Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200009 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 809 PM EDT Mon Jun 19 2017 .SYNOPSIS... A cold front will move through the area tonight and offshore by Tuesday morning. A secondary cold front will gradually approach from the northwest Wednesday before dissipating over the area Wednesday night. Bermuda high pressure looks to influence our weather once again late in the week. Another frontal system may affect the area sometime during the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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800 PM update: The remainder of the Severe Thunderstorm Watch has been cancelled. This update was to adjust PoPs and to remove the Severe Thunderstorm Watch headline. Otherwise, an upper-level trough over the Great Lakes region continues to shift eastward. This will drive a cold front across our area later this evening. The air mass in place is very warm and moist with PW values around 2 inches. This is resulting in MLCAPE of up to 2000 J/KG. The deep southwesterly flow will mostly favor a linear convective mode, however as the convective line grows upscale (moves into a stronger low-level wind field along with an instability axis) eastward into this evening there could be some embedded cells with some updraft rotation. Given the mostly unidirectional flow though, straight-line damaging wind gusts is the main threat. The wind damage threat will be locally enhanced where line segments surge forward (bow out). The mid level lapse rates do not appear to be all that steep, therefore while some hail is possible this should temper this potential. The overall high moisture content of the air mass may result in water- loaded downdrafts which can enhance the downdraft potential (downbursts) especially along the leading edge of the storms. The tropical air mass will also be conducive for convection to produce frequent lightning. As mentioned earlier the PW values will be around 2 inches. This will result in areas of very heavy rain as convection should be efficient rainfall products. While the storm motions are fairly quick, a linear mode and possible backbuilding of updrafts may result in the potential for local flash flooding. Therefore, the Flash Flood Watch remains as is. One the organized convection moves off the coast later this evening, some showers or thunder may linger in its wake as some height falls occur with the incoming upper-level trough. The extent of additional convection especially for the eastern and southern zones is less certain as this will depend on how much the air mass is turned over from the initial convective line. The dew points are expected to start lowering overnight especially in the northern and western zones.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Our area will be under the influence of an upper-level trough and associated cyclonic flow Tuesday. This will allow a cold front to push offshore early, however some lingering showers or thunder are possible near the southeast zones to portions of Delmarva in the morning. Otherwise, drying is forecast to work south and east during the day, with this most noticeable especially to the north and west of I-95. Despite a cold front clearing the area, it will be a warm day although much of the area will get a break from the humid conditions as the day progresses. High temperatures are an even blend of MOS and continuity. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Slightly cooler, but near normal temperatures, and somewhat drier air moves into the region during the midweek. A mostly dry period is expected Tuesday night through Thursday with a few exceptions. The frontal boundary that moves thru our region tonight will stall to our south tomorrow, then the northern edge of precip along the front may expand northward toward southern DE late Tuesday night and Wednesday as a disturbance tracks along it. Additionally, diurnally-driven showers may develop during peak heating Wednesday afternoon across the higher terrain of northeastern PA and northwestern NJ as a shortwave trough tracks nearby to the north. It appears that another cold front an associated upper trof will approach from the northwest Friday or Saturday, but timing is uncertain at this point. The front may also be preceded by a surge of tropical moisture from the Gulf of Mex. Given the uncertainty for forcing and the overall summer-like pattern, the forecast includes a chance of t-storms for Friday and through the weekend for the entire area. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through tonight...As of 00z, an area of rain/showers is behind a departing line of thunderstorms. Some lingering showers and local MVFR conditions may occur for awhile in the wake of the line of thunderstorms. Otherwise, improving to VFR overnight although some local light fog is possible. Southwest to west- southwest winds diminishing to less than 10 knots. Tuesday...VFR overall. A few morning showers possible near and south and east of KACY and KMIV. West-southwest to southwest winds increasing to around 10 knots. OUTLOOK... Tuesday night through Thursday...Mainly VFR conditions expected. Low possibilities for sub-VFR restrictions from stratus/fog late night/early morning each day. Southwest winds 10 kt or less. Friday and Saturday...Chance for MVFR or tempo IFR conditions in showers and thunderstorms. SW winds gust to 20 kt during the afternoon on Friday.
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&& .MARINE... The Small Craft Advisory remains in effect through Tuesday on our ocean waters. The Small Craft Advisory is in effect for Delaware Bay until 11:00 PM. A gusty south to southwest wind continues into tonight as a low- level jet moves across the region. These winds will diminish overnight. The wave heights on our ocean waters should remain in the 5 to 8 foot range through tonight. A line of gusty thunderstorms is expected to move through this evening. While the winds should be below advisory criteria Tuesday, seas on the ocean should be about 5 feet. OUTLOOK... Tuesday night through Saturday...Winds and seas expected to remain below SCA headline criteria. RIP CURRENTS... The high risk for the development of dangerous rip currents continues through this evening along the coast of Delaware and New Jersey. There is a 6 to 7 second southerly wind wave on top of a very long period (around 16 seconds) southeasterly ground swell. This combination results in an elevated risk for the development of dangerous rip currents. The primary wave period is forecast to be around 7 seconds from the south on Tuesday and Wednesday. However, the underlying 13 to 16 second southeasterly swell is expected to linger into the mid week period. As a result, the risk for the development of dangerous rip currents is anticipated to be at least moderate through the period along the coasts of Delaware and New Jersey. && .EQUIPMENT... NWS NWR and phone broadcast of the marine and surf zone forecasts. Problems continue here at NWS PHI. Hope to resolve later today or Tuesday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014- 024>026. DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ450>455. Small Craft Advisory until 11 PM EDT this evening for ANZ430- 431. && $$ Synopsis...Klein Near Term...Gorse/Meola Short Term...Gorse Long Term...AMC/Klein Aviation...AMC/Gorse/Klein/Meola Marine...AMC/Gorse/Klein Equipment... is the U.S. government's official web portal to all federal, state and local government web resources and services.