Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 060109 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 909 PM EDT Thu Aug 5 2021 .SYNOPSIS... A stationary front will continue to linger offshore through the weekend as a surface high meanders in the eastern U.S. A weak wave of low pressure will move northeast just off the Mid- Atlantic coast along the decaying front Saturday and Sunday. The surface high will remain in place across the eastern U.S. for much of next week, with a lee trough developing in the Northeast and Mid-Atlantic. && .NEAR TERM /THROUGH FRIDAY/... Expect mainly clear skies tonight as any diurnal Cu continues to dissipate and high pressure dominates. Lows will be mainly in the 60s with some upper 50s possible over the southern Poconos and NW NJ. By tomorrow, southerly/southwesterly low level return flow develops. Additionally, in the mid levels, a short wave ridge will traverse over the region. The combination of these two factors means that the warming trend will continue on Friday, with many locations seeing highs in the upper 80s to near 90. Dry conditions are expected tomorrow thanks to the larger scale subsidence with the short wave ridge. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... A mid level trough will cross the region Saturday into Sunday morning. This will be enough for storms to develop. However, as mentioned by the previous shift, there remains some timing differences between models. Continue to favor a slower solution since that has been the trend as of late. In addition to the timing, a mid level warm layer could also be a point of uncertainty as this could serve to create a cap to limit convective initiation. For now, have stayed close to the previous forecast, with the highest chances Saturday afternoon and evening. We`ll keep southerly return flow into Saturday, meaning dew points will continue to edge upward, with widespread 60s expected across the region by Saturday afternoon. Consequently, even with the increased cloud cover, and temperatures begin a degree or two lower as compared to Friday, heat index values in the 90s will be possible by Sunday. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Next week looks rather warm and humid with gradually increasing chances for convection. The large-scale pattern will feature broad ridging in the southern U.S. with faster quasi-zonal midlevel flow confined to the northern tier of the U.S. and adjacent portions of Canada. Several vorticity maxima will slowly migrate near or just south of the faster flow. This is a pattern of relatively low predictability, and the models are certainly confirming that with considerable variations in the geographic placement of the perturbations and associated troughs even by early next week. The main perturbation of interest is expected to slowly lift from the central Plains on Monday to the vicinity of southeast Canada by Wednesday, though operational runs of the GFS/ECMWF/CMC offer their usual biases in terms of its evolution. A curious issue will be the potential interaction of this system with a weak vort max cut off from the faster flow in the western Atlantic, as depicted by the 12z ECMWF. The GFS exhibits little similarity currently, as it is far more progressive (as usual) with the weak perturbation in the western Atlantic and farther north with the vort max in Canada. The CMC, meanwhile, develops a considerably deeper trough with the northern-stream system as it moves through the Northeast. Though the solutions as described are quite different in nature, they are all reasonably hinting at increasing potential for convection by the middle of next week. Thus, daily PoPs are in the forecast Monday through Wednesday, but slowly increase in value and expand in coverage (from the favored higher terrain in the north/west CWA early in the week to most of the CWA by Wednesday). In the evolving pattern preceding the midweek system, large- scale ridge amplification should ensue near the East Coast, with hot and increasingly humid conditions. However, I do think it will take a couple of days before the region enters heat- product territory, as the departing western Atlantic system this weekend may provide some lingering effects on Monday and even Tuesday, most notably with somewhat lower dew points. As a result, forecast heat indices are generally in the 90s Monday and Tuesday but begin to approach the lower 100s by midweek. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through Tonight...Mostly VFR conditions with few clouds expected. There is a possibility that patchy fog will develop tonight, especially on the coastal plains, which could mean localized MVFR visibility restrictions. Winds will be light from the S or SW early then mostly variable overnight. High confidence on most aspects of the forecast, but low confidence on the potential for fog. Friday...Once any morning fog dissipates, VFR conditions are expected. Winds will settle out of the southwest at 5 to 10 kt by mid morning. High confidence. Outlook... Friday night...Mostly VFR conditions are expected, though patchy fog is again possible for the coastal plains, including KMIV and KACY. Winds may be light and variable at times, but the dominant direction should be southerly. Moderate confidence on most aspects of the forecast, but low confidence on the potential for fog. Saturday and Sunday...Predominantly VFR conditions. There remains a chance of MVFR as showers and thunderstorms are possible Saturday, Saturday night and again Sunday afternoon. Winds predominantly out of the south or southeast at 5 to 10 kt on Saturday, becoming light and variable Saturday night and Sunday. Moderate confidence on most aspects of the forecast, but low confidence on the details of any showers and storms. Sunday night through Tuesday...Mainly VFR, though there will be at least slight chances for storms on both days (primarily northwest of the Philly area). Winds will generally be less than 10 kt, with directions primarily southerly during the day and more light and variable at night. && .MARINE...
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Seas have dropped below 5 feet on the DE and southern NJ coastal waters, so have cancelled the Small Craft Advisory for these locations. Once seas subside below 5 feet on the Central and northern NJ coastal waters, winds and seas should stay below SCA criteria through the remainder of tonight and Friday. Outlook... Friday night through Tuesday...Winds and seas should stay below SCA criteria. Rip Currents... For Friday, the onshore component from S/SE winds will continue to bring a moderate risk for the development of dangerous rip currents to the NJ shore with a low risk for the Delaware Beaches as the flow there will be more parallel the coast. Similar conditions are forecast for Saturday except that for the northern NJ coast in Monmouth County we are forecasting a low risk for rip currents while the remainder of the NJ coast has a moderate risk.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ450>452. && $$ Synopsis...CMS Near Term...Fitzsimmons/Johnson Short Term...Johnson Long Term...CMS Aviation...CMS/Fitzsimmons/Johnson Marine...CMS/Fitzsimmons/Johnson

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