Area Forecast Discussion
Issued by NWS Sterling, VA

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060 FXUS61 KLWX 181848 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 248 PM EDT Wed Apr 18 2018 .SYNOPSIS...
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Weak high pressure over our area will move east and away from the coast later this afternoon. A low pressure system will track east over the Ohio Valley this evening and into the northeastern states pushing a cold front across our region early on Thursday. High pressure will build on Friday and remain in control into the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Clear to mostly clear skies continue over our area, with some clouds over our higher elevations ahead of a developing warm front. Temperatures are between the upper 40s and the mid 50s this afternoon, and expected to rise a several more degrees through late afternoon. Winds have started to shift to southerly as a weak high pressure continues to move offshore of the southeast coast. A warm front is located to our southwest and it is expected to lift this evening into tonight with clouds increasing over us. At the same time, a low pressure system will approach from the west which is expected to increase showers over our CWA, but mainly to the Allegheny Highlands. ECMWF brings chance PoPs east of the Blue Ridge, while most other guidance is drier. Therefore, expecting precipitation mainly over areas west and near the Mason-Dixon Line, but not ruling out some showers over the rest of our area.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Low pressure will be tracking towards the northeastern states on Thursday as it pushes a cold front over us. Some showers are possible on Thursday as an upper trough axis moves overhead. Gusty northwesterly winds are expected behind the front as cold air advects over us and a dry air mass settles in. Winds gusts between 30 and 40 mph expected, with higher gusts at the ridge tops. A Wind Advisory has been issued for ridges above 2,000 ft from midnight tonight through Thursday for wind gusts greater than 45 mph. An expansion of this advisory to other areas will be evaluated by upcoming shifts (lower confidence at lower elevations since the best gradient/pressure surge pushes east prior to favorable diurnal mixing). Cold air advection behind the front will allow for snow showers west of the Allegheny Front Thursday afternoon and evening. Expecting accumulations between a coating to an inch or two. A Canadian high pressure center will from the northwest on Friday. Gusty winds will be gradually decreasing through the day and finally subsiding by Friday evening. Some clouds may remain through the day with upper troughing linger, but should be clearing Friday evening into the night.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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High pressure centered over the Great Lakes will build in for the weekend, maintaining cool and dry conditions over the area. Winds will weaken and shift from light northerly to light easterly as high pressure slides off to our north. By Sunday Night, models have a cutoff upper-level low and associated surface low tracking through the Deep South. Over the past day, models had trended weaker with a positively tilted, southeastward translating shortwave trough located over the northeast. Now it appears as though the area of low pressure associated with the cutoff upper-level trough will slowly track up the eastern seaboard (as opposed to being suppressed to the south and pushed out to sea as in previous runs). There are many complex moving parts, so forecast confidence is low at this point. However, ensembles and deterministic guidance suggest that rain could be possible at some point in the late Monday through Tuesday time frame, along with cool temperatures.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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VFR expected through Thursday night. BKN-OVC050 this evening into Thursday as low pressure passes to the north. This low will drag a cold front through early Thursday, with strong W flow 20-30 G 35+ kts in its wake. VFR conditions Friday through Monday. Breezy NW flow 10-20 G 25 kts Friday diminishes by Friday evening and remains light through the weekend.
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&& .MARINE...
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Marginal SCA gusts over northern Chesapeake Bay through late afternoon. SE SCA gusts expected tonight over middle MD Chesapeake Bay/lower tidal Potomac. Gale Warning for all waters Thursday with blustery W flow. Gale Warning continues for MD Chesapeake Bay waters Thursday night with SCA elsewhere as winds gradually subside. SCA may need to be extended into Friday. Pleasant boating conditions are expected through the weekend with high pressure overhead and light winds.
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&& .FIRE WEATHER...
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Drier air advecting into the region Thursday on gusty west winds could result in an enhanced risk of fire spread Thursday.
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&& .TIDES/COASTAL FLOODING...
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DC southwest Waterfront hit minor flood this morning due to mixed fresh and tidal input. Minor flooding is possible through tonight. Elevated water levels are expected elsewhere with light onshore flow, but flooding is not anticipated.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Wind Advisory from midnight tonight to 6 PM EDT Thursday for MDZ501. VA...Wind Advisory from midnight tonight to 6 PM EDT Thursday for VAZ503-504-507-508. WV...Wind Advisory from midnight tonight to 6 PM EDT Thursday for WVZ501-503-505-506. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ530>532-538>540. Gale Warning from 6 AM Thursday to 6 AM EDT Friday for ANZ530>534-538>541-543. Small Craft Advisory from 8 PM this evening to 6 AM EDT Thursday for ANZ533-534-537-542-543. Small Craft Advisory from 6 PM Thursday to 6 AM EDT Friday for ANZ535>537-542. Gale Warning from 6 AM to 6 PM EDT Thursday for ANZ535>537-542.
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&& $$ SYNOPSIS...IMR/DHOF NEAR TERM...IMR/DHOF SHORT TERM...IMR/DHOF LONG TERM...KJP AVIATION...IMR/DHOF/KJP MARINE...IMR/DHOF/KJP FIRE WEATHER...IMR/DHOF TIDES/COASTAL FLOODING...IMR/DHOF

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