Area Forecast Discussion
Issued by NWS Sterling, VA

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901 FXUS61 KLWX 190030 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 830 PM EDT Sun Jun 18 2017 .SYNOPSIS... A very warm and humid air mass will remain in place through Monday until a cold front clears the area Monday night. Weak high pressure will build over the area for the middle of the week. && .NEAR TERM /UNTIL 7 AM MONDAY MORNING/...
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SPC Mesoanalysis this evening depicting plenty of instability with MLCAPE values ranging from 1000-2000 J/KG; however thin stable layer around 850mb combined with lack of a true trigger has led to only isolated to perhaps scattered convective activity this evening. This activity has been mainly focused west of the Blue Ridge where terrain has helped to serve as an focus for initiation, and slightly lowering heights has provided for a bit better environment for cell development. That being said, main shear axis remains well to the west this evening, and any activity that can/does develop will be pulse in nature. Overnight main area of convection over the Ohio Valley will try to push eastward, however this should be decaying by the time it reaches the Allegheny Front later tonight. Thus severe threat should be lessening. Otherwise, warm and muggy night in store with lows in the 70s pretty much area-wide.
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&& .SHORT TERM /7 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... A cold front will approach the area from the west Monday before passing through Monday night. Showers and thunderstorms are expected along and ahead of the cold front. A southwest flow ahead of the boundary will usher in more unstable conditions and deep layer shear will increase as the upper-level trough associated with the boundary shifts toward our area. The combination of stronger shear profiles...lift associated with the cold front and unstable conditions suggests that severe thunderstorms are possible. The main threat appears to be damaging wind gusts due to the unidirectional flow with height. Still...confidence is low because there are some limiting factors. One is that mid-level clouds may cut back on instability some and the other is that convection overnight has the potential to outrun the cold front and move into our area. If this happens...it will be tougher for the atmosphere to recharge from daytime heating especially across western areas of the CWA. As of now...the better chance for stronger to severe thunderstorms is east of the Blue Ridge Mountains Monday afternoon through Monday evening. Plenty of moisture will be in place so thunderstorms will have the capability of producing torrential downpours. Contemplated a Flash Flood Watch...but the uncertainty as to exactly where the heaviest storms will develop is still high. There is a chance that the torrential rains could develop farther east where Flash Flood Guidance is higher. Will re- evaluate tonight into Monday morning. Convection will dissipate overnight behind the cold front. Weak high pressure will build overhead for Tuesday and Tuesday night. Less humid conditions along with seasonably warmer temperatures are expected. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Mostly dry conditions for most of our CWA early on Wednesday with some showers possible in the SE region due to a nearby front. Some afternoon convection possible Wednesday afternoon into the night due to departing trough, but mainly dry conditions expected. Dry conditions continue into Thursday and early Friday as zonal flow and a drier air mass settles in. On Friday and into the weekend uncertainty increases as guidance diverge on solutions. Tropical moisture and approaching boundaries will allow for what it looks like a period of showers and thunderstorms Friday and into Sunday. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Isolated showers/thunderstorms are expected through this evening, but very low likelihood of impact to any TAF site. A complex of thunderstorms well to the west may propagate towards the terminals late tonight into Monday morning...but it should weaken as it does so, with only showers and isolated thunder when it does move eastward. There is a better chance for showers and thunderstorms after noon Monday and into Monday night. Some storms may be severe and the best chance for severe storms will be across the eastern terminals. Weak high pressure will build toward the terminals late Monday night through Tuesday night. Dry/VFR conditions expected Wednesday into early Friday. Some scattered showers and thunderstorms Wednesday and Friday afternoon which could cause periods of sub-VFR conditions.
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&& .MARINE...
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South to southwest flow will continue through Monday. A Small Craft Advisory is in effect for the waters during this time. As a cold front pushes into the region, showers and thunderstorms become likely Monday through Monday evening. Some of these storms may become severe with damaging wind gusts being the primary threat. A Small Craft Advisory continues for portions of the waters Monday night and it may need to be extended for Tuesday into Tuesday night. Dry conditions expected Wednesday into early Friday. Some scattered showers and thunderstorms Wednesday and Friday afternoon. Winds will be below the small craft advisory criteria through early Friday, when wind gusts could reach 18 kt.
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&& .TIDES/COASTAL FLOODING... A southerly flow will cause tidal anomalies to increase through tonight. A Coastal Flood Advisory is in effect for sensitive areas of Anne Arundel County...Washington DC and St Marys County for the high tide cycle tonight. Elevated water levels are expected through Monday night due to the southerly flow. Additional minor flooding is possible near times of high tide. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory from 2 AM to 6 AM EDT Monday for DCZ001. MD...Coastal Flood Advisory until 4 AM EDT Monday for MDZ014. Coastal Flood Advisory until midnight EDT tonight for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory until 9 PM EDT Monday for ANZ530-531-535- 536-538-539-542. Small Craft Advisory until 6 AM EDT Tuesday for ANZ532>534-537- 540-541-543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL/MM SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/MM/IMR MARINE...BJL/MM/IMR TIDES/COASTAL FLOODING...BJL

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