500
FXUS61 KPHI 201538
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1138 AM EDT Thu Jun 20 2024

.SYNOPSIS...
Bermuda high pressure remains in control through the weekend. A
back door cold front will move in from the north on Friday and
will stall over the area on Saturday before returning north as a
warm front. A stronger cold front will pass through the region
Sunday night, then lingers over the area through Monday. High
pressure returns on Tuesday, followed by another front for
Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
For the midday update, just some subtle tweaks were made to
the hourly temperature and dewpoints.

The Heat Advisory continues for today for most of the region.
Temperatures will be a touch higher compared to yesterday with
heat indices of 93-98 within the Heat Advisory. Limit outdoor
time today and if you have to be outside, take frequent breaks
and stay hydrated!

A strong 597-598 dam ridge will retrograde to the west today,
though it will remain the dominant feature influencing the
pattern. Bermuda high pressure remains offshore, fostering a
light south/southwesterly flow. The result will be another hot
day, and temperatures will be slightly higher compared to
yesterday. Looking at low 90s within the Heat Advisory, with
heat indices climbing into the mid to upper 90s. Areas near the
coast will be a touch cooler, similar to previous days, with
upper 80s expected within South Jersey and lower Delmarva. A sea
breeze (and bay breeze where applicable) will develop, keeping
things cooler near the coastline. Given some impressive records
for today (see climate section below), not expecting any record
highs to fall. Mount Pocono has a chance, but they are the only
site with forecasted highs within 5 degrees of their record.

Mainly high cirrus today with just a touch cumulus.

For tonight, a mild and muggy night is expected. Lows will fall
into the mid to upper 60s/low 70s with dewpoints in the 60s.
Not much relief expected overall.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Hot and increasingly humid conditions remain in place for the
end of the week. The Heat Advisory remains in effect for Friday
for southeast Pennsylvania, most of New Jersey, and northern
Delaware as highs will get in the low to mid 90s along with
surface dew points in the mid to upper 60s. This will yield max
heat index values in the upper 90s to around 100 in the Advisory
area and in the low 90s elsewhere.

A broad almost 600 dam 500 mb high over the Ohio and Tennessee
Valleys, Gulf Coast states, and southern Plains will sag a bit
to the southwest. As a result, 500 mb heights will fall from
around 593 dam to around 590 dam as a back door cold front
slides in from the north. Showers and thunderstorms will develop
across areas mainly north and west of the Fall Line, with
showers and thunderstorms becoming likely over portions of
Carbon and Monroe counties in Pennsylvania and Sussex county in
New Jersey. For most of the area north and west of the Fall
Line, SB CAPE values will be upwards of 1500 to 2000 J/kg and
DCAPE values will be from 800 to 1000 J/kg. 0- 6 km Bulk Shear
will be minimal at generally less than 15 kt, and PWATs will be
1.75 to 2 inches. Slow-moving thunderstorms will produce heavy
rain and localized flooding, especially in these far northern
zones. Localized severe thunderstorms will be capable of
damaging wind gusts. The Storm Prediction Center has a Marginal
Risk (1 out of 5) for portions of the southern Poconos, northern
New Jersey, and Lehigh Valley.

Warm and humid Friday night with showers and thunderstorms
tapering off. Should be humid enough for patchy fog, especially
in areas where thunderstorms occur.

That front remains over the area, mainly along the Fall Line,
on Saturday. As a result, high temperatures will be in the upper
80s for the southern Poconos and in the low to mid 90s for
northern New Jersey and the Lehigh Valley. A slight onshore
component to the winds along the coast, as well as local sea
breezes, should keep temperatures in the 80s along the coasts as
well. Going inland, however, and highs will get into the mid
and upper 90s, with the highest temperatures along the I-95
corridor and in Delmarva. With southerly flow now taking hold
and increasing, surface dew points will climb into the upper 60s
and low 70s. Max heat index values will be in the upper 90s to
around 105. Will keep the Excessive Heat Watch in effect for
now.

Some shortwave energy approaches from the west in the afternoon
and interacts with the front bisecting over the area. Another
round of showers and thunderstorms will develop in the afternoon
and evening, with chance PoPs down to the I-95 corridor. Again,
locally heavy rain and damaging wind gusts are possible.

Even warmer and more humid Saturday night.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Excessive Heat Watch remains in effect for Sunday, and the
trend has been back hotter and more humid. NBM max temperatures
are 100 to 101 for Philadelphia and along the I-95 corridor.
However, this may be a bit too high for several reasons. A cold
front will approach from the west. With increasing clouds over
the area with the approach of that front, the cloud cover may
keep temperature from getting as hot. The other thing is
convection associated with that front, as showers and
thunderstorms will knock temperatures down and, depending on the
timing, could keep areas from reaching forecast highs.

That said, high temperatures should get up into the mid and
upper 90s, though just shy of 100, for most of New Jersey, the
Lehigh Valley, southeast Pennsylvania, and Delmarva, with the
hottest temperatures along the I-95 corridor and in Delmarva.
Surface dew points will also be in the low 70s, which results in
max heat index values generally from 100 to 105, and possibly
up to 110 in Delmarva. As a result, will expand the Excessive
Heat Watch to include the whole area, though if 110 heat index
values do not occur in Delmarva and extreme southeast New
Jersey, that Watch could be converted to a Heat Advisory.

Now, with all of this heat and humidity, that sets the stage
for a potential severe weather outbreak Sunday afternoon and
evening as a strong cold front approaches from the west. SB CAPE
values will be up around 1500 to 2000 J/kg, DCAPE values will
be up around 100 J/kg, 0-6 km Bulk Shear will increase to 25 to
30 kt, and PWATs will be up around 2 inches. The question is if
the highest shear values will line up with the highest CAPE
values, and that will depend on the timing of the front.
Damaging winds and heavy rain with localized flooding will occur
in the strongest storms.

