Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 020757 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 357 AM EDT THU OCT 2 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TONIGHT. A STRONG COLD FRONT WILL APPROACH THE AREA FRIDAY BEFORE PASSING THROUGH FRIDAY NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL RETURN FOR THE WEEKEND...BRINGING DRIER AND NOTICEABLY COOLER CONDITIONS. THE HIGH WILL MOVE OFFSHORE EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A RELATIVE REPRIEVE TODAY IN BETWEEN LOW PRESSURE SYSTEMS...W/ IN-SITU HIGH PRESSURE BUILDING BRIEFLY ACROSS THE REGION - AHEAD OF THE NEXT FRONTAL PASSAGE. THE HIGH IS CENTERED WELL OFF TO THE NORTH AND EAST...ACROSS NEW ENGLAND...SQUEEZING DOWN THE LEE OF THE APLCNS BEHIND A SLOWLY EXITING CUT-OFF UPPER LOW. THIS LOW WILL CONTINUE TO SWING BACK A COUPLE OF WAVES OF LOW LEVEL MOISTURE...LOCKING-IN THE DECENT AMOUNT OF BOUNDARY LAYER MOISTURE CAUGHT UNDERNEATH A LARGE DRY LAYER FURTHER UP. AN AXIS OF MOISTURE CONVERGENCE IS CENTERED ROUGHLY ACROSS THE SHEN VLY...CROSSING THE BLUE RIDGE DOWN TOWARD S CNTRL VA. CLOUDS ARE CONTINUING TO DEVELOP AS MOISTURE BANKS INTO EITHER SIDE OF THIS AXIS. EARLIER CLEAR SKIES OVER THE DC/BALT METRO ARE STARTING TO FILL-IN AS THE MTNS CLOUDS ARE MEETING UP W/ COASTAL STRATUS MOVING IN FROM THE NE. THE TRAPPED MOISTURE LOW LEVEL MOISTURE...AS IN THE PAST FEW DAYS...WILL GIVE THE AREA ANOTHER ROUND OF DENSE CLOUD COVER INTO THE MID-MRNG HRS. TOWARD THE EARLY AFTN HOWEVER...MIXING OF THE BOUNDARY LAYER FROM AN UPPER RIDGE AXIS PASSING OVERHEAD WILL PROMOTE SOME CLEARING AND DISSIPATE MUCH OF THE EARLIER STRATUS. WE WILL AGAIN SEE TEMPS CLIMBING INTO THE MID AND EVEN SOME UPPER 70S BY MID-AFTN - SLIGHTLY ABOVE NORMAL. ADD DEWPOINTS IN THE L60S AND THERE WILL BE A SLIGHT HUMID FEEL TO THE AIR...RELATIVE TO THE TIME OF YEAR. ANOTHER MODERATED OVERNIGHT PERIOD AGAIN TONIGHT...W/ TEMPS HOVERING IN THE 60S FOR MUCH OF THE NIGHT AND DEWPOINTS NOT FAR BEHIND. MORE LOW CLOUDS...STRATUS...PATCHY FOG AND SOME DRIZZLE POSSIBLE ACROSS PARTS OF THE REGION HEADING INTO EARLY FRI.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
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A VIGOROUS...POTENT...AND LARGE-SCALE LOW PRESSURE SYSTEM WILL BE INTENSIFYING FROM LATE THU INTO FRI - OVER A GOOD HALF OF THE CONUS. THIS WILL BE TAKING PLACE FROM THE PLAINS UP TO THE WINDWARD SIDE OF THE APLCNS. MUCH OF THE PRECIP AND THE STRONGEST PART OF THE STORM SYSTEM WILL BE MAKING ITS MARK ON THE UPPER MIDWEST AND GREAT LAKES REGION LATE THU NIGHT INTO THE AFTN HRS ON FRI...JUST BEFORE REACHING THE SPINE OF THE APLCNS. WHILE ALL THIS ACTIVITY IS HAPPENING A TIER OF STATES TO THE WEST...WE`LL STILL BE UNDER THE INFLUENCE OF HIGH-LEVELS OF MOISTURE CONTENT IN THE LOWEST FEW THOUSAND FEET. MORE CLOUDS...HUMIDITY...FOG AND SOME DRIZZLE TO START THE DAY. HEADING INTO THE LATE MRNG HRS HOWEVER...THE BOUNDARY LAYER CONDITIONS WILL BEGIN TO CHANGE RAPIDLY. LOW LEVEL WINDS WILL BEGIN TO INCREASE...GRADUALLY MIXING OUT THE DENSE STRATUS DECK AND STRENGTHENING SFC WINDS OUT OF THE S-SE. TEMPS WILL ALSO BE ON THE INCREASE FROM THE INFLUX OF WARMER AIR FROM THE SRN ATLC. THESE CONDITIONS WILL ADD SOME WEAK INSTABILITY TO THE AIR...SETTING UP FOR THE EVENTUAL COLD FRONTAL PASSAGE LATER INTO THE OVERNIGHT HRS. THE FRONT HOWEVER...IS NOT EXPECTED TO ARRIVE DURING THE WARMEST PERIOD OF THE DAY. INSTEAD...THE OVERNIGHT PASSAGE MAY NOT BE ABLE TO MAXIMIZE THE INSTABILITY AND WILL HAVE TO RELY ON SHEAR AND A DRIVER FOR ANY