FXUS62 KGSP 010142
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
842 PM EST MON NOV 30 2009
.SYNOPSIS...
IN THE WAKE OF A FAST MOVING COLD FRONT...HIGH PRESSURE WILL BUILD
ACROSS THE SOUTHEAST ON TUESDAY. THIS AREA OF HIGH PRESSURE WILL
THEN QUICKLY MOVE OFFSHORE AS A VIGOROUS LOW PRESSURE SYSTEM
APPROACHES FROM THE SOUTHWEST ON WEDNESDAY. HIGH PRESSURE IS THEN
EXPECTED TO RETURN TO THE REGION BY LATE WEEK AND LINGER THROUGH THE
WEEKEND.
&&
.NEAR TERM /THROUGH TUESDAY/...
PRESSURE RISES ON THE ORDER OF 3 TO 4 MB/3 HR ARE HELPING TO
MAINTAIN WINDY CONDITIONS ACROSS THE LARGER NW TO SE ORIENTED MTN
VALLEYS AND EVEN A LITTLE WAYS INTO THE FOOTHILLS. ON THE WSR-88D
THE GUSTIER WINDS HERE AT THE AIRPORT ARE OCCURRING WITH NARROW
BANDS OF HIGHER REFLECTIVITIES. I/M NOT SURE WHAT THE SCATTERERS ARE
AS THERE AREN/T EVEN CLOUDS IN THIS AREA. AT ANY RATE...I/VE UPPED
THE WINDS FOR ABOUT 3 HOURS WHERE IT/S CURRENTLY BLOWING...WITH
GUSTS TOPPING OUT AROUND 30 KTS. THE GRADIENT WEAKENS TOWARD
MIDNIGHT WHICH SHOULD CAUSE THE WINDS TO DIMINISH. DEWPOINTS ARE
DROPPING A LITTLE FASTER THAN THE GRIDDED FORECAST...SO I/VE TAKEN
THOSE DOWN A LITTLE. OTHERWISE THE TIMING OF THE PCPN AND CLEARING
SO FAR HAS BEEN EXCELLENT.
RIDGING SFC AND ALOFT BUILD INTO THE AREA TUE. EXPECT CLEAR SKIES
EARLY WITH CIRRUS INCREASING AND THICKENING DURING THE AFTERNOON.
LIGHT SLY WINDS DEVELOP BY AFTERNOON. THICKNESSES ACTUALLY FALL
TUESDAY...BUT NEARLY FULL SUN WILL MAKE IT FEEL WARMER THAN MONDAY.
HIGHS A FEW DEGREES ABOVE NORMAL.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 230 PM EST MONDAY...AN UPPER RIDGE WILL CROSS THE APPALACHIANS
TUESDAY NIGHT...REACHING THE EAST COAST ON WEDNESDAY...WHILE A
CLOSED UPPER LOW CROSSES TX. THIS LOW WEAKENS AND LIFTS NORTHEAST
INTO THE TN VALLEY BY WEDNESDAY EVENING...THEN REACHES SOUTHERN
CANADA BY THURSDAY MORNING. SOUTHWEST FLOW ALOFT REMAINS FROM THE
GULF TO CHESAPEAKE BAY THROUGH THURSDAY NIGHT AS A POSITIVELY TILTED
UPPER TROUGH AXIS FROM THE PLAINS INTO THE MS RIVER VALLEY.
DRY HIGH PRESSURE WILL INITIALLY BE OVER THE CAROLINAS ON TUESDAY
EVENING. AS THE HIGH MOVES INTO THE ATLANTIC...MOIST GULF AND
ATLANTIC INFLOW INCREASE OVER THE WESTERN PERIPHERY OF THE RIDGE AND
INTO THE BLUE RIDGE ESCARPMENT...PRODUCING STRONG ISENTROPIC UPGLIDE
AND UPSLOPE FLOW. THIS SETUP WILL SUPPORT HIGH POPS AND HEFTY
QPF...WITH WINDS APPROACHING ADVISORY CRITERIA IN THE MOUNTAINS...
