Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260622 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 222 AM EDT FRI AUG 26 2016 .SYNOPSIS... A weak cold front moves across the region on Friday, and then remains nearly stationary just south of the region through the weekend. High pressure builds to the north this weekend and then moves off the New England Coast on Monday. Another high settles over the area into the middle of the new week, but a series of weak disturbances will pass through the region during this time. && .NEAR TERM /THROUGH TODAY/...
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Through 12z today, a pre-frontal trough is positioned just to our west. While the instability is weakening with time, there remains enough to maintain or redevelop some showers across portions of our west/northwest zones. The forcing is not well defined, therefore it appears that a warm/moist airmass in place combined with the pre- frontal trough is just enough to keep some showers going for awhile. Therefore, increased the pops across these areas at least into the chance range for scattered activity. An upper-level ridge still centered to our south will become the main weather feature today. This ridge is forecast to actually build a bit northward into our area by late afternoon. This will keep the stronger flow from the Midwest to the Great Lakes then to New England. At the surface, a weakening cool front will continue to settle south and eastward across our area through midday. This boundary may then end up dissipating during the afternoon as it is mostly just a dew point boundary. Given the building ridge, there is a very small window of opportunity for a shower or thunderstorm mainly through midday. There will be more of a cap across the southern areas due to the building ridge and then some drying occurs from northwest to southeast during the course of the day across much of the region. This coupled with a lack of defined forcing is not good for convective chances. As a result, the forecast is currently dry after 12z. Some convective cloud debris is expected to move across at least parts of the region this morning, however some increase in subsidence especially this afternoon along with some drying should allow for less cloud cover through the day across much of the area. It will be hot however for most areas as the boundary layer flow turns to the west and northwest for areas behind the weakening cool front. The heat indices will be driven by how much the dew points lower, however a humid day overall is expected with the highest heat indices anticipated from about the Philadelphia metro on south and east. It still appears that the heat indices fall short of advisory criteria.
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&& .SHORT TERM /TONIGHT/...
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As the upper-level ridge continues to build across our region tonight, surface high pressure near the Great Lakes will slide eastward. This will allow for a more northeasterly low-level flow, although most places should have the winds decouple during the evening. While some high level clouds may drift across from time to time, overall a mostly clear sky is anticipated. It will be mild/warm, however the dew points should actually drop some allowing for a bit more radiational cooling. This is especially the case across the northern areas where dew points are forecast to be the lowest.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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High pressure builds into the Great Lakes region and will slowly track east through the weekend. Northerly flow ahead of the high will usher a much dryer airmass into the region on Saturday with surface dewpoints falling from the upper 60s to near 70 Friday evening to the upper 50s to around 60 by Saturday afternoon. High temps will only be a few degrees cooler compared to Friday, but conditions will feel more comfortable due to the lower humidity levels. The center of the high will pass over central NY/PA Saturday night, and then moves off the New England Coast on Sunday. Return flow sets up behind the departing high, and returns flow sets up with surface dewpoints creeping back up into the mid and upper 60s, making it a bit more humid compared to Saturday. Cold front then approaches on Monday and slowly passes through the region on Tuesday. Isolated showers and thunderstorms are possible Monday afternoon and evening, and then there is a better chance for showers and thunderstorms on Tuesday with the passage of the front. There currently is not much upper level support, so will keep POPs capped at low end chance for now. Thereafter, surface high pressure settles over the Great lakes and Ohio Valley into the middle of the week. However, a series of weak upper level shortwaves and vort maxes will pass through the region, touching off isolated to scattered showers and thunderstorms during that time. Will go no higher than low chance for POPs. Temperatures will continue to run several degrees above normal through the middle of next week, but should as hot as Friday.
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&& .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR overall. A ceiling mainly at and above 8000 feet for a time this morning, then thinning out. A weak cool front settles across the area, therefore most terminals will have a wind shift to the northwest with an increase to around 10 knots. ACY should take the longest to have a wind shift to the west. A few showers will move across mainly early this morning in the ABE to RDG areas. Tonight...VFR. Northwest winds diminish early, then become northeast or locally light and variable. OUTLOOK... Saturday through Sunday night...VFR. Light N winds will become NE on Saturday afternoon, and then will become SE on Sunday. Monday through Tuesday...Mainly VFR. Isolated to scattered showers and thunderstorms possible.
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&& .MARINE...
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Southwest winds 10-20 kt will continue through the overnight and early morning hours. During Friday, the winds should begin to decrease as a weakening cool front arrives and a wind shift more to the west takes place. OUTLOOK... Friday night through Tuesday...High pressure passes well north of the waters this weekend. A cold front approaches on Monday and slowly passes across the waters through Tuesday. Sub-Small Craft Advisory conditions expected to continue across the waters. RIP CURRENTS... For today...The risk for the formation of dangerous rip currents is low for the New Jersey shore and the Delaware beaches. However, if winds remain backed more out of the south than what we are currently forecasting, then a moderate risk could develop at our NJ beaches. The probable risk for the formation of dangerous rip currents on Saturday appears to be low at this time. Sunday through Wednesday...model ensemble guidance on every successive cycle continues to send 2-4 ft long period (15 to 17 second) east southeast swell into our waters from the central Atlantic - Gaston. It could be even higher but we`re taking the conservative approach at this time from this distant offshore hurricane. This is all dependent on size, strength and track but there is little doubt that swells will build here...just how much is the question. Swimming and wading dangers will probably increase. For now we`re anticipating a moderate or greater risk for Monday through Wednesday and possibly starting Sunday.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Johnson/MPS Near Term...Gorse Short Term...Gorse Long Term...MPS Aviation...Gorse/MPS Marine...Johnson/Klein/MPS

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