River Flood Warning 19, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
852 PM EDT MON OCT 29 2012

.SYNOPSIS...
POST TROPICAL CYCLONE SANDY WAS APPROXIMATELY 120 MILES EAST-
NORTHEAST OF WASHINGTON D.C. EARLY THIS EVENING. THE POST-TROPICAL
CYCLONE WILL THEN TRACK INLAND INTO SOUTHERN PENNSYLVANIA. THIS
LARGE STORM WILL BRING SIGNIFICANT IMPACTS TO THE ENTIRE REGION
THROUGH MIDWEEK. CONDITIONS WILL IMPROVE DURING THE SECOND HALF OF
THE WORK WEEK.

&&

.NEAR TERM /THROUGH TUESDAY/...
SANDY HAS ACCELERATED...AND HAS MOVED ONSHORE ERLR THIS EVNG. RGNL
RADARS DEPICT THE HEAVIEST RAFL TO THE SW OF THE CYCLONE CENTER.
STILL DO HV SOME ECHOES NEARER THE CENTER. LTST HRRR AND WRF GDNC
SUGGESTS THAT THIS AREA MAY FILL BACK IN OVNGT. ATTM WL MONITOR
RATHER THAN MAKE BIG POPS ADJUSTMENTS. BANDS OF HEAVY RAIN WILL
LEAD TO SIGNIFICANT FLOODING OF STREAMS...CREEKS AND FLOODING IN
URBAN AREAS.

HV BEEN EXPERIENCING SOME OF THE HIEST WND GUSTS SINCE 21 OR
22Z...W/ SUSTAINED WNDS 20-30 KT AND GUSTS 40 KT COMMON. HV BEEN
SEEING SOME 50 KT GUSTS. THESE STRONG WINDS WILL LIKELY RESULT IN
WIDESPREAD DOWNED TREES AND POWER OUTAGES. WHILE WNDS SHUD
DIMINISH SOMEWHAT AS CENTER OF LOW NEARS...DONT WISH TO DILLUTE
THE SCREAMING MESSAGE OF THE THREAT NEXT SVRL HRS. THEREFORE WL
HOLD THE COURSE...ANTICIPATING THAT THE WIND FCST LKLY WL NEED TO
BE UPDTD OVNGT.

ANOTHER ASPECT OF THIS STORM IS SNOW IN THE HIGHER ELEVATIONS. THE
MOST SIGNIFICANT ACCUMULATIONS WILL OCCUR ABOVE 2000 FT. WITH THE
FORECAST WINDS...THIS WILL RESULT IN BLIZZARD CONDITIONS. HV
EXPANDED BLIZZARD WRNG ONCE AGN TO INCL WRN ALLEGANY CNTY. ATTM THE
BLIZZARD WARNING IS IN EFFECT FOR THE APPALACHIANS AS WELL AS
SKYLINE DRIVE IN SHENANDOAH NATIONAL PARK.

SANDY WILL PRODUCE SIGNIFICANT IMPACTS ACROSS THE MID-ATLANTIC
REGION. FOR A CONCISE SUMMARY OF THREATS AND THEIR IMPACTS PLEASE
SEE THE LATEST SPECIAL WEATHER STATEMENT ON SANDY...SPSLWX. THERE IS
A LINK TO THIS IN BIG RED LETTERS AT THE TOP OF OUR WEBPAGE...
WEATHER.GOV/LWX.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
POST TROPICAL SANDY WILL REMAIN OVER PENNSYLVANIA TUESDAY NIGHT
BEFORE TRACKING INTO THE EASTERN GREAT LAKES WEDNESDAY. THE LOW WILL
CONTINUE TO SLOWLY WEAKEN DURING THIS TIME...BUT IT WILL REMAIN
WINDY DUE TO A STRONG PRESSURE GRADIENT. WIND GUSTS AROUND 30 TO 40
MPH ARE POSSIBLE...ESPECIALLY TUESDAY EVENING.

A DOWNSLOPING FLOW WILL ALLOW FOR DRIER CONDITIONS ACROSS MOST
AREAS. A FEW SHOWERS CANNOT BE RULED OUT...ESPECIALLY TUESDAY NIGHT
BUT ANY ADDITIONAL RAINFALL TOTALS WILL BE LIGHT. HOWEVER...UPSLOPE
SNOW IS EXPECTED TO CONTINUE FOR LOCATIONS ALONG AND WEST OF THE
ALLEGHENY FRONT. A BLIZZARD WARNING REMAINS IN EFFECT UNTIL 8 AM
WEDNESDAY FOR THESE AREAS. ADDITIONAL SNOW ACCUMULATION IS EXPECTED
LATER WEDNESDAY MORNING AND AFTERNOON.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
AN UPPER-LEVEL TROUGH WILL REMAIN OVER THE REGION THROUGH THURSDAY
NIGHT. UPSLOPE SNOW SHOWERS ARE POSSIBLE ALONG AND WEST OF THE
ALLEGHENY FRONT. MOST OTHER LOCATIONS WILL TURN OUT DRY AND CHILLY.

