Area Forecast Discussion
Issued by NWS Wakefield, VA

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104 FXUS61 KAKQ 221817 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 217 PM EDT Thu Jun 22 2017 .SYNOPSIS... Bermuda high pressure begins to shift back towards the Eastern Seaboard through Tonight. The high becomes centered off the Southeast Coast Friday and Saturday...as a surface cold front approaches the region from the northwest. Tropical moisture from the remnants of TD Cindy will push across the region ahead of the front for Friday through Saturday...before the front shifts offshore late in the weekend. && .NEAR TERM /THROUGH TONIGHT/... Latest weather analysis features Tropical Depression Cindy moving N-NE over the West-Central Gulf Coast at midday. Out ahead of the system, a broad plume of mid to upper level clouds has pushed across the Mid-South into the Carolinas. To the north, a quasi-stationary boundary remains in place along and just north of the Mason-Dixon line, extending NW into the western Great Lakes. Meanwhile, the Bermuda High is settling in off the Southeast Coast and will remain there through at least Saturday. 12z soundings indicate quick moistening out ahead of the system, with PW values already in the ~1.25 to 1.50 range...running just a bit faster than model timing. Have nudged pop up into 20-30% range for isolated to widely sct convection over the southern 1/3 of the area (mainly us-460 south). A couple of lobes of shortwave energy out ahead of TD Cindy lift ENE from the TN Valley/SE States this afternoon. Expect that showers will mainly stay SW of the local area for much of the day, with a few showers making it into the area by the late aftn into the evening before waning. Given that shear is still on the low side, expect activity over the local area to drop off quickly with loss of heating, with most pcpn remaining to our w-sw through midnight. Overall, increasing clouds, very warm/muggy this aftn with highs reaching into the lower 90s most areas and dewpoints around 70F. More widespread area of showers pushes in late tonight as theta-e ridge pushes across the piedmont toward the Eastern Shore late tonight into Friday morning. Expect a period of moderate to locally heavy rainfall during this time frame, and have therefore continued likely pop mainly NW of a FVX-RIC-SBY line. Farther south, have gone with a low chance pop for some isolated showers over south central VA and NE NC. Warm and muggy overnight with lows in the 70s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Strong high pressure remains in place over the Desert SW tonight into Friday as the Bermuda High to the east creates an omega blocking pattern...effectively "trapping" TS Cindy in the middle. Cindy`s overall movement will be highly dependent on actual location placement of the ridges over the next few days, and even more so on a broad upper level trough currently stretched across the western 2/3rds of the US/Canadian border. This trough is expected to start digging into the US tonight, however the bigger question is how far can it dig before it runs into Cindy and/or gets blocked by the Bermuda High. The good news is that 00Z model runs are in fair agreement in bringing the base of the trough into the Midwest Fri/Sat. As this occurs, surface low pressure located in eastern Ontario on Friday will drag a cold front towards the Mid Atlantic Region. The front should collect the remnants of TS Cindy and slowly push through the local area Sat/Sat night...exiting the NE NC coast Sunday morning. So what does this mean for the Mid Atlantic Region? 1. INCREASING CHANCES FOR SHOWERS/STORMS. Ample subtropical moisture (pwats around 2.00 inches) will continuously stream into the area from the Gulf and the Atlantic, and that`s before the remnants of Cindy arrive. Shortwave energy ejecting from Cindy will bring the first round of showers/storms to the region beginning Friday morning and persisting into the evening. Storm severity will be highly dependent whether or not clouds can break up during the day and allow for surface instability to occur. Otherwise, instability will be largely contingent on elevated instability from heating aloft. At this time, SPC has the northwestern half of the area in a Marginal Risk for isolated severe storms on Friday, however 850-700mb MUCAPE suggests that SE VA/NE NC would be more conducive to favorable strong thunderstorms. Overall, unidirectional shear and low-mid level dry air seen in atmospheric profiles suggests that line segments will be the primary storm type and that locally strong wind gusts will be possible under the strongest storm cores. Moderate to heavy rainfall rates within the subtropical environment anticipated. A break in precipitation is anticipated Friday night with the loss of daytime heating. This will be short-lived as the remnants of TS Cindy arrive by Saturday morning just ahead of the cold front extending down from Canada. More widespread showers/storms should be anticipated as the front slowly tracks ESE through the area... exiting the NE NC coast by Sunday morning. Once again, storm mode will primarily be line segments with locally strong wind gusts possible...especially across the southeastern half of the area during Saturday afternoon. Will highlight storm potential in the HWO for the entire forecast area. 2. POTENTIAL FOR LOCALIZED FLOODING. Moderate to heavy rainfall rates over a short period of time could lead to localized flooding issues Friday and Saturday. In addition, training of storms on Friday could pose a slightly higher risk for flooding. For Saturday, warm rain processes with the remnants of TS Cindy could further enhance and/or exacerbate any flooding issues. Will highlight heavy rain and flooding potential in the HWO for the northwestern half of the area where storm total QPF amounts are roughly 0.50-1.00 inches. Once rain begins and we can observe upstream trends, QPF amounts will likely go up (locally higher possible in thunderstorms). 