Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 171050 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 550 AM EST WED DEC 17 2014 .SYNOPSIS... A TROUGH SWINGS THROUGH TODAY WITH HIGH PRESSURE BUILDING IN FOR THE SECOND HALF OF THE WEEK. A WEAK WAVE OF LOW PRESSURE WILL CROSS THE AREA SATURDAY NIGHT. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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DENSE FOG DISSIPATING THIS MORNING...MAINLY IMPACTING WESTERN SUBURB AREAS OF DC METRO. HAVE CANCELLED THE DENSE FOG ADV FOR LOUDOUN AND MONTGOMERY WITH OBS REPORTING AT LEAST 3 MILES VIS NOW. FORECAST ON TRACK WITH THE REMAINDER OF THE AREA UNDER THE ADV TO GO NO LATER THAN 13Z...POSSIBLY EVEN CANCELLING THE ADV 1 HOUR SOONER. SFC TROUGH SLOWLY SWINGING THROUGH THE REGION THIS MORNING...INCREASING THE WESTERLY FLOW ALONG WITH INJECTING IN DRIER AIR. FOG SHOULD BE DISSIPATED COMPLETELY BY MID MORNING WITH THE TROUGH THROUGH AND HIGH PRESSURE BEGINNING TO BUILD IN AND A DRIER AIRMASS MOVING IN. AS THE HIGH BUILDS IN...INCREASING WESTERLY FLOW WILL SEE GUSTS UP TO 25 MPH PSBL DURING THE DAYLIGHT HOURS. OTHER CONCERN THIS MORNING IS PCPN FOR THE AREAS WEST OF THE ALLEGHENY FRONT. 10Z RADAR IMAGERY AND OBS INDICATING LIGHT PCPN ASSOCIATED WITH THE TROUGH AND WEAK SHORTWAVE POSITIONED OVER WESTERN WV/PA. INCREASING WESTERLY FLOW SHOULD WORK TO GENERATE SCT UPSLOPE SHOWERS...WITH THE BEST CHC THIS MORNING...THEN TAPERING OFF DURING THE AFTN. COLD AIR HAS BEEN SLOW TO MOVE IN...AND AS SUCH CAN EXPECT MIX RAIN/SNOW SHOWERS...WITH ALL SNOW AT THE HIGHEST ELEVATIONS. THE PCPN IS VERY LIGHT IN NATURE...AND ONLY A COUPLE TENTHS OF AN INCH OF SNOW AT MOST IS FORECASTED. FOR TEMPS TODAY...CAA FAIRLY WEAK AS TROUGH ALOFT TURNS MORE ZONAL...KEEPING THE COLDER TEMPS TO THE NORTH. THE BETTER SHOT OF CAA NOT EXPECTED TILL TONIGHT. SIDED MORE WITH A WARMER MAV SOLUTION AS DOWNSLOPING COMPONENT FOR MOST OF THE CWA WITH SKIES SCATTERING OUT SEEMS THE MORE REASONABLE SOLUTION.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST TONIGHT THROUGH THURSDAY...WITH THE AREA REMAINING ON THE WESTERN PERIPHERY DURING THIS TIME. ZONAL FLOW ALOFT WILL WEAKEN TONIGHT AS A TROUGH PIVOTS THROUGH...FOLLOWED BY A STRONGER SHORTWAVE TOMORROW. OVERALL EXPECTING DRY CONDITIONS THOUGH FOR MOST OF THE AREA EXCEPT WEST OF THE ALLEGHENY FRONT WHICH COULD SEE FLURRIES THIS EVENING. DESPITE DECENT FORCING ALOFT WITH THE MULTIPLE SHORTWAVES DURING THIS PERIOD...LACK OF MOISTURE WILL KEEP ANYTHING FROM FORMING...WITH THE ONLY IMPACT FROM THE ENERGY THUS BEING INCREASED CLOUD COVER. THE STRONGER CAA FINALLY DIPS SOUTH TONIGHT...WITH OVERNIGHT LOWS TONIGHT AND TOMORROW DROPPING TO NEAR NORMAL LEVELS. SIDED MORE WITH THE MET FOR LOWS AND CONTINUED WITH THE TREND OF LEANING TO THE MAV FOR THE HIGHS ON THURSDAY. && .LONG TERM /FRIDAY THROUGH TUESDAY/... RDGG OVER CWFA SFC UP THRU H5 FRI-FRI NGT. THUS KEPT BOTH PDS DRY. SHUD HV PLENTY OF SUN DURING THE DAY. MSTR INCREASES FM THE SW AT NGT...SPCLY AFTR MIDNGT. WL HV SKIES BCMG MOCLDY IN VA...NE OF PTMC RIVER MAY AVG