Flash Flood in North Carolina, September 10, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
225 PM EDT WED SEP 10 2008

.SYNOPSIS...
A COLD FRONT WILL SLOWLY MOVE SOUTHWARD ACROSS THE REGION TONIGHT AS
HIGH PRESSURE BUILDS OVER TO THE NORTH. DAMP AND MOIST CONDITIONS
WILL PERSIST IN THIS WEDGE OF COOL HIGH PRESSURE THURSDAY THROUGH
FRIDAY...WITH GRADUAL IMPROVEMENT INTO THE WEEKEND. ANOTHER COLD
FRONT WILL APPROACH THE AREA FROM THE NORTHWEST EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
HEAVY RAIN SHOWERS PERSIST ON RADAR THIS AFTERNOON ACROSS THE
PRESENT FLASH FLOOD WATCH AREA. CATAWBA COUNTY HAS ALSO RECEIVED
HIGH RAINFALL RATES...BUT FFG VALUES ARE HIGHER THERE SO WILL NOT
EXPAND THE WATCH...FOR NOW. MARGINAL INSTABILITY PERSISTS THROUGHOUT
THE NEAR TERM...BUT WITH PROFILES TOO MOIST FOR MUCH OF A STRONG
THUNDERSTORM THREAT. UPPER JET DIVERGENCE WILL PERSIST OVER THE
EASTERN PART OF THE CWFA THROUGH AT LEAST EARLY EVENING...AS ONE
FINAL 500 MB VORTICITY LOBE MOVES THROUGH THE HEART OF THE FORECAST
AREA. THE INTERACTION OF THIS UPPER FORCING WITH THE EXISTING LOW
LEVEL BOUNDARY SHOULD ALLOW HEAVY RAIN SHOWERS TO CONTINUE ALONG THE
INTERSTATE 77 CORRIDOR WHERE PRECIPITABLE WATER VALUES ARE NEAR TWO
INCHES.

