Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251850 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 250 PM EDT WED MAR 25 2015 .SYNOPSIS...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST THROUGH TONIGHT. A WARM FRONT WILL PASS THROUGH THE AREA THURSDAY MORNING FOLLOWED BY A POTENT COLD FRONT THAT WILL MOVE THROUGH LATE THURSDAY INTO THURSDAY NIGHT. AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE AREA LATER FRIDAY THROUGH SATURDAY...AND HIGH PRESSURE WILL RETURN FOR SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST THROUGH TONIGHT. LOW PRESSURE WILL TRACK THROUGH THE TENNESSEE VALLEY AND INTO THE OHIO VALLEY TONIGHT. A SOUTHERLY FLOW WILL ALLOW FOR MILDER CONDITIONS COMPARED TO RECENT NIGHTS. IN FACT...TEMPS MAY RISE A BIT AS A WARM FRONT APPROACHES FROM THE SOUTH. PLENTY OF CLOUDS WILL CONTINUE TO OVERSPREAD THE AREA DUE TO WARM AND MOIST AIR OVERRUNNING THE SURFACE COOLER AIR IN PLACE. LIGHT RAIN OR SPRINKLES CANNOT BE RULED OUT THROUGH THIS EVENING...BUT MOST OF THE TIME WILL BE DRY DUE TO LITTLE IN THE WAY OF A LIFTING MECHANISM. A PLUME OF MOISTURE WILL OVERSPREAD SOUTHERN PORTIONS OF THE AREA LATE TONIGHT...AND THIS MAY CAUSE SHOWERS TO BE MORE WIDESPREAD ACROSS THE VIRGINIA PIEDMONT INTO SOUTHERN MARYLAND. ELSEWHERE...ANY PRECIPITATION WILL BE LIGHT AND MUCH OF THE TIME WILL TURN OUT DRY.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
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THE WARM FRONT WILL PASS THROUGH OUR AREA THURSDAY MORNING. A FEW SHOWERS ARE POSSIBLE WITH THE FRONTAL PASSAGE...ESPECIALLY ACROSS SOUTHERN MARYLAND AND THE VIRGINIA PIEDMONT WHERE ATLANTIC MOISTURE WILL GET DRAWN INTO THE AREA. THERE MAY BE A SIGNIFICANT BREAK IN PRECIPITATION BEHIND THE WARM FRONT THURSDAY. GUSTY SOUTHERLY WINDS ARE EXPECTED TO DEVELOP AND THIS WILL USHER IN UNUSUALLY WARM CONDITIONS FOR THIS TIME OF YEAR. IN FACT...MAX TEMPS ARE EXPECTED TO BE IN THE 70S ACROSS MOST LOCATIONS. THERE MAY EVEN BE A FEW LOCATIONS IN THE VIRGINIA PIEDMONT THAT APPROACH 80 DEGREES. A POTENT COLD FRONT WILL MOVE INTO THE POTOMAC HIGHLANDS LATE IN THE AFTERNOON BEFORE PASSING THROUGH THE BALTIMORE AND WASHINGTON METROPOLITAN AREAS EARLY IN THE EVENING...THEN EVENTUALLY PAST SOUTHERN MARYLAND OVERNIGHT. A LINE OF GUSTY SHOWERS AND POSSIBLY EVEN A COUPLE THUNDERSTORMS WILL ACCOMPANY THE FRONT. GUSTY WINDS ARE EXPECTED...BUT AS OF NOW THE THREAT FOR SEVERE WEATHER IS LOW DUE TO A CAPPING INVERSION IN THE LOW-LEVELS LIMITING INSTABILITY. WILL HAVE TO CONTINUE TO MONITOR...BECAUSE THERE ARE PLENTY OF STRONG WINDS ALOFT THAT WILL BE ABLE TO MIX DOWN TO THE SURFACE IF THE ATMOSPHERE IS UNSTABLE ENOUGH AHEAD OF THE BOUNDARY. THE COLD FRONT WILL PUSH OFF TO THE EAST OVERNIGHT THURSDAY...BUT THE UPPER-LEVEL TROUGH WILL REMAIN WELL BEHIND OVER THE GREAT LAKES INTO THE OHIO VALLEY. AN UPPER-LEVEL DISTURBANCE AHEAD OF THE TROUGH WILL SWING THROUGH OUR AREA...CAUSING MORE RAIN BEHIND THE FRONT. NORTHWEST WINDS WILL CAUSE MUCH COLDER CONDITIONS AS WELL. IN FACT...RAIN WILL CHANGE TO SNOW ACROSS THE ALLEGHENY AND POTOMAC HIGHLANDS. SNOWFALL ACCUMULATIONS WILL BE CONFINED MAINLY TO AREAS ABOVE 2KFT ALONG AND WEST OF THE ALLEGHENY FRONT.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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FOR FRIDAY THROUGH SATURDAY...PERIOD IS DOMINATED BY H5 HEIGHT FALLS AS SHORT WAVE OVER GREAT LAKES PRODUCES CUTOFF LOW ON SATURDAY OVER THE MASON-DIXON LINE AS INDICATED BY THE 12Z GFS. SFC TEMPS DURING THIS TIME WILL BE 10-15F BELOW NORMAL. ON FRIDAY...THE SURFACE FRONT IS PROGGED BY BOTH THE 12Z GFS AND 12Z ECMWF TO BE EAST OF DELMARVA. THIS WILL PUT DECREASING POPS FROM WEST TO EAST ACROSS THE CWA IN THE MORNING...WITH THE EXCEPTION OF AN UPSLOPE COMPONENT IN THE HIGHLANDS WHERE SNOW SHOWERS WILL BE LIKELY. FRIDAY NIGHT THE CWA WILL BE PRECIP FREE XCPT FOR UPSLOPE AGAIN IN H85 CAA AND DOWNSLOPING. BY 12Z SATURDAY...H85 TEMPS ARE PROGGED