Special Marine Warning 52, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
345 PM EDT Mon Jun 26 2023

.SYNOPSIS...
A low pressure system will continue to track across the Great Lakes,
pulling a cold front toward our area tonight. As this low slides
across our area Tuesday into Wednesday, the cold front will cross
our region. Weak high pressure may settle near our area Thursday and
Friday, then a warm front lifts northward later Saturday followed by
a cold front approaching on Sunday.

&&

.NEAR TERM /THROUGH TUESDAY/...

***Continuing Severe Weather and Flash Flood Threat through this
 evening***

300 PM...As of mid afternoon, strong to severe thunderstorms
becoming more widespread near and north of a warm front
extending west to east over eastern PA into central NJ. Storms
so far have been mainly N/W of the urban corridor. The warm
front extends west and is associated with a broad area of low
pressure located over the lower Great Lakes. A diffuse cold
front associated with the system extends south and west over
western PA in West Virginia.

Storms with the warm front will continue to affect primarily
the aformentioned areas in our northern County Warning Area
over the next hour or two this afternoon. Beyond this time,
looking near and beyond 5 PM, attention shifts to another round
of storms just beginning to shape farther west over central PA
ahead of the cold front. In fact it is this that will likely be
the more severe round of storms as it moves through our area
this evening. As of 3 PM, ML CAPEs at 2000+ j/kg over portions
of eastern PA near and south of where the storms are and
especially within an area of clearing around York and Lancaster
Counties in PA. Deep layer shear values are around 25 to 30
knots with 0-3 km shear around 20-25 knots and 0-1 km shear
values around 15-20 knots near and north of the warm front.
While these shear values are not terribly impressive, they are
sufficient for significant severe weather given the very high
CAPES. Also, DCAPEs over SE PA into Maryland maxing out around
800-1000+ j/kg. The upshot of all this is expect the second
round of storms arriving around late afternoon / early evening
to be intensifying as it moves in. Any discrete cells /
supercells will likely merge into multi-cell clusters and
potentially then evolve into one ore more line segments as the
storms move through the area west to east...this second around
arriving around the 6 PM time frame over our western Counties
and then moving through the urban corridor by around 7-9 PM.
Damaging winds of 60 to 70 MPH along with large hail remain the
biggest threats for severe weather but still cannot rule out an
isolated tornado or two. In addition, flash flooding will be a
threat given the high PWATs and recent rainfall with our eastern
PA and NJ Counties from Mercer/Middlesex northward remaining in
a Flood Watch until midnight. Generally expect areas near and
north of the urban corridor to see 1 to 2 inches of rainfall
with localized amounts of 3 to 5 inches possible...especially
over NE PA into NW NJ where storms have already been ongoing.

The Storms should eventually start to weaken as they also move
eastward off the coast through the late evening / early
overnight time frame. There will be some lingering showers
overnight though. Also, some patchy fog may form overnight,
especially if there are any breaks in the clouds.

As an upper-level trough moves into the east Tuesday, surface
low pressure initially over the eastern Great Lakes is forecast
to track east-northeast. The associated diffuse cold front also
continues to move east reaching eastern PA by late day. The
upshot is there will continue to plenty of moisture and lift to
work with so more showers and thunderstorms are expected. For
the morning, think the majority of the activity will be near the
coast with showers/storms then becoming more widespread through
the afternoon over eastern PA, NW NJ through to the urban
corridor. Conditions won't be as favorable for severe weather
compared to today but still think ML CAPEs reach at least
1000-1500 j/kg so some additional severe storms may be possible.
Limiting factors will be the marginal shear and relatively lower
CAPE compared to today that should also be "skinnier" in nature.
Finally, as has been the case the past few days localized flash
flooding will also be a threat near and north of the urban
corridor.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
The short term period will look to begin Tuesday night with showers
and thunderstorms lingering as a cold front continues to treck
across our area. By Wednesday morning, showers will have tapered off
with the cold front now offshore of the region. Weak high pressure
will look to build behind this front and will build eastward with
time. However, with surface high pressure being weak with lingering
shortwave energy and troughing being present, the area will
look to remain unsettled Wednesday. A stronger grasp of surface
high pressure, though still weak overall, should take hold
Wednesday night and Thursday, finally allowing our region to see
a short break in PoPs.

For Tuesday night, the forecast with carry mainly chance PoPs
starting to taper off by 06z as the cold front pushes eastward.
Model soundings support continued instability into the first half of
the period; will include thunder/thunderstorms with the forecast.
Temperatures and dewpoints will look to remain in the 60s across the
region, some light fog/mist is possible for the early morning hours
after showers have passed.

For Wednesday, the forecast will carry mainly slight chance and
chance PoPs increasing to mainly chance and likely PoPs by the
afternoon. As showers will have access to daytime heating,
instability and thunderstorms remain possible for the
afternoon/evening. Highs in the upper 70s and low 80s can be
expected for the region with dewpoints in the low to mid 60s.

