453
FXUS61 KPHI 271045
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
645 AM EDT Mon May 27 2024

.SYNOPSIS...
A warm front lifts north through the region this morning,
followed by a strong cold front tonight. Weak high pressure
builds through the region Tuesday. Low pressure passes through
Wednesday and Wednesday night. High pressure returns to close
out the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Warm front continues to push north through the region. Showers
and embedded thunderstorms continue to move to the north and
east away from the local area, but another cluster of cells has
developed just southwest of Atlantic City. Fog has dissipated,
so the Dense Fog Advisory has been cancelled. Once these last
showers over southern New Jersey move out to sea, the lull in
convection will be in place.

Otherwise, it will be warm and quite humid. Southerly flow will
usher surface dew points well in the upper 60s to low 70s along
with high temperatures in the upper 70s to low 80s, and in the
mid 80s in Delmarva. A pre-frontal trough approaches by early
afternoon, and this will trigger the second round of convection
of the day, mainly north and west of the Fall Line. The cold
front approaches late in the afternoon, and then the third and
most significant round of convection develops.

SB CAPE values will be upwards of 2000 J/kg by this evening,
and even up to 1500 J/kg of Downdraft CAPE. Highest instability
values will be over Delmarva and into portions of southeast
Pennsylvania. 0- 6 km Bulk Shear will generally be around 30 to
40 kt, though in the evening, Bulk Shear values will be 20 to 30
kt in the southern Poconos and northern New Jersey before
rising to 30 to 40 kt with the approach of the cold front. It
does look like an area of 40 to 50 kt of 0-6 km Bulk Shear will
pass south of Delmarva. PWATs will be up around 2 inches.

Strong shortwave energy just ahead of the front will track from
Maryland and southeast Pennsylvania northward towards the
southern Poconos and northern New Jersey. Since the shear will
be lower in those areas, heavy rain could result in localized
flash flooding, especially in the Lehigh Valley.

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 these areas, the Weather
Prediction Center has a Slight Risk (2 out of 4) for Excessive
Rainfall.

The Storm Prediction Center now has the whole region 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. Cannot rule out the tornado threat, especially in the
vicinity of the cold front, but if the instability is elevated,
that should help to limit the tornado threat.

The bulk of the activity should be well east of the region
before midnight tonight, and then the initial cold front will
pass through the region in the predawn hours.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Initial cold front will be offshore Tuesday morning, and then a
secondary cold front passes through by midday. Although the air
mass will not necessarily be cooler behind the secondary cold
front, there will be a noticeable drop in humidity levels as
surface dew points drop from the upper 60s/low 70s on Monday to
the upper 50s/low 60s on Tuesday. Some shortwave energy passes
through the region in the afternoon as the base of an upper
trough sets up over the Great Lakes/Ohio Valley/Mid-Atlantic.
This may touch off isolated showers and thunderstorms Tuesday
afternoon, mainly for the southern Poconos and Lehigh Valley.
PoPs will mostly be confined to slight chance, though PoPs may
touch low end chance in far northwest portions of Carbon and
Monroe counties. Highs will be a touch above normal levels,
generally in the upper 70s to low 80s.

That upper trough will be over the Northeast/Great Lakes/Ohio
Valley/Mid-Atlantic for the mid-week period. Shortwave energy
will dive into the base of the trough Tuesday night, and surface
low pressure develops over the Appalachians. This low will the
pass through the region on Wednesday and Wednesday night.
Showers will become likely along with scattered thunderstorms
for most of the area Wednesday. With highs generally in the mid
to upper 70s and dew points mainly in the mid to upper 50s, SB
CAPE looks to be minimal, generally up around 500 J/kg and
highest 0-6 km Bulk Shear values will be 35-45 kt, mainly over
southern New Jersey and Delmarva. So while thunderstorms are
possible, there does not look to be a widespread severe weather
outbreak at this time. Showers taper off Wednesday night as low
pressure departs.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Another shortwave passes through the region on Thursday, but
the area will be fairly moisture-starved, so not expecting much
more than isolated showers or even a thunderstorm. The Long Term
period should mostly be dry as surface high pressure builds
over the area. Upper trough departs over the weekend and will be
replaced by mid- level ridging. Conditions should remain dry
into the weekend with the next system approaching early in the
new week.

Cooler Thursday and Friday with below normal temperatures, and
then temperatures return to normal levels over the weekend.

&&

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

Today...A wide variety of CIGs across the terminals, but should
settle on MVFR/IFR. The first round of showers and embedded
thunderstorms has lifted through the region. Several rounds of
SHRA/TSRA will impact the terminals throughout the day, with
stronger convection by this afternoon and evening. SE winds 5 to
10 kt, increasing to 10 to 15 kt with gusts up to 20 kt this
afternoon. Severe thunderstorms will be capable of damaging wind
gusts and large hail. Low confidence on timing details.

Tonight...SHRA/TSRA continue through 06Z. Conditions improve to
VFR thereafter. S winds around 10 kt, become W after 06Z.
Moderate confidence on the overall pattern, but low confidence
on details.

Outlook...

Tuesday through Friday...Mostly VFR, but cannot rule out a
SHRA/TSRA at KABE Tuesday afternoon. Sub-VFR conditions
Wednesday in SHRA/scattered TSRA. VFR Thursday and Friday.

&&

.MARINE...
Went ahead and extended the Marine Dense Fog Advisory until 10
am for the ocean waters, though the dense fog may be beginning
to lift as the warm front lifts north and showers with embedded
thunderstorms scours out the fog. Patchy fog will otherwise
continue on the waters into this evening. S winds 10 to 15 kt,
but will issue a Small Craft Advisory for the NJ ocean waters
for this afternoon and the first half of tonight for as winds
will increase to 15 to 20 kt with gusts up to 25 kt. For DE
ocean waters and DE Bay, S winds will average 15 to 20 kt. Winds
turn W around 10 kt late tonight.

Thunderstorms will impact the waters with potentially damaging
winds and large hail later today and tonight.

Outlook...

Tuesday through Friday...Sub-SCA conditions expected through
the week. VSBY restrictions in showers and scattered
thunderstorms expected on Wednesday.

Rip Currents...

S to SE winds will increase to 15 to 20 kt with gusts to 25 kt
along the NJ coast. This will result in a MODERATE risk for the
development of dangerous and life threatening rip currents for
NJ beaches. Since winds will be a bit lighter at DE beaches, the
rip current risk there remains LOW.

For Tuesday, winds will shift to more of a W to SW flow. There
will continue to be a MODERATE risk for dangerous rip currents
at NJ beaches and a LOW risk at DE beaches.

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 10 AM EDT this morning for ANZ450>455.
     Small Craft Advisory from 3 PM this afternoon to 1 AM EDT
     Tuesday for ANZ450>453.

&&

$$

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