Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170851 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 351 AM EST Fri Nov 17 2017 .SYNOPSIS... High pressure will build overhead through this afternoon before moving offshore tonight through Saturday. A strong cold front will cross the area late Saturday night. High pressure will build to the south of the region late Sunday through Monday before moving offshore Tuesday. Another cold front will pass through Tuesday night into Wednesday and Canadian High pressure is likely to build overhead for Thanksgiving Day. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure will gradually build overhead through the day today, leading to dry weather and mostly sunny skies. Still seeing some strato-cumulus out there early this morning in the northwest flow, but these will dissipate through the morning hours as northwest winds gradually weaken through the day. High temperatures expected to reach the 50s area-wide. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/...
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Active weather expected for the weekend as surface high pressure slides offshore and low pressure exits the Plains states, moves towards the Great Lakes, and exits through the Saint Lawrence Valley, deepening to a ~980mb low in the process. Quiet weather is expected for much of tonight with the region still under control of the departing surface high. Light southerly flow and high clouds will both be on the increase as a warm front moves towards the region, associated with the aforementioned low pressure system. A light rain shower or two are possible towards morning across western MD and WV. Lows tonight in the 30s to around 40F. Low level southwest flow will increase rapidly on Saturday as warm frontal zone moves across. Some rain showers are likely, mainly north across MD and eastern WV and mostly in the first half of the day as the strongest forcing lifts northward into PA/NY. Otherwise, south to southwest surface winds will increase through the day with gusts up 35 mph possible by late in the afternoon, likely higher across the higher elevations where wind advisories may be necessary by evening as 850mb winds approach 50 knots. Highs Saturday 50-60F. Strong cold front will cross the region Saturday night, with a period of rain showers and increasing winds. A Wind Advisory will likely be required for winds to 50 mph for at least the higher elevations, and it may be necessary area-wide as winds increase just ahead of the front out of the southwest and again behind the front out of the northwest. Can`t rule out a fine line with focused area of gusty winds immediately along the front either. Behind the front, low level temperature profiles will crash, with precipitation changing to snow in the higher elevations and taking on an upslope characterization as northwest winds increase. Lows 30s/40s. On Sunday, gusty northwest winds will continue with gusts up to 50 mph possible, especially in the morning and over the higher terrain. Upslope snow showers will continue along the Allegheny Front, with some also possible downwind as upper trough moves overhead. Several inches of snow accumulation are likely in the higher elevations near and along the Allegheny Front. Highs Sunday stuck in the 30s in the higher elevations, with 40s to low 50s elsewhere.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/... High pressure centered to the south Monday will move offshore Tuesday. Dry conditions are expected during this time. Monday will turn out chilly and Tuesday will be a bit milder due to a return southwest flow around the departing high. A cold front will pass through late Tuesday night into Wednesday. Little moisture will be associated with the boundary. An isolated shower cannot be ruled out with the frontal passage...but most places will be dry and any precipitation that does occur will be light. Canadian high pressure will build overhead later Wednesday through Thanksgiving Day...bringing dry and chilly conditions. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... VFR expected through tonight with strato-cumulus early this morning scattering out, replaced by increasing high clouds tonight. A period of sub-VFR conditions are possible Saturday night as a cold front moves across the region bringing a period of rain showers. Main aviation weather concern however will be increasing low level wind field Saturday and Sunday. This will bring wind gusts out of the southwest Saturday afternoon and evening up to 30-35 knots, and up to 40 knots behind the front late Saturday night into Sunday. Low level wind shear will also be a concern before winds gust on Saturday. Winds will gradually lessen late Sunday and Sunday night. VFR conditions are most likely for Monday and Tuesday. && .MARINE... Small Craft Advisory remains in effect for all waters through noon today for gusty northwest winds. It continues through 6 PM for the lower Tidal Potomac and parts of the Chesapeake, however winds will be lessening as high pressure moves overhead, and it may be able to be cancelled early. Sub-SCA winds then expected for much of tonight. Early Saturday morning will see an increase in southerly winds, and SCA winds are expected to develop after 4 AM Saturday across portions of the waters, with SCA in effect for all waters after 8 AM Saturday. Winds will increase through the day, and a Gale Warning may be necessary by late Saturday afternoon and Saturday evening. Gales then become more likely out of the southwest Saturday night and northwest Sunday as winds increase further associated with a potent frontal passage. Winds gradually lessen late Sunday and Sunday night, however SCA level winds still likely. High pressure centered to the south of the waters Monday will move offshore Tuesday. A cold front will pass through late Tuesday night into Wednesday. A Small Craft Advisory may be needed for portions of the waters Monday through Wednesday. && .TIDES/COASTAL FLOODING... Anomalies have dropped due to an offshore flow. However...there are anomalies around 1 to 1.5 feet in the southern portion of the Bay. The northwest flow will decrease today and then turn to the southwest tonight. This will allow for those anomalies to return north into our area. Latest forecast blends toward the ETSS and ESTOFS which keeps water levels well below minor flooding...but if all that water does return then minor flooding could take place during the high tide cycle tonight into early Saturday. A southerly flow will strengthen Saturday and Saturday night ahead of a cold front. There is a better chance for minor flooding during this time near high tide. A strong offshore flow will likely cause blowout conditions Sunday into Sunday night. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until noon EST today for ANZ530>532-535- 536-538>540. Small Craft Advisory from 8 AM to 6 PM EST Saturday for ANZ530- 531-535-536-538>540. Small Craft Advisory until 6 PM EST this evening for ANZ533- 534-537-541>543. Small Craft Advisory from 4 AM to 6 PM EST Saturday for ANZ532>534-537-541>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL/MM AVIATION...BJL/MM MARINE...BJL/MM TIDES/COASTAL FLOODING...BJL

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