Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170101 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 901 PM EDT Sun Jul 16 2017 .SYNOPSIS...
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High pressure weakens across the area tonight. Unsettled weather on tap for much of this week as a trough approaches from the west and stalls west of the Appalachians. That trough moves across the region through Tuesday night. High pressure briefly returns Wednesday, before a pair of cold fronts approach the region late this week.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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A pleasant night ahead across the entire area. Skies are clearing out this evening, but some cloud cover will likely build back in overnight. Starting with higher clouds, then lowering some overnight and through daybreak. Temperatures will be a couple of degrees warmer than last night as southwest flow aloft helps to bring in slightly warmer and more moist air. No precipitation is expected overnight. South to southwest winds will be likely become light and variable overnight. There is a small possibility for some light fog overnight through daybreak, but visibilities are not expected to lower very significantly.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
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Fair weather is expected during the morning Monday, but an approaching disturbance will bring increasing clouds and the chc for showers and a few tstms by afternoon. The SPC has mentioned a marginal possibility for severe storms across the N/Wrn areas. The Slight risk area touches the Southern Poconos region however. Gusty winds and perhaps would be the hazards if/when tstms develop. Temperatures will rise into the mid/upper 80s across the area, a bit cooler near the shore. Winds will be mostly S or SE at 5 to 10 mph.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... The main features to watch in the long term will be a mid and upper level trough which will be very slowly progressing east through the early week, and a pair of cold fronts late in the week. Monday night through Wednesday...The mid and upper level shortwave trough may be stalled Monday night just to our west, but is then expected to very slowly slide east. Interestingly, despite the trough in the area, mid and upper level flow will be relatively weak through this time, resulting in meager shear values. Therefore, expecting mostly diurnally driven convection to develop near the trough axis each afternoon, but do not expect much in the way of organized convective complexes. With relatively low precipitable water values (at least for this time of year) expect the flooding threat to be limited Monday and Tuesday. However, by Wednesday, if the surface low develops far enough south, we could see precipitable water values climb above 1.5 inches (still not unusual for late July, but on the increase). That, combined with slow storm motions could mean localized heavy rain. There are still too many contingencies to include in the HWO for now though. Thursday through Sunday...Still considerable uncertainty with the timing and evolution of features in this period. The previously mentioned mid and upper level trough should be well off shore through this period, leaving us in a northwesterly flow pattern. Consequently, a pair of cold fronts are expected to dig far enough south to propagate through and well south of our region. The first one looks on track to move through Thursday or Thursday night. There should then be a period of tranquil weather as a low and mid level short wave ridge briefly propagates over the region. Then a second, and perhaps stronger (at least in terms of temperature gradient) front is expected very late in the period (Saturday or Sunday). Favored area and timing for precipitation will be with and just ahead of each of these fronts. && .AVIATION /01Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected during the overnight hours with mostly high level clouds early, then lowering some toward daybreak. Some light fog could develop at a few TAF sites, and VSBYS drop to 5 or 6SM. On Monday, generally VFR conditions expected with CIGS 4,000-6,000 feet. Scattered showers, or an isolated thunderstorm could develop during the afternoon. We`ve kept the PROB30 for all sites except ACY and MIV where the showers may not materialize. If any showers are heavy enough, VSBYS could drop to 4SM. Winds will be mostly light from the south or southwest early, then likely become light and variable overnight. Winds will increase out of the south to southeast around 5 to 10 knots by mid morning Monday and through the afternoon. A few gusts around 15 knots may be possible for some areas. Outlook... Tuesday through Friday...mostly VFR conditions expected. Chances for showers and thunderstorms, primarily in the afternoon and evening, could lead to brief MVFR or lower conditions.
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&& .MARINE...
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Weak high pressure across the waters tonight will further weaken and low pressure will form to the west. Winds will generally be S to SE around 5 to 10 knots through Monday, although by Monday afternoon some gusts around 20 kts are possible. Fair weather expected through early afternoon Monday, then isolated showers or thunderstorms may occur late in the day. Outlook... Tuesday through Friday...Winds and seas should generally stay below SCA criteria. However, gusty winds may be possible in the vicinity of any thunderstorms (primarily in the afternoon and evening hours). Rip Currents... Low risk the rest of Sunday and again low risk expected for Monday. Seas on the ocean will be mostly 2-3 ft with periods of 7-9 sec.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Johnson Near Term...Robertson/O`Hara Short Term...O`Hara Long Term...Johnson Aviation...Johnson/Robertson/O`Hara Marine...Johnson/O`Hara

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