AND EVEN WARNING CRITERIA AT HIGH ELEVATIONS. WITH PLENTY OF
UNIDIRECTIONAL SPEED SHEAR...EVEN THE LOW CAPE OF THE GFS HINT AT A
POTENTIAL SEVERE WEATHER DAY...ESPECIALLY IF RAIN INDUCED COLD AIR
DAMMING FORMS A THERMAL MOISTURE BOUNDARY IN THE PIEDMONT AND UPPER
SAVANNAH RIVER VALLEY. FRONTAL PASSAGE IS LATE WEDNESDAY...WITH A
DRY SLOT WORKING IN FROM THE SOUTHWEST. ON WEDNESDAY NIGHT MOIST
WESTERLY LOW LEVEL FLOW WILL SUPPORT SCATTERED UPSLOPE FLOW SHOWERS
ALONG THE TN BORDER THAT CHANGE OVER TO SNOW LATE AT NIGHT. THESE
SHOWERS CONTINUE INTO THURSDAY EVENING...WITH THE SNOW LEVEL RISING
DURING THE DAY ON THURSDAY...AND LOWERING AGAIN THURSDAY NIGHT. BY
LATE THURSDAY NIGHT LOW LEVEL FLOW BACK TO THE SOUTHWEST...AND THE
UPSLOPE COMPONENT DIMINISHES.
A LIMITED DIURNAL TEMPERATURES RANGE IS EXPECTED DIURNAL THE RAIN
EVENT WEDNESDAY...WITH NORTHWEST FLOW KEEPING THE MOUNTAINS COOL ON
THURSDAY...AND WARMING THE LEE TOWARD NORMAL VALUES.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 220 PM MONDAY...SAVE FOR SOME LOW END DEGREE OF LINGERING
UPSLOPE POP ACRS THE WESTERN SLOPES...FRIDAY IS SHAPING UP TO BE
FAIR AND COOL WITHIN WEAK NORTHERLY LLVL FLOW. UPPER TROUGH AXIS
IS FCST TO BE PROGRESSIVE THRU SATURDAY AND MEDIUM RANGE MODELS ARE
PROGGING COASTAL LOW DEVELOPMENT/STRENGTHENING. GIVEN DIFFERENCES
IN HANDLING OF SFC CYCLONE...WILL SHY AWAY FROM THE 12 UTC ECMWF
RESPONSE OVER THE APPALACHIANS...AND CONTINUE WITH THE DRY AND COOL
FCST. BOTH THE OP GFS AND ECMWF ARE IN GOOD ENUF AGREEMENT FOR
SUNDAY FEATURING SFC RIDGING BUILDING A TOP THE REGION...PROVIDING
FAIR AND CONTINUED COOL TEMPS. WILL FAVOR THE ECMWF IN LINGERING
LLVL RIDGING ATOP THE REGION...KEEPING ANY MOISTURE ENCROACHING FROM
THE WEST AT BAY THRU DAY 7.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
AT KCLT AND ELSEWHERE...A BAND OF SHOWERS AND ASSOCIATED MVFR CIGS
HAD JUST MOVED EAST OF KCLT AT ISSUANCE TIME. ALL OTHER FOOTHILL AND
PIEDMONT TAF SITES SHOULD SEE VFR CONDITIONS THE REST OF THE NIGHT.
AT KAVL...MVFR CIGS ARE EXPECTED FOR THE NEXT SEVERAL HOURS BEFORE
CLEARING FINALLY SETS IN. WINDS WILL BE NORTH TO NORTHWEST AT ALL
SITES...BECOMING LIGHT OR CALM LATER TONIGHT. A PERIOD OF LOW LEVEL
WIND SHEAR WILL AFFECT KAVL THROUGH MIDNIGHT. ON TUE WINDS WILL TURN
OUT OF THE SOUTH BY LATE MORNING...THOUGH SPEEDS SHOULD STAY WELL
UNDER 10 KTS. SKIES WILL BE CLEAR...THOUGH HIGH CLOUDS WILL START TO
INCREASE LATE IN THE DAY.
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...JPT
NEAR TERM...MCAVOY/RWH
SHORT TERM...JAT
LONG TERM...CSH
AVIATION...MCAVOY
