Severe Thunderstorm Warning 199, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
339 PM EDT TUE JUL 13 2010

.SYNOPSIS...
A STRONG UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE ACROSS THE
MID ATLANTIC REGION THIS EVENING. ANOTHER TROUGH WILL IMPACT THE
AREA LATER IN THE WEEK. THE GREATEST THREAT FOR SHOWERS WILL BE
THIS EVENING...AND AGAIN WITH THE TROUGH LATER IN THE WEEK.
TEMPERATURES WILL REMAIN SEASONABLY WARM AND HUMID FOR THE
REMAINDER OF THE WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AT 18 UTC/2 PM...DISTINCT UPPER LEVEL TROUGH EVIDENT IN THE WATER
VAPOR IMAGERY...CROSSING THE CENTRAL APPALACHIANS. AXIS OF DEEP
MOISTURE AHEAD OF THIS FEATURE IS RESULTING IN NUMEROUS SHRA/TSRA
FROM SOUTHERN OH TO NRN MS/AL. SURFACE DEWPOINTS WERE IN THE 70S
AND SATELLITE PWAT ESTIMATES WERE AROUND 1.80. SKIES EAST OF THE
MOUNTAINS HAVE CLEARED...ALLOWING FOR GOOD INSOLATION...SFC TEMPS
APPROACHING 90 DEGREES ACROSS SOUTHSIDE VA INTO THE PIEDMONT OF NC.

AS WE TRANSITION INTO AND THROUGH THE EVENING...LOOK FOR TSTM
COVERAGE TO INCREASE...MOUNTAINS INITIALLY...THEN SPREADING ACROSS
THE FOOTHILLS AND PIEDMONT. POTENTIAL EXISTS FOR ORGANIZED STORMS
WITH DAMAGING WIND GUSTS...ESP AREAS THAT GOT A FULL DOSE OF
AFTERNOON SUN.

THE STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM
WATCH FROM SOUTHERN VA INTO WRN NC...WATCH #466 VALID UNTIL 02
UTC/ 10 PM. CONCERN IS THAT 30-40 KT DEEP WIND FIELD ASSOCIATED WITH
THE TROF WILL DRIVE DEVELOPMENT OF AREA OF ORGANIZED DEEP
CONVECTION. IN ADDITION...FLOW EAST OF THE MOUNTAINS IS BACKING
AHEAD OF APPROACHING TROF DRIVING POTENTIAL FOR STORM
ORGANIZATION. THE NAM12 SUGGESTS STRONGEST BACKING WILL TAKE
PLACE OVER WESTERN NORTH CAROLINA AND THE VA BORDER COUNTIES...WITH
FCST STORM RELATIVE HELICITIES OF 150-200. STORMS ON THE KFCX
RADAR HAVE EXIBITED SOME ROTATION...SO NOT OUT OF THE QUESTION
FOR ISOLD TORNADIC OCCURRENCE. THE MAIN THREAT HOWEVER WILL BE
DAMAGING THUNDERSTORM WIND GUSTS...WET MICROBURSTS POSSIBLE IN
ADDITION TO MIX DOWN OF STRONGER MID LEVEL WINDS.

IN ADDITION TO SVR WND POTENTIAL AND ISOLD TORNADIC THREAT...LARGE
SCALE LIFT WILL TAP RICH MOISTURE...PWATS NEAR 2 INCHES...TO
DRIVE VERY RAIN EFFICIENT THUNDERSTORMS. HP STORMS A GOOD BET WITH
RAIN RATES OF UP TO 4 INCHES AN HOUR. THE ONLY THING THAT IS
CURTAILING THE ISSUANCE OF A FLASH FLOOD WATCH IS FACT THAT STORM
CELLS WILL BE MOVING ALONG AT A PRETTY GOOD CLIP PER 30-40KT MID
LEVEL FLOW. IF TRAINING DOES BECOME A PROBLEM...WILL LIKELY NEED A
FFA HEADLINE. UNTIL THEN WILL MONITOR SITUATION SIMILAR TO
YESTERDAY AND PIECE THE PUZZLE TOGETHER AS WE PROGRESS THROUGH THE
EVENING.

