Severe Thunderstorm Warning 121, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
331 PM EDT TUE JUL 16 2013

.SYNOPSIS...
STRONG UPPER LEVEL HIGH PRESSURE ACROSS THE REGION WILL CONTINUE
TO DRIFT WEST AND WEAKEN THROUGH THE WEEK. WEAK UPPER LEVEL
DISTURBANCES WILL ROTATE SOUTH INTO THE AREA THIS EVENING THROUGH
THURSDAY RESULTING IN WIDELY SCATTERED SHOWERS AND STORMS AT
TIMES. A COLD FRONT WILL SINK INTO THE OHIO VALLEY NEAR THE END
OF THE WEEK BEFORE SLIDING SOUTH ACROSS THE REGION LATER THIS
WEEKEND.
&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 315 PM EDT TUESDAY...

UNUSALLY STRONG UPPER RIDGE CENTERED OVER INDIANA THIS AFTERNOON
WITH A CLOSED 600DM ISOLINE ANALYZED...SOMETHING SEEN BUT RARELY
IN THE CONUS. SEVERAL IMPULSES CONTINUE TO ROUND THIS BROAD UPPER
CIRCULATION AND DROP SOUTHEASTWARD TOWARD THE ATLANTIC COAST
PROVIDING ENOUGH LIFT FOR CLUSTERS OF STORMS TO DEVELOP WITHIN
WHAT HAS BECOME A VERY WARM AND HUMID AIR MASS. H85 TEMPS ROUGHLY
+20C OVER MUCH OF THE MID-ATLANTIC/APPALACHIAN REGION WITH STRONG
HEATING PUSHING SURFACE TEMPS INTO MID-90S OVER PIEDMONT AND UPPER
80S AND A FEW LOW 90S EVEN IN THE MOUNTAINS. PLENTY OF MOISTURE
INDICATED BY SURFACE DEWPOINTS UPPER 60S TO LOW 70S AND PWATS 1.2
TO 1.5 INCHES. THUNDERSTORMS HAVE DEVELOPED THIS AFTERNOON NORTH
OVER THE HIGHER TERRAIN OF WV AND THE BLUE RIDGE AND ARE DRIFTING
SLOWLY SOUTHWARD WITH THE MEAN STEERING FLOW INTO THE NORTHERN
CWA. THIS DIURNAL PATTERN OF THUNDERSTORM ACTIVITY SHOULD WEAKEN
LATER IN THE EVENING BUT MAY MAINTAIN ITSELF FOR SOME TIME BEYOND
SUNSET WITH THE VERY HIGH INSTABILITY IN PLACE...MESOANYALYSIS
CAPES/LIS ARE 2K-3K J/KG ACROSS MOST OF THE CWA BUT HIGHER JUST
NORTH WITH 4K-5K J/KG AND -6 TO -8 LIFTED INDEX ANALYZED. A FEW
STORMS COULD BECOME SEVERE WITH THESE PARAMETERS IN PLACE AND
DCAPES NEAR 1K. LOCALIZED FLASH FLOOD ISSUES ALSO POSSIBLE WITH
THE RELATIVELY SLOW MOVEMENT OF STORMS AND LIKELY HIGH RAINFALL
RATES. OVERNIGHT TEMPS WILL BE MUGGY AND WARM WITH UPPER 60S TO
LOW 70S AND PATCHY FOG LIKELY IN SOME AREAS.

NOT MUCH CHANGE IN OVERALL SYNOPTIC PATTERN OR TEMP REGIME ON
WEDNESDAY AS UPPER HIGH REMAINS QUASI-STATIONARY AND SURFACE
FEATURES WEAK AND DIFFUSE. TEMPS WILL BE SIMILAR AND EXPECT A
RENEWAL OF THE DIURNALLY ENHANCED CONVECTION. BEST FORCING FOR
ORGANIZED ACTIVITY REMAINS OVER THE NORTHEASTERN U.S. BUT
SCATTERED SEVERE ACTIVITY AND LOCALIZED FLOOD ISSUES AGAIN A
STRONG POSSIBILITY ESPECIALLY ALONG BOUNDARIES CREATED BY
EARLIER CONVECTION OR DUE TO TERRAIN INTERACTIONS.
&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 220 PM EDT TUESDAY...

