Special Weather Statement, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
326 PM EDT THU AUG 11 2011

.SYNOPSIS...
A WEAK COOL FRONT WILL REMAIN STALLED ACROSS THE CAROLINAS
TONIGHT. HIGH PRESSURE WILL MOVE EAST ACROSS THE MID ATLANTIC
REGION FRIDAY AND DRIFT OUT INTO THE ATLANTIC OCEAN ON SATURDAY.
ANOTHER COLD FRONT WILL MOVE THROUGH THE REGION SATURDAY NIGHT
INTO SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 325 PM THURSDAY...
SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPED IN THE UNSTABLE AIR
WITH CAPES AROUND 2000 J/KG WITH AND LIS AROUND MINUS 4 ACROSS
NORTHWEST NORTH CAROLINA. SFC COLD FRONT WITH A WEAK LOW PRESSURE
CENTER ALONG IT WILL DRIFT EAST TONIGHT. UPPER LEVEL SHORTWAVE
WILL PIVOT EAST ACROSS THE REGION TONIGHT. HIGH PRESSURE ACROSS
THE OHIO VALLEY THIS AFTERNOON WILL MOVE EAST TONIGHT INTO MID
ATLANTIC REGION FRIDAY AND DRIFT OUT INTO THE ATLANTIC OCEAN ON
SATURDAY.

CONVECTION WILL DISSIPATE OR QUICKLY MOVE OUT OF CWA THIS EVENING.
AFTERNOON CU WILL DISSIPATE THIS EVENING...WHILE MID AND HIGH CLOUDS
WILL SPREAD NORTH IN SOUTHERN PORTIONS OF CWA. CLOUD COVER AND PUSH
OF DRIER AIR MAKES LOW TEMPERATURES OVERNIGHT QUITE A CHALLENGE.
USED A BLEND OF GUID WITH READINGS FROM AROUND 50 DEGREES
IN THE MOUNTAINS TO THE MID 60S IN THE SOUTHEAST.

