Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 031858 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 258 PM EDT THU SEP 3 2015 .SYNOPSIS... A WEAK SURFACE TROUGH WILL REMAIN OVERHEAD THROUGH TONIGHT. A BACKDOOR COLD FRONT WILL PASS THROUGH LATE FRIDAY INTO FRIDAY NIGHT. HIGH PRESSURE WILL BUILD OVERHEAD DURING THE LABOR DAY WEEKEND. && .NEAR TERM /THROUGH FRIDAY/... WEAK UPPER-LEVEL RIDGING WILL CONTINUE THROUGH TONIGHT WHILE A SURFACE TROUGH REMAINS OVERHEAD. HOT AND HUMID CONDITIONS WILL CONTINUE THIS AFTERNOON AND IT WILL REMAIN QUITE WARM TONIGHT AS WELL. TERRAIN CIRCULATION HAS BEEN THE PRIMARY LIFTING MECHANISM FOR SCATTERED THUNDERSTORMS NEAR AND WEST OF THE BLUE RIDGE MOUNTAINS THIS AFTERNOON. SCATTERED THUNDERSTORMS WILL CONTINUE INTO THIS EVENING. AN ISOLATED SHOWER/THUNDERSTORM MAY POP UP NEAR THE METRO AREAS AS WELL...BUT COVERAGE SHOULD BE LIMITED DUE TO THE LACK OF A STRONG LIFTING MECHANISM. CONVECTION SHOULD DIMINISH THIS EVENING DUE TO THE LOSS OF DAYTIME HEATING. MAINLY DRY CONDITIONS ARE EXPECTED OVERNIGHT. THERE WILL BE SOME FOG...ESPECIALLY LATE TONIGHT IN SHELTERED VALLEYS AND AREAS THAT RECEIVE RAINFALL THIS AFTERNOON. HIGH PRESSURE WILL BUILD OVER NEW ENGLAND ON FRIDAY AND THIS WILL SEND A BACKDOOR COLD FRONT INTO OUR AREA. AN EASTERLY WIND WILL DEVELOP AND IT WILL NOT BE QUITE AS HOT AS TODAY...BUT STILL SEVERAL DEGREES ABOVE NORMAL. HUMIDITY WILL REMAIN AROUND WITH THE MAIN DEWPOINT AND TEMPERATURE GRADIENT REMAINING OFF TO OUR NORTH AND EAST DURING THE DAY. THE HEAT AND HUMIDITY ALONG WITH THE BOUNDARY WILL CAUSE SCATTERED THUNDERSTORMS TO DEVELOP...MAINLY DURING THE AFTERNOON AND EVENING HOURS. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... THE BACKDOOR BOUNDARY WILL STALL OUT NEAR THE ALLEGHENY AND POTOMAC HIGHLANDS INTO SOUTHERN VIRGINIA FRIDAY NIGHT. CONVECTION SHOULD DISSIPATE BEHIND THE BOUNDARY DUE TO THE LOSS OF DAYTIME HEATING...BUT A FEW SHOWERS MAY CONTINUE NEAR THE BOUNDARY ACROSS THE ALLEGHENY AND POTOMAC HIGHLANDS TOWARD CENTRAL VIRGINIA. THE EASTERLY FLOW WILL CAUSE PLENTY OF CLOUD COVER TO DEVELOP DUE TO MOISTURE OFF THE ATLANTIC OCEAN. DRIER AIR MAY EVENTUALLY SNEAK INTO NORTHEASTERN MARYLAND TOWARD MORNING AS SURFACE HIGH BUILDS FARTHER SOUTH AND WEST. HIGH PRESSURE REMAINS ANCHORED OVER NEW ENGLAND SATURDAY AND SUNDAY. ONSHORE FLOW AND CLOUDS WILL GREATLY LIMIT TEMPERATURES WITH MOST AREAS SATURDAY BELOW NORMAL. MAX TEMPS SATURDAY LOOK TO BE UPR 70S/LOW 80S. THIS IS PARTICULARLY FOR AREAS WEST FROM THE BLUE RIDGE WERE UPSLOPE FLOW SHOULD PRODUCE LIGHT RAIN INTO THE AFTERNOON HOURS. WEAK CYCLONIC FLOW BRINGS SOME CHANCES FOR LIGHT RAIN TO SRN MD SUNDAY...OTW DRY. GREATER SUNSHINE SUNDAY SHOULD BRING MAX TEMPS UP TO THE LOW TO MID 80S. