FXUS62 KGSP 020856
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
356 AM EST WED DEC 2 2009
.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL CONTINUE TO RIDE NORTHEASTWARD AND INTO
THE OHIO VALLEY TODAY AS A COLD FRONT MOVES TOWARD THE EAST COAST.
HIGH PRESSURE WILL NOSE IN FROM THE WEST THROUGH FRIDAY...BEFORE AN
UPPER LEVEL SYSTEM AFFECTS THE REGION ON SATURDAY. BEHIND THIS
SYSTEM...HIGH PRESSURE WILL RETURN TO THE FORECAST AREA AND REMAIN
IN PLACE THROUGH EARLY NEXT WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
LEADING EDGE OF LIGHT PRECIP...MOSTLY ALOFT...FORCED BY MID LEVEL
FRONTOGENESIS WILL WORK ITS WAY N ACROSS THE WESTERN CAROLINAS IN
THE PREDAWN HOURS. BY SUNRISE...AREAS OF LIGHT RAIN SHOULD COVER
MOST OF THE FORECAST AREA...WHICH WILL LOCK IN THE COLD AIR DAMMING
WEDGE ACROSS MOST OF THE FOOTHILLS AND PIEDMONT. ALL IN ALL...THE
NEW MODEL GUIDANCE IS IN LINE WITH THE PREVIOUS FORECAST SO NO
SIGNIFICANT CHANGES ARE NECESSARY AND THE MYRIAD OF HAZARDS ALREADY
IN PLACE LOOKS GOOD...IN SPITE OF CREEPING DOUBT ABOUT HOW SOME OF
THIS WILL WORK OUT. THE ISSUE THERE IS THE DEEP CONVECTION OVER THE
FL PANHANDLE AND THE LARGE GAP BETWEEN THAT ACTIVITY AND THE PRECIP
ASSOCIATED WITH THE COLD FRONT AND UPPER WAVE. WENT WITH NAM
GUIDANCE FOR THE WIND TODAY WHICH SUPPORTS STRONG WIND GUST
POTENTIAL ACROSS THE HIGHER TERRAIN. THE TREND IN THE MODEL GUIDANCE
IS FOR LESS PRECIP ACROSS THE AREA EAST OF THE MTNS AS BETTER
CONVECTION IS KEPT CLOSER TO THE WEDGE BOUNDARY. AT 07Z...RADAR
TRENDS SUPPORT THE GENERAL IDEA THAT AT LEAST THE INITIAL STRONGER
CONVECTION WILL MISS US TO THE SOUTH AND EAST...BUT IT IS EARLY YET.
WENT WITH HPC GUIDANCE WHICH TONES DOWN THE RAINFALL AMOUNTS...BUT
THINK THE FLASH FLOOD WATCH HAS AN EXCELLENT CHANCE OF WORKING OUT
ACROSS AT LEAST THE CLT METRO AREA. WE COULD SEE A RELATIVE LULL IN
PRECIP AROUND MIDDAY BEFORE A SECOND ROUND MOVES THROUGH LATE IN THE
AFTERNOON OR EARLY EVENING ASSOCIATED WITH THE MAIN SHORT WAVE. FOR
NOW THIS WILL NOT REALLY BE REFLECTED IN THE POP/WX GRIDS OR PUBLIC
PRODUCTS. IF THE LULL WORKS OUT IT COULD HELP THE CHANCES OF LIFTING
THE WEDGE BOUNDARY INTO THE SOUTHEAST PART OF THE FORECAST AREA AND
THUS THE SEVERE WEATHER THREAT LATER IN THE DAY.
AS FOR TONIGHT...EXPECT PRECIP TO LIFT NE WITH THE SHORT WAVE IN THE
EVENING...FOLLOWED BY SOME WRAP AROUND SHOWER CHANCES OVER THE MTNS.
KEPT MIN TEMPS ABOVE FREEZING WHICH KEEPS THE PRECIP ALL LIQUID.
AREAS EAST OF THE MTNS SHOULD SEE PARTIAL CLEARING BY DAYBREAK
THURSDAY.
&&
.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 350 AM WEDNESDAY...SHORT RANGE MODELS REMAIN IN REASONABLE
AGREEMENT ON THURSDAY. LLVL WRAP AROUND MOISTURE WILL REMAIN BANKED
ACROSS THE TN BORDER COUNTIES DURING THE DAY ON THURSDAY. ONLY FEW
TO ISO SHRA MAY DEVELOP ACROSS THE UPSLOPE AREAS OF NC INTO THURSDAY
AFTERNOON. I WILL REDUCE POPS TO SCHC GIVEN WEAK WEST WINDS AND
LIMITED MOISTURE. HIGH TEMPERATURES ARE FORECAST TO REACH NEAR
NORMAL LEVELS ACROSS THE CWA.
