Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241815 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 215 PM EDT SUN APR 24 2016 .SYNOPSIS...
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HIGH PRESSURE WILL MOVE OFF THE COAST THROUGH MONDAY. A COLD FRONT WILL APPROACH FROM THE NORTHEAST ON TUESDAY BEFORE PASSING THROUGH THE AREA TUESDAY NIGHT INTO WEDNESDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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HIGH PRESSURE OVERHEAD EARLY THIS AFTERNOON WILL CONTINUE TO SHIFT TOWARD THE MID-ATLANTIC COAST LATE. PLENTY OF SUNSHINE AND SEASONABLE CONDITIONS ARE EXPECTED AND THE SURFACE WIND WILL GRADUALLY VEER TOWARD THE SOUTH LATE THIS AFTERNOON. WIND SPEEDS SHOULD REMAIN LIGHT...GENERALLY UNDER 10KT. HIGH PRESSURE WILL CONTINUE TO SHIFT EAST OFF THE MID-ATLANTIC COAST TONIGHT. A LIGHT SOUTHERLY FLOW WILL ALLOW FOR MILDER CONDITIONS COMPARED TO LAST NIGHT. MIN TEMPS WILL BE IN THE MID TO UPPER 40S FOR MOST LOCATIONS.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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HIGH PRESSURE WILL CONTINUE TO MOVE OUT INTO THE ATLANTIC OCEAN MONDAY AND A SOUTHWEST FLOW WILL USHER IN NOTICEABLY WARMER CONDITIONS ALONG WITH MORE MOISTURE. A WESTERLY FLOW IS EXPECTED ALOFT...BUT MOST OF THE SHORTWAVE ENERGY WILL BE WELL OFF TO THE NORTH. THEREFORE...MONDAY WILL TURN OUT DRY FOR MOST AREAS ALONG WITH SUNSHINE. THERE MAY BE A COUPLE POPUP SHOWERS LATE MONDAY AFTERNOON IN THE POTOMAC HIGHLANDS INTO THE VIRGINIA PIEDMONT DUE TO DAYTIME HEATING. HOWEVER...MOISTURE WILL BE LIMITED SO ANY COVERAGE WOULD BE ISOLATED AT BEST AND MOST AREAS WILL END UP DRY. A SOUTHWEST FLOW WILL CONTINUE THROUGH MONDAY NIGHT...AND IT WILL REMAIN QUITE MILD. A FEW SHOWERS ARE POSSIBLE ACROSS THE NORTHERN PORTIONS OF THE CWA...BUT COVERAGE WOULD REMAIN ISOLATED TO SCATTERED DUE TO LIMITED FORCING. POTENT LOW PRESSURE BOTH AT THE UPPER-LEVELS OF THE ATMOSPHERE AND THE SURFACE WILL MOVE EAST FROM THE ROCKIES INTO THE PLAINS ON TUESDAY. THIS WILL ALLOW FOR RIDGING UPSTREAM TO STRENGTHEN OVER THE MIDWEST AND GREAT LAKES. A CONFLUENCE ZONE BETWEEN THE UPPER- LEVEL RIDGING AND UPPER-LEVEL LOW PRESSURE OVER EASTERN CANADA WILL STRENGTHEN...AND THIS WILL CAUSE HIGH PRESSURE TO STRENGTHEN OVER NEW ENGLAND. A BACKDOOR BOUNDARY WILL DEVELOP AHEAD OF THE BUILDING HIGH THAT SEPARATES WARM AND MOIST AIR OVER OUR AREA FROM MUCH COOLER AIR OVER NEW ENGLAND. THIS BOUNDARY SHOULD REMAIN TO OUR NORTH TUESDAY...WHICH MEANS THAT A SOUTHWEST FLOW WILL ALLOW FOR WARM AND MOIST CONDITIONS. MAX TEMPS WILL REACH THE UPPER 70S AND LOWER 80S FOR MOST AREAS AND DEWPOINTS IN THE UPPER 50S AND 60S ARE EXPECTED. THIS WILL LEAD TO AT LEAST SOME INSTABILITY. THE UNSTABLE ATMOSPHERE WILL COMBINE WITH A PRESSURE TROUGH...TRIGGERING A FEW SHOWERS AND THUNDERSTORMS. SUFFICIENT SHEAR PROFILES SUGGEST THAT A FEW THUNDERSTORMS COULD BECOME SEVERE...WITH LOCALLY DAMAGING WIND GUSTS AND LARGE HAIL BEING THE PRIMARY THREATS. AT THIS TIME...CURRENT THINKING IS THAT ANY SEVERE COVERAGE WOULD BE LOCALIZED DUE TO LIMITED INSTABILITY...GENERALLY LESS THAN 1KJ/KG. HOWEVER...SHOULD INSTABILITY BE HIGHER THAN ANTICIPATED THEN THE SEVERE COVERAGE WOULD INCREASE SIGNIFICANTLY. THE BACKDOOR BOUNDARY WILL DROP THROUGH MOST OF THE AREA TUESDAY NIGHT. A NORTHEAST FLOW BEHIND THE BOUNDARY WILL CAUSE NOTICEABLY COOLER CONDITIONS FOR MOST AREAS...BUT IT WILL LIKELY REMAIN WARM NEAR AND AHEAD OF THE BOUNDARY ACROSS THE POTOMAC HIGHLANDS INTO THE SHENANDOAH VALLEY. A COUPLE SHOWERS AND THUNDERSTORMS ARE POSSIBLE IN THE EVENING...BUT COVERAGE WILL BECOME MORE LIMITED OVERNIGHT BEHIND THE BOUNDARY AND EVEN AHEAD OF THE BOUNDARY DUE TO THE LOSS OF DAYTIME HEATING.