For Wednesday Night, no PoPs are included with the forecast. Lows
primarily in the low to mid 60s can be expected.

For Thursday, no PoPs are included in the forecast except some
slight chance PoPs for mainly northern NJ after 18z. These slight
chance PoPs are included due to the possibility of some
shortwave energy/troughing still holding mainly to our north.
Highs in the low to mid 80s can be expected throughout the
region.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Ensemble guidance indicates that the upper level trough over the
eastern CONUS/offshore should continue to weaken through Thursday
night. Thereafter, the upper level pattern over the region becomes
more zonal before another upper level trough approaches
Saturday/Sunday.

At the surface level, weak high pressure will be over/just south of
the region Friday as low pressure develops over the Great Lakes
region. This low pressure system will look to have
frotonogensis occuring with it with time, with a warm front
approaching the region Saturday. This warm front will look to
possibly cross the region Saturday night into Sunday, with a
cold front approaching the region then on Sunday. This cold
front may cross the region Sunday night into Monday, but
confidence in this timing right now is very low.

With the synoptic pattern described and still more lingering
shortwave energy persisting towards the beginning of the long
term, the forecast will carry mainly chance PoPs with it
throughout the long term term. The afternoon and evening time
frames will again see the chance for showers each day aided by
daytime heating and instability. Temperatures will look to be
about average to just slightly above average through the period.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through tonight...Initial storms will continue this afternoon
mainly around RDG, ABE, TTN and north and will continue to bring
restrictions if any of these move over one of the TAF sites.
For our TAF sites farther south, expect the storms to arrive
this evening as the second round of storms moves in from the
west. The urban corridor TAF sites will likely be affected right
around or just after 0z as strong to severe thunderstorms move
through. Expect IFR visbys down to a mile or less with the
potential for wind gusts of 40 knots or greater should a
stronger storm or line move over one of the sites. Storms should
move out by the late evening but sub VFR restrictions likely
overnight due to lingering showers/mist and stratus. MVFR for
most sites with IFR likely for RDG, ABE, and TTN. Winds
generally south to southeast around 10 knots diminishing to
around 5 knots overnight. Moderate confidence overall but low
confidence regarding specific timing and impacts of storms at
the individual TAF sites.

Tuesday...MVFR ceilings possible to start the day, then becoming
mainly VFR however some mainly afternoon and evening showers
and thunderstorms will result in local restrictions at times.
South to southwest winds around 10 knots.

Outlook...

Tuesday Night...Sub-VFR with VCTS/SHRA lingering. Moderate
confidence.

Wednesday...VFR conditions during the morning giving way to sub-VFR
conditions for the afternoon/evening with VCTS/SHRA possible.
Moderate confidence.

Wednesday Night...Mainly VFR through the period. Moderate
confidence.

Thursday/Thursday Night...Mainly VFR. Brief sub-VFR period possible
in the afternoon/evening due to VCTS/SHRA. Moderate confidence.

Friday/Thursday Night...Sub-VFR with VCTS/SHRA possible.
Low confidence.

Saturday/Saturday Night...Sub-VFR with VCTS/SHRA possible. Low
confidence.

&&

.MARINE...
Southerly flow will result in building seas into tonight, with
waves rising to around 5 ft at times. Thus, SCA for tonight for
all ocean waters. Winds mostly 15-20 kts though a few gusts to
25 kts possible outside storms. Otherwise, strong thunderstorm
potential will be biggest marine concern, with timing mainly
through the mid/late evening into the overnight expect beginning
by early/mid evening over the Delaware Bay.

For Tuesday, marginal SCA conditions may linger over our
northern waters with continuing showers likely with some storms
as well.

Outlook...

Tuesday Night/Wednesday...SCA conditions possible as seas
linger near 5 feet.

Wednesday Night through Saturday Night...No headlines expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until midnight EDT tonight for PAZ054-055-060>062-
     070-071-101>106.
NJ...Flood Watch until midnight EDT tonight for NJZ001-007>010-012-
     015.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT
     Tuesday for ANZ450>455.

&&

SYNOPSIS...Gorse/Wunderlin
NEAR TERM...Fitzsimmons
SHORT TERM...Wunderlin
LONG TERM...Wunderlin
AVIATION...Fitzsimmons/Wunderlin
MARINE...Fitzsimmons/Wunderlin

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Preliminary Local Storm Report
National Weather Service Mount Holly NJ
445 PM EDT Mon Jun 26 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0440 PM     Hail             Manville                40.55N 74.59W
06/26/2023  M0.50 inch       Somerset           NJ   Public

            Half inch hail in Manville, NJ. Time
            estimated via radar.

&&

Hoeflich

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
448 PM EDT Mon Jun 26 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0440 PM     Hail             Butler                  41.00N 74.34W
06/26/2023  M0.50 inch       Morris             NJ   Public

            Picture of hail inch hail in Butler, NJ sent
            in. Time estimated via radar.

&&

Hoeflich