Hail and Damaging Winds in Pennsylvania, April 4, 2025

Area Forecast Discussion
National Weather Service Mount Holly NJ
308 AM EDT Fri Apr 4 2025

.SYNOPSIS...
A cold front settles to our south today and tonight as high pressure
builds across portions of southeastern Canada and New England. As
low pressure moves up the Ohio Valley and then across the Great
Lakes tonight and Saturday, the front will move northward some as a
warm front. A cold front then moves through Sunday followed by a
stronger cold front Monday night into early Tuesday. High pressure
then builds in later Wednesday before shifting offshore into
Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Cold front continues progress through the region. The front is
rather diffuse with the strongest cold and dry air advection lagging
well behind the front.

Showers remain a possibility into mid morning with some lift as the
front continues to progress through the region. We saw mostly stable
conditions earlier, but trends over the last hour have shown
elevated instability in some high res models generally near and
south of Reading and Philly. Additionally, isolated thunderstorms
were observed in central PA as of 3 AM. Therefore, included a
mention of thunder for these areas through mid morning. Still expect
the primary mode to be showers.

We should have a lull in any rain through much of the day. The front
will stall just south of our region. However, with the cold air
advection lagging well behind the front, most areas will still be
warmer than normal with highs ranging from the upper 50s to near 70.

As the next low pressure system lifts through the Ohio Valley
overnight, the stalled front will begin to slowly work its way back
north as a warm front. This will lead to another chance for rain
overnight. Predominant mode is expected to be showers, but if the
front starts lifting north early enough, a few rumbles of thunder
are possible in Delmarva during the evening hours. As with the
previous low pressure system, the main forcing with this system will
stay well north of our region. Therefore, rain amounts overnight are
expected be light, generally less than a quarter of an inch of rain.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As high pressure slides to our north Saturday, low pressure tracks
up the Ohio Valley and then moves mostly to our north through
Saturday. This will start to pull the stalled boundary just south of
Delmarva back north as a warm front. Some additional showers develop
Saturday, although the focus should become more focused farther
northward with time. Onshore flow Saturday however will keep the
area rather cloudy and much cooler with even some morning drizzle
possible. The location of the front and associated warm sector to
its south will impact how warm the area gets. As of now, it should
get the warmest during the day Saturday across much of our Delmarva
zones with temperatures then quickly turning cooler northward.
Again, these temperatures will be highly dependent on how far north
the warm front gets however with high pressure sliding by to our
north and an onshore flow the warm front should be slow to move
northward. Some fog may begin to develop Saturday night mainly along
the coast and the adjacent marine area as dew points start to
increase and rise above the chilly ocean water temperatures.

As we go through Sunday, a significant upper-level trough slides
across central to eastern Canada and it is forecast to amplify
southward with its leading edge starting to move into the Northeast
Sunday night. This trough will drive low pressure well to our north,
however a trailing cold front will arrive in our area Sunday. The
existing warm front across the area looks to surge northward Sunday
morning however the cold front looks to be not to far behind. How
far north and inland the warm sector gets ahead of the cold front
will determine how warm areas get. The dew points will rise through
the 50s in areas that get more into the warm sector for a time.
The warm and more moist air mass may also result in marine fog that
could impact the coastal areas as well, before it gets pushed out as
the low-level flow veers from the southwest to west. While the
parent trough lags well behind the surface cold front, height falls
arriving with a greater thickness packing also arriving from the
west should result in enough forcing for ascent for showers to
develop and move in from the west especially in the afternoon and at
night. The timing consensus of the cold front looks a bit faster and
this resulted in temperatures a bit lower especially north of
Delmarva. Some thunder is certainly possible given the strength of
the incoming trough, however the intensity of any convection will
depend on the available instability and shear magnitudes in
combination of any stronger forcing for ascent.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Summary...A stronger cold front moves through Monday night followed
by high pressure arriving Wednesday into Thursday. High temperatures
falling to several degrees below average through the middle of next
week, then some warming begins on Thursday.

Synoptic Overview...An upper-level trough is forecast to
amplify into and across the East during early next week, before
starting to lift out on Wednesday. The next upper-level trough then
looks to begin to amplify across the eastern U.S Wednesday night and
Thursday. At the surface, a stronger cold front moves through Monday
night. High pressure then builds in during Wednesday before shifting
offshore into Thursday. A warm front well ahead of low pressure may
then arrive later Thursday.

