Area Forecast Discussion
Issued by NWS Wakefield, VA

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672 FXUS61 KAKQ 240017 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 817 PM EDT FRI SEP 23 2016 .SYNOPSIS... High pressure moves across the area tonight. A backdoor cold front drops south across the region Saturday. High pressure tracks across Southeast Canada early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Update...Only minor tweaks made to ongoing forecast. Overall, expect mostly clear skies overnight with patchy fog developing after midnight. High clouds should start streaming into far nrn counties closer to sunrise as a backdoor front approaches the region (see short term discussion below). Previous discussion (334 PM)... Latest MSAS showing low pressure and weakening sfc trof off the Carolina coast with high pressure building over the Mid Atlantic region. Meanwhile, a backdoor cold front drops south into northern VA by 12Z Sat. Lows in the mid-upr 60s except near 70 at the coast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... 1025+ mb high moving across southern Canada pushes a backdoor cold front across the region Sat. Day starts off partly to mostly sunny then quickly clouds up post fropa as the winds shift to the N-NE during the afternoon. NAM slowest with the fropa thus most aggressive with sct convection developing along the boundary. GFS/SREF keep it dry across AKQ FA but do develop some upslope shwrs across the mts after 21z. Will maintain a dry forecast on Sat. Tmps tricky and will depend on timing of front. Highs in the mid to upr 70s ern shore to mid 80s swrn zones. Front continues to push south into the Carolinas Saturday night in response to high pressure sliding across Southeast Canada. This high extends south across the Mid Atlantic Region Sunday and Sunday night. Latest data continues to focus on increasing low level moisture and weak isentropic lift Saturday night into Sunday night. The depth of moisture is rather shallow...favoring only low end pcpn chances for pockets of light rain or drizzle mainly along and west of the I-95 corridor. Kept slght chc pops (stratiform rain rather than showers) across the Piedmont. The onshore flow results in mostly cloudy/overcast skies for areas mainly west of the Bay during this same time and partly cloudy for the Eastern Shore. Lows Sat night in the mid 50s north to mid 60s south. Highs Sun 70-75. Lows Sun night in the mid 50s to lwr 60s. If it clears early enough...SBY could drop to near 50 by 12Z Mon. High pressure moves north of New England Monday with the next front approaching from the west during the afternoon. Slght chc shwrs across the Piedmont ahead of the front. Onshore flow and clouds keeps it cool with highs in the low to mid 70s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Medium range period has become somewhat clearer with the latest 12Z model suite trending further into at least modest agreement. There are still significant timing differences that exist regarding a cold frontal passage Tue into early Wed followed by a large area of High pressure building into the local area from the west as an upper level trough becomes centered over eastern Canada and the NE CONUS/New England Tue/Tue night, then shifts off the E coast by Thu. Have raised POPS Tue/Tue night to 30-40% with the front, along with a chc for tstms Tue aftn/evening. Beyond that, will linger 20-30% POPS mainly along the coast Wed in case the front trends slower, with mainly dry conditions expected Wed night through Fri. Temperatures will avg close to seasonal averages, with highs Tue ranging from the mid 70s NW to around 80 F S/SE (where more sun may occur ahead of the front). Highs Wed-Fri generally in the 70s with lows in the 50s, except in the 60s SE. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Mostly clear skies overnight as weak high pressure slides over the area...allowing patchy fog to develop after 24/0900Z. Visibilities should generally be 3-5SM...except KSBY and KECG where visibilities could drop as low as 2SM with SCT stratus around 400ft AGL. A backdoor cold front then drops south through the region on Saturday...primarily spreading widespread high clouds across the area during the day. Given the abundant/recent rainfall from the past several days and persistent onshore/ne winds, expect SCT cumulus to develop during the aftn...especially near coastal sites. KSBY will likely experience MVFR cigs given how early the front comes through there and overall proximity to the frontal boundary throughout the day. The front pushes south of Albemarle Sound after midnight Saturday night with stronger central high pressure sliding across Southeast Canada and building down into the Mid Atlantic Region through Sunday night before sliding off the New England coast early next week. Patchy fog may be possible once again late Saturday night into early Sunday morning, otherwise VFR conditions will prevail. && .MARINE... Latest obs continue to depict diminishing NE flow across the waters, generally 5-10 KT. Seas avg 3-4 ft with 10-12 second dominant periods and wave in the Bay are 1-2 ft. Trends are slower with the approaching cold front from the N later tonight into Sat, now the winds tonight will avg 5-10 Kt or less and gradually shifting to the SSW after midnight. On Sat, front progged to push through the waters from N to S, pushing into NC by late afternoon. Did not raise SCA headlines as winds should stay below thresholds, but there will probably be about a 3 hr period with occasional gusts to 20 KT. Waves in the Bay should build to 2-3 ft by late morning/early aftn and to 2 ft in the rivers so still not ideal boating conditions even without headlines (may need to issue an MWS). For the coastal waters, distant tropical Cyclone Karl Invof Bermuda looks to aid in seas building to 4-5 ft. Trends in wavewatch are slower and slightly weaker however, so did not issue SCA headlines as this is marginal and will be late 2nd period (will allow next shift to determine if seas ever do reach a widespread 5 ft). Wavewatch and NWPS both depict seas subsiding once again for Sunday through Sunday night. Next cold front approaching from the NW will shift winds back to the SE on Mon and increase from the S Mon night/Tue. Still some models differences/uncertainties but could see marginal SCA conditions in the Bay Mon night/Tue and probably will have SCA conditions behind the front sometime midweek as significantly cooler airmass and strong high pressure builds in from the NW. && .HYDROLOGY... The Cashie River at Windsor continues to fall but remains in the moderate flood range. The river is forecast to slowly fall below flood stage late Sunday night. See FLSAKQ for details. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...MPR NEAR TERM...BMD/MPR SHORT TERM...JDM/MPR LONG TERM...LKB AVIATION...AJB MARINE...LKB HYDROLOGY...AKQ

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