Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201858 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 258 PM EDT SAT SEP 20 2014 .SYNOPSIS...
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A SURFACE HIGH PRESSURE RIDGE WILL CONTINUE TO EXTEND SOUTHWEST ACROSS THE MID-ATLANTIC INTO TONIGHT. A SURFACE LOW OFF THE GEORGIA COAST WILL MOVE NORTHEAST BY CAPE HATTERAS SUNDAY. MEANWHILE...ANOTHER LOW WILL MOVE EAST ACROSS THE NORTHERN GREAT LAKES...WITH AN ASSOCIATED COLD FRONT MOVING THROUGH THE MID- ATLANTIC SUNDAY AFTERNOON AND NIGHT. CONTINENTAL HIGH PRESSURE WILL MOVE IN MONDAY AND PERSIST THROUGH THE REST OF THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 18Z...SFC RIDGE IS DRAPED WSW TO ENE ACROSS THE CWA WITH THE AXIS OVER DC. AN ASSOCIATED ONSHORE FLOW (WITH A BIT OF A BAY BREEZE) WILL CONTINUE UNTIL EVENING. A TROUGH IN ADVANCE OF A LOW OFF THE GEORGIA COAST EXTENDS NORTHEAST OFF THE MID-ATLANTIC COAST WHERE SCATTERED SHOWERS/THUNDERSTORMS ARE PRESENT. THIS ACTIVITY COULD APPROACH MD WATERS...WITH SLIGHT CHANCES FOR LOWER ST MARYS AND EAST. LOW/MID CLOUDS SHOULD MOVE IN FROM THE EAST...PERHAPS REACHING AS FAR WEST AS I-95. OTHERWISE...CLEAR TONIGHT WITH VALLEY AND PIEDMONT FOG. GUIDANCE IS SUGGESTING SOME FOG FOR THE METRO AREAS TOO...BUT THE CLOUD/CLEAR LINE WILL DETERMINE THAT. MIN TEMPS MID TO UPR 50S WEST OF BALT-WASH...LOW TO MID 60S FOR THE COASTAL LOWLANDS...NEAR 70F URBAN AND NEAR SHORE.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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SUNDAY...LOW PRESSURE MOVES NORTHEAST OFFSHORE AND THEN A COLD FRONT APPROACHES DURING THE DAY AND CROSSES LATE AFTERNOON THROUGH MIDNIGHT. FIVE PERCENT RISK FOR DAMAGING WIND FROM SPC ROUGHLY WEST OF THE BLUE RIDGE SEEMS REASONABLE GIVEN TIMING DURING PEAK HEATING. MAX TEMPS IN THE MID 80S (PERHAPS UPR 80S EAST OF I-95 IF MORNING CLOUDS CLEAR SOON ENOUGH) AND LIFTED INDICES FROM THE GFS AROUND -2. HIGH PRESSURE BUILDS MONDAY WITH NWLY WINDS GUSTING AROUND 20 MPH. MAX TEMPS LOW TO MID 70S. CLOUDS CLEAR THROUGH THE DAY...SUNNY BY THE AFTERNOON. CHILLY MONDAY NIGHT WITH CLEAR SKIES AND HIGH PRESSURE SETTLING OVER THE AREA. MIN TEMPS COULD BE INTO THE MID 30S IN THE ALLEGHENY HIGHLANDS WHERE FROST IS POSSIBLE. MENTIONED THIS IN THE HWO. OTHERWISE...MIN TEMPS LOW TO MID 40S...MID 50S NEAR SHORE.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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DEEP-LAYER RIDGING WILL ENTRENCH ITSELF OVER THE NORTH-CENTRAL AND EASTERN UNITED STATES BEGINNING TUESDAY...ACCOMPANIED BY A SEASONABLY COOL AND INITIALLY DRIER AIRMASS. BUT AS THE HIGH MIGRATES TO THE NORTH OF THE AREA DURING THE LATER PART OF THE WEEK AN ONSHORE FLOW BEGINS WHICH WILL LEAD TO GRADUALLY INCREASING MOISTURE. THIS COULD SQUEEZE OUT SOME DRIZZLE OR LIGHT RAIN BY THE END OF THE WEEK AS LOW PRESSURE MOVES INTO THE SOUTHEAST CONUS FROM THE ATLANTIC. TEMPERATURES WILL GENERALLY BE A FEW DEGREES BELOW NORMAL THROUGH MOST OF THE WEEK...BUT COULD REBOUND TO AROUND NORMAL LEVELS BY NEXT WEEKEND DEPENDING ON THE EXTENT OF CLOUD COVER AMIDST ONSHORE FLOW.