Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 210840 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 440 AM EDT Fri Jul 21 2017 .SYNOPSIS... High pressure builds toward the Mid Atlantic today into Saturday, bringing hot and humid conditions to the area. The hottest weather can be expected from today through Sunday. A trough of low pressure will slide across the area late Saturday into Saturday night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Early this morning, upper ridge axis was centered over the Middle MS Valley and extended ewrd toward the Mid Atlc. These higher heights will build ewrd into SW VA and wrn NC during today. The core of the highest 850 temperatures today (21-22C) will be over much of the local area, with dew pts expected to be higher (only mixing out to near 70 F inland, and to the lower to mid 70s near the coast). This will result in heat indices to be more solidly into advisory criteria (105 to 109 F), and have therefore issued a heat advisory for most of the CWA (left coastal Worcester MD/NC Outer Banks out of it, with cooler temperatures, as well as much of the far SW counties (Prince Edward, Lunenburg, Mecklenburg) where it will be slightly drier). Actual highs will be near 100 F metro Richmond to the mid/upper 90s elsewhere (locally cooler/lower 90s immediate coast). As far as precip chances, airmass appears too stable overall for much in the way of pop-up storms during today. But, with WNW flow aloft and some weak shortwave energy moving into the area late this aftn, will have ~20% PoPs over the NW 1/2 of the CWA. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... Ramped PoPs up a bit more for tonight into Sat morning, esply N/NE zones, closest to upper level shortwave energy tracking through the WNW flow aloft. 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, it will be even more humid, so expect at least southern portions of the CWA to need a heat advisory even with highs on avg only in the mid to upper 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. The entire CWA is in a marginal risk, where wind will be the primary threat. 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 Sun. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Long term period will feature near normal temps on avg and occasional chances for rain. In general expect lwr temps than this weekend as the broad upr-level ridge across the eastern CONUS breaks down in response to an approaching upr-level trough. The trough and associated low-level front will bring an increasing chance for rain Mon, but will cap PoPs at 40% for now due to uncertainties regarding timing and available moisture. Further model divergence occurs Tue and Wed, with the 12Z ECMWF keeping the low-level boundary in the vicinity and the 12Z GFS pushing things offshore, so will maintain low end PoPs (20-40%) through midweek, with the best chance over far SE areas. As for temps, after one more hot day Mon with highs up to the mid 90s, expect mid/upr 80s for Tue through Thu. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/...
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Mainly VFR conditions will prevail at the TAF sites today into Sat morning, as sfc high pressure sits well off the SE Coast with a trough to the lee of the Appalachians. Expect sctd Cu this aftn. Mainly dry most places but there will be a 20-30% of showers/tstms fm very late this aftn into Sat morning, esply at RIC and SBY. Similar conditions persist on Sat, with a 20-40% chc (highest N) fm late Sat aftn thru Sat night. A low probability of late aftn/evening showers/tstms continues Sun/Mon, but overall primarily dry. A cold front approaches from the NW late Mon/Mon night.
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&& .MARINE... Latest obs/buoy reports reflect W-SW flow ~10-15 kt across the waters this morning. Surface analysis features high pressure over the western Atlantic with a pre-frontal surface trough persisting inland from S NJ south into the VA/NC piedmont. No major changes to rather stagnant sfc pattern today, with SW winds ~10 kt persisting today, as Bermuda high remains the dominant wx feature through the weekend. Winds again increase slightly late this afternoon and late each day over the weekend into the overnight hours, and becoming a bit gusty at times in the aftn/early evening w/developing seabreeze. Seas generally 2-3 feet and waves 1-2 feet. A weakening cold front approaches the region late Monday, dropping across the region Monday night into Tuesday morning. Flow may briefly increase with tightening pressure gradient Monday night, but have held winds below SCA thresholds for now. Flow backs to the northwest to the north Tuesday at or below 10 knots due to a lack of cold advection. High pressure builds across the Northeast into Wednesday, resulting in onshore flow Wednesday. && .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... MD...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for MDZ021>024. NC...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for NCZ012>017-030>032. VA...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for VAZ048-061-062-064-067>069-075>090-092-093-095>100- 509>525. MARINE...None. && $$ SYNOPSIS...TMG NEAR TERM...LKB/TMG SHORT TERM...LKB/TMG LONG TERM...MAS AVIATION...TMG MARINE...MAM CLIMATE...AKQ

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