615
FXUS61 KPHI 221915
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
315 PM EDT Sun Jun 22 2025
.SYNOPSIS...
Hot high pressure across the western Atlantic will build west
into the Appalachian region early this week. This will result in
a significant heat wave with near record breaking temperatures
forecast. The high pressure system will begin to weaken and
retreat to the south by the middle to end of the week, and
temperatures will return closer to normal along with increasing
chances for showers and thunderstorms toward the end of the
week.
&&
.NEAR TERM /THROUGH MONDAY/...
Dangerous heat to kick into high gear on Monday, after a delay
today for most if not all of our region.
An upper-level trough sliding across New England is expected to
quickly depart by this evening, with a strong upper-level ridge
building in its wake. The tailend of the trough has energy
sliding southward across our region and this was enhanced by an
MCS last night that dropped south out of Ontario Canada and New
York State. The cloud canopy associated with this along with
showers and some thunderstorms has held the temperatures way
down so far across most of the region. This is also resulting in
heat indices much lower than forecast so far. The visible
satellite imagery shows the northeast and eastern portion of the
cloud canopy thinning as the convection continues to slowly
weaken. There has been a pressure fall/rise couplet sliding
southward in the wake of the main band of showers and this had
resulted in wind gusts 30-50 mph across several areas. These
winds are short in duration however given the continued
southward propagation and eventual weakening of the
pressure/rise couplet.
The convection associated with the decaying MCS has resulted in
a boundary across the western parts of our area and even down
into southern New Jersey. Ample instability to our west is
advecting toward our area, however given the arriving upper-
level ridge the forcing is much less. There may still be some
convergence though along this lingering boundary to initiate new
convection especially across our western zones into early this
evening. Given the less hot conditions so far the severe
thunderstorm risk looks to be low, but will have to watch this
especially if more heating can develop by late this afternoon,
with some potential becoming focused along the aforementioned
lingering boundary.
The ridge continues to build tonight and then nearly becomes
centered over our region on Monday. The much higher heights with
this ridge will bring in hotter air to our area. A rather humid
air mass will remain in place, although the dew points may mix
down a little Monday during peak heating. Given the presence of
the ridge more over our area, no convection is anticipated on
Monday. The peak heat indices on Monday are forecast to be
between 100-110F across the region, although cooler in the
higher terrain of the Poconos and along the coastal areas. It is
possible that if dew points end up higher, the heat indices
could be high enough to warrant a Extreme Heat Warning for our
southern areas that are in a Heat Advisory. We opted to keep the
advisory at this time given that some guidance may be to high
with the dew points during peak heating. Regardless, dangerous
heat is expected for nearly our entire region on Monday. A light
northwest to north wind should become onshore, keeping it not
as oppressive along much of our coastal communities. Some record
high temperatures Monday could very well be challenged as well.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Significant heat wave peaking through Tuesday with dangerously
hot and humid conditions expected.
A strong ridge of high hot and dry pressure will build across
the eastern US through Tuesday. Mid level heights, thicknesses,
and 850 mb temperatures contributing to the heat wave will all
peak during this time frame. The center of the ridge will be
positioned to our southwest, which should maximize heat
potential locally. By Wednesday, the ridge will begin to weaken
some and retreat away from our area. At the surface, winds will
be modest from the west or northwest. This will add a component
of downsloping into the temperature equation, helping to boost
temperatures by a couple degrees. The wind direction will also
lessen the influence of the sea breeze, or lack thereof, for
coastal areas. The pattern is checking a lot of boxes for a set
up capable of producing fairly widespread 100 degree
temperatures in our region, perhaps one of the most favorable
patterns in a few years.
Fortunately, the pattern will favor dewpoints mixing out
reasonably well into the afternoon hours, but the high
temperatures will still result in heat indices of around 100-110
degrees across the board Tuesday. Slightly drier air, slightly
stronger northwest flow, and perhaps deeper mixing on Tuesday
will favor slightly higher temperatures, but heat indices should
be near or perhaps a few degrees lower than Monday. Regardless
of those details, it`s going to be very hot both days!
Extreme Heat Warnings and Heat Advisories remain in effect as
previously issued. Around the Delaware Valley, Lehigh Valley,
and northern New Jersey, temperatures could be the hottest
observed in over a decade. There will be little relief overnight
as temperatures Monday night and Tuesday Night are expected to
be around 75 to 80 degrees. Heat tends to have cumulative
effects on the body and we are currently forecasting 4
consecutive days of 95+ with through Tuesday likely to feature
high temperatures around 100 degrees and heat index values
pushing 105-110 degrees. Take frequent breaks if outside, and
drink plenty of fluids.
On Wednesday, temperatures will be a few degrees cooler
compared to Monday/Tuesday, but still in the mid to upper 90s,
marking the 4th consecutive day of highs greater than 95
degrees. Heat indices will be near 100 degrees on Wednesday too,
so a slight improvement, but still hot. Some extension of the
southern New Jersey and Delmarva Heat Advisories may need to be
considered. Even if we fall shy of criteria, the cumulative
effects of the heat could warrant this.
