343
FXUS61 KPHI 210028
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
828 PM EDT Fri Jun 20 2025
.SYNOPSIS...
A weak short wave moves north of the area overnight. After that,
high pressure across the western Atlantic should build westward
through the weekend and persist for the first half of next week,
resulting in the return of the heat and humidity. The high may
then settle more to the south and west Wednesday and Thursday.
&&
.NEAR TERM /THROUGH SATURDAY/...
For tonight, high pressure is in control overall, but a wealth
of mid/upper clouds associated with an upper short wave are
across much of PA/NJ. While few showers have developed today
(mainly near KMPO) there could still be a brief shower over the
next few hours across the north areas. We`ll keep the 20% POP
until midnight. Other than that, partly cloudy skies becoming
mostly clear by dawn. A mild night with lows in the low/mid 60s
across the North/West and closer to 70 for metro Philadelphia
and Delmarva. Light West to Southwest winds expected.
As we get into the day Saturday and beyond, ridging aloft initially
situated over the southern and central US will expand and shift
northeastward into the Mid- Atlantic through the weekend. Another
shortwave will dive southeastward across portions of NY State into
New England Saturday evening into Saturday night, and may glance
northeastern PA and northern NJ.
At the surface, high pressure will continue to take hold across the
area during the day on Saturday. Under mostly sunny skies,
temperatures will warm into the upper 80s to near 90 outside of the
Poconos and coastal regions, where the low to mid 80s can be
expected. Dewpoints will generally be in the mid 60s, so while it
will be warm, significant heat impacts are not anticipated.
Saturday evening, a subtle surface trough is expected to pass
through the area. For most of the area, this will not bring any real
change to the weather other than maybe some increasing clouds.
Across far northern portions of the area where ascent from the
shortwave is greater, there could be enough of an impetus for an
isolated storm or two. Should a storm form, it could potentially be
severe, with the environment being characterized by modest
instability (around 1000 J/kg MLCAPE) and deep layer shear around 35-
40 kt. Otherwise it remains quiet with lows Saturday night that will
be warmer than tonight as the flow turns southwesterly. Expect lows
ranging mostly from the middle to upper 60s north to the low 70s
south.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
Expansive upper-level ridging along with a surface high pressure
system takes control for Sunday. For our area, this will lead to a
sunny and very warm day. There is the signal for some troughing to
try to dig into our area from New England but the current thinking
is that the expansive high pressure system suppresses any of
this activity from getting into our area. The big story will be
the building heat and humidity as high temperatures reach the
low to mid 90s across the area with it being slightly cooler
near the coast. Dew points rise into the upper 60s to low 70s
combined with the high temperatures will lead to heat indices in
the upper 90s to near 100 for most of our inland areas away
from the Poconos and coastal areas. Due to the forecast, the
Extreme Heat Watch was extended to include Sunday now.
For Sunday night, we remain warm and muggy, with lows in the 70s. It
is plausible that locations in the urban corridor could not fall
below the upper 70s.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
Summary...Dangerous heat into midweek. An Extreme Heat Watch has
been issued for southeastern PA, northern Delaware, and for areas
near the I-95 corridor and east a bit to the coast in New Jersey.
Synoptic Overview...An expansive upper-level ridge is forecast to
become situated over our region the first half of next week, before
it may weakens some and slide a bit west and south during the second
half of the week. At the surface, high pressure mostly dominates
however a weak trough may be in place, especially later in the week.
For Monday and Tuesday...A strong upper-level ridge is forecast to
be situated nearly over our area during this time frame. This, along
with surface high pressure building westward from the western
Atlantic, will result in very hot/humid conditions.
The combination of air temperatures well into the 90s and dew points
in the upper 60s to low 70s will result in widespread triple digit
heat indices. With high confidence in heat indices getting
to/exceeding 105, went ahead with an Extreme Heat Watch through
Wednesday. Other factors considered with the early watch for next
week were the quick ramp up in temperatures (most of June has been
below normal), the lack of relief at night (Philadelphia could see
lows stay at/near 80), and the potential duration of this event. The
experimental Heat Risk map also has areas within the Watch in the
highest level for heat related impacts, where impacts in most health
systems, heat sensitive industries, and infrastructure is likely.
Philadelphia has a chance to reach 100 degrees for the first time
since July 18, 2012.
The highest heat indices come Monday and Tuesday, but it will
still be very warm with heat indices near 100-105 on Wednesday which
is why the Watch continues into Wednesday. Given the ridge
aloft and the associated subsidence with it, little or no
cumulus is expected and thus no convection. The low-level winds
however should be light enough where sea/bay breezes probably
develop resulting in at least some local cooling near the coast.
For Wednesday and Thursday...The upper-level ridge may settle a
little south and westward during this time frame. While the heat and
humidity looks to continue, it may decrease at least some,
especially Thursday and Friday with some more erosion of the
northern side of the ridge. In addition, a surface trough may
become better defined and introduce a bit more clouds and also
the potential for at least some diurnally driven convection.
