Area Forecast Discussion
Issued by NWS Wakefield, VA
Issued by NWS Wakefield, VA
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447 FXUS61 KAKQ 191919 AFDAKQ AREA FORECAST DISCUSSION National Weather Service Wakefield VA 319 PM EDT Thu Sep 19 2024 .SYNOPSIS... High pressure will remain north of the region while low pressure remains well offshore. A backdoor cold front potentially drops back south across the region Saturday. High pressure builds north of the area this weekend into early next week leading to generally dry conditions. A cold front potentially approaches by the middle to later portions of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... As of 300 PM EDT Thursday... Key Messages: - Trending drier with low-end shower chances for inland areas SW of I-64. - Patchy fog possible tonight. Afternoon analysis shows sprawling low pressure offshore of the area, with several areas of low-level vorticity noted on the latest visible satellite images. A trough over the eastern CONUS aloft will act to slowly deepen this low as it gradually drifts S over the next few days. Elsewhere, a weak stationary front is located S of the area, with a remnant upper low spinning over the eastern half of the area. NNE winds from these sfc features are gradually scouring out the thicker cloud cover this afternoon and skies range from sunny/mostly sunny up on the Eastern Shore to partly-mostly cloudy over the Piedmont and in NE NC. Temps have warmed into the upper 70s or lower 80s for areas that have seen appreciable clearing, while mid 70s persist for those areas still seeing the clouds and/or showers. Speaking of showers, there are isolated showers in our western tier of counties associated w/ a weak area of convergence and the upper low. Coverage should remain on the low side and the thinking is that 30% PoPs covers this activity well. Elsewhere, could see additional isolated activity develop across the S/SW and in NE NC near the Albemarle Sound. General trend has been for drier wx so have cut back on PoPs here compared to earlier forecasts. Little to no thunder is expected given MLCAPE ~500 J/kg. Skies become mostly clear tonight before patchy fog and/or stratus develops. Not expecting widespread dense fog at this time, but could see some patches of 0.25-1.0 mile visibilities. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... As of 300 PM EDT Thursday... Key Messages: - Drier weather returns Friday into Saturday. - Showers or isolated storms possible Saturday evening into Saturday night. - Cooler and mainly dry Sunday. Fairly pleasant Friday and Saturday with high pressure over New England extending down into the local area. Meanwhile, the previously referenced coastal low will linger well off the Mid Atlantic coast. Sunshine returns in earnest for Friday, with temperatures generally in the lower 80s (70s along the immediate coast). Low temperatures Friday night range from the upper 50s to lower 60s. There is less fog potential Friday night given lower dew points, but cannot rule it out (especially S). Mostly sunny skies continue into Saturday, with highs again in the upper 70s to lower 80s. Clouds increase late in the day and especially overnight as a shortwave on the wrn periphery of the upper trough drops through the area and a backdoor cold front-type features moves through at the sfc. These features could spark showers and isolated storms NW of the area later Saturday, possibly moving S into the area by the evening and overnight hours. While moisture profiles are not overly impressive, most guidance suggests something in the way of precip moving through and have MUCAPE actually increases some overnight as the cooler air aloft moves in, so there could be some rumbles of thunder with this activity. Lows Sat night around 60 F. Sunday will be cooler behind the front with afternoon highs in the mid-upper 70s. Will maintain a dry forecast for now, but there could be some lingering showers given the nearby upper trough. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 300 PM EDT Thursday... Key Messages: - Starting off cool Monday with dry conditions. - Gradually warming temps expected by the midweek, with low-end precipitation chances potentially returning. Offshore low pressure and associated upper low will depart well to our SE by early next week. This will bring rising mid/upper heights to the area, with a SW-NE oriented ridge forecasted to develop over the eastern CONUS. Thus, temperatures should gradually moderate back into the lower 80s by Tuesday and Wednesday. Monday, however, will be dry and feature slightly below normal highs in the mid 70s with gusty NE winds (especially along the coast) and partly-mostly cloudy skies. Precip chances potentially inch back up by Tuesday and especially Wednesday as a quick-moving shortwave ejects out of the Midwest, likely interacting with the next deep-layer trough coming out of the nrn US and Canada. 12z deterministic guidance shows several waves of precip associated with various smaller-scale disturbances. Timing these disturbances is difficult at this lead time and given associated spread across the ensemble guidance, will remain near or slightly above NBM PoPs during this period. This yields slight chc PoPs Tuesday aftn across the W, with 20-30% PoPs for most of the area Wednesday-Wednesday night with the parent cold front. Sky cover averages partly-mostly cloudy. Forecast overnight lows are in the upper 50s-lower 60s Sunday night, mid-upper 50s Monday night, and lower 60s Tuesday/Wednesday night. