Flash Flood Warning 50, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
118 PM EDT SAT AUG 21 2010

.SYNOPSIS...
UNSETTLED WEATHER WILL CONTINUE THROUGH THE WEEKEND AS A WEAK COLD
FRONT PUSHES SOUTH TOWARD THE AREA. THE FRONT WILL STALL OUT OR MAKE
VERY LITTLE PROGRESS ON MONDAY...BUT IT SHOULD BE SOUTH OF THE AREA
BY TUESDAY. HIGH PRESSURE WILL BUILD IN FROM THE NORTH TUESDAY AND
REMAIN THROUGH THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
UPDATE...POPS AND QPF HAVE BEEN INCREASED FOR THE UPPER SAVANNAH
RIVER VALLEY INTO THIS AFTERNOON BASED ON RADAR TRENDS. THE UPPER
VORT APPEARS TO BE MOVING JUST SOUTH OF THE BLUE RIDGE...WHICH
SHOULD TAKE ADVANTAGE OF TERRAIN EFFECTS.

UPPER LEVEL RIDING WAS ANALYZED OVER THE APPALACHIANS THIS
MORNING...WITH A TROUGH UPSTREAM OVER FROM THE GREAT LAKES TO THE
MID MS RIVER VALLEY. A LOW TO MID LEVEL TROUGH WAS LOCATED IN
EASTERN GA AT 700 MB AND 850 MB...WHICH IS ASSOCIATED WITH THE LINE
OF CONVECTION MOVING EAST INTO THE UPPER SAVANNAH RIVER VALLEY AT
THIS TIME. A STATIONARY FRONT WAS LOCATED JUST SOUTHWEST OF THE
SAVANNAH RIVER VALLEY...CLOSE TO WHERE THE CONVECTION WAS NOTED. THE
NAM MOVES THIS UPPER FEATURE VERY SLOWLY EAST INTO SC BY
TONIGHT...WITH MOST OF ITS INSTABILITY REMAINING WEST OF INTERSTATE
77. LIGHT NORTHEASTERLY SURFACE WINDS ARE EXPECTED TO VEER TO THE
EAST TODAY...PROVIDING A BETTER UPSLOPE COMPONENT TO THE EAST
OF THE UPPER LEVEL SYSTEM. POPS WILL BE RAISED IN THE WEST TODAY...
PARTICULARLY IN SC AND GA...AND QPF RAISED AS WELL. SO FAR
PRECIPITATION HAS BEEN MOVING ENOUGH TO KEEP RAINFALL AMOUNTS
LIMITED...BUT AS THE UPPER SYSTEM SLOWS...AND INSTABILITY INCREASES
WITH HEATING...RAINFALL AMOUNTS SHOULD COME UP. FORTUNATELY...THIS
AREA HAS NOT HAS AS MUCH RECENT RAIN AS THE NC PIEDMONT...AND NO
FLASH FLOOD OR FLOOD WATCH IS ANTICIPATED AT THIS TIME. TEMPERATURES
BE SLIGHTLY ABOVE NORMAL DESPITE CLOUDS COVER...AS THE UPPER RIDGE
AXIS CROSS THE AREA TODAY.

CONVECTION WILL TAPER OFF TONIGHT...THOUGH THERE MAY BE AN INCREASE
ALONG THE TN LINE LATE AS A NRN STREAM THROUGH AS IT/S ASSOCIATED
COLD FRONT APPROACHES THE MTNS. I/M NOT LOOKING FOR WIDESPREAD
ACTIVITY ALONG THE FRONT OWING TO THE TIME OF DAY A FAIRLY WEAK
FORCING.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 240 AM SATURDAY...BETTER AGREEMENT IS SEEN THIS MORNING WRT TO
THE ULVL PATTERN SUN THROUGH MON. THE 00Z GFS IS NOW CLOSING OFF THE
UPPER LOW AND ACTUALLY DEEPENING AND KEEPING IT NORTH MORESO THAN
EITHER THE NAM OR THE ECMWF BY SUN EVENING. THIS HAS A DISTINCT
AFFECT ON THE TRANSITION OF THE SFC FRONT AND THE AMOUNT OF THETA/E
AIRMASS MIXING EXPECTED DURING THE DAY MON. BASICALLY THE GFS STALLS
THE FRONT OUT ACROSS REGION AND KEEPS THE AIRMASS STAGNANT...WHILE
THE OTHER TWO OP MODELS SWEEP THE FRONT TO THE COAST AND MIX IN A
DECENT AMOUNT OF LOWER THETA/E AIR.

