Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 041400 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1000 AM EDT FRI SEP 4 2015 .SYNOPSIS... A BACKDOOR COLD FRONT WILL SINK SOUTH ACROSS THE WATERS LATE TODAY INTO TONIGHT. HIGH PRESSURE WILL BUILD OVERHEAD DURING THE LABOR DAY WEEKEND BEFORE MOVING OFF THE COAST DURING THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... UPPER-LEVEL LOW PRESSURE WILL WEAKEN OVER THE GREAT LAKES THIS AFTERNOON INTO TONIGHT WHILE HIGH PRESSURE BUILDS OVER NEW ENGLAND. A BACKDOOR COLD FRONT WILL APPROACH THE AREA FROM THE NORTH AND EAST THIS AFTERNOON BEFORE STALLING OUT OVER THE AREA TONIGHT. A NORTHERLY FLOW LATE THIS MORNING WILL TURN TO THE EAST THIS AFTERNOON AS THE BACKDOOR BOUNDARY APPROACHES THE AREA. HOWEVER...THE TEMPERATURE AND DEWPOINT GRADIENT SHOULD REMAIN WELL OFF TO OUR NORTH AND EAST. THEREFORE...MORE HOT AND HUMID CONDITIONS ARE EXPECTED WITH MAX TEMPS IN THE UPPER 80S AND LOWER 90S ACROSS MOST LOCATIONS. THE HEAT AND HUMIDITY WILL LEAD TO MORE INSTABILITY. MODIFIED 12Z SOUNDING FROM KLWX SHOWS OVER 2KJ/KG OF MLCAPE THIS AFTERNOON. FORCING MECHANISMS WILL BE WEAK...WITH LITTLE CONVERGENCE ALONG THE BACKDOOR BOUNDARY AND TERRAIN CIRCULATION OVER THE MOUNTAINS. STILL FEEL THAT IT WILL BE ENOUGH FOR SCATTERED THUNDERSTORMS THIS AFTERNOON AND EVENING. DRIER AIR SHOULD BUILD IN BEHIND THE FRONT...CAUSING ANY THUNDERSTORMS TO QUICKLY DISSIPATE EARLY THIS EVENING NEAR WASHINGTON AND BALTIMORE. HOWEVER...A FEW SHOWERS AND THUNDERSTORMS MAY CONTINUE THROUGH MOST OF THE EVENING NEAR AND WEST OF THE BLUE RIDGE MOUNTAINS. THE BACKDOOR BOUNDARY WILL STALL OUT NEAR THE POTOMAC HIGHLANDS INTO CENTRAL VIRGINIA AND SOUTHERN LATE TONIGHT. A FEW SHOWERS ARE POSSIBLE ACROSS THESE AREAS...BUT PRECIPITATION AMOUNTS WILL BE LIGHT DUE TO LIMITED INSTABILITY. ELSEWHERE...DRY CONDITIONS WILL PREVAIL OVERNIGHT BUT LOW CLOUDS ARE EXPECTED AS MOISTURE GETS TRAPPED UNDERNEATH THE SUBSIDENCE INVERSION. && .SHORT TERM /SATURDAY/... HIGH PRESSURE CONTINUES TO MOVE SOUTHWARD SATURDAY AND COOLER DRIER AIR WILL MAKE ITS WAY INTO THE REGION. CLEARING WILL INCREASE FROM N- S AS WELL WITH THE EXCEPTION OF THE SW WHERE THE FRONT MAY STILL BE LOCATED. TEMPS IN THE 70S TO LOW 80S ARE EXPECTED SATURDAY. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... SFC HIGH PRES OVER THE NORTHEAST WILL KEEP A DRY ENE FLOW AND COMFORTABLE TEMPS THROUGH MON. SFC HIGH WEAKENS MORE RAPIDLY MON THROUGH THE END OF NEXT WEEK WHILE MID-UPPER LEVEL HEIGHTS RISE OVER THE MID ATLC RESULTING IN A WARMING TREND. IS NOT REALLY UNTIL WED WHEN SFC HIGH WEAKENS ENOUGH TO ALLOW MOISTURE RETURN INTO THE AREA. WILL KEEP FCST DRY THROUGH TUE NIGHT THEN BRING CHANCES OF SHOWERS AND T-STORMS WED AFTERNOON WEST OF THE BLUE RIDGE INTO THU FOR THE ENTIRE AREA. GLOBAL MODELS SHOW A SLOW MOVING CDFNT CROSSING THE AREA THU OR THU NIGHT BUT SHOW SIG DIFFERENCES WITH RESPECT TO TIMING AND WHETHER FRONT CLEARS THE ENTIRE AREA OR NOT. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... NORTHERLY WINDS LATE THIS MORNING WILL TURN EASTERLY THIS AFTERNOON. SCATTERED THUNDERSTORMS ARE EXPECTED AND BRIEF PERIODS OF IFR CONDITIONS AND GUSTY WINDS ARE POSSIBLE IN ANY THUNDERSTORMS. THE BEST CHANCE WILL BE DURING THE MID TO LATE AFTERNOON HOURS ACROSS THE EASTERN TERMINALS...BUT THE THUNDERSTORM CHANCES MAY CONTINUE WELL INTO THIS EVENING ACROSS THE WESTERN TERMINALS. MVFR/IFR CIGS ARE LIKELY LATER THIS EVENING AND OVERNIGHT DUE TO THE EASTERLY FLOW. LOW CLOUDS SHOULD BURN OFF SATURDAY MORNING FOR MOST AREAS...BUT THEY MAY HOLD ON INTO THE AFTERNOON ACROSS KCHO. MORE LOW CLOUDS ARE POSSIBLE OVERNIGHT SATURDAY INTO SUNDAY. NO AVIATION CONCERNS EARLY NEXT WEEK. && .MARINE... N WINDS BECOME EASTERLY TODAY. WINDS WILL INCREASE THIS EVENING BEHIND A BACKDOOR COLD FRONT AND SCA CONDITIONS ARE EXPECTED TONIGHT AND INTO SATURDAY. THE PRESSURE GRADIENT WILL BE FAVORABLE FOR GUSTY WINDS ON THE BAY THROUGH SATURDAY. CONFIDENCE IS LOWER ACROSS THE UPPER TIDAL POTOMAC AS IT IS CLOSER TO THE CENTER OF THE HIGH. SCA MAY LINGER OVER THE MIDDLE AND LOWER BAY INTO THE FIRS PART OF SUN. && .TIDES/COASTAL FLOODING... ANOMALIES REMAIN ABOUT HALF FOOT ABOVE NORMAL AS LIGHT NORTHEASTERLY FLOW OCCURS ON THE WATERS. THE FLOW WILL TURN TO THE EAST THIS AFTERNOON BUT IT SHOULD BE LIGHT ENOUGH TO KEEP WATER LEVELS BELOW FLOODING THRESHOLDS. THE EASTERLY FLOW WILL STRENGTHEN TONIGHT INTO SATURDAY. MINOR TIDAL FLOODING IS POSSIBLE NEAR TIME OF HIGH TIDE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 2 PM EDT SATURDAY FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 2 PM EDT SATURDAY FOR ANZ535-536. && $$ SYNOPSIS...LFR NEAR TERM...BJL/HAS SHORT TERM...HAS LONG TERM...LFR AVIATION...BJL/HAS/LFR MARINE...BJL/HAS/LFR TIDES/COASTAL FLOODING...BJL/HAS

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