AS HIGH PRESSURE SLIDES EAST ON FRIDAY...WINDS SHOULD VEER TO
SOUTHEASTERLY ACROSS OUR REGION. THESE SOUTHEASTERLY WINDS WILL
BRING ATLANTIC MOISTURE BACK INTO THE EAST SIDE OF THE APPALACHIANS
ON FRIDAY. EXPECT SHOWERS...AND ISOLATED THUNDERSTORMS...TO DEVELOP
ON FRIDAY AFTERNOON AND EVENING...MAINLY TO THE EAST OF THE BLUE
RIDGE...DUE BOTH TO SURFACE CONVERGENCE AROUND THE DEPARTING
HIGH...AS WELL AS THE UPSLOPE COMPONENT OF THE SOUTHEASTERLY WIND
FLOW. PLAYED THE HIGHEST POPS ALONG THE SOUTHERN BLUE RIDGE FRIDAY.
WENT WITH HIGHS CLOSE TO THE ADJMET WITH VALUES FROM THE UPPER 70S
IN THE MOUNTAINS TO THE UPPER 80S IN SOUTHSIDE.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 325 PM THURSDAY...
SURFACE HIGH PRESSURE WILL RESIDE OVER THE MID ATLANTIC FRIDAY
NIGHT AND DRIFT TO THE EAST AND OUT TO SEA SATURDAY. MOIST
SOUTHEAST FLOW AND ISENTROPIC LIFT FRIDAY NIGHT SHOULD BRING LIGHT
RAIN/DRIZZLE TO AREAS ALONG AND EAST OF THE BLUE RIDGE. WILL
MAINTAIN A 20 POP FOR AN ISOLATED SHOWER OVERNIGHT...OTHERWISE
EXPECT DRIZZLE/FOG/LOW CLOUDS. SURFACE HIGH LOOSES ITS INFLUENCE
ON THE REGION SATURDAY AFTERNOON AS FLOW BECOMES SOUTHWEST. THIS
VERY MOIST SOUTHWEST FLOW WILL BRING PWATS UP TO AROUND 2 INCHES
WHICH IS 2 STANDARD DEVIATIONS ABOVE NORMAL OVER THE WEEKEND. THE
MODEL WEATHER PATTERN HAS CHANGED BUT THE OUTCOME REMAINS THE SAME
FOR SATURDAY AND SUNDAY. MODELS ARE A LITTLE SLOWER WITH
PREFRONTAL SHOWERS ENTERING SOUTHEAST WEST VIRGINIA LATE SATURDAY
AFTERNOON. THIS SLOWER ARRIVAL IS LIKELY DUE TO A DEVELOPING
OCCLUDED LOW OVER THE NORTHERN OHIO VALLEY. THE BEST FOCUS OF
HEAVY RAIN WILL BE NEAR THIS OCCLUDED LOW AND NORTH OF THE MASON-
DIXON LINE. HOWEVER...WITH A TROPICAL-LIKE AIRMASS AND A SLOW
MOVING FRONT...PROLONG PERIODS OF HEAVY SHOWERS AND THUNDERSTORMS
SATURDAY NIGHT INTO SUNDAY MORNING WILL BRING A THREAT FOR FLASH
FLOODING. THE FRONT ITSELF WILL TRACK FROM WEST TO EAST SATURDAY
NIGHT AND EXIT THE PIEDMONT LATE SUNDAY MORNING. STORMS ALONG THE
FRONT WILL REPEATEDLY MOVE FROM THE SOUTHWEST TO NORTHEAST. THESE
STORMS WILL BE ASSISTED BY AN ENTRANCE REGION OF A 40 KT LOW LEVEL
JET. STRONGER STORMS TRAINING OVER THE SAME AREA POSES A HIGH
THREAT FOR FLASH FLOODING. SINCE THIS PERIOD IS DAY 3-4...WILL
CONTINUE TO HIGHLIGHT IN THE HAZARDOUS WEATHER OUTLOOK (HWO). WE
SHOULD SEE A DRY SLOT SUNDAY AFTERNOON THEN THE UPPER LEVEL LOW
WILL BRING ANOTHER ROUND OF SHOWERS TO THE AREA SUNDAY
NIGHT/MONDAY.

THIS STRONG FRONT WILL BE A GAME CHANGER FOR THE REGIONS WEATHER.
ONE...IT WILL HELP WITH THE DRY CONDITIONS BY BRINGING MUCH NEEDED
RAIN TO THE AREA. THE SECOND CHANGE IS A DROP IN TEMPERATURES. WE
COULD BE SEEING A 4-5 DAY STRETCH OF TEMPERATURES BEING BELOW
NORMAL. SATURDAY WILL BE THE WARMEST DAY OF THE PERIOD WITH
TEMPERATURES NEAR NORMAL. TEMPERATURES SUNDAY...DROP BELOW NORMAL
WITH MID 70S IN THE WEST AND LOWER 80S IN THE EAST.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 325 PM TUESDAY...
GFS AND ECMWF IN AGREEMENT THAT BY SUNDAY NIGHT THE COLD FRONT AND
ASSOCIATED SHOWERS AND THUNDERSTORMS WILL HAVE MOVED EAST OF THE
CWA. HOWEVER AN ANOMALOUSLY STRONG TROUGH OF 3 TO 4 STANDARD
DEVIATIONS BELOW NORMAL WILL MOVE OVERHEAD SUNDAY NIGHT INTO THE
DAY MONDAY. THIS TROUGH AND ASSOCIATED NORTHWEST WINDS WILL LIKELY
MEAN THAT SCATTERED SHOWERS WILL CONTINUE IN THE MOUNTAINS SUNDAY
NIGHT...WITH DRYING IN THE DOWNSLOPE AREAS. ON MONDAY THE TROUGH
AXIS MOVES OVERHEAD AND SHIFTS TO OUR EAST BY MONDAY EVENING. THE
TROUGH OVERHEAD WILL BRING IN COOL TEMPERATURES ALOFT...AND THIS
COMBINED WITH DIURNAL HEATING WILL LIKELY LEAD TO SCATTERED
AFTERNOON SHOWERS. INSTABILITY SHOULD BE SHALLOW AND THINK THUNDER
CHANCES WILL BE LOW WITH THIS CONVECTION. AREAS EAST OF THE BLUE
RIDGE WILL CONTINUE TO EXPERIENCE A DRYING DOWNSLOPE
WIND...HOWEVER CAN NOT RULE OUT A SHOWER EVEN THERE WHEN THE
TROUGH AXIS MOVES ACROSS DURING THE AFTERNOON.

