Severe Thunderstorm Warning 417, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
243 PM EDT SUN SEP 4 2011

.SYNOPSIS...
A COLD FRONT...CURRENTLY LOCATED OVER THE OHIO VALLEY...WILL
APPROACH THROUGH THE DAY TOMORROW BEFORE STALLING NEAR OR JUST SOUTH
OF THE WATERS TUESDAY. SHOWERS AND THUNDERSTORMS ARE EXPECTED ALONG
AND AHEAD OF THIS BOUNDARY. TROPICAL MOISTURE WILL INTERACT WITH THE
STALLED FRONT CAUSING A PROLONGED PERIOD OF SHOWERS AND
THUNDERSTORMS THROUGH THE WEEK.

&&

.NEAR TERM /THROUGH MONDAY/...
COLD FRONT SITUATED FROM THE CENTRAL GREAT LAKES BACK THROUGH THE
MID MISSISSIPPI RIVER VALLEY THIS EVENING. THE REMNANTS OF TS LEE
HAVE MOVED INLAND OVER LA/SW MISSISSIPPI. REGIONAL RADAR SHOWS A
LINE OF SHOWERS TN THUNDERSTORMS ALONG AND JUST AHEAD OF THE COLD
FRONT THIS AFTERNOON. LOCAL RADAR SHOWS ISOLD/SCT TSRA HAVE
DEVELOPED ACROSS THE HIGHER TERRAIN IN THE SE FORECAST AREA.

FOR THE REMAINDER OF THE AFTERNOON INTO THE EARLY EVENING...SCT
CONVECTION WILL CONTINUE ACROSS THE HIGHER TERRAIN OF THE WESTERN
PORTIONS OF THE CWFA. SOUNDING ANALYSIS SHOWS MODERATE SURFACE
INSTABILITY WITH STEEP LAPSE RATES. NO REAL SURFACE TRIGGER FOR
CONVECTION...SO WILL LEAVE ONLY CHANCE POPS IN AT THIS TIME. MODEL
SOUNDINGS ALSO SHOW HIGH PWATS WITH WEAK BOUNDARY LAYER
WINDS...EXCELLENT CONDITIONS FOR LOCALLY HEAVY RAINFALL. AN ISOLATED
STORM OR TWO COULD BECOME SEVERE...WITH DAMAGING WIND GUSTS AND
LARGE HAIL.

PRECIP ASSOCIATED WITH THE COLD FRONT WILL CONTINUE TO MOVE EAST
THIS AFTERNOON AND EARLY EVENING. HAVE ADJUSTED POPS DOWNWARD FOR
THE AFTERNOON...BUT KEPT THE LIKELY/CAT POPS OUT WEST FOR THE
OVERNIGHT HOURS. FRONT/PRECIP SHIELD SHOULD STRUGGLE TO CROSS THE
BLUE RIDGE OVERNIGHT...BUT SHOULD DO SO EARLY MONDAY MORNING.

WATER VAPOR LOOP SHOWS DEEP TROPICAL MOISTURE FROM THE REMNANTS OF
TS LEE BEING PULLED NORTHWARD ALONG THE FRONT. MODELS FORECAST EVEN
HIGHER PWATS TOMORROW...AOA 2 INCHES. RAINFALL IS EXPECTED TO BECOME
HEAVIER TOMORROW AFTERNOON...AS THE DEEP TROPICAL MOISTURE MAKES IT
INTO THE MID ATLANTIC. FOR NOW...THE HEAVIEST RAINFALL IS EXPECTED
ACROSS THE SHENANDOAH VALLEY/CENTRAL VA FOOTHILLS. FFG REMAINS
FAIRLY HIGH FOR THIS AREA. IN ADDITION...THIS REGION DIDN'T RECEIVE
AS MUCH RAINFALL AS EASTERN PORTIONS OF THE CWFA DID WHEN IRENE
MOVED UP THE COAST.

