Flash Flood Warning 9, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
455 PM EDT SUN APR 25 2010

.SYNOPSIS...
A POTENT UPPER LOW OVER INDIANA WILL DRIFT EAST INTO THE OHIO VALLEY
TONIGHT. AN ASSOCIATED WARM FRONT WILL BECOME NEARLY STATIONARY
ACROSS MARYLAND. THE LOW WILL TRACK ACROSS THE MID ATLANTIC REGION
MONDAY WITH A COLD FRONT CROSSING THE REGION ON TUESDAY. HIGH
PRESSURE RETURNS WEDNESDAY AND THURSDAY. A WARM FRONT WILL
APPROACH THE REGION FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 11 PM FOR THE
ENTIRE CWA WITH THE EXCEPTION OF HIGHLAND...PENDLETON...
AUGUSTA...NELSON...AND ALBERMARLE COUNTIES.

LATEST RADAR IMAGERY SHOWS SHOWERS AND THUNDERSTORMS DEVELOPING
OVER EASTERN WEST VIRGINIA. THUNDERSTORMS WILL CONTINUE TO SPREAD
EAST-SOUTHEAST DURING THE LATE AFTERNOON AND EVENING HOURS. LATEST
MESOANALYSIS SHOWS AROUND 1000 J/KG OF MLCAPE WITH LITTLE TO NO
CAPPING INVERSION. STILL FEEL THAT THE BEST CHANCE FOR THE
STRONGER THUNDERSTORMS WILL BE CLOSER TO THE BACKDOOR BOUNDARY
WHICH EXTENDS FROM EASTERN WEST VIRGINIA THROUGH NORTHERN VIRGINIA
INTO EASTERN MARYLAND.

GIVEN THE STEEP MID-LEVEL LAPSE RATES AND POTENT DEEP LAYER
SHEAR...DAMAGING WINDS AND LARGE HAIL APPEAR TO BE THE PRIMARY
THREATS. PREVIOUS DISCUSSION FOLLOWS.

SPL 17Z BALLOON SNDG WAS ISSUED TDA.

AS OF 19Z...WV LOOP SHOWS THE LARGE OCCLUDED LOW IS CENTERED OVER
THE IL/IN BORDER AND DRIFTING EAST. THE MID ATLANTIC IS IN THE WARM
SECTOR/DRY SLOT OF THE SYSTEM. VIS SATELLITE AND SFC OBS INDICATES
SFC WARM FRONT HAS REACHED AS FAR NORTH AS A LINE FROM KBWI TO KFDK
TO KMRB THEN NORTH INTO PA...WITH LITTLE N-WARD PROGRESS EXPECTED
REST OF THE AFTERNOON. SOUTH/WEST OF THE FRONT...SCT/BKN CU FIELD
HAS DEVELOPED WITH THE INSOLATION. CONVECTIVE STORM DEVELOPMENT
STILL NOT EXPECTED EAST OF THE BLUE RIDGE FOR ANOTHER FEW
HOURS...THE 17Z KIAD RAOB INDICATES A CAP AROUND 3.5 KFT ACROSS THE
DC METRO THAT WILL TAKE SOME TIME TO ERODE. LOW CLOUDS AND SUB 60F
TEMPS TO PERSIST NORTH OF THE FRONT.

SCT SHOWERS AND ISO THUNDERSTORMS CONTINUE TO INCREASE IN COVERAGE
WEST OF THE BLUE RIDGE...WERE DIFFERENTIAL HEATING IN THE TERRAIN
HAS ENABLED DEVELOPMENT. THIS ACTIVITY WILL MOVE NORTHEAST AND
SLOWLY SPREAD EAST.

STRONG BULK LAYER SHEAR /50 TO 60 KT/...GOOD MID LEVEL LAPSE RATES
/7 TO 8 C/KM/ INDICATE A LARGE HAIL THREAT. BACKED LLVL FLOW ALONG
THE FRONT COULD ENABLE TORNADO DEVELOPMENT AS STORMS CROSS CENTRAL
MARYLAND INTO THIS EVENING.

