565
FXUS61 KPHI 030114
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
914 PM EDT Fri May 2 2025

.SYNOPSIS...
Mild temperatures persist through Saturday. A cold front will
gradually work its way into the region Saturday night and
Sunday. Several waves of low pressure will be around the region
through Tuesday bringing a prolong period of unsettled weather
ahead of another cold front that crosses through the area by
Tuesday night. Broad high pressure then returns by Wednesday
into the end of next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Some showers and thunderstorms are developing out ahead of the
shortwave moving through central Pennsylvania and central New
York and are beginning to move into far western portions of the
forecast area. Will bump up PoPs a bit for the western and
northern zones into midnight or so. MUCAPE values are generally
500 to 1000 J/kg, but should be lowering as temperatures lower
through this evening with loss of diurnal heating. Not expecting
much more than a few brief downpours and a few rumbles of
thunder, and perhaps some wind gusts of 30 to 40 mph are
expected.

Overnight lows will remain quite warm, with most locations not
falling out of the 60s.

Forecast guidance continues to depict a slower progression
southward of the cold front (compared to how things looked a few
days ago) with Saturday now looking to be solidly in the warm
sector. This means we`ll be solidly in the 80s away from the
coast and the Poconos. The morning looks mostly dry with some
sun, but later in the afternoon, as the cold front approaches
from the northwest, showers and thunderstorm look likely to
break out, especially northwest of I-95. CAPE likely reaches
1500 J/kg with 30-40 kts of deep layer shear. Precipitable water
peaks up around 1.5 inches as well. So, we may have both a
severe and flash flood risk, though fortunately for the latter,
the weather has been rather dry of late. Bottom line, radar
looks likely to be quite busy late Saturday, especially from
I-95 north and west, away from the potential marine influence.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Evening convection likely begins to wane around sunset with the
loss of diurnal heating. The front will be slowing down as its
approaches up to our northwest, so another mild night is likely
with a chance of showers and lows in the upper 50s and 60s
through the night.

By Sunday, the cold front appears to stall out across the
region as the upper flow begins to take shape in an omega block
pattern. Deep upper ridge will be over the Central US with two
cut off lows, one positioned near the California coast and the
other across the Ohio River Valley. It is this upper low that
will meander over this region through Monday, which will result
in several weak disturbances and waves of low pressure to track
through the area. This will result in several periods of wet
weather for Sunday and Monday. While no specific period appears
to be a washout by any means, there likely will be showers
in/around the area through the duration of the day/night
especially with the stalled front nearby. At this time, the
severe risk looks negligible as there isn`t much instability
around with the abundance of cloud cover. On the other hand,
with the abundance and PWATs near 1.50", any shower will be
capable of heavy rainfall with localized flash flooding
possible. As a result, portions of the area are outlooked in a
Marginal Risk for excessive rainfall on Sunday by WPC, with the
entire area outlooked in a Marginal Risk on Monday. Total QPF
between Saturday night and Monday will range generally between
3/4 of an inch toward the coast to up to 1.5-2.0 inches in the
Poconos. Highs will mostly be in the 70s on Sunday, with highs a
few degrees cooler on Monday as the front drops a bit further
south across the area.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Little changes were made to the long term period as an
unsettled weather period looks to be in places through at least
Tuesday, before beginning to see some improvement and drying by
mid to late week.

Slow moving low pressure and stalled frontal boundaries will be
in place as the omega block persists into Tuesday. The blocking
pattern begins to break down by Tuesday night as the upper low
is forecast to track across the area and move off the coast of
New England on Wednesday. With this in mind, the wet weather
will continue at least through Tuesday before beginning to taper
off Tuesday night into Wednesday. Here, much of the area is
currently outlooked in a Marginal Risk for excessive rainfall on
Monday and Tuesday by WPC. High pressure then appears to
`finally` build back in by late week which will keep much of the
region dry. It should be noted though with these blocking
patterns that set-up, that the forecast will vary significantly
as to when these patterns ultimately break down. So while, it
looks like we`ll finally see some drying return by Wednesday,
this may be pushed forward/back depending on when the entire
pattern breaks down.

In terms of temperatures, we`ll likely have high and low temps
within a few degrees of normal for early May.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Mainly VFR. South-southwesterly wind around 5-10 kt
in the evening decreasing to 5 kt or less overnight. A few
isolated showers will remain possible, mainly before 6z. High
confidence.

Saturday...VFR conditions should prevail through the morning.
However, by the afternoon and evening, showers and
thunderstorms become increasingly likely, especially north and
west of the I-95 terminals. SW winds around 10-15 gusting 20 to
25 knots with higher gusts possible in any storms. Moderate
confidence.

Outlook...

Saturday night through Tuesday night...Mixed periods of sub-VFR and
VFR conditions are likely to occur with several chances for rain
showers and isolated thunderstorms. During periods of wet weather,
expect sub-VFR conditions. Outside of wet weather, conditions should
primarily be close to/or VFR.

Wednesday...VFR with a slight chance of showers. No significant
weather expected.

&&

.MARINE...
Conditions have subsided to below Small Craft Advisory on the
ocean waters, so will go ahead and cancel the SCA that was in
effect through this evening. There will be a period of sub-SCA
conditions until winds and seas ramp up Saturday afternoon. Will
issue a new SCA for the ocean waters starting Saturday
afternoon.

Lighter winds likely linger on the bay so lower risk of SCA
flag. During this time, showers and thunderstorms are possible
over the waters, though coverage still looks relatively low on
Saturday.

Outlook...

Saturday night through Sunday...SCA conditions likely. Wind gusts up
to 25-30 kt on Saturday night with seas of 4-6 feet continuing into
Sunday. Rain showers and isolated thunderstorms possible.

Sunday night through Monday...No marine headlines expected. Winds
generally less than 20 kt with seas around 3-4 feet. Rain showers
and thunderstorms likely.

Monday night through Tuesday...SCA conditions possible due to seas
building to around 5 feet. Rain showers and thunderstorms likely.

Tuesday night through Wednesday...No marine headlines expected.
Winds generally less than 20 kt with seas around 3-4 feet. Slight
chance of rain showers and thunderstorms.

&&

.HYDROLOGY...
A significant period of wet weather looks to begin late
Saturday and persist into at least Tuesday. Several inches of
rain may fall in some locations, however timing and location
will be critical to determine if any flood issues arise. If the
rain is spread out over several days, little flooding may occur,
but heavy convective rains concentrated in any location and
shorter time period may result in significant issues.
Fortunately we are coming off an extended dry spell,
particularly northwest of I-95 where indications suggest the
heaviest rains may end up falling. For the time being will
continue to monitor trends in guidance.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 1 PM Saturday to 7 AM EDT Sunday for
     ANZ450>455.

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...Cooper/Fitzsimmons/MPS
SHORT TERM...DeSilva/RCM
LONG TERM...DeSilva/RCM
AVIATION...DeSilva/Fitzsimmons/Guzzo
MARINE...DeSilva/Fitzsimmons/MPS
HYDROLOGY...