Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212010 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 410 PM EDT Mon Aug 21 2017 .SYNOPSIS... High pressure becomes centered off the Mid Atlantic coast through Tuesday. A cold front crosses the area late Wednesday, with strong high pressure building north of the area from Thursday into the upcoming weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Latest surface analysis centers ~1023mb high pressure just offshore, resulting in light south to southeast flow over the local area. A weak wave visible on water vapor and in the RAP analysis is located over the Delmarva this afternoon. The wave coupled with increasing moisture, afternoon destabilization, and a lee/thermal trough over the northern Piedmont has helped fire off scattered showers and thunderstorms generally north and west of Richmond. Overall storm strength has been limited due to westerly flow and modest lapse rates. However, cannot rule out some gusty winds and brief heavy downpours. Showers and thunderstorms push northeast through the afternoon and into the evening hours as the wave pushes offshore. Coverage wanes tonight with the loss of daytime heating/destabilization and upper level support. Warm and humid tonight with lows mainly 70-75 F tonight. Fog/stratus possible again tonight over the Piedmont into central Virginia, but not expected to be as dense as this morning. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/... Increasing return flow on the back side of departing high pressure and ahead of an approaching cold front will result in warm and humid conditions Tuesday. Highs generally in the low to mid 90`s, cooler along the coast. Dewpoints in the upper 60`s to low 70`s will produce heat indices in the 100 to 103 degree range. While the atmosphere will be quite moist with precipitable waters around 1.75 inches, warm air aloft, weak lapse rates, and a lack of appreciable forcing will limit the convective potential Tuesday afternoon. Will retain silent PoPs. Mild Tuesday night with lows in the mid 70`s. Clouds increase across the north ahead of the approaching cold front. Better forcing arrives along the front Wednesday as a lead wave drops over the Mid-Atlantic. The cold front progged to slowly push across the area Wednesday afternoon into Wednesday night. PoP`s increase during the morning, becoming likely Wednesday afternoon with the arrival of the better dynamics. The air mass ahead of the front will become modestly unstable, with mixed- layer CAPE values progged around 1000-2000 J/kg. Deep layer flow also progged around 25-30 knots as mid level flow increases, resulting in better organization and overall storm strength. Mid level lapse rates also improve to around 6 to 6.5 C/km. SPC maintains a marginal risk for severe weather, with damaging winds and heavy rainfall the main threats. Highs generally in the mid 80`s northwest to around 90 south. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Strong Sfc cold front drops south across the area Wednesday night into Thursday morning. Modest ascent accompanies the front within the RRQ of a ~110kt jet over New England, along with pw values to around 2.0" (around +1 st dev). By Wed evening, have maintained highest (70%/Likely) POP across srn VA/NE NC, with slight to low end rain chances by Wed night NW of RIC, where drier air arrives first. PoPs across SE portions gradually diminish to 20-40% by Thursday aftn. Thunder will be maintained into Wednesday evening, with showers thereafter as stable NE flow prevails in the wake of the front. Drier air gradually filters in from the NW late Wednesday night into Thursday with partial clearing across the nrn tier counties. Thereafter, the late week period will be characterized by the gradual development of a longwave upper level trough over the eastern United States for the late week period into next weekend. Meanwhile, broad 1024+ mb surface high pressure builds south over the interior northeast from Great Lakes Thursday and Friday, eventually setting up over New England and ridging down the east coast over the weekend into early next week. Resultant E-NE flow will result in markedly cooler and drier conditions over the region, with early morning lows in the 50s inland to mid 60s along the coast. Maintained a dry forecast through the forecast period. High temperatures Thu-Mon will be at or just slightly below normal through the period, mainly in the upper 70s to low 80s. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... High pressure has centered offshore early this afternoon, with flow becoming south to southeast over the area. Scattered to broken cu has developed over the region, with decks around 3500 to 4500 feet AGL. Isolated to scattered showers and thunderstorms have developed over the Piedmont, along a lee/thermal trough. Expect that activity to remain west of the TAF sites this afternoon. Otherwise, VFR conditions prevail with south to southeast winds at or below 10 knots. Continued mainly dry tonight and probably will see a little less in the way of fog/low cloud Tue morning as southerly flow becomes a little stronger. The next cold front approaches the region Wed, and flight restrictions will be possible Wed, mainly in the aftn and through Wed night in showers/tstms. Some showers may linger across SE terminals into Thu morning, but otherwise improving conditions except with a breezy NE flow near the coast Thu/Fri. && .MARINE... Latest surface analysis has a high pressure centered just off the coast. The high will continue to move out to sea overnight and Tuesday. A cold front approaches the waters Tuesday night and into Wednesday morning. The front crosses the area late Wednesday and moves SE of the area Thursday with high pressure returning for the remainder of the forecast period. Obs indicate generally S/SE winds of 10 to 15 knots over the waters with waves of 1 to 2 feet and seas around 2 feet. Winds increase out of the SSW Tuesday through Tuesday night as the front approaches the waters. Wind speeds may approach 15 to 20 over the Chesapeake Bay and ocean with seas building to 3 to 4 feet and potentially 5 feet north/20nm out, and waves building to 2 to 3 feet. A Small Craft Advisory may be needed for the Chesapeake Bay and northern two ocean zones Tuesday night into early Wednesday. Winds shift to the N/NE behind the front late Wednesday through Thursday around 10 to 15 knots. Strong surface cold front drops across the waters Wed afternoon and evening...pushing well SE of the area during Thu. Winds shift to the N/NE behind the front late Wed through Thu around 10 to 15 kt. Post-frontal, look for onshore (E-NE flow) for the remainder of the forecast period as high pressure builds NNW of the local area. Winds increase to 15-20 kt Thu night as a couple of waves move across the stalled front to the south across the Carolinas. Seas will remain choppy for the late week period into the weekend with the persistent onshore flow, remaining 3-4 ft northern waters...4-5ft southern waters. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...LKB NEAR TERM...LKB/SAM SHORT TERM...LKB/SAM LONG TERM...AJZ/MAM AVIATION...LKB/SAM MARINE...AJB/MAM is the U.S. government's official web portal to all federal, state and local government web resources and services.