Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 300743 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 343 AM EDT SAT APR 30 2016 .SYNOPSIS...
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A STALLED FRONTAL BOUNDARY WILL WAVER ACROSS THE AREA TODAY. LOW PRESSURE MOVES THROUGH THE MID- ATLANTIC SUNDAY INTO MONDAY... PULLING THE FRONT TO THE NORTH ON SUNDAY...AND THEN SENDING A COLD FRONT ACROSS THE REGION ON MONDAY. ANOTHER COLD FRONT WILL MOVE THROUGH LATE NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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CWFA REMAINS WITHIN AREA OF COLD AIR DAMMING...AND THIS WEDGE APPEARS TO HOLD THROUGH THE DAY. THE RDGG DOWN THE COAST FM THE GRTLKS APPEARS TO STRENGTHEN THRU THE DAY...WHICH HAS KEPT AREA DRY OVNGT /ASIDE FM ANY PATCHY DZ/ AND SHUD HOLD OFF ANY APPRCHG RAFL. AM SEEING THESE TRENDS IN LTST GFS/NAM RUNS...AND ITS SPCLY PREVALENT IN RECENT RAP/HRRR/WRF-ARW4 RUNS. HV THEREFORE BACKED OFF ON ARRIVAL OF PCPN TDA. THERE IS STILL A RIBBON OF STRONG ISENT LIFT AHD OF LOPRES IN THE SRN PLAINS...AND PWATS STILL RISE ABV AN INCH BY DAYS END. THE IMPACT OF THESE TRENDS ARE TO KEEP PCPN OUT OF THE FCST ENTIRELY IN NE MD TDA. ONLY CENTRAL FOOTHILLS/CENTRAL SHEN VLY/SRN PTMC HIGHLANDS HV POPS HIER THAN LKLY-- AND THATS FOR ONLY THE MID/LATE AFTN HRS. THE DAY WL START CLDY AND GREY AREAWIDE. AS HIPRES WL BRIEFLY BE CONTROLLING...CLDS SHUD LIFT... AND MAY SEE A FEW BRIGHT SPOTS. MAXT FCST WL REFLECT LESS OF A GRADIENT... ALTHO BELIEVE THERE WL BE A LARGE MARGIN FOR ERROR CONTINGENT ON IF/WHERE ANY SUN APPEARS. THTE RDG/MSTR PLUME WL OVERSPREAD CWFA TNGT. POPS INCR TO CAT W/ POCKETS OF MDT RAFL. BASICALLY...IT WL BE A RAINY NGT...BUT NOT AT A PACE WHERE FLOODING WUD BE A CONCERN.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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THERE LKLY WL BE LINGERING RAFL IN THE SRN CNTYS AT THE START OF SUNDAY...BUT IT/LL BE EXITING TO THE EAST ALONG WITH THE LEADING EDGE OF THE THTE RDG. THAT SHUD RESULT IN A PD OF DRYING...AND HV ATTEMPTED TO REFLECT THAT BY LWRG OF POPS INTO CHC FOR THE MIDDAY. SFC LOPRES AND H5 VORT TRACK UP THE OHVLY SUN-SUN NGT. THIS TRACK WL ENCOURAGE STALLED BNDRY TO LIFT NWD...BUT IT/LL RUN INTO THE STUBBORN CAD WEDGE. THIS PTTN ALWAYS A CHALLENGE FOR MDLS TO FCST...AND THE RESULT USUALLY FAVORS PERSISTENCE. AM BEGINNING TO ACTUALLY SEE THAT REFLECTED IN GDNC...SPCLY IN THE GFS...WHICH HOLDS ONTO A STBL SFC LYR IN MD THRU THE DAY. BEST H8-5 LAPSE RATES HOLD OVER THE APLCNS...BUT THERE CUD BE A LTL ELEVATED INSTBY NE OF THERE. THE MIDDAY DRYING AND HEATING SHUD PERMIT AFTN