-- Discussion containing changed information from previous version are highlighted. --
556
FXUS61 KPHI 200520
AFDPHI

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

.SYNOPSIS...
High pressure will prevail across the region through the end of
the week yielding above normal temperatures. A back door cold
front will push into the region Friday night, then stall out by
Saturday. A stronger cold front will pass through the region
Sunday night through Monday, and that front may linger near the
area through Tuesday.

&&

.NEAR TERM /THROUGH TODAY/...
-- Changed Discussion --
Forecast is on track early this morning. Only minor tweaks were
made. Quiet night overall.

Dry conditions continue through tonight as ridging aloft
remains in place across the Mid Atlantic region, while high
pressure remains offshore of the east coast. Some high clouds
continue to linger which could result in temperatures being a
touch warmer, but may also preclude low clouds and fog
development. Will see how things trend and see if any fog
develops, but think it will be confined to the more rural and
sheltered areas.

For today, the ridge aloft begins to get squeezed, but remains
across the area, while high pressure offshore sinks a little to
the south. Temperatures on Thursday are expected to be a degree
or two warmer than Wednesday, with similar dewpoint and humidity
levels. Therefore the heat index values will be similar to
Wednesday, if not slightly higher. Therefore we will keep the
Heat Advisory for Thursday. The forecast during the day Thursday
will be dry as the backdoor frontal boundary is expected to be
well to our north during the daylight hours.
-- End Changed Discussion --

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
Overall, the trend remains for somewhat lower temperatures and
somewhat lower humidity levels with a notable marine influence
across our area. Expect low temperatures in the mid 60s to near
70 degrees for Thursday night under mostly clear skies. A light
south to southwest wind should prevailing overnight.

By Friday, Bermuda high pressure will remain positioned off the
Mid- Atlantic coast. Increasing south to southwesterly flow plus
the upper ridge starting to sink farther south will usher a
warmer and more humid air mass into the region. Highs on Friday
should get solidly into the low to mid 90s, perhaps in the
upper 90s within the Philadelphia to Trenton metro area.
Regardless, this appears to most likely be the hottest day of
the heatwave through the end of the week. Surface dew points
rise into the upper 60s to low 70s, resulting in max heat index
values ranging from the mid 90s to near 100 degrees. Given the
confidence level for reaching Heat Advisory criteria, and
Warning level heat indices appearing unlikely, we have upgraded
the Excessive Heat Watch to a Heat Advisory for Friday through
Friday night. Additionally, this will be the 4th day of the
heatwave in much of the advisory area.

The other aspect for Friday is that a back-door cold front will
sag in from the north, likely initiating a few afternoon and
evening showers and thunderstorms. Will follow NBM and carry
low-end likely PoPs for the southern Poconos and far northern
New Jersey, and chance PoPs down to along the I-78 corridor.
Slight chance PoPs continue down to Philadelphia. For areas
north and west of the Fall Line, PWATs will be up around 1.75
inches and 0-6 km Bulk Shear will be less than 20 kt. SB CAPE
values should range from 1500 to 2000 J/kg. Water loaded
downdrafts could cause localized flooding due to potentially
slow- moving thunderstorms producing heavy rain, as well as the
potential for microbursts. The SPC carries a Marginal Risk (1/5)
for severe thunderstorms north of I-78.

Lows will be a couple of degrees warmer Friday night compared
to Thursday night, mainly in the upper 60s to low 70s. Urban
areas that don`t experience any convection could stay in the mid
70s. Patchy fog may develop Friday night as well.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Excessive Heat Watch will remain in effect for Saturday and
Sunday, mainly based on the cumulative impacts have based on
several days of heat and humidity with little, if any, relief at
night due to warm overnight low temperatures have.

While high temperatures seem to be trending slightly lower than
originally forecast, surface dew points are trending on the
higher side given persistent southerly flow allowing low level
moisture to build into the Northeast and Mid-Atlantic and the
upper ridge sinking farther south.

