Tornadoes in Pennsylvania, May 4, 2025

Area Forecast Discussion
National Weather Service Mount Holly NJ
926 AM EDT Sun May 4 2025

.SYNOPSIS...
Slow moving low pressure over the Ohio Valley will gradually
cross our region through Tuesday before finally pulling away to
the northeast on Wednesday. A cold front will drop southeastward
across the region on Thursday, with low pressure developing off
the coast of New England on Friday. High pressure will return
for Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
925 AM...As of mid morning, there are some leading showers
across the area with a swath of heavier and more widespread
showers approaching from Virginia and western MD. This will
overspread the area west to east through the late morning into
the early afternoon. Some minor adjustments were made to the
near term POP, weather, and temperature grids based on the
latest obs and trends but otherwise forecast remains on track.
Previous discussion follows below.

A closed 500 mb low located over portions of the Ohio and
Tennessee Valleys will make very little eastward progress today,
and enhanced mid-level flow associated with this feature will
continue to overspread the region. The associated surface
cyclone will make some slow eastward progress toward our area
through the day.

Precipitation will be much more widespread today than the
previous couple of days , with most locations seeing at least
some rain. Thankfully, today will feature significantly less
instability, and severe weather is not anticipated. However,
forecast soundings indicate very moist vertical profiles across
much of the area today, with PWATs near 1.5". Therefore, storms
today will be capable of heavy rainfall, and localized flooding
cannot be ruled out. Due to this threat, the Weather Prediction
Center has placed the entire forecast area in a Marginal Risk
for excessive rainfall today.

With plentiful clouds and widespread rain during peak heating,
today will be cooler than the past couple of days. In fact,
afternoon highs will only be in the upper 60s to near 70 across
the area. By this evening, widespread rainfall chances will
decrease from west to east as this wave departs. However, low
clouds and scattered showers will likely remain in place for
most of the area through the overnight hours. It will be another
warm night, though perhaps slightly cooler, with lows ranging
from the upper 50s to lower 60s.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Slow moving surface and upper level low pressure will very
gradually move from the Ohio Valley towards upstate New York
during the short term. This will result in continued rounds of
showers and thunderstorms, but with plenty of clouds and more of
an onshore flow, instability should be limited. Thus, the main
risk will continue to be heavy rain and flooding versus severe
weather. While nailing down the exact times of these shower and
thunderstorm intervals can be tricky with upper lows, right now
the highest chances look to be late Monday into Monday night,
with another round later on Tuesday. These likely will be
enhanced by the limited daytime heating, and also will be most
concentrated across areas northwest of the I-95 corridor. The
Poconos could send up with 3-4 inches of rain by storm's end,
while at least some parts of the coastal plain may struggle to
pick up an inch. Temperatures will have relatively low ranges
with the clouds and onshore flow Monday, with highs in the
upper 60s to low 70s and lows in the upper 50s to low 60s. The
flow starts shifting back offshore on Tuesday, so highs should
gain a few degrees with most places reaching the 70s and a few
spots in the south approaching 80. As the system pulls out to
the northeast Tuesday night, shower coverage should quickly
reduce while the drier air moving in behind it will help bring
lows down a few degrees, mostly 50s across the board.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
System will continue pulling away to the northeast on Wednesday,
but the upper low may still spark off a few showers mainly
northern areas. Overall it should be a nicer day, with at least
some sun if not an extended period of it, and highs mostly in
the 70s again.

Clouds return Wednesday night as the next cold front starts to
approach from the northwest. This will hold lows of slightly
from Tuesday night, but overall fairly similar.

Another round of showers or perhaps even steadier rain looks
possible Thursday as cold front comes through and the upper
trough starts cutting off, potentially spawning a surface low
pressure in our region as the front passes. The higher cloud
cover and better chance of showers will hold highs back a few
degrees from Wednesday, mostly upper 60s to low 70s.

Cooler air pushes southeastward as low pressure strengthens off
the New England coast Thursday night into Friday, and there
could still be a stray shower, but overall chance of precip
declines. Lows well down into the 50s with colder spots in the
upper 40s for Thursday night, with highs down in the 60s area-
wide for Friday.

High pressure slowly builds in for Saturday, with some modest
warning. After a relatively cool night in the upper 40s to low
50s Friday night thanks in part to radiational cooling, high
Saturday likely reach the low 70s for most of the region.

&&

.AVIATION /13Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...MVFR at most terminals to start the day, with lowering
ceilings through the day. Periods of IFR ceilings are possible at
all terminals, perhaps as early as 13-14Z for KRDG and KABE,
after 15Z for the I-95 terminals, and after 18Z for KMIV and
KACY. Widespread showers and embedded thunderstorms move in from
west to east from late morning to early afternoon. Some
visibility reductions are likely in the heaviest storms.
Southeast wind around 10 kt, with gusts 15-20 kt for KMIV and
KABE. Moderate confidence.

Tonight...MVFR/IFR at most terminals due to low ceilings.
Scattered showers may continue through the night with some
potential for the development of patchy fog as well. East-
southeast wind around 5 kt. Moderate confidence.

Outlook...
Intervals of MVFR with some periods of IFR likely Monday and
Tuesday as low pressure slowly crosses the region with showers
and a few thunderstorms. VFR likely becomes more dominant again
Wednesday and Thursday as weak high pressure builds in and then
a cold front drops down from the north, with some sub-VFR
intervals still possible both days during showers.

&&

.MARINE...
For the remainder of today and into tonight, conditions are
expected to be below SCA criteria with wind gusts near 20 kt and
waves as high as 4 ft into this afternoon and decreasing
further tonight.

Outlook...
Monday looks mostly below SCA levels, but showers and t-storms
will be present. Monday night into Tuesday, showers and t-storms
continue while marginal SCA conditions may develop on the ocean
mainly due to elevated waves up to 6 feet. These likely decline
by Tuesday night. Sub-SCA conditions should then prevail
Wednesday and Thursday, with only spotty showers possible.

&&

.HYDROLOGY...
Several waves of wet weather will continue today through
Tuesday. Several inches of rain may fall in some locations,
however timing and location will be critical to determine if any
flooding issues arise. If higher convective hourly rainfall
rates occur in any location in a short period of time,
especially over the urbanized areas, there will be an increasing
localized flash flooding risk due to more efficient runoff.
Fortunately, we are coming off an extended dry spell,
particularly northwest of I-95 where indications suggest the
heaviest rain may end up falling. For the time being, we will
continue to monitor trends in the guidance.

&&

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

&&

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