FRIDAY...SFC HIGH PRESSURE WILL BUILD ACROSS THE FORECAST AREA FROM
THE WEST. ALOFT...L/W TROF AXIS IS EXPECTED TO SWEEP ACROSS THE
MIDDLE CONUS...RESULTING IN FALLING HEIGHTS ACROSS THE EAST.
THICKNESSES SHOULD REMAIN FAIRLY COOL WITH INCREASING CLOUD COVER
THROUGH THE DAY. LOW TEMPERATURES ARE FORECAST TO FALL CLOSE TO
NORMAL...HOWEVER...HIGH TEMPERATURES WILL LIKELY REMAIN 3-6 DEGREES
BELOW NORMAL.
THE LONGWAVE TROF AXIS WILL PUSH EAST ACROSS THE MISSISSIPPI RIVER
VALLEY FRIDAY NIGHT. A POWERFUL JET STREAKS NORTHWARD ON THE EAST
HALF OF THE TROF LATE FRI NIGHT...PROVIDING A LARGE REGION OF UPPER
DIVERGENCE ACROSS THE SOUTHEAST BY 12Z SAT. LIFT DEEPENS ACROSS THE
CWA 15Z-21Z SATURDAY AS H7-H5 FRONTOGENESIS ON THE WESTERN SIDE OF
COASTAL LOW PRESSURE PIVOTS OVER THE WESTERN CAROLINAS. FORECAST
SOUNDINGS INDICATE THAT DEEP MOISTURE WILL ARRIVE BETWEEN 9Z-12Z SAT
AND REMAIN INTO SATURDAY EVENING. IN ADDITION...MODELS INDICATE THAT
A SMALL REGION -EPV MAY DEVELOP ACROSS THE WESTERN CAROLINAS ALONG
AND AHEAD OF THE H5 TROF SAT AFTERNOON.
IT CERTAINLY APPEARS THAT MEASURABLE PRECIPITATION WILL OCCUR ACROSS
THE CWA FROM THIS EVENT. THE MAIN CHALLENGE WILL REMAIN WITH THE
P-TYPE FORECAST. USING A BLEND OF SREF...GFS40 LLVL TEMPS...I WILL
FORECAST FREEZING TEMPS ACROSS THE MTNS WITH MID TO U30S EAST OF THE
MTNS BY SUNRISE SAT. HEATING AFTER SUNRISE WILL REMAIN LIMITED BY
PRECIP...THICK CLOUD COVER...AND ONGOING NORTH SFC WINDS. HIGH TEMPS
ARE FORECAST TO RANGE FROM FREEZING ACROSS THE HIGH TERRAIN TO LOW
TO MID 40S EAST OF THE MTNS. PARTIAL THICKNESSES AND THE TOP DOWN
METHOD YIELD MAINLY SN ACROSS THE HIGH ELEVATIONS WITH A MIX IN THE
VALLEYS. AT THIS POINT...PRECIPITATION SHOULD REMAIN RA ACROSS NE
GA...SC...AND EAST OF I-40 ACROSS NC. PRECIP WILL GRADUALLY DECREASE
EARLY SATURDAY EVENING AS THE H5 TROF RIPPLES EAST OF THE CWA. THIS
FORECAST PACKAGE WILL FEATURE SNOWFALL OF 1-3 INCHES ABOVE 3000 FEET
IN ELEVATION...WILL HIGHLIGHT IN THE HWO. SAT NIGHT...SKY COVER WILL
DECREASE WITH THE ARRIVAL OF HIGH PRESSURE. FRESH CAA AND LIGHT
WINDS SHOULD RESULT IN COLD LOW TEMPS. BY 12Z SUN...TEMPS ARE
FORECAST TO RANGE FROM THE L20S ACROSS THE MTNS WITH MID 20S TO 30
DEGREES EAST OF THE MTNS. IN FACT...IT APPEARS THAT TEMPS WILL FALL
BELOW FREEZING ACROSS THE MTNS LATE SAT EVENING. DAMP ROADS AND
ONGOING RUNOFF MAY RESULT IN SIGNIFICANT BLACK ICE SAT NIGHT...PLAN
TO HIGHLIGHT IN THE HWO.