HIGH PRESSURE WILL RETURN BUILD OVERHEAD DURING THE WEEKEND BEFORE A
COLD FRONT POSSIBLY IMPACTS THE AREA EARLY NEXT WEEK.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
SANDY MOVING INLAND TO SOUTH CENTRAL PENNSYLVANIA OVERNIGHT/TUESDAY.
SIGNIFICANT IMPACT FROM RAIN/WIND IS EXPECTED THROUGH THEN. WIND
GUSTS AOA 50 KT WILL REMAIN POSSIBLE INTO TUESDAY. CIGS HAVE
MAINLY BEEN MVFR MOST LIKELY GIVEN THE AMOUNT OF WIND...BUT VSBYS
HAVE BROUGHT IFR CONDITIONS IN MODERATE-HEAVY RAIN BANDS AND THIS
TOO WILL CONTINUE OVERNIGHT INTO TUESDAY. WNDS MAY ABATE SOMEWHAT
AS CENTER OF THE LOW NEARS TERMINALS TWD DAWN. WL BE MONITORING
WNDS...ADJUSTING AS NEEDED.

CONDITIONS WILL SLOWLY IMPROVE TUESDAY NIGHT AND VFR CONDITIONS ARE
EXPECTED FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK.

&&

.MARINE...
HURRICANE FORCE WIND WARNINGS ON THE MARYLAND CHESAPEAKE BAY AND
LOWER TIDAL POTOMAC AND STORM WARNINGS ON THE UPPER/MIDDLE TIDAL
POTOMAC REMAIN IN EFFECT THROUGH TUESDAY. STRONGEST WINDS ARE
EXPECTED NOW THROUGH TUESDAY MORNING.

WINDS REACHING/EXCEEDING SCA CRITERIA WILL CONTINUE ACROSS THE
MARINE AREA THROUGH AT LEAST WEDNESDAY. A SMALL CRAFT ADVISORY MAY
BE NEEDED FOR PORTIONS OF THE WATERS THURSDAY AND FRIDAY. HIGH
PRESSURE WILL BUILD OVERHEAD DURING THE WEEKEND.

&&

.HYDROLOGY...
RAINFALL TOTALS AROUND 8 TO 12 INCHES ARE EXPECTED IN THE I-270
CORRIDOR INTO THE BALTIMORE METROPOLITAN AREA. RAINFALL TOTALS
AROUND 5 TO 10 INCHES ARE EXPECTED IN THE WASHINGTON METROPOLITAN
AREA...LOWER SOUTHERN MARYLAND...AND THE EASTERN PANHANDLE OF WEST
VIRGINIA. THREE TO SIX INCHES OF RAIN ARE EXPECTED ACROSS THE
VIRGINIA PIEDMONT WITH ONE TO THREE INCHES LIKELY ACROSS THE CENTRAL
SHENANDOAH VALLEY INTO CENTRAL VIRGINIA.

RAINFALL RATES AROUND ONE INCH PER HOUR ARE EXPECTED IN THE
HEAVIEST BANDS OF RAIN. HEAVY RAIN OVER AN ALREADY SATURATED
GROUND SUPPORTS THE POTENTIAL FOR FLOODING...ESPECIALLY IN URBAN
AREAS AND LOCATIONS WHERE FALLEN LEAVIES /OR PERHAPS OTHER WIND
DRIVEN DEBRIS/ MAY CLOG DRAINAGE SYSTEMS. THESE FACTORS ALSO APPLY
FOR LONGER-DURATION STREAM FLOODING...WHICH IS LIKELY TO BE
SIGNIFICANT AND LENGTHY... EVEN ON STREAMS THAT ARE USUALLY FAST
TO RISE AND FALL.

THE URBAN AND SMALL STREAM FLOOD THREAT WILL CONTINUE THROUGH
TONIGHT INTO TUESDAY.