TO BE A0B -9C ACROSS THE ENTIRE CWA...WHICH WILL MAKE FOR A VERY CHILLY AND BLUSTERY DAY ON SATURDAY WITH CHC OF SNOW SHOWERS ACROSS THE ENTIRE REGION DUE TO LOW LEVEL INSTABLITY AND APPROACHING CUT UPPER LOW...WITH HIGHER POPS IN UPSLOPE AREAS AGAIN. AN UPPER-LEVEL TROUGH WILL BE MOVING AWAY SATURDAY NIGHT INTO SUNDAY WHILE HIGH PRESSURE BUILDS OVER THE REGION. THE HIGH WILL MOVE OFF THE COAST ON SUNDAY. HIGH TEMPS WILL BE IN LOW 50S. A COLD FRONT APPROCHES THE REGION AND WILL MOVE ACROSS THE AREA EARLY ON MONDAY... BRINGING A CHANCE FOR SHOWERS. HIGH PRESSURE RETURNS ON TUESDAY AND A WARM FRONT APPROACHES ON WEDNESDAY.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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CIGS WILL LOWER TO MVFR LEVELS LATE THIS AFTERNOON AND EVENING AHEAD OF A WARM FRONT. A PERIOD OF IFR LEVELS ARE POSSIBLE LATE TONIGHT INTO THURSDAY MORNING AS THE WARM FRONT SWINGS THROUGH. WILL CONTINUE WITH A LOW-LEVEL WIND SHEAR GROUP IN THE TAFS TONIGHT THROUGH EARLY THURSDAY MORNING DUE TO A POTENT LOW-LEVEL JET AND A LACK OF MIXING CAUSING LIGHT WINDS NEAR THE SURFACE. CIGS WILL IMPROVE BEHIND THE BOUNDARY LATER THURSDAY MORNING. SOUTHERLY WINDS WILL BECOME GUSTY AHEAD OF AN APPROACHING COLD FRONT THURSDAY AFTERNOON. GUSTS AROUND 25 TO 30 KNOTS ARE EXPECTED. VFR CONDITIONS WITH GUSTY NORTHWEST ARE EXPECTED FRIDAY THROUGH SATURDAY. VFR CONDITIONS ARE EXPECTED FOR SUNDAY. COLD FRONT MOVING ACROSS ON MONDAY WILL BRING A CHANCE FOR SHOWERS TO THE TERMINALS. THE COLD FRONT WILL PASS THROUGH LATE THURSDAY AFTERNOON AND EVENING. A LINE OF SHOWERS AND PERHAPS A COUPLE THUNDERSTORMS WILL ACCOMPANY THE FRONTAL PASSAGE. GUSTY WINDS ARE POSSIBLE WITH THIS LINE OF CONVECTION. WINDS WILL SHIFT TO THE NORTHWEST BEHIND THE FRONT. MORE RAIN WILL HANG AROUND FOR OVERNIGHT THURSDAY WITH POSSIBLE SUBVFR CONDITIONS.
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&& .MARINE...
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SOUTHERLY WINDS WILL INCREASE A BIT THIS AFTERNOON. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE NORTHERN PORTION OF THE BAY FOR GUSTS UP TO 20 KNOTS. ELSEWHERE...THE GRADIENT SHOULD BE WEAK ENOUGH FOR GUSTS TO REMAIN JUST BELOW SCA CRITERIA. WINDS WILL DIMINISH TONIGHT...BUT REMAIN SOUTH TO SOUTHEAST AHEAD OF AN APPROACHING WARM FRONT. THE WARM FRONT WILL PASS THROUGH THE WATERS THURSDAY MORNING AND GUSTY SOUTHERLY WINDS ARE EXPECTED BEHIND THE BOUNDARY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS DURING THIS TIME. THE SMALL CRAFT ADVISORY CONTINUES THROUGH THURSDAY NIGHT. SOUTHERLY WINDS WILL SHIFT TO THE NORTHWEST BEHIND THE COLD FRONT. A LINE OF HEAVY SHOWERS AND PERHAPS A COUPLE THUNDERSTORMS WILL ACCOMPANY THE FRONTAL PASSAGE. LOCALLY GUSTY WINDS ARE POSSIBLE AS THIS SYSTEM PASSES THROUGH. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS FRIDAY. NO MARINE HEADLINES ANTICIPATED FRIDAY NIGHT THROUGH SUNDAY. SCA MAY BE NEEDED ON MONDAY AS COLD FRONT MOVES ACROSS THE REGION.
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&& .TIDES/COASTAL FLOODING...
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SOUTHERLY WINDS WILL DEVELOP THROUGH TONIGHT AND THE SOUTHERLY FLOW WILL INCREASE AHEAD OF A COLD FRONT THURSDAY. THE INCREASED SOUTHERLY FLOW WILL CAUSE WATER LEVELS TO ELEVATE...AND TIDAL ANOMALIES MAY BE HIGH ENOUGH FOR MINOR FLOODING NEAR TIMES OF HIGH TIDE THURSDAY INTO THURSDAY NIGHT. THE COLD FRONT WILL PASS THROUGH LATER THURSDAY EVENING AND A NORTHWEST FLOW WILL CAUSE WATER LEVELS TO DECREASE LATE THURSDAY NIGHT INTO FRIDAY.
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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 6 PM EDT THIS EVENING FOR ANZ530>533-538>541. SMALL CRAFT ADVISORY FROM 10 AM THURSDAY TO 6 AM EDT FRIDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...LEE/IR AVIATION...BJL/LEE/IR MARINE...BJL/LEE/IR TIDES/COASTAL FLOODING...BJL

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