Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212015 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 415 PM EDT Fri Jul 21 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH SATURDAY/...
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Weak sfc/lee trough in place across the local area this aftn, with WNW flow prevailing aloft around the base of an upper level trough centered over eastern Canada. Hot/humid airmass in place, particularly humid over the E and SE zones with dew pts still ranging from 75 to 80 F, with somewhat lower (though still elevated) dew pts over central and S Central VA (mainly from the mid/upper 60s to around 70 F). Heat advisory remains in effect through 8 pm for most of the area (though areas that receive rain will rapidly cool). The WNW flow pattern appears to be allowing the ongoing convection/MCS along the Mtns to hold together as it approaches the NW flank of the CWA. Have ramped PoPs up to likely through 6pm for the NW, and high chance 30-50% for much of the northern 1/2 of the CWA through midnight, lingering into Sat morning for NE zones. Very warm/humid tonight 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/...
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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 theS with 20% PoPs for the N. Slightly less humid Monday, especially N. Highs Mon 90 to 95 F.
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&& .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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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.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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Mainly VFR conditions will prevail at the TAF sites this afternoon...overnight and into Sat morning, as sfc high pressure sits well off the SE Coast with a trough to the lee of the Appalachians. Scattered CU around 5-6kft is developing across the region in addition to a few isolated showers as of 18z. Convection moving into western VA will likely weaken some as it crosses the mountains...however...some shower and storm activity will make it into central VA and across the Eastern Shore late this evening. Have VCSH at RIC from 21z-00z, otherwise mainly dry most places this evening with a 20-30% of showers/tstms late this aftn. Expect a little better chance of storms late Sat especially from RIC north including the MD Eastern Shore as another wave move across in the NW flow aloft.
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&& .MARINE...
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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.
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&& .CLIMATE... Heat wave is expected to develop, mainly today 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 today through Sunday are listed below: * Date: Fri(7/21) Sat(7/22) Sun(7/23) * RIC: 104/1930 103/1952 103/1952 * ORF: 101/1926 102/2011 103/2011 * SBY: 106/1930 104/1930 103/2011 * ECG: 102/1987 104/1952 104/1952 && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Heat Advisory until 8 PM EDT this evening for MDZ021>024. Heat Advisory from 10 AM to 8 PM EDT Saturday for MDZ021>024. NC...Heat Advisory until 8 PM EDT this evening for NCZ012>017- 030>032. Heat Advisory from 10 AM to 8 PM EDT Saturday for NCZ012>017- 030>032. VA...Heat Advisory until 8 PM EDT this evening for VAZ048-061-062- 064-067>069-075>090-092-093-095>100-509>525. 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 SHORT TERM...LKB/TMG LONG TERM...MAS AVIATION...TMG/JAO MARINE...MAM/SAM CLIMATE...

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