Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 011839 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 239 PM EDT WED OCT 1 2014 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVERHEAD THROUGH THURSDAY. A STRONG COLD FRONT WILL APPROACH THE AREA FRIDAY BEFORE PASSING THROUGH FRIDAY NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL RETURN FOR THE WEEKEND...BRINGING DRIER AND NOTICEABLY COOLER CONDITIONS. THE HIGH WILL MOVE OFFSHORE EARLY NEXT WEEK. && .NEAR TERM /THROUGH THURSDAY/...
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AN UPPER LEVEL TROUGH WITH A CLOSED LOW ACROSS THE NORTHEAST CONUS WILL CONTINUE TO MOVE EASTWARD TODAY. VORT MAXES ACROSS WESTERN PA WILL MOVE IN THE CYCLONIC FLOW ALOFT. AT THE SFC...HIGH PRESSURE ACROSS NEWFOUNDLAND WILL WEDGE SOUTH INTO THE MID-ATLANTIC. AN EASTERLY COMPONENT TO THE SFC WIND WILL CONTINUE TO KEEP MARINE AIR IN PLACE. A MIX OF SUN AND CLOUDS HAVE BEEN OBSERVED AS MIXING HAS ALLOWED MOISTURE TO BE DISPLACED ALOFT. AREAS RIGHT UP AGAINST RIDGE LINES INCLUDING THE BLUE RIDGE AND ACROSS THE POTOMAC HIGHLANDS HAVE BEEN LOCKED INTO THE LOW STRATUS. THESE CONDITIONS WILL CONTINUE THIS AFTERNOON. FURTHER WEST...SUNSHINE AS ALLOWED A CU FIELD TO DEVELOP AND ISO-SCT SHOWERS ARE EXPECTED ACROSS THE VA HIGHLANDS...POTOMAC HIGHLANDS AND SHENANDOAH VALLEY THIS AFTERNOON. ALL ACTIVITY SHOULD SUBSIDE BY EVENING. THE UPPER LEVEL LOW WILL MOVE EASTWARD TONIGHT AND UPPER LEVEL RIDGING WILL TAKE ITS PLACE ACROSS THE REGION. THE WEDGE OF HIGH PRESSURE AND EASTERLY FLOW WILL CONTINUE INTO THE EVENING AND THURSDAY MORNING. LOW CLOUDS WILL SPREAD EASTWARD FROM THE RIDGELINES LATE TONIGHT AND LEAD TO A CLOUDY THURSDAY MORNING WITH THE EXCEPTION OF I-95 AND EASTWARD. CONFIDENCE IS LOW AS TO HOW FAR EAST THE STRATUS WILL REACH BUT IT WILL LIKELY TAKE UNTIL MIDDAY TO MIX OUT THE CLOUDS. PATCHY DRIZZLE AND FOG ARE ALSO POSSIBLE ESPECIALLY ALONG I-81. DENSE FOG IS POSSIBLE IN VALLEY LOCATIONS FOR THE THURSDAY MORNING COMMUTE. WITH RIDGING IN PLACE THURSDAY AFTERNOON...A MIX OF SUN AND CLOUDS ARE EXPECTED ONCE LOW STRATUS MIX OUT. FURTHER WEST...TERRAIN CIRCULATIONS MAY CAUSE A CU FIELD TO DEVELOP ACROSS THE VA HIGHLANDS.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
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MAIN STORY OF THE PERIOD WILL BE A STRONG COLD FRONT SWINGING THROUGH THE AREA. A LARGE TROUGH WILL DIG INTO THE UPPER MIDWEST DURING THE DAY FRIDAY...ASSUMING A NEGATIVE TILT AS IT PIVOTS ACROSS THE GREAT LAKES/OHIO VALLEY FRIDAY NIGHT. 500 MB LOW CUTS OFF IN THE PROCESS AND MOVES ROUGHLY FROM CHICAGO EAST TO PITTSBURGH OVERNIGHT. STRONG AND DEEP LIFT AHEAD OF THIS TROUGH ALONG A SURFACE COLD FRONT WILL DRIVE A BAND OF SHOWERS MOVING ACROSS THE AREA FROM WEST TO EAST FRIDAY AFTERNOON AND FRIDAY NIGHT. THE LATEST GUIDANCE HAS SLOWED THE TIMING OF THE FRONT SOMEWHAT SO MOST OF THE RAIN LOOKS TO BE OVERNIGHT FRIDAY NIGHT...ESPECIALLY EAST OF THE BLUE RIDGE. THE OVERNIGHT TIMING OF THE FRONTAL PASSAGE WOULD MEAN LOWER INSTABILITY LEVELS AND THUS A LOWER CHANCE OF THUNDERSTORMS OVERALL. HOWEVER THE AFOREMENTIONED LIFT AND STRONG HEIGHT FALLS/COOLING ALOFT MAY STILL RESULT IN A LINE OF HEAVIER SHOWERS WITH ISOLATED LIGHTNING STRIKES DESPITE LOW CAPE. NAM/GFS/ECMWF NOW IN BETTER AGREEMENT WITH THE STRENGTH OF THE SOUTHERLY LOW-LEVEL JET AS WELL PRECEDING THE COLD FRONT...BUT AGAIN THE OVERNIGHT TIMING WOULD TEND TO WORK AGAINST MIXING THE MAJORITY OF THIS WIND TO THE SURFACE. ANY HEAVIER BANDS OF SHOWERS COULD MIX SOME OF THIS WIND DOWN BUT OVERALL THE SEVERE THREAT APPEARS TOO LOW TO WARRANT A MENTION IN THE HWO FOR NOW. WILL CONTINUE TO MONITOR.