782
FXUS61 KPHI 121952
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
352 PM EDT Fri Jul 12 2024

.SYNOPSIS...
Several waves of low pressure will ride along a stationary front
draped over the region through Saturday. Broad high pressure returns
late Saturday night and persists through Tuesday night. A cold front
approaches from the northwest on Wednesday before crossing through
the area on Wednesday night. High pressure then builds back in from
the west to end the week.

&&

.NEAR TERM /THROUGH SATURDAY/...
A frontal boundary has lifted northward into the area from the
coast. Bermuda high pressure will continue to advect a ribbon
of rich tropical moisture back into the region along and south
of this front as well. Meanwhile, a broad jet located to our
northeast will result in broad diffluence aloft, strengthening
through Saturday. Meanwhile, a closed upper low is passing by
just offshore.

Showers and a few thunderstorms continue to spread across the
area this afternoon. The heaviest rain has occurred near the
coast, which was farther south than anticipated for the daytime
period. Localized amounts of 3-5" of rainfall have been
observed. The showers and storms should continue into this
evening, however a break in activity is expected overnight
as a lull in synoptic forcing occurs. PWats will remain around
2-2.5", near climatological maxima, along with MUCAPE near 1,000
J/kg. The more robust showers and thunderstorms that develop
will be capable of producing very heavy rainfall, with rainfall
rates near 2" per hour. The threat for severe thunderstorms is
very low. PoPs were adjusted to match the latest guidance,
including a lull overnight.

Temperatures will remain below normal through this afternoon,
topping out in the upper 70s to low 80s in most areas. With all
the cloud cover and moisture around tonight, temperatures will
remain quite mild, with lows ranging from the low to mid 70s.
Light southerly winds through Saturday, though winds will become
light and variable at times.

While the heaviest rainfall so far today has occurred near the
coast, guidance continues to pinpoint the heaviest rainfall
potential from across portions of Delmarva and into the urban
corridor through early Saturday afternoon. An additional wave of
widespread heavy showers and thunderstorms is expected to impact
this area beginning around daybreak Saturday through around
midday. Widespread rainfall amounts near 1-2" can be expected,
with locally higher amounts up to 5" possible. Rainfall rates
may exceed 1-2" per hour at times. While much of the area has
been dry recently, the rainfall rates may lead to some areas of
flash flooding, especially in urbanized and poor drainage areas.
The Flood Watch remains in effect as previously issued through
2 PM Saturday to highlight this threat.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
Low pressure riding along the stationary front will move out to sea
on Saturday night. As it does so, the stationary front finally
begins to weaken and wash out over the area as high pressure builds
in from the west. Any lingering showers will be mainly confined to
coastal locales and the Delmarva, before tapering off overnight. Due
to plenty of low-level moisture lingering around from rainfall
during the day, in addition to clearing skies and light winds,
patchy areas of fog is likely, especially near the coast. Low
temps will range from the upper 60s to mid 70s.

Going forward, high pressure will then hold influence over the
region through the remainder of the short term period. Upper heights
begin to increase and surface flow becomes southerly. This will
usher in the return of the heat and humidity on Sunday. Basis the
latest available guidance, high temps will be in the low to mid 90s
(80s down the shore and in Poconos). Dew points will also range
from the upper 60s and low 70s. This equates to heat indicies
around 100 degrees across much of the coastal plain into the
Lehigh Valley. As a result, have opted to issue a Heat Advisory
for Sunday where conditions warrant. Also, cannot rule out an
isolated shower or thunderstorm across eastern PA or the Delmarva
which lies in proximity of the dissipating front.

Rather benign conditions continue into Sunday night under mostly
clear skies. Lows may be a degree or two warmer compared to
Saturday night as southerly flow is a bit stronger than the
night before.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
High heat and humidity will continue to impact the area through
Tuesday, possibly lingering into Wednesday before a cold front
crosses through the area on Wednesday night.

Afternoon highs are forecast to be in the mid to upper 90s on Monday
and Tuesday, when the highest temperatures are likely to occur. Dew
points are also expected to further increase into the low to mid 70s
which will result in heat indicies upwards of 105-110 degrees across
most interior locations. Due to this potential, have opted to issue
an Excessive Heat Watch for Monday and Tuesday with this update
for the same areas where Heat Advisories are in effect for
Sunday. A chance of diurnally driven thunderstorms are possible
each afternoon as well.

