Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 220129 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 929 PM EDT Fri Jul 21 2017 .SYNOPSIS... Hot and humid conditions will continue over the region through Sunday. A weakening cold front will gradually push across the area late Sunday through Monday, with temperatures cooling down to near normal levels Monday through Thursday. && .NEAR TERM /THROUGH SATURDAY/...
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Weak sfc/lee trough in place across the local area this evening, with WNW flow prevailing aloft around the base of an upper level trough centered over eastern Canada. Very warm and humid as of 9 pm. Temperatures are still mainly in the 80s, with dewpoints ranging through the 70s to around 80. Earlier convection dissipated very quickly as it entered the NW corner of the CWA, and isolated convection over NE NC has dissipated as well with mainly dry conditions expected through midnight. Some isolated convection (20% chc) is possible late from the Nrn Neck to the MD Ern Shore. Remaining very warm/humid overnight with lows mainly 75 to 80 F. Not as hot most areas for Sat, due to potential for more clouds and as core of 850 mb heat shifts a bit S. However, with slightly higher dew pts than Fri expect most of the area to reach heat advisory criteria Sat aftn even with highs on avg only in the mid 90s. As airmass destabilizes more by Sat aftn/early evening, and as heights aloft drop, convection developing from the NW will be more likely to hold together for at least 30-50% PoPs across most areas (20% NE NC) from late Sat aftn through Sat night. Deep layer shear will be higher as the upper trough sharpens a bit and H5 to H7 flow increases. Most of the CWA is in a marginal risk for severe wx, with a slight risk for the far N/NE. Wind will be the primary threat with large hail also possible.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... Lows mainly in the mid to upper 70s Sat night, and continued hot and humid with additional heat headlines likely needed for some of the region on Sun. Highs mainly in the mid to upper 90s Sunday. Slight risk in place for most of the CWA, but more uncertainty exists depending on how long convective debris from Sat night hangs around and potentially keeps more clouds around. Cold front slated to pass through while weakening late Sun night through Mon. Will maintain chc PoPs all zones Sun night, and favor highest PoPs Mon across the S with 20% PoPs for the N. Slightly less humid Monday, especially N. Highs Mon 90 to 95 F. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Cold front progged to push offshore Tuesday morning as the upper trough slides over the Northeast into the Canadian Maritimes. Deepest moisture pushes offshore late Monday night, but will keep mention of slight chance to chance POPs near the coast. Southern portion of the cold front expected to stall over the Carolinas Tuesday as a baggy trough locates over the Southeast. Combination of weak energy in the upper flow and a moist air mass near the boundary, will keep mention of slight chance to chance POPs across the far southeast local area Tuesday afternoon. Otherwise, cooler Tuesday with a light north to northeast wind. Highs generally in the upper 80`s to around 90 (near seasonable norms). High pressure at the surface and aloft slides north of the region Tuesday night into Wednesday as another trough tracks across Ontario. Meanwhile, a broad upper ridge over the Southern Plains expands eastward, but the baggy trough remains over the Southeast. Best chances for measurable precip expected to be south of the region Wednesday, but will carry slight chance to low end chance POPs across the southern portions of the forecast area. Highs Wednesday generally in the mid 80`s. Another trough tracks into the Great Lakes and Northeast Wednesday night and Thursday, pushing another weakening cold front into the Mid-Atlantic region Thursday afternoon. Will need to watch for upstream convection Wednesday night in northwest flow aloft, so have added chance POPs for the Maryland Eastern Shore. With the boundary and cyclonic flow over the region Thursday, have chance POPs for diurnally driven showers and thunderstorms. Highs Thursday generally in the upper 80`s to low 90`s. Medium range guidance depicts additional energy digging down the backside of the upper trough Friday, with a wave of low pressure progged to develop along the Mid- Atlantic front. Timing and spatial differences at that timeframe of the forecast cause a great deal of uncertainty, so have only mentioned 20-40% POPs at this time. Highs back around seasonal norms, in the upper 80`s to low 90`s. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... High pressure will prevail off the Southeast Coast tonight into Saturday, with a trough to the lee of the Appalachians. This will result in primarily light SW flow of 5-10kt. Sct to occasionally bkn mid and high clouds tonight. Mainly dry conditions are expected tonight with a minimal chc of showers/tstms at SBY between 06-12z. Sct cu with bases ~5-6kft develop midday Saturday. A weak upper level system potentially triggers showers/tstms late Saturday afternoon and evening. The best chc (30-50%) is from RIC-SBY, with a 20-30% chc for PHF/ORF/ECG. A low probability of late aftn/evening showers/tstms continues Sunday/Monday, but overall primarily dry. A weak cold front pushes through the area Tuesday with high pressure building N of the region Wednesday. && .MARINE... Latest surface analysis depicts high pressure over the western Atlantic with a trough of low pressure over central Virginia. Obs indicate a light south to southeast winds at or below 10 knots. Waves are generally 1 foot and seas 2 feet. Diurnal increase in the low level winds expected again tonight over the low Bay and southern coastal waters. Hi-res guidance depicts winds around 15 knots, with an occasional gust of 18 knots, mainly centered a few hours either side of 11pm (03Z). Conditions expected to remain sub-SCA. Wave kick up to 2 feet in the lower Bay and seas 2-3 feet. Stagnant surface pattern persists through the weekend. Winds generally southwest at or below 15 knots, but near SCA conditions possible late each day into the overnight period. Seas generally 2-3 feet (upwards of 4 feet overnight) with waves of 1-2 feet. A weakening cold front approaches the region late Monday, dropping across the region Monday night into Tuesday morning. Flow backs to the northwest to north Tuesday at or below 10-15 knots. High pressure builds across the Northeast into Wednesday, resulting in onshore flow Wednesday. Another weakening cold front approaches the region Wednesday night and Thursday, stalling over the region into next weekend. && .CLIMATE...
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Heat wave is expected to continue through Sunday. The 2nd half of July is climatologically the hottest few weeks of the year, so we still may not set any daily records at our main climate sites. For reference, record highs for Saturday and Sunday are listed below: * Date: Sat(7/22) Sun(7/23) * RIC: 103/1952 103/1952 * ORF: 102/2011 103/2011 * SBY: 104/1930 103/2011 * ECG: 104/1952 104/1952
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Heat Advisory from 10 AM to 8 PM EDT Saturday for MDZ021>024. NC...Heat Advisory from 10 AM to 8 PM EDT Saturday for NCZ012>017- 030>032. VA...Heat Advisory from 10 AM to 8 PM EDT Saturday for VAZ060>062- 064>069-075>090-092-093-095>100-511>525. MARINE...None.
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&& $$ SYNOPSIS...LKB NEAR TERM...LKB/AJZ SHORT TERM...LKB/TMG LONG TERM...MAS AVIATION...AJZ MARINE...MAM/SAM CLIMATE...AKQ

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