Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 300800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Sat Jul 30 2016 .SYNOPSIS... A weak front will remain across the area today and tonight. An area of low pressure will track along the front on Sunday. The front will move southward on Monday, with high pressure building in for the middle portion of the week. && .NEAR TERM /THROUGH TONIGHT/... Surface features are somewhat nebulous this morning, as a weak boundary reamins across the Mid-Atlantic to the Ohio Valley, and a second boundary over northern NC. Obs indicate some patchy light fog across the region, although mid and high clouds will be increasing. Cluster of showers in the Roanoke-Lynchburg vicinity indicated the leading edge of a theta-e ridge which will be advecting northward this morning ahead of a baggy 850 mb low over the Ohio Valley. There is some model spread as to whether this will result in only scattered showers, or if more significant convection develops as CIN erodes by mid-morning. This evolution could affect the remainder of the day and whether there is a break as the nose of the moisture convergence pushes into PA. If this is the case, the secondary generation of storms this afternoon would be over the higher terrain, slowly drifting east this evening. If not, there could be a rather muddled conglomeration of storms over mainly the northern part of the area. Needless to say, an unsettled day is expected with low confidence in the details. These details are mildly important due to the moisture rich airmass which will be in place, a deep warm cloud layer, and steering flow around 20 kt. This could lead to a localized flash flood threat, especially in areas which have seen heavy rain in recent days. However, given the best convergence is expected to lift into PA, have opted to leave in the HWO for now. Also, if morning/midday precip is spotty or quickly exits, sufficient destabilization could lead to a few strong storms with deep layer shear around 30-35 kt. An isolated damaging wind gust would be the primary threat. Have indicated a gradual diurnal diminishing trend to the POPs, although some uncertainty exists due to the wavering front. Highs today will depend on the amount of cloud cover and precip, but could approach 90 in a few spots. Lows tonight will be the the upper 60s to lower 70s for most. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... On Sunday, upper level troughing will gradually spread east from the Ohio Valley, and weak low pressure will track along the stalled front. Combined with modest destabilization, this will likely be enough for additional showers and thunderstorms to develop, particularly during the afternoon and evening hours. Overall moisture quality looks to be lower Sunday with a more westerly low level flow, but PWAT will still be seasonably high, so more locally heavy rain can`t be ruled out. As the low tracks east, should see activity taper off overnight. On Monday, the mid-level trough axis will be crossing the area, and a secondary surface trough may also provide some convergence. Therefore, at least a few scattered storms will be possible. This axis will swing east during the evening, allowing a quick end to precipitation. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Troughing aloft and ridging at the surface will provide for relatively pleasant and dry early August weather for Tuesday and Wednesday. ECMWF hints at possible convective system in NW flow around the periphery of another building central US ridge, but will disregard for now given difficulty of pinpointing these systems days in advance, and tendency of them to curl southward into greater instability. Highs in the 80s and dew points in the 60s under mostly sunny skies. Ridging aloft begins to build back into the area by the end of the week with hotter weather likely returning. Thursday/Friday still look relatively dry, with perhaps a few isolated showers/storms, mainly terrain driven, with some moisture return. Highs back up to around or above 90F. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... BWI/MRB are nearing MVFR vsby this morning, but encroaching mid and high clouds should keep the fog in check. Complex forecast today for showers and storms. There may be at least scattered activity spreading from S to N across the area during the morning, with perhaps a break before additional storms move east from the mountains this afternoon. Heavy rain and gusty winds will be possible, especially with the afternoon storms...while the morning showers may carry a period of lower cigs. Storms will likely diminish this evening. There is a decent signal in guidance for fog and/or low clouds tonight; however am hesitant to bite on it this far in advance. Additional thunderstorms could develop Sunday afternoon and evening as a front drops into the area. A few storms can`t be ruled out for Monday either as the front finally pushes south. Predominantly VFR expected Tuesday and Wednesday of next week. Only restrictions may come in some patchy fog at night/early morning. && .MARINE... Light S/SE flow expected through the morning. There could be an increase, especially on the wider waters, this afternoon and evening, but have capped at 15 kt for now. Gusty winds from thunderstorms will be a threat as well. Overall, light flow is expected through Monday, with the main hazard coming from scattered afternoon and evening storms each day. A cold front will bring a shift to W/NW winds on Monday. Near-SCA conditions are possible Tuesday on northerly flow with high pressure building in. Winds decrease Wednesday. && .TIDES/COASTAL FLOODING... Tidal anomalies under a half foot this morning will increase this afternoon and tonight as southeast low level flow increases and additional rain/thunderstorms develop. Minor coastal flooding possible with tonight`s/early Sunday morning`s high tide cycle, especially Annapolis/Baltimore. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...MM AVIATION...ADS/MM MARINE...ADS TIDES/COASTAL FLOODING...MM

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