THE LOW PUSHES EAST INTO THE OHIO VALLEY OVERNIGHT WITH DIURNAL
CONVECTION SUBSIDING THIS EVENING. PLENTY OF LLVL MOISTURE KEEPS MIN
TEMPERATURES UP IN THE MID TO UPPER 50S.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
MONDAY...THE UPPER LOW PASSES THE MID ATLANTIC...BRINGING AREAS OF
SHOWERS WITH EMBEDDED THUNDERSTORMS MAINLY IN THE AFTERNOON. MAX
TEMPS LOW TO MID 70S BEFORE HEIGHTS FALL AFTER THE LOW PASSAGE.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
SLOW MOVING UPPER LOW WILL BE TRACKING ACROSS THE CWA MON NGT. W/
THIS HV UPPED POPS TO LKLY ACROSS THE MAJORITY OF THE AREA. WILL
KEEP A MENTION OF T DURG THE EVE ACROSS THE NRN PART OF THE CWA AS
THE UPPER LOW MOVES OVRHD ALONG W/ PTNL CAPES OF 500. THREAT OF
CNVCTN SHOULD BE WANING BY MDNGT...DIMINISHING TO RASH LKLY
OVRNGT.

BROAD CYCLONIC FLOW TO SET UP OVRHD FOR TUE WL KEEP SKIES M CLDY
W/ TEMPS ONLY IN LM60S. TUE NGT LOW EXITS THE RGN AND SKIES SHOULD
BEGIN TO CLR DURG THE EVE HRS. TEMPS SHOULD INTO THE MU30S W OF
I-95 TUE NGT. THIS MAY BRING ABT NEED FOR FRST ADVSRY.

UPPER LOW WL SLOWLY EXIT TO THE NE ON WED BUT SKIES SHOULD BE
IMPROVING - PC SKIES HIGHS IN THE M60S.

HIGH PRES WL BUILD INTO THE RGN FOR THU AND FRI...BRINGING M SUNNY
SKIES AND TEMPS WARMING INTO THE L70S THU..MU70S FRI. THE HIGH WL
MOVE OFF THE CST FOR THE WKND..ALLOWING CLDS TO INCRS BUT DAYTIME TEMPS
SHOULD CONT TO REACH THE 70S.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
LARGE LOW PRESSURE SYSTEM MOVES EAST ACROSS THE AREA THROUGH MONDAY.
CONVECTIVE STORMS...SOME SEVERE ON TAP FOR LATE THIS AFTERNOON AND
EVENING ACROSS THE TERMINALS. SHOWERS AND SOME EMBEDDED TSTMS MONDAY
AS THE LOW PASSES.

MON NGT AND TUE SHOULD BE M CLDY. CHC OF TSTMS AT MAJOR AIRPORTS
DURG THE MON EVE SHOULD DIMINISH TO RW OVRNGT. NOT XPCTG MUCH PCPN
TUE. CONDS SHOULD BE VFR TUE THRU THU.

&&

.MARINE...
SCA FOR GUSTY SWLY WINDS UNTIL 6PM FOR THE TIDAL POTOMAC BELOW
INDIAN HEAD...AND ON THE MD BAY SOUTH OF SANDY POINT. A STALLED
BOUNDARY ACROSS THE BAY INVOF THE BAY BRIDGE WITH NELY FLOW AROUND
15 KT NORTH. A LARGE LOW PRESSURE SYSTEM MOVES EAST ACROSS THE AREA
THROUGH MONDAY. CONVECTIVE STORMS...SOME SEVERE ON TAP FOR LATE THIS
AFTERNOON AND EVENING ACROSS THE WATERS. SHOWERS AND SOME
EMBEDDED TSTMS MONDAY AS THE LOW PASSES.

PD OF GUSTY WINDS PSBL TUE AFTN AS HIGH PRES BUILDS INTO THE AREA
MAY BRING THE NEED FOR AN SCA.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR
     ANZ532>534-536-537-540>543.

&&

PRODUCTS...LASORSA/BAJ/WOODY!

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