-- Discussion containing changed information from previous version are highlighted. --
108
FXUS61 KPHI 020129
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
929 PM EDT Wed May 1 2024

.SYNOPSIS...
A warm front lifts through tonight. A 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.

&&

.NEAR TERM /THROUGH TODAY/...
Following a warm and mostly sunny spring day, a sea breeze is
advancing inland into the I-95 corridor as of 8 PM. Temperatures
are forecast to drop into the 50s tonight across much of the
region, coolest across New Jersey where the marine layer
impinging inland overnight will have the greatest impact. High
pressure off to the east will result in prevailing onshore flow
at the surface overnight within the marine layer, however a
frontal boundary will return northward as a warm front by
Thursday morning. While dry and benign conditions are expected
much of the night, we should see some marine stratus and perhaps
some areas of fog beginning to advect inland across the coastal
plain and toward the I-95 corridor and even as far north and
west as the Lehigh Valley, especially after midnight or so. No
dense fog is currently anticipated though.

With winds shifting offshore on Thursday and increasing to near
10-20 mph, any morning stratus and fog will quickly scatter out
by 9 to 10 AM thanks to drier continental air advecting in from
the west. Ridging will begin building aloft as the day
progresses. The adiabatic compression, downsloping offshore
winds, ample sunshine, and 850 mb temperatures 12-15C will
support widespread high temperatures in the mid to upper 80s,
perhaps even touching near 90 degrees within the urban corridor
and interior Delmarva locations. Fortunately, dewpoints will mix
out into the 40s and 50s into the afternoon, so the Heat Index
won`t be much of a factor. Apparent temperatures will be near
actual temperatures, plus the breeze will feel quite
refreshing given the dryness of the air.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
High pressure and mostly dry conditions prevail through Friday.
Expect low temperatures in the 50s once again Thursday night
with potential for more stratus or fog development within the
marine layer. Shortwave energy could linger overnight Thursday
so an isolated shower or two could develop. Otherwise,
precipitation doesn`t arrive until late Friday night to early
Saturday morning as another front approaches. Temperatures max
out in the 60s to low 70s on Friday, coolest near the coast.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Unsettled conditions are expected for the bulk of the extended
period. Weak ridging overhead on Saturday erodes through the
weekend as a shortwave trough digs to the north. An associated
cold front brings shower activity on Saturday and Sunday, but
could fall apart before moving through completely, or stall in
the vicinity. High pressure could briefly build in again on
Monday before a second stronger cold front sweeps through to
clean out the previous boundary.

&&

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

Tonight...VFR conditions are expected to start but low cigs and
some areas of fog are expected to develop with the marine layer
as it moves inland. Guidance has trended more conservative with
how far west the marine layer extends, so for now kept it east
of PHL/PNE with prevailing restrictions included at ACY/MIV/TTN.
Conditions should improve by 13-14Z. Moderate confidence
overall, but lower confidence in the exact timing and coverage
of any restrictions.

Thursday...Any restrictions quickly scatter out by 14Z, then
VFR. West to northwest winds increase to near 10-15 kts, with
some gusts near 18-20 kts possible at times. Gusts do not appear
to prevail, so I have kept gusts out of the TAFs for now. The
winds will diminish a bit toward 00Z and shift more north to
northeasterly after 00Z. High confidence overall.

Outlook...

Thursday night through Friday night...Mainly VFR, though some
restrictions possible in stratus/fog at night.

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

&&

.MARINE...
While winds are expected to remain below SCA, onshore flow could
bring fog, potentially dense near 1 NM or less, to the near
shore waters and inland late tonight. There is some uncertainty
on if low stratus or fog is more favorable to develop, but will
continue to monitor for potential of marine dense fog. At this
time, the greatest chance for the lowest visibility in fog will
be offshore of New Jersey.

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.

&&

.FIRE WEATHER...
-- Changed Discussion --
Very warm, dry, and somewhat breezy conditions are forecast for
Thursday, May 2nd. Following some morning clouds and fog,
relative humidity is forecast to fall to around 25-35% across
much of the area along with temperatures surging into the mid to
upper 80s under sunny skies. Meanwhile, west to northwest winds
are forecast to increase to near 10-15 mph, with some gusts
near 20 mph at times. While a wetting rainfall occurred on
Tuesday across the Lehigh Valley, southern Poconos, and northern
New Jersey, remaining areas of southeastern Pennsylvania, New
Jersey, and Delmarva have not experienced a wetting rainfall in
well over a week now. This is anticipated to result in some
concerns for wildfire spread on Thursday. Coordination will be
needed with our fire weather partners to determine if any
products will be needed to highlight this potential threat.
-- End Changed Discussion --

&&

.CLIMATE...
-- Changed Discussion --
Near record breaking high temperatures are forecast on Thursday.
Records for our climate sites are listed below:

Record High Temperatures
                            May 2
Site                  Record/Year
Allentown (ABE)           90/2001
AC Airport (ACY)          91/2018
AC Marina (55N)           85/1913
Georgetown (GED)          90/2018
Mount Pocono (MPO)        83/1913
Philadelphia (PHL)        89/2010
Reading (RDG)             89/1899
Trenton (TTN)             88/2010 & 2018
Wilmington (ILG)          90/1894
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Wunderlin/Skeen
NEAR TERM...Skeen/Staarmann
SHORT TERM...Skeen/Staarmann
LONG TERM...Skeen
AVIATION...Staarmann/Wunderlin/Skeen
MARINE...Wunderlin/Skeen
FIRE WEATHER...Staarmann
CLIMATE...Staarmann