Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231836 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 236 PM EDT Sat Sep 23 2017 .SYNOPSIS... Surface and upper level high pressure will remain in place through the weekend and into early next week. The high will slowly weaken its grip over the area by the middle of the week as Hurricane Maria moves northward through the Western Atlantic. && .NEAR TERM /THROUGH TONIGHT/...
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High pressure in control of the synoptic pattern both at the surface and aloft. Anticipate that tonight`s weather will be comparable to last night. Guidance backing off slightly on fog coverage, which is slightly curious. Would think that Virginia would be preferred due to light onshore flow. Am carrying patchy coverage, favoring the valleys of the Piedmont and foothills. Lows in the mid 50s-lower 60s, except 65-70 in the urban centers.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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The synoptic pattern will change little Sunday and Monday as well. If anything, ridging aloft will only grow stronger until a weakness emerges as a result of Maria. A slight warming surface through 925 mb suggests that upper 80s/near 90 will be within reach Sunday afternoon. Highs may retreat a degree or so by Monday. Patchy fog likely to be a concern each morning. Latest guidance does suggest that Maria will be approaching the coast late Monday into Monday night. It is unclear how close or what the full impacts will be, although they likely will be minimal through Monday night. Have increased cloud cover and PoPs Monday night...but only enough for partly cloudy skies and a slight chance of precip over the tip of southern Maryland. Consult the latest bulletins from NHC on the latest thinking on the progress of Maria.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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High pressure on the surface an aloft will allow for dry conditions over the region part of Tuesday. At the same time Hurricane Maria will be moving north-northwest over the west Atlantic Tuesday. Guidance suggests that Maria will get close to the NC Outer Banks and it will stall there Tuesday night into maybe Thursday when an upper trough/cold front pushes it out to sea. Most guidance does not show significant impact to our region, but the progress of Hurricane Maria should be monitored. Please visit the National Hurricane Center`s website hurricanes.gov for more information. The cold front that is expected to move through our CWA on Thursday will increasing the chance of showers over our area. Dry conditions return behind it later on Thursday and Friday. Another front approaches on Saturday.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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VFR flight conditions will prevail for the valid TAF period, aside from early morning fog concerns. CHO/MRB terminals will be the most impacted. Am forecasting MVFR at this point. IFR possible, but its likely to be brief and would be tough to pinpoint. The pattern will be similar through Monday. There may be an increase in cloud cover on Monday night in advance of Maria; its extent unclear at this point. Mainly VFR conditions expected Tuesday into Thursday but some sub-VFR conditions possible later with maybe some showers around. A further deviation northwest in the track of Maria could bring worse conditions. Refer to latest NHC statements for up-to-date information on Maria.
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&& .MARINE...
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Light north flow (10 kt or less) will prevail thorugh Monday night. Wind gusts increase Tuesday into Thursday with Hurricane Maria over the west Atlantic Ocean. Small craft advisory anticipated. If the storm`s track deviates further northwest, more significant impacts are possible (though not likely). Refer to latest NHC statements for up- to-date information on Maria.
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&& .TIDES/COASTAL FLOODING...
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Water levels remain between a foot and a foot and a half above astronomical normals. There has been a slight weakening in this influx though, something that guidance suggests will continue. Further, the daytime tide cycle is the lower astronomically. So while the pattern will support minor inundation for several days, confidence in any inundation is highest for the upcoming tide cycle. Ensemble guidance supports this approach. As a result, will not extend Advisory beyond the overnight cycle for DC/Alexandria and Annapolis. Did extend through Sunday for St Marys and Calvert (due to Solomons only). Beyond that, will need to monitor trends and latest guidance. Anticipate the threat of minor inundation at sensitive locations will be an issue for several days at least.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 2 AM EDT Sunday for DCZ001. MD...Coastal Flood Advisory until 8 AM EDT Sunday for MDZ017-018. Coastal Flood Advisory until 1 AM EDT Sunday for MDZ014. VA...Coastal Flood Advisory until 2 AM EDT Sunday for VAZ054. WV...None. MARINE...None.
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&& $$ SYNOPSIS...JE NEAR TERM...HTS SHORT TERM...HTS LONG TERM...IMR AVIATION...HTS/IMR MARINE...HTS/IMR TIDES/COASTAL FLOODING...HTS

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