Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 040229 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1029 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/... WEAKENING TSTMS WEST OF THE BLUE RIDGE AS OF 0030Z. SBCAPE VALUES DCRSNG WITH LOSS OF DAYTIME HEATING...THOUGH MUCAPE STILL WELL ABV 2K J/KG. WEAK SFC TROUGH HAS NUDGED EAST OF THE AREA...SO NO REAL SFC MECHANISM TO TRIGGER ANY FURTHER DEVELOPMENT...AT LEAST OVER WESTERN AREAS. WEAK VORT MAX OVER EASTERN PA COULD DIP OVER EASTERN MD OVERNIGHT...WITH PSBL SHOWERS FORMING. ANY PCPN THAT DOES FORM WILL TAPER OFF LATE...WITH DRY CONDITIONS BY DAYBREAK. INCREASED LOW LVL MOISTURE ESP OVER THE VALLEYS OF SHENANDOAH AND LIGHT WINDS COULD LEAD TO PATCHY FOG. 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 /03Z FRIDAY THROUGH TUESDAY/... OUTSIDE OF FOG DEVELOPMENT TONIGHT...GENERALLY VFR CONDITIONS THRU THE TAF PERIOD. PSBL FOG AT KCHO/KMRB...REDUCING VIS 2-4 MILES. ANY FOG THAT FORMS WILL DISSIPATE 13-15Z. DRY CONDITIONS FRI MORNING...WITH SCT TSTMS BY THE AFTN...ESP KCHO/KMRB. TIMING AND LOCATION OF AFTN CONVECTION TOO LOW IN CONFIDENCE TO INCLUDE IN TAFS ATTM. ANY TSTM COULD BRING SUB-VFR CONDITIONS WITH HEAVY RAINS AND GUSTY WINDS. LIGHT/VRB WINDS TONIGHT WILL BECOME ELY BY FRI AFTN. THE ELY FLOW WILL AIDE IN LOWERING CIGS FOR FRI NIGHT. 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... SUB-SCA CONDITIONS TONIGHT THRU FRI MORNING. AN EASTERLY FLOW IS EXPECTED TO DEVELOP BEHIND A BACKDOOR COLD FRONT FRI AFTN. WINDS WILL INCREASE WITH A PRESSURE SURGE FRIDAY EVENING INTO FRIDAY NIGHT. A SMALL CRAFT ADVISORY REMAINS 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. && .CLIMATE... WELL ABOVE NORMAL TEMPERATURES ARE FORECAST TO PERSIST ACROSS THE AREA THROUGH FRIDAY. AS A RESULT...SOME SITES MAY APPROACH RECORD DAILY HIGH MINIMUM TEMPERATURES DURING THE NEXT 24 HOURS. BELOW IS A TABLE OF RECORD DAILY HIGH MINIMUM TEMPERATURES FOR SEPTEMBER 4TH. SITE.....RECORD MAX MIN FOR SEP 4................ DCA...76 (SET IN 2012 AND 1953).................. BWI...75 (SET IN 2012/1953/1944/1937 AND 1932)... IAD...71 (SET IN 2012)........................... && .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/SEARS SHORT TERM...BAJ/BJL LONG TERM...IMR AVIATION...BAJ/BJL/SEARS/IMR MARINE...BAJ/BJL/SEARS/IMR TIDES/COASTAL FLOODING...BAJ/BJL CLIMATE...DFH

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