Severe Thunderstorm Warning 172, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
356 PM EDT FRI AUG 23 2013

.SYNOPSIS...
DRIER AND SOMEWHAT COOLER HIGH PRESSURE WILL SETTLE OVER THE AREA
BEHIND A COOL FRONT TONIGHT AND INTO THE WEEKEND. MOISTURE WILL
BEGIN TO VERY SLOWLY RETURN TO THE REGION THROUGHOUT NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 342 PM EDT FRIDAY...

THE COLD FRONT CONTINUES TO MARCH TOWARDS THE AREA LATE THIS
AFTERNOON AND WILL SLOWLY MOVE SOUTH OF THE AREA TONIGHT. AREAS THAT
SAW RAIN EARLIER TODAY...SE WV-EXTREME SW VA...ARE STILL BEHIND THE
THETA-E/DEW POINT BOUNDARY. THIS BOUNDARY JUST MOVED SOUTH OF
PITTSBURGH PA AT 300 PM. THE COMBINATION OF MOISTURE AND HEATING
WILL KEEP NON-SEVERE SCATTERED CONVECTION OVER THE WEST UNTIL EARLY
THIS EVENING. THE STRONGER CONVECTION IS CURRENTLY MOVING ACROSS THE
SOUTHERN SHENANDOAH/ROANOKE VALLEYS AND SOUTH-CENTRAL VIRGINIA
PIEDMONT THIS AFTERNOON. THIS CONVECTION WILL WORK ITS WAY SOUTH TO
THE NC/VA BORDER THIS EVENING. THE PIEDMONT HAS SEEN MORE HEATING
TODAY AND SCATTERED STRONG TO ISOLATED SEVERE STORMS ARE POSSIBLE
THROUGH 10 PM. THIS STRONGER CONVECTION IS MOVING TO THE SOUTHEAST
AROUND 20 MPH WITH RAINFALL RATES OF 3 TO 5 INCHES PER HOUR. IF
THESE STORMS SLOW DOWN AND MAINTAIN THESE RAINFALL RATES...STREET
FLOODING WILL LIKELY RESULT.

ALL MODELS SHOWING VIABLE SOLUTIONS FOR THIS EVENING WITH KEEPING
SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHEAST CORNER OF RNK CWA
THROUGH MIDNIGHT. I FAVORED AND BLENDED THE 12Z NAM AND 16Z HRRR.
THESE MODELS CAPTURED CURRENT SHOWERS OVER THE AREA AT THE TIME.
ONCE THE SHOWERS EXIT...THE THETA-E BOUNDARY WILL REMAIN OVER THE
AREA. WITH A MOIST SOUTHEAST FLOW...LOW LEVEL CLOUDS AND POSSIBLE
DRIZZLE SHOULD REMAIN INTO SATURDAY MORNING. DRY AIR BY MID MORNING
WILL QUICKLY CLEAR THE SKIES BY THE AFTERNOON. ALSO WITH LOW CLOUDS
IN THE REGION...AREAS OF DENSE FOG WILL NOT BE WIDESPREAD.

COOLER THAN NORMAL TEMPERATURES AND A NOTICEABLE DRIER DEW POINTS ARE
ON TAP FOR SATURDAY. TEMPERATURES WILL RANGE FROM THE MID TO UPPER
70S ACROSS THE WEST AND UPPER 70S TO LOWER 80S IN THE EAST. DEW
POINTS FOR THE AREA WILL BE IN THE 50S.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 355 PM EDT FRIDAY...

RELATIVELY DRY AND COOL HIGH PRESSURE CENTERED OVER THE MID
ATLANTIC IS EXPECTED TO DOMINATE THIS PERIOD. NO SIGNS OF ANY
CHANCE OF RETURNING MOISTURE UNTIL POSSIBLY MONDAY AFTERNOON IN
TEH FAR WEST WITH SFC HIGH DRIFTING OVER WRN NC BY THIS TIME AND
850 FLOW WEAK BUT BEGINNING TO SHOW BETTER WESTERLY COMPONENT.
THIS TIME OF YEAR IT DOES NOT TAKE TOO LONG BEFORE JUST ENOUGH
LOVE LEVEL MOISTURE SNEAKS BACK IN FOR AT LEAST SOME ISOLATED MTN
SHOWERS. KEPT SLIGHT CHC CONFINED TO WESTERN SLOPES BASICALLY.
ADDED SOME PATCHY VALLEY FOG FOR SUNDAY MORNING GIVEN HIGH
BASICALLY OVERHEAD AND LITTLE IF ANY CLOUDS EXPECTED.