NOT A LOT OF CHANGE WITH UPPER HEIGHTS SLOWLY LOWERING THROUGH
THE PERIOD WHILE MAINTAINING AN OVERALL MEAN FLAT RIDGE ACROSS
THE REGION THROUGH THE END OF THE WEEK. FAINT VORT LOBES ROTATING
AROUND THE PARENT 5H HIGH TO THE WEST MAY HELP SPARK ANOTHER
ROUND OF MAINLY MOUNTAIN CONVECTION THU AFTERNOON WITH BEST
COVERAGE SW ZONES WHERE WILL SEE A LITTLE MORE IN THE WAY OF
LIGHT SE FLOW. OTRW EXPECT WEAK NORTHERLY FLOW TO ALLOW ENOUGH
LOCAL CONVERGENCE TO SUPPORT SCTD POPS WED EVENING...AND AGAIN
THURSDAY AFTERNOON PER GOOD INSTABILITY WHEN STORMS SHOULD AGAIN
BE SLOW MOVERS AS WELL. COVERAGE LIKELY TO TAPER PRETTY QUICK
THU EVENING UNDER LACK OF SUPPORT BEFORE REDEVELOPING WEST FRIDAY
AS RIDGING ERODES EVEN MORE. WITH THE FLOW TURNING AROUND TO THE
SW...EXPECT SHRA/TSRA TO DEVELOP FARTHER EAST AND BE A BIT MORE
ORGANIZED BUT MAINLY BLUE RIDGE AS THE LEE TROF APPEARS TOO FAR
EAST TO AID IN DEVELOPMENT AT THIS POINT. OTRW CONTINUED PC
DAYTIME TO MOSTLY CLEAR AT NIGHT BUT STILL HOT/WARM AND HUMID
WITH PERSISTENCE OF UPR 80S-MID 90S FOR HIGHS AND 60S TO LOWER
70S FOR LOWS.
&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 1235 PM EDT TUESDAY...

RETURN TO THE EASTERN UPPER TROF REGIME WILL BE UNDERWAY STARTING
THIS WEEKEND WITH THE AXIS OF THE 5H COOL POOL CROSSING THE
REGION FROM THE NW BY EARLY MONDAY. WEAK COLD FRONT AHEAD OF THE
FALLING HEIGHTS ALOFT LOOKS TO CROSS THE OHIO VALLEY SAT AFTERNOON
BEFORE BECOMING MORE EAST-WEST ORIENTED IN BACKDOOR FASHION JUST
NORTH OF THE AREA SUNDAY. INITIAL WESTERLY FLOW AHEAD OF THE FRONT
SHOULD ACT TO CAP CONVECTION SAT UNTIL LATER IN THE
AFTERNOON/EARLY EVENING WHEN MAY SEE A PRE-FRONTAL LINE OF TSRA
ARRIVE FROM THE NW PER LASTEST EC. THUS RUNNING WITH HIGH CHC/LOW
LIKELYS NW TIER SAT WITH CHANCES ELSW WITH THE LEAST SE UNTIL
EVENING. FORECAST PWATS QUICKLY INCREASE BY SUNDAY AS THE FRONT
SLOWS AND THE FLOW TURNS MORE SW. INTERACTION WITH AN EASTERN LEE
TROF AND HEATING AHEAD OF THE PREVIOUS PRE-FRONTAL BAND SHOULD
HELP ENERGIZE CONVECTION ALONG/EAST OF THE BLUE RIDGE SUNDAY SO
BUMPING POPS TO HIGH CHC/LOW LIKELYS ESPCLY SE INCLUDING DECENT
CHANCES ACROSS THE WEST. SHOULD BE QUITE HOT AHEAD OF THE FRONT
SAT GIVEN WESTERLY COMPRESSION AND EARLY INSOLATION WITH MUCH OF
THE EAST STILL IN THE 90S AND 80S WEST. SOME COOLING LIKELY
SUNDAY UNDER MORE MOISTURE/SW FLOW AND A QUICKER INIT TO
CONVECTION DURING THE AFTERNOON.

LOTS OF UNCERTAINTY THEN EARLY NEXT IN JUST HOW FAR SOUTH THE
LOW LEVEL BOUNDARY WILL GET GIVEN THE EXITING/WEAKENING 5H TROF.
APPEARS WITH AT LEAST SCTD CONVECTION MONDAY...PER THE ACTUAL
FRONT OVERHEAD...MAY SEE ENOUGH PUSH TO PERHAPS DRIFT THE
BOUNDARY INTO THE CAROLINAS MONDAY NIGHT BEFORE IT STARTS TO HEAD
BACK NORTH TUESDAY AHEAD OF THE NEXT UPSTREAM WAVE. GIVEN
POTENTIAL FOR MOISTURE TO LINGER LONGER...WONT LEAN TOWARD THE
DRIER GFS...AND KEEP SOME COVERAGE OF POPS GOING MONDAY INTO
TUESDAY WITH LESS CHANCES NORTH-NW SECTIONS MONDAY NIGHT WHERE
SOME DRYING ALOFT MAY SNEAK IN. EXPECT WILL BE BLEEDING IN SOME
SLIGHTLY COOLER AIR AS WELL EARLY NEXT WEEK ALLOWING HIGHS
TO FALL TO SLIGHTLY BELOW NORMAL WITH LOWS INTO THE 60S MOST
SPOTS.
&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
AS OF 130 PM EDT TUESDAY...

TYPICAL MID-SUMMER PATTERN TO CONTINUE NEXT 24 TO 48 HOURS WITH
DIURNAL PATTERN OF THUNDERSTORM ACTIVITY. MAINTAINING VCTS IN MOST
OF THE TAF SITES FOR A FEW HOURS LATER THIS AFTERNOON/EARLY
EVENING. EXPECT REDUCED CIGS/VSBYS FROM ANY STORM THAT MOVES
ACROSS AN AIRPORT ALONG WITH THE USUAL HEAVY RAIN FROM SLOW MOVING
CELLS.

