Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201852 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 252 PM EDT Sat Aug 20 2016 .SYNOPSIS... Weak high pressure will continue to drift east from the Mid- Atlantic coast through tonight. A cold front over northern Illinois will move through the central Mid-Atlantic Sunday afternoon into the evening. High pressure then builds over the area into Tuesday before persisting offshore through the rest of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 2pm, 1020mb surface high is over the Canadian Maritimes with a surface ridge stretching SW to the northern Mid-Atlantic coast. South winds up to 10 mph have developed over the area with dewpoints holding in the mid 60s over the Balt-Wash metro and around 70F in the SWrn zones. Cu field clearly marks where the higher dewpoints and scattered shower/isolated thunderstorm risk persists rest of the afternoon - much denser cu central VA Blue Ridge and W/NW. Diurnal showers end this evening, but the warm/moist sector ahead of the cold front over the Midwest will enter from the west overnight. T-storm chances increase west to east late tonight. Activity looks to extend as far east as central MD by sunrise Sunday. Increased moisture may allow for patchy radiation fog Piedmont and west tonight, though increased clouds will limit such development. Min temps generally low 70s as dewpoints increase. Sunday, cold frontal passage looks to enter the CWA from the west around midday and clear the Bay by 9pm. Scattered showers/t-storms spread in advance of line(s) of thunderstorms associated with the front. Pwats increase to 2.2 inches, indicating heavy rain rates. However, 25 kt bulk shear will keep the storms progressing, limiting the flash flood risk to sensitive locations that have repeating cells. 09Z SREF indicates MLCAPE struggles to exceed 1000 j/kg. Marginal shear and instability results in a marginal risk for damaging wind. Max temps to hit 90F east of I-95 where heating is longest ahead of the precip. Otherwise, max temps mid 80s. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... The cold front clears the Bay late Sunday evening with the bulk of upper trough energy PA and north. Sharp end to precip clears the Bay before midnight with NWly flow (gusting to 25 mph) and a truly dry air mass spreading across the area for the first time since late June. High pressure builds through Monday night. Sunday night min temps low to mid 60s inland, Monday max temps low to mid 80s, and Monday night min temps 50s west to low 60s east. Water temperatures are in the low to mid 80s, so near shore locations will remain warm. && .LONG TERM /TUESDAY THROUGH SATURDAY/... High pressure of Canadian origins will position itself over the area leading to cooler and much less humid conditions Tuesday into Wednesday. As the high moves off shore, southwesterly flow will bring a return to warm and humid weather by late in the week. A cold front will approach from the west and likely stall near the area late in the week into next weekend increasing chances for showers and thunderstorms. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... VFR conds persist into tonight as high pressure shifts east from the coast. Light sly flow slowly increases moisture with overnight clouds increasing in coverage. Scattered showers and isolated thunderstorms spread east from the Allegheny Mountains to the DC metros overnight. Thunderstorm coverage increases until the cold front crosses the DC metros from the west in the late afternoon/early evening. High pressure then builds overhead through Monday night with VFR conds expected. NWly flow Sunday night around 20 kt. Mainly VFR expected Tuesday-Wednesday as high pressure shifts east and flow turns southerly. && .MARINE... High pressure drifts from the coast through tonight with continued light southerly flow. Cold front approaches Sunday morning and crosses Sunday evening. Gusty showers and thunderstorms ahead of the front likely to warrant special marine warnings. High pressure then builds overhead through Monday night with clear and dry conditions expected. NWly flow Sunday night gusts 20 to 25 kt, so an SCA will be issued. High pressure over the waters and light winds below Small Craft Advisory levels during the middle of the week. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...DFH AVIATION...BAJ/DFH MARINE...BAJ/DFH

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