NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at May 31, 2:57 PM EST, 3 minutes earlier.
Area forecast discussion, May 31, 2:57 PM EST, 3 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
357 PM EDT Tue May 31 2022
.SYNOPSIS...
A backdoor cold front will slide into our region from the northeast
tonight into Wednesday and lingers over the area through Thursday
becoming the focal point for several rounds of showers and
thunderstorms before a stronger cold front moves through the region
Thursday night. High pressure builds into our region Friday and
Saturday before gradually shifting to our east Sunday and Monday.
Another surface low may move towards the region from the Midwest
into the early part of next week.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
Upper ridge is presently centered to our southwest over the
Tennessee Valley, with a weak shortwave crossing the top of the
ridge. Closed upper lows are currently centered near Nova
Scotia and just north of International Falls MN, with neither
system expected to move a whole lot in the next few days. At the
surface, Bermuda high pressure dominates the southeastern US
and Mid-Atlantic, while a back door cold front is sliding
southwest into New England. Surface low pressure is also located
over southern Canada, with a cold front extending southward
across the Midwest and south-central Plains.
There is just enough instability and moisture in our northern
and southern zones, exacerbated by sea breeze boundaries (south)
and terrain (north) to potentially spark a stray shower or two
for the rest of this afternoon into the evening, but anything
that forms should be pretty isolated. Otherwise, hot, but
relatively dry with tolerable humidity will continue into this
evening.
Backdoor cold front then pushes southwest into the area at the
same time as the weak shortwave rounding the top of the ridge
slides into the region. This will potentially help to spark off
a few showers or even an isolated thunderstorm overnight, though
odds remain less than 50 percent for any spot. Temps will remain
warm until the front passes.
Late tonight, the aforementioned backdoor front will slide
southwest across the region. The backdoor front likely enters
our northeastern zones outside NYC after midnight, crosses
Philly metro late at night and early in the morning, and stalls
across our far western zones by late morning Wednesday. Winds
will turn easterly and temps will be notably cooler behind the
front, especially in locations where a low stratus cloud deck
advects into the region. Still some notable uncertainty on just
how far this cloud deck makes it, with best odds for points from
TTN and ACY on eastward, with a considerably lower risk west of
an ABE-PHL-MIV line. This results in great uncertainty with
temp forecast as well, with our far west likely to approach 90,
while easternmost locales likely get stuck in the 60s on
Wednesday.
All the while, the cold front over the upper Midwest will be
heading toward us on Wednesday afternoon. We will need to watch
the risk of severe weather with this front closely, though right
now odds favor the bulk of the thunderstorm activity occurring
during the evening.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
***Slight Risk of Severe Thunderstorms Thursday afternoon and
evening***
The first in a series of shortwave troughs will move to our north
with a stalled frontal boundary bisecting the forecast area form
northwest to southeast, though the details of where this front will
be remains a little uncertain. The first portion of the day looks
fairly quiet ahead of the second shortwave trough as it works its
way across the Midwest into the Great Lakes. This second shortwave
will be the stronger of the two with a more pronounced negative tilt
with the parent closed 500 mb low over central Canada.
After any lingering rain departs in the morning Thursday, we should
see a little clearing in the late morning and early afternoon.
However, the greater the clearing, the greater chances for
widespread severe weather into Thursday evening. With stalled
frontal boundary remaining situated over the region, there will
likely be an appreciable temperature gradient once again with cooler
highs in the upper 70s for the northern half of the region and upper
80s to near 90 south of the front. The front will attempt to move
northward as a warm front ahead of the incoming shortwave trough and
attendant surface low. The greatest risk for severe thunderstorms
remains south of the front, which looks to be mostly south of the PA
Turnpike and AC Expressway (Philadelphia suburbs southward). The
Storm Prediction Center has a Slight Risk for Severe Weather south
of Philadelphia Thursday. With CAPE values forecast to be in the
1000 to 2000 J/kg range (perhaps upwards of 3000 J/kg MUCAPE in
areas that see enough sun to the south). The greatest threats look
to be hail and damaging wind with deep CAPE well above the freezing
level and some modest dry air aloft leading to forecast DCAPE values
from 500 to 1000 J/kg. LL shear looks to be supportive of at least
some supercells initially that will morph into a broken line or
QLCS.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Rain will gradually come to an end Friday as the cold front moves
offshore and drier air filters into the region. The southeastern
extent of a Canadian upper-level trough swings across the Northeast
and northern Mid-Atlantic regions to start Friday. The mid-level
flow is forecast to become more zonal as the aforementioned Canadian
trough becomes more elongated. Weak high pressure should build in
later Friday and Saturday, although some clouds may be tossed our
way as additional shortwaves track across the Great Lakes region. By
Sunday, the high moves directly overhead. It is forecast to be less
humid with surface dew points into the 50s, and high temperatures
each day get into the mid to upper 70s Friday and the upper 70s and
low 80s Saturday and Sunday.
