Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220104 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 904 PM EDT Mon May 21 2018 .SYNOPSIS... A front will remain over the Carolinas into the Appalachian Mountains today through tonight. The front will return north as a warm front on Tuesday with a cold front expected to pass through the area on Wednesday. Weak high pressure will build over the area for the second half of the week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Showers and thunderstorms in advance of a (very) slow moving warm front have been rather persistent over the highlands of eastern West Virginia and west-central Virginia the last few hours. Low-level warm/moist advection and residual instability should allow these storms to continue until around midnight before gradually weakening. Isolated instances of flooding are possible given high PWAT air and slow storm motion. Precipitation should gradually weaken and become less widespread as it pushes east overnight. Still, scattered showers and a thunderstorm or two are possible into Tuesday morning ahead of the slowly advancing warm front. Patchy fog is expected as well but widespread dense fog seems unlikely with scattered to broken cloud cover moving overhead tonight. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... After some morning low clouds and patchy fog, the warm front will lift northward, although the extent of which is still in question. This should place much of the region in the warm sector by mid-afternoon Tuesday, especially DC southward. Therefore, instability in this region will increase with MLCAPE values progged to reach 1000-1500 J/KG. While shear will be modest, on the order of 25-30 knots, this combination will likely be enough to support a few strong to isolated severe thunderstorms, and the region has been placed in a Marginal Risk for severe thunderstorms. Synoptically, an area of low pressure will be moving into the eastern Great Lakes, with a cold front trailing into the Ohio Valley. Across the Mid- Atlantic states, a lee trough is expected to develop, and will likely serve as the focus for thunderstorm development Tuesday afternoon, with convection then moving eastward. An area from the Blue Ridge east and DC south currently appears to have the highest chances of seeing stronger thunderstorms. In addition, with precipitable water values in excess of 1.5" and saturated soils, the risk of some isolated incidents of flooding will be increased. High temperatures Tuesday will range from the mid 70s to low 80s. The cold front will then approach the area Tuesday night, and while convection associated with the frontal boundary should be weakening, some may make it into western/central MD and eastern WV late Tuesday evening. Lows Tuesday night in the 60s. The front should complete its crossing the first half of Wednesday and settle across North Carolina Wednesday night. A few lingering showers and isolated thunderstorms may be around Wednesday, although coverage should be much less than Tuesday. Dry conditions area-wide are then expected Wednesday night. Highs Wednesday will range from 80-85F with lows in the 50s/60s. && .LONG TERM /THURSDAY THROUGH MONDAY/... A high pressure system will shift eastward into our region from the Great Lakes region on Wednesday. Winds look to remain mostly light and variable. 850 and 700 mb humidity levels look to remain fairly low which will lead to mostly clear skies Thursday through Friday. The high will shift eastward off the eastern seaboard. A south to southwesterly flow will form leading to weak warm air advection developing. Temperatures will trend upward moving into the weekend. High temperatures on Thursday will be in the upper 70s to mid 80s and will slowly trend up into mid to upper 80s on Friday. On Saturday, a strong south to southwesterly flow will be in place over the region due to a high pressure sitting off the eastern sea board. Temperatures will rise up into the upper 80s to lower 90s. Rising temperatures and influx of tropical moisture from the gulf will lead to a chance for some shower and thunderstorm development. Sunday, the interaction of tropical moisture and higher temperatures along with a approaching cold front from the west will lead to increased chances for precipitation and thunderstorms. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... A warm front gradually approaching from southern Virginia will lead to the development of lower stratus with MVFR/IFR ceilings likely by early Tuesday morning. There is also the potential for some patchy fog/br. The front will then move northward Tuesday morning before a weak cold front passes through Wednesday. Conditions will gradually improve during the day before scattered showers and thunderstorms develop Tuesday afternoon and evening. These showers/storms will then wane Tuesday night, although chances will linger into Wednesday. Light winds and mostly clear skies on Thursday will lead to VFR conditions. Friday, a weak southerly flow forms but VFR conditions are expected. && .MARINE... A few gusts to around 20 knots have been observed early this evening but will diminish with the loss of mixing. A front will then approach the waters tonight from southern Virginia and cross the region Tuesday, before a cold front passes through Wednesday. Showers and thunderstorms are likely Tuesday, especially during the afternoon and evening hours. Some storms may contain gusty winds. South to southwest winds will increase on Tuesday, followed by northwest flow behind the cold front Wednesday. Winds may reach SCA criteria Wednesday. A high pressure system will influence the region leading to light and variable winds Thursday. No small craft advisory is expected. A southerly flow is expected to form Friday leading to winds flowing northward up the Chesapeake. && .TIDES/COASTAL FLOODING... Freshwater continues to decrease as water levels on the Potomac River upstream have crested and they continue to fall. Therefore, the threat for moderate flooding has ended. Minor flooding is still expected near times of high tide through tonight, and it is possible Tuesday for Washington DC. Will continue with the advisory through tonight, and it may need to be extended into Tuesday as well. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 6 AM EDT Tuesday for DCZ001. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MM NEAR TERM...MM/DHOF SHORT TERM...MM LONG TERM...JMG AVIATION...MM/DHOF/JMG MARINE...MM/DHOF/JMG TIDES/COASTAL FLOODING...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.