textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The aviation section has been updated for the 00Z TAFs.

KEY MESSAGES

1. Dangerous heat and humidity will continue 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 continue 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 has built 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 again 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 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.

While today will likely end up being the hottest day northwest of I- 95, today and Friday will probably be almost identical along I-95, and southeast of I-95 the hottest temps will likely occur 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. Somewhat 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. 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. Heat index values on Sunday are expected to improve for much of eastern PA and northern NJ, but remain in the mid 90s to perhaps upper 90s across southeastern PA, southern NJ,and Delmarva. Even with this improvement, heat related impacts will 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 Delmarva and far southern New Jersey remains in effect through 8 PM Saturday. The hottest conditions are forecast to occur on Friday in this area. It is possible that additional heat headlines could be required for Sunday for portions of Delmarva.

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 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 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 widespread afternoon and evening thunderstorms starting late 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 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 Friday, but especially on Saturday and Sunday. Currently, PoPs are around 15-25% on Friday afternoon and evening and generally 30-50% on Saturday. Activity becomes more widespread 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. 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. SPC has highlighted this area with a day 4 15% severe risk.

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.

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).

AVIATION /00Z FRIDAY THROUGH TUESDAY/

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

Tonight...VFR. Southwest winds 5-10 kts becoming more west-northwest after 06Z. Periods of light and variable winds overnight. High confidence.

Friday...VFR. Winds more westerly and increasing to around 10 kts with some gusts up near 20 kts in the afternoon. Very low risk of isolated thunderstorms late Friday, but no confidence to place in TAFs at this time. High confidence overall.

Outlook...

Friday night...Primarily VFR. A couple of isolated showers and storms are possible mainly in the evening hours.

Saturday through Tuesday...Scattered showers and storms will be possible each day. Periods of sub-VFR conditions will be possible with any showers and storms.

MARINE

No marine headlines expected through Friday with wind gusts mainly below 25 kts and waves generally below 5 feet.

Outlook...

Friday night through Monday night...No marine headlines 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...

On Friday, 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 2 to 3 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 2 to 3 feet. 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 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>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.