Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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729 FXUS61 KPHI 051038 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 638 AM EDT Fri Jul 5 2024 .SYNOPSIS... High pressure will remain located offshore today. 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 TONIGHT/... A weak frontal boundary remains draped across the region west to east over eastern PA into NJ and extends back to a new surface low developing over the midwestern states. This boundary will likely lift north into the I-78 to I-80 corridors by this afternoon. Meanwhile weak impulses aloft will continue to move through in the upper level flow. It will remain a warm and muggy morning as weak warm advection persists. Some areas of fog and low stratus development that has occurred this morning will gradually scatter out through 10-11 AM or so, though some fog may persist near the immediate coast much of the day. A very moist and hot air mass will be in place for today with dewpoints well into the low to mid 70s, and high temperatures in the low to mid 90s along and south of I-78 (and away from the immediate coasts). This will bring two main issues... 1, the excessive heat, with a Heat Advisory remaining in effect starting late this morning through Saturday for southeast PA, portions of central and southern NJ, and Delmarva; and 2, the thunderstorm risk due to increasing instability. We`ll start out dry, with some areas of fog/low clouds early. Clearing this afternoon is now anticipated to be a bit better than previously forecast, plus convection should be more isolated in nature (and confined mainly north of I-78, more on that below). This ultimately prompted the expansion of the Heat Advisory to several adjacent zones. With the high dewpoints, expect heat indices in the Heat Advisory area ranging from around 100 to 104 degrees in PA and NJ, and ranging from 105 to 108 degrees in Delmarva. While synoptic forcing remains weak today, the heat and instability, along with the lingering weak boundary across the northern tier and a weak mid-level shortwave trough passing just to the north in the afternoon should be sufficient in initiating some convection near/north of I-78. The highest PoPs are thus in this area during the daytime period today, and PoPs elsewhere were lowered significantly. With plenty of moisture available and PWats over 2.0" again, locally heavy rain is likely biggest concern, but with the available instability some isolated severe certainly looks possible. Water loaded downdrafts leading to microbursts and locally damaging wind gusts area possible with the strongest cells. Shower and thunderstorm chances linger tonight as another more pronounced 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 impacts from heavy rain and gusts winds if any more robust cells materialize. Have maintained generally 30-40% PoPs overnight. Aside from the overnight convection potential, it will be a very warm and muggy night. Forecast low temperatures will be largely in the mid to upper 70s within the Heat Advisory area, and in the low 70s elsewhere. Some areas of fog and/or low stratus development are possible again, favoring any locations that experience appreciable rainfall. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Saturday will be the most active day of the short term for sure, with the hot and humid air mass still in place and the cold front approaching from the northwest. This should result in another heat advisory day with heat indices of 100-105 overall, along with a pretty good chance of showers and storms in the afternoon as the front approaches and instability peaks. Still expect the main threat to be locally heavy rain with storms but isolated severe storms can`t be ruled out given the high CAPE. Guidance has gotten slower with the frontal progression compared to 24 hours ago, meaning temps look hotter (hence more confidence in a heat advisory) and potential for showers and storms to linger across areas southeast of I-95 into Sunday. The front actually looks like it completely washes out during the day Sunday as it stalls over the area, though dew points do drop several degrees back into the 60s. However, highs on Sunday look just as hot as Saturday, with low 90s common and a few higher spots. But, given the lower dew points, do not expect a need for another heat advisory on Sunday. In between, Saturday night will be sultry with lows mostly in the 70s, but Sunday night should be a little more comfortable, with 60s more common and mostly dry conditions expected. && .LONG TERM /MONDAY THROUGH THURSDAY/... High pressure will try building a bit more into the area on Monday but with the front