Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 270819 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 419 AM EDT Thu Apr 27 2017 .SYNOPSIS...
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A cold front approaches the Mid Atlantic Region today, stalling near the mountains tonight. High pressure prevails off the Southeast Coast the rest of Friday through the weekend. The next cold front pushes across the region early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Latest GOES water vapor imagery depicts a broad/anomalous upper trough encompassing much of the western/central CONUS, with an upper level ridge over the East. At the surface, weak area of low pressure is located offshore the Northeast coast with high pressure well offshore extending westward over the Southeast. A cold front associated with the upper trough is located along the Mississippi River Valley. A dense fog advisory remains in effect for the lower Maryland Eastern Shore, with an area of dense fog visible in the obs and on satellite. Otherwise, only some patchy fog inland as light southerly flow and relatively dry low levels have kept widespread fog at bay. Fog expected to erode/lift shortly after daybreak in response to quickly warming temperatures. The upper level ridge axis slides offshore late morning as the central US trough de-amplifies and lifts over the Ohio Valley and into the Great Lakes region. An associated cold front will reach the central Appalachians late today. Increasing return flow ahead of the front (southwest gusts of 20-25 mph) and 850mb temperatures around +14 to +16C (+1 standard deviation) results in a warm day, with temperatures generally 10+ degrees warmer than yesterday. Highs generally in the mid 80`s. Cooler along the coast. Increasing mid to upper level clouds late today may keep some of the far western Piedmont in the low to mid 80`s. Otherwise, outside of some high clouds spreading over the region today from a decaying line of showers, a mostly sunny sky is expected.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
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Showers and thunderstorms progged to develop along the cold front this afternoon from the Ohio Valley to the Southeast. Hi- res guidance pushes a weakened version of the convective line into the Piedmont early this evening as the upper level forcing becomes displaced from the deepest Gulf moisture. Short term guidance indicating better moisture return compared to 24 hours ago thanks to a developing 30-40 kt low level jet. Good moisture flux advects anomalous precipitable water values into the region ahead of the line/pre-frontal surface trough. Thermal soundings indicate elevated instability as height falls and cold air advection aloft steepen mid level lapse rates. Showalters range from -1 to -2. Deep layer shear progged around 30-40 knots due to increasing winds aloft. However, given the lack of overall forcing and the convective line outracing the front, have kept POPs in the chance category tonight. Main threat from thunderstorms will be locally heavy rainfall. Mild tonight, with lows generally in the mid to upper 60`s. Weak surface trough/convergence boundary stalls near the coast Friday morning as the deepest moisture pushes offshore. Even though the best moisture pushes offshore, enough moisture and instability near the coast will keep mention of isolated to scattered showers and thunderstorms in the forecast through early-mid afternoon. Meanwhile, the subtropical ridge amplifies off the Southeast coast Friday. Early morning clouds and convection will temper temperatures from reaching their full potential Friday afternoon. Highs similar to today, generally in the mid (possibly upper) 80`s. Cooler near the coast. Heights continue to build into Sunday as 850mb temps warm to +16 to +18C (+2 standard deviations). The result will be the warmest day of the season with widespread readings in the low 90`s. Dewpoints in the 60`s will push heat index values into the mid 90`s inland. A backdoor front progged to drop into the northern Mid-Atlantic region late Saturday, but models indicate large spatial and timing differences. While the models indicate a great deal of instability, soundings indicate a cap just above 850mb. Moisture is also limited with precipitable water values at or below 1.25 inches. Will maintain slight chance POPs across the north near the dropping front, but believe sea-breeze boundaries will struggle to overcome the lack of moisture and warm temperatures aloft.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Temperatures are expected to remain well above normal through Sun, as an upper level ridge remains anchored just off the East coast. A backdoor cold front could affect nrn portions of the area Sat night thru Sun morning with a slgt chc of showers, then a slowly approaching cold front fm the west could produce isolated or widely sctd showers or tstms Sun aftn into Sun evening, esply wrn half of the region. Lows Sat night in the mid 60s to near 70. Highs on Sun in the upper 70s to mid 80s. That cold front will push thru the mtns by late Mon, then cross the area and move off the coast Mon night into Tue morning. Have high chc to likely Pops for showers/tstms during this period. Highs on Mon in the upper 70s to mid 80s. Lows Mon night mainly in the upper 50s to mid 60s. Weak high pressure will provide dry wx for later Tue morning thru at least most of Wed, as it slides fm the Gulf coast states to off the SE coast. Highs on Tue in the 70s, and mainly in the mid to upper 70s on Wed. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Outside of IFR conditions due to fog across the Maryland Eastern Shore, widespread VFR conditions observed early this morning. Light southerly winds and relatively dry low levels indicated in soundings will limit overall fog development, but some early morning patchy fog possible north and east of Richmond. IFR conditions prevail thru early morning for KSBY. Otherwise, SKC. Cold front approaches from the west today with increasing southwest flow late morning through the afternoon. Expect gusts of 20-25 knots. Scattered afternoon cu expected inland, with decks at 4-6k feet AGL. Weakening line of convection expected to push across the region this evening through late tonight. Lower ceilings/visibilities will be tied to convection. Outlook...Next frontal boundary will provide a focus for more shower/tstm development late Sat. Cigs/Vsbys lower in any convective activity. && .MARINE...
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A cold front approaches the waters today resulting in an increase of south and southwest winds through tonight. Deep low pressure over the upper Great Lakes will move north into Canada which will relax the pressure gradient by Friday. Southeast to south winds were generally 10 knots or less early this morning. Seas subsided overnight but remain 4 to 5 ft north of Parramore Island. While there may be lull in 5 foot seas late this morning...they are expected to build once again late today and into tonight as winds increase. Replaced SCA for Hazardous Seas with a SCA. This is avoid confusion with winds increasing today. The SCA was also expanded to ANZ654 (Parramore Island to Cape Charles) where SCA conditions are expected to develop by Thursday afternoon. There is indication the SCA may be needed for the rest of the coastal zones for a short period this evening but will let the day shift assess the need. Elsewhere conditions are expected to stay below SCA. Although winds over land are expected to gust over 20 knots today...the cool water will inhibit mixing over the marine area. The cold front that approaches the waters today will dissipate over the area Friday morning. A disorganized pressure pattern will produce light winds over the waters Friday. Seas are forecast to subside to below 5 feet by midday Friday. Benign conditions are indicated for the marine area through the weekend. Another deep low pressure system will move through the upper Midwest early next week. This will increase the pressure gradient locally and another SCA may be needed starting Monday.
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&& .TIDES/COASTAL FLOODING... During the high tide cycle early Thursday morning on the bay side of the lower Eastern Shore...some locations may approach minor flooding...especially in Maryland. Bishops Head may touch minor flooding. This may be an issue once again early Friday morning. During the next 24 hours...water level may approach or touch minor flooding on the Ocean side of the Virginia eastern shore as elevated seas continue. && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Dense Fog Advisory until 9 AM EDT this morning for MDZ021>025. NC...None. VA...None. MARINE...Small Craft Advisory until 1 PM EDT Friday for ANZ650-652-654. Dense Fog Advisory until 10 AM EDT this morning for ANZ650.
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&& $$ SYNOPSIS...ALB/BMD NEAR TERM...SAM SHORT TERM...SAM LONG TERM...TMG AVIATION...SAM MARINE...LSA TIDES/COASTAL FLOODING...

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