HIGH TEMPS AT OR BELOW SEASONAL LEVELS BUT WENT WITH WARMER
GUIDANCE GIVEN DRY RIDGE WITH PLENTY OF SUN...AND THEN LOW TEMPS
INITIALLY BELOW NORMAL GIVEN CLEAR BUT DRY NIGHTS. WENT WITH
COOLER MET GUIDANCE FOR LOWS SAT NIGHT AND SUNDAY NIGHT. BY
MONDAY NIGHT LOWS MAY GET BACK TO AT OR ABOVE SEASONAL NORMS WITH
LOW LEVEL MSTR ON THE SLOW INCREASE.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 200 PM EDT FRIDAY...

LARGE HIGH PRESSURE DOME OVER CENTRAL U.S. GRADUALLY RETROGRADES
WEST DURING THE MID TO LATE PART OF THE WEEK...WITH A GRADUAL SET UP
OF WEAK UPPER TROUGH OVER NORTHEAST U.S. AND BETTER NW FLOW AND
CHANCES FOR SOME ORGANIZED CONVECTIVE SYSTEMS RIDING OVER TOP OF
RIDGE TO MAKE THEIR WAY INTO WESTERN OR NORTHWESTERN PORTIONS OF OUR
AREA. VERY HARD TO BE ABLE TO PIN POINT WHICH DAY IS MOST LIKELY FOR
THIS TO FIRST HAPPEN. 12Z GFS MOST AGGRESSIVE AT DEVELOPING THE
UPPER LEVEL WEAKNESS BY AS EARLY AS LATE TUES INTO WED...WITH 00Z
ECMWF AND 12Z CANADIAN IN GOOD AGREEMENT THAT IT MAY BE THURS BEFORE
THIS HAPPENS.  GFS ALSO TRYING TO SHOW BETTER RETURN OF MSTR UNDER
THE RIDGE AS EARLY AS TUES FOR ISOLD TO SCT MOUNTAIN SHWRS AND
TSTORMS DEVELOPING EACH DAY...WHEREAS OTHER MODELS APPEAR TO HAVE
SUBSIDENCE WITH RIDGE DOMINATING.  BASED ON CLIMATOLOGY WITH THIS
KIND OF PATTERN...WILL LEAN TOWARD GFS IDEA OF RETURN OF DAILY
MAINLY MTN SCATTERED CONVECTION BY TUES...BUT THEN BETTER CHANCES
FOR SOMETHING MORE ORGANIZED MOVING INTO WEST BY WED OR WED
NIGHT.

THE OTHER DIFFERENCE BETWEEN THE GUIDANCE IS HOW QUICKLY THIS BACK
SIDE OF THE WEAK TROUGH IS ABLE TO SWING A BACK DOOR COLD FRONT
THROUGH THE AREA AND HOW FAR SOUTH IT MAKES IT. OF COURSE MUCH OF
THIS MAY DEPEND ON TO WHAT EXTENT ORGANIZED CONVECTION RIDING OVER
THE NE EDGE OF THE BIG RIDGE MAY DEVELOP AND HELP PULL THIS BOUNDARY
DOWN. GFS FASTEST WITH THE FRONTAL PASSAGE AND BRINGS THIS THROUGH
EARLY THURSDAY...WITH ECMWF SLOWER AND MORE LIKE LATE THURSDAY OR
THURS NIGHT. THEN BY FRIDAY ECMWF A LITTLE SLOWER TO DRAG BACK END
OF FRONT AND LINGERING LOW LEVEL MOISTURE OUT OF THE SOUTHERN
APPALACHIANS...THUS SUGGESTING BETTER LINGER THREAT OF SOME ACTIVITY
FRIDAY ACROSS OUR SOUTHWEST.  FOR NOW...USED A VERY BROAD BRUSH AND
ERRED ON THE SIDE OF SLOWER REMOVAL OF MOISTURE THINKING FRONT MAY
NOT PUSH AS FAR SOUTH OF US AS MODELS GENERALLY SUGGEST.  SO LEFT
SOME CHC POPS ACROSS THE SOUTHWEST AND KEPT SLIGHT CHC UP EVERYWHERE
ELSE.  WITH THE UPSTREAM CONVECTIVE SYSTEMS DICTATING A LOT OF WHAT
WILL HAPPEN WITH THE BALANCE BETWEEN THE STRONG UPPER RIDGE TO OUR
WEST AND WEAK TROUGH OVER NORTHEAST U.S....JUST TOO MUCH UNCERTAINTY
THAT FAR OUT TO SAY FRO SURE WHEN...IF AT ALL...IT MAY DRY BACK OUT.