washing out nearby, there could still be some spotty convection later in the day or evening. Heat indices will approach, but right now don`t look to reach, advisory levels, but highs will be in the lower 90s again. Beyond Monday, uncertainty reigns regarding the progression of a low pressure system which will reach us on Tuesday. Clouds and showers/storms look more likely across the region for Tuesday, and if the system is fast enough, we might actually try to dry out on Wednesday before the front and summertime humidity creeps back north for Thursday. GFS suggests this solution. ECMWF is a little slower, keeping activity around on Wednesday but drying us out Thursday. So, that all having been said, kept chance POPS thru midweek, but right best odds of storms appears to be Tuesday night. Heat will step downward as the system slowly moves through, so that by late week we should stay mostly in the upper 80s. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Through 14Z...MVFR to IFR conditions in fog/stratus are anticipated to develop, especially at RDG/ABE/TTN where rainfall occurred earlier. For the remaining terminals, could end up being more stratus rather than fog. Winds around 5 kts or less, favoring a southerly direction. Overall lower than average confidence given the uncertainty regarding timing/degree of overnight restrictions. Today...Any lingering restrictions will scatter out by 14-15Z, then VFR. SSW winds increasing to 5-10 kts. Some SHRA/TSRA development possible (20-30% chance for I-95 terminals, 40-50% chance for RDG/ABE). Greatest chance for TSRA will be at ABE, where a PROB30 ground has been included. High confidence in prevailing VFR conditions following any morning restrictions. Tonight...Initially VFR, however some areas of fog and/or stratus development are possible again with MVFR restrictions. Some isolated showers anticipated between roughly 00-09Z with thunder possible (20% chance). Winds diminish to around 5 kts or less, favoring a southerly direction. High confidence in initially prevailing VFR conditions, but low confidence on the occurrence and timing of any restrictions in fog/stratus/showers overnight. Outlook... Saturday through Sunday...Mainly VFR, with intervals of IFR possible due to low clouds/mist and a chance of TSRA. Sunday Night through Monday night...VFR with a slight chance of TSRA. Tuesday...Mainly VFR, with intervals of IFR possible due to low clouds/mist and a chance of TSRA. && .MARINE... Southerly winds increasing into the afternoon to around 15-20 kts, with gusts near 25 kts at times across the Atlantic waters. Seas building to 4-6 feet into tonight. Areas of fog near the immediate coast line should diminish through midday, though it may linger in some spots for much of the day. Scattered showers and thunderstorms possible during the overnight hours, but otherwise fair weather is expected. A Small Craft Advisory has been issued beginning at 2 PM through Saturday for all Atlantic coastal waters. Outlook... Saturday...SCA Conditions expected, with wind gusts to 25 kt and wave heights up to 6 feet. Chance TSRA. Saturday Night...Mainly sub-SCA Conditions expected, with localized SCA possible. Wind gusts to 20 kt. Wave heights up to 5 feet. Chance TSRA. Sunday through Tuesday...Sub-SCA. Winds less than 15 kts. Wave heights up to 4 feet. Slight chance TSRA, mainly Sunday and Tuesday. Rip Currents... Today and Saturday...A New Moon will occur today. 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 the Jersey shore, and a LOW risk for 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 today, 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. && .CLIMATE... Near record breaking warmest low temperatures are forecast on Saturday. Records for our climate sites are listed below: Record Warmest Low Temperatures July 6 Site Record/Year Allentown (ABE) 74/1999 AC Airport (ACY) 76/1999 AC Marina (55N) 80/1999 Georgetown (GED) 78/2012 Mount Pocono (MPO) 71/1999 Philadelphia (PHL) 79/1999 Reading (RDG) 75/1934 Trenton (TTN) 76/1999 Wilmington (ILG) 77/1999 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for PAZ060>062-070-071-101>106. NJ...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for NJZ009-010-012-013-015>020-027. DE...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for DEZ001>003. MD...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for MDZ012-015-019-020. MARINE...Small Craft Advisory from 2 PM this afternoon to 6 PM EDT Saturday for ANZ450>455. && $$ SYNOPSIS...DeSilva NEAR TERM...Fitzsimmons/Staarmann SHORT TERM...RCM LONG TERM...RCM AVIATION...DeSilva/Fitzsimmons/RCM/Staarmann MARINE...Hoeflich/RCM/Staarmann TIDES/COASTAL FLOODING...Wunderlin CLIMATE...Staarmann