RIVER FLOODING IS EXPECTED BEGINNING LATE THIS EVENING AND LASTING
THROUGH MUCH OF THE WEEK AHEAD. THE WORST CONDITIONS ARE EXPECTED
ALONG THE MAINSTEM POTOMAC WHERE MAJOR FLOODING IS EXPECTED
WEDNESDAY INTO THURSDAY. MAJOR FLOODING IS ALSO FORECASTED TUESDAY
AND TUESDAY NIGHT ALONG THE CONOCOCHEAGUE CREEK NEAR FAIRVIEW...THE
OPEQUON CREEK NEAR MARTINSBURG...THE ANTIETAM CREEK NEAR SHARPSBURG
AND THE GOOSE CREEK NEAR LEESBURG.

IF EVERYTHING PLAYS OUT AS FORECAST...THE CREST MAY NOT GET DOWN TO
LITTLE FALLS UNTIL THURSDAY.

&&

.TIDES/COASTAL FLOODING...
PERSISTENT NW WNDS HV LED TO BLOWOUT ON THE BAY/PTMC. MOST SITES
AOB ASTRO NORMALS...XCPT FOR LWTV2/SLIM2 WHERE DEPARTURES RUNNING
AOB 1 FT.

ONCE CYCLONE MOVES A BIT FURTHER INLAND...WNDS WL BECOME SLY.
XPCTG POSITIVE TIDAL ANOMOLIES TO RESUME ONCE THAT HPPNS. THIS WL
FOCUS ON THE TUE AM AND TUE PM TIDE CYCLES. LTST GDNC SUGGESTING
WATER WL EFFECTIVELY PILE INTO THE UPR REACHES /BALT HARBOR NWD ON
THE BAY..INVOF INSIDE THE BELTWAY FOR THE PTMC/. HV INCRSD NUMBERS
THERE...TO 2 TO 4 FT...AND WL BE KEEPING DEPARTURES ARND 2 FT
ELSW.

THE UPR TIDAL PTMC POTENTIALLY CUD BE AFFECTED BY FRESHWATER
FLOODING AS WELL BY LT WED OR ELY THU.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...HIGH WIND WARNING UNTIL 8 PM EDT TUESDAY FOR DCZ001.
     COASTAL FLOOD WARNING FROM 2 AM TUESDAY TO 8 AM EDT WEDNESDAY
     FOR DCZ001.
MD...HIGH WIND WARNING UNTIL 8 PM EDT TUESDAY FOR MDZ003>007-
     009>011-013-014-016>018-501-502.
     COASTAL FLOOD WARNING FROM 2 AM TUESDAY TO 8 AM EDT WEDNESDAY
     FOR MDZ007-011-013.
     BLIZZARD WARNING UNTIL 2 PM EDT TUESDAY FOR MDZ501.
     COASTAL FLOOD WARNING FROM MIDNIGHT TONIGHT TO 8 AM EDT
     WEDNESDAY FOR MDZ014-016>018.
VA...HIGH WIND WARNING UNTIL 8 PM EDT TUESDAY FOR VAZ025>031-
     036>040-042-050>057-501>504.
     BLIZZARD WARNING UNTIL 8 AM EDT WEDNESDAY FOR VAZ503-504.
     COASTAL FLOOD WARNING FROM 2 AM TUESDAY TO 8 AM EDT WEDNESDAY
     FOR VAZ053-054.
     BLIZZARD WARNING UNTIL 2 PM EDT TUESDAY FOR VAZ025>027-029-
     036>040.
     COASTAL FLOOD WARNING FROM MIDNIGHT TONIGHT TO 8 AM EDT
     WEDNESDAY FOR VAZ052-055-057.
WV...HIGH WIND WARNING UNTIL 8 PM EDT TUESDAY FOR WVZ050>053-055-
     501>506.
     BLIZZARD WARNING UNTIL 8 AM EDT WEDNESDAY FOR WVZ501-503-505-
     506.
     BLIZZARD WARNING UNTIL 2 PM EDT TUESDAY FOR WVZ055-502.
MARINE...HURRICANE FORCE WIND WARNING UNTIL 8 PM EDT TUESDAY FOR
     ANZ530>534-537>543.
     STORM WARNING UNTIL 8 PM EDT TUESDAY FOR ANZ535-536.

&&

SYNOPSIS...HTS/BJL
NEAR TERM...HTS/BPP
SHORT TERM...BJL
LONG TERM...BJL
AVIATION...HTS/BPP/BJL
MARINE...BPP/BJL
HYDROLOGY...HTS/BJL
TIDES/COASTAL FLOODING...HTS

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