULF LOW
DEVELOPS AND MOVES EASTWARD. THIS BRINGS SOME MOISTURE INTO THE
AREA. HOWEVER...THE MOST OF THE GUIDANCE HAS NO TO VERY LOW POP. THE
EXCEPTION IS THE SREF WHICH HAS VERY HIGH POP WITH VERY LOW QPF.
WILL KEEP THE FCST DRY FOR NOW. HIGHS A LITTLE COOLER...BUT STILL
ABOVE NORMAL.
A STRONGER SHORT WAVE ROTATES AROUND THE DEPARTING LOW AND INTO THE
AREA SUN NITE. MOST OF THE AREA WILL REMAIN DRY. HOWEVER...IT WILL
BE THE BEST PERIOD FOR NW FLOW SNOW AS LOW LEVEL MOISTURE AND NWLY
FLOW INCREASE ACROSS THE MTNS. FOR NOW...HAVE KEPT POP IN THE CHC TO
SLIGHT CHC RANGE OVER THE USUAL AREAS. THE SNOW SHOWERS END BY
AFTERNOON MONDAY. RIGHT NOW...IT LOOKS LIKE LIGHT ACCUMULATIONS ARE
POSSIBLE. LOWS AND HIGHS BELOW NORMAL.
&&
.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
AS OF 315 AM FRIDAY...STILL NO SIGNIFICANT CHANGES TO THE GOING
MEDIUM RANGE FORECAST. THE FIRST PART OF THE PERIOD WILL GENERALLY
BE QUIET AS HIGH PRESSURE BUILDS IN FROM THE WEST UNDER RIDGING
ALOFT. MODEL SOLUTIONS RAPIDLY DIVERGE FROM TUESDAY NIGHT
ONWARD...PRIMARILY WITH THEIR HANDLING OF THE NEXT SOUTHERN STREAM
SYSTEM. THE COLLECTION OF GFS...ECMWF...AND GEM ALL HANDLE THE MID
AND UPPER LEVEL ENERGY DIFFERENTLY ESPECIALLY WITH REGARD TO TRACK
AND TIMING. THE GFS CONTINUES TO KEEP THE DEVELOPING GULF LOW
PRESSURE SYSTEM SUPPRESSED TO THE SOUTH AND KEEPS ACCUMULATING
PRECIP SOUTH AND EAST OF THE FA. HOWEVER...THE ECMWF TAKE THE LOW
SLOWLY ACROSS THE NORTHERN GULF AND UP THE EAST COAST SPREADING
PRECIP INTO THE WESTERN CAROLINAS AS EARLY AS WEDNESDAY. WITH THIS
SIGNIFICANT TIMING DIFFERENCE IN MIND THE END OF THE FORECAST
CONTINUES TO BE VERY LOW CONFIDENCE. I HAVE KEPT THE CHANCE POP IN
THE FORECAST FOR WEDNESDAY AND WEDNESDAY NIGHT WITH IT DRY UP TO
THAT POINT. AT THIS POINT...ATTEMPTING TO PREDICT PTYPE FOR SUCH A
LOW CONFIDENCE FORECAST IS SUCH A FUTILE EXERCISE THAT I WILL
HANDLE WX AS RAIN OR SNOW FOR NOW.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...WILL HANG MY HAT ON THE NAM/S HANDLING OF SENSIBLE
WX BEHIND DEPARTING PCPN SHIELD...WITHIN LINGER WEAK DAMMING
REGIME. USING NAM GUIDANCE...WOULD EXPECT NNE WINDS TO GRADUALLY
BACK AND WEAKEN INTO THIS EVENING...WITH NO CIG IMPROVEMENT. IT IS
QUESTIONABLE WHETHER ENUF WIND WILL LINGER TO PREVENT WIDESPREAD
FOG DEVELOPMENT...ESPECIALLY AS THE NIGHT WEARS ON AND DRYING
ABOVE THE SFC INCREASES. EXPECT A RETURN TO VFR BY MID-MORNING
SATURDAY AS WINDS BECOME WSW.
ELSEWHERE ACRS THE FA...AGAIN WILL BASE THE FORECAST ON THE
LINGERING WEAK WEDGE CONDITIONS PROGGED BY THE NAM. EXPECTING
LOW CIGS TO CONTINUE INTO TONIGHT WITH THE PROBABILITY THAT FOG
BECOMES WIDESPREAD AS DRYING ABOVE THE SFC INCREASES. EXPECTING
VFR CONDITIONS TO RETURN BY MID-MORNING.
OUTLOOK...VFR CONDITIONS EXPECTED SATURDAY THRU TUE. MOISTURE AHEAD
OF A WEAK COLD FRONT WILL RETURN TO THE FA ON WEDNESDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...FLASH FLOOD WATCH UNTIL 4 PM EST THIS AFTERNOON FOR NCZ035>037-
056-057-069>072-082.
SC...FLASH FLOOD WATCH UNTIL 4 PM EST THIS AFTERNOON FOR SCZ009-014.
&&
$$
SYNOPSIS...BSH
NEAR TERM...CSH/JAT
SHORT TERM...RWH
LONG TERM...BSH
AVIATION...CSH/JAT
