textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Severe Thunderstorm Watch #459 is in effect for the entire County Warning area until 11PM.

KEY MESSAGES

1. Dangerous heat and humidity will continue across the region through today. The heat will start to break Sunday and especially Monday.

2. Showers and thunderstorms are expected to impact the area late this afternoon into this evening and have the potential to produce severe weather and localized flash flooding. Additional rounds of showers and thunderstorms are expected Sunday and Monday with a continuing threat for both severe weather and flash flooding.

DISCUSSION

KEY MESSAGE 1...Dangerous heat and humidity will continue across the region through today. The heat will start to break for Sunday and especially Monday.

The strong ridging that has been dominating our weather pattern is finally starting to slowly break down as the surface high departs to the east. Even so temperatures remain hot as 925mb temps stay in the 28-30C range this afternoon. Surface temps have already warmed into the mid 90s to around 100 degrees, hottest along and southeast of the I-95 corridor. Substantial mixing has churned up the boundary later with dewpoints dropping into the mid 60s for most of the area which has lead to lowered overall Heat Index Values. Nonetheless, we continue to see extreme heat risk due to the cumulative nature of the extreme heat across the region.

The Extreme Heat Warning for our entire forecast area (excluding the New Jersey barrier islands) remains in effect through 8 PM this evening.

Notably cooler temperatures are expected across the region on Sunday, with high temperatures generally in the upper 80s across most of eastern PA and NJ, and low 90s for the urban corridor as well as Delmarva. However the cumulative impacts of the heat are still going to likely take a toll of the region. With dewpoints remaining in the upper 60s to mid 70s, with heat indices getting into the mid 90s to low 100s from the Philly metro and south. By Monday, with a frontal boundary draped across the area, much cooler temperatures are expected. Placement of the front is uncertain, but north of the front temperatures will likely only be in the mid 70s, and low to mid 80s to the south. South of the front where temperatures are still fairly warm, the forecast remains complicated by the potential for widespread showers and storms.

KEY MESSAGE 2...Showers and thunderstorms are expected to impact the area late this afternoon into this evening and have the potential to produce severe weather and localized flash flooding. Additional rounds of showers and thunderstorms are expected Sunday and Monday with a continuing threat for both severe weather and flash flooding.

Severe Thunderstorm Watch #459 is in effect for the entire County Warning area until 11PM.

The mid-level ridge over the area will continue breaking down this afternoon and evening as a mid and upper level trough pivots across eastern Canada. Strong vertical mixing has already set the stage with substantial instability across the region. The CU field is beginning to bubble up across to the south and towards the north showing that conditions for Severe weather are developing rapidly across the area. ML CAPE values are progged to once again reach 2000+ j/kg with increasing amounts of shear compared to Friday. 0-3/0-6 km shear values look to be upwards of 30/40 knots by later today. Steep low and mid-level lapse rates will result in very high DCAPE values already showing up on SPC's meso A website. Damaging winds will be the biggest threat but PWATs close to 2 inches will also support at least a localized flash flooding threat. The biggest change in the guidance was that we're expecting the storms to trigger maybe an hour or so later than initially forecast this morning with the main threat still in the 7 - 11pm time frame. We certainly can't rule out any isolated convection that develops ahead of the more significant forcing so the overall time of concern is from 3pm to 11pm. Heading into the overnight period, the threat of severe weather reduces however there is some signal of potential training of storms leading to heavy rainfall over the urban corridor. Will be paying very close attention to rainfall rates as flash flooding is an increasing concern.

On Sunday, the severe weather threat is generally anticipated to remain from mainly the Philly metro and points south, but this will be dependent on frontal placement. However, widespread showers and storms are also expected north of the front. In fact, model guidance is indicating PWATs potentially exceeding 2 inches, which is above the 90th percentile for this time of year and near the daily observed maximum. CAPE also looks to be tall and "skinny", another setup that favors heavy rainfall. Given these factors, rainfall rates in storms could exceed 1 to 2 inches per hour and it's possible storms may also train over the same areas. The WPC has continues to indicated a Slight Risk (2 of 4) for the I-95 corridor and points west both Sunday and Monday, with a Marginal Risk (1 of 4) for the remainder of the area. Storms could last into a good portion of the night Sunday night. The severe threat should diminish by the overnight but the flash flood threat may continue.

Unfortunately the aformentioned front is likely to remain stalled near the area Monday as an upper level trough approaches from the west. This will lead to additional widespread showers and storms. The severe weather threat looks to be lower by this time but the flash flood threat will remain elevated, especially since the same areas have the potential of being hit with multiple rounds of showers/storms over successive days.

Even into next Tuesday there could be more showers and storms before the front should finally push south of the area by Wednesday leading to the weather trending drier.

AVIATION /19Z SATURDAY THROUGH THURSDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Today...VFR overall. Risk of scattered showers/t-storms after 21z but better chances will arrive in the evening. Winds generally westerly increasing to 10 kts with some afternoon gusts up to 20 kts. Moderate confidence.

Tonight...Showers and storms likely to affect most TAF sites in the evening bringing brief restrictions to IFR along with the potential for strong wind gusts that could briefly exceed 40 knots. Showers/storms should largely be done by the overnight period but can't rule out some localized fog/mist forming.

Outlook...

