193
FXUS61 KPHI 120651
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
251 AM EDT Mon May 12 2025

.SYNOPSIS...
High pressure remains in control today before moving out tonight.
An area of low pressure enters the region by the middle of the
week and brings unsettled weather to the area. A series of cold
fronts move through on Friday and Saturday, keeping wet weather
in the forecast.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure over the Northeast and Mid-Atlantic will slide
offshore today. Meanwhile, low pressure, both at the surface and
aloft, over the Gulf Coast states will slowly lift to the north and
east today and tonight. A warm front extending from that low will
meander over the Mid-Atlantic and Delmarva Peninsula today before
lifting north through Delmarva and into the Delaware Valley
and southern New Jersey late tonight.

Mostly clear to partly cloudy for most of today, but then clouds
will increase and lower from south to north later today and tonight.
Another warm and mild day with highs in the upper 70s to around 80,
though cooler along the coasts, mostly in the 60s, due to onshore
flow over the cooler ocean waters with sea surface temperatures in
the upper 50s to around 60. A few showers associated with that warm
front lay develop over Delmarva late this afternoon, but the showers
will hold off until tonight.

Skies become mostly cloudy tonight as that warm front lifts north
through Delmarva, the Delaware Valley, and southern New Jersey late
tonight. Showers develop in the evening over Delmarva, but the bulk
of the activity will hold off until after midnight. By late tonight,
showers will be likely mainly west of a line from Allentown to
Philadelphia to Cape May, mostly over Delmarva, the Delaware Valley,
and into southwest New Jersey. Lows tonight will be warm and muggy,
generally in the 50s to low 60s. With increasing low level moisture,
patchy fog will develop as well.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
A closed low approaches the region on Tuesday from the southwest
bringing an unsettled batch of weather for midweek. This will be in
the form of widespread rain showers Tuesday and even some isolated
thunderstorms Tuesday night for Delmarva and southern New Jersey.
Scattered showers continue on Wednesday across the area with
some isolated thunderstorms possible. The coverage of showers
starts to decrease Wednesday night as they become more isolated
and a rumble of thunder still cannot be ruled out.

For Tuesday through Wednesday night, the flooding risk is low. There
is a Marginal Risk (1/4) for excessive rainfall for southeast
Pennsylvania and Delmarva for Tuesday and Tuesday night. This is the
period when most of the rain will fall from this closed low. NBM 24
hour probability of over an inch of rain is around 40-45% for
southeast Pennsylvania and closer to 60% for Delmarva. For an inch
and a half of rain, the probability is 20% for southeast
Pennsylvania and near 40% for Delmarva. Generally, there has been an
increase in QPF values with the latest model runs. Right now,
rainfall totals from Monday night through Wednesday evening look to
be around half an inch to an inch for most of the area. Delmarva and
parts of southern New Jersey are ranging from an inch to close to an
inch and a half of rain.

As for temperatures, clouds and rain will keep the area cooler on
Tuesday and Wednesday with highs in the 60s and 70s. Lows at night
will be muggy and in the 50s to low 60s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The closed low gradually opens back up into a shortwave trough
Wednesday night as it continues moving towards the region, then
finally passes overhead on Thursday. The shower coverage may be a
bit more isolated Thursday morning before becoming a bit more
scattered again for the afternoon. For Thursday, highs reach into
the 70s for most. Temperatures do not fall too much overnight
Thursday as lows are mainly in the low to mid 60s.

There is a brief lull in the unsettled weather Thursday night into
Friday morning, as an upper-level ridge builds in with a weak
surface high pressure system. This will allow drier conditions but
does not do much in the way of cloud cover. The high pressure system
does not last long as more showers and even some thunderstorms
arrive for the second half of Friday. A low pressure system over the
Great Lakes will lead to another active stretch of weather for the
end of the week and into the weekend.

For Friday, there is a signal there for a cold front to move through
later in the day which could lead to more of a focal point for
showers and any thunderstorm potential. Another cold front arrives
later Saturday, which could have a similar scenario as Friday by
leading to a more focused area of showers and thunderstorms. Will
note that these series of fronts, both Friday and Saturday, will
have more instability available than the midweek system. These
fronts bear watching for any severe weather potential, as the 500 mb
pattern looks interesting as well. However, would not say there is
an overwhelming signal for widespread severe weather at this point
as this timeframe is a ways away with uncertainty but it does look
active. By Sunday, there is still a slight chance for some showers
to end the weekend.

&&

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

Today...VFR/SCT-BKN250. E winds 5 to 10 kt in the morning, becoming
S after 18Z. High confidence.

Tonight...VFR through around 06Z, then CIGs/VSBYs lower to MVFR
after 09Z in SHRA/BR. S winds 5 kt or less. Moderate confidence.

Outlook...

Tuesday through Wednesday...Primarily IFR with showers and low
clouds expected. Slight chance (15%) of a thunderstorm.

Wednesday Night through Friday...Periods of sub-VFR conditions
likely (80-90%) with low clouds and scattered showers. If there were
a period of VFR, it would be Thursday Night into Friday, though
stratus could hang around. Thunderstorms possible Friday afternoon
(30-40% chance).

&&

.MARINE...
Sub-Small Craft Advisory conditions through tonight. E winds around
10 kt, becoming SE later today and tonight. Seas 2 to 3 ft. VSBY
restrictions in fog and showers developing tonight.

Outlook...

Tuesday...No marine headlines expected.

Tuesday Night through Wednesday...SCA conditions expected with seas
5 to 7 feet and wind gusts near 25 kt at times, especially on the
southern waters and Delaware Bay.

Wednesday Night through Thursday...SCA conditions possible (50-60%)
with seas near 5 feet.

Thursday Night through Friday...No marine headlines expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Guzzo/Hoeflich
NEAR TERM...MPS
SHORT TERM...Guzzo
LONG TERM...Guzzo/Hoeflich
AVIATION...Guzzo/MPS
MARINE...Guzzo/MPS