POTENTIAL CONVECTIVE ELEMENTS AND ONGOING BATCHES OF INCOMING PRECIP. A STRONG COLD FRONT WILL PASS THROUGH THE AREA FRIDAY NIGHT. A SOUTHERLY FLOW AHEAD OF THE COLD FRONT WILL USHER IN PLENTY OF MOISTURE ACROSS OUR REGION. THE MOISTURE ALONG WITH FORCING FROM THE FRONTAL PASSAGE WILL CAUSE SHOWERS ALONG AND AHEAD OF THE FRONT. THE BEST CHANCE FOR SHOWERS WILL BE FRIDAY EVENING ACROSS THE ALLEGHENY AND POTOMAC HIGHLANDS...LATE FRIDAY EVENING INTO THE OVERNIGHT HOURS FOR THE SHENANDOAH VALLEY...AND DURING THE OVERNIGHT HOURS FOR THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS INTO SOUTHERN MARYLAND. THE SYNOPTIC PATTERN CONTINUES TO SUGGEST THAT A QLCS WOULD DEVELOP DUE TO THE STRONG FORCING FROM THIS SYSTEM...BUT INSTABILITY LOOKS TO BE WEAK AND IT WILL BE MOVING THROUGH AT AN UNFAVORABLE. THERE WILL BE STRONG WINDS ALOFT FROM THE LOW-LEVEL JET THAT COULD MIX DOWN...BUT WITH LITTLE TO NO INSTABILITY IT APPEARS THAT THE THREAT FOR SEVERE WEATHER IS MINIMAL. MIN TEMPS WILL RANGE FROM THE 40S IN THE POTOMAC HIGHLANDS WHERE COLDER AIR WILL FILTER IN BEHIND THE COLD FRONT...TO THE LOWER AND MIDDLE 60S IN WASHINGTON/BALTIMORE INTO LOWER SOUTHERN MARYLAND.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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THE COLD FRONT WILL MOVE OFF TO OUR EAST SATURDAY MORNING. A FEW SHOWERS MAY HANG AROUND ACROSS EASTERN AREAS EARLY...BUT NOTICEABLY COOLER AND DRIER AIR WILL FILTER INTO ALL AREAS BEHIND THE FRONT LATER SATURDAY MORNING AND AFTERNOON. HIGH PRESSURE WILL BUILD OVER THE REGION SATURDAY NIGHT INTO SUNDAY...BRINGING MORE DRY AND COOL CONDITIONS. IN FACT...IT WILL TURN OUT QUITE CHILLY ACROSS THE ALLEGHENY HIGHLANDS WHERE A FEW LOCATIONS MAY DIP BELOW FREEZING OVERNIGHT SATURDAY ALONG THE RIDGE TOPS. THE HIGH WILL MOVE OFF THE COAST EARLY NEXT WEEK AND A LONGWAVE UPPER-LEVEL TROUGH WILL DEVELOP OVER THE CENTRAL CONUS DURING THIS TIME. A SOUTHERLY FLOW WILL CAUSE MILDER CONDITIONS. A WEAK COLD FRONT MAY MOVE THROUGH DURING THE MIDDLE PORTION OF NEXT WEEK. LITTLE IMPACT IS EXPECTED WITH THIS SYSTEM...BUT A COUPLE SHOWERS CANNOT BE RULED OUT.
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&& .AVIATION /07Z THURSDAY THROUGH MONDAY/...
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THE APLCNS TO THE BLUE RIDGE CONTINUE TO BE THE FOCAL ZONE OF TRAPPED LOW LEVEL MOISTURE...WHICH IS HELPING TO CREATE A WIDE ARRAY OF LOW CLOUDS AND FOG. MOST OBS ACROSS THE MID-ATLC ARE SHOWING A HIGHER-END FOG IN THE 2-5SM RANGE...W/ ONLY ISOLATED LOWER VALUES. MORE SITES WILL CONTINUE TO DROP AS SFC CONDITIONS SATURATE BUT IT WILL BE A CHALLENGE TO GET WIDESPREAD DENSE FOG W/ THE VARYING LOW LEVEL WIND PROFILES AND SCT CLOUD DECK HEIGHTS. HIGH PRESSURE WILL EVENTUALLY HELP CLEAR OUT MUCH OF THE DENSE MRNG STRATUS TOWARD THE MID-LATE MRNG HRS...THEN WEAK ONSHORE FLOW WILL AGAIN TAKE OVER THE SFC FLOW. MORE PATCHY FOG AND LOW CLOUDS POSSIBLE AGAIN OVERNIGHT TONIGHT. A COLD FRONT WILL PASS THROUGH THE TERMINALS LATE FRIDAY NIGHT. SHOWERS AND SOUTHERLY WINDS ARE EXPECTED AHEAD OF THE FRONT. MVFR/IFR CIGS ARE ALSO EXPECTED AS MOISTURE CONTINUES TO MOVE IN FROM THE SOUTH. THE WINDS WILL SHIFT TO THE WEST-NORTHWEST EARLY SATURDAY MORNING BEHIND THE FRONT. MUCH DRIER AIR WILL MOVE IN DURING THIS TIME ALLOWING FOR VFR CONDITIONS. VFR CONDITIONS AND GUSTY WEST-NORTHWEST WINDS ARE EXPECTED FOR THE REST OF SATURDAY. HIGH PRESSURE WILL SLOWLY MOVE OFF TO THE EAST SUNDAY AND MONDAY...ALLOWING FOR A SOUTHERLY FLOW TO RETURN. VFR CONDITIONS ARE LIKELY DURING THIS TIME.