The forecast becomes a little less certain into early next week as a
shortwave and developing surface low move across the Midwest and
towards the Great Lakes. On the other hand, some of the guidance is
trying to hint at another surface low forming over the Atlantic off
the Carolina Coast, but should remain south of our region. How far
north this reaches by Tuesday and Wednesday remains highly
uncertain, but could end up blocking the incoming shortwave if it
ends up taking a northern trek near Bermuda as the EC has favored.
Highs Monday and Tuesday look to reach into the upper 70s and low
80s.
&&
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
This afternoon...VFR at all our TAF sites with just some high
clouds overhead. NWerly wind 5 to 10 knots. High confidence.
Tonight...Mainly VFR. However, MVFR ceilings are forecast to
push into our region from the northeast and east late tonight.
The MVFR ceilings are expected to reach KTTN, KPNE, and KACY.
There is less confidence that the MVFR ceilings will reach KPHL,
KMIV, KILG, KABE and KRDG although the potential exists. West
to northwest wind 8 knots or less, becoming northeast to east.
Medium confidence.
Wednesday...IFR to start most likely north and east,
transitioning to VFR southwest. High uncertainty on extent of
IFR cigs in the morning. Most areas see cigs return to VFR in
the afternoon. The greatest chance for showers/thunder is late
in the day and at night. Winds will depend on the location of a
backdoor cold front. Low confidence.
Outlook...
Thursday...MVFR and/or IFR conditions possible with several rounds
of showers and thunderstorms, especially from the Philly terminals
north then spreading south through the rest of the terminals through
the night. Winds mostly from the west in the early morning 5 to 10
knots then turning to the northwest through the day from 10 to 15
knots. Low confidence.
Friday...Sub-VFR conditions possible in the morning as rain and
thunderstorms move off to the east. VFR returning into the
afternoon. Northwest winds from 10 to 15 knots. Moderate confidence.
Saturday...VFR. Winds from west-northwest from 5 to 10 knots.
Moderate confidence.
Saturday night...VFR. Winds from the north 5 knots or less. Moderate
confidence.
&&
.MARINE...
A southwest to south wind of 10 to 15 knots late today is
forecast to shift to the northeast and east tonight with the
arrival of a cold front from the northeast. Waves on our ocean
waters will likely be 2 to 3 feet. They may build near 4 feet
late tonight on our ocean waters north of Barnegat Inlet. Waves
should remain at 2 feet or less on Delaware Bay. On Wednesday,
winds will remain mostly easterly at 5-10 knots with 2-4 foot
waves, highest on the ocean north of Barnegat Inlet.
Outlook...
Conditions are expected to be below Small Craft Advisory criteria,
though showers and thunderstorms Thursday and Thursday night could
lead to locally stronger wind gusts and wind shifts.
Rip currents...
A south to southwest wind is forecast to increase to 10 to 15
MPH today. Breaking waves should be around 1 foot with a short
to medium period swell/wind wave varying from south to east.
There is a LOW risk for the development of rip currents today
along the coasts of Delaware and New Jersey.
A northeast wind around 10 MPH on Wednesday is expected to veer
to the east, then to the southeast. Breaking waves should range
from 1 to 2 feet with a short to medium period swell/wind wave
varying from south to northeast. We will keep the rip current
risk at LOW for Wednesday with the waves remaining rather tame.
However, the risk could approach moderate at times due to the
onshore wind.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.
&&
Synopsis...Davis
Near Term...RCM
Short Term...Davis
Long Term...Davis/Gorse
Aviation...Davis/RCM
Marine...Davis/RCM