Flash Flooding and Flooding in North Carolina, September 20, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
330 AM EDT SUN SEP 20 2009

.SYNOPSIS...
BROAD LOW PRESSURE OVER THE MISSISSIPPI RIVER VALLEY WILL CONTINUE
TO BRING DEEP MOISTURE ACROSS THE SOUTHEAST TODAY AND TONIGHT. WEAK
HIGH PRESSURE WILL LINGER OVER THE REGION FOR MOST OF THE WORK WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
NUMEROUS TO WIDESPREAD SHOWER ACTIVITY CONTINUES AT 06Z ACROSS THE
WESTERN CAROLINAS IN A WARM ADVECTION UPGLIDE/SE UPSLOPE FLOW
REGIME. SOME OF THE SHOWERS HAVE BEEN CONCENTRATED/ANCHORED NEAR THE
BLUE RIDGE RESULTING IN WHAT SHOULD BE SOME IMPRESSIVE RAINFALL
TOTALS. FOR THE VERY NEAR TERM THIS WILL REQUIRE A CATEGORICAL POP
NEAR THE BLUE RIDGE AND OVER TOWARD METRO CLT...AND LIKELY
ELSEWHERE. THE INGREDIENTS FOR CONTINUED HEAVY RAIN REMAIN IN PLACE
THROUGH THIS MORNING WITH LOW LEVEL MOISTURE CONVERGENCE...HIGH
PW...AND ADDITIONAL FORCING ARRIVING FROM THE SW. HAVE GENERALLY
ACCEPTED THE HIGH MOSGUIDE POP WHICH KEEPS CATEGORICAL RAIN FORECAST
ON THE E SIDE OF THE HIGH TERRAIN...THEN TAPERING OFF ACROSS THE WRN
PIEDMONT. EXPECT TEMPS TO REMAIN COOL TODAY SO THE COOLER GUIDANCE
WAS FOLLOWED.

SUNDAY NIGHT LOOKS VERY SIMILAR TO THE SITUATION WE HAVE RIGHT
NOW...WITH CONINUED UPSLOPE/UPGLIDE. IF THIS GOES DOWN IN A SIMILAR
FASHION...THEN WE ARE GOING TO HAVE TO CONSIDER A FLOOD WATCH FOR
THE ZONES NEAR THE BLUE RIDGE. WOULD RATHER NOT ISSUE A WATCH RIGHT
NOW FOR ZONES THAT ALREADY HAVE A WARNING...SO IT WILL BE EVALUATED
LATER IN THE MORNING. TEMPS WERE KEPT CLOSE TO THE GUIDANCE FOR
LOWS.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
AS OF 240 AM SUNDAY...ON MONDAY AND TUESDAY...BOTH THE 0Z GFS AND
ECMWF AGREE THAT A MID LEVEL LOW WILL CLOSE OFF OVER THE PLAINS AS A
RIDGE BUILDS OVER THE ATLANTIC COAST. AT THE SFC...WEAK HIGH
PRESSURE WILL LIKELY CONTINUE TO NOSE SE ACROSS THE CWA. THIS
PATTERN SHOULD FAVOR A CONTINUATION OF MOSTLY CLOUDY CONDITIONS WITH
TEMPERATURES AT OR SLIGHTLY LESS THAN NORMAL. ON MONDAY...IT APPEARS
THAT UPSLOPE FLOW AND DIURNAL INSTABILITY WILL SUPPORT LIKELY
COVERAGE OF SHRA AND POSSIBLY TSRA OVER THE MTNS...SCT COVERAGE
EAST. LI/S ON THE GFS INDICATE THAT THE SOUTHERN TIER OF THE CWA IS
FAVORED FOR INCREASED INSTABILITY. ON TUESDAY...ATLANTIC RIDGE AXIS
BEGINS TO SHIFT WEST...WITH THE CENTER PIVOTING OVER THE DEEP SOUTH.
THE RIDGE SHOULD REDUCE TUESDAY/S COVERAGE FROM MONDAY...DUE TO
DECREASED AFTERNOON INSTABILITY. I WILL FORECAST CHC POPS THROUGH
EARLY AFTERNOON...WITH LIKELY COVERAGE OVER THE MTN PEAKS DURING THE
MID TO LATE AFTERNOON.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 3 AM SUNDAY...I WILL FAVOR THE ECMWF FOR ADJUSTMENTS WITHIN
THE EXTENDED PERIOD. WEAK MID LEVEL RIDGING WILL CONTINUE ACROSS THE
CWA FROM MID WEEK INTO THE EARLY WEEKEND. AT THE SFC...PRESSURES
SHOULD FAVOR SLIGHT HIGH PRESSURE...HOWEVER...A WEAK COLD FRONT
COULD SWEEP ACROSS THE REGION LATE IN THE WORK WEEK. TIMING AND
STRENGTH OF EXTENDED RANGE SFC FEATURES ARE TOO UNCERTAIN AT THIS
TIME. HOWEVER...THE CLOSED LOW OVER THE PLAINS WILL LIKELY MOVE
EAST...INCREASING MOISTURE AND LLVL RETURN FLOW ACROSS THE REGION.
OVERALL...DIURNAL SWINGS IN POPS ARE ANTICIPATED...PEAKING WITH CHC
DURING THE AFTERNOON AND EVENING WITH SCHC AT NIGHT. MOS GUIDANCE
AND PATTERN SUPPORT TEMPERATURES AT OR SLIGHTLY ABOVE NORMAL.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KCLT...A LARGE AREA OF SLOW MOVING LIGHT TO MODERATE RAIN WILL
AFFECT THE TERMINAL FOR AT LEAST THE NEXT HOUR. THIS SHOULD KEEP A
PREVAILING MVFR VISIBILITY WITH CEILING COMING IN AND OUT OF LOW END
MVFR. WHEN THE RAIN FINALLY MOVES OUT...THERE COULD BE A BRIEF
PERIOD OF VFR...BUT THIS SHOULD FILL IN QUICKLY WITH FOG AND LOW
CLOUDS. GUIDANCE IS PESSIMISTIC WITH A TREND TOWARD IFR BY 09Z AND
WITH THE AIR MASS BEING FORCED BY MOIST UPGLIDE THIS SEEMS
REASONABLE. ONCE AGAIN...THESE CONDITIONS ARE EXPECTED TO IMPROVE
DURING THE MID TO LATE MORNING. CEILING SHOULD PROGRESS UPWARD
THROUGH MVFR AND PROBABLY TO LOW END VFR IN THE AFTERNOON. IF IT
DOES BREAK OUT...EXPECT A GREATER CHANCE OF SEEING SCATTERED
THUNDERSTORMS...BUT THIS WILL NOT BE PUT IN THE TAF FOR NOW.

