Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 231934 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 334 PM EDT FRI SEP 23 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Latest MSAS showing low pressure and weakening sfc trof off the Carolina coast with high pressure building over the Mid Atlantic region. This high will continue to push any moisture south of the Albemarle sound this evening. Meanwhile, a backdoor cold front drops south into northern VA by 12Z Sat. AKQ fa between systems resulting in a dry night under mstly clr to pt cldy skies. Patchy fog possible after midnight. Lows in the mid-upr 60s except near 70 at the coast.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
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1025+ mb high moving across southern Canada pushes a backdoor cold front across the region Sat. Day starts off pt to mstly 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 the high pressure near James Bay. This high extends south across the Mid Atlantic region Sunday and Sunday night. Latest data continue to focus on increasing low level moisture and some 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 I95 corridor. Kept slght chc pops (rain vs shwrs) 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 nite 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 enuf...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 coluds keeps it cool with highs in the low to mid 70s.
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&& .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Medium range period characterized by continued large differences amongst the deterministic models and even within their member ensembles. Forecast period begins Sunday night with an amplified upper level ridge/trough pattern, with the ridge axis being centered from the OH/TN river valleys Into the central Gulf Coast. At the surface, cool air wedge will continue to ridge down across the local area from New England/QC. Have retained a slight chance for some light rain Sunday night in association with some weak overrunning moisture. Otherwise, remaining primarily dry albeit with increasing clouds once again Sunday night and Monday. Higher than average uncertainty remains for the remainder of the forecast period, although it does appear as if the models are trending toward a solution. The 00z/GFS and GEFS mean remain much stronger than the ECMWF with strong upper ridging and a potent (closed off) downstream trough over the upper midwest by later Mon/Tue. By contrast, the 00z/ECMWF and the 12z/Thu EPS before it confines blocking farther back (west) into the Canadian Rockies...with the downstream, more progressive upper trough quickly shoving through a strong cold front across the local area by mid to late week (as soon as Later Wed/Thu). The CMC remains the slowest solution wrt displacing the upper ridge off shore, and therefore is the warmest/driest solution. Taken at face value, the GFS solution would lead to more of a strong blocking pattern that would slow the eastward progression of upper ridge axis considerably, while the ECMWF would bring a quicker frontal passage and resultant cooler temps for the late week period. The good news is that the GFS has trended a bit toward the operational EC with respect to shifting the Sfc high offshore Tuesday into Wednesday...depicting a strong sfc cold frontal passage for the mid to latter portion of next week. Have made minimal changes to the going forecast for now until more definitive model consensus can be reached and ideally retained for a few cycles. For temps, Highs will start off cool, averaging in the low-mid 70s with early morning lows in the upper 50s to mid 60s Mon. Sfc high pressure becomes centered offshore by late Tue-Wed w/deeper moisture and a strong front to approach the area from the W. Pops remain a bit more broad-brushed in slight chc range 20% POP for now during this period. Highs will avg 75-80 F Tue/Wed with lows mainly in the 60-65 F range. Cooler by late in the week, with 00z MOS guidance advertising highs trending back into the low to mid 70s post-frontal by next weekend. Again, will stay close to the inherited forecast for now. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Clouds are continuing to erode and move southeast of the region this afternoon. VFR conditions are anticipated across all of the TAF sites through the first half of the night. Introduced IFR conditions after 07Z at SBY/PHF/ECG due to the possibility of fog. Expecting visibilities to improve and a return to VFR conditions after 13Z tomorrow. Outlook: A cold front sags south through the Mid Atlantic states during the weekend. There are some indications that low clouds and some patchy light rain/drizzle could impact the TAF sites Saturday night and into Sunday. && .MARINE... Latest obs reflect diminishing NNE flow across the waters as pressure gradient has relaxed over the past 3-6 hours w/weakening low pressure lingering along the NC/SC coastline, even as high pressure slowly builds south. Have dropped SCA across the waters this morning, with seas finally subsiding a bit. Winds remain sub-SCA out of the NNE today, winds 10kt or less. Seas subside to 3-4 ft, 2-3 ft on the bay. Winds pick up a bit late tonight as a weak Cold front drops across the waters late tonight into Saturday, stalling just south of the waters Sat night and Sunday before sliding south into the Carolinas on Monday. CAA surge behind the front appears minimal. Wave energy kicks up on Saturday, courtesy of distant tropical Cyclone Karl Invof Bermuda. Resultant long period swell could well bring a period of SCA for hazardous seas over the coastal waters Saturday/Sat night, averaging 4-5 ft highest out by 20 nm marker. Wavewatch and NWPS both depict seas subsiding once again for Sunday through Sunday night. && .HYDROLOGY...
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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.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...MPR NEAR TERM...MPR SHORT TERM...MPR LONG TERM...LKB AVIATION...AJB MARINE...LKB HYDROLOGY...MPR

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