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000
FXUS61 KPHI 170126
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
926 PM EDT Tue Apr 16 2024

.SYNOPSIS...
High pressure moves offshore tonight before a series of fronts and
low pressure systems affect the East Coast Wednesday through the end
of the week. High pressure looks to return to end the weekend
and start next week.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 925 PM, the sea breeze front is dissipating as it shifts
mostly northwestward of the immediate I-95 corridor. Some wisps
of cirrus clouds continue to work down from the northwest. A
mostly clear sky is expected for a while tonight. This combined
with lower dew points and a light/calm wind is resulting in the
temperatures dropping faster so far this evening. The passage of
the aforementioned sea breeze also resulted in quicker cooling
in its wake. Made some adjustments to the hourly temperature,
dew point and wind grids based on the latest observations and
trends. The adjustments to the temperature grids where to show a
quicker cooling so far given the trends.

Otherwise, an upper-level ridge will slide eastward toward our
region tonight. A surface warm front will also slowly approach
from the southwest overnight with an increase in warm air
advection at 850 mb as the flow backs to more west and southwest.
The clouds will increase, however this should be the most
notable late in the overnight. Expect lows mainly in the mid/upper
40s to low 50s.

High pressure offshore Wednesday as a cutoff low shifts over
the Great Lakes. Its warm front will get closer to our area
during the course of Wednesday with a period of stronger warm
air advection. A fairly narrow corridor of showers looks to
accompany the isentropic lift, which looks to arrive across the
I-95 corridor around midday. Showers will therefore be on the
increase especially in the afternoon. A cool onshore flow will
help keep an inversion in place for much of the day, limiting
any instability and, therefore, limiting thunderstorm
development during the afternoon hours. High temperatures will
only reach the low to mid 60s with the Poconos and immediate
coastline likely getting stuck in the mid to upper 50s.

A cold front moves through Wednesday night and brings with it showers
and possibly a few thunderstorms. Any instability, especially
surface based instability, may remain limited through this
period, so it is uncertain how widespread the coverage of storms
will be. Lows will be in the upper 40s to mid 50s. Total
rainfall amounts Wednesday and Wednesday night will be around a
half an inch or less.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
For the rest of the day Thursday, global guidance is showing
the potential for a backdoor front arriving as high pressure off
the coast of Maine interacts with a weak coastal low off the
Delmarva seaboard that will spin off from the decaying parent
cold front from the previous night. Resultant E to NE flow will
help keep temperatures much cooler than earlier in the week and
about 10 degrees below climo. Depending on how far south this
backdoor front advances, temperatures to the north will be in
the 50s with mid to upper 60s to the south. Light showers or
drizzle may linger through the day.

By Thursday night, the weak coastal low will be shunted
southward enough that surface high pressure can build in and
briefly shutoff the chances for showers. Lows Thursday night
look to fall into the 40s most everywhere across the region.

High pressure will remain in control at least through Friday
morning before the next system arrives later in the day.
Temperatures will be closer to climo with upper 50s to low/mid
60s. The next mid-level wave approaches during the afternoon,
increasing shower chances into the evening.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Low pressure continues to work through the region Friday night, and
then the cold front follows through on Saturday. Best chances for
showers will be Friday night, and then any showers taper off
Saturday morning. Due to the scattered nature of these showers, will
keep PoPs capped at chance Friday night for now.

High pressure builds in from the north and west. Meanwhile, the cold
front will sag south of the Mid-Atlantic and will become nearly
stationary over the Southeast U.S., extending back through the Gulf
Coast states and into the Southern Plains.

Several waves of low pressure will develop on that boundary, but the
boundary should remain too far south for rain to affect the local
area. Best chances for any showers look to be Tuesday.

Temperatures will be several degrees below normal, with highs
generally in the low to mid 60s and lows generally in the 30s and
40s.

&&

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

Tonight...VFR with increasing clouds late. Southeasterly winds
near 5 knots, becoming light and variable at most terminals.
Moderate confidence.

Wednesday...VFR ceilings lower to MVFR during the afternoon (after
18z). Some showers develop as well, however these should be lighter
in intensity. Light and variable winds becoming east-southeast
to east 5-10 knots. Low confidence in the timing details of the
MVFR conditions.

Outlook...

Wednesday night through Thursday...Sub-VFR conditions at times
due to stratus and showers. The most likely time for this looks
to be Wednesday night into Thursday morning. A few thunderstorms
are possible Wednesday night.

Thursday night through Sunday...VFR overall, however a brief
period of sub-VFR is possible (30 percent) Friday night through
Saturday morning.

&&

.MARINE...
Sub-advisory conditions expected through Wednesday.

Outlook...

Wednesday night through Friday...SCA conditions possible beginning
early Thursday morning, mainly due to gusty east-northeast winds
from a backdoor front and building seas. Greatest chances for
SCA conditions across the northern Atlantic waters.

Friday night through Sunday...Potential for SCA conditions Saturday
afternoon and evening, otherwise, sub-SCA conditions.

&&

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

&&

$$

SYNOPSIS...AKL/MJL
NEAR TERM...Gorse/MJL
SHORT TERM...AKL/MJL
LONG TERM...MPS
AVIATION...Gorse/MJL/MPS
MARINE...MJL/MPS