Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191529 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1129 AM EDT Mon Jun 19 2017 .SYNOPSIS... High pressure over the western Atlantic will maintain a southwesterly flow of very warm and muggy air over the region today. A cold front approaching from the west will cross the area this evening and move offshore by Tuesday morning. Temporary drier conditions through mid-week will give way by week`s end to increasing warmth and moisture as the Bermuda High builds back in. Another frontal system may affect the area by next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1120 AM update: Severe Thunderstorm Watch 354 issued (through 00z/8 PM) for eastern PA and northern NJ and the text products were sent to include the watch headline. The PoPs were also adjusted a bit. Convection continues to develop late this morning for the northwest areas, however the main organized convection should be later this afternoon. The Watch placement was based on timing but accounting for possible isolated severe earlier on. Another Watch is anticipated farther south and east later on. A convectively active afternoon is expected across at least the western half of our area, which then shifts east this evening. A cold front will be approaching later today, however ongoing showers/thunder well to our west should strengthen eastward through the afternoon as it encounters a more unstable air mass. In addition, a pre-frontal trough may help to organize a separate band of convection with storms probably tending to congeal into a single line as we get closer to the early evening. The air mass in place is rather warm and moist with PW values already near 2 inches. This is already resulting in quite a bit of instability with a mesoscale analysis indicating MLCAPE around 1500 J/KG. Some lower cloud bases had quickly developed within this very warm and moist environment, however as mixing increases these will rise some. The deep southwesterly flow will mostly favor a linear convective mode, however as the convective line grows upscale (some increase in the shear as a low-level jet strengthens) later today 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 mid level lapse rates do not appear to be all that steep, therefore while some hail is possible this may temper this potential. The 12z Sterling, VA RAOB shows a bit of dry air just above 500 MB, and this could aide in downdraft strength. The overall high moisture content of the air mass though may result in water-loaded downdrafts which can enhance the surface winds, especially with any segments that bow out. The tropical air mass should also be conducive for convective 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 should be 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.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... The main convective line should work its way across the Interstate 95 corridor early this evening before passing off the coast late this evening. The threat of severe weather and flash flooding will continue. Low clouds and lingering showers are anticipated for a few hours after the cold front passes, then some clearing is expected late tonight. Temperatures should drop into the 60s and lower 70s overnight. A light southwest to west wind is forecast. && .LONG TERM /TUESDAY THROUGH SUNDAY/... The cold front that moves across the Monday night should be off the NJ/DE coast by Tuesday morning. However with southwest flow continuing aloft further progress may be slow. The forecast keeps a chance of showers for Tuesday morning over southeast DE and the DE/NJ coastal waters. Otherwise slightly cooler and somewhat drier air should filter in behind the cold front for Tuesday into Wednesday. Temperatures are forecast to remain a few degrees above normal but lower dewpoints should make for overall pleasant conditions with no precip expected. By Thursday the upper trof moves away to the east allowing for some weak ridging aloft. Low level warm advection increases along with rising surface dewpoints. Instability may be limited but the forecast has a chance of t-storms mainly north/west of PHL. 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 GulfMex. 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 /16Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Mainly VFR for awhile. A few showers or thunderstorms into the afternoon mainly near and north and west of KABE and KRDG, however the main focus will be a strengthening line of showers and thunderstorms from the west this afternoon. Some of the storms will be capable of produce strong winds and very heavy rain. South-southwest winds 10-15 knots with gusts to about 25 knots at times, especially by mid afternoon. Tonight...A line of gusty thunderstorms move through in the evening, clearing the coast by 02z. MVFR conditions and scattered showers are expected to linger in the wake of the thunderstorms early tonight with some improvement to VFR possible late tonight. Southwest to west winds diminishing to 5-10 knots. OUTLOOK... Tuesday 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...Chance for MVFR or tempo IFR conditions in showers and thunderstorms.
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&& .MARINE... The Small Craft Advisory remains in effect for today and tonight on our ocean waters. The Small Craft Advisory is in effect for Delaware Bay until 11:00 PM. A gusty south to southwest wind is anticipated for today. Wind gusts of 25 to 30 knots are expected. While wind speeds are forecast to diminish tonight, wave heights on our ocean waters should remain in the 5 to 8 foot range. A line of gusty thunderstorms is expected to move through this evening. OUTLOOK... Tuesday...Winds veer slightly out of the W-SW and weaken to below 25 kt. However seas will be somewhat slow to subside and are expected to remain at 5 ft or higher much of the day. Therefore the SCA has been extended until 600 pm Tuesday. Tuesday night through Friday...Winds and seas expected to remain below SCA headline criteria. RIP CURRENTS... We will continue with the high risk for the development of dangerous rip currents through this evening along the coast of Delaware and New Jersey. We are expecting a 6 to 7 second southerly wind wave on top of a very long period (around 15 to 16 seconds) southeasterly ground swell. The combination will result in 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. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch through this evening for PAZ060>062-070-071- 101>106. NJ...Flash Flood Watch through this evening for NJZ001-007>010-012- 013-015>019. High Rip Current Risk until 9 PM EDT this evening for NJZ014- 024>026. DE...Flash Flood Watch through this evening for DEZ001. High Rip Current Risk until 9 PM EDT this evening for DEZ004. MD...Flash Flood Watch through this evening for MDZ008. 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...AMC Near Term...Gorse Short Term...Iovino Long Term...AMC Aviation...AMC/Gorse/Iovino Marine...AMC/Iovino Equipment...

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