Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 231021 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 621 AM EDT MON MAY 23 2016 .SYNOPSIS...
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Low pressure at the surface offshore and also in the upper atmosphere will influence our weather today through Tuesday. High pressure will then ridge across the area Tuesday night and Wednesday. A weak cold front will move towards the area Wednesday night. A few weak disturbances will keep unsettled summer like conditions for Friday and into the weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Another unsettled day is expected across our region, however a warmer day for most is also expected. This unsettled weather is courtesy of a large upper-level trough in the east, with a closed low centered to our south that pivots offshore during the course of the day. This closed low will drive another surface low east of the North Carolina coast. This surface low will help keep the winds out of the northeast overall. The forecast challenges today is the extent of the warming and the coverage/timing of showers and thunder. The day will start with fog in localized areas as the clouds have thinned in combination of light/calm winds and a moist low-level environment. This fog is expected to dissipate quickly early this morning. Some light showers will occur early this morning mainly across our south/southeast zones. Our attention then turns to the presence of the upper-level trough. There continues to be plenty of short wave energy revolving around it, however there appears to be a convergence area aloft on the west side of a thermal trough. This promotes lift with even the hint of a surface trough reflection this afternoon. The model guidance, including soundings, shows MLCAPE increasing to about 200-500 J/KG this afternoon. Given the colder air aloft with decent boundary layer heating, some low-topped thunderstorms should develop. This looks more likely across the interior and away from the cooler ocean influence. If the amount of instability is sufficient enough, then small hail cannot be ruled out with a few stronger cells. The showers/storms will tend to move from northeast to southwest given the steering flow. These may be slower moving as well and get some assistance from terrain circulations. We placed the highest pops (likely) from about I-95 on westward. As for the high temperatures, we used a GFS/NAM blend then made some local tweaks. We are expecting many areas to get into the 70s prior to the showers developing, although it will be cooler along the coast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... The center of the closed low is forecast to be slowly shifting to the northeast off of our coast. This will continue to take a surface low out to sea. The model guidance indicates that forcing may hang on for awhile tonight. This would result in showers and some thunderstorms to start the evening gradually weakening from west to east. An enhanced area of lift to the northwest side of the closed mid level center may result in an organizing area of showers across the eastern area for awhile tonight. As a result, the pops were increased to likely for a time. Any thunder should be confined to early in the evening as boundary layer cooling sets in which may be enhanced by rain-cooled air. Given the more potential for a period of enhanced lift across portions of our area in combination of convective cloud debris, there should be a decent amount of clouds around through the night. This would limit any fog formation and also slow the cooling trend. As a result, we used a MOS blend for the low temperatures but then adjusted them upward a little bit for most places. && .LONG TERM /TUESDAY THROUGH SUNDAY/... The last of the influences of the recent upper low across the Middle Atlantic region and northeast will be affecting our area during Tuesday. Pops were not changed much from earlier...in the chc range n/e and slgt chc range s/w. There will still be enough cold air aloft and sfc moisture to trigger a few showers or perhaps a isolated tstm across the area. Temperatures will be near normal with low/mid 70s in most areas. A period of drier weather and much milder temperatures is slated for Tuesday night into Wednesday Night. High pressure, rather weak, will move across the area. Afternoon maximum temperatures Wednesday will be in the 80s in most areas, except right along the shore and the highest elevations of the srn Poconos. A weakening cold front will try to push down from NY/NE later Thursday, and this could trigger a shower/tstm across the nrn/wrn parts of our region. Pops will be in the chc range for this feature.It`s possible that it could wash out and leave us with a drier day up north. This will be something to monitor over the next few days. Temperatures again summer-like in the low and mid 80s.Humidity levels Thu-Thu night will begin to increase and muggy conditions will be the result. Our area will remain just near enough to the storm track over the weekend to keep conditions rather unsettled. We will continue with slgt chc/small chc pops for mostly the nrn/wrn areas. Conditions will be summer-like with shower activity not lasting long, but in tstms they could yield some decent qpf. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...MVFR/IFR visibility due to fog early for a few terminals, otherwise VFR. Some light showers early this morning in the vicinity of KMIV and KACY. Additional showers are then expected mainly from about midday on, with the greatest chance from KTTN- KPNE/KPHL- KILG on westward. A few thunderstorms are anticipated as well. Given low coverage of thunderstorms, it was not included in the TAF`s, however a TEMPO group is carried for showers. Light and variable winds to start, becoming mostly northeast 4-8 knots then possibly becoming southeast toward evening. Tonight...Local restrictions due to showers or a thunderstorm in the evening, however the showers should be diminishing west to east through the night. Otherwise, mainly VFR. Light southerly winds overall, and if enough clearing takes place overnight then local fog should develop. outlook... Tue...mostly vfr but sct showers with lower cigs/vsbys psbl. Tue night thru Wed night...vfr. patchy fog psbl both nights. Thu thru Fri...mostly vfr. sct tstms mostly afternoon and early evening with restrictions psbl.
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&& .MARINE... The conditions early this morning are rather marginal for a Small Craft Advisory, as seas are in the 3-5 foot range on the Atlantic coastal waters. Low pressure offshore should increase the winds some today especially across the southern waters and this should build the seas some through the day. Overall the winds should remain below 25 knots, however will just keep the generic Small Craft Advisory going (extended to 15z up north to 04z southward). The conditions are expected to remain below advisory criteria on Delaware Bay. outlook... sub sca conditions expected thru the period. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ452>455. Small Craft Advisory until 11 AM EDT this morning for ANZ450- 451. && $$ Synopsis...O`Hara Near Term...Gorse Short Term...Gorse Long Term...O`Hara Aviation...Gorse/O`Hara Marine...Gorse/O`Hara

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