Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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499 FXUS61 KPHI 042243 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 643 PM EDT Thu Jul 4 2024 .SYNOPSIS... High pressure will remain located offshore through Friday. Several waves of low pressure and weak fronts approach the area through Saturday, before a cold front crosses through the area on Saturday night. High pressure returns for Sunday and Monday before another low pressure system approaches the area around the middle of next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/... Showers and thunderstorms are moving through eastern Pennsylvania and will continue to track east into New Jersey going through this evening. Lightning is fairly limited, but with an unstable airmass over the area with 1500 to 2000 J/kg of SB CAPE and up to 1500 J/kg of MU CAPE. 0-6 km Bulk Shear up to 30 to 40 kt and PWATs are just over 2 inches. PoPs range from high chance over the western zones to low chance/slight chance over the far eastern and southern zones. 21Z HRRR showing convection dissipating over the next couple of hours, but that may be overselling it and storms should continue into midnight or so. The SPC has a MARGINAL risk (1/5) for severe thunderstorms extending east into SE PA and Delmarva. Water loaded downdrafts could lead to a few strong to locally damaging wind gusts. Given the shear, convection could exhibit some organization, though widespread severe convection is not expected. Also, WPC keeps most of our area in a MARGINAL risk for excessive rain as storms will be capable of producing very heavy rain which could lead to localized flash flooding, especially if storms set up over urbanized areas. Once storms taper off, a weak frontal boundary will remain draped across the region west to east over eastern PA into NJ and this will extend back to a new surface low developing over the midwestern states. Meanwhile weak impulses aloft will continue to move through in the upper level flow. For this reason there could be some additional showers and a few storms overnight...mainly over eastern PA into adjacent portions of NJ. It will otherwise be a very warm and muggy night as weak warm advection persists. Most areas won`t see lows getting below the low/mid 70s (except 60s over the higher terrain NW). Some areas of fog development are possible overnight, especially where appreciable rainfall occurs. Lingering smoke from evening fireworks will make for ideal cloud droplet nuclei in the very warm and humid environment with light winds, despite the broken cloud cover overnight. A very moist and warm to hot air mass will be in place for Friday with dew points well into the 70s, and high temperatures approaching or exceeding 90 in many spots. This will bring two main issues... 1, the excessive heat, with heat advisory remaining in effect starting Friday morning for I-95 corridor and Delmarva (now extended through Saturday) and 2, the thunderstorm risk due to increasing instability. We likely start out fairly dry, perhaps with patchy fog/low clouds, early Friday before some clearing brings quick warming to the low 90s for much of the area, mid 90s possible in Delmarva. With the high dew points, expect heat indices around I-95 to pass 100 and Delmarva to pass 105 in some spots. There isn`t a strong source of forcing for convection, but with all the heat and instability, along with the lingering weak front there will likely be some more scattered showers and storms developing for the afternoon into the early evening period, especially around and northwest of I-95 where we`ve placed the highest POPs. With plenty of moisture available, locally heavy rain is likely biggest concern, but with the available instability some isolated severe certainly looks possible. Shower and thunderstorm chances linger Friday night as a shortwave crosses the area, increasing forcing even as instability decreases. While severe/flood risks likely diminish a bit with loss of heating, will still need to be on guard after sunset for isolated problems. Otherwise, a steamy night with lows mostly in the 70s. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... A similar weather story is expected on Saturday as the extremely moist airmass continues. Although temps may be a degree or two cooler than Friday mostly due to cloud cover expected in the afternoon, dew points are anticipated to be at least 2-3 degrees higher. In addition, PWATs are expected to remain anomalously high in excess of the 95 percentile, which essentially tells the story itself. With this in mind, the two concerns for Saturday remain being the heat and the other being the thunderstorm potential with approaching cold front. In terms of the heat, it is forecast that highs will reach into the upper 80s to low 90s across much of the area. With dew points in the 74-77 degree range, this equates to heat indicies around or in excess of 100 degrees for most of the immediate I-95 corridor, with heat indicies around 105 degrees across the Delmarva. Heat indicies in the 90s are expected up across the Lehigh Valley and north Jersey. As a result, this warrants Heat Advisory criteria for the same areas as Friday in addition to Middlesex and Somerset Counties, which have been issued with this forecast update. In terms of thunderstorm potential, there isn`t too much forcing present as the front does appear to rather weak. Despite