Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240746 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 346 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 /UNTIL 6 PM THIS EVENING/... High pressure is wedged across the Mid-Atlantic region this morning. An upper level disturbance is crossing the region and light rain is moving from west to east. The back edge of rain is currently moving through the Highlands and will end from west to east this morning. Subsidence will move into the region behind the departing disturbance. The wedge of high pressure will slowly weaken today and low stratus will persist through the day. NE flow will become SE by afternoon and will also lead to patchy fog and/or mist across the eastern slopes of the ridges through the afternoon. A southerly component to the flow will help temps climb a bit higher today with temps reaching the U60s/L70s. 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 rain will move back into the Mid-Atlantic region. Easterly flow at the sfc may enhance rainfall across the eastern slopes of the ridges. Rainfall amts will range from near an inch across the eastern slopes of the ridges and the Potomac Highlands to a third of an inch across I-95 overnight. 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. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... 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 /07Z WEDNESDAY THROUGH SUNDAY/... IFR/LIFR conditions expected at CHO/MRB/IAD this morning and MVFR conditions at BWI/MTN/DCA as rain and northeast winds persist. Cigs expected to improve however stay MVFR at most sites today with the exception of CHO which will likely stay at IFR. Rain will come to an end from west to east this morning. Conditions will worsen this evening as rain moves back into the region and cigs and vsbys expected to go sub-mvfr. Widespread rain comes to an end Thu morning however 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... NE winds will become easterly by this afternoon. NE Winds 10-15kts with gusts 18-20kts expected across the southern MD bay zones and Tidal Potomac zones early this morning. Winds will relax late this morning and through the afternoon. 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...Combination of onshore flow and new moon will result in elevated water levels with minor coastal flooding expected at Annapolis, Straits Point, and Baltimore next three days. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory until 7 AM EDT this morning for MDZ014. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Thursday for ANZ530>534-537>543. Small Craft Advisory until 9 AM EDT this morning for ANZ533- 534-537-541-543. && $$ SYNOPSIS...LFR NEAR TERM...HSK SHORT TERM...HSK LONG TERM...LFR AVIATION...HSK/LFR MARINE...HSK/LFR TIDES/COASTAL FLOODING...LFR

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