740
FXUS61 KPHI 051418
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1018 AM EDT Fri Jul 5 2024

.SYNOPSIS...
High pressure will remain located offshore today. Several waves
of low pressure and weak fronts approach the area through
Saturday, before a cold front crosses through the area on
Saturday night. High pressure returns for Sunday and Monday
before another low pressure system approaches the area around
the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
No changes to the previous discussion.

A weak frontal boundary remains draped across the region west
to east over eastern PA into NJ and extends back to a new
surface low developing over the midwestern states. This boundary
will likely lift north into the I-78 to I-80 corridors by this
afternoon. Meanwhile weak impulses aloft will continue to move
through in the upper level flow. It will remain a warm and muggy
morning as weak warm advection persists. Some areas of fog and
low stratus development that has occurred this morning will
gradually scatter out through 10-11 AM or so, though some fog
may persist near the immediate coast much of the day.

A very moist and hot air mass will be in place for today with
dewpoints well into the low to mid 70s, and high temperatures in
the low to mid 90s along and south of I-78 (and away from the
immediate coasts). This will bring two main issues... 1, the
excessive heat, with a Heat Advisory remaining in effect
starting late this morning through Saturday for southeast PA,
portions of central and southern NJ, and Delmarva; and 2, the
thunderstorm risk due to increasing instability.

We`ll start out dry, with some areas of fog/low clouds early.
Clearing this afternoon is now anticipated to be a bit better
than previously forecast, plus convection should be more
isolated in nature (and confined mainly north of I-78, more on
that below). This ultimately prompted the expansion of the Heat
Advisory to several adjacent zones. With the high dewpoints,
expect heat indices in the Heat Advisory area ranging from
around 100 to 104 degrees in PA and NJ, and ranging from 105 to
108 degrees in Delmarva.

While synoptic forcing remains weak today, the heat and
instability, along with the lingering weak boundary across the
northern tier and a weak mid-level shortwave trough passing just
to the north in the afternoon should be sufficient in
initiating some convection near/north of I-78. The highest PoPs
are thus in this area during the daytime period today, and PoPs
elsewhere were lowered significantly. With plenty of moisture
available and PWats over 2.0" again, locally heavy rain is
likely biggest concern, but with the available instability some
isolated severe certainly looks possible. Water loaded
downdrafts leading to microbursts and locally damaging wind
gusts area possible with the strongest cells.

Shower and thunderstorm chances linger tonight as another more
pronounced shortwave crosses the area, increasing forcing even
as instability decreases. While severe/flood risks likely
diminish a bit with loss of heating, will still need to be on
guard after sunset for isolated impacts from heavy rain and
gusts winds if any more robust cells materialize. Have
maintained generally 30-40% PoPs overnight. Aside from the
overnight convection potential, it will be a very warm and muggy
night. Forecast low temperatures will be largely in the mid to
upper 70s within the Heat Advisory area, and in the low 70s
elsewhere. Some areas of fog and/or low stratus development are
possible again, favoring any locations that experience
appreciable rainfall.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Saturday will be the most active day of the short term for
sure, with the hot and humid air mass still in place and the
cold front approaching from the northwest. This should result in
another heat advisory day with heat indices of 100-105 overall,
along with a pretty good chance of showers and storms in the
afternoon as the front approaches and instability peaks. Still
expect the main threat to be locally heavy rain with storms but
isolated severe storms can`t be ruled out given the high CAPE.
Guidance has gotten slower with the frontal progression compared
to 24 hours ago, meaning temps look hotter (hence more
confidence in a heat advisory) and potential for showers and
storms to linger across areas southeast of I-95 into Sunday. The
front actually looks like it completely washes out during the
day Sunday as it stalls over the area, though dew points do drop
several degrees back into the 60s. However, highs on Sunday
look just as hot as Saturday, with low 90s common and a few
higher spots. But, given the lower dew points, do not expect a
need for another heat advisory on Sunday. In between, Saturday
night will be sultry with lows mostly in the 70s, but Sunday
night should be a little more comfortable, with 60s more common
and mostly dry conditions expected.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
High pressure will try building a bit more into the area on
Monday but with the front washing out nearby, there could still
be some spotty convection later in the day or evening. Heat
indices will approach, but right now don`t look to reach,
advisory levels, but highs will be in the lower 90s again.

