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FXUS61 KPHI 281049
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
649 AM EDT Sun May 28 2023

.SYNOPSIS...
High pressure over the Northeast states and Great Lakes region will
weaken today and drift out to sea. Meanwhile, low pressure over
the Southeast will drift towards the Mid-Atlantic through mid-
week. High pressure then returns for the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest radar imagery is showing an initial weak band of light
showers entering southern Delaware and Eastern Shores. Some of
the returns could be virga, but there have been reports of light
showers reaching the ground over the last few hours across the
southern Delmarva. These showers will continue to fight a dry
airmass across our region throughout the day.

Low pressure across the coastal Carolinas will continue to creep
northward throughout the day Sunday. Some thicker clouds will begin
to overspread Delmarva and south NJ during the morning and attempt
to move northward, but is expected to remain mostly confined to the
southern half of the region. An initial band of very light showers
will attempt to clip the southern half of the Delmarva Peninsula
this morning, but coverage and precip rates will remain lackluster.
Better chances for precip will come later this evening and into the
overnight hours, but precip changes will largely remain in the 20-
40% range across extreme southern New Jersey, Delaware, and the
Eastern Shores of Maryland with only light showers to be concerned
with. High temperatures will vary across the area with the warmest
readings N/W of upper 70s/low 80s and cooler temps (low 70s) for
Delmarva and coastal NJ. Winds will increase a bit for the southern
areas as the pressure gradient tightens up. Winds will be 10 to 15
mph with gusts around 20 mph at times for the southern areas.
Overnight lows are only expected to drop into the low to upper 50s
given forecasted cloud coverage tonight.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
While high pressure will weaken and drift offshore and east of
New England Sunday night into Monday, another cold front and
upper-trough will swing southward across the Canadian Maritime
Provinces and northern New England. A reinforcing surface high
will build southward across New England and the northern mid-
Atlantic in it`s wake on Monday. This high will generally hold
firm under a blocking upper-level high anchored near and north
of our region. Coastal low pressure will be tracking northward
across North Carolina on Monday, with an associated cut-off
upper-level low catching up. That will send a plume of higher
precipitable water values northward into the mid-Atlantic, but
will struggle to make it north of Delaware Bay due to the
aforementioned blocking high.

Subsequently on Monday, we have a slight chance of showers as
far north as Philadelphia, but that is unlikely to be more than
sprinkles that far north given the amount of dry air in place,
particularly in the lower atmosphere. Clouds will thicken and
expand northward, but areas north of Reading to Tom`s River may
see some sunshine. There will be quite a contrast across our
area from portions of northern New Jersey and the Lehigh Valley
with partly sunny skies and highs in the 80s on Monday...while
coastal areas will struggle to get out of the 60s with a stiff
onshore breeze and mostly cloudy skies. There continues to be a
high amount of uncertainty regarding how much rain reaches into
our region and how far north, but for now it looks like near and
south of Delaware Bay will have the best chance at measurable
rain, with showers likely and rainfall around a tenth of an inch
possible up to southern Delaware and the Maryland Eastern Shore.
With SREF and NBM probabilities of thunderstorms over 10
percent, have included a slight chance in this area Monday
afternoon and evening as well.

With the blocking pattern and weakening low pressure struggling
to advance much farther northward on Tuesday, very little is
expected to change with respect to the northern extent of
cloud-cover and showers on Tuesday. An increasing pressure
gradient may mean stronger east-northeast winds though, gusting
20 to 30 mph at times along the shore. That will keep
temperatures there in the 60s, and even bring highs down several
degrees from Monday`s readings across the interior, with mid to
upper 70s forecast near and west of the Delaware River.
Depending on the extent of the northern edge of shower
activity, rain may gradually add up around southern Delaware
through Tuesday night. We actually have a half-inch to an inch
forecast for coastal Sussex County at the moment, but less than
a tenth of an inch for Atlantic City.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Low pressure will probably still be hanging around close by our
just offshore of the mid-Atlantic on Wednesday, which will mean
that we`ll have to keep a fair amount of clouds and a 15 to 30
percent chance of showers in the forecast, mainly south of
Philadelphia. By Thursday into Friday, high pressure will return
with a broad upper-level ridge expanding across the eastern half
of the country. Increasing temperatures aloft and subsidence,
with 850 mb temperatures possibly approaching 17C on Thursday
and Friday support forecast high temperatures well into the 80s,
if not near 90 degrees. A backdoor cold front may bring slight
cooling heading into next weekend. At this point it looks like
that front will carry very limited moisture, so that
unfortunately much of our area will remain rather rain-starved.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Early this morning (through 12Z)...VFR with SCT to BKN high
clouds with light and variable winds. High confidence.