For Monday and Tuesday...This time frame starts as more of a
day in transition on Monday as the first cold front is offshore
and we await a secondary cold front tied to the amplifying
upper-level trough. This second front may end up moving through
our area Monday night with little in the way of precipitation as
the deeper moisture is shoved offshore with the earlier cold
front. Given the strength of the incoming upper-level trough
however, cannot ruled out a few rain showers with the second cold
front mainly Monday night or early Tuesday. The arrival of the
colder air aloft along with cyclonic flow may result in a few
rain/snow showers across portions of far northwestern zones. High
temperatures Monday should be several degrees below average. The
second cold front should be offshore to start Tuesday with strong
cold air advection underway. There will be a tightened pressure
gradient in place between departing low pressure well to our
northeast and incoming high pressure from the Midwest to the Ohio
Valley. This will translate to a gusty wind on Tuesday with peak
gusts in the 25-35 mph range before diminishing some at night. High
temperatures Tuesday look to be well below average as much of the
area may not get above the 40s during the day. It will be cold
Tuesday night with most if not all areas dropping below freezing.
There may be to much wind for frost formation, however a freeze
warning may be needed where the growing season has started (most of
our Delmarva zones).

For Wednesday...The strong upper-level trough is currently
forecast to be lifting out with time. This will result in
surface high pressure building into our area before it starts to
shift offshore at night. There may still be a gusty wind in place
before a tightened pressure gradient relaxes as the center of the
surface high builds closer. High temperatures will be several
degrees below average once again, and the wind will determine how
cold it gets at night despite the air mass especially aloft starting
to modify. A clear sky with dew points below freezing would
typically yield a cold night especially if the wind is able to
completely decouple. As a result, there is some risk for frost
and/or freeze (the growing season has started for most of our
Delmarva zones).

For Thursday...The next upper-level trough looks to begin amplifying
into the Eastern U.S. A surface low is forecast to be tracking
toward the upper Ohio Valley with a warm front approaching our area
from the southwest. This will be dependent on the strength of the
developing low relative to the departing high, so much of Thursday
may end up remaining dry. Temperatures do look to begin to moderate
though as southerly flow returns in advance of this system.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through Today...Showers, with tempo reductions to MVFR are possible
through 15Z. There have been some localized and brief IFR conditions
further upstream, but given the latest trends, it appears unlikely
(20% or less) that any of our TAF sites will get that low. Winds
generally favoring SW less than 10 kt will shift to northwest
around 10kt after 09Z. High confidence on the overall pattern,
but low confidence on the timing of any flight category changes.

Tonight...Mostly VFR, though some brief MVFR will be possible as
showers move into the region from the south. Initially with sunset,
expect winds to go light and variable, but eventually will settle
out of the east near or below 10 kt. Moderate confidence.

Outlook...

Saturday...Sub-VFR conditions probable along with some showers.
Some drizzle possible in the morning.

Sunday...Sub-VFR conditions due to low clouds and/or fog should
improve some during the day from south to north. Showers and
possibly a thunderstorm especially in the afternoon and at night
will result in visibility restrictions. Southwest to west and
northwest winds could gust up to 25 knots during the day.

Monday...Sub-VFR conditions possible lingering showers ending.

Tuesday...VFR. Northwest wind gusts up to 30 knots.

&&

.MARINE...
A Small Craft Advisory remains in effect for the Atlantic Coastal
Waters through later this morning. In the last 2 hours, seas have
increased above 5 ft once again, so will keep the SCA going for now,
but will be watching trends to see if seas decrease earlier than the
current expiration time.

Once seas subside, winds and seas should stay below SCA criteria for
the remainder of today and Friday Night.

Outlook...

Saturday...The conditions should be mostly below Small Craft
Advisory criteria. Some visibility restrictions possible due to some
fog mostly at night.

Sunday...Small Craft Advisory conditions possible. Visibility
restrictions possible due to some morning fog, then showers and
possibly a few thunderstorms mainly in the afternoon and at night.

Monday...Small Craft Advisory conditions possible especially in the
morning.

Tuesday...Small Craft Advisory conditions probable.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until noon EDT today for ANZ450>455.

&&

SYNOPSIS...AKL/Gorse
NEAR TERM...Johnson
SHORT TERM...AKL/Gorse
LONG TERM...AKL/Gorse
AVIATION...Gorse/Johnson
MARINE...Gorse/Johnson