SINCE THE GFS IS BRAND NEW TO THIS IDEA...MORE WEIGHT WILL BE GIVEN
TO THE IDEA OF A FROPA DURING THE DAY MON AND LITTLE IN THE WAY OF A
PRECIP OR TSTM THREAT THEREAFTER. IN ANY SENSE...THE FRONT WILL NOT
HAVE MUCH MOISTURE TO WORK WITH AS GOM TRANS VECTORS DONT REACH THE
TN VALLEY UNTIL LATE SAT. ALSO WITH THE LLVL RIDGE PERSISTING AND
WEAK FLOW AHEAD OF THE FRONT...NO EVIDENCE IS NOTED OF AN ERN GOM OR
ATL MOISTURE FLUX INTO THE AREA SUN.

MODEL SOUNDINGS INDICATE PW/S IN THE 1.5 TO 1.8 IN RANGE AHEAD OF
THE FRONT...HOWEVER LOW INSTABILITY AND WEAK DYNAMICAL FORCING WILL
NOT ALLOW FOR MUCH OF A HEAVY PRECIP THREAT. IN FACT...MOST OF THE
PRECIP SHOULD BE ASSOCIATED WITH -SHRA AND A FEW TSTMS ACROSS THE NC
MTN COUNTIES WHERE PERHAPS AN INCH OF PRECIP WILL FALL BTW 12Z SUN
AND 12Z MON. OUTSIDE THE MTNS...MOST LIKELY AROUND A HALF INCH WILL
FALL IN SCATTERED ACTIVITY.

TEMPS ON SUN SHOULD STILL REACH A FEW DEGREES ABOVE NORMAL UNDER THE
S/W RIDGE...AND RIGHT AROUND NORMAL MON...BUT PERHAPS A COUPLE
DEGREES BELOW NORMAL ACROSS THE NC MTN VALLEYS WHERE THERE WILL BE
MORE WIDESPREAD CLOUDINESS EARLY AND PERHAPS SOME DEGREE OF AIRMASS
MIXING BY THE EARLY AFTERNOON.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 320 AM SATURDAY...THE UPPER LEVEL LOW AXIS SHIFTS TO THE EAST
OF THE CWFA TUE AND SETS UP A RATHER STRONG SUBSIDENCE ZONE ACROSS
THE REGION. THIS SHOULD LIMIT THE CONV POTENTIAL...HOWEVER A FEW
ISOL -SHRA AND TSTMS ARE POSSIBLE WITH RESIDUAL LLVL MOISTURE
POSSIBLY ENHANCED SOMEWHAT BY A WAVY SFC FRONT TO THE SOUTH. THE GFS
LIKES THIS POSSIBILITY MORE THAN THE ECMWF...BUT GIVEN THE AMOUNT OF
LARGE SCALE DOWNWARD MOTION EXPECTED...A NOD WILL BE GIVEN TO THE
DRIER ECMWF. THE MODELS DO AGREE THAT AFT TUE THE UPPER PATTERN
BECOMES QUASI/ZONAL WITH A LOW AMPLITUDE WAVE BRINGING A WEAK AND
MOISTURE CHALLENGED SFC FRONT TO THE MTNS EARLY THU. MILDER CONDS
COULD SET UP FRI THROUGH SAT AS A MID/ATL WEDGE LOOKS TO DEVELOP.
THE DEGREE OF MOISTURE AFFECTING THIS WEDGE IS STILL UNCERTAIN...BUT
LOWER THETA/E AIR COULD HOLD MAX TEMPS A COUPLE DEGREES BELOW
NORMAL. HOWEVER BEFORE THEN...MAX TEMPS SHOULD AVG RIGHT AROUND
NORMAL.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...EAST SOUTHEAST WINDS WILL BECOME CALM THIS EVENING...
ABOUT THE TIME LOW CLOUDS MOVE IN AHEAD OF THE SLOWLY ADVANCING VORT
MAX IN THE SAVANNA RIVER VALLEY. GUIDANCE ONLY SUPPORTS BRIEF MVFR
VISIBILITY IN FOG SUNDAY MORNING...WITH CEILINGS AT THE LOW END OF
VFR. LIGHT WINDS COME UP FROM THE SOUTHWEST AFTER DAYBREAK...WITH A
LOW VFR CEILING PERSISTING AS MOISTURE POOLS AHEAD OF AN APPROACHING
COLD FRONT.

