Area Forecast Discussion
Issued by NWS Sterling, VA

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298 FXUS61 KLWX 240804 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 404 AM EDT Thu May 24 2018 .SYNOPSIS... High pressure build across the Mid-Atlantic today and tonight, then move offshore on Friday. Weak disturbances may cross the area over the weekend, before a potential low pressure system approaches early next week. && .NEAR TERM /THROUGH TONIGHT/... Surface high pressure is located over the southern Great Lakes region this morning. Satellite imagery shows valley fog is most widespread west of the Appalachians, though lowering visibility observations west of the Blue Ridge suggest some fog could occur in a patchy nature through sunrise. The high will move overhead today, resulting in dry weather, light winds, and a few cirrus clouds. Thermal profiles aren`t appreciably different from Wednesday, so would expect similar high temperatures in the lower to mid 80s. The high will begin to move offshore tonight, with light winds and mostly clear skies expected. Low temperatures will range from the lower to mid 50s in outlying areas to the mid 60s in the cities. Patchy valley fog will be possible again. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Return flow on the back side of the high will become established on Friday. Increasing low level moisture will advect from the southern Appalachians toward the Ohio Valley. Lift from the terrain may spark a few showers in our western areas, though dry mid levels will likely limit coverage. This moisture will continue to advect around the ridge that will be located off the southeast coast Friday night. Have kept slight chance PoPs west of I-81 for now, though some guidance suggest showers could eventually wrap eastward along the I-70 corridor. High temperatures will likely inch into the mid to upper 80s on Friday, with increased dew points and cloud cover keeping lows in the 60s Friday night. Moisture advection will continue into Saturday. There may be a weak disturbance originating from the southeastern states which moves northward into the area as well. Lapse rates will be weak, but the warm and humid airmass will aid in shower and thunderstorm development through the day. While there`s still some uncertainty in coverage due to the location of any focus mechanism, am thinking chances for seeing rain at some point during the day will be more likely than not. Have edged PoPs upward, and it`s possible that trend will need to continue. Wind fields are forecast to be relatively weak, so any threat from these storms would come from locally heavy rain as precipitable water increases above 1.75 inches. There should be a downward trend in shower coverage Saturday night due to the loss of heating, but additional vorticity advection could keep a few showers going. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... On Sunday Bermuda high will be settled over the Atlantic as a low pressure system will be moving north along the Gulf coast Sunday into Monday. Winds will be south to southwesterly over us as moist and warm air continues to be advected into our region. This will allow temperatures to rise into the mid 80s. Diurnal heating may lead to the formation of showers and thunderstorms in the afternoon/evening hours. A front will approach our area Monday while the position of the low pressure system from the Gulf is still uncertain. Depending on it, additional moisture to our region Monday into Wednesday will continue the chance of showers and thunderstorms. Hydrology concerns will need to be monitored due to the continued threat of showers and thunderstorms in the high precipitable water environment. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... VFR is expected through Friday night as high pressure builds across the area. The chance for fog at any of the terminals through the period looks slim, although MRB would stand the highest chance. Winds will become N then NE today, generally less than 10 kts. Southerly flow will become established Friday. A disturbance will increase the chance of showers and thunderstorms on Saturday. Warm and moist air Sunday into Tuesday will allow for additional showers and thunderstorms with possible periods of sub- VFR conditions. && .MARINE... Northerly to northeasterly around 10 knots are expected today. As high pressure moves offshore tonight into Friday, southerly flow will develop, but should remain below SCA criteria. Some of the wider waters of the Bay may come close to SCA criteria Friday night as southerly flow increases. Winds may also be marginal on Saturday, although the larger threat may come from thunderstorms during the afternoon and evening. Winds will likely remain below SCA criteria from Sunday into Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...IMR AVIATION...ADS/IMR MARINE...ADS/IMR is the U.S. government's official web portal to all federal, state and local government web resources and services.