Damaging Wind in Virginia, April 23, 2011

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1140 AM EDT SAT APR 23 2011

.SYNOPSIS...
A WARM FRONT WILL PASS THROUGH THE REGION TODAY. A COLD FRONT WILL
APPROACH THE REGION TONIGHT BEFORE STALLING OUT NEAR THE MASON-DIXON
LINE LATER SUNDAY THROUGH MONDAY. THE BOUNDARY WILL MOVE NORTH AS A
WARM FRONT FOR THE MIDDLE PORTION OF THE WEEK BEFORE A STRONGER COLD
FRONT MOVES THROUGH THURSDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
NEAR-TERM MONITORING IF FOR THE DYING MCS THAT HAS SLID ACROSS THE
CNTRL APLCNS IN JUST A COUPLE OF SHORT HRS. MORE IMPRESSIVELY -
THE FEATURE HAS TRAVELED FROM FROM SRN OH/NRN KY TO I-81 CORRIDOR
IN JUST 3-4 HRS. OUTSIDE OF A FEW HEAVY SHOWERS NOW POKING OVER
THE BLUE RIDGE/I-66 INTERSECTION...MUCH OF THE MCD IS NOW THE
LEFTOVER STRATIFORM RAINS THAT ARE DISSIPATING OVER THE POTOMAC
HIGHLANDS. EVEN THOUGH THE STORM TOTAL RAINFALL FROM YESTERDAY/S
ACTIVITY WAS ON THE ORDER OF HALF INCH OR LESS /LOCALLY HIGHER
ALONG THE WRN EDGE OF THE CWA/...EVEN A FEW TENTHS OF AN INCH ON
TOP OF THIS COULD POTENTIALLY PRODUCE LOCALIZED FLASH FLOODING
ACROSS THE WRN COUNTIES.

THE WARM FRONT THAT CROSS THE REGION OVERNIGHT IS NOW MOVING WELL
TO THE NE AS A COLD FRONT CONTINUES TO INCH DOWN TOWARD THE MID
ATLC FROM THE SRN GREAT LAKES. PEAKS OF SUN APPEARING WEST OF THE
BLUE RIDGE WHICH WILL ALLOW THESE HIGHLAND AREAS TO WARM UP ABOVE
70 DAY BUT THE MORE SOCKED-IN CONDITIONS EAST OF THE MTNS WILL
KEEP THE METRO AREAS CLOSER TO A HIGH IN THE 60S-NEAR 70 LATER
THIS AFTN. A STIFF SWLY WIND WILL HELP TO BRING IN SOME RELATIVELY
WARMER AIR WHICH WILL PULL TEMPS UP A FEW DEGREES DESPITE THE
CLOUD COVER.

CLOUDS ALSO HELPING TO KEEP THE AREA FAIRLY STABLE TODAY. ANY
USABLE POTENTIAL ENERGY IN THE ATMOS WILL BE ELEVATED AND IN A
TIGHT CORRIDOR CLOSER TO THE INCOMING FRONTAL BOUNDARY. WITH THE
COLD FRONT SETTLING JUST TO THE NW OF THE POTOMAC HIGHLANDS LATER
TODAY...MOISTURE AND ANOTHER OTHER INCOMING STORM-SCALE FEATURES
WILL MOVE ALONG THE BOUNDARY - CREATING A HIGH POTENTIAL OF PRECIP
ACROSS THE NWRN QUADRANT AND ACROSS THE MASON-DIXON LINE BUT MUCH
LOWER POPS ACROSS THE SERN TIER OF THE CWA. A LOCALIZED BATCH OF
LIGHT PRECIP COULD SLIDE ACROSS THE REGION AT TIMES BUT FOR THE
MOST PART...PRECIP WILL BE LIMITED TO AREAS NORTH OF I-66 AND WEST
OF I-81 TODAY /TONIGHT AND TOMORROW - FROM THE SAME REASONS/.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
THE COLD FRONT WILL STALL OUT NEAR THE MASON-DIXON LINE FOR SUNDAY
THROUGH SUNDAY NIGHT. A SERIES OF UPPER-LEVEL DISTURBANCES WILL
CONTINUE TO PASS BY JUST TO OUR NORTH DURING THIS TIME. MORE SHOWERS
AND THUNDERSTORMS ARE POSSIBLE ACROSS THE AREA ALONG AND AHEAD OF
THE FRONT. THE BEST CHANCE FOR THUNDERSTORMS WILL BE SUNDAY
AFTERNOON AND EVENING AS THE ATMOSPHERE DESTABILIZES. A WARM AND
MOIST AIRMASS AHEAD OF THE FRONT ALONG WITH STRONG WINDS ALOFT
SUGGESTS THAT A FEW T-STORMS SUNDAY AFTERNOON AND EVENING COULD
BECOME SEVERE. FLASH FLOODING IS ALSO A CONCERN DUE TO THE GROUND
ALREADY BEING SATURATED FROM RECENT RAINFALL. MAX TEMPS SUNDAY WILL
BE IN THE 80S ACROSS MOST LOCATIONS.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
THE BOUNDARY WILL REMAIN NEAR THE MASON-DIXON LINE MONDAY BEFORE
RETREATING NORTHWARD MONDAY NIGHT AND TUESDAY AS A WARM FRONT.
MID-ATLC RGN WILL BE LOCATED IN BROAD WARM SECTOR FOR MUCH OF NEXT
WK. RESULT WILL BE MAXIMA IN THE 80S...MINIMA IN THE UPR 50S-LWR 60S
AND DIURNAL CHCS FOR TSTMS.

