Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 241914 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 314 PM EDT SAT SEP 24 2016 .SYNOPSIS... A backdoor cold front settles across the Carolinas tonight. High pressure tracks across Southeast Canada Sunday and Monday. A second and stronger cold front will cross the region Tuesday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Mid afternoon MSAS/sfc obs has the backdoor front ivof I64 with a 1025mb high centered south of James Bay. Models show this high will be strong enough to push the frontal boundary into North Carolina and south of the Albemarle Sound after 00Z. ST thickens due to the post-frontal NNE flow allowing a wedge to setup. High res data showing just enuf support for a few showers with the front this evening (given crnt temps arnd 90) and some spotty light rain/sprinkles behind the boundary across the piedmont after midnite. Lows in the mid 50s north to mid 60s south... except upr 60s sern coastal areas. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Front pushes south to near the NC/SC border Sunday in response to high pressure sliding across Southeast Canada. This high extends south across the Mid Atlantic Region Sunday and Sunday night. Per TSCTNS, have maintained mstly cldy conditions west of the Ches Bay to account for low level moisture/weak isentropic upglide. Of note is somewhat drier air progged to work its way south along the eastern shore Sun. This will allow for skies to become pt sunny there. Overcast conditions and pockets of light rain or drizzle are possible along and west of I95. Pops remain only in slight chc range with minimal chances for measuring pcpn. Highs Sun in the low to mid 70s. Lows Sun night in the mid 50s to lwr 60s except 50-55 with clearing skies across Eastern shore. High pressure moves north of New England Monday with the next front approaching from the mts during the afternoon. Cool air wedge holds firm across the piedmont resulting in another mstly cldy day with highs in the mid to upr 70s. A strong cold front progged to drop into the region late Monday night ahead of a potent northern stream trough. Latest data shows the front slowing a bit as it pushes across the region Tuesday. Moisture increases along the front with PW`s climbing above 1.75 inches along with marginal instab. Pcpn enters the region from the NW with highest pops after midnight. Lows Mon nite in the mid 60s. Models show possible weak s/w energy riding east along the boundary Tuesday. This will likely enhance pcpn and allow it to linger a bit longer especially along coastal sections. Thus, went ahead and bumped up pops to likely across the sern zones. Kept thunder chcs in as well. Highs Tuesday in the low to mid 70s. QPF generally between 1/2 to 3/4 inch. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... update to be issued shortly... Strong cold front progged to drop into the region Monday night ahead of a potent northern stream trough. Latest deterministic and ensemble guidance in good agreement with pushing the front across the region late Monday night through Tuesday. Moisture increases along the front with precipitable waters climbing above 1.75 inches. Instability progged to be marginal ahead of the front due to cloud cover and poor lapse rates, However, will keep mention of slight chance thunder in the area of highest showalter values (elevated instability) and shear around 40 knots. Both GFS and ECMWF models push the front across the region rather quickly Tuesday with much of the area seeing a decent chance for shower. Have capped at high end chance. High pressure builds in from the west late Tuesday and Tuesday night. Will linger POPs over the southeast half of the forecast area, but expect much of the precip to push offshore by late Tuesday night. High pressure prevails through the end of the week and into the weekend. Temperatures will average close to seasonable averages, with highs Tuesday ranging from the mid 70`s northwest to around 80 southeast. Highs Wednesday through Friday generally in the 70`s with lows in the 50`s, expect in the 60`s southeast. Based on the latest statistical guidance, the Piedmont may see some readings in the 40`s Thursday morning. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Backdoor cold front moving south across the region this afternoon. Wind shift to the north well ahead of it, but the boundary is denoted by a BKN-OVC ST layer between 1.5-2.5K ft. This cloud deck will lift a bit (btwn 3-4K ft) as it drifts south across the region over the next several hours. The MVFR conditions along with NNE winds at 10 mph or less continue through most of the forecast period west of the Ches Bay. Model data indicating drier air from the north begins to work its way south along the Delmarva late tonight with SCT-BKN cloud coverage. Latest data continues to support VFR conditions at SBY after 12Z Sun. A light shwr/sprnkl possible at RIC tonite as the wedge sets up, but coverage not widespread enuf to include in forecast attm. Fog not expected to be an issue tonight, but local MVFR VSBYS (3-5SM) possible towards sunrise. Outlook... The next chc for sgnfcnt pcpn comes late Monday night and Tuesday ahead and along the next cold front. && .MARINE... Weak pressure gradient observed over the waters early this morning as a cold front drops into the northern Mid-Atlantic region. Winds are generally out of the west-southwest at or below 10 knots. Seas 3- 4 feet and waves 1-2 feet. The weak front drops southward over the waters today, with flow becoming northernly. 850mb temps dip slightly behind the front, but a lack of low level cold air advection and weak gradient winds expected to keep winds sub-SCA this afternoon. Hi-resolution guidance has trended lower on speeds as well. Waves build to 2-3 feet late morning/early afternoon. For the coastal water, distant tropical cyclone Karl will aid in building seas to 4-5 feet this afternoon through tonight. Have raised SCA headlines for all coastal waters as a result. Expect a few gusts to around 20 knots, so have opted against SCA for hazardous seas. High pressure builds southward over the waters tonight, with northernly winds diminishing to around 10-15 knots. Seas subside to 3-4 feet Sunday afternoon. Waves 1-2 feet. The next cold front approaching from the northwest will shift winds back to the south to southeast Monday. Marginal southerly SCA conditions are possible ahead of the front late Monday and Monday night behind a lifting warm front. The front progged to reach the waters Tuesday morning, pushing offshore Tuesday afternoon. SCA conditions expected behind the front as a significantly cooler air mass and strong high pressure builds in from the northwest. && .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 Sunday evening. See FLSAKQ for details. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 10 AM EDT Sunday for ANZ650-652-654- 656-658. && $$ SYNOPSIS...MPR NEAR TERM...MPR SHORT TERM...MPR LONG TERM...TMG AVIATION...MPR MARINE...TMG HYDROLOGY...AKQ

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