Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 310531 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 131 AM EDT SUN AUG 31 2014 .SYNOPSIS... HIGH PRESSURE OFF CAPE COD WILL MOVE SOUTHEAST AND BECOME A BERMUDA HIGH THROUGH TUESDAY. A COLD FRONT WILL CROSS THE AREA TUESDAY NIGHT. HIGH PRESSURE WILL FOLLOW FOR THE SECOND HALF OF THE WEEK. && .NEAR TERM /THROUGH TODAY/...
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UPDATE...CANCELLED SCA FOR THE LOWER MAIN STEM ZONES OF THE MD BAY. PREV DISC... SKIES WILL BE PARTLY TO MOSTLY CLOUDY TONIGHT AS MID AND HIGH CLOUDS FROM THE CONVECTION OVER THE TN VALLEY CONTINUES TO STREAM TO THE NORTHEAST. WITH HIGH DEWPOINTS...WILL SEE AREAS OF FOG DEVELOPING...PREDOMINANTLY IN SHELTERED LOCATIONS WHERE LIGHT SOUTHERLY WINDS WILL NOT BE ABLE TO MIX THE BOUNDARY LAYER. AT 01Z...ALREADY SEEING LOW SFC TEMP/DWPT SPREADS AT STAFFORD AND WARRENTON AND MIST FORMING. BOTH MET AND MAV GUIDANCE SHOWS VSBYS LOWERING OVERNIGHT. SUNDAY WILL START OUT WITH LINGERING PATCHY FOG THROUGH MID MORNING...THEN REMAIN MOSTLY CLOUDY. THE 18Z GFS HAS A STREAK OF PRECIP WATER GREAT THAN 2.25" ACROSS OUR CWA AS A POTENT H5 VORT TRACKS FROM SW. THIS WILL LEAD TO NUMEROUS SHRA/TSTMS DEVELOPING BY MID AFTERNOON AND LASTING THROUGH MIDNIGHT. SOME OF THESE STORMS WILL HAVE THE POTENTIAL TO PRODUCE HEAVY RAINFALL...BUT THERE IS DECENT 20-30 KTS IN THE CLOUD BEARING LAYER WHICH WILL KEEP THE STORMS PROGRESSIVE.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY/... CWFA WL BE W/IN SWLY FLOW FOR THE FRIST PARTS OF THE WK. HWVR THE FLOW WL BECOME A BIT MORE WLY MON...AND SPCLY TUE. THE PLUME OF MSTR EVIDENT ON WATER VAPOR IMGRY WL BE RUNNING ATOP THE RDG. LTST GDNC SUGGESTING THAT THE SETUP WONT BE QUITE AS IDEAL AS PRVS CYCLES. THATS NOT TO SAY THERE WONT BE A MOIST/UNSTBL AMS. BUT THTE RDG/ADVTN AS WELL AS PVA DURING THE AFTN WL BE BETTER IN THE MTNS AND PTS WEST. STILL WL HV A CORRIDOR OF PWAT AOA 2 INCHES...BUT THERE/S NOT AS MUCH TO ORGANIZE/FORCE THE PCPN. AND IN THE SERN CWFA...RDGG WL ACTUALLY SURPRESS IT. HV THEREFORE BACKED OFF ON POPS SUN...STILL FOCUSING ON THE AFTN-EVE HRS. LKLY POPS WONT APPEAR TIL EVNG...WHEN LIFT ARRIVES. NOCTURNAL STABILITY WL ALLOW PVA TO SNEAK THRU OVNGT. AM FCSTG A GOOD DEAL OF CLDCVR SUN...WHICH SHUD ONCE AGN IMPEDE STRONG WARMING. HV SHADED DOWN MAXT A DEGF OR TWO. WHILE THERE WL BE A SHARP LEE TROF MON...ALL OTHER FEATURES APPEAR TO BE EITHER WEAK OR SUBTLE. WLY FLOW WL PROVIDE A LTL BIT OF DRYING...WHICH IS EVIDENT IN PROGGED PWAT VALUES. THE IMPACT IS EVIDENT IN POP VALUES...WHICH ARE LWR THAN SUN. THAT SEEMS QUITE RESONABLE. AM GNLY IN THE 30-40 PCT RANGE...AND AM KEEPING A DRY FCST IN CENTRL VA. WHATEVER TSRA THAT DO DVLP SHUD MV TO THE ERN SHORE BY NIGHTFALL...AND HV A DRY FCST FOR MON NGT-- WHICH LARGELY WL CONT INTO TUE DUE TO DOWNSLOPING. THINK THAT THE BEST CHC AT A 90 DEG DAY WL COME ON TUE...AS WLY FLOW WL KEEP POPS LOW AND PROVIDE COMPRESSIONAL WARMING. HV LWRD MON MAXT BY A CPL...AND RAISED TUE MAXT ALSO BY A CPL. MIN-T FCSTS ON TRACK...IN STEP W/ PROGGED DEWPTS. