FXUS62 KGSP 071948
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
248 PM EST MON DEC 7 2009
.SYNOPSIS...
MOISTURE WILL SPREAD ACROSS THE FORECAST AREA FROM THE WEST ON
TUESDAY AS A STRONG LOW PRESSURE SYSTEM ORGANIZES OVER THE PLAINS.
THIS LOW WILL MOVE NORTHEASTWARD TOWARD THE GREAT LAKES TUESDAY
NIGHT...PUSHING A COLD FRONT ACROSS THE SOUTHERN APPALACHIANS ON
WEDNESDAY. A LARGE AREA OF HIGH PRESSURE WILL BUILD IN FROM THE WEST
ON THURSDAY AND REMAIN OVER THE CAROLINAS THROUGH THE START OF THE
WEEKEND.
&&
.NEAR TERM /THROUGH TUESDAY/...
POWERFUL LOW PRESSURE WILL BEGIN TO DEVELOP OVER THE SOUTHERN
ROCKIES TONIGHT. EAST OF THE LOW...WARM AIR ADVECTION AND GULF
MOISTURE WILL SURGE ACROSS THE DEEP SOUTH BETWEEN 6-12Z. ANY
MEASURABLE PRECIPITATION SHOULD REMAIN WEST OF THE FORECAST AREA
THROUGH MOST OF THE NIGHT. HOWEVER...H85 WINDS WILL BECOME SOUTHWEST
LATE TONIGHT AND MAY SUPPORT A FEW SHRA ACROSS THE HIGH
TERRAIN...THESE SHOWERS MAY YIELD ONLY A FEW HUNDREDTHS OF AN INCH.
USING A BLEND OF GFS40 AND SREF...I WILL KEEP MIN TEMPS ACROSS THE
ENTIRE FORECAST AREA IN THE MID TO UPPER 30S.
TUESDAY...WEAK HIGH PRESSURE WILL REMAIN RIDGED ACROSS THE CWA. FLOW
AROUND PLAINS LOW PRESSURE SHOULD GRADUALLY STRENGTH LLVL WINDS
ACROSS THE CWA. DURING THE MORNING...UPSLOPE SHOWERS WILL GRADUALLY
INCREASE ACROSS THE FOOTHILLS AND PIEDMONT. DURING THE
AFTERNOON...EXPANDING ISENTROPIC LIFT ACROSS CAD LAYER AND SYNOPTIC
FORCING WILL SUPPORT LIKELY TO WIDESPREAD RA. AT THIS POINT...I WILL
FORECAST CATE POPS ACROSS THE MTNS AND FOOTHILLS RANGING TO LIKELY
POPS EAST. QPF AMOUNTS SHOULD FAVOR A QUARTER OF IN INCH BY 0Z WED.
INCREASING RAIN...THICK CLOUD COVER...AND PERSISTENT NORTHEAST WINDS
SHOULD KEEP HIGH TEMPERATURES LIMITED TO THE L40S ACROSS THE MTNS
AND MID TO U40S ACROSS THE FOOTHILLS AND PIEDMONT.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 215 PM MONDAY...STILL EXPECTING A STRONG SHORT WAVE TO LIFT
FROM THE PLAINS LATE TUESDAY TO THE GREAT LAKES LATE WEDNESDAY. BY
THE TIME THE SHORT RANGE BEGINS AT 00Z WEDNESDAY...UPPER DIVERGENCE
AND ISENTROPIC LIFT SHOULD BE WELL ON THEIR WAY TO FORCING A LARGE
AREA OF RAIN INVADING FROM THE SOUTHWEST. A CATEGORICAL POP IS AN
EASY AND SAFE BET. HOWEVER...THERE ARE SEVERAL FORECAST ISSUES
TUESDAY NIGHT. STRONG LOW LEVEL UPGLIDE/UPSLOPE AND MOISTURE
TRANSPORT FROM THE SOUTH SUGGEST ANOTHER HEAVY RAIN THREAT OVER NE
GEORGIA...THE WRN UPSTATE...AND THE SRN NC MOUNTAINS. STUCK CLOSE TO
THE HPC GUIDANCE ON RAINFALL AMOUNTS WHICH PUTS AN AXIS OF HEAVY
RAIN ALONG/NEAR THE BLUE RIDGE NEAR THE SC/NC BORDER. WE HAVE ENOUGH
TIME TO PLAY WITH BEFORE THE PRECIP BEGINS TO HOLD OFF WITH A FLASH
FLOOD WATCH AT THIS TIME. HIGH ELEVATION WIND IS ANOTHER CONCERN.
