Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 030757 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 357 AM EDT THU SEP 3 2015 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A SHORTWAVE TROUGH IS LOCATED ACROSS COASTAL NC THIS MORNING WHILE RIDGING MOVES INTO THE MID- ATLANTIC. HIGH PRESSURE PERSISTS AT THE SURFACE. A WARM AND HUMID AIRMASS CONTINUES ACROSS THE MID-ATLANTIC THIS CLEAR MORNING. DEWPTS ARE IN THE UPPER 60S TO LOW 70S WITH TEMPS WITHIN A FEW DEGREES. ELEVATED INSTABILITY PERSISTS ACROSS MUCH OF THE REGION INCLUDING THE OHIO VALLEY THIS MORNING. A FEW STORMS HAVE FORMED IN OH/W PA AND ARE MOVING SOUTHWARD. THESE STORMS ARE IN A FAVORABLE ENVIRONMENT WITH DECENT INSTABILITY. THE TRACK BRINGS THEM ALONG THE APPALACHIANS SKIRTING THE WESTERN EDGE OF THE CWA THIS MORNING. PATCHY FOG HAS DEVELOPED ACROSS MUCH OF THE AREA THAT RECEIVED RAIN FROM WEDNESDAY. VISIBILITIES HAVE BEEN REDUCED TO LESS THAN A MILE ALONG PORTIONS OF I-81/I-68 AS WELL AS VALLEYS IN THE POTOMAC HIGHLANDS. FOG WILL CONTINUE THROUGH SUNRISE. NO CHANGE IN AIRMASS IS EXPECTED TODAY AND WARM AND HUMID CONDITIONS WILL CONTINUE. TEMPS WILL REACH THE UPPER 80S ALONG AND WEST OF THE BLUE RIDGE TO THE LOW TO MID 90S NEAR THE I-95 CORRIDOR. A DISTURBANCE WILL MOVE INTO THE OHIO VALLEY TODAY. INSTABILITY WILL BE PRESENT AGAIN TODAY WITH MLCAPE VALUES REACHING 1-1.5 J/KG EVEN TOUCHING 2K IN SOME SPOTS. AN UPPER LEVEL RIDGE WILL KEEP THE WIND FLOW WEAK BUT THUNDERSTORMS ARE STILL EXPECTED TO FORM THIS AFTERNOON. COVERAGE WILL LIKELY BE MORE WIDESPREAD ACROSS THE OHIO VALLEY NEAR THE BETTER FORCING BUT STORMS SHOULD START TO PULSE ALONG THE HIGHER ELEVATIONS WEST OF THE BLUE RIDGE THIS AFTERNOON. STORMS SHOULD BE SLOW MOVING AND PRODUCE LOCALLY HEAVY RAIN. OTHER THAN SCATTERED SPOTS THAT SAW HEAVY RAIN WEDNESDAY...THE REGION SHOULD BE ABLE TO WITHSTAND THE HEAVY RAIN. LOCALIZED URBAN FLOODING CAN NOT BE RULED OUT BUT CHANCE IS LOW. FCST SOUNDINGS DEPICT DRY AIR IN THE MID-LEVELS THIS AFTERNOON AND THIS MAY CAUSE STRONG WINDS. AN ISOLATED SVR STORM CAN NOT BE RULED OUT TODAY MAINLY WEST OF THE BLUE RIDGE. ACTIVITY WILL MOVE EASTWARD INTO THE EVENING. ELEVATED INSTABILITY WILL STILL BE PRESENT TONIGHT AND SHOWERS AND THUNDERSTORMS CAN NOT BE RULED OUT. TEMPS IN THE UPPER 60S TO LOW 70S. PATCHY FOG IS POSSIBLE ESPECIALLY IN AREAS THAT RECEIVE RAIN TODAY.
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&& .SHORT TERM /FRIDAY/...
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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.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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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.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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SUB-VFR POSSIBLE AT CHO-MRB DUE TO PATCHY FOG THIS MORNING. SHRA/VCTS POSSIBLE THIS AFTERNOON BUT CHANCE OF IT REACHING THE TERMINALS IS LOW AT THIS TIME. BEST CHANCE WILL BE 18-00Z AT MRB- CHO. SHRA MAY MOVE EASTWARD INTO IAD-DCA THIS EVENING. SOME THUNDERSTORMS MAY CAUSE SUB-VFR VSBYS AND 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.
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&& .MARINE...
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W-NW 5-10KTS ON THE WATERS THIS MORNING. HIGH PRESSURE IN CONTROL TODAY. A FEW SHOWERS MAY PULSE UP 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.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...LFR NEAR TERM...HAS SHORT TERM...HAS LONG TERM...LFR AVIATION...HAS/LFR MARINE...HAS/LFR

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