textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for 18Z TAFs.

Slight risk of severe weather expanded southward this afternoon/evening.

KEY MESSAGES

1. Dangerous heat and humidity will build over the Northeast and Mid Atlantic through Saturday. All time record high temperatures could be challenged Thursday and Friday.

2. There is a chance for thunderstorms across portions of the area into this evening, a few of which may be severe with damaging winds.

3. There is the potential for additional and 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 over the Northeast and Mid Atlantic through Saturday. All time record high temperatures could be challenged Thursday and Friday.

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

High temperatures will climb into the mid and upper 90s today, and then from 100 to 105 degrees on Thursday and Friday. With a south to southwest flow, dewpoints are less likely to mix out significantly this afternoon. Resulting heat indices are forecast to range mainly from around 100-105 degrees. By Thursday and especially Friday, the shift to a more west or northwest flow will allow for better mixing out of dewpoints during the afternoon, and also a component of downsloping (adiabatic warming) from the Appalachians. This will support temperatures climbing above 100 degrees as dewpoints mix out into the mid 60s during the afternoon hours. Resulting forecast heat indices are mostly in the 105-110 degree range. 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) on Thursday. 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. 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. Once the details regarding the heat on Sunday becomes more clear, the current Extreme Heat Warning 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 on Thursday 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 Thursday through Saturday from 95 to 105 degrees. The advisory is also in effect beginning at noon on Thursday 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 starting at noon today through 8 PM Saturday for all of southeastern Pennsylvania, northern Delaware, and much of New Jersey. While heat indices may fall 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 3 below).

KEY MESSAGE 2...There is a chance for thunderstorms across portions of the area into this evening, a few of which may be severe with damaging winds.

Instability is forecast to be high (potentially 3000 J/kg or greater) across the area, especially along and northwest of I-95. Due to the strong subsidence and ridging building in from the west, there will also be a lot of mid level dry air contributing to high DCAPE (1000-1500 J/kg). Latest CAMs continue showing some convective initiation within this environment, despite the strong subsidence, and as of 2 PM radar is bearing this out. While coverage of any thunderstorms would be isolated to scattered, any storms that do form could be capable of producing strong microbursts with damaging winds. SPC has expanded the MARGINAL (level 1 out of 5) risk for severe thunderstorms and the SLIGHT (level 2 out of 5) significantly further south with the midday update, encompassing nearly all of the northern half of the CWA in slight. Its not impossible a severe thunderstorm watch is necessary, and have added enhanced wording to forecast, but for the moment will be watching progression of convection upstream.

KEY MESSAGE 3...There is the potential for additional and 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 may support more widespread afternoon and evening showers and thunderstorms starting on Friday, but especially on Saturday and Sunday. Currently, PoPs are around 10-30% on Friday afternoon and evening and generally 30-50% on Saturday. Activity becomes more active on Sunday and Monday, with PoPs around 60% for most of the area.

While details of this activity will not become clear until later this week, 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 would be favorable for strong to severe thunderstorms, if any storms do develop. This potential will continue to be monitored.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

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

Rest of Today into this evening...VFR. 10-20% chance of a shower or thunderstorm. South to southwest winds around 5-10 kts with gusts upwards of 20. High confidence overall, low confidence in convective impacts.

Overnight tonight...VFR. Winds settling out of the southwest around 5-10 kts. High confidence.

Thursday...VFR. Winds west-southwest 5-10 kts. High confidence.

Outlook...

Thursday night through Saturday...Generally VFR, though isolated to scattered SHRA and TSRA may result in localized sub- VFR conds.

Sunday through Monday...Sub-VFR conds in afternoon and evening SHRA and TSRA. VFR otherwise.

MARINE

A Small Craft Advisory remains in effect for all of the nearshore Atlantic coastal waters through midnight tonight.

Southerly winds 15-25 kts this afternoon across the Atlantic waters. Seas are 3-4 feet will build closer to 5 feet as well. Winds and seas will then diminish later tonight. A gusty thunderstorm also can't be ruled out, especially across the northern ocean zones.

Small Craft Conditions look likely to redevelop in a similar manner as today on the ocean zones for Thursday.

Outlook...

Thursday night...Lingering SCA conditions possible with elevated seas around 5 feet.

Friday through Monday...Generally sub-SCA conditions. Isolated to scattered showers and thunderstorms Friday and Saturday afternoons and evenings, then showers and thunderstorms become likely SUnday and Monday.

Rip Currents...

For today, breaking wave heights in the surf zone will be increasing to around 3 to 4 feet with S/SW winds around 25 mph. There will also be multiple swell groups and we'll still only be 2 days removed from the Full Moon. Given these factors, the latest indications are that shore areas in Cape May and Atlantic Counties in NJ will have a HIGH risk for the development of dangerous rip currents. For our remaining NJ shore zones as well as the Delaware Beaches, we'll continue with a MODERATE risk.

For Thursday, conditions look similar except both wind and wave heights look to come down some and we'll also be another day removed from Monday's Full Moon. 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 specific beach forecasts, visit weather.gov/beach/phi

CLIMATE

Record breaking heat is forecast from Wednesday through Saturday. 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 1 Site Record / Year Allentown (ABE) 98 / 2018 AC Airport (ACY) 99 / 1968 AC Marina (55N) 98 / 1968 Georgetown (GED) 99 / 2012 Mount Pocono (MPO) 88 / 1963, 1964, 1968, & 2018 Philadelphia (PHL) 102 / 1901 Reading (RDG) 101 / 1901 Trenton (TTN) 98 / 1898, 1901, & 1945 Wilmington (ILG) 97 / 1931 & 1963

Record Warmest Low Temperatures July 1 Site Record / Year Allentown (ABE) 74 / 1930 AC Airport (ACY) 77 / 1945 AC Marina (55N) 79 / 1945 Georgetown (GED) 76 / 1945 Mount Pocono (MPO) 67 / 1946, 1971, 2013, 2017, 2025 Philadelphia (PHL) 82 / 1901 Reading (RDG) 76 / 1968 Trenton (TTN) 77 / 1945 Wilmington (ILG) 75 / 2013

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 Thursday to 8 PM EDT Saturday for NJZ021>023. High Risk for Rip Currents until 8 PM EDT this evening for NJZ024- 025. Heat Advisory from noon Thursday to 8 PM EDT Saturday for NJZ024>026. DE...Extreme Heat Warning until 8 PM EDT Saturday for DEZ001. Extreme Heat Warning from noon Thursday to 8 PM EDT Saturday for DEZ002>004. MD...Extreme Heat Warning from noon Thursday to 8 PM EDT Saturday for MDZ012-015-019-020. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ450>455.