Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 282317 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 717 PM EDT Sun May 28 2017 .SYNOPSIS... Weak low pressure will move across the area this evening and move out to sea Monday. Upper level low pressure will drift east across the north side of the Great Lakes Monday through Friday. In the meantime, weak high pressure will prevail over the Mid- Atlantic outside of weak trough passages Tuesday night and Wednesday night. Low pressure approaches from the west this weekend. && .NEAR TERM /OVERNIGHT/...
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The southern VA low is picked up in the 12Z GFS and drifts east across the VA part of the Chesapeake Bay this evening. Moisture on southeast flow should be cutoff by this low, limiting evening rainfall over the Balt-Wash metro. Overnight the wind shifts west with some upslope rain is expected on the western slopes of the Allegheny Front, but not at an excessive rate. Mid 60s min temps tonight which are near dewpoints. Should clearing occur behind the low to our south, fog would be expected. However, the jet overhead increases overnight, so at least high clouds should remain and limit fog potential.
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&& .SHORT TERM /MONDAY MORNING THROUGH TUESDAY NIGHT/...
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Weak trough moves east across the area in the morning with advance showers ending by noon for the western shore of the Bay. 14 to 15C 850mb temps mix down in light westerly flow making for max temps low to mid 80s. The lack of rain and clouds will make for a marked difference from today! Weak surface high pressure lingers over the area as the parent upper low drifts east across the north side of the Great Lakes. A few shortwaves look to round the low and disrupt the tranquil weather. The first looks to be Tuesday night so low chance PoPs for showers were added then. Otherwise slightly above normal temps persist.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/... A weak front across the region could spawn a couple of showers or a thunderstorm in parts of the region Wednesday into Wednesday evening. Weak high pressure will build in Wednesday night through Thursday night. Dry conditions and seasonable temperatures expected. The high moves east Friday to allow for a leeside trough of low pressure to form east of the Potomac Highlands Friday night. There is a chance for rain showers along this trough both Friday and Friday night. Temperatures will be near normal. There is a better chance for rain showers and perhaps a few thunderstorms Saturday into Saturday night as a disturbance moves into the region to accompany the trough of low pressure. By Sunday, a cold front should work into the region and bring an additional threat for showers and thunderstorms. && .AVIATION /23Z SUNDAY THROUGH FRIDAY/...
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MVFR cigs/vsbys across the DC metros with rain tapering off (except for KMRB and west) this evening as low pressure passes to the south. Fog will develop in any areas that clear. Weak trough crosses from the west late tonight with light west winds and VFR Monday into Tuesday. A weak trough crosses late Tuesday with chances for rain then. VFR conditions at the terminals, except where pop-up showers or a thunderstorm develop Wednesday and Wednesday night. MVFR or IFR conditions in rainfall. Winds west-southwest 10 knots Wednesday becoming northwest 5 to 10 knots Wednesday night. VFR conditions Thursday and Thursday night. Winds northwest 5 to 10 knots Thursday, becoming light and variable Thursday night.
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&& .MARINE... Light SEly flow with low pressure over southern VA. This low crosses the VA portion of the Bay this evening with rain ending as it passes. Weak trough crosses from the west Monday morning with light westerly flow Monday into Tuesday. No marine hazards expected Wednesday through Thursday night. Winds southwest 10 knots Wednesday becoming northwest 10 knots Wednesday night. Winds northwest 5 to 10 knots Thursday then light and variable Thursday night. && .HYDROLOGY...
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Flash flood watch has been dropped. Rain over our area is stratiform. Across southern PA the rainfall looks heavier. If any of this drops into MD it looks to be progressive enough to not pose a problem.
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&& .TIDES/COASTAL FLOODING... Water levels running within a few inches of a foot this afternoon. Light onshore flow should keep the departure similar through tonight, if not rising slightly. Since we`ve just passed the new moon, there is a decent spread in the semi-diurnal cycle...with the daytime cycle preferred. Current guidance indicates that we`ll hit minor flood during this cycle for the next couple of days. However, departures a bit greater at Piney Point, such that each cycle should hit minor. It`ll be a similar story at SW DC, and perhaps Alexandria as well. Have made some Advisory adjustments, based on the above guidance and thinking. Included the next two cycles for the upper Potomac, the next three cycles (through Monday night) for St Marys (ultimately, the threat there will last longer), and the second cycle (Monday morning) in Calvert/Anne Arundel. No additional forecasted flooding at this time. Will need to monitor Dahlgren and Baltimore, both of which will come close to minor on Monday. Ensembles suggest a gradual decrease in water level by midweek. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 2 PM EDT Monday for DCZ001. MD...Coastal Flood Advisory from 3 AM to 1 PM EDT Monday for MDZ014- 018. Coastal Flood Advisory until 10 PM EDT Monday for MDZ017. VA...Coastal Flood Advisory until 2 PM EDT Monday for VAZ054. WV...None. MARINE...None.
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&& $$ UPDATE...WOODY! PREVIOUS...BAJ/HTS/KLW

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