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Mercer County, NJ
 Details for Mercer County, NJ Extreme Heat Warning  +2 additional alerts
 
389
FXUS61 KPHI 142001
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
401 PM EDT Tue Jul 14 2026

.WHAT HAS CHANGED...
Extreme Heat Warning issued for the urban corridor and adjacent
areas of central and southern New Jersey. Heat Advisory issued
for portions of the Eastern Shore of Maryland.

Small Craft Advisory issued for Atlantic coastal waters of New
Jersey north of Great Egg Inlet.

Aviation section updated for 18Z TAFs.

&&

.KEY MESSAGES...
1. Above normal temperatures beginning today and continuing
through the end of the week. Wednesday will be the hottest day
of the stretch, when dangerously hot and humid conditions are
expected. Extreme Heat Warnings and Heat Advisories are in
effect for our entire forecast area.

2. The weekend is shaping up to be active and unsettled with
chances for showers and thunderstorms each day. Some storms
could be severe and also may produce heavy rainfall leading to
flash flooding.

&&

.DISCUSSION...
KEY MESSAGE 1..Above normal temperatures beginning today and
continuing through the end of the week. Wednesday will be the
hottest day of the stretch, when dangerously hot and humid
conditions are expected. Extreme Heat Warnings and Heat
Advisories are in effect for our entire forecast area.

Heat and humidity will begin to build over the area today as an
upper level area of high pressure over the central part of the
country expands eastward towards the East Coast. This will
occur as a low pressure system moves through eastern Canada,
resulting in warm advection strengthening into Wednesday.

Temperatures today have warmed into the upper 80s this afternoon
and should peak in the upper 80s to low 90`s. Dewpoints and
humidity have stayed lower than our previous heat wave. However,
Wednesday will be a different story as the heat continues to
build over the area. High temperatures should range from the mid
90s to near 100 degrees in most areas, hottest along and
southeast of I-95, with increasing humidity. While some areas
will likely reach the century mark again, it will not be quite
to the magnitude that we experienced to start July. Humidity
will be a little less as well, and the hottest conditions will
only last for one day. However, heat index values are still
forecast to range from 100-109 degrees for most of the area,
again hottest from along and southeast of I-95. A modest
westerly, offshore wind near 10-15 mph should help keep the sea
breeze from making much inland progress during the afternoon
hours. Thus, we expect high temperatures in the mid to upper 90s
and heat indices near 100-105 degrees even for the New Jersey
Shore and Delaware Beaches. The limiting factor in how much we
heat will be smoke from Canadian wildfires. We are already
seeing the first plume of wildfire smoke dropping south into the
the Mid-Atlantic this afternoon and that will insulate the
region from the highest heat. The smoke should again help
mitigate how much heating we receive tomorrow so while temps are
going to be hot and there are no changes to any heat headlines,
we are not fully maximizing the potential heat that the thermal
profile suggests we could warm to.

A mostly dry cold front looks to pass sometime late Wednesday
which will knock down temperatures and dewpoints a bit, but
medium range guidance and ensembles indicate above normal
temperatures with highs ranging from the upper 80s into the
low/mid 90s could remain through the end of the week and
potentially into the weekend. The front should be mostly dry,
but would not be surprised to see a few isolated storms
developing along it late Wednesday afternoon and evening, mainly
across the Lehigh Valley, Poconos, and northern New Jersey north
of I-195.

Thursday will still be quite hot, with maximum heat indices in
the upper 90s to low 100s along and southeast of I-95. While we
aren`t explicitly forecasting advisory criteria to be reached,
it`s possible some additional Heat Advisories could be needed on
Thursday for our southern zones. Friday looks to bring more
relief from the humidity at least, as drier dewpoints advect in
from the north despite highs in the low to mid 90s remaining for
some areas.


KEY MESSAGE 2...The weekend is shaping up to be active and
unsettled with chances for showers and thunderstorms each day.
Some storms could be severe and also may produce heavy rainfall
leading to flash flooding.

We are still several days out, but are monitoring the severe
weather setup as we get into the weekend. At this point, the
cold front that comes through the area late Wednesday into early
Thursday looks to be mainly dry with just some spotty storms
possible over the southern Poconos into northern NJ late
Wednesday.

