Flash Flood Warning 56, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
257 PM EDT MON JUL 27 2015

.SYNOPSIS...WEAK HIGH PRES WILL BUILD OVER THE AREA TONIGHT
THROUGH WED. A CDFNT WILL CROSS THE AREA THU NIGHT AND MOVE INTO
THE SOUTHEAST FRI. WEAK HIGH PRES BUILDS AGAIN FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TUESDAY/...SCT SLOW MOVING T-STORMS EXPECTED
TO CONTINUE UNTIL MID-EVENING. DEEP MOISTURE AND SLOW MOVEMENT
SUGGEST HEAVY RAINFALL WILL BE THE PRIMARY THREAT WITH THESE. SOME
CLEARING EXPECTED TONIGHT ESPECIALLY NRN HALF OF THE FCST AREA
WITH PATCHY DENSE FOG EXPECTED OVERNIGHT. DRIER AIR WORKS INTO THE
AREA TUE WITH RISK OF SHOWERS AND/OR T-STORMS CONFINED ONLY TO
AREAS SOUTH OF I-66.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...SFC HIGH PRESSURE
BUILDS IN WED MORNING AS LINGERING FRONTAL BOUNDARY FROM THE
FIRST HALF OF THE WEEK DISSIPATES. MAIN STORY FOR MID WEEK WILL BE
WARMING TEMPS AS UPPER LVL RIDGE BROADENS ACROSS THE EASTERN
US...RESULTING IN RISING HEIGHTS WED INTO THURS. AT THE SFC...SLY
FLOW WILL CONTINUE THE WAA AND MOISTURE ADVECTION. HIGH TEMPS
EXPECTED TO REACH LOWER TO PSBL MID 90S...WHICH COMBINING WITH DEW
PTS IN THE UPPER 60S TO LOWER 70S PRODUCES HEAT INDICES IN THE
UPPER 90S TO LOWER 100S. AS THE VALUES STAND...NO HEAT ADVISORY
WOULD BE NEEDED WED. WHILE MOST THE AREA WILL REMAIN DRY...TERRAIN
DRIVEN CONVECTION WILL BE PSBL IN THE LATE AFTN/EARLY EVENING TIME
FRAME.

UPPER LVL RIDGE AXIS SHIFTS FROM THE GREAT LAKES REGION 12Z WED TO
THE NORTHEAST BY 12Z THURS AHEAD OF AN APPROACHING CLOSED
LOW/TROUGH. ASSOCIATED COLD FRONT APPROACHES FROM THE WEST...WITH
THE 12Z MODEL SUITE PROGGING THE FRONTAL PASSAGE SOMETIME LATE THURS
AFTN INTO THE FIRST HALF OF THURS NIGHT. INCRSG SLY FLOW AHEAD OF
THE FRONT WILL KEEP A WARM AND MOIST ATMO IN PLACE...WITH YET
ANOTHER DAY OF HIGHS REACHING THE LOWER TO MID 90S AS 850MB TEMPS
NEAR 20 DEGREES CELSIUS AND DEW PTS AROUND 70. SHEAR REMAINS MEAGER
DURING THE DAY...BUT EXPECTING ENOUGH RESULTING INSTABILITY TO AID
IN GENERATION IN PULSE TSTMS OUT AHEAD OF THE STORM.

FRONT SWINGS THRU THURS NIGHT...WITH PCPN TAPERING OFF WEST TO EAST
BY FRI MORNING. MINIMAL BREAK IN TEMPS...WITH 850MB TEMPS DROPPING
OFF TO AROUND 16 DEGREES CELSIUS IN THE WAKE OF THE FRONT. LOW TEMPS
WILL DROP BACK TO NEAR NORMAL.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...COLD FRONT CROSSING
REGION THURSDAY NIGHT. MARGINALLY UNSTABLE SO CAN'T RULE
CONVECTIVE DEVELOPMENT CONTINUING AFTER DARK. SURFACE HIGH WILL
TRANSPORT MUCH DRIER AIR INTO REGION...RH 20 TO 30 PERCENT...FRIDAY.
PASSAGE OF WEAK PVA AND QUASI-STATIONARY SURFACE TROUGH MAY
SUPPORT A STRAY THUNDERSTORM OR SHOWER OVER SOUTHEAST MD SUNDAY.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...SO FAR T-STORMS STAYING
OUTSIDE OF THE 5NM AIRPORT DONUT. NOTHING IMMINENT HITTING THE
AIRPORTS SO VCTS SHOULD SUFFICE FOR NOW. PATCHY FOG LIKELY AGAIN
TONIGHT ESPECIALLY AT KMRB WHERE SOME CLEARING IS EXPECTED. DRIER
AIR WORKS FURTHER SOUTH TUE WITH ONLY A RISK OF A T-STORM AT KCHO.

VFR CONDITIONS WED-WED NIGHT. PSBL SUB-VFR CONDITIONS
THURS WITH DVLPNG SHOWERS AND TSTM...MAINLY THURS AFTN/EVENING TIME
FRAME. ANY TSTM COULD PRODUCE GUSTY AND VRB WINDS. VFR CONDITIONS
RETURN THURS NIGHT.

&&

.MARINE...WINDS HAVE ABATED SOMEWHAT ON THE WATERS. SCA STILL UP
UNTIL 00Z TONIGHT. WINDS EXPECTED BELOW SCA TUE-TUE NIGHT. MAIN
THREAT IS CG LIGHTNING FROM T-STORMS.

SUB-SCA CONDITIONS EXPECTED WED. PSBL BRIEF PERIOD OF SCA
GUSTS WED EVENING ON THE CHESAPEAKE BAY. SUB-SCA CONDITIONS THEN ON
ALL WATERS THUR MORNING. INCRSG SLY FLOW AHEAD OF THE APPROACHING
COLD FRONT COULD BRING GUSTS BACK TO AROUND 18-20 KTS THURS AFTN AND
NIGHT ON THE CHESAPEAKE BAY.

&&

.TIDES/COASTAL FLOODING...MINOR FLOOD LVLS MAY BE REACHED DURING THE HIGH
TIDE CYCLE WED NIGHT WITH PERSISTENT SLY FLOW KEEPING ELEVATED
ANOMALIES IN PLACE. THE MAIN AREAS OF CONCERN WOULD BE BALTIMORE
HARBOR...ANNAPOLIS AND TIDAL POTOMAC NEAR ALEXANDRIA.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR
     ANZ531>534-537-538-542-543.

&&

SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...SEARS
LONG TERM...CEM
AVIATION...SEARS/LFR
MARINE...SEARS/LFR
TIDES/COASTAL FLOODING...SEARS

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