Special Weather Statement, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
100 PM EDT WED AUG 8 2012

.SYNOPSIS...
A STATIONARY FRONT ACROSS THE MOUNTAINS WILL GRADUALLY DISSIPATE
TODAY AS WEAK HIGH PRESSURE SLIDES EAST INTO THE REGION BY TONIGHT
BEFORE WEAKENING ON THURSDAY. A STRONG COLD FRONT WILL SWEEP
ACROSS THE REGION FRIDAY INTO FRIDAY EVENING...BRINGING ANOTHER
ROUND OF SHOWERS AND STORMS...SOME POTENTIALLY STRONG. COOLER AND
DRIER WEATHER IS EXPECTED BEHIND THE FRONT OVER THE WEEKEND INTO
EARLY NEXT WEEK AS HIGH PRESSURE BUILDS INTO THE REGION.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1255 PM ED WEDNESDAY...

ISOALTED TO SCATTERED SHOWERS AND STORMS HAVE DEVELOPED OVER THE
PAST 30 MINUTES GENERALLY ALONG AND EAST OF A LINE FROM WILKES
COUNTY NC TO APPOMATTOX COUNTY VA. ANTICIPATE THIS AREA TO BE THE
FOCUS FOR ADDITIONAL SHOWERS AND STORMS AS THE AFTERNOON
PROGRESSES. CANNOT RULE OUT VERY ISOLATED COVERAGE WEST OF THIS
REGION. HAVE MADE ADJUSTMENTS TO THE HOURLY TEMPERATURE...DEW
POINT...WINDS AND SKY COVER BASED UPON THE CURRENT OBSERVATIONS
AND EXPECTED TRENDS THIS AFTERNOON. THIS PROMPTED AN INCREASE IN
THE FORECAST HIGH TEMPERATURES BY TWO TO THREE DEGREES ACROSS THE
VIRGINIA PIEDMONT.

AS OF 952 AM EDT WEDNESDAY...

SURFACE OBSERVATIONS AND VISIBLE SATELLITE IMAGERY INDICATES A FEW
POCKETS OF LINGERING FOG IN SOME OF THE MOUNTAIN VALLEYS.
HOWEVER...ANTICIPATE THAT BY 1100 AM EDT...MOST OR ALL OF THIS
LINGERING FOG WILL HAVE DISSIPATED. PRECIPITATION HAS BEEN LIMITED
TO JUST A FEW ISOLATED SHOWERS ACROSS PARTS OF BUCKINGHAM COUNTY
VIRGINIA. ANTICIPATE LIMITED...IF ANY COVERAGE...THROUGH NOON
BEFORE COVERAGE INCREASES NEAR THE NC/VA BORDER. NO OTHER
SIGNIFICANT CHANGES. THE HOURLY TEMPERATURE...DEW POINT...WIND AND
SKY COVER GRIDS HAVE BEEN TWEAKED TO REFLECT THE LATEST
OBSERVATIONS AND EXPECTED TRENDS INTO THE EARLY AFTERNOON.

AS OF 230 AM EDT WEDNESDAY...

WEAK SURFACE BOUNDARY ACROSS THE MOUNTAINS WILL GRADUALLY
FADE TODAY AS A MID LEVEL WAVE PASSES TO THE EAST BY AFTERNOON AND
DRIER AIR ALOFT PER VAPOR LOOP ADVECTS IN FROM THE NW. HOWEVER THE
LOW LEVELS WILL REMAIN RATHER MOIST AND GIVEN ANOTHER SUBTLE S/W
PUSHING ACROSS THE WEST LATER ON CANT TOTALLY RULE OUT ADDED
ISOLATED CONVECTION...ESPCLY BLUE RIDGE AND POINTS EAST...MAINLY
SOUTH OF HIGHWAY 460 WHERE BOUNDARY LAYER MOISTURE/INSTABILITY
WILL BE BETTER. LATEST LOCAL GUIDANCE AS WELL AS THE SPC WRF AND
GFS HINT AT THIS WITH A FEW TSRA CLUSTERS DEVELOPING SW SECTIONS
ALONG THE BLUE RIDGE PER DIFF HEATING UNDER WEAK THETA-E
RIDGING...AND THEN OUT EAST JUST AHEAD OF WHAT WAS LEFT OF THE
OLD FRONT. AGAIN GIVEN WEAK STEERING AND LOCAL CONVERGENCE/OUTFLOW
COULD ALLOW FOR STORMS TO POP UP AND DUMP HEAVY RAINFALL BUT NOT
THINKING MUCH MORE COVERAGE THAN CHANCE TO ISOLATED POPS TODAY.
OTRW EXPECTING A GRADUAL RETURN TO MORE SUNSHINE AS THE HIGH/MID
LEVEL CLOUD DECK ERODES AND SHIFTS NE WITH THE PASSAGE OF THE WAVE
TO THE EAST THIS MORNING. THINK CLOUDS WILL LIMIT FOG FROM
BECOMING TOO WIDESPREAD EXCEPT PERHAPS THE FAR WEST SO WILL KEEP
MENTION PENDING RELEASE COVERAGE. WARM START AND SLIGHT 85H
WARMING UNDER A WEAK WEST/NW TRAJECTORY ALOFT SHOULD PUSH TEMPS TO
AROUND 90 EAST AND WELL INTO THE 80S WEST SO BUMPED UP CLOSER TO
THE MAV VALUES TODAY.