MODELS IN GOOD AGREEMENT THAT THE TROUGH SHIFTS TO THE ATLANTIC
COAST ON TUESDAY...ALLOWING US TO SEE SUBSIDENCE AND DRYING. THE
TROUGH ONLY MAKES SLOW PROGRESS EAST THROUGH WEDNESDAY...HOWEVER IT
WILL BE FAR ENOUGH EAST TO KEEP US IN THE DRY AIR. MODEL SOLUTIONS
DIVERGE A BIT TOWARDS THE END OF NEXT WEEK. 6Z GFS AND 0Z ECMWF SHOW
YET ANOTHER DECENT TROUGH AND ATTENDANT COLD FRONT PUSHING THROUGH IN
THE LATE THURSDAY THROUGH FRIDAY TIME FRAME...WHICH WOULD BRING MORE
SHOWERS AND COOLER TEMPERATURES. 0Z GFS AND ECMWF ENSEMBLE MEAN ARE
LESS AMPLIFIED WITH THE LATE WEEK TROUGH...WHICH WOULD RESULT IN
WARMER TEMPERATURES AND A LOWER PROBABILITY OF SHOWERS THROUGH
FRIDAY. CURRENT THINKING IS TO LEAN TOWARDS THE LESS AMPLIFIED 12Z
GFS/ECMWF ENSEMBLE MEAN SOLUTION.

TEMPERATURES DURING THIS PERIOD SHOULD START AROUND 5 DEGREES BELOW
NORMAL ON MONDAY...70S WEST AND LOW TO MID 80S EAST...WITH THE
TROUGH AND COOL 850MB TEMPERATURES OVERHEAD. TUESDAY THROUGH
THURSDAY WILL SEE SLIGHT WARMING EACH DAY AS HEIGHTS SLOWLY BUILD.
BY THURSDAY HIGHS WILL BE AROUND NORMAL...GENERALLY AROUND 80 IN THE
WEST..AND IN THE MID TO UPPER 80S EAST. DEWPOINTS WILL ALSO ONLY BE
IN THE UPPER 50S TO AROUND 60 THROUGH THE PERIOD...AND THIS COMBINED
WITH THE COOLER TEMPERATURES WILL MAKE IT FEEL MUCH MORE COMFORTABLE
THAN PREVIOUS WEEKS.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
SCT-BKN MVFR CLOUDS ARE POSSIBLE ACROSS THE WESTERN MOUNTAINS THIS
AFTERNOON. OTHERWISE...VFR CONDITIONS WILL PREVAIL THIS AFTERNOON
INTO TONIGHT. WSR-88D IMAGES SHOWED ISOLD SHOWERS AND THUNDERSTORMS
DEVELOPING IN CAPES OF 2000 J/KG OR BETTER ACROSS WESTERN NC.

THE SFC COOL FRONT HAS PUSHED INTO NORTH CAROLINA...AND A WAVE WILL
DEVELOP AND MOVE EAST ALONG THE BOUNDARY. THIS WILL GENERATE MID
AND HIGH CLOUDS THIS AFTERNOON INTO TONIGHT...WITH SCT SHOWERS AND
ISOLATED THUNDERSTORMS FROM THE VA/NC BORDER AND SOUTHWARD. THE
DANVILLE AIRPORT MAY BE AFFECTED BY SHOWERS LATE IN THE AFTERNOON
OR EVENING...BUT CHCS WERE LOW ENOUGH THAT THEY WERE NOT ADDED TO
THE TAF. THE BEST CHANCE FOR CONVECTION WILL BE ACROSS NORTHWEST
NORTH CAROLINA THIS AFTERNOON INTO THIS EVENING.

