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855
FXUS61 KPHI 010752
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
352 AM EDT Wed May 1 2024

.SYNOPSIS...
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Cold front expected to cross through this morning, then a warm front
lifts through tonight. Another cold front looks to cross through
Thursday before more weak surface high pressure builds in. Cold
front well to our west approaches slowly for Friday and the
weekend while decaying, keeping things unsettled this weekend
and even into Monday. Yet another cold front may come through
around the time frame of Monday/Tuesday.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Showers have all but dissipated across our region, with just very
isolated showers left in central New Jersey. Once the last of the
lingering showers dissipates, the rest of the day should be dry. As
mentioned by the previous shift, the training upper level trough
will still be crossing our region through the day, but with very
limited moisture, do not expect it to result in any additional rain.

In the wake of Tuesday`s front, temperatures will generally be a bit
cooler today - in the 70s for most of the region. A developing sea
breeze by mid day will only help to reinforce this for the coastal
plains.

Overnight, as the surface high sits just east of our region, expect
more widespread onshore flow to develop. The main implication for
this will be either fog or low stratus especially for the coastal
plains as the marine layer advects in. At this point, most model
soundings show fog more likely than low stratus, but given the
complexities of this setup, I don`t have very high confidence one
way or the other.
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&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Though the region will feel the influence of weak surface high
pressure Thursday, a weak frontal system centered to our north is
forecast to move southeastwards and offshore of the northeastern
CONUS with time. This will likely result in a weak cold front
crossing through the region at some point Thursday before more weak
surface high pressure builds in behind the front for the Thursday
night and Friday time frame. A more defined cold front out to our
west is expected to approach the region Friday and Friday night all
while slowing down and weakening with time.

Overall, the short term will look to be fairly benign weather wise.
However, while the synoptic evolution is fairly straightforward and
certain, the details are not. With the weakness of both the surface
low/highs and the upper-level pattern in place, forecaster
confidence in timing of the cold front coming through Thursday is
not very high. This of course will determine how high temperatures
get Thursday. The cold front expected to cross through Thursday
could stall just to our south Thursday night into Saturday. Where
exactly this front stalls (e.g., over southern Delmarva or south of
it) is not certain at this point. Also, shortwave energy could
remain in place Thursday and Thursday night.

Most model guidance supports a dry forecast Thursday into Friday
night. This makes sense given the weak high pressure in control and
the weakness of the cold front expected to cross through Thursday.
However, with lingering shortwave energy Thursday and Thursday
night, a stray isolated and pop-up shower should not be ruled out
even if most model guidance has no precipitation. During the later
half of the Friday night period, have slight chance PoPs beginning
to enter the region from the west with the approaching slow and
decaying cold front.

Not much else to write home about with this forecast. Temperatures
mainly in the 80s for most locations Thursday, much cooler for the
Poconos and coastal areas of course. High temperatures Friday cooler
than Thursday, likely the mid 60s to low 70s for most locations.
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&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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The ensembles and deterministic models continue to support an
upper-level ridge axis over/just offshore of the eastern CONUS
Saturday breaking down and moving eastward with time.
Thereafter, a more zonal pattern takes hold over the region
through much of the long term even with another ridge axis
developing to our west over the Great Lakes region.

At the surface level, the upper-level pattern corresponds to an
occluded cyclone north of the Great Lakes region Saturday slowly
continuing to drape a cold front undergoing decent frontolysis
eastward toward the region. This cold front only looks to slow down
and decay even more with time with it possibly either stalling over
the region Sunday into Monday or not crossing through until the
Sunday night time frame. Thereafter, guidance suggests another round
of surface high pressure will try to build in from the west later
Monday or Tuesday, but not before pushing a possible secondary cold
front through the region and clearing out whats left of the old cold
front if anything.

So what can be expected for the long term? Mainly unsettled
conditions. Rain showers will spread eastward from the west Saturday
into Sunday will rain showers lasting into the Sunday night and
possibly even the Monday time frame. Beyond Monday, there is not
much forecaster confidence in the synoptic situation given the upper
level pattern. Overall, expect a rainy weekend with things staying
unsettled at least until Monday morning. We will have to see how the
synoptic situation evolves thereafter.
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&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...Main aviation impacts at this point are fog potential
in the Lehigh Valley (including KABE), and low marine stratus that
has already lowered ceilings at times at KACY. The marine stratus
may also affect KMIV, KPNE, KPHL, and KILG by 12Z, but as we`ve
already seen at KACY, it may be transient at times. Winds tending
light NE, or variable at times. Low confidence.

Today...Any morning fog or low stratus should dissipate by 15Z,
leaving VFR conditions for the remainder of the day. Expect winds to
settle out of the NW for a period, but a developing seabreeze should
switch winds around to southeasterly at KACY, KMIV and possibly as
far west as KILG, KPHL, and KPNE. Moderate confidence.

Tonight...Starting VFR, but expect southeasterly onshore flow to
result in either fog or low clouds at KACY, KMIV and possibly the 95
corridor TAF sites after 06Z. Winds predominantly southeasterly at 5
kt or less, though direction may be variable, especially at KRDG and
KABE.

Outlook...

Thursday through Friday night...Mainly VFR.

Saturday/Sunday...Sub-VFR conditions probable with increasing
chances for showers.
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&&

.MARINE...
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Winds and seas will stay below small craft advisory criteria through
tonight. There is potential for near shore fog late Wednesday night.
However, low confidence if the set up will favor fog or low clouds,
so will be watching trends closely if a marine dense fog advisory
may be needed for tonight.

Outlook...

Thursday through Saturday...No marine headlines anticipated.

Sunday...SCA flag possible. Seas may build to 5 feet in some
locations, wind gusts 20-25 kts possible. Rain showers likely.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Wunderlin
NEAR TERM...Johnson
SHORT TERM...Wunderlin
LONG TERM...Wunderlin
AVIATION...Johnson/Wunderlin
MARINE...Johnson/Wunderlin