TOOK BLEND FOR TEMP/POP GUIDANCE. HOWEVER...WITH RESPECT TO THE
EVOLUTION OF THE REMNANTS OF TS LEE...PREFERRED THE GFS/EURO.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
A GENERAL SLOWING OF SYNOPTIC ELEMENTS IS PRESENT AFTER 36 HOURS FOR
THIS FORECAST PACKAGE...A TREND PORTRAYED BY THE EC. THROUGH
WEDNESDAY...A DEEP UPPER LEVEL TROUGH WILL TRANSITION EASTWARD AND
PUSH A FRONT ACROSS THE AREA BEFORE MOVING OFFSHORE WED AFTERNOON.
THE FRONT IS STILL EXPECTED TO MOVE TO THE SOUTHEAST OF THE CWA
OVERNIGHT MONDAY AS TROPICAL MOISTURE CONTINUES TO BE FUNNELED INTO
THE AREA. THE BIG STORY FOR THE SHORT TERM IS THE POSSIBILITY OF
FLOODING. MODELS VARIED AS TO TIMING OF PRECIP AND LOCATION OF
HIGHEST QPF. USED HPC/S SOLUTION...WHICH BRINGS THE HIGHEST AMOUNTS
OF 2 TO 3 INCHES TO AREAS EAST OF THE BLUERIDGE IN SOUTHERN PORTIONS
OF THE CWA THROUGH WEDNESDAY NIGHT. HEAVY RAIN IS MENTIONED THROUGH
TUESDAY NIGHT.

FLOW WILL SHIFT FROM SOUTHERLY TO NORTHWESTERLY AFTER TOMORROW
NIGHT/S FRONTAL PASSAGE. THIS WILL HELP TO USHER IN COOLER TEMPS BUT
IS NOT EXPECTED TO CAUSE SIGNIFICANT DRYING. INTERACTION BETWEEN
THE REMNANTS OF TROPICAL STORM LEE AND THE SLOW MOVING COLD FRONT
WILL CONTINUE TO CAUSE WIDESPREAD PRECIP ACROSS THE REGION.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
UPPER LEVEL FLOW WILL GRADUALLY BECOME MORE ZONAL LATER IN THE
WEEK. A SHORTWAVE WILL IMPACT THE MID-ATLANTIC THURSDAY THROUGH
FRIDAY NIGHT CREATING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS.
PWATS OF OVER 2 INCHES WILL PERSIST INTO FRIDAY BEFORE DIMINISHING
AT THE BEGINNING OF THE WEEKEND. AT THIS POINT...SUNDAY COULD BE
DRY AS CANADIAN HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
ISOL/SCT CONVECTION EXPECTED WEST OF THE BLUE RIDGE FOR THE
REMAINDER OF THE AFTERNOON INTO THE EVENING. CIGS/VSBYS VFR EAST
OF THE BLUE RIDGE. COLD FRONT BEGINS TO APPROACH THE REGION
OVERNIGHT...WITH ASSOCIATED SHOWERS AND THUNDERSTORMS. CIGS/VSBYS
EXPECTED TO BEGIN DETERIORATING AFTER 8Z. MVFR VSBYS EXPECTED FOR
MOST OF MONDAY.

VISIBILITY REDUCTIONS DUE TO HEAVY RAIN ARE EXPECTED THROUGH THE
EXTENDED PERIOD. OVERCAST SKIES WITH CIGS 5000 FT AND BELOW WILL
CONTINUE THROUGH THE WEEK. IFR CONDITIONS ARE POSSIBLE EACH DAY.

&&

.MARINE...
NO CHANGES TO THE HEADLINES. S WINDS 10-15 KT WITH GUSTS TO AROUND
20 KT ANTICIPATED OVERNIGHT AND DURING THE DAY ON MONDAY AS A COLD
FRONT APPROACHES FROM THE WEST.

