Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200046 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 846 PM EDT Sat May 19 2018 .SYNOPSIS... A warm front over southern Virginia will slowly lift northward tonight. A cold front approaching from the Ohio Valley will cross the Mid-Atlantic from west to east Sunday, then stall to the south Sunday night into Monday. This front will return northward as a warm front late Monday into Tuesday. Another cold front will approach from the Great Lakes Wednesday, with high pressure following later in the week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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845 PM: Dense Fog Advisory issued for Baltimore/Harford Counties. Light winds and humid low-level airmass have resulted in areas of dense fog, with reports of visibility near zero at times (from trained spotters). There aren`t many ASOS/AWOS observations in the advisory, but traffic cameras in the area show dense fog as well. The fog should begin to lift by midnight as southerly flow increase to 5 to 10 mph. Previous AFD: Flood Watches have been dropped. There are still ongoing Flood Warnings along main stem rivers (including much of the Potomac River), and given the amount of rain and runoff we have received, these warnings will likely last for at least the next day or two in some places. Patchy fog and drizzle with low clouds are expected as the airmass remains soupy and stagnant. Low temperatures won`t budge much from where they are now. A few scattered showers (measurable rain) are possible as well, with an isolated thunderstorm possible over the highlands this evening.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Should see some breaks in the clouds Sunday with as winds turn westerly. Scattered afternoon/early evening showers and t-storms are anticipated as cdfnt from the OH valley crosses the area. Southern MD will be again the most vulnerable area for flash flooding due to saturated soils and is the area where models show the best moisture convergence. Faster cell motion and mid- level winds nearly perpendicular to sfc front should keep cells moving and minimize flash flooding threat. The front will be returning north again on Monday with additional showers expected especially west of the Blue Ridge. && .LONG TERM /TUESDAY THROUGH SATURDAY/... A chance of showers and thunderstorms will continue into Tuesday, with a front draped across our southern zones. Temperatures will be in the upper 70`s to low 80`s across the region, depending on the exact location of the front. A chance of showers and thunderstorms again on Wednesday, as a stronger low pressure system passes by to our north. A little more agreement in the latest guidance as far as frontal passage timing. The front should be through the area by Wednesday night. Temperatures will remain in the low 80`s. Nor a lot of precipitation expected during these two days, with maybe a quarter of an inch of additional precipitation. However, higher amounts are possible in areas that experience thunderstorms. High pressure builds into the area Thursday, and quickly slides off the east coast by Friday. Expect dry conditions during this period, along with seasonable temperatures. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... LIFR/IFR conditions tonight improving rapidly to VFR after 14Z Sun as winds turn from the west. A chance of t-storm sites Sun aft mainly IAD/DCA ahead of an approaching cold front. Sub-VFR possible in patchy fog Sun night, then in increasing showers Mon-Mon night as aforementioned boundary returns north as a warm front. Mainly VFR conditions forecast Tuesday and Wednesday, with threat of sub-VFR conditions being a passing shower over the terminals. Winds will be light and favor a southwesterly trajectory on Tuesday, turning Westerly on Wednesday. && .MARINE... SCA conditions gradually expand the waters tonight, then subside by late Sunday after the passage of a cold front. Winds should be light as the front stalls to the south Sunday night, then slowly returns north as a warm front late Monday through early Tuesday. SCA possible late Tuesday into Wednesday as another cold front approaches from the Great Lakes. && .TIDES/COASTAL FLOODING... Water levels are running around 1 to 2 ft above astronomical predictions on the Bay and lower tidal Potomac. Minor coastal flooding is expected at Annapolis and Straits Point late tonight and Sunday, and is possible elsewhere. For the upper tidal Potomac around Washington DC and Alexandria, fresh water piling down from the Potomac River will cause anomalies to continue increasing tonight. This will affect Georgetown more than southwest DC or Alexandria. -For Alexandria: An advisory is in effect through 4 PM Sunday. -For Washington DC: Georgetown will be the driver due to the freshwater contribution, where moderate flooding is forecast for five cycles (with levels not dropping below minor through Sunday night). At the southwest waterfront, best confidence for moderate flooding will be near high tide tonight through Sunday; subsequent cycles may only be minor flooding. A Coastal Flood Warning is in effect for Washington DC through Sunday and it may need to be extended through Monday. A Coastal Flood Advisory is in effect for Alexandria through 4PM Sunday, and it may need to be extended through Monday as well. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Warning until 10 PM EDT Sunday for DCZ001. MD...Dense Fog Advisory until midnight EDT tonight for MDZ006-011- 507-508. Coastal Flood Advisory until noon EDT Sunday for MDZ017. Coastal Flood Advisory until 3 PM EDT Sunday for MDZ014. VA...Coastal Flood Advisory until 4 PM EDT Sunday for VAZ054. WV...None. MARINE...Small Craft Advisory until 6 PM EDT Sunday for ANZ530-531-535- 538>540. Small Craft Advisory until 6 PM EDT Sunday for ANZ532>534-536- 537-541>543.
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&& $$ SYNOPSIS...DHOF NEAR TERM...LFR/DHOF SHORT TERM...LFR/DHOF LONG TERM...CJL AVIATION...LFR/DHOF/CJL MARINE...LFR/DHOF/CJL TIDES/COASTAL FLOODING...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.