TEMPERATURE WISE...SLOW ARMING TREND EARLY PART OF PERIOD AS RIDGE
DOMINATES...THEN SLIGHT COOLING TREND WITH BETTER CHANCES FOR
CONVECTIVE AND ASSOC CLOUD COVER/PRECIP...AND POSSIBLE MORE
SIGNIFICANT DRYING OUT AND COOLER MINS BY THURS NIGHT OR FRI NIGHT
IF BACK DOOR FRONT CAN PUSH THROUGH.  HIGHS GENERALLY CLOSE TO
NORMAL...BUT LOWS PROBABLY TENDING ABOVE NORMAL WITH MSTR RETURN BY
MID WEEK. WENT CLOSE TO ECMWF MOS GUDIANCE.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
AS OF 122 PM EDT FRIDAY...

A COLD FRONT EXTENDS FROM CENTRAL WEST VIRGINIA TO NORTHERN VIRGINIA
EARLY THIS AFTERNOON. THIS FRONT WILL MOVE SOUTHEAST ACROSS THE
MOUNTAINS EARLY THIS AFTERNOON...AND BUCKLE ACROSS THE PIEDMONT
TRACKING SOUTHWARD INTO THIS EVENING.

SCATTERED SHOWERS AND THUNDERSTORMS MOVED ACROSS THE WEST
(LWB/BLF/BCB/ROA) THIS MORNING. THESE SHOWERS AND LINGERING CLOUD
COVER HAS KEPT INSTABILITIES DOWN. SCATTERED SHOWERS MAY MOVE OVER
THESE AIRPORTS UNTIL THE FRONTAL PASSAGE...BUT THUNDER CHANCES ARE
VERY LOW. THEREFORE HAVE LEFT OUT OF THE 18Z TAFS. FOR DAN AND
LYH...MOSTLY SUNNY SKIES THIS MORNING WILL GIVE THEM A BETTER CHANCE
TO SEE A THUNDERSTORMS THIS AFTERNOON. ISOLATED THUNDERSTORMS AT 17Z
WERE IN A LINE FROM KFVX TO KHKY. THUNDERSTORM MAY DEVELOP EAST OF
RNK PIEDMONT AIRPORTS THIS AFTERNOON. WILL KEEP TSRA IN THROUGH
00Z/8P THIS EVENING AS A PRECAUTION.

FOLLOWING THE FRONTAL PASSAGE THIS EVENING...MOIST LOW LEVELS AND
AND EASTERLY FLOW SHOULD KEEP LOW CLOUDS IN THROUGH THE NIGHT. SOME
PLACES ACROSS THE WEST MAY ALSO HAVE SPOTTY DRIZZLE OVERNIGHT. DRIER
AIR PUNCHES IN SATURDAY WITH SKIES BECOME CLEAR BY LATE MORNING.

HIGH PRESSURE WILL CONTROL THE WEATHER PATTERN FOR THE WEEKEND.
OTHER THAN SOME OVERNIGHT RIVER VALLEY FOG...VFR CONDITIONS ARE
EXPECTED SATURDAY INTO MONDAY. EXPECT A RETURN OF SPOTTY SHOWERS
AND THUNDERSTORMS IN THE MOUNTAINS FOR TUESDAY.

&&

.EQUIPMENT...
AS OF 345 PM EDT FRIDAY...

THE NOAA ALL HAZARDS RADIO SITE AT MOUNT JEFFERSON...LOCATED IN
ASHE COUNTY NORTH CAROLINA...AND BROADCASTING ON A FREQUENCY OF
162.500 MHZ...IS OFF THE AIR DUE TO A SUSPECTED POWER OUTAGE.
IT IS UNKNOWN AT THIS TIME WHEN SERVICE WILL BE RESTORED.

MEANWHILE...THE NOAA ALL HAZARDS RADIO SITE ON BENT MOUNTAIN IN
SOUTHWESTERN ROANOKE COUNTY...BROADCASTING ON A FREQUENCY OF
162.475 MHZ...IS BACK ON THE AIR AS OF THIS AFTERNOON BUT THE
PHONE LINE ISSUE MAY NOT BE ENTIRELY RESOLVED...AND IT IS POSSIBLE
IT MAY GO OFF THE AIR AGAIN FOR A PERIOD OF TIME.

&&

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

&&

SYNOPSIS...SK
NEAR TERM...RCS
SHORT TERM...SK
LONG TERM...SK
AVIATION...RCS
EQUIPMENT...AMS/SK

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
349 PM EDT FRI AUG 23 2013

VAZ007-009>014-017>020-022>024-034-035-047-WVZ042>045-242000-
TAZEWELL-SMYTH-BLAND-GILES-WYTHE-PULASKI-MONTGOMERY-FLOYD-CRAIG-
ALLEGHANY VA-BATH-ROANOKE-BOTETOURT-ROCKBRIDGE-BEDFORD-AMHERST-
BUCKINGHAM-MERCER-SUMMERS-MONROE-GREENBRIER-
349 PM EDT FRI AUG 23 2013

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

.DAY ONE...THIS AFTERNOON AND TONIGHT.

