-- Discussion containing changed information from previous version are highlighted. --
242
FXUS61 KPHI 261437
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1037 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/...
Earlier showers have dissipated. The biggest change with the mid
morning update was to extend out the mention of fog along a
narrow corridor of the coast from Fenwick Island, DE up through
LBI, NJ. Web cams, spotter reports, and satellite show a narrow
corridor right along the coast, dense at times. However, at
least one observation site has suggested this is already pretty
transient, and expect it to be even more so as the wind speeds
increase later this morning, so chose not to issue any dense fog
advisory at this time.

It will be dry through the early afternoon, though another
shortwave trough 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. Again, with any
thunderstorms that do develop, brief, heavy downpours and gusty
winds will be possible. 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 /15Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Today...Fog/low stratus is expected to dissipate by mid-morning.
After, VFR expected. Winds out of the south/southeast around
5-10 kt. High confidence.

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

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...
-- Changed Discussion --
There is a very narrow corridor of fog right at the coast from
Fenwick Island Delaware up to roughly the Manasquan Inlet in
NJ. For most areas, this should be transient, especially as the
winds increase later. However, concerned at the depth an
persistence from the Wildwood area through Barnegat Inlet.
Therefore, have issued a dense fog advisory in these areas.
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 today. 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.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until 3 PM EDT this afternoon for
     ANZ451>453.
-- End Changed Discussion --

&&

$$

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