Forecast Discussion

490
FXUS61 KPHI 291053
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
653 AM EDT Sat Mar 29 2025

.SYNOPSIS...
A warm front will stall over New England today, then slide back
southwestward into the region as a cold front tonight. It will
stall across the area on Sunday. This front finally lifts back
to the northeast once and for all Sunday night into early
Monday, before a more powerful front moves into the region from
the northwest Monday night. High pressure returns Tuesday and
Wednesday before another system approaches for Thursday into
Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
The warmest day so far this year is expected today, with
temperatures climbing to near 80 degrees for much of the region
this afternoon. Breezy and dry with periods of clouds and sun.

Upper ridging will build from the west today through tonight.
At the surface, high pressure will remain centered near Bermuda.
A frontal boundary will be stalled to the north of our area,
pushing southwest into New Jersey and southeast Pennsylvania
into tonight before stalling out locally.

The main story today will be the unseasonable warmth across the
region. Modest WSW flow within a vast, dry subtropical airmass
with 850 mb temperatures near 10C to 13C will support surface
temperatures climbing quickly into the 70s by afternoon.
Forecast afternoon highs are mostly in the upper 70s to low 80s
for most areas. Even the immediate coastal areas should warm up
quite well by midday before any marine influence takes hold into
the afternoon. Delaware Beaches and the New Jersey shore areas
north of Seaside Heights will have a shot at reaching 80 degrees
given the strong offshore WSW winds. For IBSP/LBI and south
(barrier islands) in New Jersey, the sea breeze will probably
start inching inland a bit into the afternoon, but temperatures
should still climb to at least near 70 degrees in those areas
too. The higher elevations in our northwest zones should top out
in the low to mid 70s too.

While it will be quite warm for late March standards, it will
also be breezy and dry. So it should be a relatively comfortable
warmth. We should be safe from records, as this date in 1945
experienced some very impressive temperatures in the mid to
upper 80s at most sites. Daily record highs have been included
in the Climate section below. WSW winds will increase to around
10-20 mph, with gusts near 25-35 mph. The stronger winds and
gusts will be mainly from around the I-95 corridor and
north/west of there. Clouds will be variable in nature, with
periods of mostly cloudy and mostly sunny skies. The clouds will
be a limiting factor in temperatures over achieving forecast
values.

The frontal boundary will return southwest into our area as a
backdoor cold front beginning in the evening. Guidance varies on
exactly where it will stall out overnight, but the general
consensus is for this to be somewhere around a line from
Atlantic City to the Philly Metro to the Lehigh Valley or Berks
County. Northeast of the frontal boundary, temperatures will
fall into the 40s and low 50s tonight with ENE winds, low
clouds, and perhaps some areas of fog or drizzle developing
late. Southwest of the boundary, will maintain the southwest
flow with temperatures gradually falling to the mid 50s to near
60 degrees overnight. Mostly cloudy southwest of the boundary as
well with plenty of mid levels clouds around.

Tonight will be dry for most areas. The exception (aside from
any potential drizzle) will be the potential for some showers
and thunderstorms developing near and north of I-80 corridor as
a weak wave passes to the north.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Front stalls across the CWA on Sunday, making for an uncertain
temperature forecast. Right now what we have is the best chance
given latest guidance but should the front end up a bit farther
north or south than currently forecast, these readings could be
quite a bit off. Otherwise, most forcing on Sunday stays off to
the north and west so only a small chance of any showers during
the day while clouds will be more abundant than Saturday. Highs
will be well into the 70s from Philly south and west but only
upper 50s to low 60s in parts of northern and eastern
NJ...again, with the caveat that uncertainty here is rather
high.

Leading energy and warm advection moving in Sunday night into
Monday morning may bring a few showers into the region, but not
expecting significant widespread precip just yet. Still, the
increasing low level jet ahead of the next strong cold front
will help push the stalled backdoor front back to our northeast
by midday Monday, reestablishing the warmth once again, though
not quite as warm as Saturday. After lows in the low 50s
northeast and low 60s southwest on Sunday night, widespread
highs in the 70s are expected on Monday.

