118
FXUS61 KPHI 061359
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
959 AM EDT Sun Apr 6 2025

.SYNOPSIS...
A cold front moves across our region through tonight as a wave
of low pressure tracks along it. A stronger cold front moves
through Monday night into early Tuesday, then high pressure
builds in Wednesday before shifting offshore into Thursday. The
next low pressure system arrives Friday and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
10 AM Update: Patchy dense fog that developed around dawn is
mixing out as northerly winds bring in slightly drier air near
the surface. This trend is expected to continue through midday.
Aside from the fog, the latest guidance has trended drier
regarding showers for today. Certainly will see some scattered
showers around, but not expecting anything widespread. Opted to
nudge PoPs down a little for the rest of the day, keeping them
mainly around 30-50%. The "main show" for widespread rain is
still expected tonight through Monday morning.

Cloudy with chances for showers will be the theme today.
Multiple frontal boundaries have turned into a quasi stationary
front that has enough mid and upper level support to see
periods of light to moderate rain occur through the morning.
Certainly can`t call the morning a washout, but light rain
chances will be somewhat persistent through the early afternoon.
By mid afternoon the first of what seems like several fronts to
our west will start to track towards the region and bring
another forcing for rainfall. The strong southwesterly low level
jet will be set up ahead of the approaching front helping
moisture transport with this round of showers. The rainfall
should be mostly in the form of beneficial rain given rates
should generally less than 1/4" per hour. With the position of
the quasi stationary front, its likely to be cool day for much
of the region except Delmarva and southeastern NJ which should
be in the warm sector for most of the morning.

Heading into the overnight hours this evening, another round of
low pressure will swing through and lead to a more pronounced
period of rainfall along another frontal system. In this case
the rainfall will likely be enhanced due to the LLJ moving
further north leaving portions of the area in the RRQ. As this
low pressure system moves through, cold air filtering in from
the north will support the potential for some mixed period to
work into the higher terrain of Carbon/Monroe counties. While
soundings show the potential for both IP and ZR, the forecast
has trends towards slightly more sleet than freezing rain
accumulation given that the warm nose doesn`t appear that strong
and there does seems to be a substantial enough layer below the
warm nose for the ice to refreeze. Accumulations and impacts
should be minor at most from either ice or sleet with only
really a trace anticipated.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Cold conditions along with increasing wind as precipitation
ends.

The main ripple of energy along with more of the trough aloft
getting closer should shift off the coast during Monday,
although this process may be slowed. As a result, showers or
periods of rain will continue for a time Monday however this
gradually tapers off from west to east. Some snow or wintry mix
is possible Monday morning across parts of our far northwestern
zones. High temperatures on Monday are forecast to only be in
the 40s to low 50s.

A secondary cold front Monday night may end up moving through
our area with little in the way of precipitation as the deeper
moisture is shoved offshore with the earlier front/wave. Some
guidance shows that this front is strong however moisture is
limited. A narrow line of showers well to our west may then
weaken or dissipate before it reaches our area Monday night.
Given the strength of the incoming upper-level trough though,
cannot ruled out some rain showers (snow showers across the far
northwest) Monday night. Low temperatures by Tuesday morning
will be mostly in the 30s. While temperatures in the mid/upper
30s are forecast all the way south into Delmarva, there will be
to much wind for any frost formation.

As we go through Tuesday, the arrival of the colder air aloft
along with cyclonic flow may result in a few rain/snow showers
across portions of our far northwestern zones. Otherwise, strong
cold air and dry advections will be well 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
northwest wind 15-25 mph on Tuesday with peak gusts in the 25-35
mph range before diminishing some at night. High temperatures
Tuesday are forecast to be well below average as most if not all
of the area should not get above the 40s during the day (it
will feel even colder given dew points in the teens and gusty
winds). It will be quite cold Tuesday night, with all areas
dropping below freezing. While the wind is forecast to diminish
quite a bit, it does look like it will probable not be enough
and this would greatly limit frost formation. However, a Freeze
Watch/Warning will be needed where the growing season has
started (most of our Delmarva zones).

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Summary...Cold air to start, then high temperatures should
return to near average for the end of the week into the weekend.
It looks to turn unsettled again to end the week.