THIS EVENING...THE SHOWERS/STORMS END AND SKIES CLEAR GRADUALLY
WITH FOG AGAIN SITUATED ACROSS THE VALLEYS/BCB/LWB/LYH/DAN...WITH
A POTENTIAL FOR DENSE FOG AT BCB/LWB. WILL HAVE TO SEE WHERE IT
RAINS TOO AS THIS WILL AFFECT DENSITY OF FOG.

AMD NOT SKED AT DAN WILL CONTINUE UNTIL VSBY SENSOR IS FIXED.

EXTENDED AVIATION DISCUSSION...
WEDNESDAY...PROGRESSIVELY MORE COVERAGE OF STORMS THROUGH THE WEEK
AS THE UPPER RIDGE FLATTENS AND A TROUGH STARTS TO BUILD SOUTH
INTO THE GREAT LAKES. ALSO...THE COASTAL TROUGH WILL STRENGTHEN A
BIT WITH THE UPPER HIGH CENTERING OVER THE ROCKIES. A BOUNDARY
WILL BE SINKING INTO THE OHIO VALLEY THIS WEEKEND. SOME MVFR/IFR
VIS/CIG CAN BE EXPECTED AT BCB/LWB EACH DAY...POTENTIALLY REDUCED
CIG/VIS DUE TO THUNDERSTORMS AT THE END OF THE WEEK.
&&

.EQUIPMENT...
AS OF 300 PM EDT TUESDAY...

VISIBILITY SENSOR AT DANVILLE IS NOT WORKING. A TECHNICIAN
IS CURRENTLY WORKING ON THE PROBLEM WITH RESTORATION EXCPECTED
LATER THIS AFTERNOON OR EARLY THIS EVENING.

&&

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

&&

SYNOPSIS...JH/WP
NEAR TERM...PC
SHORT TERM...JH
LONG TERM...JH
AVIATION...PC/WP
EQUIPMENT...JH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
342 PM EDT TUE JUL 16 2013

NCZ004>006-VAZ043>047-058-059-171945-
STOKES-ROCKINGHAM-CASWELL-HENRY-PITTSYLVANIA-CAMPBELL-APPOMATTOX-
BUCKINGHAM-HALIFAX-CHARLOTTE-
342 PM EDT TUE JUL 16 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL NORTH
CAROLINA...CENTRAL VIRGINIA AND SOUTH CENTRAL VIRGINIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

ISOLATED STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE INTO THIS
EVENING WITH THE MAIN THREAT BEING DAMAGING WIND GUSTS. HEAT INDEX
VALUES WILL ALSO REMAIN AROUND 100 DEGREES THROUGH LATE THIS
AFTERNOON.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

TEMPERATURES IN THE LOWER TO MID 90S COMBINED WITH HIGH HUMIDITY
WILL AGAIN RESULT IN HEAT INDEX VALUES AROUND 100 DEGREES FOR A
FEW HOURS WEDNESDAY AFTERNOON.

IN ADDITION...THUNDERSTORMS WILL BECOME MORE WIDESPREAD OVER THE
WEEKEND WITH THE THREAT FOR VERY HEAVY RAINFALL ALONG WITH
POTENTIAL SEVERE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

NCZ001>003-018>020-VAZ007-009>020-022>024-032>035-WVZ042>045-171945-
ASHE-ALLEGHANY NC-SURRY-WATAUGA-WILKES-YADKIN-TAZEWELL-SMYTH-BLAND-
GILES-WYTHE-PULASKI-MONTGOMERY-GRAYSON-CARROLL-FLOYD-CRAIG-
ALLEGHANY VA-BATH-ROANOKE-BOTETOURT-ROCKBRIDGE-PATRICK-FRANKLIN-
BEDFORD-AMHERST-MERCER-SUMMERS-MONROE-GREENBRIER-
342 PM EDT TUE JUL 16 2013

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...THIS AFTERNOON AND TONIGHT.

ANY THUNDERSTORMS INTO EARLY EVENING WILL BE SLOW MOVERS AND
COULD BRING ABOUT LOCALIZED FLOODING...AND POSSIBLY FLASH
FLOODING. IN ADDITION...A FEW STORMS MAY BECOME STRONG TO SEVERE
WITH THE THREAT FOR DAMAGING WIND GUSTS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

A FEW THUNDERSTORMS WEDNESDAY AFTERNOON COULD BRING ISOLATED
DAMAGING WINDS. SLOW MOVING STORMS COULD PRODUCE HEAVY RAINFALL.

THUNDERSTORMS WILL BECOME MORE WIDESPREAD OVER THE WEEKEND WITH THE
CONTINUED THREAT FOR VERY HEAVY RAINFALL ALONG WITH ISOLATED SEVERE
STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

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