SHRA/TSRA TO DVLP. IN DEFERENCE TO CLIMO...HV PULLED BACK ON THUNDER POTL THIS FCST CYCLE. STILL SEE ENUF INSTBY/SHEAR SW OF BNDRY FOR TSTMS TO DVLP. CHALLENGE WL E TO PINPOINT WHERE THAT AREA IS. ATTM WL PAINT IT S OF CHO-SHD-EKN... FOR LATE IN THE DAY. SPC HAS PEGGED THAT AREA FOR A MRGL RISK OF SVR. WL HV A THUNDER GRADIENT NEWD FM THERE. SCHC THUNDER NE OF MRB-DCA WUD ONLY BE FOR A STRAY LATE DAY ELEV RUMBLE. BEST LIFT WL ACTUALLY BE IN THAT AFOREMENTIONED AREA...ACRS THE N/NERN CWFA...AGAIN DUE TO UPGLIDE. AFTN POPS WL HOVER IN THE 70-80 PCT RANGE. SHUD LOSE ANY SFC-BASED INSTBY INSTBY W/ SUNSET...BUT LAPSE RATES AND SHEAR REMAIN DECENT WELL INTO SUN NGT. THE PARENT LOW WL TRACK TWD NEW ENGLAND...WHICH WL SEND THE CDFNT THRU OVNGT SUN OR MORE LKLY MON MRNG. POPS GRDLY TAPER OFF THRU THAT PD. QPF POTL STILL GOOD SUN EVE...AND WL CARRY SHRA W/ MDT RAFL AT THAT TIME. WL TAPER OFF THEREAFTER. LKLY TO SEE SOME SUNSHINE BY MON AFTN. TEMPS THIS PD REMAIN A CHALLENGE AS INSOLATION CUD RSLT IN TEMP SPIKES. SUN MAXT REFLECT THAT GRADIENT ACRS CWFA. BETTER DRYING AND SUBSIDENT WLY FLOW MON SUGGESTS THAT MON WL BE A WARMER DAY REGARDLESS OF CFP.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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THE SYNOPSIS FOR NEXT WEEK WILL REMAIN COOL AND UNSETTLED. THE MIDDLE PORTION OF THE WEEK FEATURES THE GREATEST UNCERTAINTY IN TERMS OF SENSIBLE WEATHER IMPACTS. THE FRONT WHICH PASSES THROUGH DURING THE EARLY PART OF THE WEEK WILL STALL ALONG THE SOUTHEAST COAST WHILE TROUGHING ALOFT DEVELOPS OVER EASTERN NOAM. MULTIPLE AREAS OF LOW PRESSURE WILL TRACK ALONG THE FRONT. IN TERMS OF THE 00Z RUNS...ECMWF AND GEM OFFER WETTER SOLUTIONS (I.E. LOW TRACKS CLOSER TO THE COAST) FOR THE LOCAL AREA...WHILE THE GFS IS DRIER. WILL BE CARRYING LOW POPS ALMOST EVERY PERIOD AS TIMING AND PLACEMENT DIFFERENCES WILL SPAN ACROSS THE DAY-PARTS OF THE FORECAST. DESPITE THE PESSIMISTIC FORECAST...TOTAL RAINFALL AMOUNTS SHOULD BE FAIRLY LIGHT UNLESS THE LOW TRACKS ARE MUCH FURTHER INLAND THAN CURRENTLY FORECAST. BY THURSDAY...ENERGY DIVING SE FROM CENTRAL CANADA WILL SEND A COLD FRONT THROUGH THE REGION. AS THIS ENERGY INTERACTS WITH THE COASTAL FRONT...A CLOSED LOW ALOFT IS EXPECTED TO DEVELOP. THIS WILL BE THE EASTERN LOBE OF A DEVELOPING OMEGA BLOCK FOR THE END OF THE WEEK / NEXT WEEKEND. THE RESULT WILL BE A SHOWERY PATTERN WITH PERHAPS SOME LOW TOPPED CONVECTION. WITH NO REAL SOURCE OF WAA...TEMPERATURES WILL LIKELY REMAIN BELOW NORMAL THROUGH THE WEEK. WITH THE STEEP LAPSE RATES...THE ALLEGHENY FRONT MAY NOT BE TOO FAR FROM SEEING SOME WET SNOW FLAKES MIX IN BY FRIDAY MORNING.
