Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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490 FXUS61 KPHI 252146 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 546 PM EDT THU AUG 25 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 /UNTIL 6 AM FRIDAY MORNING/... 530 PM update...Made some minor adjustments to the hourly PoPs/Weather grids thru tonight. Except for northern NJ, kept PoPs below 20 percent and replaced showers with a brief period of sprinkles. Additionally, showers were introduced into the forecast for late tonight in northeast PA and northern NJ as an area of convection that is currently developing late this afternoon near Lake Erie progresses eastward toward the Poconos. Showers will likely be falling apart as it advances downstream into an increasingly stable airmass that resides over the forecast area. Accordingly, the shower coverage should be isolated and rainfall amounts light. Previous Discussion... Showers have not been very persistent this afternoon thanks to the limited instability and synoptic scale subsidence from the building upper level ridge. Expect this trend to continue through the evening hours, so have only a slight chance from the I95 corridor north westward. Once we lose diurnal mixing, winds should decouple (with the possible exception of right along the coast), leading to generally light winds, but remaining out of the south or southwest. With the light winds and ample low level moisture, could see patchy fog develop, primarily in more rural locations after midnight. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Latest models trended faster with the weak cold front. GFS is the most progressive, showing the cold front arriving at the I95 corridor by 15Z. Given the upper level ridge and strength of the low level southwesterly flow ahead of the front, this appears to be too fast. Still, did speed up the timing slightly (closer to the NAM), with the front now arriving at the I95 corridor near 18Z. Given the faster arrival of the front, expect heat index values will fall short of heat advisory conditions (though we may not see significant cold air advection just behind the front, expect there will be some dry air advection through the day). As with today, do not expect much in the way of precipitation primarily because of subsidence and limited instability. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Cold front continues to push south of the region Friday night. Behind that front, 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. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Mostly VFR conditions are expected through 06Z. There may be isolated showers from the I95 corridor west through this time, but if any develop, coverage is too limited to mention in the TAFs. Additionally, an MVFR ceiling is present across northwestern portions of the area (including KABE earlier), but this should be transient for most locations, and should dissipate by sunset. After 06Z, fog may develop at some TAF sites (primarily our more rural TAF sites including KRDG, KABE, and KMIV). Any fog should dissipate shortly after 12z. There is a small chance (too small to mention in the TAFS at this time) that MVFR ceilings could move in behind the cold front tomorrow. OUTLOOK... Friday night 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. && .MARINE... Gusts at or above 20 kt will continue through the overnight hours, but are expected to stay below SCA criteria at this time. By tomorrow, winds should begin to decrease. 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. For today...The risk for the formation of dangerous rip currents is moderate for the New Jersey shore. The risk is currently low for the Delaware beaches. The probable risk for the formation of dangerous rip currents Friday and Saturday is 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. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Johnson/MPS Near Term...Johnson/Klein Short Term...Johnson Long Term...MPS Aviation...Johnson/MPS Marine...Johnson/MPS

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