Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241356 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 956 AM EDT Wed May 24 2017 .SYNOPSIS... Low pressure will impact the region through Friday. Weak high pressure will build over the region Saturday. Another low pressure system will impact the area on Sunday. Weak high pressure builds over the region next week. && .NEAR TERM /THROUGH TONIGHT/... Surface ridge from high pressure along the New England coast wedges into the area this morning. However...the high will move offshore today and an easterly flow will continue to bring unseasonably cool conditions for this time of year. Low clouds remain trapped underneath the subsidence inversion across central and southern areas this morning. There are some breaks of sunshine across northern and central Maryland. Clouds should fill in across all areas as overrunning increases ahead of developing low pressure over the Ohio Valley. Max temps will range from the 50s and 60s across central Virginia where cloud cover is expected all day to the lower 70s in northern Maryland where breaks of sunshine are expected through midday. Low pressure will continue to deepen across the Ohio Valley tonight while a closed upper low moves over the sfc low. Warm air advection will increase in the low levels tonight and a soaking rain will move back into the Mid-Atlantic region. Rainfall amounts around one inch are expected for many areas...but locally higher amounts along the eastern slopes of the Blue Ridge Mountains and Potomac Highlands are possible due to a low-level easterly flow. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... The closed upper low and the sfc low will remain stacked over the Ohio Valley Thursday morning. Low pressure will begin to transition over the mtns Thursday. Lapse rates will increase by Thursday afternoon and weak to marginal instability is expected. Although shear profiles are very weak with the sfc low overhead enhanced lift from a neg tilted upper level trough may result in a few thunderstorms east of the Blue Ridge mtns. The best chance will be across central VA/southern MD especially if sfc heating is enhanced. Temps will range from the U60s/L70s across the Highlands to the mid to upper 70s across the Piedmont/DC Metro and east. The sfc low and upper low will move to the north Thursday evening. Any thunderstorm activity should be east of the Mid-Atlantic region Thu night as post-frontal conditions are expected into Friday. Vorticity rounding the backside of the upper low will likely move across the Mid-Atlantic region into Friday leading to stubborn clouds and the chance for showers. Clouds and showers will move to the north by Friday afternoon and the sun will hopefully peak out before dusk. A few showers may linger along the Allegheny Front. Temps will reach the 70s across the region Friday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Weak ridge of high pressure sfc and aloft will build over the area Fri night into Sat. Despite this, model guidance show moisture overspreading the area from the west and even generate light QPF west of the Blue Ridge. A low pressure system near Chicago Sun morning will travel northeast into Lk Huron by Mon morning pushing a cdfnt through the area Sun night. Modest height falls and sfc pressure falls will lead to convective development Sun afternoon with severe t-storms possible especially east of the Blue Ridge and south of I-66 & U.S. Hwy 50. Dry westerly flow will prevail much of next week allowing for longer breaks of dry weather. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... Drier air has filtered in from the north and east allowing for VFR conditions across most sites this morning. VFR conditions will continue into this afternoon before low clouds return later this afternoon and tonight. MVFR conditions will return later this afternoon before falling to IFR this evening. The one exception is KCHO where low clouds will likely hang around all day. Did allow for cigs to improve to MVFR conditions for a period late this morning into this afternoon...but confidence in that is low. Widespread rain will also move into the area this evening before coming to an end early Thursday morning. However...additional showers and isolated thunderstorms are possible Thursday afternoon. Winds become westerly behind departing low pressure system Thursday night-Friday. VFR conditions expected during this time. Rain possible late Fri night and Sat, then showers and t-storms likely Sun afternoon with some possibly severe especially east of the Blue Ridge. && .MARINE... Northeast winds will turn to the east this afternoon...but speeds should remain below SCA criteria. The gradient tightens tonight and E winds will increase across the MD Chesapeake Bay and Lower Tidal Potomac. Rain returns tonight and continues through Thu morning. A SCA is in effect tonight- Thu morning. Low pressure moves over the waters Thursday afternoon and winds will relax. There is a chance for thunderstorms Thursday afternoon and SMW`s can not be ruled out mainly across the southern waters. Scattered showers expected on Friday with breezy conditions, gusting as high as 22 kt, which would require a small craft advisory. Gradient winds should remain below SCA levels Fri night into early next week, but potential for strong/severe t-storms Sun afternoon could generate locally high winds and waves. && .TIDES/COASTAL FLOODING... An onshore flow has caused elevated anomalies today...but since the next high tide will be the lower of the two astronomical norms and the flow will be light...minor flooding is not expected this afternoon. Will have to watch sensitive areas such as Straits Point in St. Marys County because it will be close. The onshore flow will strengthen tonight and tidal anomalies will increase. The next high tide will be the higher of the two and the lunar phase is at a new moon...so minor flooding is likely during the high tide cycle later tonight into Thursday morning. The flow will weaken and turn to the south Thursday before turning southwest Thursday night and eventually to the west and northwest Friday. Significant blowout should not occur until later Friday...so minor tidal flooding is possible during the high tide cycles Thursday through Thursday night. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Thursday for ANZ530>534-537>543. && $$ SYNOPSIS...BJL/LFR NEAR TERM...BJL/HSK SHORT TERM...HSK LONG TERM...LFR AVIATION...BJL/HSK/LFR MARINE...BJL/HSK/LFR TIDES/COASTAL FLOODING...BJL

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