Synoptic Overview...An upper-level trough across the Northeast
eases some Wednesday before additional energy dropping down
across the Midwest to the Tennessee Valley starts to amplify it
again eastward Thursday and beyond. Some guidance shows this
trough becoming closed off as it arrives into the Mid-Atlantic
region later Friday into Saturday. At the surface, high pressure
builds in Wednesday before shifting offshore into Thursday. Low
pressure and its associated cold front approaches Thursday
night into Friday, then it may slow as it reaches the Mid-
Atlantic region later Friday and Saturday as it potentially
becomes trapped under a closed low.

For Wednesday...The strong upper-level trough is forecast to be
lifting out and easing its grip on our area. This will result
in surface high pressure building into our area before it starts
to shift offshore at night. There should still be some wind but
less than Tuesday prior to the center of the surface high
arriving. High temperatures will be several degrees below
average once again (near 50 degrees in most areas). The wind
will diminish more at night, however it should also back to more
southerly. This will start to increase the surface dew points
at least some. While the air mass will be moderating some aloft,
dew points below freezing should yield a rather cold night
especially if the wind is able to completely decouple and dew
points remain below freezing. There may however be some clouds
increasing from the west Wednesday night and the height and
thickness of them could have some impact on temperatures.
Forecast low temperatures are not as cold as Tuesday night as a
result. While there is some risk for frost and/or freeze (the
growing season has started for most of our Delmarva zones), this
will depend on the above factors.

For Thursday through Saturday...As energy dives southeastward
out of the Midwest and into the Tennessee Valley Thursday, an
upper-level trough is forecast to then amplify eastward and
settle once again across the East. Some guidance has this trough
closing off as it reaches the Mid-Atlantic region and vicinity.
A surface low tied to this incoming trough may slow its
eastward progression especially if the trough becomes closed
off. A warm front will initially be approaching our area from
the southwest later Thursday, then the main low arrives later
Friday into Saturday. On Thursday, a slower solution would delay
the onset of showers with more of the showers or even periods
of rain developing sometime on Friday and continuing into
Saturday. Some model solutions show as the trough aloft closes
off, the surface low could become a nor`easter centered just off
Delmarva Saturday morning. The evolution of this entire system
is less certain at this time range and therefore PoPs are held
in the mid/high chance to low likely range (40-60 percent).
Temperatures do look to be close to average, although if a
nor`easter does develop with strengthening onshore flow then
temperatures would end up cooler.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...IFR ceilings to start the day, trending towards MVFR
and low VFR between 15-19Z. Most terminals will likely have low
VFR ceilings by 00Z. Light and variable winds will become
west/northwest around 10 kt with the passage of a cold front
which should be through the area by 18Z. Moderate confidence.

Tonight...Periods of rain will bring a return IFR/MVFR cigs and
visibilities and a frontal system brings a reinforcing shot of
rainfall to the region tapering off towards the morning.

Outlook...

Monday...Sub-VFR conditions improve to VFR as showers end.

Tuesday...VFR. Northwesterly wind gusts up to 30 knots during
the day, then diminishing at night.

Wednesday...VFR.

Thursday...Areas of sub-VFR conditions may develop at night
along with a chance for showers.

&&

.MARINE...
Seas have been hovering right around 5 feet for the Altantic
waters and are anticipated to briefly build to 4 to 6 in the
early afternoon before subsiding heading into the evening. On
the Delaware Bay, the concern is for reduced visibilities as
waves and winds should remain below SCA criteria.

Marine fog will remain a challenge through the remainder of the
morning, as guidance suggests it will take some time to mix dry
air down and scour out the low level inversion. The Dense Fog
Advisory remains in effect for the New Jersey coastal waters
through 11 AM.

Outlook...

Monday...Small Craft Advisory conditions possible in the
morning, then especially later at night.

Tuesday...Small Craft Advisory conditions probable, with the
conditions improving some later at night.

Wednesday and Thursday...The conditions are anticipated to be
mainly below Small Craft Advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until 11 AM EDT this morning for ANZ450>453.
     Small Craft Advisory until 6 PM EDT this evening for
     ANZ450>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...Deal/Staarmann
SHORT TERM...Gorse/Staarmann
LONG TERM...Gorse/Staarmann
AVIATION...Deal/Gorse
MARINE...Deal/Gorse/Staarmann