WITH THE COLD FRONTAL PASSAGE TOMORROW NIGHT...WIND GUSTS AROUND
15KT IN SOUTHERN PORTIONS OF THE BAY WILL REMAIN POSSIBLE
OVERNIGHT. HOWEVER DID NOT MAKE ANY CHANGES TO THE CURRENT SCA AT
THIS POINT AS EXPECT HIGHEST GUSTS TO DIMINISH MONDAY EVENING.
VISIBILITY REDUCTIONS ALL WEEK ARE POSSIBLE DUE TO FORECASTED
HEAVY RAIN AND THUNDERSTORM ACTIVITY.

&&

.TIDES/COASTAL FLOODING...
CURRENT TIDAL ANOMALIES SITTING AT AROUND 1 FT. WITH THE PERSISTENT
SOUTHERLY FLOW...EXPECT TIDAL ANOMALIES TO HOLD OR SLIGHTLY RISE
OVERNIGHT. THE OVERNIGHT HIGH TIDE IS THE PREFERRED TIDE...SO HAVE
GONE AHEAD AND ISSUED A COASTAL FLOOD ADVISORY FOR COUNTIES ADJACENT
TO THE TIDAL POTOMAC AND WESTERN SHORE OF THE CHESAPEAKE BAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO 5 AM EDT
     MONDAY FOR DCZ001.
MD...COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO 5 AM EDT
     MONDAY FOR MDZ007-011-013-014-016>018.
VA...COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO 5 AM EDT
     MONDAY FOR VAZ052>055-057.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT MONDAY
     FOR ANZ531>534-537-539>541-543.

&&

LISTEMAA/LARSEN

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
342 PM EDT SUN SEP 4 2011

WVZ501-042030-
WESTERN GRANT WV-
342 PM EDT SUN SEP 4 2011

...STRONG THUNDERSTORM TO AFFECT WESTERN GRANT COUNTY...

AT 342 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 2 MILES
EAST OF WILSONIA...MOVING NORTHEAST AT 5 MPH.

LOCATIONS IMPACTED INCLUDE BAYARD.

HEAVY RAIN WITH THIS STORM WILL REDUCE VISIBILITIES TO BELOW ONE MILE
AND MAY CAUSE PONDING OF WATER ON ROADWAYS.

WIND GUSTS OF 40 TO 50 MPH AND SMALL HAIL CAN BE EXPECTED WITH THIS
STORM.

&&

LAT...LON 3921 7949 3922 7945 3928 7938 3930 7934
      3931 7930 3933 7928 3928 7918 3919 7930
      3921 7931 3920 7938 3918 7945 3919 7949
TIME...MOT...LOC 1942Z 211DEG 6KT 3920 7941

HTS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
410 PM EDT SUN SEP 4 2011

WVZ055-501-502-042100-
HARDY WV-WESTERN GRANT WV-EASTERN GRANT WV-
410 PM EDT SUN SEP 4 2011

...STRONG THUNDERSTORMS TO AFFECT HARDY AND GRANT COUNTIES...

AT 408 PM EDT...DOPPLER RADAR INDICATED A CLUSTER OF STRONG
THUNDERSTORMS FROM 2 MILES SOUTHWEST OF KLINE GAP TO ROUGH
RUN...MOVING NORTH AT 10 MPH.

LOCATIONS IMPACTED INCLUDE STREBY...KLINE GAP...DORCAS...
PETERSBURG...MAYSVILLE...SEYMOURVILLE...ARTHUR...SCHERR AND
LAHMANSVILLE.

WIND GUSTS OF 40 TO 50 MPH...VERY HEAVY RAIN...AND SMALL HAIL CAN BE
EXPECTED WITH THESE STORMS. LOCALLY IN EXCESS OF AN INCH OF RAIN
WILL BE POSSIBLE IN LESS THAN AN HOUR. HEAVY RAIN WITH THESE STORMS
WILL REDUCE VISIBILITIES TO BELOW ONE MILE AND MAY CAUSE PONDING OF
WATER ON ROADWAYS.

&&

LAT...LON 3928 7918 3904 7899 3882 7904 3883 7916
      3905 7927
TIME...MOT...LOC 2008Z 193DEG 9KT 3905 7921 3889 7915

HTS