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... 500MB SHORTWAVE WILL TRACK FROM THE GREAT LAKES TO SOUTHERN QUEBEC AND DRAG A WEAK TROUGH THROUGH THE CWA TUESDAY NIGHT THROUGH WEDNESDAY. 500MB HIGH WILL BUILD OVER MID ATLANTIC REGION WEDNESDAY THROUGH THURSDAY. THE HIGH WILL WEAKEN ALLOWING A COLD FRONT TO ENTER NORTHWEST PA BY SATURDAY NIGHT. BAND OF MOISTURE...PVA...AND PASSAGE OF THE COLD FRONT WILL SUPPORT A SLIGHT CHANCE DEVELOPMENT OF SHOWERS/THUNDERSTORMS TUESDAY NIGHT THROUGH WEDNESDAY MORNING. MUCH DRIER AIRMASS ASSOCIATED WITH SURFACE HIGH WILL CROSS THE CWA LATER WEDNESDAY THROUGH EARLY FRIDAY. INCREASING MOISTURE DUE TO THE RETURN SOUTH TO SOUTHWEST FLOW ASSOCIATED WITH THE HIGH AND PVA OUT AHEAD OF AN APPROACHING COLD FRONT FROM THE WEST WILL SUPPORT AN INCREASED CHANCE OF MORE SHOWERS AND THUNDERSTORMS SATURDAY. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... SLY FLOW WL PROVIDE INCREASING LOW LVL HUMIDITY. THEREFORE... OVERNIGHT FOG SHUD BE AN ISSUE. FLLWG CLIMO BY KEEPING DCA AT VFR. OTRW...HV MVRG VSBYS ACRS THE BOARD PRE-DAWN. IFR A PSBLTY...BUT THINK THERE WL BE TOO MUCH HIER LVL CLDCVR FOR THICKER FOG TO DVLP. ONCE MRNG RESTRICTIONS CLR...ATM WL BE UNSTBL FOR SCT TSRA TO DVLP. CUD HV LCL IFR IN HVR RAINERS...BUT LOW CONFIDENCE IN A SPOT FCST PRECLUDE A TAF INCLUSION. OUTLOOK...SUNDAY NIGHT SHOULD SEE MVFR FOG RETURN AFTER RAINFALL...THEN MON TARGETED IFR POSSIBLE AT TIMES WITH SCT TSRA. CVRG SHUD BE LESS THAN SUN. TUE-THU...PRIMARILY VFR. && .MARINE...
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SLY FLOW ACRS THE MARINE AREA THRU THE WKND. MARINE OBS IN THE LOW-MID TEEN GUSTS. IT/LL BE A SIMLR SITUATION SUNDAY...THO DONT THINK THE MIXING WL BE QUITE AS GOOD. IN ADDITION...POTL TSRA WUD PROVIDE STRONGER WIND GUSTS. OFFSHORE HIGH PRES WILL CONTINUE TO STEER WARM/HUMID AIR UP ACROSS THE ERN SEABOARD. SETUP WUD SUPPORT PDS OF SLY CHANNELING...BUT GDNC NOT PICKING UP ON ANY JUST YET. WK CDFNT LT TUE/ELY WED... MARKED BY A SLGT SHIFT IN WIND DIRECTION FM SW TO NW.
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&& .TIDES/COASTAL FLOODING...
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DEPARTURES AT ANNAPOLIS ARE ABOUT 0.9 FEET...AND WINDS SHOULD REMAIN SLY...SO ANTICIPATE ADDTL INCREASES THROUGH THE WKND. THE NEXT HIGH TIDE SUN MRNG WL NEED TO BE WATCHED FOR POSSIBLE MINOR FLOODING. NONETHELESS...THIS WL BE AN ISSUE THROUGH THE WKND WITH NEW MOON AND SOUTHERLIES.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE.
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&& $$ UPDATE...GMS PREV DISCUSSION...LEE/HTS/CEM

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