FXUS62 KGSP 300809
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
309 AM EST MON NOV 30 2009
.SYNOPSIS...
A COLD FRONT WILL CROSS THE FORECAST AREA FROM THE WEST TODAY AND
HIGH PRESSURE WILL BUILD IN ACROSS THE SOUTHEAST ON TUESDAY. THIS
AREA OF HIGH PRESSURE WILL THEN MOVE OFF THE EAST COAST AS A STRONG
LOW PRESSURE SYSTEM APPROACHES FROM THE SOUTH ON WEDNESDAY. HIGH
PRESSURE IS THEN EXPECTED TO RETURN TO THE REGION BY LATE WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
UPSTREAM RADARS SHOW FAIRLY WIDE BAND OF SHOWERS WITH AFEW EMBEDDED
LIGHTNING STRIKES AHEAD AND ALONG THE RAPIDLY APPROACHING COLD
FRONT. THE MODELS HAVE BEEN GENERALLY CONSISTENT WITH THE UPPER WAVE
AND COLD FRONT SO NO SIGNIFICANT CHANGES TO EARLIER THINKING WILL
APPEAR IN THE NEW FORECAST FOR TODAY. EXTRAPOLATION SUGGESTS THE
LEADING EDGE OF THE PRECIP SHOULD REACH THE WESTERN MTNS IN THE
PRE-DAWN HOURS...AND THEN NE GEORGIA AND THE UPPER FRENCH BROAD
VALLEY AROUND SUNRISE. KEPT THE SAME IDEA OF CATEGORICAL POP OVER
THE MTNS/FOOTHILLS AND LIKELY EAST OF THERE...WITH THE LIKELY POP
SPREADING ACROSS THE PIEDMONT IN THE EARLY AFTERNOON. THE FORCING
APPEARS TO BE SUFFICIENT ENOUGH FOR THUNDER SO THIS WAS ADDED WHERE
POP IS LIKELY OR GREATER. TEMPS MAY REACH AN EARLY AFTERNOON HIGH
OVER THE MTNS SO A MODIFIED DIURNAL TEMP TREND WAS USED. MINOR
CHANGES WERE MADE TO THE HIGH TEMPS FOR TODAY.
THE MODELS CONTINUE TO SCREAM THAT PRECIP WILL END QUICKLY LATE IN
THE DAY. SEE LITTLE OPPORTUNITY FOR LINGERING PRECIP OVER THE EAST
OR NW FLOW UPSLOPE WITH THIS SYSTEM...SO THIS WAS LARGELY CUT FROM
THE FORECAST. THAT WILL PRECLUDE THE REMOTE CHANCE FOR SNOW SHOWERS
ON THE HIGHER TERRAIN ALONG THE TN BORDER THIS EVENING. LOW TEMP
FORECAST OVERNIGHT REMAINS IN LINE WITH GUIDANCE.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
AS OF 305 AM MONDAY...SHORT RANGE MODELS AGREE THAT TUESDAY WILL
FEATURE VERY PLEASANT CONDITIONS. THE CENTER OF MILD HIGH PRESSURE
WILL REMAIN OVER THE CWA DURING THE DAY...SHALLOW H5 RIDGING SHOULD
ALSO INCREASE DURING THE AFTERNOON. SKY COVER WILL REMAIN SUNNY
DURING THE MORNING AND MAY BECOME MOSTLY/PARTLY SUNNY DURING THE
AFTERNOON AS HIGH CLOUDS ARRIVE. HIGH TEMPERATURES ARE FORECAST TO
RANGE 3-5 DEGREES ABOVE NORMAL.