THE SFC HIGH THEN BUILDS NORTH OF THE AREA OVERNIGHT INTO
FRIDAY...ALLOWING AN EASTERLY FLOW TO DEVELOP WHICH MAY SPELL
PERIODS OF MVFR CIGS ESPCLY ALONG THE BLUE RIDGE. OF THE
BLACKSBURG FORECAST AREA AIRPORTS...THIS WOULD BE MOST LIKELY TO
IMPACT KDAN...POSSIBLY KROA AND KLYH. HOWEVER CONFIDENCE REMAINS LOW
ON SHOWERS AND HOW FAST LOWER CIGS DEVELOP THURSDAY NIGHT INTO
FRIDAY AS LATEST GUIDANCE IS SLOWER TO DEVELOP THE SE FLOW AND
TRANSPORT MOISTURE NORTHWARD.

THE SFC HIGH PASSES OFFSHORE BY THE WEEKEND...AND A RETURN
SOUTHEAST TO SOUTH FLOW WILL BRING DEEPER MOISTURE INTO THE AREA
WITH A HIGH CONFIDENCE OF A PERIOD OF SHRA/TSRA...INCLUDING AREAS
OF MVFR BY SAT NIGHT AND PERHAPS EXTENDING INTO SUNDAY. HIGH
PRESSURE SHOULD BUILD IN FROM THE WEST BRINGING A RETURN OF
WIDESPREAD VFR ON MONDAY.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

SYNOPSIS...JH/JJ
NEAR TERM...KK
SHORT TERM...RCS
LONG TERM...MC
AVIATION...JJ/KK

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
900 AM EDT THU AUG 11 2011

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>045-121300-
ASHE-ALLEGHANY NC-SURRY-STOKES-ROCKINGHAM-CASWELL-WATAUGA-WILKES-
YADKIN-TAZEWELL-SMYTH-BLAND-GILES-WYTHE-PULASKI-MONTGOMERY-GRAYSON-
CARROLL-FLOYD-CRAIG-ALLEGHANY VA-BATH-ROANOKE-BOTETOURT-ROCKBRIDGE-
PATRICK-FRANKLIN-BEDFORD-AMHERST-HENRY-PITTSYLVANIA-CAMPBELL-
APPOMATTOX-BUCKINGHAM-HALIFAX-CHARLOTTE-MERCER-SUMMERS-MONROE-
GREENBRIER-
900 AM EDT THU AUG 11 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL NORTH
CAROLINA...NORTHWEST NORTH CAROLINA...CENTRAL VIRGINIA...SOUTH
CENTRAL VIRGINIA...SOUTHWEST VIRGINIA...WEST CENTRAL VIRGINIA AND
SOUTHEAST WEST VIRGINIA.

.DAY ONE...TODAY AND TONIGHT.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

AN UNSEASONABLY STRONG COLD FRONT WILL APPROACH OUR REGION ON
SATURDAY...TRIGGERING WIDESPREAD SHOWERS AND THUNDERSTORMS.
PROLONGED EPISODES OF HEAVY RAIN WILL BE POSSIBLE FROM SATURDAY
AFTERNOON THROUGH SUNDAY MORNING...WHICH MAY LEAD TO LOCALIZED
FLASH FLOODING DURING THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

RCS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
254 PM EDT THU AUG 11 2011

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

0151 PM     TSTM WND DMG     5 WSW RONDA             36.18N 81.03W
08/11/2011                   WILKES             NC   911 CALL CENTER

            TREE DOWN

&&

EH

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
325 PM EDT THU AUG 11 2011

NCZ003-112000-
SURRY NC-
325 PM EDT THU AUG 11 2011

...A STRONG THUNDERSTORM WILL AFFECT SURRY COUNTY...

AT 321 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 4 MILES SOUTH OF
MOUNT AIRY...MOVING EAST AT 15 MPH.

