Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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288 FXUS61 KPHI 290719 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 319 AM EDT Thu Sep 29 2016 .SYNOPSIS... A frontal boundary will remain stationary to our south today through Saturday as a couple of low pressure systems pinwheel to our south and west. The low to our west will eventually lift through the Great Lakes region and into the northeast over the weekend, before weakening on Monday. This will pull the frontal boundary across our area Sunday. High pressure builds to our north for Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Model guidance hasn`t been handling overnight extend of the rain well at all, so there is considerable uncertainty even with the near term period of this forecast. However, mid and upper level mean flow is expected to shift from south southwesterly to southeasterly through the day. As a result, the axis of heavy rain, and even of widespread light rain should shift east of the region, at least through the day time hours. Thanks to extensive cloud cover, do not expect temperatures through the day to be much higher than what we saw overnight. This will also limit instability, though isolated thunderstorms are still possible thanks to meager elevated instability. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Low level flow should shift more easterly, and mid and upper level flow back to southerly. As a result, another round of rain, heavy at times will be possible for the southern half of our region. The persistent surface high just to our north and associated subsidence may be enough to keep heavy rain out of the northern half of the region, but with the onshore flow, expect at least light rain for almost all of the region. Persistent low level cloud cover will once again limit nocturnal radiational cooling overnight, meaning our lows should be within 10 degrees of Thursday`s highs. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Unsettled weather continues to be forecast for much of the extended period, especially the end of this week into the weekend. For Friday, an couple of areas of low pressure at the surface will continue to be located to our south and west, while high pressure remains to our north. In between, a stationary boundary will remain in place just to our south. This will keep an onshore flow across our area. Meanwhile, a closed low aloft will be spinning to our west as well. This will keep a persistent southerly flow aloft across the area at the same time. With the southerly flow aloft, cloudy conditions, and a chance of light rain and/or drizzle will continue across the area. It will not likely rain the entire time, but several periods of rain will be associated with several short waves/vorticity impulses rounding the closed low aloft to our west. By Saturday, and especially Sunday, the high to our north begins to move eastward, and the low to our west will begin lifting back toward the Great Lakes region. This will eventually pull the frontal boundary to our south across our area on Sunday. There will continue to be a chance of showers Saturday through Sunday as several short wave/vorticity impulses move across the area as the closed low aloft begins to break down and lift to the northeast. On Monday, the mid-level trough will be moving across the area, and the low to our north will weaken as it moves into New England. As the trough aloft crosses the area, there could be some scattered showers affecting the area. By Tuesday and Wednesday, high pressure builds to our north and noses its way across our area. With the high to our north, an onshore flow will develop, which may end up leading to more cloud cover and cooler conditions. There could also end up being some light rain and/or drizzle if enough moisture moves across the area. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Widespread IFR ceilings are spreading over the region now, and should continue through at least 15Z. There may be several hours of MVFR conditions through the mid day hours, before ceilings lower again to IFR near 00Z. There is a chance for showers through out the TAF period, bringing temporary visibility restrictions. Isolated thunderstorms are possible too, but coverage is expected to be too limited to mention in the TAFs at this time. Winds will be easterly or northeasterly through the TAF period. Sustained wind speeds of 10 to 20 kts possible with gusts up to 30 kt possible (highest gusts are expected to be at KACY primarily this evening. OUTLOOK... Friday-Saturday night...A prolonged period of MVFR or IFR conditions with periods of rain is expected to affect the TAF sites through the period. East to northeast winds are expected to gust 20-25 knots for much of the