FXUS62 KGSP 301154
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
654 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 /THROUGH TONIGHT/...
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 /TUESDAY 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 /12Z MONDAY THROUGH FRIDAY/...
AT KCLT AND ELSEWHERE...COLD FRONT AND ASSOCIATED BAND OF SHOWERS
CONTINUES TO APPROACH FROM THE WEST AT 12Z. MID AND HIGH LEVEL
CLOUDS SHOULD THICKEN IN ADVANCE WITH LIGHT SOUTHWESTERLY WIND
BEFORE FRONTAL PASSAGE. MODELS HAVE BEEN CONSISTENT WITH HANDLING
THE FRONTAL PRECIP...WHICH SHOULD ARRIVE OVER THE UPPER FRENCH BROAD
VALLEY AROUND 14Z...THEN COME OFF THE BLUE RIDGE BY 15Z...AND REACH
KCLT AROUND MIDDAY. THINK THE PREVAILING CONDITION WILL BE LOW END
VFR AS THE FRONTAL BAND MOVES THROUGH...BUT THERE COULD VERY EASILY
BE PERIODS OF MVFR CEILING AND VISIBILITY SO THIS IS HANDLED IN A
TEMPO GROUP. IF HEAVIER SHOWERS SURVIVE THE TRIP OVER THE MTNS...
SOME IFR IS NOT OUT OF THE QUESTION...BUT WILL NOT MENTION THIS FOR
NOW. THE FRONT SHOULD MAKE STEADY EASTWARD PROGRESS ACROSS THE
WESTERN CAROLINAS BRINGING AN END TO LOW CLOUDS AND PRECIP AND
SHIFTING THE WIND TO NW...BY 23Z AT THE LATEST OVER KCLT. DOWNSLOPE
FLOW WILL DEVELOP BY LATE AFTN...CLEARING OUT THE LOW CLOUDS. VFR
CONDITIONS PREVAIL BEHIND THE FRONT FOR THE REST OF THE PERIOD.
OUTLOOK...VFR CONDITIONS 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