TUESDAY NIGHT...THE CENTER OF SFC HIGH PRESSURE WILL MOVE NEARLY DUE
EAST OVER THE WESTERN ATLANTIC AS SFC LOW PRESSURE MOVES NORTH FROM
THE MISSISSIPPI DELTA. SHORT RANGE MODELS STILL SHOW SEVERAL
TIMING AND PLACEMENT DIFFERENCES WITH THE LOW AND ASSOCIATED
PRECIPITATION THROUGH WEDNESDAY. I WILL USE THE ECMWF/NAM/SREF FOR
FORECAST DETAILS. THE FORECAST AREA WILL MAINLY REMAIN DRY TUESDAY
NIGHT. HOWEVER...THE UPPER SAVANNAH RIVER VALLEY AND WESTERN NC MTNS
MAY SEE SCT AREAS OF RA DURING THE PRE DAWN HOURS. MIN TEMPERATURES
SHOULD REMAIN 3-5 DEGREES ABOVE NORMAL...WITH ALL AREAS REMAINING
ABOVE FREEZING.
WEDNESDAY...THE FORECAST BECOMES VERY CHALLENGING AND INTERESTING
THROUGH THE DAY. LOW PRESSURE WILL LIKELY CONTINUE TO TRACK NE
ACROSS THE DEEP SOUTH...EVENTUALLY PASSING WEST OF THE SRN
APPALACHIANS WEDNESDAY NIGHT. MODELS INDICATE POWERFUL LLVL WINDS
EAST AND NORTH OF THE CENTER OF THE SFC LOW. H85 WINDS ARE FORECAST
TO RANGE FROM 50-70 KTS FROM SOUTH-SOUTHEAST. THESE WINDS WILL
RESULT IN WIDESPREAD ISENTROPIC AND UPSLOPE LIFT ACROSS THE FORECAST
AREA. IN ADDITION...DEEP OMEGA AND JET DIVERGENCE WILL LIKELY SUPPORT
BANDS OF MODERATE TO HEAVY RA BY 18Z AND REMAINING INTO THE EVENING.
WIDESPREAD MODERATE TO HEAVY RAIN WITHIN WEAK SFC RIDGING WILL KEEP
HEATING LIMITED...I WILL FAVOR HIGH TEMPS IN THE U40S TO AROUND 50
ACROSS THE CWA.
WEDNESDAY EVENING AND OVERNIGHT...FORECAST SOUNDINGS INDICATE A
LAYER OF ELEVATED INSTABILITY SWEEPING SOUTH TO NORTH AS THE LOW
LIFTS OVER THE OHIO RIVER VALLEY. CAPE VALUES MAY RANGE FROM 30-50
J/KG ON THE GFS TO SEVERAL HUNDRED ON THE NAM. IN ADDITION...LLVL
WIND FIELDS REMAIN VERY IMPRESSIVE...POSSIBLY YIELDING LARGE AREAS
OF MODERATE TO STRONG HELICITY AND HIGH SWEAT EAST OF THE MTNS. THE
COMBINATION OF HIGH SHEAR AND LOW INSTABILITY WOULD FAVOR THE
DEVELOPMENT AND SUPPORT OF LINEAR CONVECTIVE BANDS...ENHANCING THE
CHC FOR HIGH WIND AND POSSIBLY SMALL TORNADOES. I WILL INTRODUCE TS
IN THE FORECAST AND WILL ADDRESS THE POSSIBLE SEVERE THREAT IN THE
HWO. STORM TOTAL RAINFALL IS FORECAST TO RANGE FROM 2.5 INCHES
ACROSS NE GA AND SC TO AROUND AN INCH ACROSS THE MTNS.
