Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201930 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 230 PM EST Mon Feb 20 2017 .SYNOPSIS...
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High pressure will build overhead through tonight. Cooler air will seep south tonight into Tuesday. A weak disturbance will cross the area Tuesday night into Wednesday. High pressure will be located off the southeast coast of the United States Thursday through Friday. A cold front will pass through the area during the weekend.
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&& .NEAR TERM /THROUGH TUESDAY/...
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Upper-level ridge will build overhead through tonight while surface high pressure builds into New England. The surface ridge axis associated with the high will build over our area during this time. An easterly flow around the high will usher in cooler air compared to recent night. In fact...some areas may decouple overnight and radiational cooling may lead to chilly conditions...especially over northern Maryland. Min temps will range from the lower 30s in northern Maryland to the upper 30s and lower 40s in central Virginia. High clouds will gradually increase as they rotate around the periphery of the upper-level ridge. A broken deck of lower clouds are possible overnight across the Shenandoah Valley into the Potomac Highlands due to light overrunning of the cooler air in place. However...no precipitation is expected. The surface high will move off the New England coast Tuesday...but it will continue to wedge into the Mid-Atlantic. The upper-level ridge will also gradually move off to the east. An onshore flow around the high will cause cooler conditions compared to recent days...but max temps will still be above climo. An upper-level disturbance will approach from the west...bringing some clouds to the area but it should remain dry.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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An upper-level disturbance associated with the northern stream of the jet will pass through our area Tuesday night into Wednesday...but it will be weakening as it moves through. Cutoff low pressure will develop in the southern stream of the jet...but that should remain well off to our south. A couple showers are possible Tuesday night into Wednesday...but with our area split between the northern and southern stream of the jet most areas may end up dry. The best chance for showers will be in the Allegheny Highlands due to an upslope component to the low-level flow. High pressure will build offshore for Wednesday and Wednesday night...allowing for unusually warm conditions to return. Max temps Wednesday will once again be well into the 60s and 70s.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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Dry conditions expected for Thursday with southerly flow over our region and high temperatures in the 60s and low 70s. A frontal boundary will be approaching the region from the north allowing for some showers Thursday afternoon into Thursday night. Warm air advection continues Friday into Friday night with an increase in PoPs as cold front approaches from the west. Deep low moves across the Great Lakes and a cold front moves across the Mid-Atlantic on Saturday... showers and thunderstorms likely. Dry conditions return Sunday into Monday as high pressure builds behind the front... high temperatures will be in the 50s and 60s, and in the 40s and 50s at higher elevations.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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VFR conditions expected most of the time through Tuesday. Northerly winds may gust around 15 knots this afternoon...but winds will turn to the northeast and diminish tonight. Southeasterly winds are expected for Tuesday around 10 knots. A bkn cu deck may lead to a period of MVFR cigs later Tuesday morning into Tuesday afternoon...especially across the western terminals. An upper-level disturbance will pass through the terminals Tuesday night into Wednesday. A couple showers cannot be ruled out...but most areas will be dry. A light south to southwest flow is expected during this time. Areas of fog are possible Tuesday night and again Wednesday night. Dry/VFR conditions expected for Thursday before a front approaches the area on Thursday night... showers possible into Saturday, when a strong cold front moves across the Mid- Atlantic. Sub-VFR conditions possible Thursday night into Saturday at moments. Gusty winds expected Friday night into Saturday, reaching up to 20 kt.
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&& .MARINE...
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Winds will turn to the northeast this afternoon into tonight. A weak pressure surge is expected over the waters this evening. Gusts may approach 20 knots...but confidence is low for a headline at this time since the pressure surge will be weak. High pressure will build over the Atlantic for Tuesday and Wednesday. Southeast winds Tuesday will turn to the south or southwest Tuesday night through Wednesday night. Wind speeds should remain below SCA criteria. Dry conditions expected for Thursday before a front approaches the area on Thursday night... showers possible into Saturday, when a strong cold front moves across the Mid-Atlantic. Gusty winds expected Friday night into Saturday, reaching up to 20 kt, therefore small craft advisory possible.
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&& .CLIMATE...
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Record high minimums were set yesterday at IAD and BWI. See RERs for more details. More record high mins are likely later this week.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR CLIMATE...BJL/LFR

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