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000
FXUS61 KPHI 201145
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
745 AM EDT Sat Apr 20 2024

.SYNOPSIS...
A cold front moves offshore this morning. High pressure builds in
from the west this afternoon which will be in place through Tuesday.
A cold front passes by Tuesday night and Wednesday. High pressure
then returns and continues through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low pressure lifting well to our north across northern Quebec
is dragging a cold front across our region from west to east
early this morning, pushing offshore by mid to late morning.
That surface front will slow as it drifts offshore while a new
wave of low pressure develops along it, near Cape Cod, then
lifts toward Nova Scotia later today. A secondary cold front
associated with the mid to upper-level trough axis will pass
through this evening, with drier and cooler air filtering into
our region in it`s wake.

Showers have increased in coverage early this morning, but have
begun to shift mainly near and east of I-95 as the cold front
begins to pass through. Expect showers will taper off from west
to east from mid- morning through midday, with the last of the
showers shifting off the NJ shore by early afternoon. Rainfall
amounts will be mainly less than a tenth of an inch. There will
be some patchy fog at times along the coast this morning.

In the wake of the cold front, skies will begin clearing back
toward Reading and the Poconos mid to late morning, reaching
I-95 around midday, with sunshine breaking out along the coast
by mid-afternoon. This will be a welcome sight for most, as it
has been a few days of fairly cool and cloudy weather. West-
northwest winds will pick up this afternoon, especially from
I-95 northwestward, with some gusts into the 30 mph range. Winds
will not be quite as gusty toward the coast, with less
opportunity for clearing, mixing and momentum transfer there.
Highs this afternoon will reach well into the 60s, except over
the Poconos and some of the nearby ridgetops of NW NJ. Would not
rule out 70F in a few spots from near Philly southward.

With a secondary push of cooler and drier air coming in for
tonight, dewpoints will continue to drop through the 20s, lowest
in areas northwest of the urban corridor. There will be some
high clouds possible, but overall skies will be fairly clear,
and with high pressure building in from the Ohio Valley, we may
see decoupling, easing winds and some rather chilly temperatures
into the 30s by Sunday morning. The growing season is set to
commence across a number of our zones from the Lehigh Valley
across northern NJ on Sunday, and just in time, model guidance
suggests some low to mid-30s possible for lows, coldest toward
Sussex County. We will probably need a Frost Advisory for some
of our zones, particularly Sussex, and probably Warren and
Morris; would not rule out patchy frost even back across the
Lehigh Valley, but that may be more of the rooftop variety
rather than a threat to vegetation.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Mostly dry and tranquil weather is expected for the short term
period. The cold front that passes through on Saturday will be
stalled out along the Southeast coast. A weak surface low is
forecast to develop along this boundary and skirt off the Carolina
coast late Sunday. At the same time, large high pressure will be
centered over the Central Plains which will build east through
Monday before shifting overhead Monday night.

The only notable change to the forecast from the previous shift is
that the track of the low has shifted a bit further north on Sunday.
While most of the global and deterministic guidance keeps the low
surpressed to the south...most of the 00Z CAM/hi-res guidance
depicts at least some sprinkles/shower activity reaching into the
Delmarva and extreme southern NJ. As a result, have introduced
slight chance of PoPs (~20%) into these areas for Sunday afternoon.
Elsewhere, skies will remain mostly cloudy. Skies then clear quickly
Sunday night as the low moves into the western Atlantic. Skies will
then remain clear through Monday night. Will have to watch the
development for patchy frost across the Poconos/Lehigh Valley region
both nights.

Highs will be in 50s to around 60 on Sunday, followed by the upper
50s to mid 60s on Monday. Lows generally in the 30s to low 40s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure begins to shift offshore on Tuesday before completely
vacating the area by Tuesday night. At the same time, low pressure
will be tracking across the northern Great Lakes while moving into
southern Quebec on Wednesday. An associated cold front will be
trailing southward from this low which will pass through the area.
Areawide showers are expected with even a few rumbles of thunder
possible depending on timing and available instability. Best chances
for this would be north and west. Once the front clears the area,
high pressure will quickly build in from the west and remain within
proximity of the area to close out the work week.

Temperatures through the long term period will run close to average
to a few degrees below-normal. Analogs toward the end of the week
and into next weekend, signal that a significant warm-up may be in
store to close out April.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Today...Mainly LIFR to IFR CIGs to start at 12Z, lifting to VFR
rather quickly from west to east from mid-morning through
midday as skies clear and showers push offshore behind a cold
front. MIV/ACY will be slower to improve. West/northwest winds
around 10-20 kt with some spots seeing gusts near 30 kt in the
midday and afternoon hours. Moderate confidence overall.

Tonight...VFR with mainly clear skies. Winds ease fairly
quickly in the evening, but remaining NW 4-8 kt perhaps through
midnight. High confidence.


Outlook...

Sunday...VFR expected. A slight chance for rain showers near
KMIV/KACY. W-NW winds around 10-15 kt. Moderate confidence.

Sunday night through Tuesday...VFR with mostly clear skies. W-NW
winds on Sunday night into Monday, becoming SE-S winds on Monday
night into Tuesday. High confidence.

Tuesday night into Wednesday...Sub-VFR conditions possible with rain
showers. S winds becoming NW following a cold frontal passage. Low
confidence.

&&

.MARINE...
While some of the buoys offshore still report seas near 5 ft,
given winds are light otherwise and seas will continue gradually
lowering, have let the SCA expire early this morning. Some
marine fog will linger through mid-morning, with some limited
areas of VSBY 1 SM or less around lower DE Bay and adjacent
ocean zones. Went with a Marine Dense Fog Advisory for that
reason. Low visibility with showers and low clouds will lift
offshore toward midday and especially for the afternoon, as west
to southwest winds pick up around 10-15 kt into this evening. A
secondary cold front will swing winds around to the NNW
tonight, with gusts over 20 kt, but probably not enough for
another advisory.


Outlook...

Sunday through Tuesday...No marine headlines expected. Fair weather.
Winds up to 15 kt and seas around 2-3 feet.

Tuesday night through Wednesday...SCA conditions are possible. Rain
showers expected. Winds up to 20-23 kt with seas around 3-4
feet.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until 10 AM EDT this morning for ANZ431-
     452>454.

&&

$$

SYNOPSIS...MPS
NEAR TERM...Dodd
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...Dodd/DeSilva
MARINE...Dodd/DeSilva