Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271857 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 257 PM EDT MON JUL 27 2015 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TUESDAY/...
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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.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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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.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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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.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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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.
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&& .MARINE...
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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.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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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.
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&& $$ 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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