Flash Flooding and Flooding in Virginia, May 21 to 24, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
948 PM EDT MON MAY 21 2012

.SYNOPSIS...
A TROUGH OF LOW PRESSURE WILL STALL OVER THE AREA THROUGH TUESDAY.
AN UPPER LOW MOVES THROUGH WEDNESDAY AND THURSDAY. HIGH PRESSURE
WILL RETURN TO THE AREA FOR THE MEMORIAL DAY WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
LATEST WV LOOP AND MODEL ANALYSIS SHOWS A BROAD LARGE-SCALE TROUGH
OVER THE ERN-THIRD CONUS..WITH SEVERAL SHORTWAVE TROUGHS ROTATING
AROUND THE TROUGH. ONE OF THESE SHORTWAVE TROUGH IS NEGATIVELY
TILTED AND HAS STALLED NEAR THE BLUE RIDGE. A SELY LLVL JET AHEAD
OF THE TROUGH HAS PRODUCED NUMEROUS TO WIDESPREAD SHOWERS OVER THE
NRN PIEDMONT...NRN VA...THE ERN WV PANHANDLE AND NORTH-CENTRAL MD
FOR MOST OF THE DAY. WITH LITTLE PROGRESSION OF THE LLVL TROUGH...
EXPECT SHOWERS TO CONTINUE OVER THE SAME LOCATIONS THRU THE
REMAINDER OF THE EVE. A STABILIZING ATMOSPHERE LATE TNGT WILL
CAUSE SHOWER ACTIVITY TO DIMINISH LATE TNGT AND ERY TUE MRNG.
ASIDE FROM SCT SHOWERS/TSTMS ACROSS THE FAR SWRN CWA THIS
EVE...THE REMAINDER OF THE CWA SHOULD NOT EXPECT MUCH MORE
THAN AN ISO SHOWER TNGT.

LOW CLOUDS AND FOG WILL DEVELOP LATE THIS EVE AND OVNGT. STRATUS
SHOULD LIMIT COVERAGE AND DENSITY OF FOG. HAVE KEPT PATCHY FOG
WORDING IN THE GRIDS...EXCEPT FOR AREAS OF FOG ALONG THE RIDGE TOPS.
WITH CLOUD COVER AND A MOIST ATMOSPHERE...MIN TEMPS WILL ONLY FALL A
FEW DEGREES FROM CURRENT READINGS...RANGING FROM THE 50S IN THE
POTOMAC HIGHLANDS TO THE MID 60S EAST OF THE BLUE RIDGE.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
AN UPPER-LEVEL TROUGH WILL APPROACH THE REGION FROM THE WEST WHILE A
SURFACE TROUGH OF LOW PRESSURE REMAINS OVER THE REGION. LOW CLOUDS
AND PATCHY FOG WILL SLOWLY MIX OUT DURING THE LATE MORNING AND EARLY
AFTERNOON HOURS. SOME AFTERNOON SUNSHINE IS EXPECTED AND THAT WILL
POTENTIALL LEAD TO MODERATE AMOUNTS OF INSTABILITY.

MODERATE INSTABILITY WILL COMBINE WITH FORCING FROM THE SURFACE
TROUGH TO TRIGGER SOME SHOWERS AND THUNDERSTORMS...MAINLY DURING
THE AFTERNOON HOURS. THUNDERSTORMS WILL BE SLOW MOVING AND
CONTAINING MAY CONTAIN LOCALLY HEAVY DOWNPOURS. WILL HOLD OFF ON
ISSUANCE OF A FLASH FLOOD WATCH ATTM AS FFG IS HIGH AND COVERAGE
OF STORMS ARE UNCERTAIN.

