Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 181853 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 253 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 /THROUGH TONIGHT/... Low clouds have given way to sunshine and a south to southwest flow has ushered in hot and humid conditions. Max temps will range from the upper 80s to lower 90s for most locations. The hottest conditions are expected along the Interstate 95 urban corridor...with heat and humidity causing heat indices around 100 degrees. Did cancel the heat advisory for Washington DC since max temps will be a couple degrees cooler. This should keep heat indices around 100 degrees instead of 105 degrees. The heat and humidity has led to an unstable atmosphere this afternoon. Latest mesoanalysis shows 1500-2500 J/KG of MLCAPE. Shear profiles remain relatively weak and there is no strong lifting mechanism to initiate convection. Therefore...thunderstorm coverage is expected to remain isolated to widely scattered through early this evening. Any convection should dissipate after sunset. However...additional showers and thunderstorms may propagate into western portions of the CWA overnight ahead of an approaching cold front. Confidence is low due to the unfavorable timing...but with the warm and humid conditions overnight there will be some instability. Also...shear profiles will be strengthening as a cold front and its associated upper-level trough approach from the west. A few severe thunderstorms cannot be ruled out overnight...mainly toward the Allegheny and Potomac Highlands. && .SHORT TERM /MONDAY 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 /18Z SUNDAY THROUGH FRIDAY/... Isolated to widely scattered thunderstorms are expected through early this evening. A line of thunderstorms well to our west may propagate toward the terminals late tonight into Monday morning...but it should weaken as it does so and confidence is low that it even makes it at all. Did allow for a VCTS during this time. There is a better chance for showers and thunderstorms later Monday 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. && .MARINE... South to southwest flow will continue through Monday. A Small Craft Advisory is in effect for the waters during this time. Isolated thunderstorms are expected late this afternoon and evening. Thunderstorms may produce locally gusty winds but most places will end up dry due to the limited coverage. There is a better chance for thunderstorms later Monday through Monday evening. Some of these storms may become severe with damaging wind gusts being the primary threat. A Small Craft Advisory is in effect for portions of the waters Monday night. A Small Craft Advisory may be needed for portions of the waters 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. && .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... DC...Coastal Flood Advisory from 2 AM to 6 AM EDT Monday for DCZ001. MD...Coastal Flood Advisory from 11 PM this evening to 4 AM EDT Monday for MDZ014. Coastal Flood Advisory from 7 PM this evening to midnight EDT tonight for MDZ017. VA...Heat Advisory until 6 PM EDT this evening for VAZ054. 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. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR TIDES/COASTAL FLOODING...BJL

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