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Mercer County, NJ
 Details for Mercer County, NJ Special Weather Statement  +1 additional alert
 
021
FXUS61 KPHI 291639
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1239 PM EDT Tue Apr 29 2025

.SYNOPSIS...
A warm front arrives today, followed by a cold front overnight
into Wednesday morning. High pressure briefly returns late
Wednesday into Thursday. Another low pressure system tracks to
our north on Friday with a cold front moving through by early
Saturday. High pressure then builds in by Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
A warm and breezy afternoon is expected well ahead of a cold
front late tonight. Temperatures have already warmed well into
the 70s as of 12:30 PM with increasing SSW winds.

The axis of a mid level ridge is forecast to crest across our
area through this morning before shifting to our east and south
this afternoon into tonight. This will take the center of
surface high pressure farther southeast of our area. A
tightening pressure gradient will develop across our area
through this afternoon between high pressure to our southeast
and well ahead of a cold front. As the boundary layer warms
through the morning, strengthening winds above the surface will
mix down to the surface and this will result in a gusty south to
southwest wind. As the winds increase later this morning and
peak during the afternoon, sustained winds of 15-20 mph are
forecast with gusts up to 30 mph. The strongest winds may occur
from about the I-95 corridor on south and east where some deeper
mixing occurs. Some high level cloudiness will be cresting the
ridge axis today, and it is possible that some cumulus clouds
develop this afternoon pending convective temperatures being
reached.

The strengthening southwesterly flow will boost the low-level
warm air advection today and this evening ahead of a cold front.
This will result in temperatures well above average, with highs
in the upper 70s to low 80s (cooler in the higher elevations).
Given a south to southwest wind, it will be cooler along much of
the coastal areas. Along with the warm air advection, moisture
advection will get underway as well through the day. This will
bring an increase in the surface dew points, although with
deeper mixing through the afternoon some lowering of the dew
points should occur especially across much of New Jersey and
Delaware.

As we go through tonight, a mild night for the region ahead of
a cold front although the cold front will be working its way
across parts of the region overnight. An upper-level trough will
pivot across the eastern Great Lakes and adjacent Canada,
however the main forcing looks to track to our north. A cold
front tied to this feature though will arrive in our area. A
line of showers and thunderstorms or even a few clusters are
expected to develop this afternoon with or ahead of the cold
front well to our west. The timing into our area is not ideal as
any convection does not look to arrive into our far western
zones until this evening.

The model forecast soundings indicate an increase in shear as a
low-level jet increases ahead of the cold front, however the
instability is on the lower side. Given diminishing forcing with
time, the organized convection well to our west looks to be
weakening quite a bit as it approaches and moves into our far
western zones. If the convection remains organized enough and
therefore does not weaken as quickly, then there is some
potential for locally strong/damaging winds across the Poconos
to perhaps parts of the Lehigh Valley and Berks County. This is
mostly due to lingering dry air in the boundary layer and even
some mid level dry air that could accelerate downward momentum
within a downdraft. The SPC continues with a Marginal Risk
(level 1 out of 5) for possible severe thunderstorms across the
Poconos to parts of the Lehigh Valley and Berks County. The
gradient surface winds will also settle down some tonight as the
deeper mixing wanes after sunset. Low temperatures are forecast
to be in the mid 50s to mid 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Cold front will be continuing to sink south as Wednesday
begins. There remains a bit of uncertainty in how quickly the
front will be south of the region. If it doesn`t get southeast
of SE NJ and S DE until closer to mid day, than highs on
Wednesday in Delmarva and the coastal plain of NJ will be close
to if not a few degrees warmer than Tuesday.

High pressure will then be the dominant feature through
Thursday. Even with the cold front, day time temperatures are
expected to be up to 5 degrees warmer than normal.

The warm front associated with the next low pressure system
could arrive as early as late Thursday, bringing the next chance
for showers and storms.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Warm front will continue to lift north through the region on
Friday. Showers and thunderstorms become more likely Friday into
Friday night as the warm front will be followed close behind by
a cold front. Still lots of uncertainty about intensity, but
we`ll be watching any severe weather risk closely.

Some of the latest guidance is a bit slower with the cold
front, depicting it crossing through the region during the day
on Saturday. Consequently, there is high uncertainty in the
precipitation chances and temperatures on Saturday. However, by
Sunday into Monday, expect temperatures to be slightly below
normal

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. South to southwest winds around 15 knots with
gusts up to 25 knots. High confidence.

Tonight...VFR overall with an increase in mainly mid to high
level clouds. Some showers or a thunderstorm cannot be ruled out
especially around KABE and KRDG, and given chances look low
enough just included a VCSH there for now. Southwest winds near
10-15 knots and becoming northwest by 12Z. Low confidence on
timing/coverage of any showers and thunder, especially with an
eastward extent. High confidence on prevailing VFR and winds.

Outlook...

Wednesday into Thursday...VFR expected.

Thursday night through Saturday...periods of MVFR and even IFR
with showers and thunderstorms possible.

&&

.MARINE...
Small Craft Advisory conditions are forecast to develop this
afternoon as southwesterly winds increase with gusts 25-30 knots
on the ocean zones. This will continue most of tonight. It may
take some time however for the stronger winds to reach the
surface given much warmer air moving over the cool ocean water
(water temperatures mostly in the 50s). Seas will also build in
response to the period of stronger winds. For Delaware Bay,
opted to issue a Small Craft Advisory for this afternoon into
early this evening as gusts to around 25 knots are anticipated
to occur especially closer to the coast.

Outlook...

Wednesday through Thursday night...Once seas subside below 5 ft
Wednesday morning, winds and seas should stay below SCA
criteria.

Friday...Southerly winds above 25 kt and seas above 5 ft are
possible.

Saturday...Winds and seas are forecast to remain below SCA
criteria.

&&

.FIRE WEATHER...
For today, while the dewpoints will be much higher than
yesterday, they will remain low enough and when combined with
very warm temperatures this afternoon will result in the
relative humidity dropping to mostly between 25 and 35 percent
across most of New Jersey and Delaware. The relative humidity
looks to stay higher in most of eastern Pennsylvania and
Marylands Eastern Shore. In addition, south to southwest winds
will increase to 15-20 mph with gusts up to 30 mph. The
strongest winds may end up being from about I-95 south and east.
Based on the latest forecast and earlier coordination with
State Fire partners, a Special Weather Statement has been issued
for most of New Jersey and all of Delaware to cover the
elevated risk of rapid fire spread this afternoon.

For Wednesday, minimum relative humidity will range from around
20 to 30 percent with temperatures mostly in the 70s. Northwest
winds 10-15 mph with gusts near 20 mph possible.

For Thursday, minimum relative humidity will range from around
25 to 35 percent with temperatures mostly in the 70s again.
Southeast winds near 10 mph with gusts near 15-20 mph possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ430-
     431.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...Johnson/RCM/Staarmann
NEAR TERM...Gorse/Staarmann
SHORT TERM...Johnson/Staarmann
LONG TERM...Johnson/Staarmann
AVIATION...Gorse/Johnson/Staarmann
MARINE...Gorse/Johnson
FIRE WEATHER...Gorse/Staarmann

NWS PHI Office Area Forecast Discussion