Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190129 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 929 PM EDT THU SEP 18 2014 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD OVERHEAD FOR LATE TONIGHT THROUGH SATURDAY. THE HIGH WILL MOVE OFF THE COAST SUNDAY AND A STRONGER COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT INTO MONDAY. HIGH PRESSURE WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK.
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&& .NEAR TERM /THROUGH FRIDAY/...
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MOISTURE CONTINUES TO POOL AND BANK UP AGAINST THE LEE SIDE OF THE SRN APLCNS AND THE FOOTHILLS...WHILE A WEAK COLD FRONT SCRAPES THE NRN EDGE AS IT MOVES TOWARD THE COAST. THE FRONT HAS ALLOWED ANOTHER DRIER AIR SURGE TO RETURN FROM THE NORTH. DEWPOINTS ACROSS THE NRN HALF OF THE CWA ARE STARTING TO DROP INTO THE M-U40S...A GOOD SIGN THAT IT WILL BE A COOL NIGHT THERE. THE STRATIFICATION OF MOISTURE HOWEVER MAKES A DECENT-SIZED LEAP ON THE ERN SIDE OF THE BLUE RIDGE AND PARTICULARLY ALONG THE LOWLANDS OF THE I-95 CORRIDOR/COASTAL ZONES. DEWPOINTS WILL HANG TIGHT IN THE U50S/L60S...KEEPING THESE AREAS MORE MODERATED FOR OVERNIGHT LOWS AND DOWN ACROSS THE CHO/I-64 CORRIDOR W/ ADDITIONAL DENSE OVC SKIES. USED A BLEND OF THE ADJMAV AND LOCAL WRF GUIDANCE FOR OVERNIGHT LOWS. FRIDAY... HIGH PRESSURE WILL CONTINUE TO WEDGE INTO THE MID-ATLANTIC THROUGH FRIDAY...BRINGING MAINLY DRY CONDITIONS ALONG WITH BELOW NORMAL TEMPERATURES. HOWEVER...THE FLOW WILL TURN ONSHORE AND THIS MAY CAUSE CLOUDS TO GET TRAPPED UNDERNEATH THE SUBSIDENCE INVERSION. THE DEEPEST MOISTURE WILL BE ACROSS SOUTHERN MARYLAND...CENTRAL VIRGINIA AND THE POTOMAC HIGHLANDS WHERE A FEW SPRINKLES CANNOT BE RULED OUT. MAX TEMPS WILL RANGE FROM THE LOWER TO MIDDLE 60S IN THE POTOMAC HIGHLANDS TO THE LOWER AND MIDDLE 70S NEAR WASHINGTON AND BALTIMORE.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... HIGH PRESSURE WILL MOVE OFF THE NEW ENGLAND COAST AND THE SURFACE RIDGE AXIS WILL CONTINUE TO EXTEND SOUTH AND WEST TOWARD THE MID- ATLANTIC COAST FRIDAY NIGHT THROUGH SATURDAY. AN ONSHORE FLOW WILL CONTINUE DURING THIS TIME...AND IT MAY LEAD TO SOME LOW CLOUDS ALONG WITH PATCHY FOG...ESPECIALLY LATE FRIDAY NIGHT INTO SATURDAY MORNING. CLOUDS SHOULD GIVE WAY TO SUNSHINE SATURDAY...AND THAT WILL CAUSE MAX TEMPS TO BE A BIT WARMER COMPARED TO FRIDAY...RANGING FROM THE 70S IN THE MOUNTAINS TO NEAR 80 ACROSS WASHINGTON AND BALTIMORE. A STRONGER COLD FRONT WILL APPROACH THE AREA SATURDAY NIGHT...BUT THE SURFACE RIDGE AXIS SHOULD REMAIN IN PLACE. AREAS OF LOW CLOUDS AND FOG ARE POSSIBLE OVERNIGHT SATURDAY INTO SUNDAY MORNING. THE COLD WILL MOVE INTO THE AREA SUNDAY AFTERNOON. A SOUTHERLY FLOW AHEAD OF THE FRONT WILL CAUSE WARM AND HUMID CONDITIONS. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AHEAD OF THE COLD FRONT. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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A COLD FRONT WILL MOVE ACROSS THE REGION TO THE EAST COAST SUNDAY NIGHT. THERE IS A CHANCE FOR SHOWERS ALONG THE FRONT...MAINLY FROM THE SHENANDOAH VALLEY EAST TO THE CHESAPEAKE BAY. AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL SWEEP ACROSS THE REGION MONDAY. THERE COULD BE A FEW INSTABILITY SHOWERS THAT DEVELOP ENLIGHTEN TO THIS TROUGH. FOR THE MOST PART...MOST AREAS SHOULD BE DRY. HIGH PRESSURE WILL GRADUALLY BUILD INTO THE REGION MONDAY NIGHT. HIGH PRESSURE SHOULD HANG ON TO THE MID ATLANTIC COAST TUESDAY BEFORE IT MOVES OFFSHORE AND A SURFACE COLD FRONT SAGS IN FROM THE NORTHWEST AND NORTH LATE TUESDAY INTO TUESDAY NIGHT. WITH LIMITED MOISTURE IN PLACE...MOST AREAS WILL BE RAIN-FREE. A SECOND AREA OF HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT AND USHER IN COLDER THAN NORMAL AIR INTO THE REGION WEDNESDAY THROUGH THURSDAY.
