236
FXUS62 KGSP 042339
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
739 PM EDT SAT JUL 4 2009
SYNOPSIS
A WEAK COLD FRONT WILL APPROACH THE AREA FROM THE WEST EARLY SUNDAY.
THEN GRADUALLY MOVE SOUTHEAST THROUGH THE CAROLINAS ON MONDAY. WEAK
HIGH PRESSURE WILL BUILD IN DURING THE EARLY PART OF NEXT WEEK.
NEAR TERM /THROUGH SUNDAY/
SURFACE LOW PRESSURE WAS LOCATED OVER NW MO AS OF 1700 UTC SAT. BOTH
THE NAM AND GFS MOVE THIS LOW ESE OVERNIGHT AND SUNDAY. FAIRLY
WIDESPREAD STRATIFORM RAIN WITH EMBEDDED TSTMS WILL DEVELOP NORTH OF
THE LOW CENTER. THIS ACTIVITY SHOULD STAY NORTH OF THE FA...IN LINE
WITH THE NAMS AREA OF STRONGEST H4-H2 DIVERGENCE. MCS ACTIVITY IS
LIKELY ALONG AND SOUTH OF THE LOW. THERE IS A LARGE AREA OF
DRY...STABLE AIR OVER AL...NRN AND CENTRAL GA...SC AND NC. A SHARP
MOISTURE DISCONTINUITY IS FOUND SOUTH OF THIS AREA. THIS MOIST AIR
WILL INITIALLY LIFT OUT OF THE GULF OVER MS AND TN...BEFORE
SPREADING INTO OUR REGION LATE SUNDAY. AS RESULT...THE GFS MCS
ACTUALLY DROPS SOUTH AND BACKBUILDS OVERNIGHT INTO THAT UNSTABLE
AIR...EVEN THOUGH GOOD LLVL WARM ADVECTION DEVELOPS OVER THE WARM
SECTOR LATE TONIGHT. THE NAM DOES SOMETHING SIMILAR...THOUGH IT/S
MCS IS MORE PROGRESSIVE...JUST BARELY CLIPPING THE SW PART OF THE FA
BY AROUND 1200 UTC.
BASED ON THE STRONG WAA AND GOOD DEEP LAYER SHEAR...I THINK A
NON-SEVERE MCS IS STILL LIKELY TO ROLL INTO THE MTNS BY...OR A
LITTLE AFTER...SUNRISE TOMORROW. HOWEVER...THE PCPN WON/T BE NEARLY
AS HEAVY AS IT WILL BE BOTH NORTH AND SOUTHWEST OF THE FA. THIS WILL
STILL WARRANT HIGH POPS...PROBABLY IN THE LIKELY RANGE...BUT A LOW
QPF.
THINGS ARE MORE UNCERTAIN LATER IN THE DAY ON SUNDAY. SO MUCH
DEPENDS ON HOW MUCH DEBRIS CLOUDS AND STRATIFORM RAIN AFFECTS THE
REGION IN THE MORNING. IF THE MORNING ACTIVITY IS WEAK AND WE SEE A
FAIR AMOUNT OF SUN...THEN THERE IS A GOOD CHANCE OF REDEVELOPMENT IN
THE AFTERNOON. THE BULK SHEAR LOOKS WEAK...BUT THAT ALSO DEPENDS ON
EXACTLY WHERE ANY REMNANT MCV/S TRACK. WITH A WARM FRONT LIFTING
FROM THE SOUTH...A COLD FRONT CLOSING IN ON I-40 TO THE NORTH...AND
OUTFLOW BNDRY/S JUST ABOUT EVERYWHERE...WE WON/T BE LACKING FOCUSING
MECHANISMS. I/LL KEEP LIKELY POPS GOING THROUGH THE DAY. IF THE MCS
IS A LITTLE SLOWER THAN I THINK...IT MIGHT EVEN STRENGTHEN AS IT
CROSSES THE FA. HOWEVER...THE LACK OF SUPPORT FOR THIS IDEA FROM THE
GFS...NAM AND NCEP/S 4KM WRF HAS ME SKEPTICAL.
SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/
AS OF 210 PM SATURDAY...THE REMNANT MCS WILL BE CROSSING EASTERN
PARTS OF THE FORECAST AREA INTO SUNDAY EVENING AND MOVING EAST OF
OUR AREA AS THE FRONT DRAPES DOWN FROM WEST TO EAST AND SLOWLY MOVES
SOUTH. WENT WITH THE SREF MODEL AS IT SEEMS TO BE A GOOD BLEND OF
EACH AND MAINTAINS SOME CONSISTENCY WITH LITTLE LOWLETS MOVING ALONG
THE FRONT. THERE WILL BE LITTLE INSTABILITY BUT CONTINUED THE
POSSIBILITY OF SCATTERED THUNDER DEPENDING ON COMBINATION OF FRONTAL
POSITION AND FOCUS FROM THE LITTLE LOW CENTERS. THE FRONT SHOULD BE
MOVING SOUTH OF THE PIEDMONT LATE MONDAY AND ALL RAIN ENDING FROM
THE NORTH. DRIER AIR WILL MOVE INTO MID WEEK WITH TEMPERATURES NEAR
NORMAL.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
AS OF 220 PM SATURDAY...CONFIDENCE IS TOWARD THE ECMWF MODEL DURING
THE LAST HALF OF THE WEEK AS THE OLD FRONTAL BOUNDARY SLOWLY WASHES
OUT NEAR THE GULF COAST. THE RIDGE MAINTAINS DRY WEATHER FOR OUR
AREA WITH A SLOW INCREASE IN DIURNAL CONVECTION MAINLY OVER THE
HIGHER TERRAIN. THE EC SHOWS THE AXIS OF THE 500MB SHORTWAVE
PASSING OVER THE NORTHEAST AND UPPER MID ATLANTIC LATE WEDNESDAY.
