Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 031340 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 940 AM EDT THU SEP 3 2015 .SYNOPSIS... LOW PRES WILL REMAIN ALONG THE COAST THROUGH TODAY. BACKDOOR CDFNT WILL CROSS THE AREA FRI AFTERNOON AND NIGHT. HIGH PRES WILL BUILD FOR THE LABOR DAY WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... UPPER-LEVEL RIDGING IS EXPECTED TO CONTINUE BETWEEN A DEPARTING SHORTWAVE OFF THE NORTH CAROLINA COAST AND SHORTWAVE ENERGY MOVING INTO THE OHIO VALLEY THIS AFTERNOON. NO CHANGE IN AIRMASS IS EXPECTED TODAY WITH HOT AND HUMID CONDITIONS CONTINUING. TEMPS WILL REACH THE UPPER 80S ALONG AND WEST OF THE BLUE RIDGE TO THE LOW TO MID 90S NEAR THE I-95 CORRIDOR. THE HEAT AND HUMIDITY WILL LEAD TO MORE INSTABILITY TODAY WITH MLCAPE VALUES AROUND 1-2J/KG OF MLCAPE DEVELOPING. THERE IS A LACK OF A STRONG LIFTING MECHANISM TODAY COMPARED TO WEDNESDAY SO CONVECTION IS NOT EXPECTED TO BE AS AS WIDESPREAD. HOWEVER...WITH A LIGHT FLOW IN PLACE THIS IS FAVORABLE FOR TERRAIN CIRCULATION TO ACT AS A WEAKER LIFTING MECHANISM. THE LIFT FROM TERRAIN CIRCULATION SHOULD BE ENOUGH TO TRIGGER ISOLATED TO SCATTERED THUNDERSTORMS ALONG AND WEST OF THE BLUE RIDGE THIS AFTERNOON INTO THIS EVENING. DID ALLOW FOR ISOLATED CONVECTION TOWARD THE WASHINGTON METRO AREA AND SOUTHERN MARYLAND FOR A PERIOD THIS EVENING DUE THE LIGHT NORTHWEST STEERING FLOW. A BACKDOOR BOUNDARY WILL APPROACH THE REGION FROM THE NORTH AND EAST LATE TONIGHT...THIS MAY TRIGGER A COUPLE MORE SHOWERS BUT FORCING WILL BE WEAK AND DUE TO THE UNFAVORABLE TIMING ANY SHOWER COVERAGE SHOULD BE ISOLATED. TEMPS IN THE UPPER 60S TO LOW 70S. PATCHY FOG IS POSSIBLE ESPECIALLY IN AREAS THAT RECEIVE RAIN TODAY. && .SHORT TERM /FRIDAY/... HIGH PRESSURE BUILDS IN FROM THE NORTHEAST FRIDAY AS A BACKDOOR COLD FRONT MOVES INTO N MD FRIDAY MORNING. THIS WILL BRING AN AIRMASS CHANGE FOR THE WEEKEND. THE FRONT WILL SAG SOUTHWARD FRIDAY AND SHOWERS ARE EXPECTED TO FORM FRIDAY MORNING AND INTO THE AFTERNOON. THUNDERSTORMS ARE ALSO POSSIBLE FRIDAY AFTERNOON. EASTERLY FLOW BEHIND THE FRONT WILL LEAD TO ONSHORE FLOW AND SHOWERS AND THUNDERSTORMS MAY INCREASE IN COVERAGE. EASTERN SLOPES SUCH AS THE BLUE RIDGE FOOTHILLS MAY EXPERIENCE RAINFALL ENHANCEMENT DUE TO UPSLOPE CONDITIONS. AT THIS TIME DUE TO RECENT DRY CONDITIONS NO FLOOD THREAT IS IMMINENT HOWEVER THIS WILL NEED TO BE WATCHED CLOSELY. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... BACKDOOR CDFNT WILL BE CROSSING THE AREA FRI NIGHT WITH SCT SHOWERS/T-STORMS ENDING FROM EAST TO WEST LATE FRI NIGHT. LOW CLOUDS ARE EXPECTED TO GET BANK UP AGAINST THE BLUE RIDGE AND APPALACHIANS MTNS ON EASTERLY FLOW. LOW CLOUDS WILL THEN GRADUALY MIX OUT SAT MORNING. HIGH PRES BUILDS FOR THE WEEKEND GIVING WAY TO FAIR WEATHER THROUGH LABOR DAY. HOWEVER...GFS IS SUGGESTING SOME MOISTURE WILL BE ADVECTED FROM THE ATLC INTO THE CHESAPEAKE BAY AS A WEAK LOW PRES (POSSIBLE REMNANT LOW OF ERIKA) LIFTS NORTHEAST. FOR NOW WILL CONTINUE TO KEEP FCST DRY AS THIS SEEMS A LOW PROBABILITY OUTCOME ACCORDING TO GEFS ENSEMBLE DATA. SFC HIGH PRES WEAKENS FURTHER MID NEXT WEEK WHILE MOISTURE GRADUALLY INCREASES INCREASING THE RISK OF SHOWERS AND T-STORMS. TEMPERATURES WILL ALSO BE ON THE RISE THROUGH MID NEXT WEEK WITH 90S MAKING A RETURN. WEAK FRONTAL PASSAGE INDICATED BY GFS AND ECMWF IN THE WED-THU TIME FRAME BUT ENSEMBLES SHOW A HIGH DEGREE OF UNCERTAINTY WITH RESPECT TO TIMING. ALSO...HIGH PRES BUILDING BEHIND FRONT LOOKS PRETTY WEAK SO FRONT MAY NOT GET ENOUGH PUSH TO MAKE IT THROUGH THE AREA. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS EXPECTED THROUGH THIS EVENING. AN ISOLATED THUNDERSTORM CANNOT BE RULED OUT THIS AFTERNOON AND EVENING...BUT MOST OF THE TIME SHOULD BE DRY. ANY THUNDERSTORMS THAT DO DEVELOP WILL CAUSE SUB- VFR VSBYS AND POSSIBLE GUSTY WINDS. A COLD FRONT MOVES FROM NE TO SW FRIDAY. SHRA/VCTS EXPECTED MAINLY IN THE AFTERNOON. SOME TS MAY PRODUCE HEAVY RAIN. LOW CLOUDS EXPECTED FRI NIGHT ALONG AND WEST OF THE BLUE RIDGE FRI NIGHT INTO SAT MORNING WITH IFR CIGS LIKELY AT KCHO. SOME REMNANT SMOKE FROM THE GREAT LKS MAY ALSO BE ADVECTED INTO THE REGION FROM NEW ENGLAND. && .MARINE... HIGH PRESSURE WILL CAUSE LIGHT NORTHWEST WINDS OVER THE WATERS TODAY INTO THIS EVENING. A COLD FRONT WILL MOVE INTO THE WATERS FROM THE NE FRIDAY MORNING. WINDS WILL BECOME NE FROM N TO S ON THE WATERS. WINDS WILL ALSO BEGIN TO GUST NEAR SCA CONDITIONS BY FRIDAY AFTERNOON. A SCA IS POSSIBLE FRIDAY AFTERNOON INTO FRIDAY NIGHT. SCA CONDITIONS APPEAR LIKELY SAT INTO SAT EVENING ESPECIALLY ON THE CHESAPEAKE BAY. SCA POSSIBLE AGAIN ON MONDAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...LFR NEAR TERM...BJL/HAS SHORT TERM...HAS LONG TERM...LFR AVIATION...BJL/HAS/LFR MARINE...BJL/HAS/LFR

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