ANY CONVECTION SHOULD QUICKLY FADE WITH LOSS OF HEATING THIS EVENING
GIVEN LACK OF SUPPORT...WITH MAINLY CLEAR SKIES AFTER MIDNIGHT AS WE
SLIDE IN BETWEEN THE DEEP MOISTURE LOBE TO THE SE AND THE NEXT
UPSTREAM 5H TROF. THUS WILL CARRY SOME ISOLATED EVENING POPS MAINLY
SOUTH/EAST THEN GO DRY WITH PERHAPS SOME PATCHY FOG UNDER WEAK HIGH
PRESSURE LATE. THIS SHOULD ALSO ALLOW LOW TEMPS TO DROP CLOSER TO
THE COOLER MAV FOR THE MOST PART WITH RANGE FROM AROUND 60 VALLEYS
TO UPPER 60S SE AND RIDGES.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 430 AM EDT WEDNESDAY...

ACTIVE WEATHER WILL BEGIN THE SHORT TERM PERIODS AS THE UPPER FLOW
AMPLIFIES ACROSS THE U.S...FEATURING A DEEPENING NEGATIVELY TILTED
UPPER TROUGH FROM THE GREAT LAKES TOWARD THE MID-ATLANTIC THU-FRI.
THE POPS AND SEVERE THREAT FOR THU SOMEWHAT QUESTIONABLE...BUT A
MORE DEFINITE POSSIBILITY FOR FRI AS THE ENTIRE SYSTEM SHIFTS ACROSS
THE CWA. NORMALLY SUCH A PATTERN WOULD SUGGEST A HIGH THREAT OF
SEVERE WX ACROSS THE REGION...ESPECIALLY FRI. HOWEVER...EXTENSIVE
CLOUD COVER AND MORNING SHRA FRI WILL LIKELY LIMIT HEATING...WITH
THE GREATER LIKELIHOOD FOR SEVERE PROBABLY FOCUSED ACROSS THE
PIEDMONT AND TOWARD THE COASTAL PLAIN FRI AFTERNOON/EVENING. AT THIS
POINT...HAVE ONLY MENTIONED GUSTY WINDS AND LOCALLY HEAVY RAIN. SPC
HAS OUTLOOKED THE WESTERN SECTIONS ON DAY2 AND THE ENTIRE CWA ON
DAY3...BUT AGAIN FEEL MAIN THREAT ON DAY3 SHOULD BE EAST OF THE BLUE
RIDGE. MODEL AND HPC QPF NOT OVERLY IMPRESSIVE AND INDICATIVE OF A
SKIP OVER EFFECT OF THE HEAVIEST PRECIPITATION AS AFOREMENTIONED
TOWARD EASTERN VA/NC. NONETHELESS...WITH FAIRLY WIDESPREAD HEAVY
RAIN ACROSS THE MOUNTAIN AREAS DURING THE PAST COUPLE OF
WEEKS...LATER SHIFTS WILL NEED TO EVALUATE THE ISSUANCE OF AN FFA
WEST OF THE BLUE RIDGE WHERE 1HR FFG VALUES GENERALLY LESS THAN 2
INCHES. WITH REFERENCE TO POP TIMING...ENOUGH FORCING APPEARS
EVIDENT COMBINED WITH PRE-SYSTEM HEATING TO SUPPORT GOOD CHC POPS
EAST TO LIKELY POPS WEST BY FRI EVENING. WILL HAVE LIKELY POPS TO
ALL AREAS FRI...WHICH MAY WELL BECOME CATEGORICAL WITH LATER
FORECASTS.

