Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220759 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 359 AM EDT MON SEP 22 2014 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD OVER THE AREA EARLY THIS WEEK. A CUT OFF UPPER LEVEL LOW PRESSURE SYSTEM WILL SETTLE NEAR THE SOUTHERN ATLANTIC COAST INTO MID-WEEK...POSSIBLY DRIFTING UP THE COAST AND INTO THE AREA TOWARD THE LATTER HALF OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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NOW WELL INTO THE POST-FRONTAL REGIME...WE`RE RECEIVING A TRUE COLD AIR SURGE BEHIND IT. THE 3AM TEMP AT IAD WAS 64...DCA 72. DEWPOINTS HAVE ALREADY DROPPED A SUBSTANTIAL 10-15F DEG - EVEN LOWER IN SOME AREAS - FROM THE AFTN LEVELS. AFTER POKING INTO THE MIDDLE-UPPER 80S YESTERDAY AFTN FOR HIGHS...TEMPS ARE STEADILY DROPPING DOWN INTO THE 60S - EXPECTED TO BOTTOM-OUT IN THE U50S BY DAWN. GUSTY NW WINDS BRINGING IN THIS SURGE OF COOLER/DRIER AIR... AS WELL AS CLEARING OUT THE RESIDUAL MID-LEVEL STRATUS FROM THE FRONTAL BAND. DENSE LOWER STRATUS NOW PULLING INTO THE APLCNS FROM THE OHIO VLY...PART OF THE DEEP UPPER TROUGH ROUNDING THE GREAT LAKES ATTM. MUCH OF THIS CLOUD DECK WILL DISSIPATE OFF BEFORE REACHING THE METRO AREAS/I-95 CORRIDOR...THOUGH PART OF IT WILL SCRAPE THE MASON-DIXON LINE AS THE TROUGH AXIS PASSES OVERHEAD. THIS AXIS IS CURRENTLY EXITING THE POTOMAC HIGHLANDS...MOVING ACROSS THE NRN SHEN VLY. A BULK OF THE ENERGY W/ THIS SYSTEM IS ALREADY WELL TO OUR NORTH AND TAKING OFF TOWARD THE NE...BUT ANOTHER STRAGGLER PIECE OF THE UPPER WAVE WILL CONTINUE TO DIG DOWN TO OUR SW AND SWING ACROSS THE SRN APLCNS TODAY. THIS WILL HELP KEEP OUR AREA UNDER THE COOLER AIRMASS FOR A BIT LONGER AND ALLOW HIGHS TODAY TO BARELY CRACK 70F...THE HIGHEST VALUES WILL BE ALONG AND E OF I-95. A MUCH SMALLER DIURNAL TEMP DIFFERENCE ACROSS THE MTNS...UNDER THE SHELTERING DENSE STRATUS - THEIR LOWS TO START THE DAY WILL BE IN THE L50S HIGHS WILL JUST REACH THE L60S THIS AFTN...STILL UNDER BROKEN SKY COVER. WINDS WILL REMAIN GUSTY THROUGHOUT THE DAYTIME HRS...GIVING THE AREA SOMEWHAT OF A CHILL TO THE AIR - TO KICK OFF THE FIRST DAY OF AUTUMN.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
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THE LEFTOVER PIECE OF UPPER ENERGY SLIDING DOWN TOWARD THE CAROLINAS IS EXPECTED TO ESSENTIALLY BREAK FROM THE PARENT UPPER TROUGH LATER TODAY/TONIGHT. THIS MAY EVENTUALLY BECOME A WX-MAKER FOR OUR AREA AND OVER TO THE COASTAL AREAS LATER IN THE WEEK. UNTIL THEN...THE LARGE CANADIAN AIRMASS GOVERNED BY HIGH PRESSURE WILL BUILD OVER MUCH OF THE REGION FOR THE EARLY PART OF THE WEEK. DEWPOINTS TONIGHT WILL DROP AND BOTTOM-OUT IN THE L40S ACROSS MUCH OF THE AREA...W/ 30S SPREADING ACROSS THE HIGHER TERRAIN. UNDER GENERALLY CLEAR SKIES OVERNIGHT...THIS WILL ALLOW OUR LOW TEMPS TO MAKE A SIMILAR DROP. STILL W/ SOME NEAR-COASTAL MOISTURE EFFECTS...THE I-95 CORRIDOR WILL REMAIN IN THE U40S/L50S TAPERING DOWN INTO THE L-M40S FOR THE REMAINDER OF THE AREA. USED A BLEND OF THE BIAS-CORRECTED GFS AND MOS/WRFARW. TUESDAY...CONDITIONS WILL BE EVEN MORE PLEASANT AS WINDS DROP OFF WHILE HIGH PRESSURE SETTLES IN. CLEAR SKIES AND TEMPS BARELY ABOVE 70F W/ A LIGHT NLY BREEZE...WHILE THE JET STREAM RETREATS BRIEFLY TO THE NORTH AND A CUT-OFF UPPER LOW HANGS OUT OFF THE CAROLINA COAST.