3. WARM AND MUGGY CONDITIONS. Tonight through Saturday...Highs in the upper 80s inland and mid 80s beaches. Lows in the lower 70s inland and mid 70s beaches. Dewpoints generally 70-75F will result in muggy conditions in the subtropical environment. Lows Saturday night in the mid 60s NW to lower 70s SE as drier, cooler air moves in behind the departing cold front. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Cold front stalls along the Southeast coast Saturday night into Sunday as an upper level trough deepens over the Great Lakes region into the Ohio Valley. Deepest moisture pushes south of the local area Saturday night, but have kept low end chance POPs across the far southeast forecast area. Frontal boundary expected to remain in the vicinity of northeast North Carolina Sunday due to southwest flow aloft. Isolated to scattered diurnally driven showers and thunderstorms are possible across the southeast Sunday afternoon, nearest the boundary and better instability, but expect much of the forecast area to remain dry Sunday. Highs generally in the mid 80`s. Thereafter, medium range guidance drops a stronger cold front Monday/Monday night as additional energy dives down the back side of the upper trough. Guidance indicates the moisture and instability will be limited ahead of the front, but given the dynamics, have kept chance POPs Monday afternoon. Cooler Monday, with highs ranging from the low to mid 80`s. Trough axis swings across the region Tuesday as the front pushes offshore. Drying conditions expected Tuesday, but have kept slight chance to low end chance POPs across the far southeast given model uncertainty with respect to the front. Highs generally around 80 Tuesday as 850mb temperatures level off at 10-12C (-1 standard deviation). Inland locations (and along the immediate coast) could only warm into the upper 70`s. Dewpoints mix into the 50`s, resulting in pleasant afternoon conditions. Dry conditions forecast Wednesday as the trough pushes offshore and heights build over the Ohio Valley. Surface high pressure settles over the Mid-Atlantic. Highs Wednesday generally in the low 80`s. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR conditions are expected through this afternoon and evening. Mid and high level clouds will continue to increase this afternoon as shortwave energy from TD Cindy tracks ENE from the TN Valley/SE States. Patchy rain showers will work into primarily western and northern portions of the region overnight, potentially impacting RIC and SBY. There will also be the potential for MVFR stratus, particularly at RIC, tomorrow morning. Winds increase out of the SW on Friday afternoon, gusts in excess of 20 knots will be possible. Outlook: Additional showers and thunderstorms are expected to redevelop on Friday afternoon and again on Saturday as the remnants of TD Cindy arrive just ahead of a cold front. Periods of MVFR will be possible in heavier showers on Friday and Saturday. The front exits the NE NC coast by Sunday morning with winds shifting to the NW and conditions improving to VFR as cooler, drier air arrives in its wake.
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&& .MARINE... High pressure is situated off the Southeast coast early this morning as TS Cindy moves onshore along the nrn Gulf coast. Additionally, a weak front is immediately north of the local marine area. High pressure is expected to prevail off the Southeast coast through Saturday as the remnant low of Cindy tracks through the Tennessee Valley Friday and Friday night, and then across the nrn Mid-Atlantic Saturday. A SW wind will average 10-15kt today through tonight and Friday, with 2-3ft seas and 1-2ft waves in the Bay. A cold front will push into the Ern Great Lakes Friday and this combined with the approach of the remnant low will result in a tightening pressure gradient and strengthening low- level jet Friday night through midday Saturday. A SW wind will increase to 15-25kt (gusts up to 30kt possible in the ocean/Bay), with 4-6ft seas possible out near 20nm mainly north of Parramore Island, with 3-4ft seas farther south. SCA conditions are increasingly likely Friday night into Saturday. A cold front pushes across the coast Saturday night, followed by a stronger cold front Monday night with high pressure building over the region through the middle of next week. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...BMD NEAR TERM...BMD/MAM SHORT TERM...BMD LONG TERM...MAM AVIATION...AJB/BMD MARINE...AJZ

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