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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A BACKDOOR COLD FRONT WILL CONTINUE TO PUSH SOUTHWARD WEDNESDAY AND WEDNESDAY NIGHT. THERE IS A BETTER CHANCE OF ENCOUNTERING RAIN SHOWERS ACROSS THE VIRGINIA PIEDMONT AND CENTRAL SHENANDOAH VALLEY THAN NORTHEAST MARYLAND AND THE MASON-DIXON REGION THROUGHOUT THIS PERIOD. THE FRONT WILL TRY TO WORK ITS WAY NORTHWARD THURSDAY THROUGH FRIDAY...KEEPING THE THREAT FOR SHOWERS AND A COUPLE OF THUNDERSTORMS ACROSS THE REGION. AN AREA OF HIGH PRESSURE OVER THE GREAT LAKES WILL NUDGE THE FRONT TO THE SOUTHEAST AND OFFSHORE FRIDAY NIGHT AND SATURDAY BEFORE THE FRONT CAN REACH THE MASON-DIXON LINE. THE HIGH WILL MOVE INTO SOUTHERN NEW ENGLAND AND OFFSHORE NEW JERSEY TO ALLOW FOR A SOUTHERLY FLOW TO DEVELOP AND BRING IN ADDITIONAL WARMTH AND MOISTURE INTO THE REGION SATURDAY AND SATURDAY NIGHT. THERE IS A CHANCE FOR SOME STRATIFORM RAIN AND PERHAPS A CLAP OF THUNDER AS A WARM FRONT DEVELOPS ACROSS THE SOUTHERN SHENANDOAH VALLEY AND PROPAGATES NORTHWARD. THROUGHOUT THE DAY SUNDAY...THE INSTABILITY OF THE ATMOSPHERE BECOMES MORE PRONOUNCED AND THE CHANCE OF RAIN SHOWERS AND THUNDERSTORMS BECOMES MORE SCATTERED IN THE REGION.
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&& .AVIATION /17Z SUNDAY THROUGH THURSDAY/...
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VFR CONDITIONS ARE EXPECTED THROUGH MONDAY. A SOUTHERLY FLOW WILL DEVELOP LATE THIS AFTERNOON AND EVENING...BUT WIND SPEEDS SHOULD REMAIN LIGHT. WINDS WILL INCREASE A BIT MONDAY WITH GUSTS AROUND 15 TO 20 KNOTS EXPECTED IN THE AFTERNOON. THE SOUTHWEST FLOW WILL CONTINUE TUESDAY WITH GUSTS AROUND 20 TO 25 KNOTS EXPECTED. THERE IS A CHANCE FOR AFTERNOON THUNDERSTORMS. SOME THUNDERSTORMS MAY CONTAIN GUSTY WINDS AND HAIL ALONG WITH SUBVFR CIGS/VSBYS. A COLD FRONT WILL PASS THROUGH THE TERMINALS TUESDAY NIGHT. WINDS WILL SHIFT TO THE NORTHEAST BEHIND THE BOUNDARY. SUBVFR CIGS ARE POSSIBLE BEHIND THE BOUNDARY. MVFR TO IFR CONDITIONS POSSIBLE WITH RAIN SHOWERS IN THE VICINITY NEAR CHO TERMINAL WEDNESDAY...THEN AT ANY TERMINAL WEDNESDAY NIGHT. WINDS NORTHEAST AROUND 5 KNOTS WEDNESDAY...BECOMING SOUTHEAST AROUND 5 KNOTS WEDNESDAY NIGHT.
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&& .MARINE...
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A SOUTHERLY FLOW WILL INCREASE TONIGHT INTO MONDAY. WINDS WILL BE CLOSE TO SCA CRITERIA FOR THE MIDDLE PORTION OF THE BAY AND LOWER TIDAL POTOMAC RIVER DURING THIS TIME. DID NOT ISSUE AN SCA AT THIS TIME BECAUSE CONFIDENCE WAS TOO LOW GIVEN THE RELATIVELY COOLER WATERS. HOWEVER...IT WILL BE CLOSE AND THIS WILL HAVE TO BE MONITORED. THE SOUTHERLY FLOW WILL INCREASE MONDAY NIGHT...AND A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MIDDLE PORTION OF THE BAY AND LOWER TIDAL POTOMAC RIVER. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR ALL OF THE WATERS TUESDAY. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE TUESDAY AFTERNOON INTO TUESDAY EVENING. THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL. A BACKDOOR COLD FRONT WILL PASS THROUGH THE WATERS TUESDAY NIGHT AND WINDS WILL SHIFT TO THE NORTHEAST BEHIND THE BOUNDARY. A NORTHEAST FLOW WILL CONTINUE BEHIND THE BOUNDARY FOR WEDNESDAY INTO THURSDAY. WIND SPEEDS SHOULD REMAIN BELOW SCA CRITERIA.
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&& .FIRE WEATHER...
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VERY DRY CONDITIONS WILL CONTINUE THIS AFTERNOON WITH RH VALUES DROPPING 20S AND TEENS. HOWEVER...WINDS WILL REMAIN LIGHT. A SOUTHWEST FLOW WILL INCREASE MONDAY WITH GUSTS AROUND 15 TO 20 MPH EXPECTED. THE SOUTHWEST FLOW WILL LEAD TO MORE ATMOSPHERIC MOISTURE WHICH SHOULD KEEP RH VALUES ABOVE 30 PERCENT. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE TUESDAY. A COOLER AND WETTER WEATHER PATTERN MAY DEVELOP FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 8 PM MONDAY TO 6 AM EDT TUESDAY FOR ANZ532>534-537-540>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...KLW AVIATION...BJL/KLW MARINE...BJL/KLW FIRE WEATHER...BJL

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