Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201358 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 958 AM EDT SUN APR 20 2014 .SYNOPSIS...
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HIGH PRESSURE OVER QUEBEC WILL BUILD INTO THE AREA TODAY AND MONDAY. A COLD FRONT WILL BRING SHOWERS TO THE AREA TUESDAY AND TUESDAY NIGHT. HIGH PRESSURE BUILDS BACK IN FOR THE SECOND HALF OF THE WORK WEEK.
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&& .NEAR TERM /TODAY AND TONIGHT/...
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DEFORMATION BAND BETWEEN LOW PRESSURE OFF THE CAROLINA COAST AND HIGH PRESSURE OVER NEW ENGLAND IS THINNING THIS MORNING. SUNSHINE WILL BE ABUNDANT BY EARLY AFTERNOON AND TEMPERATURES WILL WARM INTO THE MID 60S METRO AREAS TO 70S WEST AND SOUTH. UNDER HIGH PRESSURE...SKIES WILL CLEAR AND WIND WILL BE LIGHT. RADIATIONAL COOLING WILL DROP TEMPERATURES INTO THE 30S EVEN IN THE METRO AREAS OVERNIGHT. THE MAV GUIDANCE IS THE COOLEST WITH TEMPERATURES BELOW 32 DEGREES OUT IN FREDERICK CO MD AND FAUQUIER CO VA TONIGHT WHILE OTHER GUIDANCE IS WARMER. WE WILL EVALUATE THE NEED FOR A FROST ADVISORY IN THE AFTERNOON PACKAGE.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/... MONDAY WHILE WE ARE EXPERIENCING ANOTHER QUIET WX DAY ACROSS THE REGION...A COUPLE OF FAST-MOVING SHORTWAVES WILL BE DRIFTING ACROSS SRN CANADA. THE WRN SHORTWAVE WILL BE SLIDING TOWARD THE NRN PLAINS AND WILL PICK UP A DISSIPATING CUT OFF LOW OVER THE CNTRL PLAINS. COMBINING THE MOISTURE FROM THE TWO AND PHASING THEM INTO ONE MUCH LONGER SHORTWAVE TROUGH WILL OCCUR DURING THE DAYTIME HRS ON MON. THIS WAVE WILL BE A SERIES OF SMALLER ZONES OF FORCING/LIFT - SO NOT A STEADY LINE OF CONVECTION OR STRATIFORM PRECIP BUT INSTEAD MERELY BATCHES OF THEM ALL ALONG THE TROUGH AXIS. BY LATE MON...THE TROUGH AXIS WILL BE ON THE DOORSTEP OF THE APLCNS...READY TO THRU OUR REGION ON TUE. BEFORE THEN...WE`LL TOP OUT AGAIN IN THE U60S/L70S OVER THE AREA ON MON AFTN FOR DAYTIME HIGHS. TEMPS AHEAD OF THE UPPER TROUGH WILL ONLY DROP INTO THE L50S MON NIGHT. AS LOW LEVEL MOISTURE INCREASES AHEAD OF THE TROUGH PASSAGE EARLY TUE...IT WILL HELP TO ADD SOME INSTABILITY - ALONG W/ ANOTHER RELATIVELY WARM DAY. CLOUDS WILL STREAM OVER THE REGION IN EARNEST TUE MRNG...WHICH MAY LIMIT HEATING A FEW DEGREES ULTIMATELY AND HELP SLIGHTLY INHIBIT A STRONGER CONVECTIVE POTENTIAL FOR THE DAY. ONLY A COUPLE HUNDRED J/KG OF CAPE APPEARING ON AREA MODELS SOUNDINGS FOR TUE...FOR MULTIPLE MODELS AND OVER THE BEST POTENTIAL PART OF THE DAY FOR TSTMS. UNLIKE THE OTHER CONVECTIVE AND A FEW NON-CONVECTIVE EVENTS SO FAR THIS YEAR...SHEAR WILL BE LACKING - LESS THAN 20KT BULK AND MEAN LAYER SHEAR AT THE HEIGHT OF THE AFTN