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... As of 145 PM EDT Thursday... Conditions have been improving through the late morning and early afternoon hours at the terminals as relatively drier air filters into the area from the N. Generally seeing MVFR- VFR CIGs, with the thickest cloud cover (BKN-OVC) across the Piedmont and in NE NC. Seeing FEW-SCT cloud cover elsewhere, including at SBY. Similar conditions through the rest of the daylight hours today, with CIGs expected to lift a little more (to 3-4k ft AGL) and skies averaging SCT-BKN. Additional IFR (and possible LIFR) could develop tonight from low stratus and/or fog. Guidance is not in the best agreement, thus confidence is on the low side. However, the best chance for dense fog appears to be at ECG, with patchy fog or stratus elsewhere. Will not explicitly show IFR/LIFR in the TAF as of now, but have introduced MVFR VSBY in the 07-13z timeframe. Conditions improve after 13-14z Friday and mostly sunny skies are expected by the early afternoon. N-NNE winds average 5-10 kt this afternoon and become 5 kt or less tonight. Similar winds expected Friday. Outlook: Gradually improving and primarily VFR conditions are expected Friday through the weekend and into early next week. && .MARINE... As of 320 PM EDT Thursday... Key Messages: - Small Craft Advisories have been lowered for now. - Additional Small Craft Advisories possible as early as tomorrow afternoon for seas, with SCA likely this weekend into early next week. - Stronger NE winds develop late Saturday and Sunday, with persistent long period swells keeping seas elevated this weekend into the middle of next week. Latest obs and buoy reports reflecting N/NE winds 10-15 kt over the waters this afternoon. Deepening ~1004 mb sfc low pressure continues meander just south of the southern New England coast, with the system stalled due to a blocking area of high pressure centered off the coast of Nova Scotia. Meanwhile, weak 1015+mb sfc high pressure builds NW of the waters. Resultant NNE winds continue this evening, backing to the NW as the surface high starts to build overhead. Buoy obs reflect seas subsiding largely as expected this afternoon. Seas were 3-4ft S of Cape Charles Light and ~4-5ft to the N. SCAs were lowered earlier today south of Parramore Island, and will be allowed to expire with the issuance of the afternoon package. Winds slowly diminish and back to the NW as the pressure gradient relaxes with high pressure building across the lower mid-Atlantic. will allow for further improvement in marine conditions. Expect seas to gradually improve as well with winds turning offshore and diminishing. Seas generally 3-4 ft, waves 1-2 ft. Previously referenced blocked low pressure south of Nantucket remains more or less in place on Fri. While N/NE winds will be sub- SCA at 10-15kt Fri-Sat, E-NE wind waves (8-10 second swell) from the offshore low arrives Fri morning into the afternoon, leading to seas increasing once again. Northern coastal waters will see 5-6ft seas by midday Friday, and by late Friday evening into Sat morning across southern coastal waters and the mouth of Chesapeake Bay. The pressure gradient over the waters also starts to tighten up again late Saturday and Sunday as the low dives SE. This should increase NE winds during this period, especially over coastal waters. The bay/rivers will likely need SCAs for winds ~20kt as early as late Sat night, but more likely on Sunday. Winds over coastal waters look to be 20-25kt. Building swell combined with elevated winds should allow seas to build to 6-8ft in the N and 5- 7ft S. While winds look to improve early next week, but energetic long period (E-NE, ~10 second) swells from the lingering low well offshore of New England will keep seas in 4-6 ft range over the coastal waters through at least the middle of next week. && .TIDES/COASTAL FLOODING... As of 320 PM EDT Thursday... Astronomical tides continue to increase with the approach of the coming full moon (Harvest moon) cycle. Astronomically higher astro tides, along with prolonged onshore flow will continue to produce tidal anomalies of 1-1.5 ft, resulting in nuisance to low-end minor tidal flooding across much of the area along the bay and tidal rivers through the end of the week. Have opted to extend the Coastal Flood Advisories given similar water levels near minor flood thresholds through Friday evening`s high tide cycle. While winds briefly diminish and turn offshore, the ebb tide will be short- lived, as winds turn back onshore over the weekend. Additional extension of advisories or perhaps Coastal Flood Warnings are likely to be needed over the weekend. Will hold coastal flood headlines at Friday night for now. Winds turning back onshore and gradually increasing Sat night and Sunday should bring building flood tide Saturday into Saturday night. With anomalies increasing once again, the potential for tide levels reaching moderate Coastal Flood Thresholds (best chances northern coastal zones and lower bay) does increase for tide cycles over the upcoming weekend. Coastal Flood Watches may be issued in upcoming forecast cycles for the weekend. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...Coastal Flood Advisory until 6 AM EDT Saturday for MDZ021>023. Coastal Flood Advisory until 2 AM EDT Saturday for MDZ025. NC...Coastal Flood Advisory until 2 AM EDT Saturday for NCZ102. VA...Coastal Flood Advisory until 6 AM EDT Saturday for VAZ075-077. Coastal Flood Advisory until 2 AM EDT Saturday for VAZ078- 084>086-095>100-523>525. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ650- 652. && $$ SYNOPSIS...AJB/SW NEAR TERM...SW SHORT TERM...AJB/SW LONG TERM...SW AVIATION...SW MARINE...MAM TIDES/COASTAL FLOODING...