Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230117 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 917 PM EDT Thu Sep 22 2016 .SYNOPSIS...
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Low pressure remains off the Carolina coast while high pressure is centered over New England. A backdoor cold front will move through the area Saturday. High pressure returns to the region Sunday through early next week.
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&& .NEAR TERM /THROUGH FRIDAY NIGHT/...
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There has been little change in the synoptic setup this evening...and for that matter, since yesterday evening. Clouds have been southeast of a CHO-EZF-NAK line. No precipitation has been detected, and don`t believe any will tonight. Therefore, will be running with a dry forecast. Elsewhere, mostly clear skies overnight might allow for some patchy radiational fog to develop across the typically favored valley locations. See no reason to make many changes to going forecast. Remaining warm Friday with warm air advection ahead of cold front. Limited cloud cover should allow for nearly full insulation...with high temperatures a few degrees warmer than today and nearly 10F above climatological normals.
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... Backdoor cold front pushes through the area Saturday morning. Models often have a difficult time capturing sensible weather trends (e.g., sky cover, temperature, winds) with backdoor cold fronts...so have nudged these elements accordingly. Front is moisture starved, so most areas will remain dry...though maintained slight chance PoPs for a spotty shower over the higher terrain. Cloud cover will keep temperatures cooler then previous days. Though, highs near 80s still appear possible as cooler/drier air remains displaced further north behind frontal boundary and doesn`t move in till later Saturday. Low dewpoints will allow overnight low temperatures to fall into the L60s across much of the area (50s across the north) Saturday into Sunday. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Deep ridging will traverse the region during the second half of the weekend into early next week. The center of surface high pressure will pass to the north and east of the region, so although high pressure will be in control onshore flow will likely lead to increasing low-level moisture and clouds. An upper-trough will cut off over the upper Midwest and try to move towards the area during the middle of next week, but the blocking high pressure over the northwestern Atlantic will likely slow its forward progress. The blocky/cutoff nature of the pattern lends to greater than normal uncertainty in the forecast during this time. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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VFR conditions expected tonight in the metros. Potentially there could be patchy fog, but confidence remains quite low so have kept it out of TAFs. At the typically favored locations (e.g., CHO and MRB) it`s a different story. Flight restrictions seem likely with IFR conditions possible. Generally have preserved the going forecast. VFR expected Friday through Saturday night. Expect a sudden wind shift to northerly as front moves through Saturday morning. Sub-VFR possible Sunday into Monday as low clouds may develop in onshore/easterly flow around 10 knots.
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&& .MARINE... Winds remain below SCA values this afternoon through Friday night with high pressure building into the area. Small Craft Advisories are possible Saturday and Saturday night with increased northerly flow behind frontal passage. Easterly flow around 10 knots around high pressure over the northwestern Atlantic should stay below Small Craft Advisory levels Sunday into Monday. && .TIDES/COASTAL FLOODING...
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Although higher than normal, water levels haven`t been high enough to achieve minor flood thus far. Annapolis on track to reach caution. No issues elsewhere on the Bay/lower Potomac. Washington DC and Alexandria at low tide right now, with levels below the previous HEC-RAS forecast. A rerun of the model this evening suggests the same result as in Annapolis-- both sites should reach caution but not minor flood. Elevated tidal levels remain after tonights cycle...though current forecast keeps levels below minor flood stage.
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&& .CLIMATE... Unusually warm weather has persisted over the area for quite some time. Autumn-like temperatures will finally make an appearance over the weekend likely bringing low temperatures at DCA below 60 degrees for the first time since June 9th, or 104 days ago. The record most consecutive days at or above 60 degrees in the Washington DC area is 112 set in 2012. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MSE NEAR TERM...HTS/MSE SHORT TERM...MSE LONG TERM...DFH AVIATION...HTS/MSE/DFH MARINE...MSE/DFH TIDES/COASTAL FLOODING...HTS CLIMATE...DFH

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