Flash Flood in Pennsylvania, May 14, 2025

Area Forecast Discussion
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
926 AM EDT Wed May 14 2025

.SYNOPSIS...
Low pressure will linger across the Mid Atlantic through the
Thursday, resulting in mild and showery conditions. Brief period
of ridging comes in Thursday Night, with a warm front coming
through on Friday morning. Unsettled weather continues through
Saturday until a strong cold front comes through on Saturday
Night. Drier high pressure will settle into the region by Sunday
into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
An upper level low over the Tennessee River Valley is
transitioning to an open trough, with deep south/southwesterly
flow set up over the eastern US.

Periods of showery rains will move north as the morning goes
on, and we may get a break in the rainfall through the midday
hours. Some areas, mainly in southern Delmarva, may actually see
some areas of sunshine. This will allow some instability to
build, potentially resulting in a few thunderstorms as another
shortwave comes in. Otherwise, scattered showers will remain
around through the day, though it does not look as dreary as
yesterday. Thinking rainfall amounts will end up around a half
inch to three quarters of an inch, on top of the 0.25"-0.75" we
received yesterday. Certainly need the rainfall and thinking the
only hydro issues will be poor drainage flooding. Temperatures
get into the mid to upper 60s, with 70s over Delmarva with less
cloud cover and more heating.

Stays mild tonight, though only expecting some scattered light
showers. Some may stay dry though as PoPs are only 30-40% or so
with any accumulations under a tenth of an inch. Lows end up in
the upper 50s/low 60s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A trough axis passes overhead on Thursday, which will result in
continued showers remaining across the region. Showers should
be relatively light, though with daytime heating, cannot rule
out a few scattered to isolated thunderstorms, mainly from the
I-95 corridor on west. Setup is not overly impressive is
instability is meager and the forcing is not the strongest, but
would expect more of this unsettled pattern to continue through
the day until the trough passes late Thursday. Temperatures get
into the mid to upper 70s.

A brief period of quiet weather comes Thursday night as a brief
period of ridging moves overhead. Skies may actually clear out
some Thursday evening into the first half of Thursday Night
before a warm front moves in late Thursday/early Friday morning.
Mainly dry through Thursday Night though but still mild, with
lows in the upper 50s/low 60s.

A warm front lifts through Friday morning, bringing some light
showers as warm air advection ramps up. This will allow
temperatures to climb into the 80s on Friday, with more
instability in place as well. Forcing looks rather weak though
with ridging not far away and only a weak shortwave coming in
and no advancing cold front until Saturday. Thus, thinking it
will be just unsettled with scattered showers, primarily in the
afternoon with a few thunderstorms mixed in. Showers diminish in
coverage with the loss of daytime heating on Friday Night, but
still cannot rule out some light sprinkles through the night.
Mild pattern continues with low to mid 60s for lows.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Saturday looks to be the day to monitor for any severe weather.
Forcing strengthens with an incoming potent shortwave digging
from the Great Lakes. At the surface, an area of low pressure
slides by to the north Saturday into Saturday Night, with a cold
front advancing towards and eventually through the region.
Temperatures will climb into the 80s and it will feel quite
muggy ahead of the front. Instability looks to be on the order
of around 1000 J/kg with relatively favorable shear. Thinking
any showers and thunderstorms will come in the afternoon and
evening as the front arrives. Main concern would be damaging
wind gusts and heavy downpours, but still a good amount of
uncertainty being a few days out. Coverage in showers and
thunderstorms diminishes into the night with the loss of daytime
heating and passage of the front.

Sunday and beyond actually looks pretty nice for now. With the
front coming through, it should result in dry conditions and
seasonable weather to close out the weekend and start next week.
Perhaps a little gusty on Sunday, but nothing that looks too
significant.

&&

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

Today...MVFR and some IFR vsby/cigs have finally materialized
this morning with scattered -RA/SHRA around. This should
continue for much of the day, with a low chance of thunder this
afternoon. Have kept this out of TAFs given the low confidence
and low probability. ESE winds 10 to 15 kt with 20 to 25 kt
gusts. The gusts will decrease by midday, and winds down to
around 10 kt or less for the afternoon and evening. Moderate
confidence.

Outlook...

Sub-VFR with intervals of IFR likely through Thursday with
showers and a few thunderstorms. Conditions should improve a bit
Friday and Saturday during the day before showers and
thunderstorms move in for the afternoon and evening. VFR
conditions look to come Saturday Night and beyond.

&&

.MARINE...
The Gale Warning was canceled, as gale force wind gusts never
materialized and no additional threat of gale force gusts is
expected. A Small Craft Advisory is now in effect for all
coastal waters. The Delaware Bay advisory runs through noon.
Southern ocean waters goes through tonight, and the northern
waters through Thursday morning.

Winds will diminish considerably by this afternoon, however
seas will remain elevated near 4-6 feet through tonight into
early Thursday morning.

Outlook...

Advisory conditions with seas persisting near 5 feet on the
ocean waters until during the daytime on Thursday could result
in an extension to the SCA. Showers and spotty thunderstorms
will also be a concern on the waters through this entire period.

Sub-SCA conditions should then take hold by Thursday evening
and continue through Sunday However, showers and spotty
thunderstorms may continue to be a risk through Saturday,
especially during the afternoon and evening hours.

&&

.TIDES/COASTAL FLOODING...
A new Coastal Flood Advisory has been issued for the tidal
Delaware River for the high tide late tonight into early
Thursday morning. Elsewhere, no additional coastal flooding is
expected.

Minor coastal flooding is forecast with the overnight high
tides Thursday night and Friday night as well, especially along
the upper reaches of the tidal Delaware River. Additional
advisories may be needed.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Coastal Flood Advisory from 2 AM to 7 AM EDT Thursday for
     PAZ070-071-106.
NJ...Coastal Flood Advisory from 2 AM to 7 AM EDT Thursday for
     NJZ017>019.
DE...None.
MD...None.
MARINE...Small Craft Advisory until noon EDT today for ANZ430-431.
     Small Craft Advisory until noon EDT Thursday for ANZ450>452.
     Small Craft Advisory until 6 AM EDT Thursday for ANZ453>455.

&&

SYNOPSIS...Hoeflich/Staarmann
NEAR TERM...Hoeflich/Staarmann
SHORT TERM...Hoeflich
LONG TERM...Hoeflich
AVIATION...DBR/Hoeflich/Staarmann
MARINE...Hoeflich/Staarmann
TIDES/COASTAL FLOODING...