ELSEWHERE...MVFR TO IFR CEILINGS AND VISIBILITY WILL BE INDUCED BY
PRECIPITATION AND A GRADUALLY VEERING UPSLOPE FLOW COMPONENT AS A
MID LEVEL VORT MAX CROSSES THE UPPER SAVANNAH RIVER VALLEY. LOW
LEVEL MOISTURE IN THE WAKE OF THIS SYSTEM WILL KEEP RESTRICTIONS
GOING OVERNIGHT...WITH WINDS GOING CALM. GUIDANCE SUPPORTS THE WORST
RESTRICTIONS AT KAVL AND KAND...WHICH MAKES SENSE BASE ON WHERE THE
TRACK OF THE VORT...THE STALLED SURFACE FRONT... AND TERRAIN EFFECTS
COINCIDE. GUIDANCE SUPPORTS MVFR FOG BUT VFR CEILINGS AT KGSP AND
KGMU...AS WELL AS KHKY WHERE IFR IS ONLY HINTED AT. LIGHT WEST
SOUTHWEST WINDS COME UP AFTER DAYBREAK SUNDAY. LOW VFR CEILINGS ARE
EXPECTED FROM MID MORNING THROUGH MID DAY AHEAD OF AN APPROACHING
COLD FRONT.

OUTLOOK...A COLD FRONT WILL BRING SCT SHRA/TSTMS AND ASSOCIATED
RESTRICTIONS TO MOST OF THE REGION ON SUNDAY. BEHIND THE FRONT DRIER
WEATHER IS EXPECTED MON-WED.

&&

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

&&

SYNOPSIS...SBK
NEAR TERM...JAT/MCAVOY
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...JAT

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
526 AM EDT SAT AUG 21 2010

GAZ010-017-018-026-028-029-NCZ048-051>053-058-059-062>065-SCZ001>006-
010>012-019-220930-
RABUN-HABERSHAM-STEPHENS-FRANKLIN-HART-ELBERT-MADISON-SWAIN-HAYWOOD-
BUNCOMBE-GRAHAM-NORTHERN JACKSON-MACON-SOUTHERN JACKSON-TRANSYLVANIA-
HENDERSON-OCONEE MOUNTAINS-PICKENS MOUNTAINS-GREENVILLE MOUNTAINS-
GREATER OCONEE-GREATER PICKENS-GREATER GREENVILLE-ANDERSON-ABBEVILLE-
LAURENS-GREENWOOD-
526 AM EDT SAT AUG 21 2010

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

.DAY ONE...TODAY AND TONIGHT.

