183
FXUS61 KPHI 052007
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
407 PM EDT Fri Jul 5 2024

.SYNOPSIS...
High pressure dissipates offshore this evening. Several waves of low
pressure and weak fronts approach the area through Saturday night,
before a cold front slowly crosses the area on Sunday. High pressure
returns for Sunday night and Monday before another slow moving low
pressure system encroaches upon the area through the middle of next
week.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
A very hot and humid afternoon persists with heat indicies exceeding
100 in numerous locations. Heat Advisories are now in effect for all
counties except Carbon and Monroe in PA. Convection is beginning to
initiate in and around the I-78 corridor and points north. No
changes to the thinking this afternoon and evening with the storms.
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 20-35% PoPs
overnight. Aside from the overnight convection potential, it will be
a very warm and muggy night, leading to little relief from the
daytime heat. 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.

We are still maintaining a very active Saturday to start off the
weekend. A very hot and humid airmass remains in place in
combination with an approaching cold front likely brings numerous
showers and thunderstorms across the region. Heat advisories are up
again for the entire region, minus Carbon and Monroe counties in PA,
with heat indicies of 100-105 across the urban corridor north and
heat indicies 105+ for the Delmarva and extreme southern NJ. In
terms of storms, PWAT values will be in excess of 2 inches across
the region, so we are still expecting the main threat to be locally
heavy rain with storms. That said, isolated severe storms can`t be
ruled out given the high CAPE. Guidance is in a bit of a
disagreement where the frontal boundary will set up by early
afternoon. Wherever it does arrive, we continue to expect numerous
scattered showers and thunderstorms to form along and ahead of the
front.

Storms will gradually push south and east offshore as the
cold front crawls along, though it does look to wash out a bit by
early Sunday morning. Some relief with overnight lows cooling to the
upper 60s and low 70s behind the front, though dew points will lag a
bit in the same region, still leading to a slight cooler, but still
rather humid night.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
Not much change in the short-term forecast through Monday. The cold
front still looks on pace to cross the area on Sunday but as it does
so, it will be washing out and moving at a snails pace. Ultimately,
the front should just leave a remnant boundary behind. As a result,
Sunday should be a fairly nice day for most as high pressure builds
in from the north and west with just a slight chance of showers
across the Delmarva and southern NJ. High temps should again be in
the upper 80s to low 90s, but dew points will fall back into the 60s
behind the front. At this point, no heat headlines are expected, but
if the front hangs up a bit more to the north and west this may need
to be reconsidered. Skies should begin to clear out a bit into
Sunday night except over the Delmarva where a few showers may
linger. Lows will remain though in the upper 60s to mid 70s as
moisture content is still quite high.

High pressure will win out on Monday for most areas leading to a
mostly tranquil day with a mix of sun and clouds during the
afternoon. However, with the remnant boundary lingering overhead and
subtle increase in moisture return with dew points rising back into
the lower 70s, a few showers or thunderstorms will be possible north
and west of the I-95 corridor. As mentioned above, dew points will
be slightly higher and air temps will be a degree or two higher as
well on Monday. Heat indicies will hover between 95-99 degrees for
much of the area. Will continue to evaluate trends amongst T/Td
guidance over the next several days in order to determine if any
heat headlines will be needed for Monday.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The long term period as a whole is summarized to be quite unsettled
with seasonable temperatures. An upper level trough will be over the
Great Lakes region Monday night into Tuesday before shifting east
over the Northeast US through Wednesday. But this is where the
forecast details becomes uncertain because there will be several
impulses embedded in the upper flow, allowing several fronts and
boundaries to be near our region. This will result in several
opportunities for some showers and thunderstorms, mostly in the
afternoon and evening hours due to diurnal effects. Right now, the
greatest chance for showers/storms looks to be Tuesday into
Wednesday. After Wednesday, deterministic and ensemble guidance
differs significantly, so have held a chance of showers/storms
through the end of next week to account for variability amongst
guidance suites.

&&

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

Rest of today (through 00Z)...Prevailing VFR, but 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 TSRA TEMPO group has been added. SSW
winds 5-10 kts. High confidence in prevailing VFR conditions,
lower confidence in storm coverage.

Tonight...Initially VFR, however some areas of fog and/or
stratus development are possible again with sub-VFR
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.

Saturday...Lingering fog/low stratus in the morning, giving way
to VFR by mid to late morning. Intervals of sub-VFR returns with
scattered showers and thunderstorms in the afternoon. Low
confidence.

Outlook...

Saturday night...Sub-VFR possible. Showers and storms in the
evening give way to fog/low stratus developing overnight. Low
confidence.

Sunday through Monday night...VFR expected. A slight chance of a
shower or thunderstorm possible Sunday night into Monday. Otherwise,
no significant weather anticipated.

Tuesday through Wednesday...Sub-VFR conditions possible. A chance of
showers and thunderstorms possible with occasional mist/fog.

&&

.MARINE...
Small craft advisories in effect through Saturday evening.

South winds 15-20 kts with gusts near 25 kts across the Atlantic
waters. Seas 4-5 feet build to 4-6 feet Friday night.

Winds and seas remain elevated through the first part of
Saturday with showers and storms possible. Winds and seas begin
to diminish later afternoon/early evening.

Outlook...

Saturday Night...Winds and seas fall below SCA criteria late
evening. Wind gusts to 20 kt. Wave heights up to 5 feet,
diminishing to 3 to 4 feet. Chance TSRA.

Sunday through Monday night...No marine headlines expected. Winds
generally less than 15 kt and seas of 2-3 feet. A slight chance of a
shower or thunderstorm into Sunday night, otherwise fair weather
expected.

Tuesday through Wednesday...No marine headlines expected. Winds
generally less than 20 kt and seas of 2-3 feet. A chance of
thunderstorms expected.

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 NJZ001-007>010-012-
     013-015>023-027.
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 until 8 PM EDT Saturday for ANZ450>455.

&&

$$

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