Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260148 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 948 PM EDT Thu May 25 2017 .SYNOPSIS... An area of low pressure will move across the area tonight, then move away to our northeast through Friday. A weak surface trough is expected to cross the area during the day Friday. Weak high pressure may briefly move across the area Friday night into early Saturday. A weak low is forecast to move along a developing stationary front to our south Saturday into Saturday night. Another area of low pressure is forecast to weaken as it moves into the eastern Great Lakes Sunday into Sunday night, then an occluded frontal system is expected to affect the area Sunday night into early Monday. A series of cold fronts are forecast to move across the area Monday through Wednesday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Focus of convection is a line from just south of Reading, PA to Mount Holly, NJ, to Atlantic City, NJ. This wave continues to lift to the north and east. The first wave of convection that impacted SW NJ and SE PA has lifted into northern NJ and is dissipating. Weak low pressure over southern NJ continues to lift to the north and east, and strong H5 vort max just lifting into SE PA and the Delmarva. With loss of diurnal heating, SB CAPE values are dropping back to around 250 J/kg, but MUCAPE values are still upwards of around 500 J/kg, so there still is enough instability to keep these storms going for a while. Will follow with the timing trend of the latest HRRR, and have the heaviest showers and storms north of the region by 06Z, but will then keep slight chance-chance PoPs for lingering showers into daybreak Friday. PWATs generally 1-1.25", and there have been some locally heavy downpours. Additional rain will be light, as the bulk of the lift will be gone once the vort max lifts to the north and east. With abundant low level moisture across the region, fog has developed, so it was added to the forecast. With a drying westerly wind developing behind the departing low, most of the fog should dissipate prior to daybreak. Lows generally in the 50s, maybe near or slightly above 60 near the coast and in Delmarva. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... The main upper low shifts into New England on Friday, with westerly flow prevailing across the area during the day. Several perturbations in the flow are likely to move through the area during the day, especially in the morning. This should keep skies partially to mostly cloudy most of the day, and may allow for a sprinkle or light shower to occur, especially north of the Mason-Dixon Line. The 18Z NAM has a few showers farther to the south as a vort max rotates southeastward through the Mid- Atlantic around midday, but there is not a lot of support from higher-resolution guidance at the moment. As such, kept PoPs low or non-mentionable for the most part south of the I-78/I-195 corridor. Main sensible weather impact tomorrow may be the winds, with some stronger mixing likely to occur during the afternoon hours. Winds above the boundary layer are not particularly strong (20-30 kts), but gusts of 20-30 mph are likely by afternoon across most of the area. Forecast max temperatures range from the mid 60s in the Poconos to the mid 70s in the urban corridor to around 80 in southern Delmarva. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... An unsettled weather pattern continues for much of the extended forecast with several periods of rain possible. Friday night through the early part of Saturday is expected to be mostly dry as weak high pressure quickly moves across the area. However, later in the day, a weak area of low pressure will be approaching from the west but passing to our south along a developing frontal boundary to our south. Also, a short wave/vorticity impulse is expected to move across the area during the day, so there will be a chance of an isolated shower during the day Saturday. On Saturday night, the frontal boundary is expected to remain to our south, but should begin lifting northward toward the area Sunday. It will likely not make its way into the area until Sunday night. There will be a chance of showers overnight Saturday into Sunday, but the best chance of showers is expected to be Sunday night as the occluded front moves into the area. A series of cold fronts are forecast to move across the area Monday through Wednesday of next week as low pressure remain nearly stationary across southern Canada just north of the Great Lakes region.As any short wave/vorticity impulses slide across the area, they could lead to additional showers or thunderstorms early next week. High pressure tries to build back into the area for Thursday, which would provide a dry forecast. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Low confidence forecast for the TAF period through 12Z Friday. SHRA/TSRA mixing up the atmosphere enough to scour out some of the low CIGs, resulting in brief MVFR/VFR conditions. Once the rain taper off, winds should be light enough for fog/stratus to redevelop into Friday morning. Westerly winds pick up (5-10 KT) prior to daybreak, and that should help scour out the fog/stratus during the early morning hours. SHRA/TSRA will lift to the north and east through the overnight, and should be through northern NJ between 06-08Z. A few lingering showers possible thereafter. VFR conditions develop Friday morning. Winds veer to the W-NW late Friday morning, and increase to 15-20 KT with gusts up to 23 KT. OUTLOOK... Friday night...Generally VFR. Saturday...Generally VFR. Showers moving into the area later in the day, which could lead to lowering ceilings. Saturday night-Sunday...MVFR CIGS possible. Chance of scattered showers. Sunday night...MVFR to IFR conditions possible with periods of low clouds and rain. Monday...Generally improving to VFR during the morning. Scattered showers and thunderstorms possible during the day. Monday night-Tuesday...Generally VFR. Chance of showers or thunderstorms on Tuesday. && .MARINE... Small craft advisory continues, mainly for high seas, through Friday afternoon. Seas at the buoys have increased to 5-6 feet. Gusts to 25 KT will develop tonight, and then gusty W-NW winds could continue to gust to 25 KT on Friday. Showers and thunderstorms likely on the waters tonight. Gusty winds, small hail, and frequent cloud-to-ground lightning are all threats from these storms. Locally strong winds/rough seas are likely in vicinity of these storms. Winds become westerly on Friday. A light shower or two may occur, especially off the New Jersey coast. RIP CURRENTS... With increasing westerly winds developing during the day Friday, will keep a moderate risk for the development of dangerous rip currents in the forecast. OUTLOOK... Friday night-Tuesday...Conditions expected to remain below advisory levels, although winds may gust around 20 knots at times. && .TIDES/COASTAL FLOODING... Coastal Flood Advisory remains in effect through 1 AM for coastal counties of Delaware and New Jersey, as well as counties along the Delaware and Raritan Bays. The astronomical tides with the new moon are particularly high with the evening high tide cycle, and the persistent onshore flow has lead to a 1-2 foot tidal departure. It is possible that additional spotty flooding may occur with the evening high tides Friday and Saturday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory until 1 AM EDT Friday for NJZ012>014- 020>027. DE...Coastal Flood Advisory until 1 AM EDT Friday for DEZ002>004. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ450>455. && $$ Synopsis...Robertson Near Term...CMS/MPS Short Term...CMS Long Term...Robertson Aviation...CMS/Robertson/MPS Marine...CMS/Robertson/MPS Tides/Coastal Flooding...

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