Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221930 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 330 PM EDT Tue May 22 2018 .SYNOPSIS... A warm front has lifted through the area this afternoon and a cold front will approach from the northwest tonight before passing through Wednesday morning. In the wake of the frontal passage, high pressure will build over the area through Thursday before migrating over the western Atlantic Friday and Saturday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Before a brief break in the showers earlier today, showers have once again developed west of the Blue Ridge, with thunderstorms across the southern Shenandoah Valley and central Blue Ridge. Visible satellite imagery shows clouds clearing ahead of this activity which is helping destabilize the atmosphere as expected. Dewpoints are sultry in the mid to upper 60s with temperatures in the mid to upper 70s, with lower 80s in our southern zones. A nose of MLCAPE on the order of 1000-1500 J/kg stretches across central Virginia northward in to northern Virginia, just to the west southwest of the District. Couple this with steepening low-level lapse rates and shear values approaching 30 knots, potential for severe thunderstorms producing damaging wind gusts exists this afternoon. As such, SPC has put portions of northern and central Virginia, portions of central and southern Maryland, and the District of Columbia in a Severe Thunderstorm Watch. These thunderstorms will also be capable of producing heavy rainfall, with some hi-res guidance indicating 1-2 in/hr rates. However, given the speed at which they`ll be moving (~25kts), this should help keep the flash flooding threat somewhat limited but still possible given the very moist soils from recent rains. Convection will wane this evening and a cold front will approach from the northwest tonight and cross the area towards morning. This could trigger some additional showers or perhaps a thunderstorm, but expect coverage will be mostly isolated in nature due to the nocturnal passage and meager support aloft. Lows will hold in the lower to middle 60s for all. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... A weak cold front will sweep through the area overnight and early on Wednesday, ushering in a northwest flow in its wake, bringing drier air to the region. Showers and perhaps a thunderstorm may accompany the frontal passage, but coverage will likely be limited to isolated to scattered at best. High pressure will build overhead for Wednesday night through Thursday night, bringing dry conditions along with lower humidity. Expect highs near 80 degrees and lows near 60 degrees each day and night. && .LONG TERM /FRIDAY THROUGH TUESDAY/... A high pressure system will be in place over the region early on Friday. The high will shift eastward off the Atlantic coast Friday afternoon. A south to southwesterly flow will be in place leading to warm and moist air being advected into the region. Temperatures will rise up into the low to mid 80s. National Blend guidance currently has the area seeing dewpoints in the upper 50s to low 60s. Saturday into Sunday, the high pressure will remain centered over the Atlantic Ocean near Bermuda. A strong southerly flow will continue to be in place advecting warm and moist temperatures into the region. 850 and 700mb flows will be out of the south to southwest and a tropical system looks to form in the Gulf region. GFS 12Z and Euro are hinting at tropical moisture being transported northward into our region again. The higher temperatures coupled with rising dew points and the influx of tropical moisture will make the environment conducive for thunderstorm development Saturday and Sunday. Both GFS and Euro have precipitation starting later in the day on Saturday and continuing chances for precip into Sunday. Temperatures will rise up into the upper 80s with some areas seeing the low 90s on Saturday. Sunday temperatures are expected to be cooler in the mid 80s. Monday, a week frontal boundary is forecasted to approach from the west. This boundary may act as a lifting mechanism for the development of convection. If temperatures remain high and the influence of tropical moisture continues to be transported into the region then showers and thunderstorms could be possible on Monday. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Showers and potentially severe thunderstorms will cross the terminals this afternoon and early evening, potentially bringing winds gusts on the order of 40 to 50 knots. As this activity moves across the terminals, IFR/LIFR VIS/CIGs are likely in the strongest activity. Conditions improve later this evening and overnight as convection wanes. Some late night visibility restrictions are possible with fog at MRB/IAD. A weak cold front will move across the terminals overnight, shifting winds out of the northwest and bringing drier conditions through Thursday night. VFR conditions are forecast through this period. Friday, a high pressure will be in place just off the eastern sea board. Skies should remain mostly clear. Saturday, a southerly flow coupled with tropical moisture being transported into the region could lead to the formation of thunderstorms. && .MARINE... Showers and potentially severe thunderstorms will cross the waters this afternoon and early evening. These storms will be capable of producing strong gusty winds, and heavy rain that briefly reduces visibility to below 1 nautical mile. While conditions are forecast to remain sub-SCA, thunderstorm activity will likely result in the need for Special Marine Warnings, so remain alert if on the waters today. A cold front will approach the waters tonight. A shower or thunderstorm cannot be ruled out, but coverage should be limited due unfavorable timing. This weak cold front will pass through the waters Wednesday. A north to northwest flow will develop behind the boundary. Winds may come close to SCA criteria, but have gusts capped around 15 knots for now due to the relatively cooler waters. High pressure will build over the waters Wednesday night through Friday before moving offshore during the weekend. A return southerly flow will develop during the weekend and this may result in popup showers and thunderstorms, especially during the afternoon and evening hours. A southerly flow on Friday may warrant the need for a small craft advisory. On Saturday, the southerly flow coupled with a chance for thunderstorms will likely lead to the need for a continue small craft advisory. && .TIDES/COASTAL FLOODING... The latest water levels were below minor flooding thresholds for Washington DC. Freshwater continues to decrease upstream so that is having less of an impact. However, the southerly flow will continue today and the high tide this afternoon will be the higher of the two. A Coastal Flood Advisory remains in effect until 5pm encompassing the the high tide cycle this afternoon. The best chance for minor flooding will be at the Washington Channel with Potomac River at Georgetown likely remaining below minor flooding thresholds. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 5 PM EDT this afternoon for DCZ001. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...JMG AVIATION...BKF/JMG MARINE...BKF/JMG TIDES/COASTAL FLOODING...BJL/BKF is the U.S. government's official web portal to all federal, state and local government web resources and services.