Flash Flood Warning 74, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
350 PM EDT THU AUG 5 2010

.SYNOPSIS...
A COLD FRONT APPROACHES THE REGION FROM THE NORTH TODAY AND STALLS
NEAR THE VIRGINIA/NORTH CAROLINA BORDER FRIDAY MORNING. THIS FRONT
WILL FINALLY GET SCOOTED SOUTH BY FRIDAY NIGHT AS HIGH PRESSURE
PUSHES IN FROM THE GREAT LAKES. A WEDGE OF HIGH PRESSURE WILL
SETTLE ALONG THE NEW ENGLAND AND MIDDLE ATLANTIC COASTS THIS
WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
MAIN AREA OF CONCERN THIS EVENING WILL BE PIEDMONT AND
SOUTHSIDE...ALTHOUGH SVR STORMS WILL OCCUR ACROSS THE ENTIRE CWA.
LINE OF SVR STORMS JUST NOW AT KLWB HAS WEAKENED
SLIGHTLY...COMPARED TO ITS INTENSITY OVER CENTRAL WEST VA.
IMPRESSIVE HEAT AND HUMIDITY REMAINS ALONG THE LYH/DAN CORRIDOR.
AS THE LINE NEAR KLWB WEAKENS A BIT CROSSING THE MOUNTAINS...IT
WILL POSSIBLY RE INTENSIFY RAPIDLY WHEN ENCOUNTERING THE HIGH CAPES
BLUE RIDGE AND EAST. WIDESPREAD WIND DAMAGE WITH THIS LINE...IF IT
HOLDS TOGETHER EAST OF ROANOKE/BLACKSBURG/PULASKI IS LIKELY.
CURRENT MESOSCALE ANALYSIS PUTS 4500 J/KG LYH/DAN WHERE THE HEAT
ADVISORY IS IN EFFECT. 0-1KM STORM RELATIVE HELICITY IS CURRENTLY
PROGGED AT 50 M2/S2 OVER THESE AREAS...AND WITH STRONGER UPDRAFTS
STORMS MAY SHOW BETTER ROTATION THAN WHAT IS OCCURRING RIGHT NOW
OVER THE WEST. STORMS OVR KENTUCKY TAKING MORE OF A RIGHT TURN
THAN EARLIER TODAY...WITH THE COLD FRONT GETTING INVOLVED. STORMS
NOT BACKBUILDING/TRAINING AS MUCH TO THE WEST...HOWEVER...MOVEMENT
IS WEST TO EAST CURRENTLY IN THE BLF/JFZ CORRIDOR...OR THE
SOUTHERN HALF OF THE FLASH FLOOD WATCH. BASED UPON TRENDS THE
WATCH MAY NEED TO BE EXTENDED INTO NW NC. SHWS/STORMS ONLY REMAIN
VA/NC BORDER AND SOUTH AFTER 8Z TONIGHT.