Sunday...VFR with increasing clouds. Winds holding a mostly E to SE
component at 5 to 10 kts, though closer to 5 kts can be expected for
sites northwest of the I-95 corridor. Some forecast guidance showing
rains and low clouds (MVFR CIGS) for KMIV/KACY late Sun
afternoon, but confidence in this remains low. Will include the
mention of a few showers with VFR CIGS for now. Overall, medium
confidence.

Sunday night...Mainly VFR, but sub-VFR possible in SHRA at KMIV/KACY
and possibly KILG. LGT/VRB winds. Moderate confidence.


Outlook...

Monday through Wednesday...VFR conditions will likely persist
for most of our TAF sites, though showers will try to advance
northward at times, possibly reaching as far as KPHL or so. KACY
and KMIV could possibly have occasional MVFR ceilings, but that
would probably be the reasonable worst case. Lower conditions
with MVFR VSBY in showers will be possible closer to Delaware
Bay on southward. Winds will be steady from the ENE, generally
10 to 15 kt but a bit higher on Tuesday, with some gusts 20 to
25 kt possible near the coast.

Thursday...VFR conditions expected. Light northerly winds
trending southeasterly 5 to 10 kt from I-95 SE-ward.

&&

.MARINE...
Coastal low offshore the Carolinas will continue to slowly inch
northward through the day, running into a ridge of high pressure
across the Northeast. As a result, the pressure gradient will
increase over the southern NJ and DE waters, helping to promote
higher winds and seas. Latest obs from 44009 buoy continue to show
that seas are around 5ft and should remain there through Sunday. The
SCA flag in place will therefore continue. For the NJ coastal waters
north of Great Egg Inlet, overall fair weather is expected to
persist with marine conditions remaining below SCA criteria.


Outlook...

Monday through Wednesday...East-northeast winds 10-15 kt early
Monday will increase to 15-20 kt with some gusts up to 25 kt
possible from late day Monday through Tuesday. That will be
accompanied by building seas, with an easterly swell aiding
combined seas rising above 5 ft Monday night. That will likely
require a Small Craft Advisory for our coastal waters outside of
Delaware Bay. Conditions should improve by Wednesday as the
pressure gradient weakens between high pressure to our north
and weakening low pressure approaching from the south. A chance
for showers will exist most of this period from around Cape May
or Atlantic City southward, with wet weather most likely off
the Delaware Coast.

Thursday...Winds are expected to veer to the east and southeast
at around 10 kt with combined seas diminishing to near 3 ft.


Rip Currents...

A MODERATE risk for the development of dangerous rip currents
continues for both the New Jersey and Delaware Beaches Sunday and
Memorial Day. The onshore wind pattern will generally continue over
the next two days with the exception of weak southerly flow
developing along the central and northern NJ shore for a few hours
tomorrow. Additionally, seas remain elevated in the 4 to 6 ft range,
and the dominant swell is a easterly/southeasterly swell with a
period of approximately 8 seconds. NWPS rip probabilities are
surprisingly high, but chose to continue with the moderate risk as
the pattern won`t be significantly different from today and
observations today support a moderate risk. Additionally, our local
program supports a moderate risk.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ453>455.

&&

$$
SYNOPSIS...Dodd/MPS
NEAR TERM...MJL
SHORT TERM...Dodd
LONG TERM...Dodd
AVIATION...Dodd/MJL
MARINE...Dodd/MJL

NWS PHI Office Area Forecast Discussion