A strong cold front will approach the area late day Monday.
Forecast guidance continues to favor a somewhat later arrival
time of the front compared to earlier thinking with it likely
arriving sometime in the late evening or overnight hours. That
said, there is still some uncertainty on this timing. Showers
and storms are expected ahead of the front with POPs ramping up
across the area beginning late afternoon with the highest
chances occurring during the evening timeframe. CAPE does not
look to be terribly impressive however there will be very strong
dynamics and shear so the area remains in a SLIGHT risk of
severe weather from the Storm Prediction Center. Also worth
noting, PWATs will be maxing out around 1.5 inches which is near
the climatological max for this time of year so there will also
be the threat for heavy rainfall and even some possible
localized flooding. Once the cold front pushes through,
overnight lows will cool down into the 40s with even some 30s
over the Poconos and NW NJ.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure will make for a breezy and much cooler day
Tuesday with sunshine returning. Highs mainly in the 50s. Cold
Canadian air mass builds overhead for Tuesday night with
reducing winds, so most areas away from the coast and marine
waters may be near or below freezing Tuesday night. Depending on
how it plays out, might need frost advisories or freeze
warnings for the Delmarva south of Wilmington, where the growing
season is defined to begin on April 1, though at this moment we
are not forecasting temps to drop quite that much. Wednesday
starts with some partial sun, then clouds increase as the next
system approaches. Highs again in the 50s for most. Multiple
waves of low pressure look to then move through the area later
next week in the Thursday through Saturday timeframe. While
there is uncertainty regarding the details, the general trend
will be for it to become more unsettled with plenty of chances
for clouds and rain during this timeframe. Temperatures,
however, will be warming with highs in the 60s and 70s through
this period.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR with variable clouds. WSW winds increasing to 10-20
kts with gusts near 25-30 kts. LLWS before 15Z this morning,
with 2kft winds from the SW near 40 kts. High confidence.

Tonight...Initially VFR. MVFR ceilings will push inland, likely
impacting most terminals by 06-09Z. RDG, ILG, and MIV could
stay VFR for the period however. Initially SW winds 5-10 kts
will shift ENE when and where low ceilings arrive. Moderate
confidence on the overall forecast progression, but lower
confidence on exact timing of MVFR ceilings arriving.

Outlook...

Mostly VFR Sunday, though backdoor front could present low cig
issues, with highest chance at KTTN. Scattered showers may be
more of an issue Sunday night into Monday morning as the
backdoor cold front lifts back north as a warm front, then
widespread showers and scattered thunderstorms will be the
biggest concern late Monday into Monday night with restrictions
likely. VFR Tuesday and Wednesday.

&&

.MARINE...
Advisory conditions developing across the Atlantic coastal
waters this morning into the afternoon. Southwest winds
increasing to 15-20 kts, with some nearshore gusts near 25 kts
possible for all coastal waters, including Delaware Bay. Have
held off on expanding the current Small Craft Advisory to the
bay for now, however would not be surprised if this is warranted
in a future update if 25 kt gusts materialize nearshore. Seas
building to 3-6 feet across the Atlantic waters. Seas and winds
diminishing into the evening.

A backdoor cold front will push southwest from southern New
England and Long Island this evening, which will shift winds
from southwest to northeast around 10-15 kts for areas mainly
north of Atlantic City. This area will also have potential for
fog and drizzle development, which could lower visibility to
near 1 NM at times.

Outlook...

Most of Sunday looks sub-SCA, but late in the day wave heights
increase again. Southerly winds also increase with gusts up to
30 kts Sunday night and Monday, then become northwesterly Monday
night through Tuesday behind a cold front before subsiding.
While winds will diminish by Tuesday night, seas may remain
elevated at SCA levels through Wednesday.

&&

.FIRE WEATHER...
Conditions will be near critical fire weather thresholds today.
WSW winds increasing to 10-20 mph, with gusts of 25-35 mph
possible. This will be combined with minimum relative humidity
values near 30-35% and temperatures climbing into the upper 70s
to low 80s in most areas. The Special Weather Statement for
increased risk of rapid fire spread will remain in effect
through today.

Conditions should be less volatile Sunday as a backdoor front
brings slightly cooler and more humid air to at least
northeastern portions of the region, while the chance of showers
will be a bit higher and cloud cover looks more widespread.
Minimum relative humidity will be near 50%.

&&

.CLIMATE...
Unseasonably warm temperatures are forecast today through
tonight. Records for our climate sites are listed below:

Record High Temperatures
March 29
Site Record/Year
Allentown (ABE) 86/1945
AC Airport (ACY) 87/1945
AC Marina (55N) 82/1998
Georgetown (GED) 87/1945
Mount Pocono (MPO) 79/1945
Philadelphia (PHL) 87/1945
Reading (RDG) 87/1907
Trenton (TTN) 86/1945
Wilmington (ILG) 85/1945

Record Warmest Low Temperatures
March 29
Site Record/Year
Allentown (ABE) 57/1985
AC Airport (ACY) 56/1985
AC Marina (55N) 58/1985
Georgetown (GED) 61/1989 & 1998
Mount Pocono (MPO) 60/1998
Philadelphia (PHL) 63/1907
Reading (RDG) 62/1989
Trenton (TTN) 56/1902 & 1907
Wilmington (ILG) 61/1989

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
ANZ450>453.
Small Craft Advisory until 2 PM EDT this afternoon for ANZ454-
455.

&&

$$

SYNOPSIS...Fitzsimmons/RCM
NEAR TERM...Staarmann
SHORT TERM...Fitzsimmons/RCM
LONG TERM...Fitzsimmons/RCM
AVIATION...Fitzsimmons/Staarmann
MARINE...Fitzsimmons/Staarmann
FIRE WEATHER...Staarmann
CLIMATE...Staarmann

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Data at: 0000 UTC 03 Sep 2023

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