area. Sunday-Monday...Some improvement, possibly to VFR. Showers remain possible. && .MARINE... The gale warning was extended for the coastal waters as the latest guidance indicates that gale force gusts are possible through at least the overnight hours tonight. Waves are expected to build through the day and could approach 10 ft by this evening. Outlook... Friday...Gale Warning continues across the northern half of the Atlantic coastal waters. Small Craft Advisory level likely to remain elsewhere. Friday night-Saturday...Winds expected to drop below Small Craft Advisory levels, however, seas may remain above advisory levels through the period. Saturday night-Sunday...Winds and seas expected to drop below Small Craft Advisory levels. Sunday night-Monday...Conditions expected to remain below Small Craft Advisory levels. RIP CURRENTS... There is a high risk for the formation of dangerous rip currents along the NJ shore and the DE beaches today. Wave heights may even approach 10 ft later today, but have held off on issuing a high surf advisory as guidance is currently running a little high. && .HYDROLOGY... Have expanded the flash flood watch to include all of Delaware, and extended all of the watch to continue through tonight. Steering flow has been slower to shift than previously forecast. As such, the heavy rain in our area has stayed confined to Delaware through 3 AM, expect this to change through the early morning hours. Based on the latest guidance, it looks like there may be a bit of a lull, especially with heavy rain, through the day time hours, before picking up again this evening. As mentioned by the previous shift, widespread 1 to 3 inches are possible, but shouldn`t cause problems. The concern is with any embedded thunderstorms which will produce locally higher amounts in a short period of time (ones earlier tonight were showing rain rates upwards of 4 inches per hour). && .TIDES/COASTAL FLOODING... Based on the departures we saw with last evening`s tide and the fact that the high tide this morning is the lower of the astronomical tides, a few locations may reach minor flooding with the morning high tide, but will hold off on issuing a coastal flood advisory as it is not expected to be widespread. Minor tidal flooding is likely with this evening`s high tide and a few locations may even get into moderate flooding. For now, have held off on any advisories or warnings until we get a better idea of the departures with this morning`s high tide. && .CLIMATE... September will be/is a top 10 warmest month through most of our forecast area, for the 3rd consecutive month! Also September will be/is enjoying a second consecutive top 5 warmest month in the period of record for PHL and ABE. We`ve run the actual numbers through the 28th, then added the forecast high/low for 29th and 30th. Philadelphia: Expect a 73.8 degree average or about 5 degrees above the monthly normal of 69.1. This will be a #4 or #5 warmest September on record for Philadelphia. Philadelphia September average temperature rankings 75.4 -1881 74.5 -2015 74.1 -1931 74.1 -1930 73.8 -2005 and 2016 #4 (small chance PHL avg will be 73.7 or #5 ranking) 72.9 -2010 72.9 - 1921 Philly ranked #7 warmest July followed by a warmest ever August in the POR dating back to 1874. Atlantic City: Expect a 71.2 degree monthly average temperature, or 4 degrees above the monthly normal of 67.2. This would equate to an 8th warmest September in the period of record dating back to 1874. Atlantic City recorded a #7 warmest July and then a warmest ever August. 73.3 - 1961 72.8 - 1881 72.3 - 1931 and 1930 71.7 - 1921 71.6 - 2015 71.5 - 1933 71.3 - 2005 71.2 - 2016 #8 71.0 - 2010 70.6 - 2011 and 1906 Allentown: Expect a monthly average of 69.4 degrees, or 5.5 degrees above the monthly normal of 63.9 and a 4th warmest September on record. Allentown ranked 8th warmest July and #2 warmest August in the period of record. 70.8 - 1961 70.3 - 1980 69.7 - 2015 69.4 - 1931 and 2016 (small chance Allentown will rank #5 at 69.3 degrees) 68.7 - 2005 Daily rainfall records for September 29 where there is maybe a small chance of exceeding: PHL 1.87 1963 ILG 1.97 1963 GED 1.35 2015 RDG 3.55 1934 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk through this evening for NJZ014-024>026. DE...High Rip Current Risk through this evening for DEZ004. Flash Flood Watch through late tonight for DEZ001>004. MD...Flash Flood Watch through late tonight for MDZ008-012-015-019- 020. MARINE...Gale Warning until 6 AM EDT Friday for ANZ452>455. Gale Warning until 6 PM EDT Friday for ANZ450-451. Gale Warning until 2 AM EDT Friday for ANZ430-431. && $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson Hydrology...Johnson Tides/Coastal Flooding...Johnson Climate...Drag

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