River Flood Warning 52, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
324 AM EDT WED MAY 18 2011

.SYNOPSIS...

A CUTOFF UPPER LOW OVER THE SOUTHERN APPALACHIANS WILL DRIFT NORTH
THROUGH THE END OF THE WORK WEEK...WITH UNSETTLED WEATHER CONTINUING
INTO FRIDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH THE WEEKEND.

&&

.NEAR TERM /TODAY/...

UPPER-LEVEL LOW OVER SOUTHWESTERN VIRGINIA THIS MORNING WILL SLOWLY
DRIFT NORTH TOWARD SOUTHEASTERN OHIO THIS AFTERNOON. SURFACE LOW
ASSOCIATED WITH THIS SYSTEM WILL BE DIRECTLY UNDERNEATH THE
UPPER-LEVEL LOW. AN EASTERLY FLOW IN BETWEEN HIGH PRESSURE NEAR NOVA
SCOTIA AND THE SURFACE LOW MOVING INTO SOUTHEASTERN OHIO WILL
CONTINUE TO USHER IN PLENTY OF MOISTURE FROM THE ATLANTIC OCEAN. AS
THE UPPER-LEVEL LOW PASSES BY TO THE WEST...UPPER-LEVEL DISTURBANCES
WILL ROTATE AROUND THIS SYSTEM MOVING THROUGH OUR CWA. THE
UPPER-LEVEL DISTURBANCES WILL ACT AS LIFTING MECHANISMS TO TRIGGER
SHOWERS AND THUNDERSTORMS.

ABUNDANT MOISTURE ALONG WITH UNUSUALLY COLD AIR ALOFT DUE TO THE
UPPER-LEVEL LOW WILL CONTINUE TO CAUSE AN UNSTABLE ATMOSPHERE. THE
INSTABILITY ALONG WITH THE DEEP MOISTURE WILL CAUSE SHOWERS AND
T-STORMS TO PRODUCE LOCALLY HEAVY RAINFALL. TRAINING CONVECTION IS
ALSO LIKELY WITH THE STORM MOTION BEING FROM SOUTHEAST TO NORTHWEST.
THE HEAVIEST RAINFALL IS EXPECTED LATE THIS MORNING THROUGH THIS
AFTERNOON WHEN INSTABILITY WILL BE AT ITS HIGHEST. A FLASH FLOOD
WATCH IS IN EFFECT FOR THE ENTIRE FORECAST AREA THROUGH THIS
AFTERNOON.

ISOLATED THUNDERSTORMS MAY BECOME SEVERE GIVEN THE INSTABILITY LATE
THIS MORNING THROUGH THIS AFTERNOON. THE PRIMARY THREAT WILL BE
DAMAGING WINDS...LARGE HAIL AND EVEN AN ISOLATED TORNADO.
HOWEVER...THE COVERAGE OF SEVERE WEATHER APPEARS THAT IT WILL REMAIN
ISOLATED DUE TO EXTENSIVE CLOUD COVER. SHOULD THERE BE MORE BREAKS
OF SUNSHINE THIS MORNING INTO THIS AFTERNOON THEN MORE WIDESPREAD
SEVERE WEATHER IS POSSIBLE. WILL CONTINUE TO MONITOR THROUGHOUT THE
DAY.

&&

.SHORT TERM /TONIGHT/...

UPPER-LEVEL LOW WILL REMAIN NEARLY STATIONARY OVER SOUTHEASTERN OHIO
TONIGHT WHILE THE SURFACE LOW ASSOCIATED WITH THIS SYSTEM SLOWLY
TRACKS THROUGH OUR CWA. SHOWERS AND T-STORMS ARE EXPECTED ESPECIALLY
THIS EVENING WHEN INSTABILITY WILL BE AT ITS HIGHEST. THE FLASH
FLOOD WATCH CONTINUES THROUGH THIS EVENING. CONVECTION COVERAGE WILL
LIKELY DIMINISH OVERNIGHT DUE TO THE LOSS OF INSTABILITY. PATCHY FOG
IS POSSIBLE LATE TONIGHT DUE TO LIGHT WINDS AND ABUNDANT MOISTURE.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

THIS HAS TO BE ONE OF THE MOST PERSISTENT UPPER LOWS I'VE
EXPERIENCED HERE...BUT THE END WL BE OCCURRING SOON. THU THE
OMNIPRRESENT UPPER LOW RMNS OVER THE MID ATLC. THIS WL KEEP THE RGN
LOCKED IN CLDS W/ RW/TRW...AND W/ XTRMLY LOW FFG VALUES THE THREAT
OF FLDG WL CONT.