For details regarding the last 100 degree day and temperature
records during the upcoming heat wave, see the Climate section
below.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The upper-level ridge will continue to weaken and flatten
out/erode toward the end of the week, especially on the
northern periphery. While the heat and humidity will remain, it
will be not nearly as oppressive as earlier in the week. High
temperatures will remain in the upper 80s to low 90s Thursday,
and should be largely in the 80s for Friday. In addition, a
surface trough should become better defined and introduce a bit
more clouds and also the potential for some scattered diurnally
driven convection. This will include a threat of localized
severe thunderstorms. A back door cold front will draw near by
Thursday, but there is a decent amount of uncertainty with how
quickly it will drop south given the strength of the ridge. Due
to this front, there is an increasing chance (30-60%) of
showers and thunderstorms Thursday and through the weekend. We
should finally be below any heat hazard criteria by Thursday,
and especially by Friday.
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 and over the weekend. Unsettled weather looks to
continue into the weekend with temperatures near to slightly
below normal.
&&
.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Rest to this afternoon...Some lingering showers or a
thunderstorm mainly near and north/west of KPHL can result in
local brief MVFR conditions, otherwise VFR. Southwest to west-
southwest winds 10-15 knots with some gusts to 20 knots. Low
confidence.
Tonight...VFR. West-southwest winds diminishing to 5 knots or
becoming light and variable, then becoming northwesterly late.
Moderate confidence.
Monday...VFR. North-northwest winds 5-10 knots, becoming west-
northwest. The winds should become northeast to east-southeast
at KACY in the afternoon. Low confidence regarding the wind
details.
Outlook...
Monday night through Tuesday Night...VFR. No significant
weather.
Wednesday through Friday...Prevailing VFR, though chances of a
shower/thunderstorm increase (20-50%), especially for Thursday
and Friday.
&&
.MARINE...
Following a burst of strong winds late this morning and early
afternoon mainly for the New Jersey Atlantic coastal waters, the
conditions are anticipated to be below Small Craft Advisory
through Monday.
Outlook...
Monday night through Friday...No marine headlines expected.
Increasing chances for showers/thunderstorms by Thursday and
Friday, otherwise fair weather.
Rip Currents...
For today, SW winds increase to 10 to 20 mph with breaking
waves of 2 to 3 feet. This will result in a MODERATE risk for
the development of dangerous rip currents for the Jersey Shore
counties of Ocean, Atlantic, and Cape May. For the Jersey Shore
county of Monmouth, as well as Delaware Beaches, flow will be a
bit more offshore, resulting in a LOW risk for the development
of dangerous rip currents.
For Monday, W to NW winds of 5 to 10 mph will turn S in the
afternoon behind developing sea breezes. Since winds will be
fairly light and breaking waves around 1 to 2 feet, there will
be a LOW risk for the development of dangerous and life
threatening rip currents for the Jersey Shore and for Delaware
Beaches.
For specific beach forecasts, visit weather.gov/beach/phi
&&
.TIDES/COASTAL FLOODING...
With the New Moon approaching on June 25th, astronomical tides
are expected to increase. Spotty minor tidal flooding is
anticipated for the immediate coastline and back bays as well as
within Delaware Bay beginning with the high tide on Monday
Night. Cannot rule out the need for advisories later this week
as astro tides peak. No tidal flooding is expected within the
tidal Delaware River or Chesapeake Bay.
&&
.CLIMATE...
Near record breaking heat is expected across the area through
the middle of next week. Below is a look at the last 100 degree
day, daily record high maximum and minimum temperature for all
of our climate sites.
Most Recent 100 Degree Day
Site Date/Temperature
Allentown (ABE) July 22, 2011/104
AC Airport (ACY) July 21, 2019/100
AC Marina (55N) July 5, 1999/101
Georgetown (GED) July 21, 2019/100
Mount Pocono (MPO) July 3, 1911/103
Philadelphia (PHL) July 18, 2012/100
Reading (RDG) June 22, 2024/101
Trenton (TTN) July 18, 2012/100
Wilmington (ILG) July 18, 2012/101
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 Warning until 8 PM EDT Wednesday for PAZ060>062-
070-071-101>106.
Heat Advisory until 8 PM EDT Tuesday for PAZ054-055.
NJ...Extreme Heat Warning until 8 PM EDT Wednesday for NJZ001-
007>010-012-013-015-017>020-027.
Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for NJZ014-
016-021>026.
DE...Extreme Heat Warning until 8 PM EDT Wednesday for DEZ001.
Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for
DEZ002>004.
MD...Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for MDZ012-
015-019-020.
MARINE...None.
&&
$$
SYNOPSIS...Hoeflich/Staarmann
NEAR TERM...Gorse
SHORT TERM...Hoeflich/Staarmann
LONG TERM...Hoeflich/Staarmann
AVIATION...Gorse/Staarmann
MARINE...Gorse/Staarmann
TIDES/COASTAL FLOODING...Hoeflich
CLIMATE...Hoeflich/Staarmann