WIND GUSTS TO 40 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THIS STORM.
VERY HEAVY RAIN WILL FALL FROM THIS STORM...AND WILL CAUSE WATER TO
POND ON ROADS AND QUICKLY FILL ROADSIDE DITCHES AND SMALL STREAMS.

THIS STORM WILL BE NEAR ARARAT AROUND 340 PM.

LAT...LON 3646 8047 3637 8051 3643 8067 3647 8065

DS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
350 PM EDT THU AUG 11 2011

NCZ003-112015-
SURRY NC-
350 PM EDT THU AUG 11 2011

...A STRONG THUNDERSTORM WILL AFFECT SURRY COUNTY...

AT 346 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 4 MILES NORTH OF
BOTTOM...MOVING SOUTHEAST AT 15 MPH.

WIND GUSTS TO 40 MPH ARE POSSIBLE WITH THIS STORM. VERY HEAVY RAIN
WILL FALL FROM THIS STORM...AND WILL CAUSE WATER TO POND ON ROADS AND
QUICKLY FILL ROADSIDE DITCHES AND SMALL STREAMS.

THIS STORM WILL BE NEAR PINE RIDGE AROUND 355 PM...TOAST AROUND 410
PM AND FLAT ROCK AROUND 415 PM.

LAT...LON 3652 8081 3656 8079 3656 8064 3654 8055
      3645 8060

DS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
403 PM EDT THU AUG 11 2011

NCZ004-VAZ032-112030-
PATRICK VA-STOKES NC-
403 PM EDT THU AUG 11 2011

...A STRONG THUNDERSTORM WILL AFFECT PATRICK AND STOKES COUNTIES...

AT 359 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 5 MILES NORTH OF
FRANCISCO...MOVING EAST AT 15 MPH.

WIND GUSTS TO 40 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THIS STORM.
VERY HEAVY RAIN WILL FALL FROM THIS STORM...AND WILL CAUSE WATER TO
POND ON ROADS AND QUICKLY FILL ROADSIDE DITCHES AND SMALL STREAMS.

THIS STORM WILL BE NEAR COLLINSTOWN AROUND 410 PM.

LAT...LON 3658 8020 3649 8027 3656 8045 3661 8042

DS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
416 PM EDT THU AUG 11 2011

NCZ003-VAZ032-112045-
PATRICK VA-SURRY NC-
416 PM EDT THU AUG 11 2011

...A STRONG THUNDERSTORM WILL AFFECT PATRICK AND SURRY COUNTIES...

AT 412 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 4 MILES SOUTHWEST
OF ARARAT...MOVING SOUTHEAST AT 15 MPH.

WIND GUSTS TO 40 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THIS STORM.
VERY HEAVY RAIN WILL FALL FROM THIS STORM...AND WILL CAUSE WATER TO
POND ON ROADS AND QUICKLY FILL ROADSIDE DITCHES AND SMALL STREAMS.

THIS STORM WILL BE NEAR WOODVILLE AROUND 440 PM.

LAT...LON 3656 8062 3656 8061 3659 8062 3662 8060
      3656 8039 3655 8039 3655 8044 3649 8044
      3647 8046

DS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
459 PM EDT THU AUG 11 2011

VAZ032-043-112130-
HENRY VA-PATRICK VA-
459 PM EDT THU AUG 11 2011

...STRONG THUNDERSTORMS WILL AFFECT HENRY AND PATRICK COUNTIES...

AT 458 PM EDT...STRONG THUNDERSTORMS WERE ALONG A LINE FROM STUART TO
SPENCER...MOVING EAST AT 25 MPH.

WIND GUSTS TO 30 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THESE
STORMS. VERY HEAVY RAIN WILL FALL FROM THESE STORMS...AND WILL CAUSE
WATER TO POND ON ROADS AND QUICKLY FILL ROADSIDE DITCHES AND SMALL
STREAMS.

THESE STORMS WILL BE NEAR SPENCER AROUND 505 PM...CRITZ AROUND 510
PM...HORSE PASTURE AROUND 515 PM AND MARTINSVILLE AIRPORT AROUND 525
PM.

LAT...LON 3667 8007 3663 7972 3657 8003 3662 8037

DS