THE UPPER LEVEL TROUGH IS EXPECTED TO PASS EAST OF THE FCST AREA
AFTER MIDNIGHT...WINDS ALOFT BECOMING WESTERLY...THE PROFILE
DRYING FROM THE TOP DOWN. LOOK FOR THUNDERSTORM THREAT TO WANE
WITH ITS PASSAGE...BUT LINGERING SHOWERS MAY PERSIST ESP ERN CWA.
FOG AND STRATUS FORMATION A GOOD BET FOR THE LATE NIGHT PER VERY
MOIST BOUNDARY LAYER AND WET GROUND.

LOW LEVEL MOISTURE WILL LINGER THROUGHOUT THE DAY WEDNESDAY PER
LACK OF ANY SIGNIFICANT SURFACE FRONTAL PASSAGE (NO AIRMASS CHANGE).
THE MID AND UPPER LEVELS HOWEVER SHOULD EXIBIT SOME DRYING IN THE
WAKE OF THE PASSAGE OF THE UPPER LEVEL TROUGH. THIS SUGGESTS
PRECIP POTENTIAL WILL BE LOW IN SPITE OF THE WARM HUMID BOUNDARY
LAYER THAT WILL REMAIN. MORNING CLOUDS/FOG SHOULD LIFT INTO A BKN
CU FIELD DURING THE AFTERNOON.

STUCK PRETTY CLOSE TO MOS TEMPS TONIGHT AND WEDNESDAY. ELEVATED
DEWPOINTS SHOULD KEEP READINGS FROM FALLING MUCH BLO 70 TONIGHT.
LOOKING AT READINGS IN THE 80S WEDNESDAY...MAYBE 90 SOUTHSIDE
PENDING A GOOD BIT OF AFTERNOON SUN.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
LOWERED POPS FOR WEDNESDAY EVENING INTO WEDNESDAY NIGHT. TROUGH WILL
SLIDE EAST ALLOWING AN UPPER RIDGE TO BUILD INTO THE REGION FROM THE
WEST WEDNESDAY NIGHT INTO THURSDAY. PLAYED LOW TEMPERATURES
WEDNESDAY NIGHT CLOSE TO THE ADJMETBC FROM THE LOWER 60S TO AROUND
70 DEGREES. WITH INCREASING 85H TEMPERATURE...HIGH TEMPERATURES ON
THURSDAY WILL RANGE FROM THE MID 80S IN THE MOUNTAINS TO THE MID 90S
IN SOUTHSIDE. LATE AFTERNOON PEAK HEATING WILL CREATE ISOLATED TO
WIDELY SCATTERED SHOWERS AND THUNDERSTORMS...WITH THE BEST COVERAGE
OVER THE NORTHERN MOUNTAINS OF NORTH CAROLINA AND ADJOINING PORTIONS
OF SOUTHWEST VIRGINIA.