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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LIGHT ONSHORE FLOW WITH VFR CONDS THROUGH TONIGHT AS LOW PRESSURE MOVES UP THE COAST FROM GEORGIA. A COLD FRONT CROSSES SUNDAY AFTERNOON AND EVENING WITH ISOLATED THUNDERSTORMS AS BEST EAST OF THE BLUE RIDGE. A FEW THUNDERSTORMS COULD HAVE DAMAGING WIND GUSTS WEST OF THE BLUE RIDGE. NW FLOW SUNDAY NIGHT AND MONDAY...COULD GUST AROUND 20 KT. HIGH PRESSURE THEN BUILDS THROUGH TUESDAY WITH CONTINUED VFR. VFR LIKELY TUE-WED NIGHT...WINDS GENERALLY NE 10 KTS OR LESS.
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&& .MARINE...
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LIGHT ONSHORE FLOW FROM SFC HIGH RIDGE OVER THE AREA WITH A BAY BREEZE THAT WILL ENDS THIS EVENING. LOW PRESSURE DEVELOPING OFF GEORGIA WILL STRENGTHEN AND LIFT NORTHEAST ALONG THE CAROLING COAST TONIGHT AND MOVE OFF THE MID-ATLANTIC SUNDAY. THE ONSHORE FLOW WILL CONTINUE UNTIL THE LOW PASSES MIDDAY SUNDAY. A COLD FRONT WILL CROSS THE WATERS SUNDAY NIGHT. JUST A SLIGHT CHANCE OF SHOWERS SUNDAY EVENING WITH THE PASSAGE. NWLY FLOW BEHIND THE FRONT WILL INCREASE TO 15 KT OR SO. SCA GUSTS TO 20 KT CURRENTLY LOOK TO WAIT UNTIL MONDAY MORNING...THOUGH THEY COULD ARRIVE WITH THE COLD FRONT LATE SUNDAY NIGHT. LATER SHIFTS WILL NEED TO MONITOR THAT. SUB-SCA CONDITIONS EXPECTED TUESDAY AS HIGH PRESSURE MOVES ACROSS...WITH SCA GUSTS POSSIBLE AT TIMES DURING THE SECOND HALF OF THE WEEK AS THE HIGH BEGINS TO PULL AWAY AND THE GRADIENT TIGHTENS WITH LOW PRESSURE DEVELOPING WELL TO THE SOUTH.
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&& .TIDES/COASTAL FLOODING...
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COASTAL FLOOD ADVISORY FOR CALVERT AND ANNE ARUNDEL COUNTIES UNTIL 6PM (CALVERT CAN BE CANCELED EARLIER) FOR ONGOING MINOR FLOODING. THE DEPARTURE AT BALTIMORE/FT MCHENRY HAS REMAINED AT 1.4FT. A 1.6FT DEPARTURE WOULD BE REQUIRED TO HIT THE MINOR THRESHOLD OF 3.0FT. DEPARTURES WILL REMAIN ELEVATED...UP TO 1.5 FT ABOVE NORMAL...SO MORE COUNTIES ARE ANTICIPATED TO BE IN THE ADVISORY FOR THE HIGH TIDE TONIGHT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...COASTAL FLOOD ADVISORY UNTIL 9 PM EDT THIS EVENING FOR DCZ001. MD...COASTAL FLOOD ADVISORY UNTIL 6 PM EDT THIS EVENING FOR MDZ014- 018. VA...COASTAL FLOOD ADVISORY UNTIL 9 PM EDT THIS EVENING FOR VAZ054. WV...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...DFH AVIATION...BAJ/DFH MARINE...BAJ/DFH TIDES/COASTAL FLOODING...BAJ

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