There is a cold front that tries to slide southward on Wednesday
but there is a decent amount of uncertainty with how far south
the cold front makes it given the strength of the ridge. Due to
this front, there is a slight chance to chance of showers and
thunderstorms late Wednesday. As mentioned above, the ridge
erodes a bit towards the end of the week with a signal for some
troughing building in from the north that could lead to showers
and thunderstorms both days to end the week. Given uncertainty,
PoPs were capped at slight chance to chance. The temperatures
look to still hold near 90 for most towards the end of next week
with heat indices still in the 90s but this will be lower than
earlier in the week.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Tonight...VFR. Mid/high clouds diminishing overnight. Winds west
to southwest 5-10 kts. High confidence.
Saturday...VFR with SW winds 5 to 10 knots and once against just a
slight chance for a shower or storm around ABE. High confidence.
Outlook...
Saturday night through Wednesday...VFR. No significant weather.
&&
.MARINE...
No Marine headlines are expected through Saturday and Saturday
night. Fair weather expected.
Outlook...
Sunday through Wednesday...No marine headlines expected.
Rip Currents...
For both Saturday and Sunday, mostly shore parallel wind around
10-15 kt, to slightly onshore in spots as winds become more S/SW
in the afternoon. We`ll continue with a MODERATE risk for rip currents
for our NJ zones except for Monmouth County where the risk should
be LOW due to the flow being more shore parallel. For the Delaware
beaches we will also carry a LOW risk for the development of dangerous
rip currents.
For specific beach forecasts, visit weather.gov/beach/phi
&&
.CLIMATE...
Potentially record breaking heat is expected across the area next
week. Here are a look at the daily record high maximum and minimum
temperature for all of our climate sites.
Record High Temperatures
June 23
Site Record/Year
Allentown (ABE) 96/2024
AC Airport (ACY) 98/1988 & 2024
AC Marina (55N) 91/1909
Georgetown (GED) 100/1988
Mount Pocono (MPO) 90/1954
Philadelphia (PHL) 98/2024
Reading (RDG) 98/2024
Trenton (TTN) 97/1894
Wilmington (ILG) 100/1894
Record Warmest Low Temperatures
June 23
Site Record/Year
Allentown (ABE) 71/2017 & 2024
AC Airport (ACY) 75/2024
AC Marina (55N) 74/2010
Georgetown (GED) 76/1988
Mount Pocono (MPO) 69/2024
Philadelphia (PHL) 76/1888
Reading (RDG) 77/2024
Trenton (TTN) 74/2017 & 2024
Wilmington (ILG) 75/2024
Record High Temperatures
June 24
Site Record/Year
Allentown (ABE) 98/1923
AC Airport (ACY) 99/2010
AC Marina (55N) 95/2002
Georgetown (GED) 97/2010
Mount Pocono (MPO) 92/1914
Philadelphia (PHL) 99/1923
Reading (RDG) 98/1908 & 1923
Trenton (TTN) 98/1894
Wilmington (ILG) 102/1894
Record Warmest Low Temperatures
June 24
Site Record/Year
Allentown (ABE) 71/2010
AC Airport (ACY) 72/1951, 2013, 2017 & 2024
AC Marina (55N) 72/1924, 2002, 2010, 2011, 2013 & 2020
Georgetown (GED) 74/2010
Mount Pocono (MPO) 66/1960, 1964 & 2002
Philadelphia (PHL) 75/1909, 1921, 1994 & 2020
Reading (RDG) 73/1909, 1994 & 2010
Trenton (TTN) 76/1894 & 2010
Wilmington (ILG) 74/1994
Record High Temperatures
June 25
Site Record/Year
Allentown (ABE) 98/1923
AC Airport (ACY) 96/1997
AC Marina (55N) 95/1952
Georgetown (GED) 96/1952
Mount Pocono (MPO) 91/1952
Philadelphia (PHL) 98/1952
Reading (RDG) 99/1943
Trenton (TTN) 99/1997
Wilmington (ILG) 98/1894
Record Warmest Low Temperatures
June 25
Site Record/Year
Allentown (ABE) 74/1923 & 1976
AC Airport (ACY) 80/1950
AC Marina (55N) 75/1997 & 2002
Georgetown (GED) 75/2019
Mount Pocono (MPO) 69/1952
Philadelphia (PHL) 76/1909, 1976 & 2002
Reading (RDG) 75/1943 & 1949
Trenton (TTN) 75/1976
Wilmington (ILG) 75/1976
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Extreme Heat Watch from Sunday morning through Wednesday
evening for PAZ060>062-070-071-101>106.
NJ...Extreme Heat Watch from Sunday morning through Wednesday
evening for NJZ001-007>010-012-013-015-017>020-027.
DE...Extreme Heat Watch from Sunday morning through Wednesday
evening for DEZ001.
MD...None.
MARINE...None.
&&
$$
SYNOPSIS...Cooper/Guzzo/Hoeflich/po
NEAR TERM...Fitzsimmons/RCM/po
SHORT TERM...Guzzo
LONG TERM...Guzzo/Hoeflich
AVIATION...Cooper/Fitzsimmons/Guzzo/po
MARINE...Cooper/Fitzsimmons/Guzzo
CLIMATE...Hoeflich