Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221408 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1008 AM EDT SUN MAY 22 2016 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/... Shortwave energy evident on water vapor loop across western Pennsylvania this morning. Corresponding light rain and drizzle has moved south into the forecast area. Database has been updated. Already had periods of rain in there; timing and areal coverage were adapted to account for latest trends, and increased PoPs to near 100 percent. Otherwise, forecast looks to be on track. It`s a wet and gloomy day across much of the area. There may be a few breaks in the overcast across central Virginia, but guidance suggesting that these will fill in by mid-afternoon. 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. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... 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. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... 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. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... MVFR/IFR flight conditions across the area at this time. The lower cloud deck has been intermittent, which is only part of the reasoning behind the variable conditions. Light rain and drizzle have developed; its intensity varies, which also is a contributing factor. Expect similar conditions through the midday hours. 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. && .MARINE... North winds generally around 10 kt this morning. 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. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...HTS/ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...HTS/ADS/RCM MARINE...HTS/ADS/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.