TSTM CVRG MAY BE BEST WED-THU AS SFC TROF SHARPENS TO W AND SHRTWV
TROF PROVIDES BETTER LIFT SPREADING ATOP WARM AND MOIST LOW-LVL
AMS. SFC TROF AXIS AND SUBSEQUENT CDFNT WILL CROSS THE FCST AREA
ON THU WITH AN ATTENDANT LINE OF SHWRS/TSTMS. COLD AIR ADVCTN IN ITS
WAKE WILL LEAD TO TEMPS CLOSER TO NRML LATE NEXT WK.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
WMFNT LIFTING NWD TDA...WHICH ULTIMATELY WL PERMIT CIGS TO RISE
TO VFR CONDS LATER TODAY. STILL SOCKED-IN FROM EARLIER RAINFALL
AND NOT REALLY MUCH REGIME CHANGE IN BETWEEN AN EXITING WNFNT AND
AN INCOMING COLD FRONT. NOT ENOUGH DRY AIR PUSHING IN FROM THE SW TO
MIX THINGS OUT SINCE WE/RE UNDER ZONAL FLOW WHERE SYSTEM AFTER
SYSTEM SLIDES IN - ONE BEHIND THE OTHER. THE MOST RECENT IS A
DYING CONVECTIVE COMPLEX THAT HAS QUICKLY PUSHED INTO THE NRN
SHENANDOAH VLY. A POCKET OF THIS ACTIVITY HAS NOW MADE A RUN AT
THE DC AREA TAF SITES...MOVING DUE EAST ALONG I-66 W/ ISOLATED
BATCHES OF HEAVY RAIN BUT LITTLE/NO LIGHTNING.

IF THERE IS SUFFICIENT TIME IN THE WARM SECTOR...THEN TERMINALS
WL EXPERIENCE A SMALL TSRA RISK. THE BEST CHC OF THAT OCCURRING WL
BE AT MRB. ATTM...CHCS TOO SMALL TO WARRANT MENTIONING AT ANY
SITE...BUT IT WAS WORTH INCLUDING HERE. THOSE CHCS INCREASE TNGT
AS A COLD FRONT DROPS SEWD ACRS TERMINALS. AGN...MRB AT HIEST
RISK. THE POTENTIAL WL BE ADDRESSED FURTHER IN THE 12Z CYCLE.

AS THE COLD FRONT NEARS AND THEN STALLS JUST N OF TERMINALS SUN...
IT/LL BRING ANOTHER OPPORTUNITY FOR MAINLY DIURNALLY DRIVEN
TSRA. MAY SEE LCL FLGT RESTRICTIONS W/IN ANY POTENTIAL STORMS...
MOST LKLY MVFR-BRIEF IFR. MRB/MTN/BWI AT HIEST RISK...BUT THEY MAY
MAKE IT S TO DCA-IAD AS WELL.

WMFNT RETREATS NWD MON. ALL TERMINALS WILL BE LOCATED IN MOIST
WARM SECTOR MON-THU. TSTM CHCS INCR WED AS SFC TROF SHARPENS ALONG
MTNS.

&&

.MARINE...
A WARM FRONT WILL PASS THROUGH THE WATERS TODAY. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR ALL OF THE WATERS THIS AFTERNOON INTO
EARLY THIS EVENING BEHIND THE WARM FRONT. THE PRESSURE GRADIENT
WILL REMAIN STRONG ENOUGH FOR WIND GUSTS AROUND 20 KNOTS ACROSS
THE BAY AND LOWER TIDAL POTOMAC RIVER TONIGHT. SOUTH-SOUTHWEST
WINDS WILL GUST OVER 20 KNOTS ACROSS THE WATERS SUNDAY AS WELL. A
SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL OF THE WATERS SUNDAY.