SOUTHWEST FLOW ON FRIDAY WILL INCREASE MOISTURE WITH ADDITIONAL
CLOUD COVER AND SCATTERED SHOWERS AND THUNDERSTORMS. PLAYED HIGHS
FRIDAY FROM THE MID 80S IN THE WEST TO THE LOWER 90S IN THE
SOUTHEAST. WENT WITH THE HIGHEST POPS IN THE WESTERN MOUNTAINS.
NUDGED LOW TEMPERATURES UP A FEW DEGREES ON FRIDAY NIGHT WITH
VALUES CLOSE TO HPCGUIDE FROM MID 60S TO THE LOWER 70S.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
UPPER TROUGH WILL CONTINUE IN THE MEDIUM RANGE WITH A WEAK FRONT
LATE SATURDAY SAGGING SOUTH ACROSS REGION. NO SIGNIFICANT CHANGE IN
AIRMASS COOLER OR DRIER BEHIND THE BOUNDARY. WEAK SHORTWAVES
MOVING ACROSS THE REGION WILL RESULT IN SCATTERED STORMS OF VARYING
DEGREE THROUGH THE REST OF THE FORECAST. KEPT TEMPERATURES SLIGHTLY
ABOVE NORMAL DURING THE PERIOD.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
NUMEROUS TO WIDESPREAD SHRA/TSRA ANTICIPATED THROUGH SUNSET.
SOME ORGANIZATION POSSIBLE WITH THUNDERSTORM CLUSTERS OR SHORT
LINE SEGMENTS POSSIBLE THROUGH THE EVENING HOURS.
MVFR/IFR CONDITIONS LIKELY IN THE VCNTY OF THE SHOWERS/STORMS...
RAIN RATES IN THE DEEPER CONVECTION OF 4 INCHES AN HOUR DRIVING
LCL VSBYS UNDER 1SM. GUSTY THUNDERSTORM OUTFLOWS ARE ALSO LIKELY
PER 30-40 KT 5-10KFT AGL WINDS. DOWNDRAFTS OF 30-50 KTS WILL BE
COMMON WITH POTENTIAL FOR SVR GUSTS (50-70 KTS) WHERE TSTMS BECOME
ORGANIZED.

THE UPPER TROUGH IS EXPECTED TO MOVE EAST OF THE AREA
TONIGHT...ENDING RAIN THREAT...BUT LEAVING AREA VERY MOIST. AS
SUCH...HIGH CONFIDENCE OF WIDESPREAD MVFR/IFR CONDITIONS
DEVELOPING TONIGHT DUE TO LOW STRATUS AND FOG.

THE WEATHER PATTERN IS EXPECTED TO DRY OUT A BIT WITH WARMER
TEMPERATURES FOR THURSDAY AND FRIDAY. THERE WILL STILL BE A
SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS...WITH THE GREATEST
COVERAGE WILL LIKELY DURING THE PEAK HEATING PART OF THE DAY. MVFR
FOG WILL ALSO BE A POSSIBILITY EACH NIGHT THROUGH LATE IN THE
WEEK. A COLD FRONT COMING THROUGH THE REGION ON SATURDAY WILL
BRING ANOTHER MORE ORGANIZED CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.HYDROLOGY...
PWATS AROUND 2 INCHES WILL DRIVE THE RAIN EFFICIENCY. FLASH FLOOD
QUIDANCE VALUES ARE DOWN ABOUT A HALF INCH IN THE AREAS THAT
RECEIVED THE 1-3 INCH RAINS MONDAY...PRIMARILY THE HIGHLANDS AND
SOUTHERN SHENANDOAH VALLEY OF VA AND INTO PARTS OF THE NEW RIVER
AND GREENBRIER VALLEYS. WILL HAVE TO MONITOR THIS PART OF THE FCST
AREA CLOSELY FOR POTENTIAL FLASH FLOOD WATCH IF TRAINING OF
THUNDERSTORMS DEVELOP.

&&

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

&&

SYNOPSIS...PM
NEAR TERM...PM
SHORT TERM...KK
LONG TERM...KK
AVIATION...PM
HYDROLOGY...PM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
354 AM EDT TUE JUL 13 2010

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>045-140800-
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-
354 AM EDT TUE JUL 13 2010

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.

SHOWERS WILL ONCE AGAIN BE NUMEROUS ACROSS THE REGION BY THIS
AFTERNOON. RAIN WILL BE HEAVY AT TIMES AND COULD CAUSE LOCALIZED
FLOODING. THERE IS ALSO A THREAT OF ISOLATED SEVERE THUNDERSTORMS
WHICH COULD BRING STRONG WIND GUSTS DURING THE AFTERNOON AND EARLY
EVENING.

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

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BLACKSBURG VA
325 PM EDT TUE JUL 13 2010

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

0245 PM     TSTM WND DMG     HOT SPRINGS             38.00N 79.83W
07/13/2010                   BATH               VA   PUBLIC

            THREE TREES REPORTED DOWN IN HOT SPRINGS ALONG US 220.

&&

CHENARD