Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190321 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1121 PM EDT Tue Apr 18 2017 .SYNOPSIS...
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A ridge of high pressure extending from the lower St. Lawrence Valley southwest to the mid- Atlantic Coast tonight will shift offshore and gradually weaken through Wednesday and Thursday. Low pressure will move east across the Great Lakes and into the Northeast on Thursday and Friday, with a trailing cold front to cross the mid-Atlantic on Friday. Weak high pressure on Saturday will gave way by Sunday to a storm system approaching from the Ohio Valley. Although the storm center is forecast to remain to our south, it will bring a good chance of rain for Sunday and Monday of next week.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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11 PM: No change in the fcst anticipated at this time. Low clouds over LI at 03z are modeled by the 00z/19 NAM to spread wnw along and n of I80 overnight. Patchy fog may yet form elsewhere. Otherwise an ordinarily fair quiet night is in progress with a light southeast wind. Lows near normal. Wednesday...A partly sunny start probably gives way to overcast midday or afternoon. There may be an afternoon sprinkle in the northern part of our forecast area? Max temps a few degrees cooler than what occurred Tuesday, near normal, due to cloud cover. We do note this 00z/19 NAM cycle has increased its modeled temps. This part of the 330 AM Wednesday forecast will probably be a 50 50 blend of the 00z/19 GFS/NAM MOS unless otherwise noted in a later AFD update.
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&& .SHORT TERM /WEDNESDAY NIGHT/...
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Mostly cloudy. Stratus should develop by midnight over parts of eastern PA and develop sewd to near I95. Instability aloft is increasing and there may be a few showers near and N of I-80 late at night. Lows will be milder...10 to 15 degrees above normal. Light south to southwest wind. This part of the 330 AM Wednesday forecast will probably be a 50 50 blend of the 00z/19 GFS/NAM MOS unless otherwise noted in a later AFD update.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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The long term period starts out with sfc high pres off the coast and a S to SW flow around it. There is low-level WAA over the area ahead of a weak frontal boundary approaching from the north. Weak ridging is noted aloft with weak impulses in the westerly flow. For Thu the forecast maintains chances for showers mainly N of PHL, and also some sct t-storms Thu afternoon. Some instby may develop attm in an increasingly moist and unseasonably warm air mass. For Thu night and Fri...a fairly strong shrtwv trof moves E through the GrtLks with an assocd sfc cold front moving E through PA Thu night. The front should move through NJ and vcnty during the day on Friday, although models seem to indicate that most forcing for UVV remains N of PA. In spite of the frontal passage, max afternoon temps are fcst to reach the mid 70s to around 80, before cold advection picks up behind the front. Fair weather is expected for Saturday with weak high press building in and the frontal boundary well to the south. However clouds may increase late in the day as another low press develops over the lower MS valley. This system is expected to spread rain back into the area from the SW on Sat night and through Sun into Sun night. However the brunt of the system looks like it will remain to our south, and there should be a gradual improving trend on Mon and Tue as it slowly pulls away into the Atlantic.
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&& .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 12z Wednesday...VFR with a light s-se wind. Patches of cigs 500-1500 ft developing now in DE may become more widespread after 09z. After 12z Wednesday...After any early day clouds/cigs 500-1500 ft dissipate...VFR with cigs near 10000 ft developing midday or afternoon and lowering late in the day. Southeast wind may gust 15 kt. Wednesday night...VFR cigs with probable cigs 500-1500 ft developing late over eastern PA (KRDG/KABE)...possibly to KPHL toward 10z Thursday. Light south wind. OUTLOOK... Thursday...Possible MVFR or IFR st/fog to start. Otherwise mainly VFR, but variable brief IFR conditions in scattered showers and thunderstorms. Southwest wind. Friday...Mainly VFR cigs with variable brief IFR conditions in st/fog/showers ending during midday. Becoming VFR sct-bkn aoa 5000 ft during the afternoon as a southwest wind in the morning shifts to northwest...gusts 20 kt. Friday night and Saturday...Mainly VFR conditions expected. Northwest to north winds. Saturday night and Sunday...VFR conditions Saturday evening becoming MVFR/IFR on Sunday in widespread showers and fog. East to northeast winds.
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&& .MARINE...
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No headlines anticipated with a general southeast flow through Wednesday...gusting 15-20 kt. Winds turn south Wednesday night and then southwest by dawn Thursday. OUTLOOK... Thursday and Thursday night...Sub-advisory conditions expected. Seas 2 to 4 feet with south to southwest winds around 10 knots. Fog may develop. Friday...Seas will build on Friday and may be near 5 feet on the ocean. Saturday...Seas may be near 5 feet on the outer edges of the ocean zones early but will be diminishing through the day. Sunday...SCA conditions are possible with east to northeast winds and seas building to 6 feet or higher.
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&& .CLIMATE...
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We will update the post at 5am Wednesday regarding a continued top 10 warmest April projection.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...AMC Near Term...CMS/Drag 1120 Short Term...Drag 1120 Long Term...AMC Aviation...AMC/Drag 1120 Marine...AMC/Drag 1120 Climate...1120

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