850MB TEMPS NEAR +20C ACROSS THE PIEDMONT REGION THU WILL STILL
SUPPORT WELL ABOVE NORMAL TEMPS IN THE LOW TO MID 90S EAST OF THE
BLUE RIDGE...WITH MOSTLY 80S TO THE WEST...EXCEPT 70S IN THE
MOUNTAINS ABOVE 3000 FT. EXTENSIVE CLOUD COVER AND SHRA/TSRA FRI
SHOULD HOLD TEMPS TO THE 70S IN THE MOUNTAINS TO 80S EAST OF THE
BLUE RIDGE.

LATEST MODELS HAVE COME INTO BETTER AGREEMENT IN PUSHING THE MAIN
UPPER TROUGH EAST OF THE REGION BY EARLY SAT...WHICH SHOULD TAKE THE
BULK OF THE PCPN WITH IT. HOWEVER...THE PARENT...RATHER DEEP UPPER
LOW FOR MID-AUGUST...WILL SWEEP THROUGH CENTRAL PA SAT AND COULD
PROMOTE ENOUGH LIFT IN UPSLOPE AREAS OF WV/N VA TO SUPPORT ISOLD
-SHRA DURING DAYTIME HEATING...THUS HAVE INCLUDED SLIGHT CHC POPS
ACCORDINGLY. 850MB TEMPS DROP TO THE LOWEST LEVELS SEEN IN OVER TWO
MONTHS...WITH +10C ACROSS ALL EXCEPT THE PIEDMONT BY 12Z SAT. THIS
SHOULD ALLOW FOR SOME RATHER REFRESHING HIGHS IN THE 70S WEST OF THE
BLUE RIDGE AND 80S EAST...WITH DEWPOINTS DROPPING INTO THE 50S WEST
OF THE BLUE RIDGE AND 60S ACROSS THE PIEDMONT.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 430 AM EDT WEDNESDAY...

HAVE NOT MADE ANY SIGNIFICANT CHANGES TO THE LONG TERM AT THIS TIME.
IT APPEARS THAT A RATHER UNSETTLED WEATHER PATTERN WILL REMAIN IN
PLACE THROUGHOUT THE EXTENDED AS A SERIES OF NW FLOW DISTURBANCES
TRACK ACROSS THE REGION. THE ECMWF/GFS ARE AT ODDS WITH RESPECT TO
THE AMPLIFICATION OF THE NEXT UPPER TROUGH TOWARD THE MIDDLE OF NEXT
WEEK... WITH THE GFS FAVORING A FLATTER...MORE ZONAL FLOW. AT ANY
RATE...IT APPEARS THAT AT LEAST CHC POPS FOR SHRA/TSRA WILL CONTINUE
THROUGHOUT THE EXTENDED WITH TEMPS RETURNING BACK TO AOA NORMAL
LEVELS. LOW-LEVEL MOISTURE WILL ALSO BE INCREASING...RESULTING IN
INCREASINGLY MORE HUMID CONDITIONS AS WELL.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 645 AM EDT WEDNESDAY...

EXTENSIVE MID AND HIGH CLOUD CANOPY ASSOCIATED WITH WAVE/UPPER JET
CONTINUES TO SLOWLY PUSH EAST AND SHOULD EXIT THE AREA BY MID
MORNING IF NOT SOONER. MAY SEE A FEW ADDED SHRA DEVELOP OVER THE
SW THIS MORNING BUT MOSTLY SOUTH OF THE TAF SITES. OTRW FOG THE
MAIN CONCERN AGAIN EARLY THIS MORNING WITH AREAS OF IFR/LIFR IN
THE VALLEYS/ALONG THE WESTERN RIDGES...PRIMARILY KLWB/KBLF AND
KBCB IN THE WEST AND KLYH IN THE EAST. MAY STILL SEE A BRIEF
PERIOD OF MVFR IN FOG AT KDAN OTRW VFR AROUND KROA. SHOULD SEE
MOST OF THE FOG/STRATUS ERODE BY 14Z...10AM WITH ONLY KLWB LIKELY
HANGING ONTO POCKETS OF LOWER VSBYS A WHILE LONGER.