A COLD FRONT WILL STALL OUT NEAR THE WATERS LATER SUNDAY. SHOWERS
AND T-STORMS ARE POSSIBLE SUNDAY AND SUNDAY NIGHT. SOME T-STORMS
SUNDAY AFTERNOON/EVENING COULD BECOME SEVERE.

THE BOUNDARY WILL REMAIN NEAR THE WATERS MONDAY BEFORE MOVING NORTH
AS A WARM FRONT TUESDAY. A STRONGER COLD FRONT MAY IMPACT THE WATERS
BY THURSDAY.

&&

.HYDROLOGY...
SHOWERS AND THUNDERSTORMS ARE APPROACHING THE AREA FROM THE OHIO
VALLEY EARLY THIS MORNING. THIS ACTIVITY WILL PASS THROUGH THE
REGION THROUGH MID-MORNING BUT IT SHOULD WEAKEN AS IT MOVES
THROUGH. HOWEVER...FLASH FLOOD GUIDANCE REMAINS QUITE LOW DUE TO
THE RECENT RAINFALL.

ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS
AFTERNOON INTO THIS EVENING ACROSS THE NORTHERN AND WESTERN PORTIONS
OF THE CWA. A FLASH FLOOD WATCH IS IN EFFECT FOR MOST LOCATIONS WEST
OF THE BLUE RIDGE AND INCLUDING NORTH-CENTRAL MARYLAND WHERE THE
BEST CHANCE FOR T-STORMS EXIST.

RIVER IMPACT WL BE MINIMAL IN TERMS OF NO WARNINGS ANTICIPATED
ATTM. W/IN BANK RISES ARE XPCTD. BRKM2 ONLY SITE ABV CAUTION
ATTM. A FEW OTHERS WL REACH THAT LVL...W/ MOST CRESTS HOLDING OFF
TIL SUNDAY. HIEST QPF IN THE UPR PTMC BASIN...LEAVING FAVM2 MOST
SUSCEPTIBLE.

&&

.TIDES/COASTAL FLOODING...
LATEST WATER LEVELS ACROSS THE BAY AND MUCH OF THE TIDAL POTOMAC
MISSED MINOR FLOODING DURING THEIR EARLIER HIGH TIDE CYCLE - ALL
EXCEPT DC/ALEX WHICH IS CURRENTLY ON ITS WAY TO THE 5.5-6.0 FT LEVEL
/DC WATERFRONT/. WILL PROBABLY PEAK JUST BELOW 6 FT. STILL RUNNING
ABOUT A FOOT ABOVE NORMAL THERE. LITTLE FALLS WILL DROP TO THEIR
LOWEST LEVELS /IN A FEW DAYS/ OVER THE NEXT 24 HRS THEN RISE
SLOWLY FROM THE RECENT UPSTREAM RAINS. THIS WILL KEEP DC/ALEX IN A
WAIT-AND-SEE SITUATION FOR ALL HIGH TIDE CYCLES FROM THE NEXT
SEVERAL DAYS - COUPLING THAT W/ PERIOD SLY WINDS KEEPING WATER
LEVELS HIGHER THAN NORMAL THROUGH THIS PERIOD. WILL LIKELY CANCEL
THE CURRENT ADZY IN THE NEXT COUPLE OF HRS AFTER HIGH TIDE...THEN
AWAIT MORE GUIDANCE FOR THE NEXT HT CYCLES.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR
     DCZ001.
MD...FLASH FLOOD WATCH FROM 2 PM THIS AFTERNOON TO 10 PM EDT THIS
     EVENING FOR MDZ003-004-501-502.
VA...FLASH FLOOD WATCH FROM 2 PM THIS AFTERNOON TO 10 PM EDT THIS
     EVENING FOR VAZ026>031-503-504.
     COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR
     VAZ054.
WV...FLASH FLOOD WATCH FROM 2 PM THIS AFTERNOON TO 10 PM EDT THIS
     EVENING FOR WVZ050>053-055-501>506.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT SUNDAY FOR ANZ532>534-537-
     540>543.
     SMALL CRAFT ADVISORY UNTIL 6 PM EDT SUNDAY FOR ANZ530-531-538-
     539.
     SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ535-
     536.
     SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EDT SUNDAY FOR ANZ535-
     536.