THERE IS A LOW PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER THIS
AFTERNOON AND TONIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

NCZ001>006-018>020-VAZ015-016-032-033-043>046-058-059-242000-
ASHE-ALLEGHANY NC-SURRY-STOKES-ROCKINGHAM-CASWELL-WATAUGA-WILKES-
YADKIN-GRAYSON-CARROLL-PATRICK-FRANKLIN-HENRY-PITTSYLVANIA-CAMPBELL-
APPOMATTOX-HALIFAX-CHARLOTTE-
349 PM EDT FRI AUG 23 2013

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

.DAY ONE...THIS AFTERNOON AND TONIGHT.

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED
INTO THIS EVENING. LOCALLY HEAVY RAIN IS POSSIBLE WHICH MAY CAUSE
MINOR FLOODING. SOME OF THE STRONGER STORMS MAY PRODUCE STRONG
GUSTY WINDS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

RCS

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
349 PM EDT FRI AUG 23 2013

VAZ034-044-045-232015-
BEDFORD VA-PITTSYLVANIA VA-CAMPBELL VA-
349 PM EDT FRI AUG 23 2013

THE NATIONAL WEATHER SERVICE IN BLACKSBURG HAS ISSUED A

* SPECIAL WEATHER STATEMENT FOR...
  SOUTHERN BEDFORD COUNTY IN SOUTH CENTRAL VIRGINIA...
  NORTHEASTERN PITTSYLVANIA COUNTY IN SOUTH CENTRAL VIRGINIA...
  CAMPBELL COUNTY IN CENTRAL VIRGINIA...

* UNTIL 415 PM EDT

* AT 346 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS
  TRACKING A LINE OF THUNDERSTORMS WITH HEAVY DOWNPOURS ALONG A LINE
  EXTENDING FROM BOCOCK TO HUDDLESTON... MOVING TO THE SOUTHEAST AT
  25 MPH.

* VERY HEAVY RAIN IS FALLING...AND WILL CAUSE WATER TO POND ON
  ROADWAYS. THIS WILL MAKE DRIVING HAZARDOUS.

* LOCATIONS IMPACTED INCLUDE...
  EVINGTON...
  HUDDLESTON...
  HURT...
  RUSTBURG...
  AND GRETNA.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

PROLONGED HEAVY RAINFALL MAY CAUSE WATER TO FLOW OVER THE ROADWAY. DO
NOT DRIVE YOUR VEHICLE WHERE THE ROAD HAS BECOME FLOODED.

&&

LAT...LON 3718 7890 3692 7942 3715 7961 3739 7910
      3730 7898
TIME...MOT...LOC 1946Z 323DEG 20KT 3735 7909 3714 7953

MBS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
414 PM EDT FRI AUG 23 2013

VAZ044>046-058-059-232045-
HALIFAX VA-CHARLOTTE VA-APPOMATTOX VA-PITTSYLVANIA VA-CAMPBELL VA-
414 PM EDT FRI AUG 23 2013

THE NATIONAL WEATHER SERVICE IN BLACKSBURG HAS ISSUED A

* SPECIAL WEATHER STATEMENT FOR...
  NORTHERN HALIFAX COUNTY IN SOUTH CENTRAL VIRGINIA...
  CHARLOTTE COUNTY IN SOUTH CENTRAL VIRGINIA...
  SOUTHERN APPOMATTOX COUNTY IN CENTRAL VIRGINIA...
  PITTSYLVANIA COUNTY IN SOUTH CENTRAL VIRGINIA...
  SOUTHERN CAMPBELL COUNTY IN CENTRAL VIRGINIA...

* UNTIL 445 PM EDT

* AT 411 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
  STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM RED HOUSE TO
  HODGES TO CLIMAX...MOVING TO THE SOUTH AT 25 MPH.

* WIND GUSTS UP TO 40 MPH ARE EXPECTED WITH THESE STORMS. VERY HEAVY
  RAIN IS FALLING...AND WILL CAUSE WATER TO POND ON ROADWAYS AND
  QUICKLY FILL ROADSIDE DITCHES AND SMALL STREAMS.

* LOCATIONS IMPACTED INCLUDE...
  CHATHAM...
  HURT...
  BROOKNEAL...
  NATHALIE...
  AND GRETNA.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

PROLONGED HEAVY RAINFALL MAY CAUSE WATER TO FLOW OVER THE ROADWAY. DO
NOT DRIVE YOUR VEHICLE WHERE THE ROAD HAS BECOME FLOODED.

&&

LAT...LON 3690 7854 3684 7909 3670 7937 3694 7959
      3702 7949 3701 7948 3702 7946 3703 7947
      3721 7923 3726 7877
TIME...MOT...LOC 2011Z 343DEG 22KT 3720 7884 3716 7921 3692 7953

MBS