HEATING. ADD TO THAT THE LATEST MODEL TREND OF NEARLY DISINTEGRATING THE PRECIP ALONG THE SFC BOUNDARY AS IT HAS MOVED ACROSS OUR AREA LATE TUE AFTN/EVE. STILL SOME RESIDUAL ACTIVITY ACROSS DELMARVA AND THE TIDEWATER TUE NIGHT....BUT A QUICK DROP OFF IN PRECIP CHANCES TOWARD AND AFTER SUNSET. A MODEST REGION OF SUBSIDENCE WILL THEN SPREAD ACROSS THE AREA ON WED...BRINGING GUSTY NW WINDS AND DRIER/COOLER AIR. NOT NEARLY AS POTENT AS THE STORM SYSTEM A WEEK AGO AT THE SAME TIME...BUT STILL ONLY ALLOWING TEMPS TO RISE BARELY INTO THE L60S ACROSS MUCH OF THE AREA W/ A BRISK 15-25MPH NW WIND. A POTENT CUT-OFF UPPER LOW OVER THE NRN ROCKIES WILL LOSE SOME OF ITS PUNCH AS IT SLIDES EAST OF THE MISS RVR LATE THIS WEEK...AS HIGH PRESSURE AGAIN GIVES THE MID ATLC ANOTHER QUIET WX DAY ON THU. ANOTHER COLD AND CLOSED UPPER LOW WILL BARREL ACROSS THE NRN PLAINS AND THE GREAT LAKES THU INTO FRI. BY THE TIME THE TAIL END OF THE ASSOCIATED COLD FRONT SWINGS ACROSS THE REGION...IT SHOULD BE LOSING MUCH OF ITS PRECIP W/ ONLY SCATTERED BATCHES MOVING ACROSS THE AREA FRI INTO SAT. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/...
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VFR CONDITIONS XPCD TDA THRU MON MRNG. HIGH PRESSURE WILL BRING CLEAR SKIES BEFORE HIGH CLOUDS INCREASE OVER THE AREA LATER TONIGHT - JUST AHEAD OF ANOTHER STORM SYSTEM. THE FRONTAL SYSTEM LOOKS RELATIVELY WEAK FOR TUE AFTN/EVE...THOUGH A FEW TSTMS ACROSS STILL POSSIBLE FOR SCATTERED AREAS OF THE MID ATLC REGION. THE FRONTAL SYSTEM WILL THEN WORK ITS WAY OFF THE COAST INTO THE LATE NIGHT HRS. HIGH PRESSURE AND SOME GUSTY NW WINDS ON WED - QUIETING DOWN OUR WX FOR THU BRIEFLY BEFORE A FRONTAL BOUNDARY SWEEPS THRU THE AREA ON FRI.
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&& .MARINE...
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SCA CONDITIONS IN PLACE AS THE PRES GRAD BTWN THE SERN CSTL LOW AND THE NERN HIGH PRES GROWS STRONGER. SCA IS IN EFFECT FOR THE DAYLIGHT HRS THEN WINDS WKN TNGT. WINDS WILL SLACK OFF OVER THE WATERS BY EARLY TUE...AS THE CENTER OF SFC HIGH MOVES OFF THE COAST AND WINDS TURN SLY. A COLD FRONT WILL PUSH THRU THE REGION LATE TUE...BRINGING SOME SCATTERED SHOWERS AND POSSIBLY SOME ISOLATED TSTMS JUST SOUTH OF THE METRO DC AREA. BREEZY NW WINDS OF WED AFTN...THOUGH HIGH PRESSURE WILL AGAIN OVERTAKE THE REGION FOR THE SECOND HALF OF THE WEEK.
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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 2 PM EDT THIS AFTERNOON FOR ANZ530- 535-536-538>540. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ531>534-537-541>543.
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&& $$ SDG/WOODY

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