SOUTHERLY 850 MB FLOW IS FAIRLY WEAK EARLY THIS AFTERNOON...BUT
SHOULD SLOWLY IMPROVE FROM THE SOUTHEAST...INCREASING UPGLIDE AND
UPSLOPE THROUGH THE PERIOD. IN FACT SHOWERS ARE STEADILY FILLING IN
ON RADAR OVER THE WESTERN SECTIONS OF THE FORECAST AREA AND THIS
TREND WILL CONTINUE INTO THE EARLY EVENING. COLD AIR DAMMING HAS
BEEN VERY SLOW TO DEVELOP ACROSS THE REGION...LARGELY BECAUSE OF
LIMITED PRECIPITATION THROUGH THE NOSE OF THE HIGH PRES RIDGE JUST
EAST OF THE ESCARPMENT. IT MAY TAKE ALL NIGHT FOR THE 1400 M LOW
LEVEL THICKNESS LINE TO PUSH SOUTHWEST ACROSS THE CWFA...AND EVEN
THEN THE NAM SUGGESTS SOME REBOUNDING OF THICKNESSES DURING THE DAY
THURSDAY WITHOUT ANY SIGNIFICANT SURFACE BASED STABLE LAYER IN
PLACE. WILL THUS REMAIN FAIRLY CONSERVATIVE ON WEDGE TEMPERATURES
AND JUST GO WITH A SLIGHTLY SMALLER DIURNAL RANGE THAN MOS. LIGHT
ISENTROPIC LIFT WILL REMAIN THE MAIN PRECIPITATION DRIVER OVERNIGHT
THROUGH THURSDAY AS THE UPPER SUPPORT DEPARTS UNDER A BUILDING RIDGE.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
AS OF 200 PM WEDNESDAY...WEAK CAD REGIME WILL STILL BE IN PLACE FOR
THURSDAY NIGHT. MODEL RESPONSE IN REGARD TO QPF AT ODDS WITH GFS
PRODUCING WIDESPREAD...ALBEIT LIGHT QPF...WHILE THE NAM IS JUST
GENERATING QPF IN FAVORED UPSLOPE AREA OVER THE WESTERN PORTION OF
THE FORECAST AREA. SREF MORE SUPPORTIVE OF MORE WIDESPREAD QPF AND
WITH WEAK ISENT LIFT EXPECT AT LEAST SCATTERED SHOWERS...SO WILL STAY
CLOSER TO HIGHER MAV POPS BUT SCULPTED HIGHER POPS TO FAVOR THE
SOUTHERN AREA NEAR THE BOUNDARY AND UPSLOPE AREAS. FRI STILL LOOKS
TO BE A TRANSITION DAY FROM THE WEAK CAD AIRMASS TO A SUPTROPICAL
ONE AS UPPER ANTICYCLONE BUILDS OVER THE REGION. MODELS MORE OFTEN
THAN NOT ARE TOO FAST ERODING A CAD...BUT THIS ONE CERTAINLY IS NOT
WHAT WOULD BE CONSIDERED A STRONG ONE. EXPECT THERE SHOULD BE AT
LEAST SCATTERED SHOWERS/THUDNERSTORMS ON FRI DUE TO WEAK BOUNDARY
CONVERGENCE AND THEN UPSLOPE IN THE AFTERNOON AS WINDS SLOWLY VEER.
LOOKS LIKE MOUNTAINS/FOOTHILLS SHOULD HAVE THE BEST COVERAGE DURING
THE AFTERNOON. SUBTROPICAL SURFACE HIGH BUILDS INTO THE AREA FRI
NIGHT WHICH SHOULD SQUASH ANY CONVECTION DURING THE OVERNIGHT WITH
AT LEAST PARTIAL CLEARING. TYPICAL SUMMERTIME WEATHER EXPECTED ON
SAT WITH ONLY ISOLATED AFTERNOON CONVECTION AND TEMPS REBOUNDING TO
A COUPLE CATEGORIES ABOVE AVERAGE FOR MID SEPT. USED A MOS BLEND FOR
MAX/MIN TEMPS THROUGH FRI NIGHT...BUT SHAVED A COUPLE DEGREES OFF ON
FRI EXPECTING WEAK CAD/CLOUDS TO BE A LITTLE SLOWER TO ERODE THAN
MODELS INDICATED. SEASONALLY HOT GMOS NUMBERS FOR MAX TEMPS ON SAT
LOOK GOOD UNDER SUBTROPICAL RIDGE.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 220 PM WEDNESDAY...A SIGNIFICANT DISAGREEMENT EXISTS IN THE
MODELS WRT TO THE HANDLING OF THE REMNANTS OF IKE. ON SUN...THE
ECMWF AND THE GGEM BOTH HAVE IKE MOVING NORTH ACROSS EASTERN
TX...WHILE THE OUTLIER GFS KEEPS IKE TO THE SOUTHWEST ABOUT 200 MI.
THIS RELATIVELY SMALL VARIANCE IN LATITUDE IS ENOUGH FOR IKE TO BE
PICKED UP BY A NORTHERN STREAM S/W AND DEEPEN THE OVERALL H5 TROF
AS IT NEARS THE EASTERN CONUS. MODELS CONTINUE TO KEEP VERY STRONG
ANTICYCLONE IN PLACE ACROSS THE SE REGION SUN AND WILL EXPECT MAX
TEMPS 8/10 DEGREES ABOVE NORMAL. DIURNAL CONVECTION IS CERTAINLY
POSSIBLE AS THE ATMOS WILL REMAIN UNSTABLE AND SOUTHERLY MOIST FLOW
CONTINUES INTO THE CWFA.

THE MODEL SOLNS REALLY BEGIN TO DIVERGE MON THROUGH THE REMAINDER OF
THE EXT PERIOD. THE GFS KEEPS VERY STRONG STACKED RIDGING IN PLACE
AND PUSHES A BACK DOOR COLD FRONT OR WEDGE INTO THE AREA LATE TUE.
THE ECMWF CAMP HOWEVER...LOWERS H5 HEIGHTS AND INCREASES CYCLONIC
FLOW SIGNIFICANTLY LATE MON THROUGH THE PERIOD. THE ECMWF SOLN IS
PREFERRED BY HPC AND WITH OTHER MODELS CATCHING ON TO THIS SOLN SEE
NO REASON TO DIVERGE FROM LATER PERIOD PROGS. WITH THIS IN
MIND...WILL EXPECT FAIRLY STRONG UPPER TROF TO CROSS THE REGION
EARLY TUE FOLLOWED BY A NOTICEABLE CP AIRMASS CHANGE. POPS ARE LEFT
IN THE DECENT CHANCE RANGE THROUGH TUE WITH COLD FRONT APPROACHING
THE AREA AND EXITING EAST LATE DAY. TEMPS MON WILL BE BACK TO NORMAL
AS UPPER RIDGE BREAKS DOWN...HOWEVER TEMPS TUE AND WED LOOK TO BE A
FEW DEGREES BELOW NORMAL...WITH COOLER DEWPOINTS MIXING IN MAKING
FOR PLEASANTLY SEASONAL DAYS.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
KHKY TO KCLT WILL SEE THE BEST CHANCE OF HEAVY RAIN SHOWERS AND
ASSOCIATED IFR CEILINGS WITH FAIRLY WIDESPREAD CONVECTION IN THE
PIEDMONT. PRECIPITATION SHOULD BEGIN TO FILL IN THROUGHOUT THE
REGION THROUGH EARLY EVENING AS SOUTHEASTERLY UPSLOPE FLOW IMPROVES
AND UPPER WAVES CROSS THE AREA FROM THE WEST. ANY VFR CEILINGS ARE
LIKELY TO BE SHORT LIVED...WITH GENERALLY MVFR EXPECTED THROUGH
EVENING...TRANSITIONING TO IFR OVERNIGHT. CEILINGS WILL REMAIN QUITE
VARIABLE THROUGH THE EVENING UNTIL THE BEST UPGLIDE FLOW GETS
ESTABLISHED LATER TONIGHT AND SOLID IFR CONDITIONS DEVELOP. A SLIGHT
REBOUND BACK TO MVFR CONDITIONS IS POSSIBLE FROM KCLT TO KAND BY MID
MORNING THURSDAY...BUT LOCATIONS DEEPER IN THE COLD WEDGE FROM KHKY
TO KGSP SHOULD REMAIN IFR THROUGH THE PERIOD WITH LIGHT RAIN AND/OR
SHOWERS.