Sunday through Monday night...Scattered to widespread showers and thunderstorms with sub-VFR conditions expected at times.

Tuesday through Wednesday...Primarily VFR. Isolated to scattered showers and storms will be possible, especially in the afternoon hours each day, which could lead to brief periods of sub-VFR conditions.

MARINE

Southwest winds 10-15 kt this afternoon, with some gusts up to 20 knots nearshore by mid to late afternoon with the increasing seabreeze. Some heavy showers and strong to severe storms could affect the waters this evening, leading to locally strong winds over 40 knots and reduced visibilities.

Outlook...

No marine headlines are currently anticipated through Wednesday, with winds below 25 kt and seas remaining below 5 ft. Relatively benign boating conditions are expected outside of thunderstorms. However, a cold front drops into the area then stalls and slowly weakens over the local waters. That front will be the focus for additional showers and storms possible each day through Tuesday, with activity being the most widespread Sunday afternoon/evening and again on Monday afternoon. Reduced visibility and strong winds remain possible with the strongest storms.

Winds back to the E-NE behind the front tomorrow afternoon and evening through midweek. This will build seas slightly Monday afternoon through Wednesday, especially north of Barnegat Light, though again remaining below 5 ft.

Rip Currents...

For Sunday, winds will be from the east around 10 mph with gusts up to 15 mph in the afternoon. Breaking waves will be around 1-2 feet or less. There will be a weak southeast swell with a period around 8 seconds. This results in a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore and at Delaware Beaches.

For Monday, winds remain east around 10 to 15 kt, with gusts to 20 kt in the afternoon. Resulting increasing NE wind wave could drive an elevated MODERATE Rip Current Risk along the Jersey Shore, with LOW risk persisting over the Delaware Beaches.

For specific beach forecasts, visit weather.gov/beach/phi

CLIMATE

The record breaking heat is forecast to continue across our area through today. Temperature records for our climate sites are listed below:

All Time Record High Temperatures

Site Record / Date Allentown (ABE) 105 / July 3, 1966 AC Airport (ACY) 106 / June 28, 1969 AC Marina (55N) 104 / August 7, 1918 Georgetown (GED) 104 / July 22 & 23, 2011 Mount Pocono (MPO) 103 / July 3, 1911 Philadelphia (PHL) 106 / August 7, 1918 Reading (RDG) 106 / July 22, 2011 Trenton (TTN) 106 / July 9, 1936 & July 22, 2011 Wilmington (ILG) 107 / August 7, 1918

All Time Record Warmest Low Temperatures

Site Record / Date Allentown (ABE) 79 / July 15, 1995 AC Airport (ACY) 84 / July 23, 2011 AC Marina (55N) 82 / July 21, 2019 Georgetown (GED) 84 / July 23, 2011 Mount Pocono (MPO) 76 / July 12, 1952 Philadelphia (PHL) 83 / July 24, 2010 & July 23, 2011 Reading (RDG) 81 / August 7, 1918 Trenton (TTN) 84 / August 11, 1895 Wilmington (ILG) 84 / August 7, 1918

Record Number of Consecutive 100+ Degree Days

Site Record / Date Allentown (ABE) 3 days / July 9-11, 1936 & July 2-4, 1966 AC Airport (ACY) 3 days / July 2-4, 1966 & July 22-24, 2011 AC Marina (55N) 1 day / Occurred multiple times Georgetown (GED) 2 days / Most recent June 24-25, 2025 Mount Pocono (MPO) 1 day / July 3, 1911 Philadelphia (PHL) 3 days / July 2-4, 1966 & July 8-10, 1993 Reading (RDG) 3 days / Most recent July 21-23, 2011 Trenton (TTN) 3 days / Most recent July 21-23, 2011 Wilmington (ILG) 3 days / Most recent July 9-11, 1936

Record High Temperatures July 4 Site Record / Year Allentown (ABE) 102 / 1949 AC Airport (ACY) 102 / 1966 AC Marina (55N) 99 / 1966 Georgetown (GED) 100 / 1966 Mount Pocono (MPO) 99 / 1911 Philadelphia (PHL) 103 / 1966 Reading (RDG) 100 / 1911 & 1966 Trenton (TTN) 99 / 1919, 1999, & 2010 Wilmington (ILG) 102 / 1966

Record Warmest Low Temperatures July 4 Site Record / Year Allentown (ABE) 75 / 1999 AC Airport (ACY) 75 / 1974, 1983, 1999, & 2002 AC Marina (55N) 79 / 2002 Georgetown (GED) 75 / 1999 & 2012 Mount Pocono (MPO) 70 / 2002 & 2013 Philadelphia (PHL) 79 / 1919 Reading (RDG) 78 / 1966 Trenton (TTN) 78 / 1966 Wilmington (ILG) 76 / 1999

PHI WATCHES/WARNINGS/ADVISORIES

PA...Extreme Heat Warning until 8 PM EDT this evening for PAZ054- 055-060>062-070-071-101>106. NJ...Extreme Heat Warning until 8 PM EDT this evening for NJZ001- 007>010-012>023-027. Heat Advisory until 8 PM EDT this evening for NJZ024>026. DE...Extreme Heat Warning until 8 PM EDT this evening for DEZ001>004. MD...Extreme Heat Warning until 8 PM EDT this evening for MDZ012- 015-019-020. MARINE...None.