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&& .MARINE...
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AN UPPER LOW SLOWLY MOVING OFF THE NEW ENGLAND COAST AND HIGH PRESSURE CENTERED JUST NORTH OF THERE ARE PUMPING IN ELY ONSHORE FLOW OVERNIGHT AND WILL CONTINUE TO THROUGHOUT THE DAY. DRY WX TODAY AND ONLY A LIGHT E-SE ONSHORE FLOW TONIGHT INTO THU...AS A HIGH PRES RIDGE MOVES ACROSS THE AREA INTO EARLY FRI. A STRONG COLD FRONT WILL BE ON THE WAY ON FRIDAY...THOUGH STILL FAIRLY FAR OFF TO THE WEST DURING THE DAYTIME HRS. EVEN STILL...SCA CONDITIONS WILL BECOME MORE PROBABLE LATER IN THE AFTN AS THE FRONT NEARS THE AREA. A COLD FRONT WILL PASS THROUGH THE WATERS LATE FRIDAY NIGHT INTO SATURDAY MORNING. GUSTY SOUTHERLY WINDS ARE EXPECTED AHEAD OF THE FRONT. WINDS WILL SHIFT TO THE WEST-NORTHWEST BEHIND THE FRONT. HIGH PRESSURE WILL BUILD OVERHEAD SATURDAY NIGHT BEFORE SLOWLY MOVING OFF THE COAST SUNDAY AND MONDAY. WINDS WILL SHIFT TO THE SOUTH FOR SUNDAY AND MONDAY. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR PORTIONS OF THE WATERS FRIDAY NIGHT THROUGH MONDAY.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES ARE AROUND ONE FOOT ABOVE NORMAL EARLY THIS MORNING. THIS HAS CAUSED MINOR TIDAL FLOODING NEAR HIGH TIDE. THE TIDAL ANOMALIES SHOULD REMAIN NEARLY STEADY THROUGH TODAY. THE NEXT HIGH TIDE CYCLE THIS AFTERNOON WILL BE THE LOWER OF THE TWO...SO WATER LEVELS SHOULD NOT BE QUITE AS HIGH AS THEY WERE LATE WEDNESDAY NIGHT AND EARLY THIS MORNING. HOWEVER...MINOR TIDAL FLOODING FOR SENSITIVE AREAS IS STILL POSSIBLE NEAR HIGH TIDE THIS AFTERNOON FOR THE WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY ESPECIALLY FROM ANNE ARUNDEL COUNTY THROUGH ST MARYS COUNTY. THE POSITIVE TIDAL ANOMALIES WILL CONTINUE TONIGHT AND THE HIGH TIDE WILL BE THE HIGHER OF THE TWO ASTRONOMICAL NORMS. THEREFORE...MINOR FLOODING IS EXPECTED WITH THIS HIGH TIDE CYCLE. CONFIDENCE IS HIGHEST FROM ANNE ARUNDEL THROUGH ST MARYS COUNTIES SO A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THESE AREAS. HOWEVER...A COASTAL FLOOD ADVISORY MAY STILL BE NEEDED FOR AREAS ALONG THE UPPER TIDAL POTOMAC RIVER AND THE REST OF THE WESTERN SHORE ALONG THE CHESAPEAKE BAY. A SOUTHERLY FLOW WILL INCREASE AHEAD OF A COLD FRONT FRIDAY INTO FRIDAY NIGHT. MINOR TIDAL FLOODING IS LIKELY NEAR HIGH TIDE...WITH THE HIGHEST WATER LEVELS EXPECTED DURING THE HIGH TIDE CYCLE FRIDAY NIGHT INTO EARLY SATURDAY. THE FLOW WILL TURN OFFSHORE BEHIND THE COLD FRONT LATER SATURDAY AND ANOMALIES SHOULD SHARPLY DECREASE.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...COASTAL FLOOD ADVISORY UNTIL 4 AM EDT FRIDAY FOR MDZ014-017- 018. VA...NONE. WV...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL/GMS SHORT TERM...BJL/GMS LONG TERM...BJL AVIATION...BJL/GMS MARINE...BJL/GMS TIDES/COASTAL FLOODING...BJL

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