GFS/ECMWF BOTH SHOW THE UPR LOW OVR NJ ON FRI. THIS IS BETTER THAN
WHAT WE'VE HAD...THO STILL NOT IDEAL. ANOTHER M CLDY DAY W/ THE
PSBLTY OF RW/TRW. AFTN TEMPS BOTH DAYS IN THE M70S.

AND THEN...FINALLY...FOR THE WKND THE LOW PULLS OUT AND IS
REPLACED BY AN UPR RDG FOR THE WKND. XPCTG M SUN SKIES W/ AFTN
HIGHS GETTING INTO THE 80S.

UPR FLOW WL RUN WSW-ENE DURG THE ERLY PART OF NEXT WK. WE HV LOW
CHC POPS IN THE FCST FOR MON/TUE...BUT SUSPECT THE BULK OF THE
TIME WL BE DRY. HIGHS TEMPS CONTINUING IN THE 80S.

&&

.AVIATION /TODAY THROUGH SUNDAY/...

ABUNDANT MOISTURE MAY BRING A PERIOD OF IFR CIGS/VSBYS EARLY THIS
MORNING. ANY IFR CIGS/VSBYS WILL LIKELY IMPROVE BY LATE MORNING.
MORE SHOWERS AND T-STORMS ARE EXPECTED TODAY THROUGH TONIGHT. THE
MOST WIDESPREAD ACTIVITY WILL BE THIS AFTERNOON AND EVENING. LOCALLY
HEAVY RAINFALL MAY REDUCE CIGS AND VSBYS TO IFR LEVELS AT TIMES. A
FEW T-STORMS WILL CONTAIN GUSTY WINDS AND HAIL. PATCHY FOG IS
EXPECTED LATER TONIGHT DUE TO LIGHT WINDS AND AN ABUNDANT AMOUNT OF
MOISTURE.

THE EVER PRESENT UPR LVL LOW PRES AREA WL BE ON A SLOW TRACK OVR
NJ ON FRI...KEEPING MID ATLC IN RW/PSBL AFTN TRW. CONTINUED RW/TRW
PSBL ON THU... W/ MVFR CIGS PSBL FRI. THEN...HIGH PRES FINALLY TO
MOVE INTO THE AREA FOR THE WKND.

&&

.MARINE...

AN SCA IS IN EFFECT UNTIL 6 AM FOR THE MARYLAND PORTION OF THE
CHESAPEAKE BAY AND TIDAL POTOMAC SOUTH OF INDIAN HEAD. THE GRADIENT
SHOULD DIMINISH TODAY CAUSING WINDS TO WEAKEN BELOW SCA VALUES. MORE
SHOWERS AND T-STORMS ARE EXPECTED WITH THE MOST COVERAGE DURING THE
AFTERNOON AND EVENING HOURS. SOME T-STORMS MAY BE CAPABLE OF
PRODUCING GUSTY WINDS...HAIL...AND EVEN THE SLIGHT CHANCE FOR A
WATERSPOUT. HOWEVER...AT THIS TIME ANY COVERAGE OF SEVERE T-STORMS
WILL BE ISOLATED DUE TO EXTENSIVE CLOUD COVER LIMITING INSTABILITY.

ON THU AND FRI GUSTS PSBL INTO THE M TEENS..THEN LGT WINDS OVR
THE WKND. TSTSMS PSBL ON THE WATERS THU.

&&

.TIDES/COASTAL FLOODING...