SCATTERED SHOWERS AND THUNDERSTORMS WILL AFFECT THE SOUTHWEST
MOUNTAINS OF NORTH CAROLINA...NORTHEAST GEORGIA AND THE UPSTATE
WEST OF GREENVILLE TODAY. BRIEF...HEAVY RAIN AND CLOUD TO GROUND
LIGHTNING WILL BE THE MAIN THREAT FROM THUNDERSTORMS THIS
AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

NONE.

NCZ033-035>037-049-050-056-057-068>072-082-501>510-SCZ007>009-013-
014-220930-
AVERY-ALEXANDER-IREDELL-DAVIE-YANCEY-MITCHELL-CATAWBA-ROWAN-
CLEVELAND-LINCOLN-GASTON-MECKLENBURG-CABARRUS-UNION NC-
CALDWELL MOUNTAINS-GREATER CALDWELL-BURKE MOUNTAINS-GREATER BURKE-
MCDOWELL MOUNTAINS-EASTERN MCDOWELL-RUTHERFORD MOUNTAINS-
GREATER RUTHERFORD-POLK MOUNTAINS-EASTERN POLK-SPARTANBURG-CHEROKEE-
YORK-UNION SC-CHESTER-
526 AM EDT SAT AUG 21 2010

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

.DAY ONE...TODAY AND TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

NONE.

14

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1203 PM EDT SAT AUG 21 2010

GAZ010-017-018-026-028-029-SCZ001-004-010-211745-
ANDERSON-ELBERT-FRANKLIN-GREATER OCONEE-HABERSHAM-HART-OCONEE
MOUNTAINS-RABUN-STEPHENS-
1203 PM EDT SAT AUG 21 2010

...AN AREA OF HEAVY RAIN WILL AFFECT FRANKLIN...HABERSHAM...
HART...OCONEE... RABUN...SOUTHWESTERN ANDERSON...STEPHENS AND
WESTERN ELBERT COUNTIES THROUGH 145 PM EDT...

AT 1152 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LARGE AREA OF SHOWERS THAT WAS PRODUCING RAINFALL AMOUNTS UP TO 1
INCH PER HOUR. THE HEAVIEST RAIN WAS MOVE THROUGH STEPHENS AND RABUN
AND HART COUNTIES. RUNOFF FROM THESE STORMS WILL CAUSE MINOR
FLOODING OF SMALL CREEKS AND STREAMS...URBAN AREAS...HIGHWAYS...
STREETS AND UNDERPASSES AS THE RAIN BECOMES HEAVIER DURING THE
AFTERNOON.

HEAVY RAINS MAY FLOOD LOW LYING AREAS SUCH AS DITCHES AND
UNDERPASSES. AVOID THESE AREAS AND DO NOT CROSS FLOODED ROADS. WATER
LEVELS OF SMALL STREAMS AND RIVERS MAY ALSO RISE...THEREFORE SEEK
HIGHER GROUND IF THREATENED BY FLOOD WATERS.

LAT...LON 3411 8304 3417 8311 3426 8312 3425 8334
      3432 8340 3446 8340 3448 8356 3443 8362
      3447 8365 3476 8363 3479 8368 3488 8366
      3499 8355 3500 8309 3466 8284 3461 8286
      3464 8282 3449 8271 3416 8273 3404 8289

PAT

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
158 PM EDT SAT AUG 21 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0156 PM     FLASH FLOOD      4 N MOCCASIN CREEK STAT 34.91N 83.58W
08/21/2010                   RABUN              GA   LAW ENFORCEMENT

            MUD SLIDE CAUSED BY HEAVY RAIN ON HIGHWAY 76 WEST NEAR
            TOWNS COUNTY LINE.

&&

PTANNER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
200 PM EDT SAT AUG 21 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0156 PM     FLASH FLOOD      CLAYTON                 34.88N 83.40W
08/21/2010                   RABUN              GA   LAW ENFORCEMENT

            HIGHWAY 76 EAST IN CLAYTON GA CLOSED DUE TO FLOODING

&&

PTANNER