502
FXUS61 KPHI 272005
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
405 PM EDT Mon May 27 2024

.SYNOPSIS...
A cold front crosses through our region tonight into Tuesday
morning. 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/...
The severe thunderstorm watch has been expanded to include all
of the region. The watch continues through 9 PM EDT. That should
cover the peak of the severe risk period, but may have storms
and showers linger a few hours later than that.

Starting to see discrete storm development over central PA and
central MD now, which is likely the start of our next round of
storms (probably won`t be entering our region until closer to 6
PM)

We have seen some brief breaks in the clouds, but it hasn`t
lasted long enough yet to make a significant impact on low level
lapse rates. Temperatures across our region remain in the lower
to mid 70s. Thus, the big question remains how much instability
and convective inhibition will be in place once the next round
of storms arrives. 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.

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. There remains a low tornado threat, especially in the
vicinity of any outflow boundaries that may develop, 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 THURSDAY/...
That upper trough will be over the Northeast/Great Lakes/Ohio
Valley/Mid-Atlantic for the mid-week period. A short wave trough
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.

Another shortwave trough is expected to cross on Thursday, but
by then, moisture will be very limited, so only have a slight
chance of showers and storms at this time.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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 Friday with below normal temperatures, and then
temperatures return to normal levels over the weekend.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through Tonight...Expect periods of MVFR and even IFR during
the direct impacts of the storms. The prime period for storms
looks to be between 22 and 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.

Tuesday...Mostly VFR. Westerly winds 10 to 15 kt. Moderate
confidence.

Outlook...

Wednesday...Sub-VFR conditions Wednesday in
SHRA/scattered TSRA.

Thursday through Saturday...VFR.

&&

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