Area Forecast Discussion
Issued by NWS Wakefield, VA

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989 FXUS61 KAKQ 261117 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 717 AM EDT MON SEP 26 2016 .SYNOPSIS... High pressure over New England will move off the coast early today. A strong cold front will cross the region onTuesday. An upper level low will track across the area later in the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Latest wx analysis features 1025+ sfc ridge centered over New England, ridging south into the lower Mid-Atlantic region. To the west, a potent upper level low continues to take shape as it slides from the Canadian Prairies toward the Western Great Lakes/Ontario today. The attendant cold front extending from the Western Great lakes and through the Mississippi River Valley. Aloft, upper level ridging is dampening as it translates east of the Oh/Tn River Valleys, as the mid level trough pushes east today. Closer to home, will continue to see low clouds linger across the piedmont as cool air wedge lingers inland, reinforced by onshore flow out of the SE (veering to the S late). High-Res models in relatively good agreement in taking some sct showers across the sw third of the area (mainly west of I-95). QPF with these showers would be low given minimal lift and PW still ~1-1.5 (highest along and south of the VA/NC border per Blended TPW Satellite product and supported by regional 00z soundings. As this happens, sfc high pressure will slide east to the coast as the strong cold front reaches the mtns by late in the day. Kept a slight chc in out west in the aftn, but lift is minimal for the aftn, and thus areal coverage of any showers would be quite low. Highs today in the mid to upr 70s, warmest along the coastal plain just west of the Bay where some more peeks of sun are expected. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... Models continue to slow frontal timing slightly, with frontal passage looking to wait until after sunrise Tuesday. Will continue to orient best pops along pre-frontal trough tonight. Complex forecast for Tuesday, with models still struggling to diagnose position of the mid/upper trough. Models can agree that front will stall across the eastern half of the area on Operational ECMWF has up until now been nudging the trough a bit farther south than the GFS. However, latest 00z ECMWF has trended a bit farther toward the GFS solution. At the sfc, front will slow/stall across the coastal plain Late Tuesday, with showers likely focused along the boundary as weak s/w energy slides along it Tuesday afternoon and night. Good feed of moisture along and ahead of it with PW`s climbing to around 1.75 inches. Instability is marginal, but kept low chcs for thunder in place. Models show drier air filtering across NWRN zones Tues afternoon to lower areal coverage of pcpn there. Kept high chc pops across the SE into Wed night. QPF btwn 1/2 to 1 inch inland...1.25 to 1.75" along the MD counties and Northern Neck of VA. Forecast for the mid week period becomes problematic, and a conditional strong storm threat exists across the SE coast on Wednesday. Uncertainty continues to revolve around location/orientation of the Upper Low and resultant available moisture. Blending the GEFS and WPC preferred UKMET solution, thinking at this time is that front stands a good chance of lingering along the SE coastal plain on Wednesday. Much uncertainty attm, so will keep grids as general as possible. However, Thunder wording has been added across the southeast, with chc pops inland as upper low lingers just to the west. Highs each day in the 70s (near 80 SE coast). && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Still some uncertainty in the extended due to the presence of anomalous heights over the higher latitudes and an (possibly cut off) upper-level closed low over the eastern CONUS. Latest consensus digs the upper low over the central Appalachians Wednesday night and Thursday. The upper low then meanders over the region Friday into Saturday (possibly later) until an upstream deepening trough kicks the low northeastward. At the surface, a frontal boundary remains along the coast in southwesterly flow aloft. Height falls and energy rounding the upper low will produce waves of low pressure along the front. The end result will be unsettled weather conditions into the weekend. Have increased cloud cover and POPs Thursday to mostly cloudy and solid chance, respectively. Surface low pressure shifts to the north Friday, with lower POPs and less cloud cover forecast. Will retain slight chance to chance POPs due to uncertainty, but the GFS/GEFS indicates less moisture. Confidence is increasing for a dry/cool weekend, but it will depend on how the upper low is absorbed into the approaching trough. Will keep mention of slight chance across the northeast half of the forecast area Saturday, and remaining dry Sunday. Highs through the period will be below normal, generally in the low to mid 70`s. Temperatures may struggle to get out of the 60`s inland Thursday and Friday. Lows generally in the mid/upper 50`s to low 60`s. && .AVIATION /11Z MONDAY THROUGH FRIDAY/...
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High pressure over the Northeast States will move off the coast early this morning, with low level flow becoming S-SE by late morning/afternoon. A moist layer around 2-4K ft continues to result in sct-bkn clouds this morning, mainly over inland locations west of KRIC. As moisture increases through the period ahead of a complex frontal system...expect that MVFR cigs over the Piedmont will expand slowly east through the late afternoon and evening on Monday. Some sct showers are possible across the piedmont this morning, but will likely not impact terminals before this afternoon, and have therefore held out of the TAF for the 06 issuance. OUTLOOK...The next chance for widespread precipitation arrives late tonight into Tuesday ahead of a strong cold front. Periods of IFR can be expected especially at RIC and SBY. Showers will linger through much of the work week ahead as an upper level low tracks across the region.
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&& .MARINE... Surface ridge axis currently located over the waters this morning, with generally east to southeast winds observed. Speeds are generally at or below 10 knots. Waves 1-2 feet and seas 3-4 feet. High pressure shifts offshore later this morning, with flow becoming southeast 10-15 knots. A warm front lifts over the waters late today ahead of a cold front approaching from the northwest. Gradient winds ramp up, with models indicating favorable low level lapse rates to produce low end SCA conditions in the Chesapeake Bay. South winds increase to 15 to 20 knots tonight. Have raised SCA headlines for the Bay and Rappahannock River. Strongest winds expected in the upper Bay and Rappahannock River. Waves build to 2-3 feet and seas up to 4 feet north of Parramore Island. The cold front crosses the region late tonight, reaching the waters Tuesday. The front then stalls just offshore Tuesday night. High pressure briefly builds into the region Tuesday night as another area of low pressure drops over the Great Lakes region. Perhaps a modest surge is possible Tuesday night, but a lack of gradient winds and limited cold air advection will generally produce sub-SCA conditions. Flow becomes briefly onshore Wednesday and the southerly Wednesday night as low pressure drops just west of the waters. Seas build to 3-4 feet Wednesday. Low pressure remains over the waters through the end of the work week, resulting in unsettled weather conditions. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 6 PM this evening to 4 AM EDT Tuesday for ANZ632-634-635. Small Craft Advisory from 6 PM this evening to 7 AM EDT Tuesday for ANZ630-631. && $$ SYNOPSIS...MAM NEAR TERM...MAM SHORT TERM...MAM LONG TERM...SAM AVIATION...MAM MARINE...SAM is the U.S. government's official web portal to all federal, state and local government web resources and services.