Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 010136 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 936 PM EDT TUE MAY 31 2016 .SYNOPSIS... A cold front has weakened and pushed offshore today, and a secondary backdoor front will push southward across the area tonight into Wednesday morning. Our area will be on the southern edge of high pressure located across eastern Canada through early Thursday. A cold front will move across the area Friday. An area of low pressure and associated frontal boundaries will move across the Great Lakes region Saturday into Sunday, and across the Northeast Monday into Tuesday, bringing unsettled weather to our area early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... The sea breeze has slid as far west as the Delaware Valley, but should be dissipating soon. Exactly how far west it goes will have impacts for fog potential tonight, as east of the sea breeze, dew points are generally in the mid to upper 60s, while west of the see breeze, dewpoints range anywhere from the upper 50s to lower 60s. With limited moisture advection (may even see dew point values drop behind the back door cold front) tonight do not expect fog to develop west of the sea breeze. Patchy fog should develop east of the sea breeze where dewpoint depressions as of 9 PM are already less than 5 degrees in some locations. One possible caveat is for locations, even west of the sea breeze, that have had heavy rain over the past 3 days, if the ground remains very wet, patchy fog could develop. Thus adjusted the grids to have a mention of patchy fog generally along and east of the fall line. Lows tonight should generally be in the 60s for much of the region, with the exception of the higher terrain of the Poconos and NW NJ, where 50s will be possible. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... The high pressure to the north of the area Wednesday morning will move into eastern Canada. The will place our region in the erly flow on the south side of the high. This should provide some fair weather for Wednesday with cooler temperatures (compared to Tuesday). Highs will be in the upper 70s to low 80s in most areas. Sky cover will be mostly sunny early with some clouds developing late across the srn/wrn areas. We have included a small chc for a shower across the Delmarva and se PA areas. Some of the operational models show some qpf output. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Our area will continue to be on the far southern edge of an area of high pressure that will be residing across central and eastern Canada Wednesday night through Thursday. Mostly dry conditions are expected, although an isolated shower could be possible overnight Wednesday into early Thursday as a weak vorticity impulse slides across the area and could interact with some increased moisture within the return flow at the surface. Another vorticity impulse is forecast to approach the area late in the day and overnight, which could bring additional isolated showers by the afternoon. However, there will be a greater potential for showers overnight as this short wave/vorticity impulse moves across the area. On Friday, we expect a cold front to move across the area from west to east as an area of low pressure moves across eastern Canada. there will be an increase in instability, along with PW values reaching 1.75 inches. Therefore, we can expect scattered showers and thunderstorms to develop ahead of and along the frontal boundary during the day. The flow is not very strong, so any slow moving storms could produce some high amounts. But the front should still be fairly progressive, so no widespread flooding is expected at this time. The front will slowly make its way offshore Friday night, so there could still be some lingering showers and thunderstorms during the evening and early in the night Friday. All showers should be ending overnight. There could be a dry period Saturday as high pressure across central Canada tries to nose its way down across the area. It would not be surprising if an isolated shower were to occur, but we`ll keep this out of the forecast for now as the chances are small at this time. Unsettled weather returns for Sunday through Monday as an area of low pressure will be moving through the Great Lakes region and into the northeast. A warm front should be lifting across the area late Sunday into Sunday night, then a cold front will move across the area late Sunday night into early Monday. A period of showers and isolated thunderstorms should move across the area through this time period. PW values approach 2 inches during this time, so there could be some periods of heavy rainfall possible. There will continue to be a chance of showers Monday night into Tuesday as the low slowly pinwheels to our north through New England, especially during the afternoon Tuesday as a secondary surface trough/frontal boundary crosses the area. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For KPHL, KPNE, KTTN, and KILG...The sea breeze has made it to KPHL, KTTN, and KPNE, though KILG still remains west of the sea breeze. Will continue to monitor the dew points through 06z, but will continue with the forecast of patchy fog reducing visibilities to generally the MVFR range, with the highest risk between 08 and 11Z. Tomorrow, winds will be shifting out of the East and East Southeast by late morning, but VFR conditions are expected through the day. For KABE and KRDG...VFR conditions should continue through the TAF period. Earlier concerns about fog development have decreased as dew point temperatures are in the 50s and are not expected to recover much overnight. Winds will be light and variable overnight, but eventually settling in out of the east and southeast by late tomorrow morning. For KMIV and KACY...VFR conditions will continue through at least 03z. After that, expect fog to begin to develop on the coastal plains. Visibilities are expected to drop into the IFR range before 12Z, but confidence is low as to when this will happen or how long it will last. Visibilities should begin to improve after sunrise. Winds will be light and variable overnight, but should settle out of the east and southeast by 18Z. OUTLOOK... Wednesday night-Thursday...Generally VFR inland. Lower clouds and/or fog possible near the coast may push inland. Mostly light east to southeast flow. Thursday night...MVFR ceilings may develop across the area, with showers possibly developing from west to east. Friday-Friday night...MVFR and/or IFR ceilings possible. Showers and thunderstorms possible, especially later in the day. Improving conditions later in the evening and overnight. Saturday...Generally VFR. Saturday night-Sunday...Diminishing conditions, possible becoming IFR by Sunday morning. Rainfall becoming more widespread Sunday. Gusty southeast winds possible Sunday. && .MARINE... Patchy fog is expected to develop later tonight, but confidence is low on how low the visibilities will be. So for now, will continue to monitor, but have not issued a dense fog advisory. Winds and seas are expected to remain below small craft advisory conditions tonight and tomorrow. OUTLOOK... Wednesday-Sunday...Conditions forecast to be below Small Craft Advisory levels through the period. Winds could gust around 20 knots at times. Generally east to southeasterly winds, except west to northwest briefly behind frontal boundary passage Friday night. && .TIDES/COASTAL FLOODING... Onshore flow is expected to develop on Wednesday and continue into Friday. We will need to monitor the possibility of minor tidal flooding at times of high tide along the coast late this week owing to the persistent onshore flow and the approaching new moon this Saturday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Robertson Near Term...Johnson Short Term...O`Hara Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson/O`Hara Tides/Coastal Flooding...

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