Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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167 FXUS61 KPHI 282237 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 637 PM EDT SAT MAY 28 2016 .SYNOPSIS...
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A Bermuda high will maintain very warm weather with generally southwest winds over our area through Monday. Low pressure associated with Tropical Storm Bonnie should remain well to our south. However, moisture from this system will be drawn northward Sunday into Monday. High pressure will build in Tuesday through Thursday, then a frontal system is forecast to approach from the west late in the week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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High pressure anchored well off the Mid Atlantic coast will continue to dominate our weather through tonight. The combination of ample heating and enough moisture and instability has resulted in some convection across portions of northeastern Pennsylvania and northern New Jersey. This was initiated mostly by terrain, as earlier visible satellite imagery showed towering cumulus over the ridges. The flow is light and therefore the convection has been slow moving with some earlier backbuilding with pulsing updrafts. There is now a gradual downward trend in the intensity, and the remaining activity is expected to rain itself out eastward early this evening. Locally heavy rain has resulted from this slow moving convection. Otherwise, clear to partly cloudy through the night with the potential for local fog to develop. This may have the most opportunity where rainfall occurred across the far northern areas. Otherwise, it will be a warm night. The temperature and dew point grids were adjusted based on the latest obs, then the lamp/lav guidance was blended in. The pops have been adjusted based on radar trends.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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Sunday will start out dry, but moisture associated with Tropical Storm Bonnie will move northward during the day. Across the southern areas, showers could move in late morning to early afternoon, but most areas will hold off until later in the afternoon. The northern areas may remain dry through the balance of the day. Once the showers start, some locally heavy rain may occur given increasing PW values especially across the Delmarva. Given the idea of some more cloudiness, temperatures are forecast to be a bit cooler.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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It looks like the most significant weather will be occurring at the beginning of the long term period, i.e., Sunday night into Monday. At that time rather deep moisture, PWAT up to 2 inches, from Tropical Storm Bonnie is forecast to move across the area with widespread showers and T-storms. Although CAPE and UVV seem to be rather limited, believe some areas could see 1 to 2 inches, depending on how the convection sets up. Locally higher amounts are possible. Heaviest rain should occur overnight Sun night into Mon morning, then shift SE and gradually decrease through afternoon and evening of Memorial Day. The pattern changes some from Mon into Tue/Wed as the upper trof currently over the central US lifts NE and suppresses the East Coast upper ridge. This results in more westerly winds and drier air. However, some remnants of the tropical circulation are forecast to remain invof east NC through mid-week and could result in some showers well S of PHL. This is rather uncertain and is not strongly represented in the PoP/Wx grids. Surface high pressure is forecast to build SE out of Canada and across New England by Wed. This will result in onshore flow with slightly cooler (but near normal) daytime temps and somewhat higher RH. Another shortwave trof and associated frontal system is forecast to approach the area on Fri/Sat. The latest GFS and ECMWF are somewhat similar with this feature although the GFS is a bit more amplified. The forecast reflects increased chance for showers and diurnal T-storms for this time.
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&& .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Lingering showers and thunderstorms north/northeast of KABE dissipating this evening, otherwise VFR overall. However, some fog should develop at most terminals overnight resulting in MVFR visibilities. It is possible local IFR occurs, however confidence is not high. Southerly winds diminishing to 5 knots or less. Sunday...MVFR/IFR visibilities to start for some terminals due to fog, otherwise mainly VFR. Clouds increase from south to north as moisture from Tropical Storm Bonnie moves northward, with ceilings nearing MVFR toward evening for some areas. While some showers or thunderstorms should develop especially in the afternoon, these may be mainly west and south of KPHL. South to southwest winds up to 10 knots, although turning south-southeast at KACY, KILG and KMIV. OUTLOOK... Sunday Night and Monday...MVFR to IFR conditions are likely in low clouds, fog, and +SHRA. Sustained winds mostly under 10 kt. Tuesday through Thursday...Mainly VFR conditions. Sustained winds mostly under 10 kt, with some daytime gusts 10 to 15 kt.
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&& .MARINE...
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No marine headlines are anticipated during the near and short term periods. OUTLOOK... Sub-SCA conditions are expected through early to mid-week. Some reduced VSBYs are possible in rain and fog Sun night through Mon night.
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&& .HYDROLOGY...
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There is some potential for heavy rain and localized flooding from Sunday night through Monday. This is due to an influx of tropical moisture from Tropical Storm Bonnie. PWATs are forecast to be near 2 inches, well above normal for late May. Depending on how the heavier showers and t-storms set up, some locations could receive 2 inches or more of rainfall. This may result in localized flooding. The potential for heavy rain was added to the forecast.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...AMC/Gorse Near Term...Gorse Short Term...Gorse/Nierenberg Long Term...AMC Aviation...AMC/Gorse Marine...AMC/Nierenberg Hydrology...

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