283
FXUS61 KPHI 171016
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
616 AM EDT Wed Jul 17 2024

.SYNOPSIS...
A ridge of high pressure will weaken across the area today.
Meanwhile, a strong cold front will cross the Middle Atlantic
region later today and tonight. It will be followed by high
pressure for the end of the week and into the weekend. Another
upper system and surface front will arrive for early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
615 AM...The large scale pattern continues to feature a ridge
of high pressure in the western Atlantic with low pressure over
northern Quebec into Labrador. A cold front extends south and
west from this low across the lower Great Lakes. This setup will
keep the area in a SW flow with dangerous heat continuing into
today. Once again, expect to see many locations seeing heat
index values over 100 by the afternoon. While cloud coverage and
possible storms (severe weather and hydro discussion below) may
limit temperatures from getting too out of hand, dew points
will likely increase a bit and linger in the low 70s during the
afternoon hours, leading to continuing oppressive heat. As a
result, the heat headlines continue through today given the
compounded effect from numerous days with dangerous heat.

For the storms later today, a slow-moving cold front will create a
marathon of severe weather and hydro concerns beginning early
afternoon through at least the evening hours into the overnight.
Abundant instability and PWAT values over 2 inches will fuel the
potential for training thunderstorms across the region. Much of the
storms during the afternoon will stay north and west of the I-95
corridor with storms in the evening and nighttime largely impacting
areas near and south and east of the I-95 corridor. SPC now has our
entire area in a s SLIGHT Risk of severe weather (level 2 out of 5).
T he biggest threat looks to be damaging winds given deep layer
shear around 25 to 30 knots and ML CAPES of 1500-2000+ j/kg. The WPC
has a Slight Risk for excessive rainfall for the urban corridor with
a Marginal Risk for the rest of the CWA.

Scattered thunderstorms are expected to continue through the first
half of tonight ahead of the advancing cold front. Heavy rain and
locally gusty winds will be the main threats as the line of storms
work their way through the area. Storms should eventually give way
to just some residual showers before tapering off from northwest to
southeast overnight. Low temps will fall in the upper 60s to low 70s.

The cold front should fully cross through the region by Thursday
morning but will begin to slow down as it passes to our south and
east. So while, the northern half of the area will begin to see some
clearing, the southern half of the area (especially near the coast),
will see cloud cover linger throughout the day. Isolated showers and
storms may hang up along the coast as well, but overall, this chance
remains uncertain/low. On the bright side, this cold front will
knock down temps and humidity with highs mainly in the low to mid
80s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
A great stretch of more pleasant weather is expected during the
short term. Thursday night will be the first in a while without
significant amounts of humidity and temperatures will be cool as
well. Lows are expected to drop into the upper 50s/low 60s for the
far NW areas while the remaining locations will have lows in the
mid/upper 60s. There could be some patchy fog around too, especially
in areas that get some heavier rains in the near term.

Weak high pressure ridges across the Middle Atlantic region Friday.
A dry day is expected with seasonable temperatures and comfortable
humidity levels. High temperatures will mostly be in the low/mid 80s
for the region. The dew points will be in the upper 50s/low 60s for
the area, so much lower humidity levels which are welcome. Winds
will be West to Northwest at 5 to 10 mph. Fair weather continues
Friday night with temperatures seasonably mild, just like the
previous night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Compared to the temperatures and humidity of the week so far, the
long term is going to be quite an improvement. However, the more
pleasant conditions of the weekend will gradually yield to a return
of uncomfortable humidity as we get towards the middle of next week.
As is usually the case, more humid conditions will be across
Delmarva and southern NJ while the Southern Poconos and north NJ
will be drier and more comfortable. An upper trough that will bring
the more seasonable conditions will move away over the weekend and
the upper high will build back northward next week.

Temperatures for the weekend and into next week will generally be
within a few degrees of normal with Sunday being the warmest day and
Tuesday the `coolest`. Highs will range from the mid/upper 80s for
the NW areas and upper 80s/low 90s for Delmarva and metro
Philadelphia. Lows mostly 60s N/W and low 70s S/E.

