Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191550 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1050 AM EST Thu Jan 19 2017 .SYNOPSIS... High pressure will settle overhead today before moving off to the east tonight. A warm front will move into the area Friday and stall out nearby through Saturday. Low pressure will affect the area Sunday and Monday. Weak high pressure may approach the area Tuesday before a cold front approaches Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface high pressure will crest overhead today, leading to dry conditions and light winds. Guidance from yesterday has considerably underestimated both low and high level moisture, with plenty of lower cumulus clouds stuck under the subsidence inversion as well as some high cirrus moving in aloft from the southwest. Temperatures remain mild, with highs in the 50s area- wide.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Low pressure system will then push northeastward out of the Mississippi Valley and into the Lower Great Lakes late today and tonight before weakening on Friday. This will send an area of rain towards the Mid Atlantic states for Friday along the weakening warm frontal boundary. Current indications are that rain will begin to overspread the region from southwest to northeast in the late night/early morning hours, reaching the DC metro area between 8 AM and 10 AM. The period of rain will continue into the afternoon, tapering off by late afternoon. Low clouds as well as areas of fog and drizzle likely to continue into Friday night. Rainfall amounts on the light side, on average one to two tenths. Lows tonight in the 30s and 40s with highs on Friday from 45-55F, coolest northeastern Maryland where rain will be occurring during peak heating, warmest across the Shenandoah Valley and portions of eastern WV where rain ends earliest. Friday night lows drop back to around 40F or so. Saturday, while mainly dry, will likely see a continuation of low clouds with little flow, especially east of the Blue Ridge. Temperatures mild, with highs in the low-mid 50s east of the Blue Ridge under more clouds to low-mid 60s west where there`s better chance at some sun. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... A potent jetmax in the southern stream of the jet will continue to develop into a cutoff low Sunday over the Gulf Coast States. The low will track northeast into the Mid-Atlantic Sunday night and it will slowly pass by just to our east later Monday through Monday night. Warm and moist air from the Gulf of Mexico and Atlantic will overrun the surface cooler air in place well ahead of the low Sunday. A soaking rain is likely during this time. Soaking rains are likely to continue for Sunday night through Monday as the low approaches from the south. Rain may taper off Monday night or Tuesday as the low slowly moves off to our north and east and weak high pressure approaches. Precipitable waters over one inch are likely Sunday into Monday due to the moisture from the Gulf of Mexico and Atlantic. This is unusually high for this time of year. In is well above the 90th percentile for this time of year at KIAD. The moisture combined with the forcing from the low suggests that moderate to locally heavy rainfall is possible. 00z GEFS members are indicating around 2-3 inches of rain are possible with this system Sunday through Monday. Localized flooding is possible later Sunday and Monday...but confidence is too low to put in the Hazardous Weather Outlook at this time since rain will be spaced out over a couple days and our area will remain on the cool side of the boundary. A cold front may impact the area during the middle portion of next week...but unusually warm conditions are possible ahead of the boundary Wednesday. && .AVIATION /16Z THURSDAY THROUGH MONDAY/...
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Scattered to broken strato-cumulus clouds will continue this morning and into this afternoon, with generally VFR conditions. Will be some lingering periods of MVFR, especially MRB. In addition, some high clouds will overspread the region as well. Winds generally light at around 5 knots. VFR continues into tonight. IFR conditions then expected to develop on Friday with period of rain and lowering ceilings as a warm front crosses the region. Low clouds and areas of fog likely to persist Friday night, and possibly into Saturday as well. Low pressure will impact the terminals Sunday through Monday night. A soaking rain is likely along with IFR/subIFR conditions.
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&& .MARINE... Sub-SCA winds from the northwest today will turn light southerly tonight and into Friday with warm frontal passage. Light flow continues through Saturday, turning southeast and gradually increasing Saturday night. Low pressure will impact the waters Sunday through Monday. Weak high pressure will approach the waters Tuesday behind the departing low. A Small Craft Advisory will likely be needed for the waters during this time. A Gale Warning may be needed for portions of the waters Sunday night and Monday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BJL NEAR TERM...MM/RCM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM/RCM MARINE...BJL/MM is the U.S. government's official web portal to all federal, state and local government web resources and services.