Back-door cold front through the northern half of the forecast
area Friday night remains nearly stationary on Saturday. This
situations tend to see the boundary stall out from around the
Lehigh Valley southeast toward Trenton and the northern NJ
coast. As a result, highs will be in the upper 80s to low 90s
for the northern portion of the forecast area, and even along
the coasts, highs will be in the low to mid 80s due to flow
coming off the cooler ocean waters. Just inland, including the
I-95 corridor from Trenton to Wilmington and areas west, as well
as Delmarva, highs should get in the mid 90s again. Surface dew
points will be in the upper 60s to low 70s. Max heat index
values in these areas will be in the upper 90s to low 100s.

A thermal trough sets up over central Pennsylvania and some
approaching shortwave energy may initiate some afternoon and
evening showers and thunderstorms, with the highest PoPs north
and west of the Fall Line. Again, heavy rain and localized
flooding possible along with potential for microbursts.

A cold front approaches on Sunday. Southwesterly flow ahead of
the front ushers warm and humid air with highs in the mid to
perhaps upper 90s and surface dew points in the lower 70s. The
temperatures have trended up slightly for Sunday, although this
will be conditional based on the approaching front and
associated clouds and convection. Will keep an eye on potential
severe weather on Sunday. Ahead of the front, SB CAPE values
rise to around 1500 J/kg and 0-6 km Bulk Shear will rise to 35
to 40 kt in the afternoon and evening. DCAPE values will be up
around 600 to 800 J/kg. PWATs will be up around 2 inches.
Damaging winds and heavy rain possible Sunday afternoon and
evening.

Cold front comes through on Monday and may get hung up over the
area into Tuesday. With the front over the area, additional
scattered showers and thunderstorms possible Monday afternoon.
Highs will be in the upper 80s to around 90, with surface dew
points in the mid and upper 60s. Max heat index values will not
be much higher than the actual surface temperatures. Tuesday
looks to be dry with temperatures a few degrees above normal,
topping off in the upper 80s to low 90s.

&&

.AVIATION /05Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Tonight...Prevailing VFR for much of the night. Some
patchy fog at KACY possible around daybreak, reducing
visibilities to MVFR levels briefly. Fog should mix out by 11z
though. Everywhere else should stay VFR with south/southwest
winds at 5 kt or less. Moderate confidence.

Thursday...VFR Winds increase out of the south to southwest
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 south/southeast
wind at KILG as well. High confidence.

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

Outlook...

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

Sunday...Generally VFR. Scattered afternoon SHRA/TSRA may
result in sub-VFR conditions.
-- End Changed Discussion --

&&

.MARINE...
No marine headlines expected through tonight. Winds will be out
of the south around 10-20 kt with 2 to 3 foot seas.

Outlook...

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

Sunday...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.

Rip Currents...

Thursday...Southerly winds around 10 mph and breaking waves will
be around 1-3 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...
Record high temperatures for today. Reading and Mount Pocono
are the only climate sites with a forecast high within 2 degrees
of the record. Highly unlikely any other sites match or break a
record.

Location          Record High (6/19)

Philadelphia, PA      100/1994
Allentown, PA         96/1994
Reading, PA           95/1929
Mount Pocono, PA      86/1929
Trenton, NJ           96/1994
AC Airport, NJ        96/1994
AC Marina, NJ         93/1952
Wilmington, DE        100/1994
Georgetown, DE        96/1952

Record high temperatures Thursday.

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.
DE...Heat Advisory until 6 AM EDT Saturday for DEZ001.
     Excessive Heat Watch from Saturday morning through Sunday
     evening for DEZ001.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...MPS/Staarmann
NEAR TERM...Hoeflich/MJL/Robertson
SHORT TERM...MPS/Staarmann
LONG TERM...MPS/Staarmann
AVIATION...Hoeflich/MJL/MPS/Robertson/Staarmann
MARINE...DeSilva/MPS/Robertson/Staarmann
CLIMATE...