Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 250722 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 322 AM EDT THU AUG 25 2016 .SYNOPSIS...
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High pressure will move out to sea today. A cold front will move across the area Friday and stall to our south over the weekend. High pressure builds to our north over the weekend, then offshore Monday. An area of low pressure may pass to our north Monday, bringing a front across the area Monday into Tuesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A weakening short wave trough lifts well to our north early this morning. As this occur, weak surface low pressure also lifts into Canada. A weak surface cold front is then forecast to be draped from Ontario Canada southwestward down the Ohio Valley. This weak front will ever so slowly move eastward today. Meanwhile, a lee side trough should develop from about south-central Pennsylvania southward to central Virginia. As we look aloft, a persistent ridge remains centered across the southern states with our area mainly on the northern periphery of it. A southerly flow will be maintained along with some downstream warm air and moisture advection well ahead of the aforementioned weak cold front. This will allow for a warmer afternoon along with some added humidity. A plume of high PW (near 2 inches) is forecast to shift eastward by late in the day from the Ohio Valley into our region. As this occurs, some convection is expected well to our west ahead of the weak cold front. This activity could organize into a line as it shifts eastward along with the high PW plume. Early this morning, convection was entering western Pennsylvania and this may be tied to a weakening MCV. There is enough instability forecast to potentially allow some convection to arrive in our western zones this afternoon. Overall the model guidance, including several convection-allowing, tends to dissipate the convection as it approaches the I-95 corridor by early this evening. This is mostly due to the influence of the upper-level ridge farther south and east along with any convection outrunning the main forcing. The forcing overall is forecast to remain farther to the west from the eastern Great Lakes to the Ohio Valley. As a result, we continued with slight chance to low chance pops across the western areas this afternoon. The slight chance pops then edge into the I-95 corridor toward evening however it is less certain if thunder occurs here. Otherwise, more cloudiness is expected today in part due to some incoming convective cloud debris. A south to southwest breeze should increase this afternoon and may become a bit gusty at times especially across the coastal plain.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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The upper-level ridge anchored to our southwest is forecast to build a bit northeastward, however much of our area remains on its northern periphery. As the main upper-level energy remains near and north of the Great Lakes, a weak cold front is forecast to slowly approach our area from the west tonight. There appears to be a pre- frontal trough in our vicinity, although the weak cold front may try and jump into this weakness toward morning. Backing up a bit, any lingering convection should dissipate mostly early as it nears the I-95 corridor and it encounters more influence from the southern ridge and shifts east of the main forcing. We therefore lower the pops through the evening. This will leave behind some cloudiness especially the first half of the night, however more importantly it will be a much warmer and more humid night. This could lead to patchy fog, however there may be enough mid to high level clouds around especially across the northern areas to prevent any development.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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A return flow will continue into Friday ahead of an approaching frontal boundary. There will again be a chance for isolated showers or thunderstorms to develop during the day, but overall chances are small. 925/850 mb temperatures and thicknesses will continue to increase, making Friday the warmest and most humid day of the week. Heat index values could approach 100 degrees across for portions of the Delmarva, southern New Jersey, and the Philly metro area. The frontal boundary will sag south of the area Friday night, and stall just to our south over the weekend while high pressure builds to our north. This high will keep dry weather in place across the area through the weekend. Temperatures will remain warm over the weekend, but humidity levels will be much lower with dewpoints only in the 60s. The high pressure will build offshore of New England Sunday night into Monday, and a cold front will begin approaching the area Monday into Tuesday as an area of low pressure passes to our north. There are a couple of short wave/vorticity impulses forecast early next week, so there will continue to be a chance for isolated showers or thunderstorms Monday into Tuesday. Another frontal boundary could follow behind the Monday/Tuesday frontal boundary around Wednesday into Thursday. Additional showers or thunderstorms could develop as a couple of short wave/vorticity impulses continue to move across the area each day. Temperatures through next week will continue to be several degrees above normal, but not as warm as Friday.
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&& .AVIATION /07Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR, with a ceiling developing between 5000 and 15000 feet at most terminals. Isolated to scattered showers/thunderstorms are possible from the west, however these should be mainly into the ABE and RDG areas after 16-18z. Given low coverage expected, no mention included in the TAF`s. South to southwest winds increasing to around 10 knots, with some local gusts up to 20 knots possible this afternoon. Tonight...VFR overall. Isolated to scattered showers or thunderstorms possible mostly early, mainly west of a TTN to PHL to ILG line. Local MVFR visibility may develop late due to fog/haze. South-southwest wind diminishing to near 5 knots. OUTLOOK... Friday...Generally VFR conditions expected. A chance of isolated showers and thunderstorms which may lead to temporary lower conditions. Friday night through Sunday night...VFR conditions expected. Monday...Generally VFR expected. A chance of isolated showers and thunderstorms.
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&& .MARINE...
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High pressure to our east will maintain a southerly flow across the region through tonight. Meanwhile, a weak cold front approaches from the west late tonight. The southerly flow is a bit stronger, with some enhancement taking place especially this afternoon and evening. This should be more notable across the northern coastal waters. While some gusts may reach 25 knots mainly later this afternoon and evening, confidence is not all that high for how long and widespread it can get. As a result, we carried 15-20 knots but capped the gusts before 25 knots and held off on a Small Craft Advisory. OUTLOOK... Friday through Monday...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 moderate for the Ocean and Monmouth county beaches, especially later this afternoon when the southerly wind increases to 20 mph and the tide is moving into the lower half of the tide cycle. The risk is currently low elsewhere. Friday and Saturday are outlooking low enhanced risk. Then this coming Sunday-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- Wednesday and possibly starting Sunday.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Robertson Near Term...Gorse Short Term...Gorse Long Term...Robertson Aviation...Gorse/Robertson Marine...Gorse/Robertson/Drag

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