On Wednesday, the heat and humidity will continue but is expected to
be a touch lower compared to the days prior as a cold front
approaches. This should result in a more widespread chance for
showers and storms late in afternoon into the evening hours.
Depending on the progression of the front, shower activity may
linger into Thursday as well. However, with the front working
its way through the region, temperatures by late week are
expected to be a few degrees below normal.


&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR conditions have generally prevailed thus far today,
however a trend toward more persistent MVFR conditions can be
expected through 00Z or so. Numerous showers and a few
thunderstorms will persist as well, with locally IFR conditions
possible with this activity. Winds will remain near 5 kts
favoring a southerly direction, although will be light and
variable at times. Moderate confidence on overall pattern, but
lower confidence on timing details.

Tonight...Conditions trending toward IFR by 06Z. A lull in the
shower activity is expected early in the night, however another
round is expected to develop after 09Z. Winds light and
variable, favoring a southerly direction. Moderate confidence.

Saturday...Initially MVFR to IFR conditions with potential for
heavy showers and thunderstorms through 18Z, then conditions
improve to VFR thereafter. Southerly winds near 5-10 kts.
Moderate confidence.

Outlook...

Saturday night through Tuesday night...VFR. Patchy areas of fog
possible on Saturday night which may reduce visibilities especially
near KACY/KMIV. Otherwise, a slight chance of a shower or
thunderstorm each afternoon.

Wednesday...Primarily VFR but sub-VFR conditions possible. A chance
for rain and thunderstorms in the afternoon.

&&

.MARINE...
Southerly winds 10-15 kts with some gusts near 20 kts possible.
Seas will be around 4-5 feet through this evening, so we`ve
extended the Small Craft Advisory through 10 PM.

VSBY restrictions in showers and fog. Rain may be heavy at
times. Scattered thunderstorms possible as well.

Outlook...

Saturday night through Tuesday night...No marine headlines expected.
Wind gusts generally between 10-20 kt and seas around 2-4 feet.

Wednesday...SCA conditions possible due to winds around 20 kt and
seas build to around 4-5 feet.

Rip Currents...

South to southeast winds will range from 10 to 15 mph with
breaking waves of 2 to 4 feet. With the flow slightly onshore or
parallel to the shore in New Jersey, there is a MODERATE risk
for the development of dangerous rip currents at the Jersey
Shore. For Delaware, the flow will be more onshore if not a bit
offshore. As a result, there is a LOW risk for the development
of dangerous rip currents at Delaware Beaches.

Conditions on Saturday will be similar to conditions today,
though Jersey Shore beaches in Monmouth county will have a LOW
risk, while the rest of the Jersey Shore will have a MODERATE
risk for dangerous rip currents. Delaware Beaches will once
again have a LOW risk for the development of dangerous rip
currents.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through Saturday afternoon for PAZ070-071-101>106.
     Heat Advisory from 10 AM Sunday to 6 AM EDT Monday for
     PAZ060>062-070-071-101>106.
     Excessive Heat Watch from Monday morning through Tuesday
     evening for PAZ060>062-070-071-101>106.
NJ...Flood Watch through Saturday afternoon for NJZ001-007>010-012-
     013-015>019.
     Heat Advisory from 10 AM Sunday to 6 AM EDT Monday for NJZ009-
     010-012-013-015>022-027.
     Excessive Heat Watch from Monday morning through Tuesday
     evening for NJZ009-010-012-013-015>022-027.
DE...Flood Watch through Saturday afternoon for DEZ001-002.
     Heat Advisory from 10 AM Sunday to 6 AM EDT Monday for DEZ001.
     Excessive Heat Watch from Monday morning through Tuesday
     evening for DEZ001.
MD...Flood Watch through Saturday afternoon for MDZ012-015-019-020.
MARINE...Small Craft Advisory until 10 PM EDT this evening for
     ANZ450>455.

&&

$$

SYNOPSIS...DeSilva/Wunderlin
NEAR TERM...Staarmann
SHORT TERM...DeSilva
LONG TERM...DeSilva/Wunderlin
AVIATION...DeSilva/Staarmann
MARINE...DeSilva/Staarmann