572
FXUS61 KPHI 101058
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
658 AM EDT Wed Jul 10 2024

.SYNOPSIS...
A weak front positioned across portions of our region lifts
north as a warm front late this morning. A cold front will then
arrive later Wednesday night and Thursday as the remnant low of
Beryl tracks northwest of our region. The front remains in our
area Friday and Saturday before dissipating into Sunday. The
next cold front may approach during Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Another very hot and humid day on tap for Wednesday. With a
similar airmass as yesterday with perhaps a touch higher dew
points, we expanded the Excessive Heat Warning to the Lehigh
Valley in PA and Warren/Morris counties in NJ. The greatest heat
index values (up to 105) in these locations will be confined to
the lower elevations and valleys, but little relief will be
felt in the higher elevations with heat index values still in
the low-100s. The Excessive Heat Warning for the greater 95
corridor remains in effect as well as a Heat Advisory for all
remaining counties (with the exception of Cape May). Long story
short, it will be dangerously hot and humid this afternoon
across the entire region.

We will also be closely watching the remnant low of Beryl. The
center of the low is still forecast to remain well west of our
region as it treks across the Great Lakes before pushing a cold
front across the Mid Atlantic into our region later tonight. Latest
guidance does suggest most of the Delaware Valley should remain
precip-free through today, but there is a chance a few thunderstorms
could develop near and along the lingering boundary late
morning/early afternoon north and west of the 95 corridor across the
Lehigh Valley, Poconos, and northern NJ. Primary concern with any
storms that develop will be heavy rain due to the very high
precipitable water values and deep warm cloud layer. However, storm
motions should be relatively fast which may limit the flash flood
threat somewhat. Also can`t rule out some severe thunderstorm
potential with a primary threat of straight line winds. Come mid-to-
late afternoon, as the warm front lifts well north of us, we will be
firmly in the warm sector with little large-scale ascent around to
trigger widespread storms. While we can`t rule out a rogue
thunderstorm, much of the region will stay precip-free during this
time. The approaching cold front, however, will help tighten our
pressure gradients, leading to quite a windy afternoon with gusts up
to 25-30 mph.

After sunset, guidance expects the cold front to begin reaching our
neck of the woods and bringing a line of thunderstorms with it. With
the loss of daytime heating, the severe threat will begin to
diminish by the time these storms arrive, though an isolated severe
thunderstorm wind gust cannot be ruled out. Storms should reach the
Poconos and Lehigh Valley by sunset and slowly push towards the 95
corridor by midnight before beginning to wash out. The slow nature
of this frontal passage in combination with high PWAT values will be
the main driver of flooding concerns as these storms make their way
across the region. The boundary looks to wash out and stall near and
around the 95 corridor overnight. West of the boundary, temperatures
look to cool into the low 70s with dew points dropping into the 60s.
East of the boundary, still rather mild with lows in the mid to
upper 70s with humid air lingering.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As the remnants of Beryl push towards western NY we`ll see some
slightly cooler air push towards the Mid Atlantic.  This lessens the
impact of the heat and humidity for Thursday however its only a
brief reprieve as the humid air returns on Friday albeit with
cooler temperatures.

Showers should be continuing to push offshore early Thursday morning
as the front slides through however it will stall just offshore and
then start to slide back along the coastal plain. This will be the
trigger that initiates convective activity early Friday morning that
continues through much of the day Friday. A plume of 2.0-2.5
inches of precipitable water is forecast to shift westward with
building instability and increasing forcing for ascent within
the high precipitable water axis. Therefore showers and some
thunderstorms are expected to increase through the day. The
freezing levels are forecast to be high with warm cloud depths
in the 11-12,000 ft range and therefore convection will be
efficient rainfall producers.

The southerly flow may also result in some training or backbuilding
convection at least for a time, and if this becomes realized it will
enhance the local very heavy rain/flash flooding risk. Where
excessive rainfall rates occur, local flash flooding will certainly
be possible. This looks to be focused across much of the coastal
plain, however this could also extend farther north and west. With
the expectation of much more cloud cover and increased convection,
temperatures will be noticeably cooler although it will be very
humid. The convection may continue for much of Friday night before
weakening or shifting eastward closer to daybreak Saturday.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Heat and humidity are anticipated to return in the longer term
as high pressure is forecast to gradually build over the region
Saturday into Sunday. Some lingering showers are anticipated
Saturday morning but dry air advection should quickly end the
shower threat on Saturday. As the high pressure starts to slide
offshore, temps push back into the the low to mid 90s for Sunday
and building into the mid to upper 90s through the beginning of
the week. Anticipate heat index values to push back into the
upper 90s to triple digits by Sunday so heat headlines might be
needed Sunday through Tuesday.