NOT SURE IF THE TIMING WILL PAN OUT...BUT THIS COULD ENHANCE THE
DIURNAL CONVECTION A BIT. THE NEXT WEAK COLD FRONT SHOULD REACH THE
SOUTHERN APPALACHIANS NEXT SATURDAY NIGHT AND SUNDAY...AT THE VERY
END OF THIS FORECAST PACKAGE. I HAVE INCREASED POPS A BIT AS THE
FRONTAL CONVECTION MOVES INTO THE AREA. THE 12Z RUN OF THE GFS DOES
MORE CLOSELY MATCH THE OLD EC ON NEXT WEEKENDS FRONT AND PERHAPS IN
TIME THEY WILL COME EVEN CLOSER TOGETHER.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
SATELLITE IMAGERY SHOWS PATCHES OF MID AND HIGH LEVEL CLOUDS
STREAMING OVERHEAD...WITH WEAK SURFACE HIGH PRESSURE MOVING OFF TO
THE EAST ON THE LATEST SURFACE ANALYSIS. THIS SHOULD KEEP A LIGHT SW
OR S WIND AT ALL TAF SITES OVERNIGHT AS CLOUDS THICKEN AT MID LEVELS
AHEAD OF THE NEXT SYSTEM. UPSTREAM CONVECTION SHOULD WEAKEN BEFORE
IT ARRIVES LEAVING ONLY CONVECTIVE DEBRIS. THE GUIDANCE SHOWS SOME
CONCERN FOR MVFR VISIBILITY IN THE VALLEY AT KAVL AROUND SUNRISE...
BUT THIS HAS NOT OCCURRED WHEN FORECAST FOR THE LAST FEW NIGHTS AND
TONIGHT SEEMS LESS LIKELY WITH THICKENING CLOUDS KEEPING TEMPS
WARMER. LOW LEVEL MOISTURE SHOULD INCREASE AS WELL...BUT FOR NOW
PREFER TO KEEP IT OUT OF THE KAVL TAF.
LATEST MODEL GUIDANCE CONTINUES TO DELAY THE ARRIVAL OF ANY SHOWER
OR THUNDERSTORM ACTIVITY...AND HENCE ANY LOW CLOUD CEILINGS...UNTIL
EVEN LATER IN THE DAY ON SUNDAY. IT NOW APPEARS AS THOUGH THE THREAT
WILL NOT INCREASE UNTIL AFTER 18Z. SO...UP UNTIL A TIME SUCH THAT
THUNDERSTORMS COULD THREATEN...WILL CONTINUE WITH LOWERING AND
THICKENING CLOUDS AT ALL TAF SITES AND AN INCREASING SW WIND. THE
GUIDANCE UNIFORMLY SHOWS MVFR CEILINGS DEVELOPING AFTER 18Z...WHICH
CERTAINLY COULD HAPPEN...BUT FOR THIS ISSUANCE PREFER TO REMAIN
OPTIMISTIC AND BRING THEM DOWN ONLY TO THE LOW END OF VFR. EXPECT
LATER ISSUANCES TO EVALUATE THIS IN MORE DETAIL.
AT KCLT...NEAR TERM ISSUE IS THE SURFACE WIND DIRECTION. THE
POSITION OF THE WEAK HIGH AND THE WIND PROFILE SEEN ON THE TCLT
RADAR SUPPORT KEEPING WINDS TO THE SOUTH OF WEST. IF ANY WIND MIXES
DOWN FROM ABOVE 5000 FEET...WHICH WILL HAPPEN FROM TIME TO TIME
UNTIL THE MIDDLE PART OF THE EVENING...SOME SENSORS WILL GO NORTH OF
WEST. HOWEVER...FEEL THAT PREVAILING CONDITION WILL BE SOUTH OF WEST
SO THAT WILL BE WHAT IS PUT IN THE TAF. WIND SHOULD GO LIGHT AND
MAINLY SOUTH AFTER THE EVENING PUSH...THEN COME UP FROM THE SOUTH OR
SOUTHWEST SOME TIME IN THE MIDDLE PART OF SUNDAY MORNING.
OUTLOOK...THERE WILL BE A CHANCES OF THUNDERSTORMS OVER THE UPSTATE
ON MONDAY. DRY WEATHER IS THEN EXPECTED THROUGH THE REST OF THE
WEEK. RESTRICTIONS SHOULD MAINLY BE ASSOCIATED WITH THUNDERSTORMS
AND PATCHY MORNING FOG ON MONDAY.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...PAT
NEAR TERM...MCAVOY
SHORT TERM...DEO
LONG TERM...DEO
AVIATION...MCAVOY/PM
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