Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 150201 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 901 PM EST Tue Nov 14 2017 .SYNOPSIS... High pressure will remain over the area through Wednesday. A weak cold front will move across the area early Thursday. High pressure will return briefly Thursday night into Friday before a strong cold front moves through during the first half of the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Surface high pressure will continue to build overhead tonight bringing dry and chilly conditions. A thin stratus deck remains trapped underneath the subsidence inversion this evening...primarily across the northeastern half of the CWA. Usually when this happens the stratus clouds hang around for a while because of lack of mixing down dry air that remains above the inversion. With high pressure building overhead tonight...and ridging aloft ahead of the next cold front over the Midwest...this should allow the subsidence inversion to lower overnight. The lowering of the inversion should allow for clouds to gradually break late this evening into the overnight hours. The latest forecast reflects this and latest satellite imagery is showing more breaks in the cloud deck developing. However...confidence is low due to the strong inversion. With light winds and more breaks in the clouds developing...that will provide a good setup for radiational cooling. Min temps will range from the mid and upper 20s in the colder valleys and rural areas to the upper 30s/near 40 in downtown Washington and Baltimore.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
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An onshore flow will cause moisture to move in from the Atlantic...and this will cause more low clouds to develop and spread across the areas from east to west Tuesday morning through midday. The low clouds are most likely near/east of the Blue Ridge and Catoctin Mountains. Dense high clouds will also spread rapidly ewd through the day with skies likely to become overcast across all areas by early to mid afternoon. Drizzle and a light rain may break out in the marine layer near and east of the Blue Ridge and Catoctin Mountains Wednesday evening. Rain showers will also overspread western portions of the CWA after 7PM ahead of a cold front. The weak cold front will cross the area around 12Z Thu with drying conditions and breezy conditions developing. Warmer on Thu due to strong downslope flow.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... High pressure system will keep dry conditions on Friday into Friday night with light winds over our area. A strong low pressure system will move northeast over the Great Lakes as its associated cold front pushes east over our area sometime on Saturday. The timing of the front passage is still uncertain, but deterministic and ensemble guidance suggests showers -that could be heavy at times- are likely Saturday afternoon into the night. Breezy conditions are expected behind the front in a cold air advection regime. Some upslope snow showers are possible Saturday into Sunday. A high pressure builds behind this front Sunday into Tuesday with returning dry conditions. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
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Stratus deck is forecast to slowly clear late this evening into the overnight. Patchy fog is possible overnight into early Wednesday...but did not mention in the TAFS at this point since dry airmass should keep any fog localized at best. Low clouds will likely increase from east to west Wednesday morning through midday as moisture from the Atlantic moves in on an easterly flow. MVFR cigs are likely Wednesday afternoon. Areas of drizzle and IFR conditions are possible across the eastern Terminals Wednesday evening. A cold front will pass through late Wednesday night into Thursday morning and cigs/vsbys will improve during this time. Gusty NW winds expected Thu behind fropa. VFR conditions expected Friday. Precipitation possible Saturday as a strong cold front moves trough our area. Dry/VFR conditions return on Sunday.
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&& .MARINE...
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A weak pressure surge is likely to develop overnight into Wednesday morning and this will cause wind gusts up to 20 knots. Have issued an SCA for the Bay and lower Tidal Potomac River due to the relatively warmer waters enhancing mixing. However...it will be marginal. Winds will dissipate later Wednesday into Wednesday night. A cold front will pass through early Thursday and solid SCA conditions are expected behind the boundary into Friday morning. Winds are expected to stay below threshold later Friday into Friday night. Winds will increase on Saturday and remain breezy into Sunday, therefore, a small craft advisory is anticipated Saturday into Sunday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until noon EST Wednesday for ANZ532>534- 537-540-541-543.
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&& $$ SYNOPSIS...LFR NEAR TERM...BJL/LFR SHORT TERM...LFR LONG TERM...IMR AVIATION...BJL/IMR/LFR MARINE...BJL/IMR/LFR

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