Area Forecast Discussion
Issued by NWS Sterling, VA

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356 FXUS61 KLWX 220801 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EDT SUN MAY 22 2016 .SYNOPSIS...
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A low pressure near Cape Hatteras today will head northeast through Monday. High pressure will slide southeastward from the Ohio Valley on Monday into the southeast on Tuesday and then move off the coast Wednesday, where it will remain for the rest of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Upper level low is currently taking shape in north-central PA per water vapor and radar. Locally, low level moisture and weak lift is producing drizzle with pockets of steadier rain. This is reducing visibility some, but fog/mist is not expected to be dense outside of the mountaintops (due low clouds). The suite of hi-res models paint the gloomy picture in store for today as the upper low drifts south to VA. Expect rain over PA to likewise move southward, eventually encompassing roughly the northern two-thirds of the area. Have changed forecast wording to periods of rain (where POPs categorical) through early afternoon. Didn`t go with 100 POPs yet due to some placement uncertainties, but a fairly widespread area will likely see a period of steady rain. Slightly drier air will begin to wrap into the low this afternoon. Simulated reflectivity suggest precip will become more showery by this time. In addition, some weak instability may build generally west of I-81, so can`t rule out a few thunderstorms there. Expect another day where temperatures struggle to reach 60, especially the eastern half of the area where rain is expected to persist longest. By tonight, the upper low will be drifting to SE VA, and combined with the diurnal trend, precip should diminish in coverage, eventually becoming focuses in the Fredericksburg-S MD vicinity. Low clouds and light fog will develop again, and can`t rule out some drizzle. Close to persistence for lows...upper 40s to mid 50s.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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The upper low will be pivoting near the Outer Banks and offshore on Monday as it spawns a surface low pressure. This will keep a moisture feed into the area and would thus expect mostly cloudy skies to continue. Models insist on higher cloud bases though and perhaps even a few glimpses of sun. This deeper mixing is giving highs in the upper 60s to perhaps lower 70s, but I`m a little skeptical it gets that warm. Also with this heating, there should be some instability building by afternoon, so showers will likely develop with perhaps a few thunderstorms, especially the further west you go. By Monday night, the low will be moving toward Cape Cod, so expect showers to diminish, with any lingering activity east of the Blue Ridge. Unfortunately, there will still be enough moisture wrapping around the low to keep a small chance of showers east of I-95 through midday Tuesday, perhaps extending into the afternoon (along with an isolated rumble of thunder). However, with diminishing cloud cover, it looks like a majority of the area will make it into the 70s. Ridging at the surface and aloft arrives in earnest Tuesday night with lows in the 50s to near 60.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Generally warmer and more humid through the long term as a much more summer-like pattern develops. Ridge axis will remain to our west on Wednesday with a northwest flow aloft likely suppressing any convection despite increased instability. By Thursday the ridge axis is passing and a weak shortwave is approaching. Combined with the still increasing warmth and moisture...thunderstorm chances over the higher terrain to the west will increase. Some may try to reach the lower elevations to the east before dissipating. Another ridge axis approaches Friday but by this point instability may be great enough thanks to continued increase in warmth and humidity that convection may develop along the terrain to the west regardless. Saturday a ridge of high pressure aloft looks to develop directly overhead...but the excessive warmth and moisture may still overcome any suppressive effects and cause spotty showers and thunderstorms to develop over the mountains and potentially advect east before dissipating. By this point highs in the lower elevations may reach 90 for the first time this year...notably later than normal by several days. Lows will be sultry with 70s possible in the urban centers.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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Currently a mixture of MVFR, IFR, and localized LIFR across the area early this morning, with light rain and drizzle at times. Have some gradual improvement after daybreak, but this will likely be minimal, especially northern parts of the area, as light rain become more widespread. Tough to time in any breaks except perhaps CHO. Precip may become more showery by late afternoon, and this may be the best chance for a solid push of MVFR. However, expect low clouds and fog to redevelop tonight. Have limited this to MVFR for now though. Winds light and generally N or NW. Monday will remain cloudy, but models insist on higher cloud bases, perhaps VFR at times. Showers will redevelop quickly by midday though and there could be a thunderstorm. As precip diminishes Monday night, there is a chance of lower clouds and perhaps fog, especially eastern areas. Conditions will improve Tuesday as high pressure builds with light NW winds. VFR later next week.
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&& .MARINE...
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Northerly winds persisted up to 20 kt quite a bit into the night, but looks like they are falling below SCA criteria now, so will let it expire. With a second area of low pressure developing offshore, winds will remain northerly through Monday night or so, but at this time, magnitudes appear to be less than 15 kt. High pressure will begin building Tuesday with winds become NW then W. Light winds overall thru late next week.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...None.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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