481
FXUS61 KPHI 271823
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
223 PM 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 TUESDAY/...
A severe thunderstorm watch has been issued for areas generally
along and north of the PA/MD State line. For areas further
south, including far south NJ and Delmarva, we are still
monitoring those areas, and a watch may be issued there later if
conditions warrant.

Round two of showers and storms are moving through the region
now. It is looking like there may be more of a lull, and even
some breaks in the clouds before the next round comes in late
this afternoon (after 4 PM). Not sure if the clearing will
arrive in time to cause much destabilization.

Models are still depicting surface based cape values near 2000
J/kg by this evening, and even up to 1500 J/kg of Downdraft
CAPE. However, given the earlier convection and cloud cover, the
big question is if the low level cap/inversion will erode enough
to realize that instability. One thing that isn`t lacking is
wind shear; 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.

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. A secondary cold
front will pass through later in the day on Tuesday. Temperature
gradient across either front isn`t significant, so temperatures
tomorrow may be close to what we are seeing today. However, the
big change will be noticed in the humidity. Surface dew points
drop from the upper 60s/low 70s on Monday to the upper 50s/low
60s on Tuesday.

We should have mostly dry conditions tomorrow, though isolated
storms are possible in the southern Poconos as a lagging mid and
upper level short wave trough slides just northwest of the
region.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...

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 /18Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Today...Some breaks to VFR this morning, but in general expect
prevailing MVFR, with lower conditions in TSRA. 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 03Z. 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...
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...Small Craft Advisory until 1 AM EDT Tuesday for ANZ450>453.

&&

$$

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