425
FXUS61 KPHI 141047
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
647 AM EDT Mon Jul 14 2025

.SYNOPSIS...
A very warm and humid airmass will be over the region this week
with multiple rounds of showers and thunderstorms expected. A
cold front will move eastward into the region through tonight,
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 TONIGHT/...
Tropical air mass sits over the region presently as southerly
winds ahead of an approaching cold front bring extremely moist
air northward. Even early this morning, just enough forcing is
present for scattered showers and thunderstorms mainly north of
our region but extending into our northern zones, producing
locally heavy rain as a result. These should mostly move away
and weaken early this morning.

Clouds will gradually break again today, with some sun most
areas by midday. This in turn will help increase CAPE to near
or above 2000 j/kg as PW`s approach 2.5 inches. This will all
occur just ahead of an approaching shortwave which will slowly
cross the region this evening. Thus... we should have no trouble
getting good thunderstorm coverage, and with very high moisture
available and relatively slow movement, flash flooding is a big
concern later today into tonight. Guidance suggests there could
be locations in the CWA which receive 3-5 inches of rain in
just an hour two late today/this evening, so have expanded flood
watch area by one tier of counties in both directions and
extended time several hours, given what`s happening now just to
our north and also based on several models suggesting that
convection won`t wind down til after midnight. Til storms roll
through, however, its gonna be another very warm and humid day,
with highs in the mid- upper 80s for most and heat indices well
into the 90s.

After storms do finally start to wind down later tonight, low
clouds and fog will become a concern again with plenty of
moisture and light winds. Lows near or above 70 again.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Unsettled weather along with very warm and humid conditions are
expected through the middle of the week. Several rounds of
showers and thunderstorms can be expected, with locally heavy
rainfall leading to flash flooding being the primary threat.

Today`s frontal boundary will stall out across the central or
southern portion of the forecast area by early Tuesday. This
along with any remnant outflow boundaries will act as focusing
mechanisms for Tuesday`s convection. Some activity could be
ongoing in the morning still, but this should increase in
coverage into the afternoon. Similar to today`s convective
environment, mid level flow and deep layer shear are quite low,
so convection will be slow moving and transient in nature. With
that said, mid to upper level flow will be generally westerly
(parallel to the frontal boundary) with southwesterly low level
flow feeding warm, moist air into the frontal boundary region.
This setup is anticipated to result in an additional round of
widespread showers and scattered thunderstorms, mainly near and
south of the frontal boundary. The placement of the boundary
remains uncertain at the moment, but it should be somewhere
between the Philly metro and our Delmarva areas into far
southern New Jersey.

WPC has introduced a Slight Risk for excessive rainfall in this
area, which will have the greatest threat for localized flash
flooding Tuesday. Similar to today, PWats will be high, around
2" near and south of the boundary. Training storms could result
in localized rainfall totals of 3-5" or more within just a
couple hours. Flash flooding could result in some areas if these
totals are realized. Given the uncertainty in where the
boundary will end up and thus where the heaviest rain may fall,
we do not currently have any Flood Watches to highlight the
threat for Tuesday. However, one could be needed in a future
update as confidence increases.

For Wednesday, the frontal boundary should begin lifting
northward some with time, but again its exact placement remains
uncertain at the moment. Shortwave ridging will be passing
overhead of Wednesday, and this could act to introduce some dry
mid level air into the equation. Synoptic forcing will not be
strong, and shear will again be weak. At least scattered showers
and thunderstorms should develop again into the afternoon and
evening due to the diurnal instability and lack of any
significant subsidence or CIN. PoPs remain around 50- 70% for
our inland areas. No severe probabilities are currently included
from SPC, but there could be an isolated damaging wind gust
from any stronger thunderstorms that develop. PWats will again
by high around 2" or so, so the tropical downpours will also
remain a threat.

As for temperatures, highs will remain in the mid to upper 80s
with lows in the low to mid 70s across the board. Remaining
quite humid as well. Dewpoints will trend higher by Wednesday
though, so it will certainly feel a bit hotter by then. Heat
indices should be mostly in the mid to upper 90s on Wednesday,
which should stay just shy of Heat Advisory criteria. Nocturnal
radiational cooling fog is possible each night as well,
especially in areas that receive heavy rainfall.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Heat and humidity for the week will peak from Thursday through
Friday, along with continued unsettled weather including daily
chances of showers and thunderstorms.

Subtropical ridging will remain to our southwest through the
end of the week and into the weekend with a quasi zonal jet
streak just to our north. Shortwave troughing should pass
offshore late Friday, pushing a weak frontal boundary into our
area with some subsidence arriving in its wake for Saturday. The
boundary should remain nearby through Sunday.

Southwest return flow builds Thursday and Friday, which will
help push temperatures and dewpoints up a few degrees from
earlier in the week. This pattern should focus convection near
and northwest of I- 95, where lee side surface troughing and
terrain will act as forcing for convection. Drier mid level air,
steep low level lapse rates, and more modest deep sayer shear
values should result in a greater severe thunderstorm threat
during the late week period than earlier in the week. PWats will
remain high as well, so locally heavy rainfall will remain a
possibility each day. Long story short, the active stormy
pattern will continue through Friday.

The increased temperatures and dewpoints should push some of
the region into Heat Advisory territory. Highs will be in the
low to mid 90s with dewpoints in the mid 70s. This will
translate to heat indices around the mid 90s to mid 100s. Lows
mostly in the mid to upper 70s.

Heading into the weekend, Saturday should experience the lowest
chance of convection with a surge of slightly drier air, lower
instability, and some subsidence from the departing trough.
Temperatures returning back closer to normal. Chances for
convection should increase again some for Sunday as the boundary
start lifting north with return flow.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Overall, mainly MVFR becoming VFR this morning.
Afternoon SHRA/TSRA will result in MVFR or lower conditions.
Have VCTS with TEMPOs where/when confidence greatest. S winds 5
to 10 kt. Moderate confidence.

Tonight...Sub-VFR in SHRA/TSRA in the evening. Sub-VFR
conditions in fog and stratus possible thereafter. Low
confidence.

Outlook...

Tuesday through Friday...Overall, prevailing VFR conditions.
However, afternoon and evening SHRA/TSRA may result in brief
restrictions daily. Restrictions conditions are also possible
overnights/early mornings due to low clouds and fog, but
uncertainty remains on this potential, so confidence is low on
any daily details.

&&

.MARINE...
Winds and seas should generally stay below Small Craft Advisory
criteria through tonight. Gusty winds could be possible in the
vicinity of any thunderstorms late today/this evening.

Outlook...

Tuesday through Friday...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...

Today, 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 is not expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from 2 PM EDT this afternoon through late tonight
     for PAZ054-055-060>062-070-071-101>106.
NJ...Flood Watch from 2 PM EDT this afternoon through late tonight
     for NJZ001-007>010-012-013-015>019.
DE...Flood Watch from 2 PM EDT this afternoon through late tonight
     for DEZ001.
MD...Flood Watch from 2 PM EDT this afternoon through late tonight
     for MDZ012-015-019.
MARINE...None.

&&

$$

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