Dry air across the region should result in limited convection
potential early in the week however with the amount of heat and
humidity, we can`t rule out any diurnally driven showers and or
thunderstorms especially over the interior areas.

&&

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

Wednesday...Some early morning restrictions as ACY, MIV, RDG,
and ABE as noted above but this should become VFR by around 14z.
After 15Z, there is an increasing chance for showers and storms
to spread into the region from west to east. Most TAF sites
(aside from KABE and KRDG) are unlikely to see TSRA before 18Z,
and may not see much before 00Z. Winds prevailing from the SW
around 10 kt with some gusts to around 20 kt. Moderate
confidence on the overall pattern, but low confidence on timing
of storms.

Wednesday night...VFR likely to start, but a line of
thunderstorms is expected to impact terminals from west to east
through the nighttime hours. Added VCTS to signal when storms
are most likely, though confidence on timing remains low. Sub-
VFR conditions expected with strongest storms with low stratus
developing behind the frontal passage. Winds Srly ahead of the
front with gusts 15-20 kts turning WSW behind the front and
diminishing to around 10 kts.

Outlook...

Thursday and Friday...Periods of sub-VFR probable especially
Thursday night and Friday with an increase in showers and some
thunderstorms.

Saturday and Sunday...Some local sub-VFR conditions possible
associated mostly with a shower and thunderstorm.

&&

.MARINE...
Marine Dense Fog Advisory continues through 18Z Wednesday. We don`t
have any significant changes coming in the wind direction, so the
fog is expected to persist until we start to get rain showers or
stronger winds, which will likely not come until Wednesday afternoon
at the earliest.

Winds and seas should stay below SCA criteria through Wednesday
morning. By Wednesday afternoon though, gusts 25 to 30 KT and seas
approaching 5 ft are expected on the Atlantic Ocean waters. Thus,
have issued a Small Craft Advisory for Wednesday afternoon and
night.

On the Delaware Bay, issued a SCA as well for wind gusts up to 25
kts through tonight.

Outlook...

Thursday...Southerly winds could be strong enough for some gusts to
25 knots which may build the seas to 5 feet, warranting a Small
Craft Advisory. Showers and some thunderstorms should be on the
increase especially at night and some storms could produce
locally gusty winds.

Friday through Sunday...The conditions should be below Small Craft
Advisory criteria. Showers and some thunderstorms are expected
especially Friday into Saturday with locally gusty winds
possible.


Rip Currents...

Southerly winds will continue to increase through midweek and will
generally be around 15 to 20 mph for both Wednesday and Thursday.
This will result in waves around 2 to 3 feet in the surf zone. Given
the wind component and some higher breaking waves developing, there
is a MODERATE risk for the development of dangerous rip currents
through Thursday for the New Jersey Shore. Due to somewhat lower
waves for the Delaware Beaches, we went with a LOW risk for the
development of dangerous rip currents both days.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT this evening for
     PAZ060>062-070-071-101>106.
     Heat Advisory until 8 PM EDT this evening for PAZ054-055.
NJ...Excessive Heat Warning until 8 PM EDT this evening for
     NJZ007>010-012-013-015-017>020-027.
     Heat Advisory until 8 PM EDT this evening for NJZ001-016-021-
     022.
DE...Excessive Heat Warning until 8 PM EDT this evening for DEZ001.
     Heat Advisory until 8 PM EDT this evening for DEZ002-003.
MD...Heat Advisory until 8 PM EDT this evening for MDZ012-015-019-
     020.
MARINE...Small Craft Advisory from 2 PM this afternoon to 2 AM EDT
     Thursday for ANZ430-431.
     Dense Fog Advisory until 2 PM EDT this afternoon for ANZ431-
     450>455.
     Small Craft Advisory from 2 PM this afternoon to 6 AM EDT
     Friday for ANZ450>455.

&&

$$

SYNOPSIS...Deal
NEAR TERM...MJL
SHORT TERM...Deal
LONG TERM...Deal
AVIATION...Deal/MJL
MARINE...Deal/MJL