Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191813 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 213 PM EDT FRI AUG 19 2016 .SYNOPSIS... High pressure over the Appalachians will continue to build eastward into the region today and tonight with a trough of low pressure to our south. The high Pressure system will then move offshore on Saturday giving way to an approaching cold front on Sunday. This front will move through the region Sunday night with high pressure building southeast into the region for the early and middle parts of next week. && .NEAR TERM /UNTIL 9 PM THIS EVENING/...
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2 PM...Sent a quick update within the past hour to put isolated showers in the forecast thru mid afternoon across the higher terrain of northeastern PA and northern NJ. The equipment section of the AFD was also updated with additional radar outages to contend with. Previous Discussion... A surface trough is forecast to develop in New England and the mid- Atlantic this afternoon. The trough axis will likely reside somewhere between I-95 and the coastal plain. Boundary-layer convergence near the boundary will become better defined this afternoon as the sea-breeze circulation advances inland and the flow turns southeasterly to the east of the trough axis while remaining northwesterly farther inland. Model guidance, including the latest hires CAM models, show convection initiating over coastal NJ and DE within the abovementioned convergence zone during peak heating between 1 and 3 PM this afternoon. The mesoscale focus for convection will propagate westward through the coastal plain late this afternoon and I-95 corridor this evening as the sea-breeze front moves inland. Updated hourly PoP/Weather grids reflect this thinking. Without deeper, more organized lift over the area today, convection should be isolated in coverage. 12Z IAD/OKX RAOBs and model forecast soundings at locations in our area show a mid-level subsidence inversion present that could hinder convective growth, especially with a limited degree of instability (MLCAPE generally less than 1250 J/kg) to tap into. Therefore, expect the bulk of the activity this afternoon to be showers with only a rogue thunderstorm or two. Otherwise, we are anticipating a mostly sunny day for most of the area. High temperatures will generally be in the mid to upper 80s with our warmest spots in the city and Delmarva to reach 90F. The exception to the above will be along the coast and Poconos where highs will be in the lower 80s.
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&& .SHORT TERM /9 PM THIS EVENING THROUGH 6 AM SATURDAY/... Some of the guidance is signaling the potential for isolated rain showers continuing after dark late this evening in the Delaware Valley. They may develop in advance of a weak impulse traveling in the mid level flow. As a result, we will mention a slight chance for showers at that time. Otherwise, we are expecting scattered clouds for tonight along with a light wind. Minimum temperatures should be in the 60s in the north and in the upper 60s and lower 70s elsewhere. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Saturday and Saturday night...Weak high pressure will be in place across the region with a trough of low pressure to our south on Saturday. As the high pressure moves east, winds will shift to the southeast with moisture advecting into the region from the atlantic and gulf. Enough moisture will be in place with peak heating to produce a few widely scattered showers and thunderstorms during the afternoon and evening hours. It will also be another hot day with highs pushing 90 across most of the region. Used a blend of MET/MAV and ECMWF guidance as the overall spread in terms on most weather elements is small. Sunday and Sunday night...A cold front is expected to approach the area late in the day Sunday and move into the area Sunday night, and progress east of the region by Monday morning. Overall, ensemble agreement is pretty good on the timing of the front. Moisture will continue to stream northward into the region ahead of the front allowing PW values to climb to over 2 inches. Enough lift will be present along the front to develop showers and thunderstorms in the afternoon and nighttime hours to our west that then move eastward through the region. Given the good model agreement on timing, kept pops in the likely range. With high PW values, heavy rainfall will be a threat with most thunderstorms. Some of the ensemble guidance is indicating a higher likelihood for the heaviest rainfall to occur across eastern PA into the Delmarva, as these locations are closer to the front during peak heating hours. Some locations could see a quick inch or even more of rainfall which could lead to some localized flooding concerns. Used a blend of WPC/SREF and the 00z ECMWF for qpf totals, with the overall impression the ECMWF has a better handle on the heavy rainfall idea than the