


Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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519 FXUS61 KPHI 071731 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 131 PM EDT Mon Jul 7 2025 .SYNOPSIS... Bermuda high pressure will remain in place offshore through the week. Chantal`s remnants will pass offshore of Delmarva this evening, then a few additional weak systems and a slow moving frontal boundary will impact the region through the remainder of the week. This will result unsettled conditions, with daily chances for showers and thunderstorms through much of the week. && .NEAR TERM /THROUGH TONIGHT/... A Flood Watch has been issued for the potential for flash flood across portions of the forecast area this afternoon. The well advertised tropical airmass has pushed into the region as the CIRA Advected PW plots show that the deep moisture plume is currently moving across New Jersey this morning. HIRES guidance is still struggling this morning dealing with the convection as the HRRR is about 3 hours late on the DelMarVa showers. Given the struggle overnight last night and the current underperforming of guidance, I anticipate were still on track to see the potential for flash flooding later today. The surge of moisture is expected to continue through the morning as the remnants of Chantal move into the region this afternoon. HREF LPMM guidance highlights the potential for DelMarVa and portions of central Jersey to see as much as 5+ inches of rain this afternoon. With PWATs forecast to be above the 90th percentile of climo, warm cloud depths quite high, light steering flow, and favourable upper level jet dynamics the potential for flash flooding is concerning. Hires guidance has been under performing on the convection from Chantal this morning across NC leading to the concern that guidance may even be underdone with respect to qpf totals for our areas. For the reasons mentioned above, WPC has also increase the ERO potential to a SLGT risk for flash flooding. With the increase in humidity and cloud cover, temps will be a few degrees cooler than yesterday however heat index values will be much higher with apparent temps getting close to 100 for the urban corridor this afternoon. Heading towards the evening hours, we`ll see an upper level trough start to dig into the region shunting the remnants of Chantal offshore. The surface front wont actually reach the area until Tuesday but it should act to bring the rain threat to an end this evening by around 10pm. The net impact will be another evening of overnight lows in the low to mid 70s in very muggy conditions. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Unsettled and active weather with tropical humidity will persist Tuesday through Wednesday. Tuesday still has the greatest potential for the most widespread showers and thunderstorms, although Wednesday will also see scattered showers and thunderstorms developing again. The showers and thunderstorms will be capable of producing locally heavy rainfall that could lead to flash flooding. The threat for flooding could be exacerbated by multiple rounds of rainfall over multiple consecutive days. There will also be a risk of locally damaging wind gusts with any stronger storms both days. Details follow below. Shortwave troughing will settle across the upper Midwest and Great Lakes regions Tuesday then slowly push closer toward the east coast through Wednesday night. This combined with a broad jet streak downstream will place our region locally in a persistent region of broad upper diffluence, which will be favorable for supporting multiple rounds of convection. At the surface, high pressure will be located offshore with south to southwest flow persisting through the period. The remnants of Chantal will be offshore by Tuesday, however its tropical environmental conditions will linger Tuesday and Wednesday thanks to the persistent warm/moist advection sourced from the Gulf. A slowly moving frontal boundary will settle into the area late Tuesday, then linger through Wednesday. This could act as a focusing mechanism for convection leading to flooding and severe threats. Tuesday and Wednesday will feature similar convective environments, although coverage of convection is anticipated to be greater on Tuesday. Cloud cover on Wednesday should help suppress coverage of convection somewhat, especially toward the north of where ever the subtle frontal boundary stalls out. PWats in the 1.8-2.3" range; tall, skinny CAPE on the order of 1500-3000 J/kg; and relatively low unidirectional effective shear near 15-20 kts could support training convection where any surface boundaries are in place. There won`t be much dry air to speak of for increased DCAPE, however steep low level lapse rates combined with water loaded downdrafts will yield a localized damaging wind threat with any stronger or more organized cells. So to summarize, a marginal severe environment, but more concerning is the heavy rainfall and flash flooding threat this setup will present. We`ll continue to monitor this potential closely in the coming forecast updates, but the main take away here is that we`re growing concerned about the potential impacts of multiple consecutive days of locally heavy rainfall and maringal severe risks. It will be a busy and active stretch of weather ahead this week. As for temperatures, Tuesday will be the hottest day of the short term period and hottest day of the entire week ahead with forecast high temperatures in the upper 80s to mid 90s in most areas. Dewpoints will be in the low to mid 70s, resulting in heat indices in the mid 90s (north) to mid 100s (south). Given the forecast and increasing confidence for heat indices around 100 degrees for the urban corridor and adjacent areas of central New Jersey and southeastern Pennsylvania, we`ve gone ahead with a Heat Advisory to highlight this threat for Tuesday. This advisory could need to be expanded south into far southern New Jersey and Delmarva (where criteria is 105 degrees) if