&&
.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 245 AM WEDNESDAY...THE BULK OF THE MEDIUM RANGE WILL BE QUIET
WITH BELOW NORMAL TEMPS. ALOFT...THE PERIOD SUNDAY THROUGH TUESDAY
WILL BE DEFINED BY QUASI ZONAL FLOW WITH SOME AMPLIFICATION OF THE
PATTERN ON TUESDAY AS A TROF BEGINS TO MOVE OUT OF THE FOUR CORNERS
REGION. AT THE SURFACE...HIGH PRESSURE WILL SETTLE IN ACROSS THE FA
ON SUNDAY AND LARGELY REMAIN IN PLACE THROUGH TUESDAY. THE VARIOUS
MODEL SOLUTIONS DO DEPICT SOME MOISTENING FROM THE WEST BY TUESDAY
AFTERNOON...AND I DO CONTINUE TO ADVERTISE SLIGHT CHANCE POPS DURING
THIS PERIOD AS A COMPROMISE BETWEEN THE ECMWF AND THE GFS. OVERALL
TEMPS WILL REMAIN BELOW CLIMO AS COOL LOW LEVEL NERLY FLOW WILL
DOMINATE THE PERIOD AND UPPER HEIGHTS REMAIN LARGELY UNCHANGED IN
THE QUASI ZONAL FLOW ALOFT. THIS RESULTS IN TEMPS ABOUT 3-5 DEGREES
BELOW CLIMO THROUGH EARLY NEXT WEEK.
&&
.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE...THE LEADING EDGE OF THE PRECIP ALOFT...WHICH
CORRESPONDS TO A MID LEVEL CLOUD CEILING...WILL SPREAD ACROSS THE
WESTERN CAROLINAS THROUGH SUNRISE. LIGHT RAIN SHOULD BREAK OUT IN
THE 08Z TO 10Z TIME FRAME...WHICH SHOULD DO THE TRICK TO BRING THE
CEILING DOWN INTO THE MVFR RANGE AND INSTALL THE COLD AIR DAMMING
WEDGE. THE MORE SIGNIFICANT RAIN WILL ARRIVE SHORTLY THEREAFTER
WHICH WILL BRING IFR CEILING/VISIBILITY FOR THE BULK OF THE MORNING.
ALTHOUGH THE MODEL DATA DOES NOT SHOW IT...WE COULD SEE A BRIEF LULL
IN THE PRECIP DURING THE EARLY AFTERNOON WHICH MIGHT IMPROVE THE
VISIBILITY A BIT...BUT THINK CEILING WILL REMAIN IFR. THE UPPER
SYSTEM WILL MOVE PAST LATE IN THE AFTERNOON WHICH SHOULD BREAK UP
THE LOW CLOUDS AND ALSO BRING THE POSSIBILITY OF A LINE OF
THUNDERSTORMS. WENT WITH A PERIOD OF MVFR CEILING FOR A FEW HOURS
BEFORE SCATTERING IT OUT ENTIRELY AS THE DRY SLOT WORKS IN FROM THE
SOUTHWEST IN THE EVENING.
WINDS WILL GENERALLY BE OUT OF THE NE THIS MORNING. AS THE LOW
APPROACHES THE WINDS WILL BECOME SUSTAINED OVER 10 KTS AT MOST SITES
AND GUSTY AT TIMES. LOW LEVEL WIND SHEAR IS LIKELY AT MOST SITES
STARTING AROUND SUNRISE AS THE WINDS AROUND 2KFT INCREASE TO 45 TO
50 KTS FROM THE SE. SITES WHERE THE COLD AIR DAMMING KEEPS THE SFC
WINDS OUT OF THE NE WILL SEE THE MOST SIGNIFICANT WIND SHEAR...
THOUGH THE STRONG WINDS BLOWING ACROSS THE FRENCH BROAD VALLEY WILL
CAUSE PROBLEMS AT KAVL AS WELL.
OUTLOOK...CONDITIONS SHOULD IMPROVE DRAMATICALLY LATE WEDNESDAY
NIGHT AS WINDS TURN OUT OF THE WEST AND SCOUR OUT THE LOW CLOUDS.
VFR EXPECTED FRIDAY. ANOTHER PERIOD OF MVFR CONDITIONS IS POSSIBLE
ON SATURDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR GAZ010-017-018-026-
028-029.
WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR GAZ010-017.
NC...FLASH FLOOD WATCH THROUGH THIS EVENING FOR NCZ035>037-056-057-
062>065-068>072-082-501>510.
WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR NCZ033-048>053-
058-059-062>065-501-503-505-507-509.
SC...FLASH FLOOD WATCH THROUGH THIS EVENING FOR SCZ001>014-019.
WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR SCZ001>003.
&&
$$
SYNOPSIS...BSH
NEAR TERM...PM
SHORT TERM...NED
LONG TERM...BSH
AVIATION...MCAVOY/PM
