316
FXUS61 KPHI 050614
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
214 AM EDT Sat Apr 5 2025

.SYNOPSIS...
The cold front settles to our south tonight as high pressure builds
across New England. As low pressure tracks up into the Great Lakes
on Saturday, the front will lift back north across the area as a
warm front. A cold front then crosses through the region on Sunday,
followed by a stronger, secondary front that passes through on
Monday night. High pressure returns by late Tuesday through
Thursday, before another disturbance approaches by the end
of next week.

&&

.NEAR TERM /THROUGH TODAY/...
Lowered PoPs through the overnight hours as we are currently in
a lull of any precip. High pressure north of the Great Lakes
will build east tonight, passing north of New York State and
moving into the Canadian Maritimes by Saturday morning.
Meanwhile, the stationary front remains to our south. There have
been some scattered showers that have developed along the front,
but not confident it will get as far north and northern Delmarva.

Low pressure will organize and develop over the Southern Plains
tonight and will lift north towards the Great Lakes and Ohio
Valley. As it does, it will slowly pull that stationary
boundary back north as a warm front. However, because of the
position of the high to the northeast, there are some concerns
as to how far north that from will track. Quite possible that
with the low moving through the Great Lakes and Ohio Valley on
Saturday that the front will snake around the area, with the
warm front getting just as far north as southern Delmarva.

Several additional waves of rain will pass west and north of the
area, so most rain will be confined to areas mainly north and west
of the Fall Line. Will carry chance PoPs for rain most elsewhere.

High temperatures on Saturday will be seasonally chilly, generally
around 5 degrees below normal for most areas. This will be highly
dependent on how far north the warm front can get. Highs in southern
Delmarva should get into the upper 60s to low 70s, while the rest of
the area should be in the 50s to low 60s. But if that front can make
its way north just a little bit more, then a bit more of the area
would be warmer than forecast.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
The front will gradually work its way north on Saturday night, but
will continue to struggle with its progress. Showers will also
continue especially north and west of the I-95 corridor, where
embedded thunder is possible. Elsewhere, just some isolated showers
are possible. With onshore flow continuing, expect a widespread
swath of fog to develop and push inland as dew points will be on the
rise. Low temperatures will vary depending on location, with 40s/50s
across most areas with 60s across southern most areas.

Heading into Sunday, a strong and deep upper level trough slides
across central to eastern Canada and it is forecast to amplify by
Sunday night. This trough will cause low pressure to track well to
our north with a cold front trailing to the southwest which will
cross through our area on Sunday. The temperature gradient on Sunday
will be quite diverse, with in the upper 40s/50s north with 70s
across the Delmarva. How far the front/warm sector reaches is yet to
be known, but will ultimately determine how warm areas get. While
the parent trough lags well behind the 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 best chance for thunder does appear
to be over the Delmarva into extreme southern New Jersey where
instability and moisture transport is greatest.

For Sunday night, we`ll likely see another period of showers move
into the region while lingering into the first part of Monday as a
secondary wave of low pressure forms along the cold front that moved
through during the day on Sunday. Rain may be heavy at times as
well, but overall not looking at anything all that significant, just
some more beneficial rain with up to 1 inch of rain possible. In
fact, we`ll start to see some cooler air ushering in on the back
side of the front, so may see some rain mixing with some wet snow
across the higher terrain on the Pocono Plateau. All in all, a few
tenths of accumulation do look plausible, considering cold air
advection filling in its wake. Otherwise, plain rain is expected
elsewhere. This disturbance should move off the coast by Monday and
we`ll see a much cooler airmass move into the region and some drying
from northwest to southeast. High temps on Monday should only range
from the upper 40s to mid 50s, which will put us a few degrees below
normal for early April.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Summary...A stronger, secondary cold front moves through Monday
night followed by high pressure arriving later Tuesday into
Thursday. High temperatures will fall several degrees below-normal
through the middle of next week, with the return of seasonable
temperatures by the end of the week.

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
with the trough moving into the region by Friday. At the surface, a
strong, secondary cold front moves through Monday night. High
pressure then builds in late Tuesday into Wednesday before shifting
offshore into Thursday. Another low pressure system then approaches
Thursday night into Friday.

For Monday night and Tuesday...The secondary front may end up moving
through our area Monday night with little in the way of precip
associated with it 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. The
secondary 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 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 and Friday...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 /06Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...Should keep mostly VFR conditions as it looks like
lower ceilings will hold off until after 12Z. Winds should
generally favor an easterly direction with speeds less than 10
kt.

Today...Ceilings may start for the first few hours as VFR, but
are expected to lower to MVFR and eventually IFR through the
day. Temporary visibility restrictions possible with passing
showers and BR development. Winds should favor ESE direction
around 10 to 15 kt. Increasing concern of periods of low level
wind shear as will have a SW low level jet near the area through
out the TAF period. At this point though, period of most concern
is early afternoon, and mostly for TAF sites from the I-95
corridor eastward.

Tonight...Continued IFR conditions (primarily due to low
ceilings) is expected. KMIV and KACY could see some improvement
late overnight as winds shift to more SW, but low confidence on
the timing of that. Winds will start E or NE at 10 Kt or less,
but could become light and variable late overnight. Another
period of low level wind shear with a SW low level jet is
possible between 00 and 06Z.

Outlook...

Saturday night through Monday...Sub-VFR conditions likely with
several rounds of showers and isolated thunderstorms possible.
Patchy fog on Saturday night too.

Monday night through Wednesday...VFR expected. Winds may
occasionally gust upwards of 25-30 kt on Tuesday.

&&

.MARINE...
W-NW winds 10 to 15 kt, becoming E-SE tonight through Saturday.
Seas will average 2 to 4 feet. Sub-Small Craft Advisory
conditions on tap for tonight through Saturday.

Outlook...

Saturday night through Sunday...SCA conditions likely on the
Atlantic coastal waters due to wind gusts up to 25 kt and seas
around 4-6 feet. Showers likely with isolated thunderstorms.

Sunday night through Monday night...Lingering SCA conditions
possible mainly due to seas near 3-5 feet. Rain showers likely.

Tuesday through Tuesday night...SCA conditions probable due to wind
gusts up to 30 kt and seas around 5 feet. Fair weather outside of
SCA conditions.

Wednesday...No marine headlines expected. Fair weather.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 2 AM to 6 AM EDT Sunday for ANZ451-
     452.
     Small Craft Advisory from 11 PM this evening to 6 AM EDT
     Sunday for ANZ453>455.

&&

$$

SYNOPSIS...DeSilva/Gorse
NEAR TERM...Johnson/MPS
SHORT TERM...DeSilva/Gorse
LONG TERM...DeSilva/Gorse
AVIATION...DeSilva/Johnson
MARINE...DeSilva/MPS