047
FXUS61 KPHI 260807
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
407 AM EDT Sun May 26 2024

.SYNOPSIS...
A frontal boundary remains over the area today. A warm front
lifts north through the region late tonight, followed by a
strong cold front Monday night. Weak high pressure builds
through the region Tuesday, and then low pressure will pass
through on Wednesday. High pressure returns to close out the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Showers and storms have largely dissipated though a few may re-
ignite early this morning as a weak cold front dissipates
across the region. The most likely location would be near the
I-95 corridor where low-level lapse rates remain slightly higher
as the boundary moves through. PoPs remain low overall though
(around 15-25%). Temperature and dew point forecast remain on
track with temperatures mainly in the 60s with some low 70s in
the urban corridor. Lows early this morning are forecast to be
in the low to mid 60s for most locations. Some fog has begun to
form, particularly in areas near and northwest of the urban
corridor which received rainfall. Additional marine induced
fog/low stratus is expected to move into coastal areas early
this morning.

Heading into the daytime hours today, any fog/stratus will mix
out by mid-morning. It will be mainly dry through the early
afternoon, though another shortwave approaches. This will result
in some scattered showers/isolated thunderstorms developing,
especially near a stalled boundary north and west of
Philadelphia. PoPs are only around 15-30% outside of the
immediate coast where conditions should remain dry. However,
with any thunderstorms that do develop, brief, heavy downpours
will be possible along with gusty winds. Temperatures will climb
into the mid- 80s with low to mid 70s at the coast.

For tonight, boundary lifts northward as another trough begins
to push towards the region. Most of the showers/storms look to
hold off until after midnight tonight when the trough begins to
get closer but some lingering convection from the daytime hours
can`t be ruled out for late this evening. PoPs this evening are
15-30% then increase to 40-60% after midnight, with the higher
PoPs northwest of the I-95 urban corridor. Lows look to again be
in the low-mid 60s for most locations.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Warm front continues to lift north through the region Monday
morning, and showers and thunderstorms will continue through the
morning commute. There should be a lull in the activity
starting around midday. Although the warm front will be north of
the area, and southerly flow develops, clouds and rainfall
should keep temperatures down compared to Sunday. Highs will top
off in the mid to upper 70s to around 80 for most of southeast
Pennsylvania and New Jersey, and in the low to mid 80s for
Delmarva. However, the bigger change will be in surface dew
points, as dew points will rise well into the 60s and even the
low 70s in Delmarva. These dew points are about 5 degrees higher
than Sunday, but once dew points are in the 60s, any change
higher can be quite noticeable.

A cold front approaches from the west as low pressure moves
into the Great Lakes and continues to lift to the northeast.
This will be the triggering mechanism for convection in the
afternoon and at night.

Models are indicating that the highest instability levels will
be over Delmarva, which is where the warmest temperatures and
highest dew points will be. SB CAPE values look to get as high
as 2000 to 2500 J/kg, with slightly higher MUCAPE values. DCAPE
across Delmarva will be up around 1000 J/kg as well. 0-6 km Bulk
Shear values will get up around 35 to 40 kt over Delmarva, and
will generally be 25 to 30 kt across areas north and west of the
Fall Line. PWATs throughout will be 1.5 to 2 inches.

The Storm Prediction Center has most of the region south and
west of Philadelphia in a Slight Risk (2 out of 5) for severe
weather. The strongest storms will be capable of damaging wind
gusts and even large hail. Although given the relatively warm
boundary layer, the risk for hail is not as high as the risk for
damaging wind gusts. Interesting to note that the 00Z/26 NAM
3km is indicating a bowing squall line moving through Delmarva
and southeast New Jersey.

Although heavy rain is a threat throughout the region, given
the lower shear values across northern areas, there is a higher
potential for bands of heavy rain to develop across areas north
and west of the Fall Line. In this areas, the Weather Prediction
Center has a Slight Risk (2 out of 4) for Excessive Rainfall.

Convection winds down after midnight as cold front passes
through the region. A secondary cold front then passes through
the region by Tuesday morning. Weak surface high pressure builds
into the region. Hard to say cold air advection will develop
behind the cold front, as highs on Tuesday will end up being
several degrees warmer than Monday. The big difference will be
in surface dew points, as a much dryer air mass spreads into the
region. Surface dew points fall from the upper 60s/low 70s to
the upper 50s/low 60s. Cooler Tuesday night as well. A weak
upper disturbance passing north of the region may touch off some
showers and thunderstorms in the southern Poconos, but PoPs
will be capped at mostly slight chance.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A deep upper trough will envelop the Northeast and Mid-Atlantic
on Wednesday. Surface low pressure will develop over the areas
as shortwave energy dives into the base of the trough south and
west of the region. This will touch off another round of showers
and possible thunderstorms, though severe risk looks to be low.

Surface high pressure then builds over much of the eastern
United States to close out the week. Conditions will mainly be
dry, but cannot rule out an isolated shower or thunderstorm by
the weekend. It will also be cooler with below normal
temperatures.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Early this morning...Mostly VFR with mid/high level clouds. Fog
developing where rain occurred earlier (KRDG/KABE). Low/medium
confid overall. Light winds.

For KMIV/KACY, some marine stratus/fog will make its way
inland. Have rather high confidence in some sort of restrictions
at KACY, with a lower confidence that the marine layer makes it
to KMIV. Confidence in timing and extent of restrictions is
also low. Winds will also go light/variable, though favor a
southerly direction at times at 5 kt or less.

Today...Any fog/stratus will dissipate shortly after daybreak.
After, VFR expected. Winds out of the south/southeast around
5-10 kt. High confidence.

Tonight...Sub-VFR conditions possible with chances for showers
and storms (I-95/Lehigh Valley terminals) and marine fog/low
stratus (KMIV/KACY). South/southeast winds around 5-10 kts.
Moderate confidence on sub-VFR conditions occurring.

Outlook...

Monday through Thursday...MVFR or lower in SHRA/TSRA Monday
through Monday night, then VFR Tuesday. Brief sub-VFR conditions
in SHRA/TSRA Wednesday. VFR on Thursday.

&&

.MARINE...
A Marine Dense Fog Advisory is in effect through 6 AM for
Atlantic Ocean coastal waters off of New Jersey as areas of
dense fog are expected to develop. Sub-Small Craft Advisory
conditions are expected through tonight with winds out of the
south/southeast around 10 kt and 1-2 foot seas.

Outlook...

Monday through Thursday...Sub-SCA conditions overall, but a
brief period of SCA conditions with 25 kt wind gusts and seas
around 5 feet may occur Monday night through Tuesday morning.
Thunderstorms Monday afternoon and night could result in strong
wind gusts and VSBY restrictions in heavy rain. Fog possible
Monday morning.

Rip Currents...

A LOW risk for the development of rip currents will continue
through Sunday. While there will be a light onshore flow with
south/southeast winds, breaking waves of only 1 to 2 feet and a
short period of less than 8 seconds will mitigate the rip current
potential.

On Monday, the onshore flow will strengthen as southeast winds
increase to around 15 to 20 knots. This will lead to larger breaking
waves increasing the rip current risk to MODERATE for the NJ
beaches. For the Delaware Beaches, the rip current risk will remain
LOW for Monday as the winds will have somewhat less of an onshore
component.

As always, rip currents can still develop, and often occur in the
vicinities of jetties and piers. Utilize any guarded beaches this
holiday weekend if venturing out into the water.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until 6 AM EDT early this morning for
     ANZ450>453.

&&

$$

SYNOPSIS...MPS
NEAR TERM...AKL
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...AKL/MPS
MARINE...AKL/MPS