Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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140 FXUS61 KPHI 272030 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 430 PM EDT Thu Jun 27 2024 .SYNOPSIS... High pressure builds in from the north and west before sliding offshore by Saturday. A warm front lifts north through the region on Saturday, followed by a cold front on Sunday and Sunday night. High pressure returns for the start of the new work week before departing by the middle of next week. && .NEAR TERM /THROUGH FRIDAY/... A secondary cold front will move across the area this afternoon into this evening, then high pressure to our west will move to our north overnight as it shifts eastward. Winds will shift to the north the northeast overnight, an drier/cooler air will move in as well. Temperatures overnight will end up being close to or slightly below normal. The stratocumulus clouds from today will dissipate later this evening into the overnight hours for much of the area and be replaced by high level clouds, although southern New Jersey, southern Delaware, and southern Maryland could hold on to the lower clouds longer. On Friday, the high to our north will shift offshore, and winds will shift from northeast, to east, then southeast through the day. Temperatures will remain near or slightly below normal or one more day. Mostly sunny to partly cloudy skies are expected, and no rain is expected. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... Unsettled conditions on tap for the weekend. Heat and humidity return, and there is the potential for convection. Quiet conditions Friday night with increasing low level moisture as surface dew points rise into the low to mid 60s. Fairly warm with lows in the low to mid 60s, and in the upper 60s in the more urban areas. Patchy fog may develop as well, but that is far from certain. Low pressure moves from the Great Lakes into the Province of Quebec on Saturday. Ahead of this low, a warm front will approach from the west. However, most of the 12Z suite of guidance has slowed the approach and passage of this front from Saturday afternoon to more Saturday night. During the day, highs will be in the mid to upper 80s and with increasing southerly flow due to a tightening pressure gradient between the approaching front and the offshore high, surface dew points will rise through the 60s. This results in max heat index values generally in the lower 90s, though the highest heat index values will be across the southern portions of the forecast area. Warm front lifts north through the region Saturday night. Showers and thunderstorms develop late in the afternoon, mainly in the far western zones, and then continue through the overnight. With PWATs well in excess of 2 inches, possibly even approaching 2.5", showers will be capable of heavy rainfall. With the slower approach of the warm front, and storms developing at night, the lack of daytime heating may be a limiting factor in the severity of thunderstorms. MU CAPE values will be up around 500 J/kg, and 0-6 km Bulk Shear will range from 30 to 40 kt. DCAPE values may rise to 500 to 1000 J/kg by daybreak Sunday, but the bulk of the activity may be over by then. Widespread flash flooding may be limited by shear in the 30 to 40 kt range, given that storms may be moving fairly quickly. Uncomfortably warm and humid otherwise Saturday night with lows generally in the 70s, though not much below 80 for the urban corridor from Philadelphia to Wilmington and also into Delmarva. Hot and humid ahead of an approaching cold front on Sunday, though it will be the humidity that pushes up heat index values as opposed to the heat. High temperatures are expected to be in the upper 80s to low 90s. In most cases, those temperatures are quite warm and can be borderline hot, but surface dew points will be well in the 70s, resulting in max heat index values in the upper 90s to around 100, and even a few spots in southern New Jersey and Delmarva may get close to 105. Low pressure over the Province of Quebec tracks east and departs, it will drag a cold front through the region Sunday afternoon. Ahead of this front, a pre-frontal trough develops and should trigger another round of showers and thunderstorms will develop in the afternoon and evening. With peak heating of the day and abundant low level moisture, there is the potential for severe thunderstorms, as well as another round of heavy rain. Confidence is low, though, because model trends seem to have this trough passing through the region ahead of any upper level support. Both the 12Z NAM and the 12Z GFS seem rather stingy with QPF in the 18Z Sunday to 00Z Monday timeframe, but this seems unlikely given the setup ahead of the trough and front. Will continue to carry likely PoPs for most of the area, and chance PoPs for the southern Poconos and Lehigh Valley. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Cold front then slowly works its way south through the region Sunday night, and showers and thunderstorms will taper off from west to east. Rain may continue to be heavy at times, especially in the first part of the night, and could result in localized flooding. A drier airmass spreads into the Northeast and Mid- Atlantic with surface dew points dropping from the upper 60s and low 70s Sunday evening to about 10 degrees lower by daybreak Monday. The first half of the new work week look to be mild and pleasant with low humidity levels. High pressure over the Great Lakes on Monday will be right over the local area on Tuesday, and then offshore by Wednesday. Highs will generally be in the lower 80s on Monday, before warming into the mid 80s on Tuesday, then into the upper 80s on Wednesday. Temperatures will also be about 10 degrees cooler in the mountains and along the coasts each day. In addition, surface dew points will generally be in the 50s on Monday and Tuesday before rising into the low 60s on Wednesday as return flow sets up behind the departing high. A nice run, compared to the recent heatwave. The trend for Thursday is for a return to the heat and humidity with temperatures back in the upper 80s to low 90s and dew points in the 60s to near 70. An approaching frontal system may touch off some afternoon and evening showers and thunderstorms. && .AVIATION /21Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of Today...Stratocumulus clouds will continue through today with VFR conditions expected with bases around 4,000 feet. Northwest winds 5 to 10 kt, with occasional gusts 15-20 kt in the afternoon are expected. A sea breeze may develop around 21-23Z and turn winds more south-southwesterly at KACY and possibly KMIV. High confidence Tonight...VFR. Northwest winds 5-10 knots, shifting to north- northeast this evening and overnight. High confidence. Friday...VFR. Northeast winds 5-10 knots, shifting to the east after day break, then shifting to southeast by the afternoon. High confidence. Outlook... Friday night...VFR. Saturday through Sunday night...SHRA/TSRA will result in sub- VFR conditions. VSBY restrictions in fog possible Saturday night. Conditions improve late Sunday night. Monday through Tuesday...VFR. && .MARINE...
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Tonight-Friday...Conditions are expected to remain below advisory levels through Friday. However, there could be occasional gusts near 25 knots offshore of the central and southern New Jersey waters late tonight. Outlook... Friday night...Sub-SCA conditions. Saturday through Sunday night...SCA conditions likely. Showers and thunderstorms Saturday afternoon and evening, then again Sunday afternoon and evening, may produce locally strong wind gusts and VSBY restrictions in heavy rain. VSBY restrictions in fog also possible. Monday...SCA conditions possible for occasional 25 kt wind gusts. Tuesday...Sub-SCA conditions. Rip Currents... Friday...Northeast winds in the morning becoming east-southeast winds in the afternoon around 10-20 mph. Breaking waves of 2-3 feet for all beaches. Due to an onshore component of the wind, have maintained a MODERATE risk for the development of dangerous rip currents for the New Jersey and Delaware beaches. Saturday...Southeast winds around 15-20 mph with breaking waves around 2-3 feet at all beaches. Due to similar wind and wave conditions compared to Friday, have opted to continue with a MODERATE risk of rip currents for both the New Jersey and Delaware Beaches on Saturday. For specific beach forecasts, visit weather.gov/beach/phi
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...MPS NEAR TERM...Robertson SHORT TERM...MPS LONG TERM...MPS AVIATION...MPS/Robertson MARINE...DeSilva/MPS/Robertson