textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The aviation section has been updated for the 12Z TAFs.

No significant changes to the weather forecast through Saturday.

KEY MESSAGES

1. Dangerous heat and humidity will continue across the region through Saturday. All time record high temperatures could be challenged again today with widespread triple digit temperatures.

2. There is the potential for more afternoon and evening thunderstorms starting on Friday and lasting through the holiday weekend.

DISCUSSION

KEY MESSAGE 1...Dangerous heat and humidity will continue across the region through Saturday. All time record high temperatures could be challenged again today with widespread triple digit temperatures.

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 will shift more west to northwest today. The ridge will finally start to break and retreat some starting Saturday, and especially into Sunday.

High temperatures are forecast to range between 100 to 105 degrees in most areas again today. The shift to a more west to northwest flow aloft will allow for better mixing out of dewpoints during the afternoon, and also a component of downsloping (adiabatic warming) from the Appalachians. This phenomenon should be a little stronger today and dewpoints should mix out a fair amount in the afternoon. This setup will support temperatures climbing above 100 degrees across most non mountainous inland areas as dewpoints mix out into the mid to upper 60s during the afternoon hours. Resulting forecast heat indices are mostly in the 105-110 degree range, though localized values upwards of 115 degrees are possible again if dewpoints stay closer to 70 degrees.

Today will likely end up being the hottest south of I-78 by a degree or two due to aforementioned meteorological factors. This will be especially the case for coastal areas and Delmarva, where the stronger west to northwest low level flow should keep the marine layer offshore a bit later into the daytime hours before the sea breeze develops. See the Climate section below for more information on record temperatures. 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. It will still be quite humid though, with heat indices getting into the mid 90s to low 100s from the Philly metro and south. By Monday, in the wake of a cold front, temperatures look to top out in the mid 80s for most locations, though slightly cooler in the Poconos and slightly warmer across Delmarva. Even with this improvement, heat related impacts may continue beyond Saturday, especially for the urban corridor and Delmarva. All this being said, increasing shower and thunderstorm chances do complicate the temperature forecast some for this time period.

Confidence remains high for significant impacts 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. It is looking less probable that any heat headlines will be needed for Sunday, but we'll continue to monitor this.

A Heat Advisory remains in effect for the New Jersey Shore (barrier islands), including coastal Ocean, coastal Atlantic, and coastal Cape May Counties. The strong southerly coastal jet and resulting local upwelling of cooler ocean temperatures should prevent the islands from getting too hot during the afternoons, though the wind direction will be more southwesterly today and Saturday. This should allow for temperatures to rise into the mid 90s to potentially near 100 degrees before the sea breeze develops, resulting in daily maximum heat indices through Saturday from 95 to 105 degrees. The advisory is also in effect through 8 PM Saturday. The hottest conditions are forecast to occur today in this area as well. The Extreme Heat Warning remains in effect for coastal Monmouth County.

The mid-level ridge will break and retrograde back towards the south and west beginning Saturday, and a mid-level trough will dig southeastward across portions of New England with enhanced northwesterly mid-level flow across the region. In addition to the pattern change allowing for cooling temperatures, shower and thunderstorm chances will increase for the holiday weekend (see Key Message 2 below).

KEY MESSAGE 2...There is the potential for more afternoon and evening thunderstorms starting on Friday and lasting through the holiday weekend.

The mid-level ridge looks to break down and retrograde back to the south and west starting later today, 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 starting late this afternoon, but especially on Saturday and Sunday. Currently, PoPs are around 10-25% this afternoon and evening and generally 30-60% on 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 today, Saturday, and Sunday. As indicated by the PoP forecast above, coverage of storms is anticipated to be relatively low today, mainly isolated to scattered in nature at best. Coverage and organization of storms should be a bit greater on Saturday though. Damaging winds will be the main threat with any thunderstorm development. On Sunday, the severe weather threat may begin to become confined mainly to Delmarva where destabilization is greatest ahead of an approaching cold front. With that being said, the entire area could see showers and a few storms.

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

After the cold front moves through on Sunday, it may stall for a period near or just south of the region before high pressure begins to build back in by mid-week. This, in combination with a mid-level impulse moving eastward across the region, is expected to lead to scattered to widespread showers and a few storms Sunday night through Monday night. Thereafter, daily chances for isolated, primarily diurnally driven convection, could continue into the middle of next week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...VFR. West to northwest winds 5-10 kts early, shifting west to southwest in the afternoon. Very low risk of isolated thunderstorms after 20Z (about 10-20% chance), but the risk is too low to include a TAF mention. High confidence overall.

Tonight...VFR. Southwest winds near 5 kts shifting west to northwest overnight. High confidence.

Outlook...

Saturday through Tuesday...Scattered showers and storms will be possible each day. Restrictions will be possible with any showers and storms.

MARINE

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

Outlook...

Saturday through Monday night...No marine hazards currently anticipated with winds under 25 kt and seas under 5 feet. Scattered showers and storms will be possible each day.

Tuesday...Winds will increase out of the east and gusts may approach 25 kt. Seas may also increase to above 5 feet, especially for northern marine zones. Scattered showers and storms will be possible.

Rip Currents...

For today, winds will start from the northwest at around 10 mph, then will turn to the southwest at 10 to 15 mph with gusts up to 20 mph in the afternoon. Breaking waves will be 1 to 2 feet. There will be a light southerly swell with a period around 6 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.

On 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 foot or less. There will be a light southeast swell with a period around 6 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.