WILL CONTINUE WITH A COASTAL FLOOD WARNING FOR WASHINGTON DC...
ALEXANDRIA AND THE LOCATIONS ALONG THE WESTERN SHORE OF THE
CHESAPEAKE BAY THROUGH THE HIGH TIDE CYCLE THIS MORNING. A FULL
MOON ALONG WITH A PERSISTENT ONSHORE FLOW WILL LIKELY LEAD TO
MODERATE FLOODING NEAR TIMES OF HIGH TIDE. ELSEWHERE...MINOR
COASTAL FLOODING IS EXPECTED THROUGH THE HIGH TIDE CYCLE THIS
MORNING.

MINOR COASTAL FLOODING NEAR TIMES OF HIGH TIDE WILL LIKELY CONTINUE
THIS AFTERNOON THROUGH TONIGHT NEAR TIMES OF HIGH TIDE. A COASTAL
FLOOD ADVISORY IS IN EFFECT FOR ALL AREAS NEAR THE TIDAL POTOMAC
RIVER AND WESTERN SHORE OF THE CHESAPEAKE BAY DURING THIS TIME.

THE FLOW WILL BE SLOW TO TURN OFFSHORE THURSDAY. ELEVATED WATER
LEVELS MAY CAUSE MINOR COASTAL FLOODING NEAR TIMES OF HIGH TIDE. FOR
WASHINGTON DC AND ALEXANDRIA COASTAL FLOODING MAY PERSIST THROUGH
FRIDAY AS FRESH WATER COMES DOWN FROM THE POTOMAC RIVER. WILL
CONTINUE TO MONITOR RAINFALL AND WATER LEVELS FURTHER NORTH ALONG
THE POTOMAC RIVER. MINOR TO MODERATE FLOODING IS POSSIBLE DURING
THIS TIME.

&&

.HYDROLOGY...

GIVEN THE RAIN THAT HAS FALLEN OVERNIGHT IN THE CENTRAL SHEN
VALLEY...AS WELL AS DURG THE PAST SVRL DAYS THIS HAS CAUSED RIVER
LVLS TO RISE. ATTM PETERSBURG HAS PEAKED..BUT MORE RAIN IS FALLING
IN THE S PTMC BASIN. HOWEVER THIS IS STILL FCST TO RMN BLO FLD STAGE.

PAW PAW CONTS TO RISE. CURRENTLY AT 17.5'. FCSTD TO RISE TO 25.8'
AT 2 PM TDA WHICH IS JUST ABV FLD STAGE. HANCOCK CURRENTLY AT
13.7' AND RISING...PROGGED TO GET TO 23.5' TNGT WHICH IS JUST BLO
CAUTION STAGE.

HARPERS FERRY AND SHEPERDSTOWN FCST TO PEAK ON THURSDAY. PT OF
ROCKS AND LTL FALLS ON FRI.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD WARNING UNTIL NOON EDT TODAY FOR DCZ001.
     COASTAL FLOOD ADVISORY FROM NOON TODAY TO 6 AM EDT THURSDAY
     FOR DCZ001.
MD...COASTAL FLOOD ADVISORY UNTIL 6 AM EDT THURSDAY FOR MDZ013-016.
     FLASH FLOOD WATCH UNTIL 6 AM EDT EARLY THIS MORNING FOR MDZ501-
     502.
     COASTAL FLOOD WARNING UNTIL NOON EDT TODAY FOR MDZ007-011-014-
     017-018.
     COASTAL FLOOD ADVISORY FROM NOON TODAY TO 6 AM EDT THURSDAY
     FOR MDZ007-011-014-017-018.
VA...COASTAL FLOOD ADVISORY UNTIL 6 AM EDT THURSDAY FOR VAZ052-053-
     055-057.
     FLASH FLOOD WATCH UNTIL 6 AM EDT EARLY THIS MORNING FOR
     VAZ025>027-029-036>038-503-504.
     COASTAL FLOOD WARNING UNTIL NOON EDT TODAY FOR VAZ054.
     COASTAL FLOOD ADVISORY FROM NOON TODAY TO 6 AM EDT THURSDAY
     FOR VAZ054.
WV...FLASH FLOOD WATCH UNTIL 6 AM EDT EARLY THIS MORNING FOR WVZ050-
     055-501>506.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR
     ANZ530>534-536>543.

&&

PRODUCTS...BJL/WOODY!

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