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&& .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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ONSHORE FLOW WILL DEVELOP LATE TONIGHT THROUGH FRIDAY...AND THIS MAY LEAD TO LOW CLOUDS ACROSS KCHO. ALSO PATCHY BR IS POSSIBLE LATE TONIGHT INTO FRIDAY MORNING FOR KMRB AND KCHO. VFR CONDITIONS ARE EXPECTED FOR MOST OF THE TERMINALS FRIDAY...BUT LOW CLOUDS MAY PERSIST ACROSS KCHO WHICH COULD LEAD TO MVFR CONDITIONS. LOW CLOUDS MAY BECOME MORE WIDESPREAD LATE FRIDAY NIGHT INTO SATURDAY...AND AGAIN LATE SATURDAY NIGHT INTO SUNDAY AS AN ONSHORE FLOW PERSISTS. A COLD FRONT WILL MOVE INTO THE TERMINALS SUNDAY AFTERNOON...AND A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE.
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&& .MARINE...
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A PRESSURE SURGE IS EXPECTED TO DEVELOP BEHIND AN EXITING COLD FRONT OVERNIGHT INTO EARLY FRIDAY MORNING...CAUSING WINDS TO INCREASE AND A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. HOWEVER...IT WILL BE MARGINAL WITH GUSTS NEAR 20 KNOTS. AN EAST TO SOUTHEAST FLOW WILL CONTINUE FRIDAY THROUGH SATURDAY AS HIGH PRESSURE BUILDS OFF THE NEW ENGLAND COAST. WIND GUSTS MAY APPROACH SCA CRITERIA AT TIMES...BUT THE GUSTS HAVE BEEN CAPPED AT 15 KNOTS FOR NOW DUE TO A RELATIVELY WEAK PRESSURE GRADIENT. A COLD FRONT WILL APPROACH THE WATERS SUNDAY. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE LATE IN THE DAY INTO SUNDAY NIGHT. WINDS WILL SHIFT TO THE NORTHWEST BEHIND THE FRONT...AND A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS SUNDAY NIGHT INTO MONDAY.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES HAVE INCREASED TO ABOUT 1 TO 1.5 FEET ABOVE NORMAL FROM THE SOUTHERLY FLOW WEDNESDAY. THE FLOW WILL BE CONTINUE TO BE LIGHT THROUGH THIS EVENING...BEFORE INCREASING AND TURNING TOWARD THE NORTHEAST LATE TONIGHT. WITH NO OFFSHORE FLOW TO PUSH THE WATER OUT OF THE BAY...THESE TIDAL ANOMALIES ARE LIKELY TO CONTINUE THROUGH TONIGHT. A COASTAL FLOOD ADVISORY REMAINS IN EFFECT FOR THE HIGH TIDE CYCLE LATE TONIGHT INTO EARLY FRIDAY FOR ANNE ARUNDEL COUNTY THROUGH ST MARYS COUNTY. ELSEWHERE...MINOR TIDAL FLOODING IS POSSIBLE NEAR HIGH TIDE LATE TONIGHT INTO EARLY FRIDAY. HOWEVER...CONFIDENCE IS NOT HIGH ENOUGH FOR A COASTAL FLOOD ADVISORY AT THIS POINT. AN ONSHORE FLOW IS EXPECTED TO CONTINUE THROUGH SUNDAY...CAUSING ELEVATED WATER LEVELS AND THE POSSIBILITY OF MINOR TIDAL FLOODING.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...COASTAL FLOOD ADVISORY UNTIL 2 AM EDT FRIDAY FOR MDZ017-018. COASTAL FLOOD ADVISORY UNTIL 5 AM EDT FRIDAY FOR MDZ014. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO NOON EDT FRIDAY FOR ANZ530>534-537-539>541-543.
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&& $$ UPDATE...GMS PREV DISCUSSION...BJL/KLW

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