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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THE FRONT PULLS EAST OF THE AREA SATURDAY MORNING LEAVING IN ITS WAKE A MUCH COOLER AND DRIER AIRMASS OVER THE WEEKEND. AS THE TROUGH AXIS PIVOTS OVER THE AREA...FAVORABLE TRAJECTORIES FOR UPSLOPE WILL BE LIKELY WITH SHOWERS POSSIBLE OVER THE WESTERN SLOPES. SOME SNOWFLAKES MAY BE MIXED IN AS WELL GIVEN 850 MB TEMPS CRASHING TO BETWEEN 0 AND -2 C SATURDAY NIGHT. SPOTTY FREEZING TEMPERATURES WILL BE POSSIBLE ALONG THE RIDGES AS WELL OVERNIGHT SATURDAY NIGHT. THE AIRMASS WILL QUICKLY MODERATE AS HIGH PRESSURE MOVES EAST RESULTING IN A LOW-LEVEL SOUTHWESTERLY FLOW BY EARLY NEXT WEEK. THE NEXT STORM SYSTEM AND CHANCE OF RAIN WILL MOVE ACROSS THE AREA FROM WEST TO EAST MONDAY NIGHT THROUGH TUESDAY.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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VFR/MVFR CONDITIONS EXPECTED THROUGH THE AFTERNOON. CONDITIONS WILL WORSEN THIS EVENING AND OVERNIGHT AS LOW CLOUDS...DRIZZLE AND PATCHY FOG FORM. IFR CONDITIONS ARE EXPECTED AT MRB/CHO INTO THURS MORNING. DUE TO THE LACK OF CONFIDENCE AS TO HOW FAR THE LOW CLOUDS WILL MOVE EASTWARD...MVFR EXPECTED AT IAD BUT IFR CIGS ARE POSSIBLE. CONDITIONS WILL IMPROVE TOWARDS THURSDAY MIDDAY AND A VFR/MVFR CONDITIONS EXPECTED THROUGH THURS AFTERNOON. LOW CIGS/VSBYS TO IFR OR LWR PSBL FRI-SAT AM IN MOIST SOUTHERLY FLOW 10-20 KTS AND GUSTY AHEAD OF STRONG FRONT. LLWS PSBL FRI NIGHT. MODELS COMING INTO BETTER TIMING/STRENGTH AGREEMENT LENDING TO MODERATELY HIGH CONFIDENCE DURING THIS TIME. VFR RETURNS SAT PM AND PERSISTS THROUGH THE WEEKEND...WINDS TURNING WEST 10-20 KTS BEHIND FRONT.
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&& .MARINE...
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NE-E FLOW WILL CONTINUE ON THE WATERS THROUGH THURSDAY. WINDS 10-15 KTS ARE EXPECTED. THE TIGHTER GRADIENT AND THEREFORE STRONGER GUSTS ARE ACROSS THE OCEAN WATERS. A ISOLATED GUST OF 18-20KTS IS POSSIBLE ACROSS TANGIER SOUND INTO THURSDAY AFTERNOON. SCA CONDITIONS VERY LIKELY IN SOUTHERLY CHANNELING AHEAD OF STRONG COLD FRONT FRIDAY. A BAND OF HEAVY SHOWERS WHICH MAY ENHANCE GUSTY WINDS WILL APPROACH THE WATERS FROM THE WEST FRIDAY NIGHT. THE FRONT CLEARS THE WATERS SATURDAY WITH GUSTY NORTHWEST FLOW TO SCA LEVELS POSSIBLE THROUGH THE REMAINDER OF THE WEEKEND.
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&& .TIDES/COASTAL FLOODING...
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NE-E WINDS HAVE LED TO ANOMALIES INCREASING TO OVER A FOOT ACROSS THE WESTERN SHORE OF THE CHESAPEAKE BAY THIS AFTERNOON. A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR ST.MARYS TO ANNE ARUNDEL COUNTIES TONIGHT. WINDS ARE EXPECTED TO RELAX SOME THIS EVENING WHICH MAY CAUSE ANOMALIES TO DROP BUT DUE TO THE PREFERRED HIGH TIDE AND AN ONSHORE COMPONENT TO THE WIND WATER LEVELS WILL LIKELY INCREASE THIS EVENING AND THEREFORE AN ADVISORY WAS ISSUED. THIS ADVISORY MAY NEED TO BE EXTENDED TO INCLUDE BALTIMORE AND DC/ALEXANDRIA/PRINCE GEORGES COUNTIES.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...COASTAL FLOOD ADVISORY FROM 6 PM THIS EVENING TO 4 AM EDT THURSDAY FOR MDZ014-017-018. VA...NONE. WV...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...DFH LONG TERM...DFH AVIATION...HAS/DFH MARINE...HAS/DFH TIDES/COASTAL FLOODING...HAS

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