Area Forecast Discussion
Issued by NWS Sterling, VA

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417 FXUS61 KLWX 251915 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 315 PM EDT Thu May 25 2017 .SYNOPSIS... Low pressure and associated cold front will move through the area this evening. Weak high pressure will return to the area later Friday and Friday night before moving off the coast Saturday. A warm front will stall out overhead later Saturday through Sunday. A stronger cold front will pass through the area Monday. && .NEAR TERM /THROUGH TONIGHT/... Cutoff low pressure over the Ohio Valley will pass through our area this evening. As of this afternoon...an occluded front associated with the low extends southeast into our area. Weak surface low pressure is also developing along this boundary over northern Virginia. Low clouds have given way to some sunshine and this has caused instability to increase over the last couple hours. Latest mesoanalysis around 500 J/KG over central Virginia into southern Maryland. Instability should increase ahead of the occluded boundary over the next few hours. Showers and thunderstorms have begun to pop up across the Potomac Highlands into central Virginia near the boundary. As the boundary moves north and east...convection is expected to increase in coverage and perhaps intensity. This is due to the destabilizing atmosphere both from colder air aloft and breaks of sunshine. Despite weakening shear profiles...there is an elevated threat for severe thunderstorms due to the colder air aloft and potential for downbursts due to mid-level dry air. The best chance for stronger storms will be across eastern West Virginia into northern Virginia and the Washington Metropolitan area as well as central and southern Maryland. Due to recent rainfall...any heavy rainfall from thunderstorms does pose a threat for flash flooding. However...a watch has not been issued at this time thinking that storms should be progressive and torrential downpours will be widely scattered. These factors should keep any flash flood threat localized. Low pressure and the occluded boundary will move off to our northeast later this evening and overnight. Convection will dissipate in coverage...but a few showers are possible overnight as moisture wraps around the departing low. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Low pressure will continue to move away from the area Friday while high pressure approaches from the west. A west to northwest flow will usher in seasonable conditions...but it will be breeze due to a tight gradient between the departing low and building high. An isolated shower cannot be ruled out from daytime heating...but much of the time will be dry. Weak high pressure will build overhead Friday night before moving off off the coast Saturday. A warm front will stall out over the area later Saturday through Saturday night. Marine air will allow for cooler conditions across northeastern portions of the CWA while much warmer and more humid conditions are expected across central and western areas behind the boundary. There is still some uncertainty as to exactly where the boundary will setup. However...with warm and humid conditions in place showers and thunderstorms will likely develop. Sufficient shear suggests that some storms could be severe...mainly along and south/west of the boundary. Convection should dissipate in coverage later Saturday night due to the loss of daytime heating. && .LONG TERM /SUNDAY THROUGH THURSDAY/... A warm front will settle near/over our CWA Sunday before a cold front moves across late Sunday night into Monday morning. Showers and thunderstorms possible with periods of heavy rain during these days. Conditions start to dry out into Tuesday as westerly flow settles in. Another -weaker- front approaches on Tuesday night into Wednesday, increasing PoPs slightly. Several pieces of upper level energy could bring a chance of precip to our area Wednesday into Thursday, but looking into mostly dry conditions. High temperatures will be in the 70s and 80s... some 60s at higher elevations. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Popup showers and thunderstorms are expected late this afternoon into this evening. A few storms may become severe...with locally damaging winds and large hail being the primary threats. IFR/subIFR conditions are expected in stronger storms. Convection will dissipate in coverage later this evening. VFR conditions are expected most of the time Friday through Saturday night. West to northwest winds will gust around 20 to 25 knots Friday. A few showers and thunderstorms are possible Saturday. Some storms may become strong to severe during the afternoon and evening hours. Sub-VFR conditions expected Sunday into Monday with rounds of showers and thunderstorms moving through our region with a boundaries stalled/moving through. Conditions become drier/VFR Monday night into Tuesday. && .MARINE... Showers and thunderstorms will increase in coverage late this afternoon into this evening. Storms will be capable of producing locally damaging winds and large hail. Special Marine Warnings may be warranted. Low pressure will develop over the waters this afternoon before moving off to the north and east tonight. A lull in the winds has occurred due to a weaker gradient this afternoon. However...winds from the southwest will pick up behind the low late this afternoon through tonight. A Small Craft advisory is in effect for most of the waters behind the boundary. A Small Craft Advisory is in effect for all of the waters Friday due to gusty west to northwest winds expected behind departing low pressure. Winds will quickly diminish toward sunset. Weak high pressure will build overhead Friday night before moving offshore Saturday. A warm front will stall out near the waters later Saturday through Saturday night. Additional showers and thunderstorms are possible during this time...especially Saturday afternoon and evening. && .TIDES/COASTAL FLOODING... Combination of high astronomical tides due to a new moon and onshore flow will result in minor coastal flooding near times of high tide through tonight for most areas and into Friday morning for sensitive areas. Coastal Flood Headlines are in effect during this time. Moderate flooding is possible at Straits point...but confidence is too low for a warning at this point since the flow will turn west of south this evening. Tidal anomalies should decrease rapidly later Friday due to strengthening west to northwest flow. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 11 PM EDT this evening for DCZ001. MD...Coastal Flood Advisory until 8 PM EDT this evening for MDZ014- 018. Coastal Flood Advisory until 6 PM EDT this evening for MDZ016. Coastal Flood Watch late tonight for MDZ017. Coastal Flood Advisory until 2 AM EDT Friday for MDZ017. VA...Coastal Flood Advisory until 6 PM EDT this evening for VAZ057. Coastal Flood Advisory until 11 PM EDT this evening for VAZ054. WV...None. MARINE...Small Craft Advisory from 8 PM this evening to 6 PM EDT Friday for ANZ530-531-536-538-539. Small Craft Advisory until 6 PM EDT Friday for ANZ532>534-537- 540>543. Small Craft Advisory from 6 AM to 6 PM EDT Friday for ANZ535. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR TIDES/COASTAL FLOODING...ADS

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