Showers and thunderstorms will continue through Sunday night
before tapering off Monday. The front will be hung up over the
area and will not move offshore until Monday night.

Weak high pressure builds back into the region Tuesday,
followed by another front on Wednesday. Temperatures will not be
as hot, but will still be above normal on Monday and Tuesday
with highs in the upper 80s to low 90s. Highs on Wednesday will
be in the low to mid 90s. Fairly humid on Monday with highs in
the upper 60s before drier air builds into the region Tuesday.
Humidity returns on Wednesday.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. South to southwest winds 5-10 knots. More
southerly winds expected yet again at KMIV/KACY this afternoon
with the passage of the sea-breeze. Funneling up the Delaware
Bay will result in a more southerly wind at KILG as well. High
confidence.

Tonight...VFR. Winds out of the south/southwest 5 kt or less.
High confidence.

Outlook...

Friday through Saturday...Overall, VFR. Afternoon evening
SHRA/TSRA with sub-VFR conditions possible at
KRDG/KABE/KTTN/KPNE/KPHL Friday and Saturday.

Sunday through Monday...Generally VFR Sunday. SHRA/TSRA
developing Sunday afternoon, continuing through Sunday night
before tapering off on Monday will result in sub-VFR conditions.

&&

.MARINE...
No marine headlines expected through tonight. South winds 10-20
kts, with the highest speeds across Monmouth and Ocean
counties. Seas 2 to 4 feet.

Outlook...

Friday through Saturday...Sub-SCA conditions, though persistent
15 to 20 kt winds may develop at northern NJ ocean waters each
afternoon.

Sunday through Monday...SCA conditions may develop with S winds
15 to 20 kt with 25 to 30 kt gusts and Seas building to 3 to 5
feet. Showers and thunderstorms will develop Sunday afternoon
and continue through Sunday night before tapering off on Monday.
VSBY restrictions in heavy rain and damaging wind gusts
possible.

Rip Currents...

Today...Southerly winds around 10-15 mph and breaking waves
will be around 2-3 feet. Portions of the southern NJ coast will
keep an onshore component of the wind, in addition to the Full
Moon on Friday. For this reason, have maintained a MODERATE Risk
for all New Jersey beaches except Monmouth County. For the
Delaware Beaches and Monmouth County, maintained the LOW Risk of
dangerous rip currents.

Friday...Similar weather conditions are expected on Friday in
addition to the occurrence of a Full Moon. With this in mind,
saw no reason to change Rip Risks for NJ/DE beaches from what is
currently posted for Thursday.

Rip currents occur often in the vicinities of jetties and
piers. Utilize any guarded beaches if venturing out into the
water. For specific beach forecasts, visit weather.gov/beach/phi

&&

.CLIMATE...
Mount Pocono is the only site that could come close to its
record today. No other records are in jeopardy today based on
the forecast. No record high minimum temperatures will be set
today based on the temperatures observed this morning.

Location          Record High (6/20)

Philadelphia, PA      98/1931
Allentown, PA         100/1923
Reading, PA           101/1923
Mount Pocono, PA      89/2012
Trenton, NJ           98/1923
AC Airport, NJ        95/2012
AC Marina, NJ         90/1908
Wilmington, DE        97/2012
Georgetown, DE        98/2012

Record high temperatures Friday.

Location          Record High (6/21)

Philadelphia, PA      99/1923
Allentown, PA         100/1923
Reading, PA           99/1923
Mount Pocono, PA      90/1953
Trenton, NJ           97/1923
AC Airport, NJ        97/1988
AC Marina, NJ         94/2012
Wilmington, DE        98/2012
Georgetown, DE        99/2012

Record high temperatures Saturday.

Location          Record High (6/22)

Philadelphia, PA      100/1988
Allentown, PA         95/1941
Reading, PA           96/1921
Mount Pocono, PA      90/1908
Trenton, NJ           99/1988
AC Airport, NJ        100/1988
AC Marina, NJ         92/1949
Wilmington, DE        98/1988
Georgetown, DE        97/2012

Record high temperatures Sunday.

Location          Record High (6/23)

Philadelphia, PA      97/1888
Allentown, PA         95/1965
Reading, PA           96/1908
Mount Pocono, PA      90/1908
Trenton, NJ           97/1894
AC Airport, NJ        98/1988
AC Marina, NJ         91/1909
Wilmington, DE        100/1894
Georgetown, DE        100/1988

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 6 AM EDT Saturday for PAZ054-055-060>062-
     070-071-101>106.
     Excessive Heat Watch from Saturday morning through Sunday
     evening for PAZ054-055-060>062-070-071-101>106.
NJ...Heat Advisory until 6 AM EDT Saturday for NJZ001-007>010-012-
     013-015>020-027.
     Excessive Heat Watch from Saturday morning through Sunday
     evening for NJZ001-007>010-012-013-015>020-027.
     Excessive Heat Watch from Sunday morning through Sunday
     evening for NJZ014-021>026.
DE...Heat Advisory until 6 AM EDT Saturday for DEZ001.
     Excessive Heat Watch from Saturday morning through Sunday
     evening for DEZ001.
     Excessive Heat Watch from Sunday morning through Sunday
     evening for DEZ002>004.
MD...Excessive Heat Watch from Sunday morning through Sunday
     evening for MDZ012-015-019-020.
MARINE...None.

&&

$$

SYNOPSIS...MPS
NEAR TERM...Hoeflich/Kruzdlo
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...Hoeflich/MPS/Kruzdlo
MARINE...Hoeflich/MPS/Kruzdlo
CLIMATE...WFO PHI