the moisture rich atmosphere, it doesn`t appear that there will be too much of a severe threat this go around which supports the thinking from the SPC of just a general thunderstorm risk for the region. The main concern should be in terms of heavy rainfall thanks to the the moisture-loaded atmosphere where any storm will be capable of heavy rain. As a result, the WPC has the eastern half of the forecast area in a Marginal Risk (Level 1/4) for excessive rainfall for Saturday and Saturday night. The cold front slowly crosses the area on Saturday night with drier air gradually filtering into the region in its wake. Overall, this should lead to a pretty nice day on Sunday under a mix of sun and clouds as high pressure builds in from the north and west. Although afternoon temps will reach into the upper 80s to around 90 degrees, it will feel a bit drier compared to Saturday as dew points fall into the mid 60s. Mostly clear skies are expected to continue into Sunday night as high pressure persists. Lows for Saturday and Sunday night will both be in the mid 60s to low 70s. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... High pressure remains in control through Monday with above normal temps continuing. A slight chance of a shower or thunderstorm may approach our western counties late in the day as the next weather system approaches toward the middle portion of next week. An upper trough will be located over the Great Lakes on Tuesday and Wednesday as some shortwave energy spreading east into our neck of the woods. Due to uncertainty of timing and spread amongst model guidance, heavily based the forecast on NBM guidance. This generally yields a 30-50% chance of showers and/or thunderstorms each day through Thursday. This is not an indication that any one day will be a washout, instead there will likely be some shower activity around each day as variability exists amongst current forecast guidance. Temps for the middle portion of the week are expected to remain seasonable to a few degrees above normal. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Through tonight...Scattered SHRA/TSRA may affect the terminals into 04Z or so, and restrictions are likely should a storm pass over a given terminal. Best chances for this look to be a RDG, ILG, PHL, PNE. Showers/storms diminish by the late evening however some areas of fog/haze and/or stratus development are possible overnight with MVFR restrictions. Winds diminish to around 5 kts or less, favoring a southerly direction. Overall lower than average confidence given the uncertainty regarding both the convection and timing/degree of overnight restrictions. Friday...Lingering restrictions in the morning should give way to period of VFR by around midday with further restrictions possible by later in the day due to more showers storms. South to southwest winds 5 to 10 knots. Moderate confidence. Outlook... Saturday through Saturday night...Sub-VFR probable with a chance of showers and thunderstorms. Locally gusty winds possible in thunderstorms. Sunday through Monday...VFR. No significant weather expected. Monday night through Tuesday...Sub-VFR conditions possible. A slight chance of a shower or thunderstorm. && .MARINE... No marine headlines anticipated through tonight. Southerly winds 10 to 20 knots with seas 2 to 4 feet. Scattered showers and thunderstorms possible during the evening hours, but otherwise fair weather is expected. Conditions should stay Sub SCA for Friday but by Friday night both winds and seas could approach Small Craft Advisory levels. Outlook... Saturday through Saturday night...SCA conditions likely due to seas around 4-6 feet. Winds are likely to remain below 25 kt during this period, however. A chance of thunderstorms possible. Sunday through Tuesday...No marine headlines expected. Winds are expected to remain below 20 kt and seas of 2-4 feet. Fair weather through Monday, with a slight chance of a thunderstorm on Tuesday. Rip Currents... Friday and Saturday...A New Moon will occur on Friday. Winds will be around 10-15 MPH out of the south both days, with an onshore component to the wind in some spots. There is a MODERATE risk for rip currents for Cape May, Atlantic, Ocean counties in NJ, and a LOW risk for Monmouth NJ and the Delaware Beaches. Breaking waves of 2 to 4 feet within the moderate risk and 1 to 3 feet within the low risk. For specific beach forecasts, visit weather.gov/beach/phi && .TIDES/COASTAL FLOODING... With the New Moon to occur Friday, some locations may see some spotty minor coastal flooding during the next few high tide cycles. With continuing S/SE flow and the approach of the New Moon, some guidance has areas of Cumberland County NJ seeing advisory minor coastal flooding with the upcoming evening high tide cycle. Though guidance may be running a bit high, a short-fused coastal flood advisory may be needed later on. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory from 10 AM Friday to 8 PM EDT Saturday for PAZ070-071-102-104-106. NJ...Heat Advisory from 10 AM Friday to 8 PM EDT Saturday for NJZ010-012-015>019. DE...Heat Advisory from 10 AM Friday to 8 PM EDT Saturday for DEZ001>003. MD...Heat Advisory from 10 AM Friday to 8 PM EDT Saturday for MDZ012-015-019-020. MARINE...None. && $$ SYNOPSIS...DeSilva NEAR TERM...Fitzsimmons/MPS/Staarmann SHORT TERM...DeSilva LONG TERM...DeSilva AVIATION...DeSilva/Fitzsimmons MARINE...Fitzsimmons/Hoeflich TIDES/COASTAL FLOODING...