OUT PTCLDY. GDNC CONTINUING TO CONVERGE ON A SOLUTION THRU THE WKND...WHICH TAKES AN OPEN SRN STREAM WV WELL SOUTH OF THE CWFA SAT. LTST ECMWF MUCH LESS DVLPD WRT CSTL LOW. NONETHELESS...THIS TRACK...AND A NRN STREAM S/WV...WL BE SUFFICIENT TO TOSS LGT PCPN THIS WAY. COLD AIR WL BE MARGINAL AT BEST...SUGGESTING THERE MAY BE A DIURNAL AND ELEV COMPONENT TO PTYPE. STILL HV SNOWY/MIXED PDS...SPCLY W OF THE I-95 CRRDR. THE WETTEST PD MAY TURN OUT TO BE SAT NGT...WHICH WUD BE ABT WHEN LOW WL TRANSFER ITS ENERGY TO THE COAST...AND WE/LL ALSO HV PVA ALOFT. AM KEEPING SCHC/CHC POPS INTO SUNDAY...MORE OUT OF RESPECT TO ECMWF...AND THE TIMING/STRENGTH DIFFS THAT LINGER. SUBSIDENCE BLDS BHD THIS SYSTEM FOR SUN NGT-MON NGT. H5 FLOW STILL QUITE ZNL...SO THERE WONT BE A LOT OF COLD AIR AVBL. HV TEMPS ONLY A CPL DEGF BLO AVG. THERE MAY BE YET ANOTHER STORM SYSTEM ON THE HORIZON BY DAY 7. WL BE GENERIC ATTM...AS THERE/S A LOT OF WX TO GET THROUGH FIRST. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... ALL TAF SITES ON THE IMPROVING TRACK THIS MORNING AS KIAD AND KDCA HAVE BOTH INCREASED TO MVFR. VFR CONDITIONS FOR THE REMAINING SITES. SHOULD SEE VFR CONDITIONS AT KIAD AND KDCA BY 12Z WITH VFR THEN IN PLACE DURING THE DAY TODAY. LIGHT FLOW EARLY THIS MORNING WILL INCREASE FROM THE WEST AFTER DAYBREAK...WITH GUSTS AROUND 20-25 KTS MIXING IN BETWEEN 14-16Z. GUSTS END BY 00Z TONIGHT...WITH W FLOW CONTINUING OVERNIGHT...GENERALLY LESS THAN 10 KTS. OCNL GUSTS PSBL KDCA OVERNIGHT...BUT NOT ENOUGH CONFIDENCE TO INCLUDE IN TAF. VFR CONDITIONS TONIGHT THROUGH THURSDAY. VFR FRI-FRI NGT. FLGT RESTRICTIONS SHUD OVERSPREAD TERMINALS SAT... AND LINGER INTO ELY SUN. PCPN MAY BE ON THE LGT SIDE...WHICH WUD SUGGEST THAT MVFR MAY PREVAIL...W/ PDS OF IFR. PTYPE STILL IN QSTN. && .MARINE... SCA IN EFFECT FOR TODAY FOR ALL WATERS WITH INCREASING WEST WINDS...GUSTING UP TO 20 KTS. THE SCA REMAINS IN EFFECT THROUGH TONIGHT AND THROUGH THURSDAY. THERE COULD BE PERIODS TONIGHT WHERE THE WINDS DROP BELOW 18 KTS...BUT THE WINDOW SMALL ENOUGH TO WARRANT THE CONTINUATION OF THE SCA. THE SCA REMAINS ON ALL WATERS THURSDAY MORNING...THEN WITH HIGHER CONFIDENCE OF THE GUSTS REMAINING ABV 18 KTS OVER JUST THE NORTHERN CHESAPEAKE BAY MAINTAIN THE SCA THERE TILL THURS EVENING. HIPRES OVER THE WATERS FRI. WK LOPRES PASSING WELL S OVER THE WKND. WHILE PCPN XPCTD TO REACH WATERS...THE GRADIENT SHUD BE ON THE LGT SIDE. FOR THAT REASON...NO FLAGS XPCTD ATTM. && .TIDES/COASTAL FLOODING... WATER LEVEL DEPARTURES DOWN TO A FOOT OR SLIGHTLY LESS. THAT TREND SHOULD CONTINUE FOR THE NEXT DAY OR TWO. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR VAZ040- 051>053-501-502. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 6 PM EST THURSDAY FOR ANZ530>532-538>540. SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 1 PM EST THURSDAY FOR ANZ533>537-541>543.
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&& $$ SYNOPSIS...SEARS/HTS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS TIDES/COASTAL FLOODING...HTS

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