MAX TEMPS WILL BE WARMER TUESDAY COMPARED TO MONDAY DUE TO MORE
AFTERNOON SUNSHINE. MAX TEMPS WILL RANGE FROM THE UPPER 60S ALONG
THE RIDGE TOPS TO THE UPPER 70S AND LOWER 80S ACROSS MOST OTHER
LOCATIONS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
UPPER LEVEL TROUGH OF LOW PRES XPCTD TO MOVE OUT OF THE TN VLLY
TUE NGT AND BECOME A CLOSED LOW OVR THE MID ATLC WED. NOT A
PARTICULARLY DEEP CLOSED LOW...BUT STILL ENOUGH OF ONE THAT HV
PUSHED POPS ACROSS THE ENTIRE CWA TO LKLY FOR WED AFTN. THERE
CERTAINLY COULD BE THUNDER...BUT AT THIS TIME SVR THREAT LOOKS
MINIMAL. THIS LOOKS TO SLOWLY NE AWAY FM THE AREA...AND HV POPS
SLOWLY DIMINISHING AS WELL.

WED AND THU XPCT HIGH TEMPS A80 MUCH OF THE AREA. LOWS IN THE LM60S.

AFTR THE UPR LOW EXITS A PATTERN SHIFT OCCURS. UPR LVL TROF PUSHES
DOWN THE PACIFIC CST..AND IN RESPONSE HGTS START TO RISE IN THE
ERN 1/3 OF THE COUNTRY. AFTR A MUCH-ABV-NRML MAR TEMPS IN APR AND
MAY HV BEEN MORE TEMPERATE. 1000-500 HGTS MAY EXCEED 590 DM...AND
TEMPS COULD TOP 90 DEG...ESPECIALLY SUN AND MON. GIVEN THIS IS
"THE UNOFFICIAL START OF SUMMER" PLUS MEMORIAL DAY WKND WE'RE A
BIT CONCERNED OF HOW PEOPLE WL REACT TO THE CHG. WE'RE A LONG WAY
FM ISSUING ANY HEAT SPECIFIC PRODUCTS BUT WE'VE ADDED MENTION OF
THE WARMER TEMPS/HOLIDAY WKND TO THE HWO. ONLY PTNL FOR TSTMS THIS
WKND LOOKS TO BE DIURNALLY DRIVEN OVR THE MTNS. OTHERWISE SKIES
SHOULD BE M SUN DURG THE DAY.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
A LLVL TROUGH REMAINS STATIONARY NEAR THE BLUE RIDGE THIS EVE.
NUMEROUS SHRA WILL CONTINUE TO IMPACT MRB/IAD THIS EVE...WHICH
WILL ALLOW FLIGHT CAT TO DEGRADE TO IFR LVLS /MAINLY DUE TO CIGS/.
ELSEHWERE...CIGS WILL LOWER TO IFR AROUND OR SHORTLY AFTER
MIDNIGHT. VIFR CIGS LIKELY FOR MOST TERMINALS LATE TNGT AND ERY
TUE MRNG. LOW STRATUS SHOULD LIMIT SFC VSBY IMPACT FROM FOG.

CIGS WILL BE SLOW TO IMPROVE TUE MRNG...AND MAY NOT IMPROVE TO
MVFR UNTIL MIDDAY/ERY AFTN. THE TROUGH WILL REMAIN OVER THE AREA
TUE WHILE BREAKS IN THE CLOUDS TUE AFTN WILL FUEL THE DEVELOPMENT
OF SHRA LATER IN THE DAY. HAVE NOT MENTIONED TS IN THE 00Z
TAFS...BUT IT MAY NEED TO BE ADDED IN LATER TAF CYCLES AS
CONFIDENCE INCREASES.

LOW CIGS/VSBYS XPCTD TUE NGT THRU WED NGT W/ PDS OF RAIN/ISOLD TSTMS.
CONDS SHOULD BE IMPRVG DURG THE 2ND HALF OF THE WK INTO THE WKND
AS A LARGE AREA OF HIGH PRES SETS UP OVR THE ERN U.S.

&&

.MARINE...
LOW PRESSURE WILL REMAIN WEST OF THE WATERS TNGT. AN EAST-SOUTHEAST
FLOW IS EXPECTED DURING THIS TIME. SLY TO SELY WINDS UNDER 15 KT
EXPECTED TNGT.

THE SURFACE TROUGH WILL REMAIN WEST OF THE WATERS TUESDAY. WIND
SPEEDS WILL REMAIN BELOW SCA CRITERIA. SHOWERS AND T-STORMS ARE
POSSIBLE...MAINLY IN THE AFTERNOON.