MODELS ARE STRONGER WITH COLD FRONTAL PASSAGE THAN YESTERDAY'S
RUNS FOR FRIDAY...WITH MID 60S DEWPOINTS GETTING CLOSE TO THE
VA/NC BORDER. THIS SHOULD PLUNGE ANY SHWS/STORMS MAINLY SOUTH OF
THE NEW RIVER VALLEY. NOT MUCH IN THE WAY OF COLD AIR ARRIVING
THOUGH WITH H85 TEMPS ONLY FALLING TO +17C AT H85 ACROSS SE WEST
VA, BASED UPON SREF TRENDS...WHICH HAVE BEEN PUSHING MEASURABLE
PRECIP FURTHER SOUTH WITH EACH RUN...DID REDUCE POPS A TAD IN
SOUTHERN VIRGINIA. IN FACT...BOTH THE GFS/NAM PROFILES ARE BLO 1K
J/KG CAPE EVEN INTO KDAN FRIDAY. THIS SHOULD KEEP ANY STRONG CELLS
SOUTH OF THE CWA PER LATEST SPC DAY 2. BASED UPON THE FURTHER
SOUTHWARD PROGRESSION OF THE FRONT...MAX T MAY COME IN A FEW
DEGREES COOLER THAN CURRENTLY FORECAST.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
THE COLD FRONT WILL MOVE SOUTH OF THE FORECAST AREA AS HIGH
PRESSURE BUILDS SOUTHEAST FROM THE GREAT LAKES. KEPT LIGHT POPS FOR
CONVECTION ACROSS SOUTHERN PORTIONS OF CWA EARLY FRIDAY NIGHT.
SURFACE DEW POINTS WILL DROP INTO THE 50S AND 60S AS DRIER AIR MOVES
IN FROM THE NORTH AND NORTHEAST. BY SATURDAY MORNING...850 MB
TEMPERATURES WILL BE +14 TO +18. WENT WITH LOW TEMPERATURES FRIDAY
NIGHT CLOSE TO ADJMETBC WITH READINGS FROM THE UPPER 50S TO THE
UPPER 60S IN THE SOUTHEAST. HIGH PRESSURE WILL BUILD SOUTH ACROSS
OUR AREA ON SATURDAY. ALLOWED FOR AN ISOLATED THUNDERSTORMS ACROSS
THE HIGHER ELEVATION IN THE SOUTHWEST. WITH SOME SUNSHINE ON
SATURDAY PLAYED HIGH CLOSE TO THE ADJMETBC FROM AROUND 80 IN THE
MOUNTAINS TO NEAR 90 IN THE PIEDMONTS. EASTERLY WINDS WILL DEVELOP
SATURDAY NIGHT AS HIGH PRESSURE SHIFTS EAST. INCREASED CLOUD COVER
AND ADDED LIGHT POPS ALONG THE SOUTHERN BLUE RIDGE MOUNTAINS. FOR
LOW TEMPERATURES SATURDAY NIGHT...USED A BLEND OF CONTINUITY AND GFS
ENSEMBLE MOS.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
SOME OF THE FORECAST CHALLENGES ON SUNDAY ARE THE POTENTIAL FOR
A COOL WEDGE WITH EASTERLY FLOW AND TEMPERATURE FORECAST WITH
A LARGE BUST POTENTIAL. THE NAM SHOWED A STRONG EASTERLY FETCH ON
SUNDAY. 12Z GFS HAD THE EASTERLY WINDS AND INCREASED RH ACROSS
THE SOUTH AND EAST. WITH MOIST LLVLS AND UPSLOPE FLOW SUPPORT
INCREASED POPS NORTHWARD ALONG THE BLUE RIDGE MOUNTAINS...AND
KEPT CHC ACROSS EXTREME SW VA AND NW NC. UNDERCUT MOSGUIDE AND
BLENDED TOWARDS GFS ENSEMBLE HIGHS ON SUNDAY. KEPT LIGHT POPS FOR
SUNDAY NIGHT WITH LOWS FROM THE MID 60S IN THE WEST TO THE LOWER 70S
IN THE EAST.  UPPER HIGH OVER THE CENTRAL CONUS WILL MOVE EAST EARLY
NEXT WEEK. ALLOWING FOR A SOUTHERLY FLOW WITH A WARM UP INTO THE
UPPER 80S MOUNTAINS AND MID/UPPER 90S LOWLANDS. WILL ALLOW FOR SOME
ISOLATED TO SCATTERED CONVECTION MAINLY DURING THE AFTERNOON AND
EVENING HOURS...ESPECIALLY ACROSS THE HIGHER TERRAIN...AHEAD OF THE
NEXT COLD FRONT.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
LINE OF SVR TSTORMS PROGGED TO BE AT KLWB 1930Z...WIND GUSTS TO
50KTS MAY OCCUR. GUSTS TO 30KTS MAY OCCUR AHEAD OF THE LINE. STILL
SOME QUESTION AS TO HOW WELL THE LINE HOLDS TOGETHER ACROSS THE
MOUNTAINS INTO KROA/KLYH. ALTHOUGH IT MAY WEAKEN...OUTFLOWS FROM
OTHER STORMS WILL LIKELY LEAD TO MORE SCATTERED STRONG TO SVR
CELLS LATER THIS PM AND EVENING. SCATTERED STRONG STORMS WILL
AFFECT KBLF...BEFORE A MORE ORGANIZED STRONG LINE OF STORMS POSSIBLY
ARRIVES AROUND 22Z. COLD FRONT WILL POSSIBLY BE LOCATED BETWEEN
KLYH/KDAN NEAR 12Z. CONFIDECNE IS LOW REGARDING AMOUNT OF CLEARING
OCCURS BEHIND THE FRONT...IF IT OCCURS KLWB WILL LIKELY EXPEREINCE
LIFR VIS/CIG. FAVORING MORE CLDS THAN MODELS ARE FORECASTING THUS
ONLY GOING WITH IFR VIS ATTM. AS FRONT LINGERS ALONG THE VA/NC
BORDER...MORE STORMS WILL FIRE ESPECIALLY AT KDAN ON FRIDAY...MORE
WIDELY SCATTERED TO ISOLATED ROA/LYH/LWB.

DRIER CONDITIONS ARE POSSIBLE THIS WEEKEND INTO MONDAY WITH
OVERNIGHT FOG. A WEDGE OF HIGH PRESSURE MAY BRING SOME LOWER
CLOUDS INTO THE AREA SUNDAY...SUB-VFR POSSIBLE.

A RETURN TO VFR CONDS IS EXPECTED TUESDAY..

&&

.EQUIPMENT...
FAA TECHNICIANS ARE STILL WORKING ON THE ISSUE WITH THE LYH ASOS
OBSERVATIONS BEING TRANSMITTED.

ALSO...THE LYH NOAA WEATHER RADIO TRANSMITTER IS DOWN AND VERIZON
IS GOING TO BE WORKING ON THE PHONE LINES TO TRY AND RESTORE
SERVICE BY LATER THIS MORNING.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...HEAT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR VAZ044>047-058-
     059.
     FLASH FLOOD WATCH UNTIL 9 PM EDT THIS EVENING FOR VAZ007-009-
     010-020.
NC...HEAT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR NCZ005-006.
WV...FLASH FLOOD WATCH UNTIL 9 PM EDT THIS EVENING FOR WVZ042>045.

&&

SYNOPSIS...KM/WP
NEAR TERM...KM
SHORT TERM...KK
LONG TERM...KK
AVIATION...KM/WP
EQUIPMENT...

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
438 PM EDT THU AUG 05 2010

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

0420 PM     FLASH FLOOD      BLOWING ROCK            36.13N 81.67W
08/05/2010                   WATAUGA            NC   TRAINED SPOTTER

            MORE THAN SIX INCHES OF WATER FLOWING ACROSS HIGHWAY 321.
            EVENT STARTED AT 420 PM AND IS CONTINUING AT 435 PM.

&&

BS

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