Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191420 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1020 AM EDT SUN OCT 19 2014 .SYNOPSIS...
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AN UPPER TROUGH AXIS WILL CLEAR TODAT...WITH HIGH PRESSURE BUILDING TROUGH MONDAY. A SLOW MOVING UPPER LEVEL LOW WILL CROSS THE REGION TUESDAY AND PERSIST ALONG THE COAST THROUGH THURSDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A SHARP UPPER TROUGH AXIS NOW PULLING AWAY FROM THE AREA AND THIS LAST WAVE OF SUBSIDENCE WILL CONTINUE MAKING IT A BREEZY DAY. SOLID 20-30KT GUSTS THAT BEGAN JUST AFTER DAWN WILL CONTINUE THROUGHOUT THE AFTN AS GOOD BOUNDARY LAYER MIXING PUSHES THE HIGHER GUSTS TOWARD THE SFC. THE EXIT OF THIS UPPER WAVE ALSO TAKES THE CLOUD COVER AWAY OVER TIME. ONLY THE UPSLOPE STRATUS WILL CONTINUE INTO THE AFTN HRS...CLEAR ELSEWHERE. A SECOND- STRAIGHT DAY OF THE COOL/DRY CANADIAN AIRMASS BRINGING IN THE DRY AIR. NOT ONLY WILL TEMPS BE PREVENTED FROM MAKING TOO MUCH OF AN INCREASE TODAY BUT DEWPOINTS WILL DECREASE INTO THE L-M30S. THIS BRINGS BACK THE CHILL TO THE AIR. THIS WILL SET THE AREA UP FOR ONE OF THE COLDEST NIGHTS OF THE SEASON SO FAR.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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HIGH PRESSURE BUILDS OVERHEAD TONIGHT...AND THEN SHIFTS SEWD TO THE NC COAST BY EARLY MONDAY MORNING. MOSTLY CLEAR SKIES AND LIGHT WINDS WILL MAKE FOR AN IDEAL RADIATIONAL COOLING NIGHT. USED COMBINATION OF MAV/MET GUIDANCE AND SREF FOR LOW TEMPS...WHICH ARE FORECAST TO BE NEAR OR BELOW FREEZING ACROSS THE HIGHLANDS AND PORTIONS OF THE CENTRAL SHENANDOAH VALLEY. A FREEZE WATCH HAS BEEN ISSUED FOR THESE AREAS. FROST WILL ALSO BE POSSIBLE OVER A GOOD PORTION OF THE FORECAST AREA. ONLY UNCERTAINTY REGARDING FROST AND FREEZING TEMPS WILL BE THE ONSET OF WARM AIR ADVECTION AROUND THE HIGH AS IT SHIFTS TO THE SE OF US...AND POTENTIAL ARRIVAL OF MID- HIGH LEVEL CLOUDS. WILL LET LATER SHIFTS ASSESS THIS...SO WILL REFRAIN FROM A FREEZE WARNING AND FROST ADVISORIES AT THIS TIME. MONDAY...QUICK WARM UP AFTER A CHILLY NIGHT SINCE RETURN FLOW WILL BE INCREASING AS HIGH PRESSURE SHIFTS OFFSHORE. A LOW PRESSURE SYSTEM APPROACHES FROM THE GREAT LAKES MONDAY NIGHT. MOISTURE SLOWLY RETURNS WITH SLIGHT POPS FOR RAIN BY LATE MONDAY AFTERNOON IN THE POTOMAC HIGHLANDS. LOW CHANCE POPS THEN SPREAD EAST TO THE BLUE RIDGE OVERNIGHT AS THE THE PARENT LOW CROSSES BUFFALO NY. THE SFC TROUGH CROSSES THE CWA MONDAY NIGHT. THE LOW CROSSES THE CWA TUESDAY NIGHT. LOW CHANCES FOR LIGHT RAIN ACROSS THE CWA AS DOWNSLOPING FLOW WILL GREATLY LIMIT THE COVERAGE OF RAIN. TEMPERATURES NEAR NORMAL WITH DOWNSLOPING FLOW COUNTERACTING CLOUD COVER FROM KEEPING TEMPERATURES TOO LOW.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... CUT OFF LOW PRESSURE LINGERS ALONG THE MID-ATLANTIC COAST WEDNESDAY AND THURSDAY. 00Z GFS/ECMWF OPERATIONAL RUNS DEPICTING UPR LOW CROSSING THE CENTRAL MID-ATLANTIC TUESDAY NIGHT...THEN LINGERING ALONG THE MID-ATLANTIC COAST THROUGH INTO THURSDAY NIGHT. NWLY FLOW WITH PERIODIC RAIN...ALONG WITH NEAR NORMAL TEMPERATURES. COLD AIR COMES IN THE WEST SIDE...AND MOISTURE NOW LOOKS GREATER...SO SOME HIGHLAND SNOW IS POSSIBLE BOTH DAYS. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/...
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VFR CONDS THROUGH THE TAF PERIOD...THROUGH GUSTY NW WINDS WILL BE A CONCERN THROUGHOUT THE DAYTIME HRS. PEAK SFC GUSTS WILL BE THE IN 25-30KT RANGE. HEADING INTO THE POST-SUNSET HRS TONIGHT...WINDS WILL GRADUALLY DROP OFF W/ ONLY OCCASIONAL GUSTS 10-15KT THROUGH AROUND 3-4Z. VFR CONTINUES THROUGH MONDAY AS THE HIGH SHIFTS OFFSHORE WITH RETURN FLOW. LOW PRESSURE APPROACHES FROM THE NORTHWEST TUESDAY WITH DOWNSLOPING FLOW LIMITING RAIN CHANCES. LOW LINGERS ALONG THE COAST THROUGH THURSDAY WITH GUSTY NORTHWEST FLOW STARTING WEDNESDAY.
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&& .MARINE...
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A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL OF THE WATERS INTO THE EVE HRS. NWLY FLOW WITH GUSTS 25 TO 30 KT EXPECTED. WINDS DIMINISH LATE TONIGHT AS HIGH PRESSURE CENTER CROSSES THE BAY LATE IN THE NIGHT. RETURN FLOW MONDAY AS HIGH PRESSURE MOVES OFF SHORE. LOW PRESSURE DRIFTS OVER THE REGION MONDAY NIGHT AND TUESDAY...THEN LINGERS OFF SHORE WEDNESDAY AND THURSDAY. EXTENDED SCA EXPECTED IN NWLY FLOW ON BACK SIDE OF LOW WEDNESDAY INTO FRIDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR MDZ501-502. VA...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR VAZ025>027-029-503-504. WV...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR WVZ050-055-501>506. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ531>534- 537-539>541-543. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ530- 535-536-538-542. && $$ UPDATE...GMS PREV DISCUSSION...KCS/BAJ

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