GFS and GEFS. In terms of any severe weather, instability looks limited with 1,000 J/KG of CAPE or less. However, modeling shows somewhat steep low level lapse rates which could contribute to storms having some locally strong wind gusts. For now have added heavy rain wording to the grids and will continue mentions of heavy rain and gusty winds in the HWO. In terms of temperatures, highs have a chance to warm a few degrees more than what MET/MAV guidance indicates given the boundary layer temperatures still around 20C. Where sunshine comes out highs will likely push 90 again in the Delmarva and Southern New Jersey. highs will be cooler further northwest where the rain arrives sooner. Temperatures will start off muggy in the 60`s to near 70. Monday through Thursday...The front will be offshore by Monday allowing high pressure to build southeast into the region early next week then moves over the region for the middle part of next week. The airmass with this high pressure system will be much drier and cooler. High temperatures will be closer to normal with 70`s and 80`s for most of next week. Little spread in modeling and ensemble guidance, so stuck close to WPC guidance.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Conditions are forecast to be VFR through the TAF period with one exception. Expect mainly scattered cu field with cigs between 1.5-3 kft this afternoon, increasing to 3-5 kft this afternoon. There may be some isolated rain showers this evening, especially in New Jersey. However, their potential is not high enough to include in the TAFs. A light north to northwest wind is anticipated for today. The flow should provide limited resistance for the sea and bay breeze fronts. The boundaries are expected to progress inland reaching KACY, KMIV and KILG during the afternoon and early evening hours. A light and variable wind is forecast for tonight. OUTLOOK... Saturday and Saturday night: VFR. Can`t rule out a brief reduction due to a stray shower or thunderstorm in the afternoon and nighttime hours. Sunday and Sunday night: lower than VFR conditions likely by late Sunday afternoon with showers and thunderstorms that last into Sunday night. Southeast winds around 15 knots, gusts around 20 knots. Monday...VFR. Northwest winds around 15 knots with gusts around 20 knots. Tuesday: VFR. Winds 10 knots or less from the northwest. && .MARINE... Weak surface features are expected to influence the coastal waters of New Jersey and Delaware for today and tonight. Wind speeds are forecast to remain generally less than 15 knots and the direction will vary due to local influences. Wave heights on our ocean waters will be around 2 feet and waves on Delaware Bay should be 1 foot or less. OUTLOOK... Friday-Tuesday... Seas will start off rather light through Saturday night before increasing gradually from two to three feet on Sunday. Seas may reach four feet for a time on Monday before decreasing to around three feet on Tuesday. The highest winds will be in association with a cold frontal boundary passing through Sunday night. Wind gusts could push 25 knots from the southeast late sunday before becoming northwesterly on Monday. Winds are likely to decrease Monday night. RIP CURRENTS... There is a low risk for the development of dangerous rip currents today. The wind along the coasts of New Jersey and Delaware should be variable this morning, then onshore in the afternoon at 10 mph or less. A 2 foot southerly swell is anticipated. The probable risk for the development of dangerous rip currents is low for Saturday. However, it may approach moderate in the afternoon with the establishment of a synoptic scale southeasterly wind around 10 MPH. && .CLIMATE... The heat wave of the past 7 to 8 days at many locations has ended. This lists the number of 90 degree or warmer days (as of August 18) and the mean number of 90 degree days for each climate site (computed from when the period of record began). We are above normal for 90 degree days at all climate sites. Site 90 deg days beginning of climate record 2016 mean POR ABE 28 17 1922 ACY 26 10 1874 GED 30 27 1998 PHL 33 21 1873 RDG 30 21 1999 TTN 27 20 1998 ILG 28 20 1894 && .EQUIPMENT...
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Due to equipment failure (A/C unit and computer), the KDIX WSR- 88D radar remains out of service. Return to service is still unknown at this time. Surrounding WSR-88D radars, including KDOX (Dover), KCCX (State College) and KAKQ (Wakefield), are down with either equipment issues or maintenance. We will use TEWR and TPHL terminal doppler radars as well as KLWX (Sterling), KBGM (Binghamton), and KOKX (Upton) WSR-88D radars to help fill in the radar coverage gaps as much as possible.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gaines Near Term...Klein Short Term...Iovino Long Term...Gaines Aviation...Gaines/Iovino/Klein Marine...Gaines/Iovino Climate...Drag Equipment...Klein

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