Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 140154 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 954 PM EDT Fri Oct 13 2017 .SYNOPSIS... High pressure over New England will extend into the area through Saturday before moving offshore Sunday. A cold front will push into the Mid Atlantic Sunday night followed by a return to high pressure early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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An onshore flow will continue around high pressure over New England overnight, though it has weakened. Low-level moisture will remain trapped underneath the subsidence inversion...resulting in more low clouds along with areas of mist and drizzle. The best chance for any light rain or drizzle will be near the bay tonight. Some patchy dense fog may develop in parts of eastern West Virginia where some clearing has occurred, but most of the CWA remains socked in with low clouds, so fog should be limited to mist, primarily due to drizzle. Otherwise, the only dense fog will be on ridges which intersect the low clouds. Lows will remain mild, in the 50s overall.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... High pressure will extend into our area Saturday before moving offshore Saturday night into Sunday. The building high pressure will cause the marine layer to dissipate Saturday. Morning low clouds and fog/drizzle will give way to sunshine...but it may take a while into the afternoon hours for locations along/east of the Blue Ridge Mountains. For locations farther west...clouds and fog should dissipate in the morning. Max temps will be in the 70s Saturday for most areas. Mild conditions will persist Saturday night with a southerly flow. A cold front will approach Sunday morning before passing through later Sunday afternoon through Sunday night. Unusually warm conditions are expected ahead of the boundary Sunday with max temps in the 80s for many locations. A few showers will accompany the frontal passage later Sunday afternoon across the north and west...and across the rest of the area Sunday night. Noticeably cooler conditions are expected behind the boundary overnight. && .LONG TERM /MONDAY THROUGH FRIDAY/... A strong cold front moving east across the Chesapeake Bay could spawn a rain shower or two early Monday in the vicinity of southern Maryland; otherwise, high pressure will build into the region midday Monday through Friday. Dry conditions midday Monday through Friday. Temperatures should fall throughout the day Monday with the high possibly occurring early Monday morning and the low occurring just before midnight Monday night into early Tuesday morning. We could see temperatures falling from the middle 60s early Monday morning, through the 50s during the day, before getting into the lower to middle 40s by late Monday evening. As for Tuesday, temperatures will be about 5 degrees below normal despite plenty of sunshine. Wednesday, Thursday and Friday will be warmer with plenty of sunshine despite starting off chilly in the morning. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
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An onshore flow will persist through tonight before dissipating Saturday. Low clouds and areas of drizzle/mist are expected through Saturday morning before gradually dissipating Saturday afternoon. Therefore, MVFR to IFR cigs/vis for most of the terminals into early Saturday morning. Cigs will gradually improve Saturday. High pressure will move offshore Saturday night and Sunday. A southerly flow is expected. Areas of low clouds and fog are possible Saturday night into early Sunday. A cold front will pass through late Sunday and Sunday night. Showers are possible with the frontal passage and brief MVFR conditions cannot be ruled out. A wind shift from the southwest to northwest is expected with the frontal passage. VFR conditions Monday through Tuesday night. Winds northwest 5 to 10 knots Monday, becoming light and variable Monday night through Tuesday night.
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&& .MARINE...
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An east to northeast flow will continue through tonight. The gradient has subsided, and winds have also been on the decline. A Small Craft Advisory remains in effect for the Maryland Chesapeake Bay south of Drum Point and for the Tidal Potomac River south of Cobb Island until midnight, and at this time expect no further extension. High pressure will build overhead Saturday before moving offshore Saturday night through Sunday. A cold front will pass through the water Sunday night. A Small Craft Advisory may be needed for portions of the waters Sunday and Sunday night. Small craft advisory possible Monday and Monday night. Winds northwest 10 to 15 knots gusts to 20 knots. No marine hazards expected Tuesday and Tuesday night. Winds becoming northwest then southwest around 5 knots.
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&& .TIDES/COASTAL FLOODING...
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A persistent onshore flow had caused tidal anomalies around 1.5 to 2.0 feet above normal. The onshore flow will continue to weaken through tonight. Anomalies have also started to decline. Previously...minor to moderate flooding was anticipated through the high tide cycle Saturday morning. Coastal Flood Advisories and warnings were therefore issued and as of this writing remain in effect. However, given the falling anomalies, will re- evaluate advisories and warnings over the next hour, with some possibly being downgraded or cancelled. That said, with anomlies potentially remaining elevated, additional minor flooding is possible later Saturday into Sunday.
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&& .CLIMATE... A surge of warm air is expected Sunday ahead of the cold front. We are not currently forecasting records, but we are expecting temps to be close. Warm Temperature Records for October 15 (Sunday)... High Warm Low DCA 87 (1975) 67 (2008) BWI 86 (1989, 1975) 66 (1941) IAD 88 (1989) 64 (1985) && .EQUIPMENT... The NWS 88D Sterling radar (KLWX) will be down during the day from 7 AM through at least 5 PM through Saturday. This is for nationally scheduled maintenance on the radome. Surrounding 88D radars as well as FAA terminal radars will be operational during this downtime. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 7 AM EDT Saturday for DCZ001. MD...Coastal Flood Advisory until 2 PM EDT Saturday for MDZ016-018. Coastal Flood Advisory until 10 AM EDT Saturday for MDZ508. Coastal Flood Advisory until 8 AM EDT Saturday for MDZ011. Coastal Flood Warning until 4 AM EDT Saturday for MDZ014. Coastal Flood Advisory until midnight EDT tonight for MDZ014. Coastal Flood Advisory from 4 AM to 5 PM EDT Saturday for MDZ014. Coastal Flood Warning until 1 PM EDT Saturday for MDZ017. VA...Coastal Flood Advisory until 2 PM EDT Saturday for VAZ057. Coastal Flood Advisory until 7 AM EDT Saturday for VAZ054. WV...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ534-537- 543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL/RCM SHORT TERM...BJL LONG TERM...KLW AVIATION...BJL/KLW/RCM MARINE...BJL/KLW/RCM TIDES/COASTAL FLOODING...BJL/RCM CLIMATE...LWX EQUIPMENT...LWX

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