ONCE THE FOG FADES AND THE MID DECK EXITS SHOULD SEE MAINLY VFR
FOR MOST OF THE DAY WITH SCTD-BKN 4-6K FT CU FIELDS. ISOLATED
CONVECTION AGAIN POSSIBLE ESPCLY IN SPOTS ALONG THE BLUE RIDGE AND
OUT EAST SO INCLUDED A VCTS MENTION FROM KROA EAST BASED ON THE
LATEST HRRR MODEL WHICH SHOWS A FEW CLUSTERS DEVELOPING FROM NW NC
INTO THE VA PIEDMONT BY MID AFTERNOON. ELSW WILL LEAVE OUT FOR NOW
GIVEN ISOLATED NATURE. AGAIN EXPECT ANY STORMS TO DIMINISH WITH
LOSS OF HEATING FOLLOWED BY MAINLY CLEAR SKIES WITH ANOTHER ROUND
OF MVFR/IFR FOG ESPCLY VALLEYS GIVEN LESS CLOUD COVER OVERNIGHT.

PROXIMITY OF THE OLD FRONT AND TROPICAL AIRMASS JUST TO THE
SOUTH... WHICH WILL BEGIN A NORTHWARD RETURN BY LATE WEEK...WILL
MAINTAIN A DAILY THREAT FOR PATCHY FLIGHT RESTRICTIONS IN VICINITY
OF MAINLY DIURNALLY DRIVEN SHOWERS/STORMS FOR MUCH OF THE REST OF
THE WEEK...WITH A CONTINUED THREAT FOR RESTRICTIONS INTO THE
OVERNIGHT PERIODS WHERE FOG DEVELOPS. MORE WIDESPREAD SHRA/TSRA
LIKELY BY WEEKS END AHEAD OF A STRONGER COLD FRONT THAT LOOKS TO
DIVE THRU THE REGION FRIDAY INTO FRIDAY NIGHT. IMPROVING
CONDITIONS TO VFR LIKELY BEHIND THE FRONT ESPCLY ACROSS THE EAST
FOR THE WEEKEND.

&&

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

&&

SYNOPSIS...JH
NEAR TERM...DS/JH
SHORT TERM...RAB
LONG TERM...PH/RAB
AVIATION...DS/JH/KM

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BLACKSBURG VA
605 AM EDT WED AUG 8 2012

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>045-091015-
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-
605 AM EDT WED AUG 8 2012

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...THURSDAY THROUGH TUESDAY.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
AND EVENING AS BANDS OF THUNDERSTORMS MOVE EAST AHEAD OF A STRONG
COLD FRONT. DAMAGING WINDS WILL BE THE PRIMARY THREAT WITH VERY
HEAVY RAINFALL ALSO LIKELY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
1223 PM EDT WED AUG 8 2012

NCZ003-004-081700-
STOKES NC-SURRY NC-
1223 PM EDT WED AUG 8 2012

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

AT 1220 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 7 MILES WEST OF
FRANCISCO...MOVING SOUTHEAST AT 10 MPH.

WIND GUSTS TO 40 MPH AND HAIL UP TO DIME SIZE 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 WESTFIELD AROUND 1240 PM...FRANCISCO AROUND
1250 PM...FRANCISCO AROUND 1255 PM AND PILOT MOUNTAIN AROUND 100 PM.

LAT...LON 3634 8044 3648 8056 3656 8047 3655 8043
      3648 8026

16

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
101 PM EDT WED AUG 8 2012

NCZ005-VAZ043-044-081745-
HENRY VA-PITTSYLVANIA VA-ROCKINGHAM NC-
101 PM EDT WED AUG 8 2012

...A STRONG THUNDERSTORM WILL AFFECT HENRY...PITTSYLVANIA AND
ROCKINGHAM COUNTIES...

AT 1259 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 5 MILES SOUTH OF
AXTON...MOVING SOUTHEAST AT 15 MPH.

WIND GUSTS TO 40 MPH ARE POSSIBLE WITH THIS STORM.

THIS STORM WILL BE NEAR CASCADE AROUND 115 PM...DRAPER AROUND 120
PM...OREGON HILL AROUND 135 PM...MAYFIELD AROUND 140 PM AND RUFFIN
AROUND 145 PM.

LAT...LON 3658 7983 3667 7974 3654 7951 3638 7952
      3633 7953

16