confidence increases for heat indices near 105 degrees to occur. Wednesday will experience similarly oppressive humidity, especially south of the frontal boundary, however the cloud cover and coverage of convection should moderate temperatures compared to Tuesday with highs in the mid to upper 80s for most areas. The should keep heat indices below advisory criteria, however it will still be quite muggy and tropical feeling out there. Low temperatures will be in the upper 60s to mid 70s both nights and humid. && .LONG TERM /THURSDAY THROUGH SUNDAY/... The early week troughing to our west will push into our region and linger nearby to close out the week Thursday and Friday. This should yield below normal temperatures, though still with high humidity, and a continuation of daily chances of showers and thunderstorms. There is greater uncertainty regarding any impacts and threats from this activity though. At the surface, a backdoor cold front could push into the area as surface ridging tries to build across coastal New England Thursday, and especially by Friday. However, a lack of any real dry air advection will still leave humid and moist conditions in place during this period. Ultimately, this pattern will still support scattered showers and some thunderstorm potential, but details on any impacts remain unclear. What we do know is that temperatures will moderate some, with high temperatures in the upper 70s to mid 80s in most areas and lows in the 60s to low 70s. Even greater uncertainty for the forecast into next weekend as guidance begins to diverge significantly in solutions. Stuck with the NBM given the uncertainty, which includes chances of convection each day. However, confidence in this period is very low. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of Today...VFR conditions expected for the remainder of the afternoon. Showers and isolated thunderstorms expected mainly between 19Z-00Z for all terminals, included in TEMPO groups. VSBY/CIGS restrictions down to MVFR possible. Souhterly winds around 10 kt, with gusts up to 20 kt at KMIV/KACY. Moderate confidence. Tonight...Primarily VFR. Scattered mid-high clouds with a few low clouds possible. Southwest winds around 3-5 kt, becoming VRB/calm at times. High confidence. Tuesday...VFR expected for much of the day with sub-VFR conditions possible late in the afternoon as scattered thunderstorms move into the region after 19Z. Southwest winds around 5-10 kt with gusts up to 15 kt possible. Moderate confidence. Outlook... Tuesday night through Friday...VFR should generally prevail during the daytime periods with daily chances for thunderstorms, especially in the afternoon and evening hours. Areas of fog and low clouds with restrictions more probable at night. && .MARINE... No marine headlines in effect though this evening. Winds generally southerly 15-20 kt with seas increasing to 3-4 feet. Isolated showers and thunderstorms will be in an around the Delaware Bay during the morning and afternoon with the showers and thunderstorms eventually dragging east over the Atlantic waters this evening. Locally strong winds and seas will be possible in and around any thunderstorms. Winds and seas should be sub SCA criteria heading into the overnight hours. Outlook... Tuesday through Friday...Winds and seas are forecast to remain below advisory criteria. Daily chances of showers and thunderstorms. Some areas of fog possible at times. Rip Currents... For today, southerly winds will increase to 10-15 mph. Breaking wave heights increase to 3-4 feet with a primary SE swell around 1-3 feet and an 8 second period increasing to around 12-14 seconds during the afternoon. With the winds looking more onshore, have opted to increase the rip current risk to HIGH for dangerous rip currents from Cape May to LBI. Will maintain MODERATE for the easterly facing beaches across Delaware and Monmouth in NJ. For Tuesday, winds shift southwesterly becoming more alongshore flow around 5-10 mph in the morning increasing to 10-15mph in the afternoon. Breaking wave heights should be in the 2-4 foot range depending on beach orientation with a primary SE swell increasing to 4 feet at a 6-8 second period. Given the tides will be around low tide in the morning with the increase in swell, will maintain a HIGH risk for rip currents for the easterly facing beaches and MODERATE elsewhere. Rip currents occur often in the vicinities of jetties and piers and the speed of the currents are generally maximized at low tides. For specific beach forecasts, visit weather.gov/beach/phi && .HYDROLOGY... A Flood watch is in effect for Monday. A tropical airmass with precipitable waters in excess of 2" will persist over the region today. Slow moving steering flow and a tropical moisture will lead to highly efficient rainfall across the region. Basin wide rainfall totals are anticipated to be in the 1 to 2 inch range with the potential for up to 5 inches in heavier thunderstorms. Main stem river flooding is not anticipated but flash flooding of smaller streams/creeks and areas of poor drainage will be possible. Please heed any road closures and law enforcement instructions in case of flooding. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flood Watch until 10 PM EDT this evening for PAZ070-071- 101>106. Heat Advisory from 10 AM to 8 PM EDT Tuesday for PAZ070-071- 101>106. NJ...Flood Watch until 10 PM EDT this evening for NJZ009-010-012- 013-015>019-021. Heat Advisory from 10 AM to 8 PM EDT Tuesday for NJZ009-010- 012>023-027. High Risk for Rip Currents until 8 PM EDT this evening for NJZ024>026. DE...Flood Watch until 10 PM EDT this evening for DEZ001>003. Heat Advisory from 10 AM to 8 PM EDT Tuesday for DEZ001>003. MD...Flood Watch until 10 PM EDT this evening for MDZ012-015-019- 020. Heat Advisory from 10 AM to 8 PM EDT Tuesday for MDZ012-015- 019-020. MARINE...None. && $$ SYNOPSIS...Staarmann NEAR TERM...Deal/DeSilva SHORT TERM...Staarmann LONG TERM...Staarmann AVIATION...Deal/DeSilva/Staarmann MARINE...Deal/Staarmann HYDROLOGY...PHI