Precipitation will be limited to just slight chance pops for
Delmarva for the weekend. As we head into next week, the moisture
begins to return from south to north so chance pops will be common
for next week. Lowered pops in many areas Tue. from the NBM 50%.

&&

.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Today...VFR in the morning before showers and thunderstorms in
the afternoon and into the evening could result in sub-VFR
conditions beginning by as early as around 18-20z for ABE and
RDG but mainly after 21z for the I-95 TAF sites and points
south/east. Winds mainly out of the southwest around 10 kts.
Moderate confidence.

Tonight...Sub-VFR conditions likely with scattered
thunderstorms. A few storms may be severe with locally damaging
winds. Storms should move out by the overnight but sub VFR cigs
likely in their wake. Winds southwest around 10 knots early this
evening veering to northwest 5 to 10 knots overnight. Moderate
confidence.


Outlook...

Thursday...Some lingering sub VFR cigs early in the morning with
a few lingering showers possible at MIV and ACY. Otherwise VFR.
NW winds around 5 to 10 knots. Moderate confidence.

Thursday night through Sunday... Mostly VFR. Patchy pre-dawn fog
possible.

&&

.MARINE...
Winds and seas will be increasing into today with Small Craft
Advisory conditions expected for the ocean zones beginning this
afternoon. Generally expect southwest winds 20 gusting up to 25
knots with seas around 5 feet.

SCA conditions continue tonight and there will also be some storms
moving over the waters that could bring locally stronger winds
potentially gusting over 40 knots.

By Thursday, winds/seas should be sub SCA but there still could be
some lingering showers and storms over the waters.

Outlook...

sub-SCA conditions are expected for the end of the week and into the
weekend. Fair weather will be around much of the time. Scattered
showers and tstms will arrive for Monday and Tuesday.

Rip currents...

For today, the south-southwest flow will increase to around 15-
20 mph with gusts up to 25 mph. Wave heights in the surf zone
are again forecast to be around 1-3 feet with a 5-7 second
period. Therefore, a MODERATE RISK for the development of
dangerous and life threatening rip currents is in place for the
Jersey Shore and a LOW risk is in place for the Delaware
Beaches.

Late day showers and thunderstorms are possible along both the
Jersey Shore and Delaware Beaches.

Some areas of fog at times will cause reduced visibility along the
shoreline.

For Thursday, winds will turn more offshore out of the west to
northwest and decrease to around 10 mph. Wave heights will mainly
remain around 1-2 feet with a 5-7 second period. As the winds should
be weaker and directed offshore across the region, the risk for the
development of dangerous and life threatening rip currents is
forecast to decrease to LOW on Thursday for all coastal zones.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.CLIMATE...
One more day of forecast high temperatures near the record
levels. Here are the records for today.

Record High Temperatures (today)
                          July 17
Site                  Record/Year
Allentown (ABE)           99/1999
AC Airport (ACY)          99/2012
AC Marina (55N)           95/1937
Georgetown (GED)         100/2019
Mount Pocono (MPO)        91/1999
Philadelphia (PHL)       102/1988
Reading (RDG)            102/1988
Trenton (TTN)            100/1988
Wilmington (ILG)         100/1988

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT this evening for
     PAZ060>062-070-071-101>106.
     Heat Advisory until 8 PM EDT this evening for PAZ054-055.
NJ...Excessive Heat Warning until 8 PM EDT this evening for
     NJZ007>010-012-013-015>023-027.
     Heat Advisory until 8 PM EDT this evening for NJZ001-014.
DE...Excessive Heat Warning until 8 PM EDT this evening for
     DEZ001>003.
     Heat Advisory until 8 PM EDT this evening for DEZ004.
MD...Excessive Heat Warning until 8 PM EDT this evening for MDZ012-
     015-019-020.
MARINE...Small Craft Advisory from 2 PM this afternoon to 8 AM EDT
     Thursday for ANZ450>455.

&&

$$

SYNOPSIS...OHara
NEAR TERM...Fitzsimmons
SHORT TERM...OHara
LONG TERM...OHara
AVIATION...Fitzsimmons/OHara
MARINE...AKL/Fitzsimmons/OHara
CLIMATE...