Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211404 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1004 AM EDT Sun May 21 2017 .SYNOPSIS...
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High pressure from eastern Canada to New England will move offshore this afternoon. A cold front will move east into Mid-Atlantic states later Monday then stall just off the New Jersey and Delaware coasts Tuesday while weak high pressure spreads to our north. Low pressure will pass east of New Jersey early Wednesday. A cold front will cross our area Thursday, followed by a secondary cold frontal passage on Friday. High pressure will build across the southeastern United States, and ridge up into our area over the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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930 AM ESTF: raised temps inland a few degrees and lowered dewpoints with some adjusted wind speeds skycover due to reality and 12z hrrr blended with prior guidance. Lots of cloudiness today DE/MD e shore northward into e PA while NJ appears to enjoy the nicest weather. East to southeast wind gusting 15-20 mph this afternoon. Rain is expected to begin to move into the area close to midnight as the mid level vorticity max and the warm front get closer to the region. Precipitable water values will continue to increase through the overnight hours, and should be well above normal by late tonight. That, combined with a deep warm cloud layer, suggests that there is a risk for heavy rain. However, storm motions aren`t particularly slow, and there doesn`t appear to be much risk for training storms. These factors will limit a widespread flooding threat. However, if convection develops, localized flooding in poor drainage areas is possible. As for thunderstorms, some model soundings show very meager elevated instability through the later half of the night, primarily across Delmarva. Therefore, stayed close to the previous forecast with a slight chance of thunderstorms across Delmarva 08Z and later. Otherwise, expect showers across the region through the overnight hours.
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&& .SHORT TERM /MONDAY/...
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Monday...A wet day is in store for the region as a cold front approaches and moves through our area. Elevated instability looks good enough to maintain thunderstorms and we continue to mention this in the forecast throughout the day. Rain may be heavy at times, especially in convection, as precipitable water values remain near 1.25-1.75 through Monday with this possibly leading to some poor drainage flooding.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Monday night...Rain will end from west to east. The air doesn`t really get the chance to dry out behind the cold front and as a result there may some fog that forms late Monday night. Tuesday...This should be a fairly quiet day this week as we are somewhat in between systems. Expect much of the area to remain dry but there will remain a chance for some showers over Delmarva and southern New Jersey. Tuesday night through Thursday...There remains uncertainty with the respect to a potential coastal low developing during this week and the state of the deepening mid-level trough. The GFS is much more robust with these features developing and strengthening as it moves eastward and into the Mid-Atlantic. The ECMWF has a hint of a surface low developing but does not have the same organization as seen in the GFS and the mid-level trough appears to progress to the east slower. Impacts across our area, will vary based on just how strong this potential system becomes. One thing both of the aforementioned models agree on is that we will see more rain on Wednesday with some thunderstorms possible later Wednesday into Thursday. Friday through Saturday...Some showers possible Friday but a general clearing trend is expected as we head into the weekend. Warming is noted at 850mb and we should rise to near normal temps on Friday and then to above normal temps by Saturday.
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&& .AVIATION /14Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with CIGS aoa 4000 ft developing enewd. e-se wind may gust 15-20 kt this afternoon. Pls see TAFS for details. Tonight...VFR CIGS to start. By 06Z, expect rain showers to be moving into much of the region. With these rain showers, expect conditions to first lower to MVFR, and then IFR by 10z Monday. There is a slight chance of thunderstorms very late tonight, but it is too unlikely to include in the TAFs at this time. southeast wind. Monday...MVFR/IFR conditions expected in rain, heavy at times. Slight chance of thunderstorms. southeast to south wind. OUTLOOK... Monday night...MVFR/IFR conditions. Rain will end from west to east late Monday night. Fog possible Monday night. South to southwest will become north to northwest late. Tuesday and Tuesday night...mainly VFR conditions expected. North wind early will become more easterly through the day. Wednesday...VFR conditions expected early. MVFR/IFR conditions possible in showers. Thunder possible late. Light east to southeast winds. Thursday...VFR conditions expected with periods of MVFR/IFR in showers/thunderstorms. South to southwest winds.
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&& .MARINE...
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No change in the hazard grid at this time. SE wind may gust near 25 kt late this afternoon off DE. Monday...Winds may near 25 knots on the ocean with seas nearing 5 feet later in the day. A SCA may be needed. OUTLOOK... Tuesday through Thursday...Both winds and waves are expected to stay below SCA criteria. Rip Currents: Onshore wind and continuing easterly swell argues for a moderate risk for the formation of dangerous rip currents. Water temps this Sunday morning were highly variable along the coast...upper 50s to mid 60s. Todays safety message: during this pre Memorial Day weekend... if you`re a weak swimmer, swim with a strong swimmer and a flotation device nearby. Do not swim near piers and jetties where any rip currents tend to be stronger. Respect the power of water, and do not overestimate your swimming ability. Ocean surf swimming is quite different than swimming in the pool or lake. When departing the surf zone...be aware of incoming waves. Sometimes a much larger than expected wave can knock down a surf zone swimmer/walker, especially if your back is turned away from the ocean. The wave knock down-face plant can cause disabling upper extremity injury.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ454- 455. && $$ Synopsis...Meola/Drag 1004 Near Term...Drag/Johnson 1004 Short Term...Drag/Johnson 1004 Long Term...Meola Aviation...Drag/Johnson/Meola 1004 Marine...Drag/Johnson/Meola 1004

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