WINDS XPCTD TO RMN BLO SCA TUE NGT THRU THE END OF THE WORK WK.
RW/TSTMS LKLY ON WED.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES REMAIN AROUND THREE-QUARTERS TO ONE FOOT ABOVE
NORMAL THIS EVE. POSITIVE TIDAL ANOMALIES SHOULD REMAIN THE SAME
OR INCREASE GRADUALLY DUE TO THE SELY FLOW. ANOMALIES OF THIS
MAGNITUDE WILL LEAD TO MINOR COASTAL FLOODING ALONG THE UPPER
TIDAL POTOMAC RVR AND WRN SHORE OF THE MD CHSPK BAY FROM
ANNAPOLIS-NWD DURING THE TUE MRNG HIGH TIDE. HAVE ISSUED A COASTAL
FLOOD ADVISORY FOR THESE LOCATIONS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY FROM 6 AM TO NOON EDT TUESDAY FOR
     DCZ001.
MD...COASTAL FLOOD ADVISORY FROM 6 AM TO NOON EDT TUESDAY FOR
     MDZ007-011-014.
VA...COASTAL FLOOD ADVISORY FROM 6 AM TO NOON EDT TUESDAY FOR
     VAZ054.
WV...NONE.
MARINE...NONE.

&&

UPDATE...KLEIN
PREV DISC...BJL/WOODY!

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
902 PM EDT MON MAY 21 2012

ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
221000-
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-
902 PM EDT MON MAY 21 2012

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...TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

A COASTAL FLOOD ADVISORY IS IN EFFECT TUESDAY MORNING FOR COASTAL
LOCATIONS ALONG THE UPPER TIDAL POTOMAC RIVER AND ALONG THE
WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY FROM ANNE ARUNDEL
COUNTY NORTHWARD TO HARFORD COUNTY.

MEMORIAL DAY WEEKEND...TEMPERATURES MAY EXCEED 90 DEGREES DURING
THE AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME.

MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504-
WVZ050>053-055-501>506-221000-
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-
902 PM EDT MON MAY 21 2012

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...TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

MEMORIAL DAY WEEKEND...TEMPERATURES EAST OF THE BLUE RIDGE
MOUNTAINS MAY EXCEED 90 DEGREES DURING THE AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1117 PM EDT MON MAY 21 2012

MDZ003-004-VAZ031-042-052-053-501-502-WVZ051>053-220445-
FREDERICK MD-WASHINGTON MD-CLARKE VA-MORGAN WV-JEFFERSON WV-
BERKELEY WV-NORTHERN FAUQUIER VA-SOUTHERN FAUQUIER VA-
PRINCE WILLIAM/MANASSAS/MANASSAS PARK VA-LOUDOUN VA-FAIRFAX VA-
1117 PM EDT MON MAY 21 2012

...LOCALLY HEAVY RAIN TO AFFECT
FREDERICK...WASHINGTON...CLARKE...MORGAN...JEFFERSON...BERKELEY...
NORTHERN FAUQUIER...SOUTHERN FAUQUIER...PRINCE
WILLIAM/MANASSAS/MANASSAS PARK...LOUDOUN AND FAIRFAX COUNTIES...

AT 1111 PM EDT...DOPPLER RADAR INDICATED A LINE OF SHOWERS PRODUCING
LOCALLY HEAVY RAINFALL. THIS LINE OF PRECIPITATION EXTENDS ALONG A
LINE FROM CLEAR SPRING MARYLAND TO MANASSAS VIRGINIA. THIS LINE OF
SHOWERS WILL HAVE THE POTENTIAL TO PRODUCE UP TO ONE INCH OF
RAINFALL AN HOUR IN AREAS THAT HAVE ALREADY RECEIVED ONE TO ONE AND
A HALF INCHES OF RAINFALL TODAY.

LOCATIONS IMPACTED INCLUDE FALLING
WATERS...HILLSBORO...LEESBURG...BRAMBLETON...ASHBURN...CATHARPIN...
MANASSAS PARK AND MANASSAS.

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

&&

LAT...LON 3972 7768 3917 7752 3913 7753 3911 7750
      3862 7735 3855 7760 3973 7816
TIME...MOT...LOC 0311Z 180DEG 0KT 3878 7724