Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 212359 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 759 PM EDT Wed Sep 21 2016 .SYNOPSIS... High pressure will build over the region through early Thursday then weaken through Friday. A cold front will move through the area early Saturday. High pressure builds again over the region early next week. && .NEAR TERM /THROUGH THURSDAY/... A few light showers are seen on radar over southern MD and the Fredericksburg area, but these are expected to dissipate early tonight as high pressure builds in and air mass dries out. Biggest question for tonight is whether high clouds will thin out and skies become clear. Latest 12Z ECMWF and HRRR simulated cloud IR imagery show high clouds sticking over the area around much longer than earlier runs with clearing not indicated now until after midnight or early Thu. Fog is not expected as models show sfc dewpoints dropping tonight. A few high clouds still possible Thu if the ECMWF is correct, but any high clouds are likely to be thin enough for a mostly sunny day. High pressure will be in control, although it will be weakening. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... Weak high pressure in control during this period. Temperatures are expected to warm up into the upper 80s and possibly reach 90F in a few spots on Fri. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Surface cold front will likely have passed south of the region by Saturday morning, behing pushed along by a 1030+ mb high pressure center originating near Hudson Bay Canada. The center of this high and coolest air will pass over New England, but much cooler weather is expected over the Mid-Atlantic as well especially during the second half of the weekend into early next week. Onshore flow may result in elevated humidity and low clouds and drizzle especially early next week. The operational GFS runs have been the quickest with an approaching cold front next week but have been trending slower towards a GEFS/EC blend. A slower solution seems more likely given the large blocky nature of the high pressure center that will be stationed just northeast of the region next week. This should keep more substantial rain chances at a minimum through much of the forecast period. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... VFR conditions next 24 hrs, except for possible 3-5SM mist at KCHO. Mainly VFR expected Saturday with northerly winds 10 to 15 knots. Sub-VFR possible later in the weekend with lower clouds as winds become easterly around 10 knots. && .MARINE... Winds will gust to around 15kt in the lower Bay through midday Thu before they begin to diminish. A pressure surge, aided by northerly channeling, will likely push winds into Small Craft Advisory territory on Saturday. Winds should gradually diminish and veer to the east Saturday night into Sunday. && .TIDES/COASTAL FLOODING... Water levels running less than a foot above astronomical normals, but departures are on the rise. Nonetheless this is proving to be enough to flirt with minor inundation thresholds at sensitive locations. Forecast has been running right on track...adding confidence for the upper tidal Potomac. Have added DC and Alexandria to the Coastal Flood Advisory. Anne Arundel County continues. Allowed St. Mary`s County to expire at 8pm. Elevated water levels persist through the rest of the week due to low pressure off the Carolina coast. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory from 11 PM this evening to 2 AM EDT Thursday for DCZ001. MD...Coastal Flood Advisory until midnight EDT tonight for MDZ014. Coastal Flood Advisory until 8 PM EDT this evening for MDZ017. VA...Coastal Flood Advisory from 11 PM this evening to 2 AM EDT Thursday for VAZ054. WV...None. MARINE...None. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...DFH AVIATION...LFR/DFH MARINE...LFR/DFH TIDES/COASTAL FLOODING...HTS/LFR

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