textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Severe Thunderstorm Watch #448 has been cancelled.

Confidence has increased in potential flash flooding impacts across portions of the area on Sunday and Monday. Otherwise, the forecast remains in track.

KEY MESSAGES

1. Dangerous heat and humidity will continue across the region through Saturday. Record high temperatures could be challenged again Saturday

2. Daily chances for showers and storms continue into early next week. Some severe storms are possible each day through Sunday. There is a risk of flash flooding Sunday and Monday.

DISCUSSION

KEY MESSAGE 1...Dangerous heat and humidity will continue across the region through Saturday. Several record high temperature records were set or tied across the area on Friday. More records are possible Saturday, especially across Delmarva and south NJ.

Strong mid-level ridging across the Mississippi Valley, Great Lakes, and Ohio Valleys has built eastward into the Northeast and Mid Atlantic and will persist into the holiday weekend. The flow is west to northwest today. The ridge will finally start to break and retreat some starting Saturday, and especially into Sunday.

Temperatures will begin to abate somewhat on Saturday as the ridge begins to break and retreat to the southwest. However, high temperatures will still be in the mid 90s to around 100 degrees, hottest along and southeast of I-95. Another day of west to northwest flow of similar magnitude should once again support the immediate coastline warming up considerably before the sea breeze develops. Elsewhere, a gradually weakening ridge aloft will result in the slightly cooler temperatures. Dewpoints should mix out again into the upper 60s to near 70 degrees by afternoon, which results in 100-108 degree heat indices.

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. With that said, dewpoints will remain in the upper 60s to low 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.

Significant impacts will continue from the 3 to 4 day excessive heat and humidity, with heat indices reaching into the 100-110 degree range each day. The Extreme Heat Warning for our entire forecast area (excluding the New Jersey barrier islands) remains in effect through 8 PM Saturday. The hottest conditions are forecast to occur through today south of I-78. While heat indices may fall just shy of warning criteria by Saturday, impacts will likely be worsened by the multiple days of heat and busy outdoor holiday festivities.

KEY MESSAGE 2...Daily chances for showers and storms will begin across the area today and continue into early next week. Some severe storms are possible each day through Sunday. There is a risk of flash flooding Sunday and Monday.

The mid-level ridge looks to break down and retrograde back to the south and west through tonight, and this will allow a mid- level trough to dig southeastward into New England. With several shortwaves riding over the top of the ridge and into the local area, this will support increasing coverage of afternoon and evening showers and thunderstorms on Saturday and Sunday as a cold front enters the region and then likely stalls. PoPs are around 30-60% for Saturday. Activity becomes more widespread on Sunday and Monday, with PoPs around 60- 90% for most of the area.

SPC has highlighted portions of our area in a Slight Risk (level 2 out of 5) for severe thunderstorms for Saturday and Sunday. As indicated by the PoP forecast above, coverage of storms is anticipated to be a bit greater on Saturday (compared to Friday) though. Damaging winds will be the main threat with any thunderstorm development.

While there is still some uncertainty in the details of the thunderstorm activity Saturday, it is important to point out that any holiday weekend festivities could be impacted by thunderstorms (in addition to the extreme heat).

On Sunday, the severe weather threat is expected to become confined to 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. The severe weather threat looks low on Monday, but additional rounds of showers and storms appear likely through Monday night.

Concern has grown this afternoon that a threat for flash flooding could evolve Sunday into Monday, given a slow moving or stationary frontal boundary draped across the area, and tall, skinny CAPE profiles with deep moisture. 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. Given these factors, rainfall rates in storms could exceed 1 to 2 inches per hour. As of now, the WPC has placed 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.

The front is expected to finally clear the area Tuesday, with high pressure at least briefly building back into the region. However, daily chances for isolated, primarily diurnally driven convection, could continue through the middle of next week.

AVIATION /02Z SATURDAY THROUGH WEDNESDAY/

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

Overnight...Largely VFR. Patchy fog possible. West winds near 5 kts. High/medium confidence.

Saturday...VFR overall. Risk of scattered showers/t-storms after 18Z (about 30-50% chance). Winds generally westerly increasing to 10 kts with some afternoon gusts up to 20 kts. Moderate confidence.

Outlook...

Saturday night...Scattered showers and storms will be possible, especially during the evening showers. Sub-VFR conditions are likely with any heavier showers or storms.

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

No marine hazards expected through Saturday. South to southwest winds 10-15 kts. Seas 1-3 feet. 10-20% chance of a showers or a thunderstorm overnight, 20-40% Saturday afternoon, otherwise fair weather and hazy.

Outlook...

No marine headlines are currently anticipated through Wednesday with winds below 25 kt and seas below 5 feet. Showers and storms are possible each day, with activity being the most widespread Sunday through Monday night. Visibility restrictions and strong winds are possible with the strongest storms.

Rip Currents...

For Saturday, winds will be from the west to southwest at 10 to 15 mph with gusts up to 20 mph in the afternoon. Breaking waves will be around 1 to 2 feet. 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 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 foot 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 specific beach forecasts, visit weather.gov/beach/phi

CLIMATE

Record breaking heat is forecast through Saturday. On Thursday, July 2nd, daily records were tied or broken at the Atlantic City Airport, Mount Pocono, Philadelphia, Reading, Trenton, Wilmington, and Georgetown. 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 3 Site Record / Year Allentown (ABE) 105 / 1966 AC Airport (ACY) 104 / 1966 AC Marina (55N) 99 / 1919 Georgetown (GED) 101 / 1954 Mount Pocono (MPO) 103 / 1911 Philadelphia (PHL) 104 / 1966 Reading (RDG) 103 / 1898 & 1966 Trenton (TTN) 102 / 1966 Wilmington (ILG) 102 / 1966

Record Warmest Low Temperatures July 3 Site Record / Year Allentown (ABE) 75 / 2018 AC Airport (ACY) 78 / 2018 AC Marina (55N) 76 / 1983, 2002, & 2018 Georgetown (GED) 79 / 1953 Mount Pocono (MPO) 69 / 2013 Philadelphia (PHL) 77 / 1876, 1901, &2002 Reading (RDG) 76 / 2018 Trenton (TTN) 76 / 1901 & 1966 Wilmington (ILG) 76 / 2002

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