THE LATEST GUIDANCE SUGGESTS TWO LOW LEVEL JET CORES...ONE OF WHICH
TRANSLATES PAST TO OUR SOUTH AND THE OTHER OF WHICH LIFTS N THROUGH
THE TN VALLEY. THIS LEAVES OUR MTNS IN A RELATIVE LULL...WHICH STILL
BRINGS WIND GUST POTENTIAL CLOSE TO WARNING CRITERIA. FOR NOW...THE
WARM ADVECTION PATTERN STILL FAVORS ADVISORY LEVEL WIND AND IT
REMAINS TOO EARLY TO ISSUE ONE. SEVERE WEATHER IS THE THIRD THREAT
AS SHEAR WILL BE EXTREME...BUT THE DEGREE OF BUOYANCY IS VERY MUCH
IN DOUBT. IN FACT...THE NAM SUGGESTS WE WILL NOT REALIZE ANY
BUOYANCY BECAUSE OF THE LINGERING COOL POOL E OF THE MTNS. THE GFS
LOOKS MORE REASONABLE WITH SOME LIMITED WEAK BUOYANCY ESSENTIALLY
ALONG/S OF I-85. WILL CONTINUE TO FEATURE THE POSSIBILITY IN THE
HWO. OTHERWISE...EXPECT TEMPS TO RISE SLOWLY AFTER MIDNIGHT AS WARM
ADVECTION AND PRECIP MODIFY THE COOL POOL.
THE TIMING OF THE BACK END OF THE PRECIP ACCORDING TO A BLEND OF
MODEL GUIDANCE IS SUCH THAT A LIKELY POP WILL HAVE TO BE RETAINED
FOR THE EASTERN ZONES ON WEDNESDAY MORNING. EXPECT A FASTER END TO
THE PRECIP THAN WHAT MIGHT CURRENTLY BE SUGGESTED BY THE FORECAST
GRIDS AS DRY AIR WRAPS IN QUICKLY IN THE AFTERNOON. THIS WILL BE
FINE TUNED BY LATER SHIFTS. TEMPS WILL REBOUND NICELY ON WEDNESDAY
WITH DOWNSLOPE E OF THE MTNS. SOME UPSLOPE SHOWERS MAY LINGER ON THE
TN BORDER INTO WEDNESDAY EVENING...BUT MOISTURE IS NOT GREAT AND
WIND DIRECTION IS TOO WESTERLY FOR MUCH PRODUCTION.
THE REMAINDER OF THE SHORT RANGE IS RELATIVELY QUIET. A FAST MOVING
NEARLY ZONAL FLOW WILL PERSIST ACROSS THE REGION THURSDAY AND FRIDAY
WHICH WILL SUPPORT A DRY AND COOL SURFACE HIGH. THIS WILL KNOCK OUR
TEMPS DOWN A GOOD TEN DEGREES FOR HIGHS ON THURSDAY...AND ANOTHER
5-10 DEGREES FOR FRIDAY.
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AS OF 230 PM SUNDAY...USED ECMWF/GFS BLEND SAT-MON...FAVORING THE
ECMWF IN LINE WITH HPC. SFC HI MOVES OFFSHORE FRI NIGHT-SAT WITH A
WEDGE OF COOLER AIR RIDGING INTO THE AREA FROM THE NE. AT THE SAME
TIME...A SFC LOW DEEPENS IN THE N GULF AND TRACKS E TOWARD THE LOWER
SAVANNAH VLY. WEDGE REMAINS IN PLACE AS MOISTURE TRACKS NE AND POPS
WILL INCREASE FROM THE SW FRI NIGHT. MODEL SOUNDINGS...THKNS
PROFILES...ETC CONTINUE TO INDICATE A WINTRY MIX WITH CHC SNOW
DEVLOPING FRI EVE NC MTNS...N FOOTHILLS AND NW PIEDMONT...AND A
RAIN/SNOW MIX ELSEWHERE. SLEET IS EXPECTED TO DEVELOP OVER NE GA
AND UPSTATE SC AS SFC TEMPS COOL WITH IN-SITU STRENGTHENING OF CAD.