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... HIGH PRESS DOMINATES CONDITIONS FOR SUN NIGHT AND MON BRINGING DRIER CONDITIONS FOR THE END OF THE LABOR DAY WKND. BOTH THE GFS AND ECMWF ARE SUGGESTING A WEAK LOW PRESS SYSTEM WILL DRIFT NORTH OFF THE SOUTHEAST COAST THAT WILL ADVECT MOISTURE FROM THE ATLC INTO OUR REGION MON INTO TUE. THIS COULD BRING SHOWERS AND TSTMS TO OUR REGION... MAINLY TO THE SOUTHEAST OF OUR CWA ON MONDAY AND OVER ALL OF OUR CWA TUE AS THE SYSTEM APPROACHES. HIGH PRESS BUILDS IN ON WED BEFORE A COLD FRONT APPROACHES ON THU INCREASING THE CHANCE OF SHOWERS AND TSTMS. TIMING AND STRENGTH OF THE COLD FRONT IS STILL SOMEWHAT UNCERTAIN. HIGH TEMPS WILL BE IN THE LOW 80S TO THE UPR 90S NEAR THE METRO AREA AND LOW 80S TO OUR WESTERN COUNTIES. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... A SHOWER OR THUNDERSTORM IS POSSIBLE THROUGH EARLY THIS EVENING...BUT COVERAGE WILL REMAIN ISOLATED TO SCATTERED. PATCHY FOG IS POSSIBLE LATE TONIGHT INTO EARLY FRIDAY MORNING. FEEL THE BEST CHANCE FOR FOG WILL BE ACROSS THE WESTERN TERMINALS WITH A LIGHT GRADIENT WIND KEEPING VSBY UP FARTHER EAST. A BACKDOOR COLD FRONT WILL PASS THROUGH THE REGION FRIDAY. AN EASTERLY FLOW IS EXPECTED. SCATTERED THUNDERSTORMS ARE POSSIBLE DURING THE AFTERNOON AND EVENING HOURS. LOW CLOUDS MAY REDUCE CIGS/VSBY TO MVFR AND IFR LEVELS FRIDAY NIGHT DUE TO THE EASTERLY FLOW. ONSHORE FLOW FROM HIGH PRESSURE ANCHORED OVER NEW ENGLAND SATURDAY AND SUNDAY. MVFR CIGS LIFT SATURDAY WITH VFR THEN THROUGH SUNDAY. VFR CONDITIONS EXPECTED SUN NIGHT AND MON. && .MARINE... A NORTH TO NORTHWEST FLOW IS EXPECTED THROUGH TONIGHT...BUT WINDS WILL REMAIN BELOW SCA CRITERIA. AN ISOLATED THUNDERSTORM IS POSSIBLE THIS AFTERNOON THROUGH EARLY THIS EVENING. THUNDERSTORM MAY CONTAIN BRIEF GUSTY WINDS. A BACKDOOR COLD FRONT WILL PASS THROUGH THE WATERS FRIDAY. AN EASTERLY FLOW IS EXPECTED TO DEVELOP. WINDS WILL INCREASE WITH A PRESSURE SURGE FRIDAY EVENING INTO FRIDAY NIGHT. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS DURING THIS TIME. SCATTERED THUNDERSTORMS MAY ALSO PRODUCE BRIEF GUSTY WINDS FRIDAY AFTERNOON AND EVENING. ONSHORE FLOW FROM HIGH PRESSURE ANCHORED OVER NEW ENGLAND SATURDAY AND SUNDAY. SCA FOR MOST WATERS EXPECTED SATURDAY INTO THE EVENING...THEN SOME CHANCES AGAIN SUNDAY WITH MOST WIND CURRENTLY EXPECTED TO BE AOB 15 KT. SUB-SCA CONDITIONS EXPECTED FOR SUN NIGHT INTO MON. SOME SHOWERS AND TSTMS PSBL OVER THE WATERS. && .TIDES/COASTAL FLOODING... A NORTH TO NORTHWEST FLOW HAS WEAKENED OVER THE WATERS AND THIS HAS ALLOWED FOR ANOMALIES TO INCREASE. THE FLOW WILL TURN TO THE EAST FRIDAY BUT IT SHOULD BE LIGHT ENOUGH TO KEEP WATER LEVELS BELOW FLOODING THRESHOLDS. THE EASTERLY FLOW WILL STRENGTHEN FRIDAY NIGHT 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 6 PM FRIDAY TO 6 AM EDT SATURDAY FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY FROM 6 PM FRIDAY TO MIDNIGHT EDT FRIDAY NIGHT FOR ANZ535-536. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BAJ/BJL LONG TERM...IMR AVIATION...BAJ/BJL/IMR MARINE...BAJ/BJL/IMR TIDES/COASTAL FLOODING...BJL

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