textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes to the forecast.

Very hot and humid conditions expected to peak across the region today through Friday, but dangerous heat will continue through Saturday.

KEY MESSAGES

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

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

DISCUSSION

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

Strong mid-level ridging across the Mississippi Valley, Great Lakes, and Ohio Valleys is building eastward into the Northeast and Mid Atlantic and will persist into the holiday weekend. A west to southwest flow will shift more west to northwest by Friday. The ridge will finally start to break and retreat some starting Saturday into Sunday.

High temperatures are forecast to range between 100 to 105 degrees in most areas today and Friday. 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 on Friday with low level flow being slightly stronger, but regardless dewpoint should still mix out a fair amount this 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 if dewpoints stay closer to 70 degrees.

This is indeed the type of synoptic pattern that could challenge all time record high temperatures in our region. Areas north of I-78 are forecast to experience the hottest air temperatures (upper 90s to near 100 degrees, even as high as 95 degrees at Mount Pocono) today. Further south, the hottest air temperatures (mainly in the 100-105 degree range, and in the upper 90s to near 100 degrees for the New Jersey Shore and Delaware Beaches) are forecast to occur on Friday. See the Climate section below for more information on record temperatures. Temperatures may 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. The prevailing flow direction will dictate how much mixing out of dewpoints occur on Saturday. Currently, we have upper 60s to near 70 degree dewpoints, which results in 100-108 degree heat indices. Highs will remain in the low to mid 90s Sunday, though may drop into the mid and upper 80s on Monday. Heat index values on Sunday may still be in the mid 90s to around 100, so heat related impacts will continue beyond Saturday despite a slight improvement in temperatures. The temperature and heat index forecast will become a bit more challenging as there will be greater chances for afternoon thunderstorms. Once the details regarding the heat on Sunday becomes more clear, the current Extreme Heat Warning could be extended or a new Heat Advisory may be issued.

Confidence remains high for significant impacts from the 3 to 4 day (and potentially 5 day) excessive heat and humidity, with heat indices reaching into the 100-110 degree range each day. The Extreme Heat Warning for Delmarva and far southern New Jersey remains in effect starting at noon today and continuing through at least 8 PM Saturday. The hottest conditions are forecast to occur on Friday in this area.

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 should prevent the islands from getting too hot during the afternoon, though the wind direction will be more southwesterly on Friday. This should allow for temperatures to rise into the mid 90s to potentially near 100 degrees, resulting in daily maximum heat indices today through Saturday from 95 to 105 degrees. The advisory is also in effect beginning at noon today through 8 PM Saturday. The hottest conditions are forecast to occur on Friday in this area. The Extreme Heat Warning remains in effect for coastal Monmouth County.

For the remainder of the area, the Extreme Heat Warning remains in effect through 8 PM Saturday for all of southeastern Pennsylvania, northern Delaware, and much of New Jersey. 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.

The mid-level ridge will break and retrograde back towards the south and west beginning Saturday, and a mid-level trough will try to slide down into the Northeast. This pattern change will begin to favor slightly cooler temperatures and a break in the extreme heat by Sunday and Monday, as well as the potential for showers and thunderstorms for the holiday weekend (see Key Message 2 below).

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

The mid-level ridge looks to break down and retrograde back to the south and west starting on Friday, and this will allow mid- level troughiness to develop over the Northeast. With several shortwaves riding over the top of the ridge and into the local area, this will support more widespread afternoon and evening showers and thunderstorms starting on Friday, but especially on Saturday and Sunday. Currently, PoPs are around 10-20% on Friday afternoon and evening and generally 30-50% on Saturday. Activity becomes more active on Sunday and Monday, with PoPs around 60-70% for most of the area.

SPC has highlighted much of our area in a Slight Risk (level 2 out of 5) for severe thunderstorms both Friday and Saturday. As indicated by the PoP forecast above, coverage of storms is anticipated to be relatively low on Friday, 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.

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). The environmental setup will be favorable for strong to severe thunderstorms, if any storms do develop. This potential will continue to be monitored.

AVIATION /07Z THURSDAY THROUGH MONDAY/

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

Through 12Z...VFR. Southwest winds 5-10 kts. High confidence.

Today...VFR. Westerly winds 5-10 kts may tend to shift a bit more southwest after 18Z, especially at PHL/ILG/MIV/ACY. High confidence.

Tonight...VFR. Southwest winds 5-10 kts shifting northwest after 06Z. High confidence.

Outlook...

Friday through Saturday...Generally VFR, though isolated to scattered TSRA may result in localized restrictions.

Sunday through Monday...Restrictions in afternoon and evening SHRA and TSRA. VFR otherwise.

MARINE

The forecast for winds and seas has lessened some for this afternoon and evening. Southerly winds 10-20 kts with seas 2-4 feet expected, though can't rule out a few sporadic 25 kt gusts at times. The winds and seas will diminish again into the overnight hours.

Outlook...

Friday through Monday...No prevailing marine hazards expected. However, isolated to scattered showers and thunderstorms are forecast for Friday and Saturday afternoons and evenings, then showers and thunderstorms become more likely Sunday and Monday.

Rip Currents...

For today, winds will be out of the south-southwest at 15-20 mph with gusts upwards of 25-30 mph. Seas also build to 3-4 feet. There is a southeast swell with a period of around 8 seconds. For these reasons we're forecasting a MODERATE risk for the development of dangerous rip currents for our NJ shore zones and a LOW risk for the Delaware beaches.

For Friday, winds will be out of the southwest at 10-15 mph. Seas are around 2-3 feet. There is a southeast swell with a period of around 8 seconds. For these reasons we're forecasting a LOW risk for the development of dangerous rip currents for our NJ shore zones and the Delaware beaches.

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

CLIMATE

Record breaking heat is forecast through Saturday. On Wednesday, July 1st, the only station that set new records was Mount Pocono. Both the record high and record warmest low temperature were broken. 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 2 Site Record / Year Allentown (ABE) 102 / 1966 AC Airport (ACY) 100 / 1966 AC Marina (55N) 97 / 1968 Georgetown (GED) 99 / 1953 Mount Pocono (MPO) 93 / 1911 Philadelphia (PHL) 103 / 1901 Reading (RDG) 102 / 1966 Trenton (TTN) 100 / 1901 Wilmington (ILG) 98 / 1941 & 1966

Record Warmest Low Temperatures July 2 Site Record / Year Allentown (ABE) 75 / 2013 AC Airport (ACY) 79 / 2002 AC Marina (55N) 76 / 2012 Georgetown (GED) 77 / 1959 Mount Pocono (MPO) 70 / 1903 Philadelphia (PHL) 82 / 1901 Reading (RDG) 79 / 1901 Trenton (TTN) 79 / 1901 Wilmington (ILG) 75 / 1941 & 2014

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

Annual temperature extremes For Trenton (TTN), this may be the first year with temperatures both below zero and 100+ since 1988. The low so far this year was -1 on 1/21.

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>020-027. Extreme Heat Warning from noon today to 8 PM EDT Saturday for NJZ021>023. Heat Advisory from noon today to 8 PM EDT Saturday for NJZ024>026. DE...Extreme Heat Warning until 8 PM EDT Saturday for DEZ001. Extreme Heat Warning from noon today to 8 PM EDT Saturday for DEZ002>004. MD...Extreme Heat Warning from noon today to 8 PM EDT Saturday for MDZ012-015-019-020. MARINE...None.