OUTLOOK...IFR RESTRICTIONS WILL LIKELY PERSIST OR DEVELOP ONCE AGAIN
THURSDAY NIGHT INTO FRIDAY. THE COLD WEDGE IN PLACE ACROS THE AREA
WILL SLOWLY BREAK DOWN INTO THE WEEKEND...BUT WITH IFR TO MVFR
CONDITIONS LIKELY EACH NIGHT. A COLD FRONT WILL APPROACH FROM THE
NORTHWEST TOWARD THE BEGINNING OF NEXT WEEK TO BRING THE NEXT ROUND
OF SHOWERS AND THUNDERSTORMS.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR NCZ035>037-
     057-071-072-082-501>504.
SC...NONE.

&&

SYNOPSIS...HG
NEAR TERM...HG
SHORT TERM...LG
LONG TERM...SBK
AVIATION...HG

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1105 AM EDT WED SEP 10 2008

GAZ010-017-018-026-028-029-NCZ033-048>053-056-058-059-062>065-
068>070-505>510-SCZ001>014-019-111515-
RABUN-HABERSHAM-STEPHENS-FRANKLIN-HART-ELBERT-AVERY-MADISON-YANCEY-
MITCHELL-SWAIN-HAYWOOD-BUNCOMBE-CATAWBA-GRAHAM-NORTHERN JACKSON-
MACON-SOUTHERN JACKSON-TRANSYLVANIA-HENDERSON-CLEVELAND-LINCOLN-
GASTON-MCDOWELL MOUNTAINS-EASTERN MCDOWELL-RUTHERFORD MOUNTAINS-
GREATER RUTHERFORD-POLK MOUNTAINS-EASTERN POLK-OCONEE MOUNTAINS-
PICKENS MOUNTAINS-GREENVILLE MOUNTAINS-GREATER OCONEE-
GREATER PICKENS-GREATER GREENVILLE-SPARTANBURG-CHEROKEE-YORK-
ANDERSON-ABBEVILLE-LAURENS-UNION SC-CHESTER-GREENWOOD-
1105 AM EDT WED SEP 10 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST GEORGIA...PIEDMONT
NORTH CAROLINA...WESTERN NORTH CAROLINA AND UPSTATE SOUTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

NUMEROUS SHOWERS WILL DEVELOP ACROSS THE REGION TODAY...WITH
EMBEDDED ISOLATED TO SCATTERED THUNDERSTORMS. THE MAIN THREAT WILL
BE AN OCCASIONAL CLOUD TO GROUND LIGHTNING STRIKE AND LOCALLY
HEAVY RAINFALL WITH ANY THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

NCZ035>037-057-071-072-082-501>504-111515-
ALEXANDER-IREDELL-DAVIE-ROWAN-MECKLENBURG-CABARRUS-UNION NC-
CALDWELL MOUNTAINS-GREATER CALDWELL-BURKE MOUNTAINS-GREATER BURKE-
1105 AM EDT WED SEP 10 2008

...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PIEDMONT NORTH CAROLINA AND
WESTERN NORTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FLASH FLOOD WATCH.

EMBEDDED SCATTERED THUNDERSTORMS COULD ALSO PRODUCE AN ISOLATED
LIGHTNING STRIKE.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO RELAY ANY REPORTS OF FLOODING TO THE
NATIONAL WEATHER SERVICE.

HG