Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221440 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC Issued by National Weather Service Mount Holly NJ 1040 AM EDT WED JUN 22 2016 .SYNOPSIS... High pressure will briefly build in from Canada today. A warm front will lift north across the region tonight and the boundary will drop south as a cold front later Thursday into Thursday night. High pressure will return for Friday into the weekend. && .NEAR TERM /THROUGH THURSDAY/...
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As of mid to late-morning the current forecast remains on track. A quasi-stationary frontal boundary cuts west to east across the forecast area with more humid and unstable air to the south. The nearest thunderstorms at this time are over northern KY, remnants of the overnight mid-west MCS. Rather dense cirrus from the MCS has overspread the area SW of DC. These could result in slightly lower max temps this afternoon but otherwise are not significant. Previous discussion below: Low pressure is located in northeastern New England this morning. A frontal boundary is stretched from the New England coast across southern PA. An upper level trough will swing across New England this morning and northwest flow aloft will set up by this afternoon. Light winds across the region have led to a mild morning with patchy fog in some low-lying areas. The frontal boundary will move slowly southward across the region today. Sunny conditions expected today as the Mid-Atlantic is between two upper level features. Temps will reach the mid to upper 80s today. Attention turns to the potential for severe weather and flooding late tonight into Thursday across the Mid-Atlantic region. A shortwave trough is expected to barrel across the Mid-West and Ohio Valley today and tonight initiating convection across this region. Surface low pressure will deepen in response to the convection and due to the northwest flow aloft convection will come towards the Mid- Atlantic. Conditions will be favorable for thunderstorms overnight as a surge of high pwat air are collocated with a 40-50kt LLJ reaching the Potomac Highlands after midnight tonight. There is uncertainty with the timing of thunderstorms moving into the region however there is a model consensus that showers and thunderstorms will move through the region overnight into Thursday morning. Thunderstorms have the potential for strong winds. In addition to upper level support for these thunderstorms the frontal boundary will be across the region and may lead to redevelopment of showers and thunderstorms resulting in multiple rounds of rain. Low flash flood guidance is across much of the region due to the rain on Tuesday and a flash flood watch is in effect for the Potomac Highlands. A extention in space and time is possible for the flash flood watch as flash flood guidance is lower further east and across the metros however due to the uncertainity of size and timing of thunderstorm complext will hold off and let future shifts re- evaluate. Low pressure will move along the frontal boundary Thursday and showers and thunderstorms are expected again. There is some question as to the severity of thunderstorms since morning convection may stabilize the environment however the Mid-Atlantic region will be in the warm sector of a highly sheared environment so attention is needed for Thursday. Thunderstorms have the potential to be strong to severe Thursday afternoon.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/... The frontal boundary will sag southward Thursday night and into Friday. Dry northerly flow will move into the region but it will be slow. Showers and a few thunderstorms are possible mainly in Central VA and the VA highlands Friday afternoon. Max temps will be cooler with temps in the U70s/L80s and low humidity. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... High pressure will build into the region Friday night through Sunday...bringing drier and cooler conditions to the area. An isolated shower cannot be ruled out near the Blue Ridge Mountains and Potomac Highlands...but even across these areas much of the time will be dry. High pressure will move offshore Monday and a return flow will allow for more humid conditions. A few showers and thunderstorms are possible during this time. A cold front may impact the area Tuesday into Wednesday. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... VFR conditions expected today and into tonight. Mid-high level clouds will increase from the west late this afternoon and spread across the region overnight. SHRA are expected late tonight into Thursday morning with the potential for TSRA after 6z tonight into Thursday morning. TSRA will bring gusty winds as wind flow aloft increases and LLWS may also be a concern Thursday morning. Winds at 2k feet may be close to 40kts 12z Thurs coupled with TSRA may make for a high impact aviation period across all terminals. Sub- vfr conditions expected late tonight through Thursday as SHRA/TSRA redevelop into Thursday afternoon. Gusty winds are possible in activity Thursday afternoon. High pressure will bring VFR conditions most of the time Friday night through the weekend. High pressure will move offshore Monday and a few showers and thunderstorms are possible. && .MARINE... Westerly winds persist on the waters this morning. Gusty winds around 20kts are expected on the lower tidal potomac and lower bay this morning. Winds will become SW today and gusty winds around 20kts are expected on all the waters. Winds will likely diminish in the late afternoon and SCA conditions will end during this time. Winds should stay below SCA tonight however winds will likely increase Thursday morning. Showers are also expected across the waters Thursday morning and will continue into the afternoon. Thunderstorms are possible and gusty winds will likely bring SMW conditions. High pressure will bring an easterly flow to the area Friday night through the weekend. Winds should remain below sca criteria. The high will move off the coast Monday and a cold front may impact the waters during the middle portion of next week. More showers and thunderstorms are possible during this time. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Flash Flood Watch from late tonight through Thursday afternoon for MDZ003-501-502. VA...Flash Flood Watch from late tonight through Thursday afternoon for VAZ027-028-030-031-503-504. WV...Flash Flood Watch from late tonight through Thursday afternoon for WVZ050>053-055-501>506. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...AMC/HAS SHORT TERM...HAS LONG TERM...BJL AVIATION...BJL/HAS MARINE...BJL/HAS

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