Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191447 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1047 AM EDT Sat May 19 2018 .SYNOPSIS... A stationary front over central Virginia will slowly lift northward today. A cold front approaching from the Ohio Valley will cross the region from west to east Sunday, then stall to the south early next week. && .NEAR TERM /THROUGH TONIGHT/...
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Steady rainfall for the most part has pretty much ended with light rain or drizzle persisting through the afternoon. Up to a quarter of an inch may still fall mainly over southern MD along the slow moving front. So, no new or additional flooding is expected through tonight. Previous afd... Rain showers and perhaps a rumble of thunder could revisit our western zones from the Potomac Highlands to the Shenandoah Valley tonight. Of course, additional rain amounts would just exacerbate the flooding in parts of the region, but the duration of any rain showers shouldn`t be nearly as long as the past couple of days.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... A cold front will approach the region from the northwest Sunday. A few showers and a thunderstorm should accompany the front in the Potomac Highlands Sunday morning and midday, while the chance pushes east and south into northeast Maryland and eastern Virginia Sunday afternoon. The front pushes into central Virginia Sunday night and stalls across the state Sunday night and Monday. Showers and afternoon and evening thunderstorms on Monday could develop and move from west to east across our CWA. The highest rain amounts should be generally along the eastern slopes of the Blue Ridge Monday afternoon and Monday night. Temperatures on Monday should reach the lower 80s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... A chance of showers and thunderstorms will continue Tuesday with a front across our southern zones. The forecast for Wednesday into Thursday is very uncertain at this point. What is known is that a stronger low pressure system will pass well to our north, dragging a cold front through our area in its wake. The timing of this front is highly variable at this time, so will keep chance PoPs in the forecast for Wednesday, moving to slight chance for Thursday. The key thing to note here is that, upon passage, this front should bring in some much drier air behind it. Temperature forecasts for this scenario will almost certainly change, but for now, highs should be in the low 80`s on Wednesday, followed by a slight cool down on Thursday in the wake of the aforementioned cold front, with temps in the upper 70`s. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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IFR conditions today slowly improving to IFR/MVFR late today mainly at eastern TAF sites. Western TAF sites are more likely to remain in IFR/LIFR category. Mainly VFR conditions forecast Monday and Tuesday, with the only threat of sub-VFR conditions being a passing shower over the terminals. Winds will be light and favor a southerly trajectory. A frontal boundary will drop southward through the terminals late Monday, before stalling south of the terminals through mid week. A moist easterly flow north of the aforementioned boundary will bring the potential for sub VFR VIS/CIGs through mid week.
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&& .MARINE... Small craft advisory conditions through Sunday for all waters due to gusty southeast flow. Generally sub-SCA conditions expected Monday through Tuesday, with winds remaining light. A frontal boundary will cross the waters late Monday which will help increase shower activity, resulting in the potential for periodic gusty winds. && .HYDROLOGY...
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No new or additional flooding is expected today. Additional rainfall up to 0.25 inches is possible mainly over southern MD along the slow moving front.
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&& .TIDES/COASTAL FLOODING...
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Water levels are running around 1 to 2 ft above astronomical predictions on the Bay and lower tidal Potomac. For the upper tidal Potomac around Washington DC and Alexandria, fresh water piling down from the Potomac River will cause anomalies to continue increasing today. 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 today 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.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Flood Watch until 8 PM EDT this evening for DCZ001. Coastal Flood Warning until 10 PM EDT Sunday for DCZ001. MD...Flood Watch until 8 PM EDT this evening for MDZ003>006-011-013- 014-016>018-503>508. Coastal Flood Advisory until 4 PM EDT this afternoon for MDZ508. VA...Flood Watch until 8 PM EDT this evening for VAZ025>031-036>040- 050>057-501-502-505>508. Coastal Flood Advisory until 4 PM EDT Sunday for VAZ054. WV...Flood Watch until 8 PM EDT this evening for WVZ050>053-055. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 PM EDT Sunday for ANZ530>543.
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&& $$ SYNOPSIS...KLW NEAR TERM...LFR SHORT TERM...KLW/DHOF LONG TERM...KJP AVIATION...KLW/KJP MARINE...KLW/KJP HYDROLOGY...LFR TIDES/COASTAL FLOODING...LFR

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