&&

UPDATE...GMS
PREV DISCUSSION...BJL/HTS/MRK

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
243 PM EDT SAT APR 23 2011

ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
241000-
CHESAPEAKE BAY NORTH OF POOLES ISLAND MD-
CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD-
CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD-
CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD-
CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA-
TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD-
TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD-
TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA-
PATAPSCO RIVER INCLUDING BALTIMORE HARBOR-
CHESTER RIVER TO QUEENSTOWN MD-EASTERN BAY-
CHOPTANK RIVER TO CAMBRIDGE MD AND THE LITTLE CHOPTANK RIVER-
PATUXENT RIVER TO BROOMES ISLAND MD-
TANGIER SOUND AND THE INLAND WATERS SURROUNDING BLOODSWORTH
ISLAND-DISTRICT OF COLUMBIA-NORTHERN BALTIMORE-HARFORD-
SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS-
CALVERT-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-
243 PM EDT SAT APR 23 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MARYLAND PORTION OF THE
CHESAPEAKE BAY...TIDAL POTOMAC RIVER...AND ADJACENT COUNTIES IN
CENTRAL MARYLAND AND NORTHERN VIRGINIA AS WELL AS THE DISTRICT OF
COLUMBIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A SMALL CRAFT ADVISORY IS IN EFFECT THIS AFTERNOON FOR THE
MARYLAND CHESAPEAKE BAY AND THE TIDAL POTOMAC RIVER. A SMALL CRAFT
ADVISORY IS IN EFFECT TONIGHT FOR THE MARYLAND CHESAPEAKE BAY AND
FOR THE TIDAL POTOMAC RIVER FROM COBB ISLAND TO SMITH POINT.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A SMALL CRAFT ADVISORY IS IN EFFECT SUNDAY FOR THE TIDAL POTOMAC
RIVER AND MARYLAND CHESAPEAKE BAY. A SMALL CRAFT ADVISORY IS IN
EFFECT SUNDAY NIGHT FOR THE MARYLAND CHESAPEAKE BAY FROM DRUM
POINT TO SMITH POINT.

A SMALL CRAFT ADVISORY LIKELY WILL BE NEEDED FOR PORTIONS OF THE
WATERS MONDAY THROUGH THURSDAY.

SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY. A FEW
THUNDERSTORMS MAY BECOME SEVERE DURING THE AFTERNOON AND EVENING
AND WILL BE CAPABLE OF DAMAGING WIND GUSTS AND LARGE HAIL.

SOUTHERLY WINDS WILL MAINTAIN ABOVE-NORMAL WATER LEVELS ON THE
TIDAL POTOMAC RIVER AND MARYLAND PORTION OF THE CHESAPEAKE BAY
THROUGH SUNDAY. MINOR COASTAL FLOODING MAY BE POSSIBLE SUNDAY
MORNING AND AFTERNOON DURING HIGH TIDE NEAR ALEXANDRIA AND
WASHINGTON DC.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD MONITOR THE LATEST FORECASTS FOR SUNDAY AND BE
PREPARED IF ACTIVATION BECOMES NECESSARY.

MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504-
WVZ050>053-055-501>506-241000-
WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD-
EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-AUGUSTA-
ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-NELSON-
ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER-
NORTHERN FAUQUIER-SOUTHERN FAUQUIER-WESTERN HIGHLAND-
EASTERN HIGHLAND-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY-
WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-
WESTERN PENDLETON-EASTERN PENDLETON-
243 PM EDT SAT APR 23 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN WEST VIRGINIA...
NORTHERN AND CENTRAL VIRGINIA...AND CENTRAL AND WESTERN MARYLAND
WITH THE EXCEPTION OF GARRETT COUNTY.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A FLASH FLOOD WATCH IS IN EFFECT THIS AFTERNOON AND EVENING FOR
NORTH-CENTRAL MARYLAND AND MOST LOCATIONS WEST OF THE BLUE RIDGE
MOUNTAINS. PLEASE REFER TO THE LATEST HAZARD MESSAGE /FFALWX/ FOR
DETAILS.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING FOR THE POTOMAC HIGHLANDS AND CENTRAL AND NORTHERN
SHENANDOAH VALLEY. A FEW STORMS WILL BE CAPABLE OF PRODUCING LARGE
HAIL AND DAMAGING WIND GUSTS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY. A FEW
THUNDERSTORMS MAY BECOME SEVERE SUNDAY AFTERNOON AND EVENING AND
WILL BE CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WIND GUSTS.

.SPOTTER INFORMATION STATEMENT...

LIMITED SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON. SPOTTER
ACTIVATION MAY BE NEEDED AGAIN ON SUNDAY. SPOTTERS SHOULD MONITOR
THE LATEST FORECASTS.

KRAMAR