Area Forecast Discussion
Issued by NWS Sterling, VA

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249 FXUS61 KLWX 121833 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 233 PM EDT Thu Oct 12 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure over New England will extend south toward our area through this tonight. An onshore flow has allowed for low- level moisture to be trapped underneath the subsidence inversion...resulting in low clouds along with patchy drizzle/light rain. Upper-level ridging will increase a bit this afternoon and evening while a trough digs into the western CONUS. This will allow for the low-level flow to veer toward the southeast...causing warm and moist air to overrun the surface cool air in place. Therefore...light rain and drizzle are likely to increase in coverage...especially for locations along and east of the Blue Ridge Mountains into the eastern Panhandle of West Virginia and western Maryland. This is where there will be an upslope component to the low-level flow. Areas of light rain/drizzle are possible over the Shenandoah Valley as well but coverage may not be as widespread this afternoon due to a downslope flow off the Blue Ridge Mountains. Upper-level ridging will continue to build overhead tonight and this may shrink the marine layer a bit overnight...causing overrunning to diminish. Therefore...coverage of rain will likely diminish but areas of drizzle and fog will continue overnight. Min temps will be in the 50s across most areas to the lower 60s in southern Maryland.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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High pressure over New England will continue to extend south and west into our area through Saturday morning. An onshore flow will continue and moisture will remain trapped underneath the subsidence inversion...resulting in low clouds along with areas of light rain and fog/drizzle. High pressure will begin to move offshore Saturday and some sun may break out as the marine layer thins out...but confidence is low for this happening along/east of the Blue Ridge Mountains. Max temps will be well into the 70s.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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A cold front will push across the eastern Ohio Valley into the mid-Atlantic region Sunday into Sunday night. Ahead of the front, there is a chance for rain showers, mainly Sunday night into Monday morning. High temperatures ahead of the front, on Sunday, will reach the lower to middle 80s. As the front passes, temperatures will cool late Sunday through Monday. High pressure is expected to build into the region Sunday night through Thursday. Dry conditions and cooler temperatures expected Monday afternoon through Thursday.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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An onshore flow will continue to cause low-level moisture to be trapped underneath the subsidence inversion...resulting in low clouds along with areas of light rain/drizzle through Saturday morning. Mainly IFR conditions are expected...but periods of low end MVFR conditions are possible as well. Cigs should improve later Saturday...but confidence is low at this time. Areas of low clouds/fog may develop again Saturday night as a southwest flow ushers in plenty of moisture. VFR to MVFR conditions possible with any rain showers Sunday night and Monday morning. Otherwise, VFR conditions will be expected at the terminals. Wind southwest 5 to 10 knots Sunday, becoming northwest around 10 knots gusts up to 20 knots Sunday night through Monday night.
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&& .MARINE...
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A pressure surge has caused gusty east to northeast winds today. High pressure will continue to extend south and west into our area into this evening. A Small Craft Advisory is in effect for all of the waters. Winds should gradually diminish later tonight through Friday...but a Small Craft Advisory remains in effect for portions of the waters. High pressure will build overhead Saturday before moving offshore Saturday night. No marine hazards expected Sunday. Small craft advisories are possible Sunday night through Monday night. Winds southwest around 10 knots Sunday, becoming northwest 10 to 15 knots gusts 20 knots Sunday night through Monday night.
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&& .TIDES/COASTAL FLOODING...
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Onshore flow will continue through Friday. Minor Coastal Flooding is likely. A Coastal Flood Advisory is in effect for the Maryland Chesapeake Bay from Anne Arundel County southward through tonight. The advisories may need to be extended north into the Potomac River and northern Bay for the high tide cycle later tonight. Coastal Flood Advisories will likely be needed Friday into Saturday as well. Moderate flooding cannot be ruled out...especially near Straits Point. A Coastal Flood Watch may be needed for the high tide cycle Friday night.
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&& .EQUIPMENT... The NWS 88D Sterling radar (KLWX) will be down during the day from 7 AM through 5 PM through Saturday this week. This is for nationally scheduled maintenance on the radome. Our surrounding 88D radars as well as FAA terminal radars will be operational during this downtime. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory from 6 PM this evening to 2 AM EDT Friday for MDZ018. Coastal Flood Advisory from 10 PM this evening to 3 AM EDT Friday for MDZ014. Coastal Flood Advisory from 6 PM this evening to 2 PM EDT Friday for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ531>533- 539>541. Small Craft Advisory until midnight EDT tonight for ANZ530-535- 536-538-542. Small Craft Advisory until 6 PM EDT Friday for ANZ534-537-543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...KLW AVIATION...BJL/KLW MARINE...BJL/KLW TIDES/COASTAL FLOODING...BJL EQUIPMENT...BJL

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