CAA WILL BEGIN OVER THE NC MTNS LATE WEDNESDAY NIGHT. TEMPERATURES
SHOULD COOL ENOUGH TO RESULT IN A HIGH ELEVATION MIX OF RA AND SN
LATE WEDNESDAY NIGHT INTO THURSDAY. WEST TO NORTHWEST WINDS AND LLVL
MOISTURE SHOULD CONTINUE TO SUPPORT UPSLOPE PRECIPITATION ACROSS THE
NC MTNS THROUGH THURSDAY. LITTLE TO NO SNOW ACCUM IS EXPECTED BY THE
END OF THURSDAY AFTERNOON.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 230 AM MONDAY...I HAVE PRIMARILY FOLLOWED THE 00Z ECMWF FOR
THE DETAILS OF THE MEDIUM RANGE. ALOFT THE MAIN STORY WILL BE THE
DEEPENING EASTERN CONUS TROF THAT LINGERS THROUGH SUNDAY. HEIGHTS
FALL PRETTY DRAMATICALLY THROUGH THE WEEKEND AND WILL SUPPORT SOME
FAIRLY COOL TEMPS. EXPECT THERE TO BE SOME LINGERING NW FLOW SNOW
SHOWER ACTIVITY THURSDAY NIGHT BUT THE MOISTURE DRIES UP QUICKLY ON
FRIDAY AND THE FLOW TURNS MORE WESTERLY AND IS QUITE WEAK. DRY HIGH
PRESSURE BUILDS IN THROUGH THE REMAINDER OF THE FORECAST...KEEPING
THINGS DRY. I HAVE TWEAKED TEMPS DOWNWARD JUST A BIT AS LOW LEVEL
THICKNESSES ON THE ECMWF ARE SUB 1300 DAM ACROSS THE ENTIRE FA FROM
FRIDAY NIGHT ONWARD. H85 TEMPS SHOW A DOWNWARD TREND THROUGH THE
ENTIRE FORECAST AS WELL...REACHING -12C ACROSS THE MOUNTAINS BY SUNDAY
MORNING. FURTHERMORE...H85 TEMP ANOMALIES FROM THE GEFS ARE ON THE
ORDER OF 2 TO 3 STANDARD DEVIATIONS BELOW NORMAL ACROSS THE
SOUTHEAST THROUGH MUCH OF THE PERIOD. THIS RESULTS IN VALUES 6-10
DEGREES BELOW CLIMO FRIDAY THROUGH SUNDAY.
&&
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
AT KCLT AND ELSEWHERE...MID AND HIGH LEVEL CLOUDS AND SOUTHWESTERLY
WINDS WILL CONTINUE THROUGH THE REST OF THE NIGHT. MODELS HAVE BEEN
CONSISTENT WITH HANDLING A RAPIDLY APPROACHING COLD FRONT...WHICH
SHOULD ARRIVE OVER THE MTNS AROUND SUNRISE AND MAKE STEADY PROGRESS
EAST ACROSS THE WESTERN CAROLINAS. A BAND OF SHOWERS SHOULD
ACCOMPANY THE FRONT WITH VISIBILITY EXPECTED TO BE MAINLY VFR...BUT
THERE COULD VERY EASILY BE BRIEF PERIODS OF MVFR VISIBILITY IF
HEAVIER SHOWERS SURVIVE THE TRIP OVER THE MTNS. CEILING SHOULD DROP
INTO MVFR RANGE WITH THE SHOWER BAND BUT SOME IFR NOT OUT OF THE
QUESTION. FOR NOW...WILL FORGO A TEMPO FOR THE LATE MORNING/EARLY
AFTERNOON AND LEAVE THE PREVAILING CONDITION MVFR BECAUSE OF
CEILING. THE FRONT SHOULD MAKE IT EAST OF KCLT BY 21Z AND DOWNSLOPE
FLOW WILL DEVELOP BY LATE AFTN...CLEARING OUT THE LOW CLOUDS AS THE
WINDS TURN OUT OF THE WEST NORTHWEST. AT KAVL THE WIND SHIFT WILL
HAPPEN SEVERAL HOURS EARLIER WITH WINDS GUSTING OVER 20 KTS BY LATE
IN THE DAY. VFR CONDITIONS PREVAIL BEHIND THE FRONT.
OUTLOOK...VFR CONDITIONS LATE MONDAY NIGHT AND TUESDAY. TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT...A STRONG AREA OF LOW PRESSURE WILL
LIFT FROM THE NRN GULF OF MEXICO ACROSS THE WESTERN CAROLINAS.
WIDESPREAD RAIN AND CEILING/VIS RESTRICTIONS WILL ACCOMPANY THE
PASSAGE OF THE LOW. CONDITIONS SHOULD BEGIN TO IMPROVE EARLY
THURSDAY...WITH VFR EXPECTED FRIDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...PM
SHORT TERM...NED
LONG TERM...BSH
AVIATION...PM
