Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 180425 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1225 AM EDT Tue Jul 18 2017 .SYNOPSIS...
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An upper level trough will slowly move through the region through Tuesday. Weak high pressure will build into the region for Wednesday. A cold front will drop down from the north and slowly move through our area late Thursday through Friday before stalling to our south. The front will then move north as a warm front on Sunday followed by another cold front on Monday.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Showers and thunderstorms have tapered off across the local forecast area and model guidance showing few additional thunderstorms developing through the overnight. Temps have fallen off. With abundant low level moisture across the region, skies clearing out, and light winds, will expect patchy fog throughout. Lows will generally be in the 60s except in Philly metro and along the coast, were low 70s are possible.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... The overall pattern will not change much Tuesday. The upper trough will be weaker and will be crossing our area during the day. We do expect sct showers and tstms again Tue, but overall the coverage will be less than on Monday. We will have chc pops for the N/W areas and slgt chc elsewhere. High temperatures Tue will be in the mid to upper 80s across the area. Humidity levels, much like today or perhaps a bit more humid. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Tuesday night...convection will be winding down across the region, especially after sunset. A shortwave may cross the region overnight which would allow for some showers/thunderstorms to develop so keep a mention of a slight chance through Tuesday night. For the most part, we should be mainly dry across the region overnight. Some patchy fog may develop as low level moisture remains and we should see some breaks developing in the clouds. Wednesday through Thursday...High pressure will build into the area for Wednesday. The upper trough slides to the east during this time. A cold front will start to drop down from the north on Thursday. As the high builds in, we will see a return to more of a west to southwest flow, ushering in some hotter, moister air to the region. With 850mb temperatures back into the 18-19C rang, we will see highs creep back up into the upper 80s to lower 90s by Wednesday and then into the low to mid 90s for Thursday. Increasing moisture will also mean increased humidity across the area. Seems reasonable that some showers and thunderstorms may develop during the afternoon and evening on both days but location of activity is too difficult to pinpoint this far out. Additionally, with not much flow at the surface, storms may be slow movers and efficient rain producers, leading to flash flooding. Again, too hard to pinpoint any exact locations at this juncture. Heat index values look to fall below 100F through the midweek period but may get close. Friday...Friday may still be pretty hot out but with a cold front dropping down through the region, we should start to feel some relief from the humidity, especially to the north and west of the I-95 corridor. Areas to the south and east of I-95 may still have a hot and humid day to contend with but relief will come later in the day for those areas. Temperatures on Friday will be in the upper 80s to lower 90s across the forecast area with some low to mid 80s across the Poconos and parts of northwestern New Jersey. Saturday through Monday...Another stretch of unsettled weather as several fronts move through the region during the weekend. A chance for some showers and thunderstorms seems likely each day. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. The potential for low clouds and/or fog continues through the overnight. Thanks to onshore low level flow low stratus will move in at times over the Coastal Plains (highest risk for KILG, KMIV, and KACY, but also possible at KPHL, KPNE, and KTTN). There is poor model guidance as to when and how low the ceilings will be. Unfortunately, high cirrus clouds from the earlier convection are masking the extent and location of low clouds now, adding to the uncertainty with timing. For now, have gone with the climatologically favored time of 10 to 15Z, and kept the ceilings at least at MVFR. However, IFR ceilings are possible. In addition, fog will be possible, primarily at locations that had heavy rain today or at locations where the low stratus may be delayed. This may include KABE, KRDG, KMIV, and KACY. As with the stratus, kept visibilities no lower than MVFR though localized IFR is possible. Tue...Low clouds/fog should dissipate by 15Z. Otherwise, expect mid level cumulus to develop and persist through the day time hours. There is a chance for afternoon showers and thunderstorms across the region, though the highest chances are expected to be west of the Delaware Valley (including KRDG and KABE). At this time, coverage is expected to be too limited to mention in the TAFs this far out. OUTLOOK... Tuesday night through Thursday...Mainly VFR conditions expected. Afternoon showers and thunderstorms with MVFR or lower conditions possible. Southerly winds around 10 knots or less...becoming westerly on Thursday. Friday...Mainly VFR conditions expected. West to northwest winds around 10 knots or less. Saturday...Mainly VFR conditions expected. Afternoon showers and thunderstorms with MVFR or lower conditions possible.
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&& .MARINE... Low pressure inland and high pressure offshore will continue to produce a generally S to SE flow over the waters tonight and Tuesday. Wind speeds will increase somewhat through the evening, but should remain sub-SCA conditions thru the period. Seas will be mostly 2-3 ft on the ocean. Widely sct showers and tstms are possible tonight and Tuesday. OUTLOOK... Tuesday night through Saturday...Sub-Small Craft Advisory conditions are expected on the area waters through Saturday. Locally strong winds will be possible in the vicinity of any thunderstorms. RIP CURRENTS... Thanks to a slight onshore flow, and an underlying long period swell, there is a moderate risk for the formation of dangerous rip currents along the New Jersey shore on Tuesday. For the Delaware Beaches, winds are expected to be slightly off shore, leading to a continued low risk for the formation of dangerous rip currents. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Meola Near Term...MPS Short Term...O`Hara Long Term...Meola Aviation...Johnson/Meola/O`Hara Marine...Johnson/Meola/O`Hara

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