Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 160148 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 948 PM EDT Tue Aug 15 2017 .SYNOPSIS... Weak low pressure moves off the Mid-Atlantic coast this evening, and then a cold front works its way through the East Coast late tonight. High pressure returns on Wednesday before moving offshore on Thursday. A warm front lifts north across the region Thursday night through Friday morning, followed by a cold front Friday night through Saturday morning. Weak low pressure may affect the area Sunday, then high pressure builds back for the new week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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The main area of showers continued to move farther off the coast this evening. However, a frontal boundary was dropping down from the north and into the Poconos and far northern New Jersey around 9:30 PM. There were additional showers with the front but they were in the process of dissipating with the loss of daytime heating. The frontal boundary is forecast to progress southward through our forecast area during the night. There does not appear to be a strong push of drying with the front. The wind is expected to remain light and variable in our region. The abundance of low level moisture will likely result in areas of fog and low clouds. It seems possible that widespread dense fog will develop in parts of our region, especially the south, and a Dense Fog Advisory may become necessary for some areas. Minimum temperatures are anticipated to favor the 60s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... West-northwesterly midlevel flow will become established Wednesday with weak subsidence in the wake of the passing shortwave trough today. Northwest surface winds will become established, which (in combination with morning insolation) should aid in the rapid dissipation of fog. Wednesday looks to be a mostly dry day for the region with the lack of any synoptic-scale lift to speak of. However, the 12Z NAM Nest does develop an isolated storm or two in the northern CWA during peak heating - so a dry forecast is not exactly a slam dunk. On the other hand, coverage would be sparse enough, and confidence is certainly low enough, to preclude mention of any PoPs at the moment. With some subtle downsloping and ample surface heating expected, temperatures look to warm to just above seasonal averages. Forecast highs are near 80 in the Poconos, near 90 in the urban corridor, in the lower 80s at the beaches, and mid to upper 80s elsewhere. Used a combination of MAV (warm) and MET (cool) guidance, with some subtle extra weighting for the MAV given the cool bias of MOS this summer in such patterns. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... High pressure over the area Wednesday night will gradually slide offshore, and will then anchor itself over the western Atlantic on Thursday. Meanwhile, H5 trough digs into the Northern Plains and western Great Lakes, and surface low pressure organizes and develops. That low will slowly track east on Thursday, and a warm front extending out ahead of that low will lift north into the Mid-Atlantic and Northeast late Thursday and Thursday night. Several shortwaves will slide across the region as well, and this will touch off scattered showers and thunderstorms across the region Thursday afternoon and Thursday night. With the warm front north of the region on Friday, strong southerly flow will usher a very warm and humid airmass into the region. Although highs on Friday will generally top off in the mid to upper 80s, with the warmest temps (near 90) along and south of I-95 from Trenton to Philadelphia to Wilmington, surface dewpoints will be well into the lower 70s. This results in a heat index around 95 from Philadelphia to Wilmington, and possibly near 100 for northeast Maryland and Delaware. Cold front then approaches Friday afternoon and evening as low pressure over the Great Lakes lifts northeast into eastern Canada. Showers and thunderstorms are likely Friday with the passage of this front, but conditions only marginally cool off and dewpoints only marginally fall back into the upper 60s/low 70s on Saturday. A secondary cold front will pass through the region on Saturday afternoon, and then dewpoints drop back into the low/mid 60s on Sunday. Weak low pressure may have an impact on the region Sunday, hence slight chance PoPs, but confidence is low. High pressure then returns for the start of the new week. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Some improvement took place this evening as the main area of rain showers moved off the coast. However, abundant lingering low level moisture will likely result in the development of fog and low clouds overnight with deteriorating conditions anticipated. The low clouds and fog should linger until the 1200Z to 1400Z time frame then improvement to VFR and scattered cloud cover is forecast for the balance of Wednesday. A light and variable wind overnight is expected to settle into the northwest and west at 4 to 8 knots on Wednesday. A sea breeze front may push inland past KACY early in the afternoon. OUTLOOK: Wednesday night...Sub-VFR conditions possible in fog/stratus. Thursday through Friday...Sub-VFR conditions in mainly afternoon and evening showers and thunderstorms. Late night and early morning fog/stratus possible as well. Saturday...Scattered showers and thunderstorms possible. Sunday...VFR.
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&& .MARINE...
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Seas have risen to 4-5 feet at the buoys off the NJ/DE coast as Hurricane Gert churns well offshore. Longer-period swell is reaching the buoys (generally 12-14 seconds) and will continue into Wednesday. Seas are expected to build to 4-7 feet tonight and Wednesday, and have continued the small craft advisory to account for this. Meanwhile, east to southeast winds around 5 kts will veer to the north and northwest late tonight before veering to a southeast direction again by Wednesday afternoon. Some fog may develop near the coast and near Delaware Bay late tonight, with some visibility restrictions possible. However, this fog should dissipate rapidly during the morning, with a nice/dry day expected, save for the aforementioned higher seas. OUTLOOK... Wednesday thru Sunday...Sub-SCA conditions expected through this week and into the early part of the weekend. Scattered thunderstorms may bring locally higher winds and seas. Southerly wind gusts 20-25 KT possible Friday afternoon as a cold front works its way east. RIP CURRENTS... We have upgraded to a high risk for the development of dangerous rip currents for the balance of today and for Wednesday. Long period swells from Hurricane Gert will continue to impact the coasts of Delaware and New Jersey. Swim only in the presence of lifeguards where safety prevails. Otherwise, you`re on your own with any rescue potentially critically delayed. There have been numerous drowning fatalities this year along the NJ coast.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...High Rip Current Risk through Wednesday evening for NJZ014- 024>026. DE...High Rip Current Risk through Wednesday evening for DEZ004. MD...None. MARINE...Small Craft Advisory for hazardous seas until 2 PM EDT Wednesday for ANZ451>455. Small Craft Advisory for hazardous seas until 2 PM EDT Wednesday for ANZ450.
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&& $$ Synopsis...MPS Near Term...Iovino Short Term...CMS Long Term...MPS Aviation...Iovino/MPS Marine...CMS/MPS

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