ELSEWHERE...SHOWERS AIDED BY UPSLOPE/WARM ADVECTION SHOULD CONTINUE
TO DEVELOP ACROSS THE REGION THROUGH AT LEAST MID MORNING.
WIDESPREAD FLIGHT RESTRICTIONS ARE EXPECTED LATE TONIGHT WITH AREAS
OF IFR LIKELY TOWARD SUNRISE. DIURNAL IMPROVEMENT IS ALSO LIKELY ON
SUNDAY...WITH CIGS/VSBY IMPROVING FROM MID-MORNING ONWARD AND
PROBABLY BECOMING UNRESTRICTED ACRS MUCH OF THE FA DURING THE
AFTERNOON. HOWEVER...THIS SHOULD FILL RIGHT BACK IN DURING THE
EVENING HOURS.

OUTLOOK...A STAGNANT PATTERN WILL FAVOR PERIODS OF RAIN THROUGH MID
WEEK. EXPECT RESTRICTIONS...MAINLY MVFR...ESPECIALLY AT NIGHT...WITH
IFR POSSIBLE AROUND DAWN.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

SYNOPSIS...NED
NEAR TERM...PM
SHORT TERM...NED
LONG TERM...NED
AVIATION...PM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
500 AM EDT SUN SEP 20 2009

GAZ010-017-018-026-028-029-NCZ033-048>053-058-059-062>065-501>510-
SCZ001>007-010-210900-
RABUN-HABERSHAM-STEPHENS-FRANKLIN-HART-ELBERT-AVERY-MADISON-YANCEY-
MITCHELL-SWAIN-HAYWOOD-BUNCOMBE-GRAHAM-NORTHERN JACKSON-MACON-
SOUTHERN JACKSON-TRANSYLVANIA-HENDERSON-CALDWELL MOUNTAINS-
GREATER CALDWELL-BURKE MOUNTAINS-GREATER BURKE-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-ANDERSON-
500 AM EDT SUN SEP 20 2009

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

.DAY ONE...TODAY AND TONIGHT.
PERIODS OF MODERATE TO HEAVY RAIN WILL CONTINUE ACROSS THE NORTH
CAROLINA MOUNTAINS AND ADJACENT FOOTHILLS THIS MORNING. SEVERAL INCHES OF
RAIN HAS ALREADY FALLEN ACROSS THE EAST FACING SLOPES EARLIER THIS
MORNING. ADDITIONAL RAINFALL TODAY COULD RESULT IN RAPID RISES
ALONG SMALL STREAM AND CREEKS AND POSSIBLY DEEP STANDING WATER
WITHIN AREAS OF POOR DRAINAGE. IN ADDITION...ISOLATED MUD SLIDES
MAY OCCUR DURING HEAVY RAINFALL RATES ACROSS STEEP TERRAIN.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE REQUESTED TO FORWARD ANY REPORTS OF FLASH
FLOODING TO OUR OFFICE.

NCZ035>037-056-057-068>072-082-SCZ008-009-011>014-019-210900-
ALEXANDER-IREDELL-DAVIE-CATAWBA-ROWAN-CLEVELAND-LINCOLN-GASTON-
MECKLENBURG-CABARRUS-UNION NC-CHEROKEE-YORK-ABBEVILLE-LAURENS-
UNION SC-CHESTER-GREENWOOD-
500 AM EDT SUN SEP 20 2009

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

.DAY ONE...TODAY AND TONIGHT.

SCATTERED TO NUMEROUS SHOWERS...A FEW HEAVY AT TIMES...WILL
CONTINUE ACROSS THE PIEDMONT THIS MORNING. HIGH RAINFALL RATES WILL
LIKELY LEAD TO STANDING WATER WITHIN AREAS OF POOR DRAINAGE.
OTHERWISE...NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE REQUESTED TO FORWARD ANY REPORTS OF FLASH
FLOODING TO OUR OFFICE.

NED