MUCH OF CWA IS LIKELY TO SEE SLEET BEFORE BULK OF AREA WARMS ENOUGH
DURG DAY SAT FOR A COLD RAIN...WHILE SOME SLEET COULD CONT OVER SOME
MTN AREAS. CHC POPS CONT SAT NIGHT WITH MODELS SHOWING WEDGE HOLDING
ON AND SFC TEMPS COOLING ENOUGH FOR SOME FREEZING RAIN TO DEVELOP.
POPS DIMINISH SUN AND PRECIP SHOULD WARM TO ALL RAIN BEFORE ENDING
IN THE AFTN. TEMPS STAY BELOW AVG SAT-SUN. MOISTURE MOVES E OF AREA
SUN NGT-MON WITH MID-LEVEL RIDGE BUILDING OVER REGION AND TEMPS ARE
EXPECTED TO WARM TO NEAR AVG MON AFTN.
&&
.AVIATION /20Z MONDAY THROUGH SATURDAY/...
AT KCLT...AT 1745Z...SATELLITE IMAGE INDICATES A BAND OF MVFR
CEILINGS ALONG AND EAST OF I-85 ACROSS SC. BASED ON THE IMAGE AND
LATEST OBS...THE TIP OF THE BAND WAS LOCATED NEAR KUZA. MVFR
MOISTURE WILL REMAIN OVER THE TERMINAL...POSSIBLY ALLOWING PERIODS
OF SCT TO BKN MVFR CEILINGS THROUGH MID AFTERNOON. I WILL HIGHLIGHT
POSSIBLE MVFR CONDITIONS WITH A TEMPO FROM 18Z-20Z.
OVERNIGHT...CALM TO LIGHT WINDS WILL REMAIN ACROSS THE TERMINAL.
LIGHT WINDS...MID TO HIGH CEILINGS...AND LOW DEWPOINT DEPRESSION MAY
A ALLOW A LIGHT PRE DAWN FOG TO DEVELOP. BY 14Z...NORTHEAST WINDS
MAY STRENGTHEN TO 6-9 KTS WITH INCREASING CLOUDS AROUND 050 KFT.
ELSEWHERE...A BAND OF MVFR CEILINGS WILL REMAIN ALONG AND EAST OF
I-85 TROUGH 20Z. CEILINGS MY MIX TO 030-040 BY LATE AFTERNOON AND
REMAIN INTO THE LATE EVENING. WINDS ARE FORECAST TO REMAIN CALM TO
LIGHT AND VARIABLE THROUGH TONIGHT. AFTER SUNRISE...WINDS SHOULD
BECOME NORTHEAST AROUND 6-9 KTS. LOWER CEILINGS AND PATCHES OF RA
WILL ADVANCE ACROSS THE WESTERN CAROLINAS FROM THE SOUTHWEST. RA MAY
REACH KAVL AND KAND BY 14Z...AND WITHIN THE VICINITY OF KGSP AND KGMU
BY THE END OF THE TAF PERIOD.
OUTLOOK...WIDESPREAD CEILING AND VISIBILITY RESTRICTIONS WILL SPREAD
ACROSS THE REGION TUESDAY EVENING AND SHOULD REMAIN TUESDAY NIGHT. A
COLD FRONT WILL SWEEP EAST OF THE CWA BY MID WEDNESDAY
MORNING...FOLLOWED BY GUSTY WEST-SOUTHWEST WINDS. VFR EXPECTED
WEDNESDAY INTO WEDNESDAY NIGHT.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...RB
AVIATION...NED