Beyond Monday, uncertainty reigns regarding the progression of
a low pressure system which will reach us on Tuesday. Clouds
and showers/storms look more likely across the region for
Tuesday, and if the system is fast enough, we might actually try
to dry out on Wednesday before the front and summertime
humidity creeps back north for Thursday. GFS suggests this
solution. ECMWF is a little slower, keeping activity around on
Wednesday but drying us out Thursday. So, that all having been
said, kept chance POPS thru midweek, but right best odds of
storms appears to be Tuesday night. Heat will step downward as
the system slowly moves through, so that by late week we should
stay mostly in the upper 80s.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Today...Any lingering restrictions will scatter out by 14-15Z,
then VFR. SSW winds increasing to 5-10 kts. Some SHRA/TSRA
development possible (20-30% chance for I-95 terminals, 40-50%
chance for RDG/ABE). Greatest chance for TSRA will be at ABE,
where a PROB30 ground has been included. High confidence in
prevailing VFR conditions following any morning restrictions.

Tonight...Initially VFR, however some areas of fog and/or
stratus development are possible again with MVFR restrictions.
Some isolated showers anticipated between roughly 00-09Z with
thunder possible (20% chance). Winds diminish to around 5 kts or
less, favoring a southerly direction. High confidence in
initially prevailing VFR conditions, but low confidence on the
occurrence and timing of any restrictions in fog/stratus/showers
overnight.

Outlook...

Saturday through Sunday...Mainly VFR, with intervals of IFR
possible due to low clouds/mist and a chance of TSRA.

Sunday Night through Monday night...VFR with a slight chance of
TSRA.

Tuesday...Mainly VFR, with intervals of IFR possible due to low
clouds/mist and a chance of TSRA.

&&

.MARINE...
Southerly winds increasing into the afternoon to around 15-20
kts, with gusts near 25 kts at times across the Atlantic waters.
Seas building to 4-6 feet into tonight. Areas of fog near the
immediate coast line should diminish through midday, though it
may linger in some spots for much of the day. Scattered showers
and thunderstorms possible during the overnight hours, but
otherwise fair weather is expected. A Small Craft Advisory has
been issued beginning at 2 PM through Saturday for all Atlantic
coastal waters.

Outlook...

Saturday...SCA Conditions expected, with wind gusts to 25 kt
and wave heights up to 6 feet. Chance TSRA.

Saturday Night...Mainly sub-SCA Conditions expected, with
localized SCA possible. Wind gusts to 20 kt. Wave heights up to
5 feet. Chance TSRA.

Sunday through Tuesday...Sub-SCA. Winds less than 15 kts. Wave
heights up to 4 feet. Slight chance TSRA, mainly Sunday and
Tuesday.

Rip Currents...

Today and Saturday...A New Moon will occur today. Winds will be
around 10-15 MPH out of the south both days, with an onshore
component to the wind in some spots. There is a MODERATE risk
for rip currents for the Jersey shore, and a LOW risk for the
Delaware Beaches. Breaking waves of 2 to 4 feet within the
moderate risk and 1 to 3 feet within the low risk.

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

&&

.TIDES/COASTAL FLOODING...
With the New Moon to occur today, some locations may see some
spotty minor coastal flooding during the next few high tide
cycles.

With continuing S/SE flow and the approach of the New Moon,
some guidance has areas of Cumberland County NJ seeing advisory
minor coastal flooding with the upcoming evening high tide
cycle. Though guidance may be running a bit high, a short-fused
coastal flood advisory may be needed later on.

&&

.CLIMATE...
Near record breaking warmest low temperatures are forecast on
Saturday. Records for our climate sites are listed below:

Record Warmest Low Temperatures
                           July 6
Site                  Record/Year
Allentown (ABE)           74/1999
AC Airport (ACY)          76/1999
AC Marina (55N)           80/1999
Georgetown (GED)          78/2012
Mount Pocono (MPO)        71/1999
Philadelphia (PHL)        79/1999
Reading (RDG)             75/1934
Trenton (TTN)             76/1999
Wilmington (ILG)          77/1999

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT Saturday for PAZ060>062-070-071-
     101>106.
NJ...Heat Advisory until 8 PM EDT Saturday for NJZ009-010-012-013-
     015>020-027.
DE...Heat Advisory until 8 PM EDT Saturday for DEZ001>003.
MD...Heat Advisory until 8 PM EDT Saturday for MDZ012-015-019-020.
MARINE...Small Craft Advisory from 2 PM this afternoon to 6 PM EDT
     Saturday for ANZ450>455.

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...Fitzsimmons/MJL/Staarmann
SHORT TERM...RCM
LONG TERM...RCM
AVIATION...DeSilva/Fitzsimmons/RCM/Staarmann
MARINE...Hoeflich/RCM/Staarmann
TIDES/COASTAL FLOODING...
CLIMATE...