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&& .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
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LOW CLOUDS AND PATCHY DRIZZLE CONT ACRS THE TERMINALS ELY THIS MRNG. RESTRICTIONS...MAINLY IFR...ARE A RESULT OF CIGS. CUD BE HEADED TWD LIFR TWD SR. ALREADY SEEING HINTS OF THAT AT CHO. CONDS WL GRDLY IMPRV DURING THE DAY. AM STARTING TO FEEL CONFIDENT ENUF TO CARVE OUT A PD OF VFR FOR BALT-DC TERMINALS MID-LT AFTN. FLGT CONDS WL DROP SAT EVE AS RA OVERSPREADS THE AREA. RA MAY BE MDT TO BRIEFLY HVY SAT NGT INTO ELY SUN. FLGT RESTRICTIONS WL BE WIDESPREAD...AT LEAST IFR IF NOT LIFR. POOR FLYING CONDS CARRY OVER INTO SUN...THO BREAKS IN THE OVC LKLY AS BDRY ATTEMPTS TO WIGGLE N OF THE TERMINALS. ONCE AGN XPCT IMPRVMNT DURING THE DAY AS RAFL HEADS EAST. THAT WL RESULT IN A RENEWED CHC AT SHRA DURING THE AFTN. CUD BE THUNDER TOO...SPCLY INVOF CHO. CONDS BECOME MORE STBL TWD THE NE. CDFNT WL CROSS THE TERMINALS ELY MON...WHICH SHUD RESULT IN W/NWLY FLOW. MAY STILL HV RESTRICTIONS TO START...BUT AM HOPEFUL FOR IMPROVEMENT TO VFR DURING THE DAY. LOW CONFIDENCE FORECAST FOR TUESDAY-WEDNESDAY WITH FRONT STALLED ALONG SE COAST. GFS SUGGESTS MAINLY VFR WHILE OTHER MODELS WOULD BRING IN SOME PERIODS OF RAIN AND POSSIBLE IMPACTS TO CIGS/VSBYS.
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&& .MARINE...
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LLVLS REMAIN STBL THROUGH THE WKND AS A WEDGE OF HIPRES REMAINS TRAPPED E OF THE BLURDG. THAT WL RESULT IN MAINLY E FLOW AT 5 TO 10 KT...WITH OCNL PDS CLSR TO 15 KT. WNDS WL VEER A BIT MORE TWD THE SE AS AN APPCHG WMFNT TRIES TO DISLODGE THE MARINE AMS. ALTHO WINDS WL BE STRONGER ALOFT...DONT BELIEVE THE STBL LLVLS WL PERMIT ANY STRONGER WINDS TO REACH THE WATERS EDGE. THEREFORE...HV BACKED AWAY FROM SCA POTL. LIGHT NW FLOW EXPECTED TUESDAY BEHIND DEPARTED COLD FRONT. WINDS MAY BECOME SW BY WEDNESDAY BUT GRADIENT LOOKS WEAK ENOUGH TO KEEP WINDS AT 10-15 KT. SHOULD A STRONGER LOW PRESSURE SYSTEM DEVELOP ALONG A STALLED COASTAL FRONT...HIGHER WINDS MAY BE REALIZED.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES REMAIN AROUND ONE-HALF TO THREE QUARTERS OF A FOOT ABOVE NORMAL. A PERSISTENT ONSHORE FLOW WILL CAUSE ANOMALIES TO HOLD NEARLY STEADY OR EVEN INCREASE A BIT THROUGH THE WEEKEND. HOWEVER...THE FLOW SHOULD BE LIGHT ENOUGH FOR WATER LEVELS TO REMAIN BELOW MINOR FLOODING THRESHOLDS. THERES ROOM FOR THIS FORECAST TO CHANGE...ESPECIALLY TOWARD SUNDAY...SO WE WILL CONTINUE TO MONITOR THIS SITUATION.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...ADS AVIATION...HTS/ADS MARINE...HTS/ADS TIDES/COASTAL FLOODING...HTS

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