Area Forecast Discussion
Issued by NWS Wakefield, VA

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748 FXUS61 KAKQ 211757 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 157 PM EDT THU JUL 21 2016 .SYNOPSIS... High pressure prevails through the weekend, with heat returning Friday into early next week. Heat indices will climb to 100 to 108 degrees Saturday and Sunday. The next cold front approaches the region late Monday. && .NEAR TERM /THROUGH TONIGHT/... High pressure prevails over the region this morning, resulting in quiet conditions. An anomalous upper ridge over the Midwest builds eastward today, but the heat remains suppressed west of the mountains for one more day. The surface high center slides off the coast this afternoon, with winds remaining light and onshore. Light flow will result in afternoon seabreeze boundaries, but BUFR soundings indicate very little available moisture. However, cannot rule out an isolated to widely scattered thunderstorm along the seabreeze boundary due to instability and favorable mid level lapse rates. Best chances over the Eastern Shore, but also possible southeast VA and northeast NC. Otherwise, dry conditions expected. 850mb temps warm slightly compared to yesterday, but similar low level thicknesses place highs in the upper 80`s. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Anomalous upper ridge over the nation`s mid section dampens and builds eastward through the short term. 850mb temps warm to +20 to +22 C (+2 standard deviation) Friday afternoon. Thicknesses and dry adiabatic lapse rates place highs solidly in the low to mid 90`s Friday. A southwest wind around 10 mph will help mix dewpoints into the mid to upper 60`s, resulting in heat indices in the upper 90`s. High pressure remains over the western Atlantic as pressure falls on the lee side of the mountains induce lee/thermal troughing over the Piedmont. Lack of appreciable forcing, limited moisture, and warm temperatures aloft expected to keep the local area dry Friday. Expect some afternoon cumulus. Mostly clear Friday night with lows in the low to mid 70`s. Few degrees warmer Saturday as the ridge builds eastward. Highs solidly in the mid 90`s area wide. Mixed layer dewpoints cool back into the mid to upper 60`s, with heat indices of 100 to 105. Retained silent POP`s due to warm air aloft (cap) but can`t rule out an isolated thunderstorm over the Piedmont as better moisture arrives ahead of a weak cold front in northwest flow aloft. The weak frontal boundary is expected to reach the northern Mid Atlantic region Saturday night into Sunday morning as a shortwave drops over New England. Models indicate some elevated instability, but moisture and forcing remain weak resulting in silent POPs. Lows back into the mid 70`s. Upper trough drops off the Canadian Maritimes/Northeast coast Sunday as flow aloft becomes more zonal. Hot again with temperatures back into the mid 90`s. Heat indices 100 to 109. Will carry slight chance POPs with the thermal trough and increasing moisture ahead of the next northern stream shortwave tracking across the upper Midwest/southern Canada. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... A thermal trough is expected to remain in place Mon-Wed for continued very warm to hot conditions. 595dm upper ridge also remains situated off the SE coast. A slight buckle in the ridge across the Northeast/Mid- Atlantic due to a weak upper trough passage will knock a few degrees off max temps but still remain above normal. Highs in the mid/upr 90s Monday and low to mid 90s Tue/Wed. Thunderstorm chances will mainly be tied to the aftn/eve hours. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Surface high pressure settles over the western Atlantic and Southeast Coast through the weekend...resulting in primarily VFR conditions. Weatherwise, isolated seabreeze thunderstorms are possible near the coast this aftn/early evening. A brief period of shallow fog development is possible at KRIC and KSBY between 22/1000-1200Z. KECG may also experience shallow fog within this timeframe, however confidence is much lower and can be added as a tempo group if needed. Otherwise, conditions are dry on Saturday with another round of isolated to scattered storms possible across the area on Sunday. A cold front approaches the region on Monday and then crosses the area on Tuesday. There is enough incoming moisture to interact with a thermal trough on Monday and with the cold front on Tuesday to trigger a higher chance for scattered thunderstorms both days...primarily during the afternoon/evening hours. Locally heavy downpours, strong gusty winds, and brief reductions in flight conditions to MVFR/IFR ceilings and visibilities will be the primary impacts with thunderstorms early next week.
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&& .MARINE... Headlines are not anticipated over the next several days, though conditions may come close to reaching SCA thresholds Fri night. High pressure over the area today will slide offshore and become centered off the mid- Atlantic/SE coast Thu- Fri as a weak front approaches from the NW Fri night into Sat. This front looks to remain N of the CWA, with a pre-frontal trough in place over the region on Sat. Winds today will be light from the E-NE (<10kt) and transition to the S to avg around 10 KT tonight into Fri morning. Bay waves avg 1-2 ft with coastal seas 2-3 ft. The pressure gradient will increase a bit by late Fri, especially by fri night so S/SW winds will ramp up and avg around 15 KT during this period. A few gusts may reach SCA thresholds across the Bay (20 KT) and northern coastal waters (25 KT) Fri night as warm water temperatures will be conducive to mixing the low level nocturnal Jet. Still would be marginal at best, with waves over the Bay building to 2-3 ft, and coastal seas to around 4 ft N and 3 ft S. The sfc trough/boundary drops into the area on Sat with lighter W/SW flow turning back to the S Sat night. The front then washes out/dissipates on Sun. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...SAM NEAR TERM...AJZ/SAM SHORT TERM...SAM LONG TERM...JDM AVIATION...BMD MARINE...LKB

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