Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211910 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 310 PM EDT Sun May 21 2017 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/...
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Rest of this afternoon...Clouds generally increase and thicken. Max temps generally several degrees below normal except 5 to 10 below normal far s NJ and the DELMARVA. East southeast winds continue gusting 15-20 mph. Tonight...models have been differing timing of onset of rain tonight. Am still unsure as we go to press, but since the HRRR is still very very late tonight, have followed. no certainty of .01 in ne pa so kept pops generally as previous but arrived at those pops a little slower. Looks like with the PWAT advection that the heavier showers may be occuring the Delmarva prior to sunrise. 09z/21 SREF modeled PWAT increases to 1.7" by morning Delmarva. Thunder remains in the fcst but low confidence of occurrence on the Delmarva and i could more easily easily see it not occur. Forecast basis was a 50 50 blend of the 12z/ 21 GFS/NAM MOS. LOWS normal to 5 degrees above.
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&& .SHORT TERM /MONDAY/...
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Monday...A wet morning-early afternoon is in store for the region as a cold front approaches and moves into our area during the afternoon. A little thunder maintained far south portion of the forecast area but not probable and so a low confidence part of the fcst. Model consensus is for the heavier rain to occur southeast of I95, near the path of any warm frontal wave of low pressure and closer to the better instability. PWAT 1.5 to 1.75 inches so a period or two of heavier showers and associated brief poor drainage flooding possible. This rainfall should lower flood guidance thresholds for mid week events. The DELMARVA and southern NJ should be able to handle 2 inches of rain in 6 hours Monday morning. Am expecting that nuisance poor drainage flood statements that impact travel will need to be issued sometime between 10z and 20z se of I-95. The afternoon may see very little rain along and west of I-95 but showers could break out again late in the day if it warms enough. Fog should develop in the light and moistened boundary flow off the ocean late in the day along the Atlantic coasts. Forecast basis was a 50 50 blend of the 12z/21 GFS/NAM MOS. These high temps may be several degrees too warm depending on on the persistence of showers through the afternoon. If it quits sooner, it would warm to our fcst values. For now the 330 Pm fcst temps indicate about 5 to 8 degrees below normal, 10 below near and north of I80 and only 2 below normal southern DE. Uncertainty regarding temps and how persistent the afternoon rain.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... 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. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...VFR CIGS aoa 4000 ft developing enewd through NJ. E-SE wind gusting 15-20 kt this afternoon. Pls see TAFS for details. Tonight...VFR CIGS to start. scattered showers develop between 02z-06z and then showers should become more widespread after 06z at which time MVFR conditions are expected, with IFR conditions possible toward 10z/22. There is a slight chance of thunderstorms very late tonight vcnty KMIV, but it is too unlikely to include in the TAFs at this time. southeast wind. Monday...MVFR/IFR conditions expected in bands of showers/developing stratus and maybe patchy fog. Rain may be heavy for a time during the morning-midday. Fog may be dense vcnty KACY after 21z/22. Slight chance of thunderstorms vcnty KMIV but not likely. 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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Probably extending the SCA hazard grids for the Atlc DE waters through midnight and then it may need a further extension thereafter. Its a marginal SCA. Elsewhere, isolated southeast wind gusts to 25 kt late this afternoon should subside this evening. Southeast wind tomorrow but wind and seas just below SCA criteria. 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...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ454-455.
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&& $$ Synopsis...Meola Near Term...Drag 309 Short Term...Drag 309 Long Term...Meola Aviation...Drag/Meola 309 Marine...Drag/Meola 309

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