488
FXUS61 KPHI 132031
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
431 PM EDT Sun Jul 13 2025

.SYNOPSIS...
Very warm and humid air will be over the region this week. A
cold front will move eastward into the region late Monday, and
then become stationary in our area on Tuesday and Wednesday. It
will move northward as a warm front on Thursday. Another cold
front approaches toward the end of week.

&&

.NEAR TERM /THROUGH MONDAY/...
The biggest concern through this period is the potential for
heavy rain and flash flooding, particularly with the storms late
Monday into Monday night.

Radar showing a north to south band of convection from the
lower Susquehanna Valley into the southern Poconos, grazing
Berks and Carbon counties. Latest hires guidance has convection
moving slowly eastward for the rest of the afternoon but it
should weaken by the time it reaches the Delaware Valley area by
early to mid evening.

With light winds and surface dew points in the lower 70s
tonight, low clouds and patchy fog will develop again. Best
chance for lower visibilities in fog are in southern New Jersey,
the Poconos, and Lehigh Valley.

On Monday, a front will approach the area at the surface at the
same time a short wave trough in the mid and upper levels
crosses our area. Models have trended slightly later with the
arrival of the front. Storms will happen well ahead of the
front, but it may mean especially for places like Delmarva and
South Jersey that storms are much later to arrive.

Heavy Rain/Flash flooding risk: More detail of the heavy
rain/flash flooding risk is below in the hydrology section.
However, this remains the main concern with any showers and
thunderstorms on Monday, particularly in the afternoon and
evening. There is enough of a risk that a flood watch for flash
flooding was issued for southeastern PA and in New Jersey from
the I-195 to I-80 corridors. Depending on what guidance depicts
with the 00Z model runs, the watch may need to be expanded to
include far NW NJ and the southern Poconos. To the southeast of
the watch (including Delmarva and South Jersey), given the
slightly later trend, not as confident that storms will be as
prolific rain producers by the time they reach those areas.

Other hazards: Aside from lightning, the only other risk to
talk about with the storms tomorrow is a small (5 to 15%) chance
for gusty winds. Overall, DCAPE values are very low, but there
is potential for precip loading to develop into a wet downburst
with stronger storms.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
The previously mentioned front is expected to stall over our
region through mid week. A mid to upper level short wave ridge
will try to build in from the southwest, which could work to
suppress coverage of convection despite the presence of the
decaying frontal boundary. However, there is uncertainty in how
quickly this ridge will build east.

Scattered showers and storms are probable Tuesday and
Wednesday, primarily in the afternoon and evening, and
especially along and south of where ever the frontal boundary
ends up. Precipitable water values will remain well above
average, so locally heavy downpours will remain possible. At
this point, the risk for severe hazards is low.

Seasonable temperatures with humid conditions can be expected
through this period. High temperatures will be mainly in the mid
to upper 80s, with muggy nighttime low temperatures in the low
to mid 70s. Fog formation is possible for areas during the late
nighttime and early morning periods, but this will be dependent
on precipitation occurrence and mixing.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
This period will start off with a focus of dangerously hot
conditions, before another cold front approaches the region late
in the week.

Humid air will remain in place, and with continued
southwesterly flow (before the next cold front arrives), warm
air advection will continue. As such, heat index values near or
above 100F will be possible across most of the area (excluding
higher terrain in the Poconos and NW NJ) on Thursday. Depending
on the timing of the cold front, similar hot and muggy
conditions could continue on Friday.

This pattern supports a continuation of the showery and stormy
summertime pattern. Expect mostly diurnally driven
afternoon/evening showers and thunderstorms, that will be
limited in coverage. However, the next cold front will probably
end up being a focus for more widespread rain. As for severe
hazards, no strong signal either way; if the front comes in
during peak heating (which is unlikely at this point), then the
risk for severe storms could increase. Heavy downpours will
remain possible through the entire week. The severe thunderstorm
potentially will probably be more mesoscale drive than
synoptic, typical of July.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

This afternoon...MVFR ceilings becoming VFR. Thunderstorms
possible west of the Delaware valley. Light Southeast winds.

Tonight...Scattered thunderstorms this evening west of the
Delaware valley, otherwise VFR early. MVFR to IFR in low
ceilings after midnight. Light south wind.

Monday...VFR. MVFR in scattered afternoon thunderstorms. South
wind 5 to 10 knots.

Outlook...

Monday night through Friday...Overall, prevailing VFR
conditions. However, afternoon and evening SHRA/TSRA may result
in brief periods of sub-VFR conditions daily. Sub-VFR conditions
are also possible overnights/early mornings due to low clouds
and fog, but uncertainty remains on this potential, so
confidence is low.

&&

.MARINE...
Winds and seas should generally stay below Small Craft Advisory
criteria through Monday. gusty winds could be possible in the
vicinity of any thunderstorms late tomorrow.

Outlook...

Monday night through Thursday...Winds and seas should stay
below Small Craft Advisory criteria through this period. Showers
and thunderstorms are possible daily, primarily in the late
afternoon and evening hours.

Rip Currents...

Monday, winds will be out of the south-southeast at 5-10 mph
with breaking waves around 1 to 2 feet. This combined with a 1-2
foot easterly swell around 6 seconds in length will result in a
LOW risk for the development of dangerous and life threatening
rip currents at all beaches.

Tuesday, southerly winds 5-10 mph with breaking waves around 1
to 2 feet. This combined with an easterly swell around 1 foot at
6-7 seconds in length will result in a continued LOW risk for
the development of dangerous and life threatening rip currents
at all beaches.

Rip currents occur often in the vicinities of jetties and piers
and the speed of the currents are generally maximized at low
tides.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.HYDROLOGY...
As mentioned above, there is a risk for heavy rain leading to
flash flooding with any showers and storms Monday. A flood watch
for flash flooding was issued for southeastern Pennsylvania,
and the I-195 to I-80 corridor in New Jersey.

As mentioned by the previous shift, there are a lot of factors
that are increasing our risk for flash flooding. To start, the
pattern shows some similarities to the Maddox Synoptic Event
pattern, with the front becoming quasi stationary and limited
wind shear between the low and upper levels. Model soundings
indicate a tall, skinny CAPE profile typical of a heavy rain
pattern. Expect precipitable water values well above the 90th
percentile for this time of year, and possibly close to daily
records. Additionally, the warm cloud layer should be quite
deep, and storm motions, although slightly faster than what we
have seen Friday and Saturday, will still be less than 20mph.

The only factors not present that typically are with heavy rain
events is that wind shear will be weaker than typical (near or
below 10 kt), and there doesn`t look like there will be much of
a low level jet for moisture transport. This could limit how
long individual cells last before dissipating. Additionally,
confidence is lower than normal on the placement and amount of
precip given how poorly high resolution models have depicted the
showers and thunderstorms today.

At this point, the biggest concern is for flash flooding on
roadways, in urban areas, and for small streams and creeks. What
areas have flash flooding will be highly dependent on where the
heaviest downpours set up.

Significant main stem river flooding isn`t expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from Monday afternoon through Monday evening for
     PAZ060>062-070-071-101>106.
NJ...Flood Watch from Monday afternoon through Monday evening for
     NJZ007>010-012-015.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Franklin
NEAR TERM...Franklin/Johnson
SHORT TERM...Johnson/Staarmann
LONG TERM...Johnson/Staarmann
AVIATION...Franklin/Johnson/RCM
MARINE...Franklin/Johnson/RCM
HYDROLOGY...Johnson