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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HIGH PRESSURE WILL BE CENTERED OVER NORTHERN NEW ENGLAND AND WILL KEEP THE MIDDLE ATLANTIC IN A WEDGE OF COOLER AIR WITH ONSHORE FLOW WEDNESDAY INTO THURSDAY. AS THE HIGH WEAKENS AND BECOMES MORE ELONGATED...THERE IS SOME POTENTIAL FOR AN UPPER LEVEL CUTOFF LOW/TROUGH TO SWING OFF THE SOUTHEAST U.S COAST AND AID IN THE DEVELOPMENT OF A WEAK SURFACE LOW OFF THE CAROLINAS THURSDAY INTO FRIDAY. THERE IS MUCH UNCERTAINTY BETWEEN THE GFS WHICH KEEPS THE HIGH A BIT STRONGER AND SUPPRESSES MOISTURE TO THE SOUTH AND THE ECMWF WHICH IS WEAKER WITH THE HIGH AND FURTHER NORTH WITH THE MOISTURE. THE NORTHWARD EXTENT OF THE RAINFALL WILL BE DEPENDENT ON HOW STRONG THE HIGH IS AND ITS PLACEMENT. ATTM...CONTINUED TO SIDE TOWARD THE GFS AND KEPT CHANCE POPS RELEGATED TO THE SOUTHERN PORTION OF THE LWX CWFA. CLOUD COVER AND ONSHORE WIND COMPONENT WILL KEEP HIGHS GENERALLY IN THE 70S WITH LOWS IN THE 40S AND 50S. HIGH PRESSURE IS PROGGED TO RESTRENGTHEN FRIDAY THROUGH SUNDAY WITH PLEASANT CONDITIONS EXPECTED ACROSS THE REGION. TEMPERATURES NEXT WEEKEND MAY CLIMB BACK INTO THE UPPER 70S TO NEAR 80 DEGREES FOR THE FIRST WEEKEND OF FALL.
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&& .AVIATION /07Z MONDAY THROUGH FRIDAY/...
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AN UPPER LEVEL TROUGH IS PASSING OVERHEAD...CARRYING GUSTY WINDS - A VERY FALL-LIKE SYSTEM W/ DRY AND COOL NW WINDS OF 15-25KT STEADY. EVEN W/ BRIEF LULLS IN THE WIND FIELD...THESE GUSTS WILL CONTINUE ALL-DAY AND THEN QUICKLY DROP OFF AFTER SUNSET TONIGHT. VFR CONDS OTHERWISE INTO TUE. MAINLY VFR CONDITIONS EXPECTED WEDNESDAY INTO THURSDAY. THERE IS SOME POTENTIAL FOR LOWER CEILINGS AND SOME LIGHT RAIN OR SHOWERS THURSDAY INTO FRIDAY ESPECIALLY FROM KBWI TO KDCA TO KCHO AND POINTS SOUTH. VFR CONDITIONS ARE EXPECTED OVER THE WEEKEND.
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&& .MARINE...
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SOLID SCA GUSTS SPREADING ACROSS THE WATERS. THE LAND AREAS TO THE WEST STAYING IN THE 15-25KT RANGE AND SO WILL THE WATERS THRU THE DAYTIME AREAS TODAY. A PERSISTENT ONSHORE FLOW WILL DEVELOP LATER WEDNESDAY AND PERSIST INTO THURSDAY OR FRIDAY. SMALL CRAFT CONDITIONS MAY BE POSSIBLE FOR A PORTION OF THE WATERS DURING THIS TIME FRAME. WINDS WILL REMAIN BELOW SCA LEVELS AS HIGH PRESSURE BUILDS OVER THE MIDDLE ATLANTIC NEXT WEEKEND.
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&& .TIDES/COASTAL FLOODING...
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A PERSISTENT ONSHORE FLOW IS EXPECTED TO DEVELOP BY MIDWEEK. THIS WILL LEAD TO HIGHER THAN NORMAL WATER LEVELS PARTICULARLY OVER THE WESTERN SHORE OF THE CHESAPEAKE BAY. MINOR TIDAL INUNDATION WILL BE POSSIBLE DURING THE TIMES OF HIGH TIDE.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ530>543.
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&& $$ SYNOPSIS...GMS NEAR TERM...GMS SHORT TERM...GMS LONG TERM...KRW AVIATION...GMS/KRW MARINE...GMS/KRW TIDES/COASTAL FLOODING...KRW

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