Area Forecast Discussion
Issued by NWS Sterling, VA

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732 FXUS61 KLWX 201858 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 258 PM EDT Wed Jul 20 2016 .SYNOPSIS...
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High pressure will build southeast over the area through tonight before drifting offshore through Thursday. A cool front will sag into the area Friday night before stalling to our south over the weekend. High pressure will be in control of the area weather Saturday through Monday. A cool front looks to enter the area Monday night and linger just south of the area into the midweek.
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&& .NEAR TERM /THROUGH THURSDAY/...
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As of 3pm, upper 50s to low 60s dewpoints have settled over the area with 1025 mb surface high pressure just SE of Lake Erie. This high will shift southeast and overhead tonight. Clear and calm overnight with typical valley and piedmont fog/ground fog. Min temps low 60s inland (around 60F west of the Blue Ridge) with low to mid 70s along the shoreline (water temps low to mid 80s). High pressure shifts east offshore Thursday with a Sly return flow developing in the afternoon across the area. Moisture returns. Max temps around 90F with dewpoints rising to the mid 60s, just a couple degrees heat index. 850mb temps rise to 20C west of the Blue Ridge by 00Z Friday, closer to 17C east at that time.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
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Tranquil Thursday night with high pressure still over the region. Light Sly flow with a warmer night than tonight, upper 60s inland and mid 70s nearshore. Low pressure tracks east across northern Quebec Friday into Friday night. Associated cold front will be quite strung out by the Mason-Dixon line Friday evening. Ahead of this front, expect 850mb temps to increase to 20 to 22C with max temps mid 90s, upper 90s possible in best mixing. Dewpoints mid to upper 60s with heat indices around 100F in the coastal plains. May need a very targeted heat advisory for urban centers. PoPs delayed to Friday evening with the weak forcing from the cool front enough to cause scattered thunderstorms. Severe thunderstorms are possible any time the temperature reaches the mid 90s with dewpoints in the 60s. Any activity should wane in the late overnight.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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Extended stretch of hot and humid weather over the weekend into at least early next week as broad ridge that has been across the CONUS noses into the mid-Atlantic. High temperatures near 100F combined with dewpoints AOA 70F will combine to create heat index values near 105F...with heat related headlines possible during this time. Urban areas will also see little nighttime relief as lows remain well into U70s in the humid airmass. Shower/Thunderstorm chances remain low over the weekend...with best chances with terrain induced circulations. Vort max passes well to our north Monday into Tuesday...allowing for H5 heights to fall some and for a cold front to approach the area. While the uncertainty regarding how far cold south front makes into our area is rather high, nearby frontal boundary could allow for some afternoon/evening showers and thunderstorms Monday and Tuesday, which could provide some relief from the heat.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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VFR through Friday night under high pressure that builds tonight and lingers offshore Thursday afternoon through Friday night. Best fog chances tonight, though not expected to be more than ground fog at TAF sites. VFR prevails this weekend through early next week under high pressure. Thunderstorm chances are low over the terminals during this time.
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&& .MARINE...
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High pressure builds southeast across the area through tonight with a north wind 5-10kt in advance. Light return southerly flow begins Thursday afternoon. Southerly flow continues through Friday night. Channeling may require an SCA Friday afternoon into the night. High pressure in control over the weekend, with southerly channeling developing overnight leading to elevated winds near SCA criteria.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...MSE AVIATION...BAJ/MSE MARINE...BAJ/MSE

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