Another cold front will approach on Friday. Some models are
trending stormier with this period. For now though, the
consensus blend of guidance is still mostly dry through this
period, but will be watching trends within this period closely.

Regardless, most models are still focusing storm chances when
the front finally sinks into the region Saturday. The front will
stay over or at least near the region into Sunday. As is often
the case with these patterns following a building heat pattern
mid week, there is some potential for both severe threats and
heavy rain/flash flooding threat. At this early vantage point
the shear looks to be moderate to potentially strong with the
main question being how unstable it will get. This will
determine the extent of any severe weather threat but at this
point we see at least some potential for severe threats.
Precipitable water values will also be increasing to around 2+
inches. That is well about the 90th percentile for this time of
year, increasing the risk for heavy rain/flash flooding.

There`s uncertainty though regarding how fast this front pushes
through and also whether it may get hung up near the area into
early next week. If it moves through faster as the GFS is
indicating, things could start to clear out by later Sunday
afternoon with fair weather to follow for Monday. However the
ECMWF hangs up the front over the area into next Monday with
continuing chances for showers and storms.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Southwest winds increasing to around 10-12 kts by
16Z. Some gusts 18-20 kt possible. High confidence.

Tonight...VFR. Southwest winds 5-10 kts. High confidence.

Wednesday...VFR. Smoke could briefly bring down visibility
below 6 miles but confidence is not high. Generally west winds
8-12kts.

Outlook...

Wednesday night through Thursday night...Mainly VFR, however
some smoke moving in from the wildfires in western Ontario could
result in some MVFR visibility at times. Otherwise, no
significant weather.

Friday through Saturday...Restrictions will be possible in
isolated to scattered showers and storms. The chance for impacts
to terminals currently appears greatest Saturday afternoon and
evening.

&&

.MARINE...
South to southwest winds increasing as the day progresses to
near 15-25 kts, strongest north of Atlantic City. Seas building
3-5 feet. A Small Craft Advisory is in effect from 2pm through
2am issued for the New Jersey Atlantic coastal waters north of
Great Egg Inlet. Winds and seas diminishing overnight.

Outlook...

Wednesday through Friday...No marine hazards expected. A few
thunderstorms possible Wednesday evening.

Saturday...Winds could get near advisory levels by the
afternoon.


Rip Currents...

On Wednesday, west winds will average 10 to 15 mph with a light
southeast swell with a period of 6 to 8 seconds. Breaking waves
will average 1 to 2 feet. As a result, there is a LOW risk for
the development of dangerous and life threatening rip currents
at the Jersey Shore and at Delaware Beaches.

On Thursday, south to southwest winds will average 10 to 15 mph
with a light southeast swell with a period of 6 to 8 seconds.
Breaking waves will average 1 to 2 feet. As a result, there is 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...
A brief 1-day spike in temperatures is expected, with highs
likely to approach records. Here are the records for Wednesday,
July 15:

Allentown/ABE      98 in 1995
AC Airport/ACY    100 in 1995
AC Marina/55N      99 in 1995
Georgetown/GED     96 in 2024 and 1993
Mount Pocono/MPO   92 in 1954
Philadelphia/PHL  103 in 1995
Reading/RDG       100 in 1995
Trenton/TTN       101 in 1995
Wilmington/ILG     99 in 1997 and 1995

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Extreme Heat Warning from 10 AM to 8 PM EDT Wednesday for
     PAZ070-071-104-106.
     Heat Advisory from 10 AM to 8 PM EDT Wednesday for PAZ054-055-
     060>062-101>103-105.
NJ...Extreme Heat Warning from 10 AM to 8 PM EDT Wednesday for
     NJZ010-012>015-017>020-027.
     Heat Advisory from 10 AM to 8 PM EDT Wednesday for NJZ001-
     007>009-016-021>026.
DE...Extreme Heat Warning from 10 AM to 8 PM EDT Wednesday for
     DEZ001.
     Heat Advisory from 10 AM to 8 PM EDT Wednesday for DEZ002>004.
MD...Heat Advisory from 10 AM to 8 PM EDT Wednesday for MDZ012-015-
     019-020.
MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ450>452.

&&

$$

DISCUSSION...Deal/Fitzsimmons/Hoeflich/Johnson/Staarmann
AVIATION...Deal/Staarmann
MARINE...AKL/Deal/MPS/Staarmann

NWS PHI Office Area Forecast Discussion