Area Forecast Discussion
Issued by NWS Sterling, VA

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524 FXUS61 KLWX 191818 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 218 PM EDT Fri Aug 19 2016 .SYNOPSIS... Weak high pressure builds in through Saturday with a cold front crossing the area Sunday evening. High pressure returns for the first half of next week. && .NEAR TERM /THROUGH TONIGHT/...
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Surface high pressure over the region this afternoon heading into the weekend. Main area of showers and thunderstorms currently on going down near the VA/NC border where a surface trough has aligned. North of this boundary, a passing shortwave combining with marginal instability and terrain influences could produce isolated to scattered showers and thunderstorms. Expecting sub- severe. Any storms that do form will diminish in coverage with loss of daytime heating this evening as well as with the shortwave energy pushing to the east. Patchy fog possible in the valleys with moisture lingering in the lower levels. Lows tonight right near normal.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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Similar synoptic setup on Saturday with the persisting surface high and an approaching mid level trough. Another shortwave passing through on Saturday could trigger showers and thunderstorms, again expecting sub-severe with marginal instability and weak shear. High temps similar to today, though could be 1-3 degrees too warm if precipitation becomes more scattered. A cold front will swing through the region on Sunday, with the 12z model suite in general agreement with the passage late afternoon/evening time frame. Ahead of this front, strong moisture advection will push PWATs up to at least 2 inches. The best forcing along the trough looks to be centered over PA, but there is some suggestions in the models that enhanced heavy rain could extend down into northeast Maryland. Thinking overall central Maryland into areas to the north of DC and then east into southern Maryland have the highest confidence/best chance of seeing showers and thunderstorms with activity more scattered in nature over the remainder of the CWA. Will continue to highlight enhanced flood threat in the HWO with around one inch possible along the 95 corridor between DC-Baltimore. Flooding will be the main threat, though cannot rule out isolated stronger gusts with some of the heavier rain showers. As the front sweeps through, drier air in the wake will dry things out fairly quickly, with only lingering showers possible over the eastern fringe of the CWA by Monday morning.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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A cold front should push offshore by Monday morning thanks to a 1022+mb surface high building in from the west. The weather across the Mid-Atlantic will then be dominated by high pressure through much of next week. This will likely result in near to below normal temperatures and a mainly clear sky for at least the first half of the week. As the center of the high slides offshore during the second half of the week, temperatures will begin to warm. A pop up shower or thunderstorm cannot be ruled out over the terrain during this time as well.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions expected through the TAF period. Isolated showers/thunderstorms possible at KMRB/KCHO this afternoon but too low of confidence to include in TAF. Showers and thunderstorms possible at all TAF sites on Saturday, which could produce brief sub-VFR conditions. Winds through the period less than 10 kts from the NW today, becoming SE on Saturday. A cold front will cross the area Sunday, bringing widespread showers and possible thunderstorms. Sub-VFR conditions are likely, with the stronger storms producing heavy rain and gusty winds. Mainly VFR conditions are expected during the first half of next week in the wake of the cold front.
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&& .MARINE...
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Sub-SCA conditions on all the waters through Sunday. An isolated shower or thunderstorm is possible this afternoon and Saturday afternoon which could bring gustier winds. More widespread showers and thunderstorms expected on Sunday. Small craft advisory conditions are likely Sun night and possibly Monday and Monday night due to northerly channeling. Winds will then become light as high pressure builds over the waters Tuesday into Wednesday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...Sears/DFH NEAR TERM...Sears SHORT TERM...Sears LONG TERM...DFH AVIATION...Sears/DFH MARINE...Sears/DFH

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