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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 090123
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
923 PM EDT Sat May 8 2021

.SYNOPSIS...
Low pressure will move north into the Canadian Maritimes
tonight while high pressure builds in to our south over the
western Atlantic. Low pressure is forecast to track across our
area Sunday night into Monday morning, with a cold front
crossing our area during Monday. Strong high pressure builds in
later Tuesday and Wednesday before weakening and shifting
offshore during Thursday. Low pressure moving across the
southern states Thursday may then track near our region Friday.

&&

.NEAR TERM /THROUGH SUNDAY/...
-- Changed Discussion --
The earlier showers have almost completely dissipated, and the
one lingering area of showers in Burlington County should
dissipate within the next hour. We`ll have a brief window of
opportunity for mostly clear skies, but it appears that high-,
and eventually mid-, level clouds will build in quickly towards
sunrise especially west of the fall line in advance of the warm
air advection. Therefore, do not expect to have particularly
efficient radiational cooling conditions, so most areas should
stay well above any frost thresholds. A possible exception is in
the southern Poconos, which could get close, but at this point,
expect temperatures to stay right at or just above 36 degrees.

Clouds will continue to increase through the day tomorrow as a
50+ knot low level southwesterly wind jet is forecast to push
over our region during the afternoon. It will result in a strong
punch of warm advection aloft. However, we`ll have a competing
factor in that with the 00Z RAOBs, there was significant mid
level height rises upstream. Expect those height rises, along
with a robust mid level dry layer to slow the eastward
expansion of the rain during the day tomorrow. It now looks like
for areas mostly east of the fall line, rain is not likely to
arrive until at least late tomorrow afternoon, if not tomorrow
night. For areas west of the fall line, rain could begin to move
in near mid day.

The wind is expected to back to the southwest and south on
Sunday around 10 MPH. Highs should range from the lower and
middle 50s in the Poconos to the middle 60s in eastern Maryland,
and in central and southern Delaware.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
Low pressure will move ENE across the area Sunday night into
early Monday likely passing near or just north of the I-95
corridor. This will bring a period of rain through the region
mostly through the evening and the first half of the overnight
and mostly north of the I-95 corridor. In fact portions of our
southern Delmarva zones and southern NJ may see little to no
precip.

Any lingering rain/showers should quickly come to an end Monday
morning as low pressure quickly exits off the coast. Total rain
amounts look to generally be a tenth to a quarter inch or less
except possibly over a half inch over portions of NE PA and NW
NJ. Otherwise Monday should be mostly dry and a bit breezy in
the wake of the low with some sunshine developing by afternoon.
Highs will be mostly in the 60s to low 70s except 50s over the
southern Poconos.

The upper level trough located to our north and west looks to
finally swing through the region Monday night into Tuesday with
surface high pressure building into the midwestern states. This
should set conditions up for a dry but fairly gusty day for
Tuesday as there looks to be a very deep mixed layer due to the
colder air aloft combined with surface heating. Winds may gust
to 20 to 30 mph or higher by the afternoon. Precip associated
with the upper level trough looks to stay to our north.
Temperatures will be a bit cooler Tuesday with highs mostly in
the low to mid 60s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Mainly clear conditions look to dominate for Wednesday through
Thursday as the upper level trough moves out to our north and
east and surface high pressure moves in. Temperatures will also
warm a few degrees each day with highs by Thursday reaching back
into the upper 60s to around 70 for much of the region.

Conditions may turn unsettled again by the end of the week into
next weekend but there remains a lot of forecast uncertainty at
this time. GFS depicts a coastal storm developing near or off
the coast and moving northeast into Friday but it is the outlier
solution so we just keep POPs at the lower end of the "Chance"
category. Additional energy approaching from the west could
bring some showers into the area by late Saturday. Temperatures
look to remain near if not just a bit below average for this
time of year.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Into this evening...TAF sites are all VFR this evening as a weak
surface low/ trough slowly exits the coast of NJ. In the mid-
levels of the atmosphere, an upper level wave is currently
overhead and is responsible for producing numerous showers and
isolated rumbles of thunder across the region. The coverage of
these showers will continue to rapidly decrease through the
evening hours as the sun sets and instability is lost. Winds
will mainly be out of the northwest around 10 knots. High
confidence.

Tonight...VFR. VFR clouds rapidly clearing. Northwest to west
wind 6 knots or less. High confidence.

Sunday...Initially clear skies very early Sunday morning will
give way to rapidly increasing cloud cover with cirrus quickly
thickening across the TAF sites. Cigs will lower through the day
as a mid-level wave approaches from the southwest, but remain
VFR. Strong warm air advection in association with a low level
warm front will be the primary initial forcing mechanism. The
best chance of precipitation will initially be towards KABE in
the morning hours, with KMIV and KACY likely remaining dry
Sunday morning. By Sunday afternoon the warm front will lift
north of the TAF sites with any precipitation temporarily coming
to an end. VFR conditions are expected through Sunday.

Outlook...

Sunday night and Monday...A period of sub-VFR conditions will
be possible with some rain Sunday night into Monday morning,
mainly for KRDG and KABE. Otherwise VFR ceilings. Southwest to
southeast surface winds 5-10 knots, becoming northwest Monday
10-15 knots with gusts to 20 knots. A period of low-level wind
shear possible Sunday night and early Monday morning. Moderate
confidence.

Tuesday...VFR. Northwest winds around 15 knots with gusts 20-25
knots. High confidence.

Wednesday...VFR. Northwest wind 10-15 knots. High confidence.

Thursday...VFR with NW winds around 5 knots becoming SW.

&&

.MARINE...
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A northwest wind 10 to 20 knots is expected for tonight. Earlier
gusts above 25 kt on the Delaware and southern NJ waters have
subsided. Therefore, the Small Craft Advisory has been canceled.

A northwest to west wind around 10 knots is forecast to back to
the southwest and south on Sunday, increasing to around 15
knots.

Waves heights on our ocean waters should be 3 to 4 feet, with
waves on Delaware Bay generally 1 to 3 feet.

Outlook...

Sunday night...Small Craft Advisory conditions probable as
southwest winds increase and seas build. Some warmer air will be
arriving ahead of a cold front, therefore the extent of the
vertical mixing is a little less certain.

Monday...Small Craft Advisory conditions probable at least in
the morning. Gusty winds shift to the west and northwest then
diminish some through the day. Elevated seas will subside into
Monday night.

Tuesday and Wednesday...Small Craft Advisory conditions are
possible Tuesday and Tuesday night with conditions improving
during Wednesday.

Thursday...conditions are expected to be below Small Craft
Advisory levels.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.
-- End Changed Discussion --

&&

$$
Synopsis...Fitzsimmons
Near Term...Iovino/Johnson
Short Term...Fitzsimmons
Long Term...Fitzsimmons
Aviation...Fitzsimmons/Haines
Marine...Fitzsimmons/Iovino/Johnson