Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201425 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1025 AM EDT Sun May 20 2018 .SYNOPSIS... A warm front will lift to our north this morning and a cold front over the Ohio Valley will drop southeast into our area tonight. The boundary will stall out overhead for Monday before another cold front passes through on Wednesday. Weak high pressure may build overhead for late in the week. && .NEAR TERM /THROUGH TONIGHT/... Deep moisture has been shunted to the east as seen on Blended TPW and differential water vapor RGBs. With continued mid-level drying today convection will be isolated at best. Will be trimming coverage to isold for this afternoon. Warmer with temps climbing into the 80s. Best moisture convergence and thus best chance of showers will be over southern MD. Previous afd... A weak cold front will drop south into the area tonight. A few showers and thunderstorms are possible ahead of the boundary, especially across central Virginia into southern Maryland. Again, coverage should be isolated to widely scattered. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The cold front will stall out over central Virginia by midday Monday and high pressure will build over the Atlantic during this time. This will cause the boundary to slowly return north and east as a warm front, and moisture will increase once again due to a southwest flow through all levels of the atmosphere. Therefore, popup showers and thunderstorms are more likely along and behind the boundary where instability will be highest. Latest guidance shows the highest likelihood for convection to be across the Potomac Highlands into central Virginia Monday afternoon. Convection may spread farther north and east toward the Washington and Baltimore Metropolitan areas Monday night as the boundary slowly retreats as a warm front. Thunderstorms Monday afternoon into Monday night may contain locally heavy rain and this could cause issues with flooding since the ground is saturated. The boundary will remain nearby Tuesday and with plenty of moisture in place, popup showers and thunderstorms are likely. Again, some thunderstorms may contain gusty winds and locally heavy rainfall. Convection should wane a bit with the loss of daytime heating Tuesday night, but with an other cold front approaching from the north...a few showers and thunderstorms remain possible. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... A front across the center portions of our CWA could spawn a couple of showers and thunderstorms Wednesday into Wednesday evening. High temperatures will be about 5 to 7 degrees above normal. By Wednesday overnight into Thursday, the front pushes farther to from the north. High pressure will remain in control Thursday night. High temperatures Thursday could be 2 to 5 degrees cooler than Wednesday, but might still be slightly above normal for late May. The high will move off of the coast Friday and Friday night. A slight southerly return flow should develop and help to bring in more humid air to our CWA. Conditions should remain dry Friday into Friday night. A pre-frontal trough of low pressure could develop on the leeside of the Potomac Highlands and over the Shenandoah Valley Saturday. Any threat for showers and thunderstorms could start over the Potomac Highlands before making their way east and over the pre-frontal trough. High temperatures could be a few degrees above normal. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... VFR conditions today and tonight. A slight chance of a shower or t-storm this afternoon, not enough coverage or confidence even for a VCTS mention. A weak cold front will pass through the terminals tonight, some drier air will move in but it will not be much. With light winds, patchy fog is possible overnight into early Monday. The boundary will get hung up over central Virginia Monday and return north as a warm front Monday night into Tuesday. Showers and thunderstorms are likely near the boundary both Monday and Tuesday. For Monday, the best chance will be near KCHO, and for Monday night and Tuesday the best chance will be across all of the terminals. Low clouds are possible Monday night into Tuesday as well. Coverage of convection may wane some for Tuesday night. Mainly VFR conditions Wednesday through Thursday night. Showers and any thunderstorms could briefly reduce conditions to MVFR or IFR Wednesday and Wednesday evening. Winds northwest 5 to 10 knots Wednesday, becoming light and variable Wednesday night and Thursday. Winds becoming southeast 5 to 10 knots Thursday night. && .MARINE... Will continue with an SCA for the waters through today as the gradient strengthens just a bit ahead of a cold front. The SCA may need to be extended into this evening, but confidence is too low at this time. A weak cold front will pass through the waters tonight and it will stall to the south Monday before retreating toward the waters Monday night and Tuesday as a warm front. Showers and thunderstorms are likely ahead of the boundary, especially Tuesday. No marine hazards expected Wednesday through Thursday night. Winds northwest around 10 knots Wednesday becoming light and variable Wednesday night and Thursday. Winds veering to the southeast around 10 knots Thursday night. && .TIDES/COASTAL FLOODING... A persistent onshore flow has led to elevated water levels. For Washington DC and Alexandria, elevated water levels will continue through today due to freshwater coming down from the Potomac. A Coastal Flood Warning remains in effect for Washington DC through this evening. The highest water levels will be around high tide this afternoon and moderate flooding is expected. Water levels should gradually fall later tonight through Monday, but minor flooding is still likely. A Coastal Flood Advisory may be needed. A Coastal Flood Advisory is in effect for Alexandria through this afternoon, and that may need to be extended into tonight. && .CLIMATE... It has been an unusually wet pattern over the last week. For DCA (Reagan National), there has been at least 1/4" of rain each of the last 7 days. This is the longest streak on record. The previous longest was 5 days in 2011, 2009, 1975, 1950, 1942, and 1937. Precipitation records date back to 1871. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Warning until 10 PM EDT this evening for DCZ001. MD...Coastal Flood Advisory until noon EDT today for MDZ014. VA...Coastal Flood Advisory until 4 PM EDT this afternoon for VAZ054. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543. && $$ SYNOPSIS...BJL NEAR TERM...LFR SHORT TERM...BJL LONG TERM...KLW AVIATION...BJL/KLW MARINE...BJL/KLW TIDES/COASTAL FLOODING...LFR CLIMATE...LFR

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