Lower Macungie, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

679
FXUS61 KPHI 161048
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
648 AM EDT Wed Jul 16 2025

.SYNOPSIS...
A very warm and humid airmass will be over the region through
Thursday with multiple rounds of showers and thunderstorms
expected. A frontal boundary will remain stalled across the
northern portion of the area today before lifting north of the
area as a warm front on Thursday. A cold front will pass through
the region Thursday night into Friday, with high pressure
building in for Saturday. Another cold front approaches late in
the weekend, then stalling and lingering to our south through
the early part of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Not much change to the overall forecast is expected today as
mostly clear skies and dry conditions this morning will give way
to increasing clouds and wet weather late this afternoon and
especially into the evening hours. This is due to a shortwave
aloft currently located over Ohio which translate east this
afternoon, ultimately crossing through our area tonight. With
the weak but stalled surface boundary still draped over the
area, isolated showers and thunderstorms are expected to develop
early this afternoon, but shouldn`t be anything more than the
usual garden variety as shear is weak initially.

Once better forcing from the shortwave trough arrives late this
afternoon into this evening, should begin to see an overall
increase in coverage and some stronger and heavier convection
move in from the west. Basis latest 00Z HREF guidance and CAMs,
it doesn`t appear that the heavier convection will reach our
area until after 6 PM, which means this is looking more like an
evening/overnight event for our area. WPC has expanded the
SLIGHT risk for excessive rainfall further south and east, now
encompassing all of our PA counties, northern and western NJ and
the northern Delmarva. However, due to hi-res guidance
struggling with the depiction and placement of where convection
will be this evening, have not made any changes to the Flood
Watch this morning - where the watch over northern NJ remains in
effect due to extremely low FFG values due to recent heavy
rainfall. Upon collaboration with neighboring offices, have
opted to reconvene later today to issue more targeted Flood
Watches elsewhere. SPC has also expanded the MARGINAL risk for
severe weather a bit south and east, basically north and west of
the I-95 corridor. The overall severe threat doesn`t look all
that promising however, as most of the convection shouldn`t
reach our area until late in the day limiting the potential to
tap into the max period of diurnal heating. Regardless, the
primary threat will be for isolated damaging wind gusts
associated with moisture loaded downdrafts. Convection should
continue through the overnight hours, before waning in the pre-
dawn hours on Thursday morning.

In terms of temperatures, highs are anticipated to be in the
upper 80s to low 90s. Heat indicies should reach well into the
mid to upper 90s (perhaps topping 100 degrees in some spots).
Largely, should fall just shy of needing heat advisories though,
due to increasing clouds this afternoon keeping temperatures at
bay. Lows tonight will remain mild in the 70s; 60s in the
Poconos.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Heat and humidity for the week will peak on Thursday, along
with continued unsettled weather including daily chances of
showers and thunderstorms through Friday.

Subtropical ridging will remain to our southwest through the
end of the week and into the weekend with a quasi zonal jet
streak just to our north. Broad troughing will approach on
Thursday then pass offshore on Friday, pushing a weak cold
frontal boundary into our area late Thursday night into early
Friday. Some weak surface high pressure and subsidence with
slightly cooler, but noticeably drier air arriving in its wake
by Friday night into Saturday.

Southwest return flow will strengthen Thursday ahead of the
frontal boundary, which will help push temperatures and
dewpoints up a few degrees from earlier in the week. Forecast
high temperatures are in the upper 80s to mid 90s across much of
the area. The kicker will be the mid to upper 70s dewpoints,
which will make for oppressively hot and humid conditions with
heat indices near 100-105 across much of the area outside the
higher elevations northwest. Even the immediate coast and
beaches will not be immune from the oppressive humidity. Ocean
water temperatures are in the mid 70s to near 80 degrees. While
temperatures may be a few degrees cooler at the coast, dewpoints
will be higher resulting in heat indices in the 100-105 degree
range, especially earlier in the day before the sea breeze gets
stronger. A Heat Advisory was issued for the entire forecast
areas, except for Carbon and Monroe Counties where heat indices
should remain in the mid 80s to mid 90s at most.

The environmental setup Thursday should focus convection near
and northwest of I-95, where lee side surface troughing and
terrain will act as forcing for convection ahead of the front.
Drier mid level air, steep low level lapse rates, and more
modest deep layer shear values should result in a greater severe
thunderstorm threat for Thursday than earlier in the week.
PWats will remain high as well (on the order of 2"), so locally
heavy rainfall will remain a possibility, but storms should be
much more progressive, resulting in a lower threat of flash
flooding. It should be noted that there is a great deal of
uncertainty regarding timing and coverage of convection on
Thursday. Tonight`s activity could linger into Thursday morning,
which would limit any convection until much later in the day or
into the evening.

The weak cold front should push into the area overnight
Thursday night into early Friday morning. This will result in a
much lower chance of convection on Friday, with only 20-30% PoPs
for areas near and west/south of the Philly metro. Any activity
should be quite isolated in nature, and should not have any
notable severe or flash flood threats. Temperatures and
especially dewpoints/humidity will be on the decline for Friday,
with dewpoints finally dropping into the 60s for northern
areas. Highs mainly in the 80s to perhaps near 90 degrees near
the coast. Friday night will be quite pleasant by mid July
standards, with dewpoints continuing to fall under a light
northerly breeze. Dewpoints in the mid 50s are forecast
northwest of I-95! Lows in the 60s to near 70 degrees at the
coast and Delmarva as the frontal stalls out across southern
Delaware.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Heading into the weekend, Saturday should be a nice summer day
with the drier airmass lingering. Highs in the mid 80s and 60s
dewpoints. The stalled frontal boundary near Chesapeake Bay will
yield potential for some isolated to scattered showers and
storms, but nothing significant is expected at the moment.
Chances for convection and humidity should increase again for
Sunday as the boundary starts lifting north with return flow and
another weak cold front approaches. Much greater uncertainty
with the forecast heading into early next week, but temperatures
near normal and modest humidity levels can be anticipated along
with chances for diurnally driven convection.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Primarily VFR expected outside of lingering low clouds
early. Scattered Showers and isolated thunderstorms expected to
develop in the afternoon, so have maintained VCSH at all
terminals. South-southwest winds around 5-10 kt with occasional
gusts up to 15 kt. Moderate confidence.

Tonight...Primarily VFR expected. Scattered showers and
thunderstorms become more widespread into the evening hours, so
have included PROB30 groups at all terminals between 00Z-06Z
from west to east. Localized sub-VFR conditions possible in
heavy showers/storms. South-southwest winds around 5 kt or less.
Low confidence.

Outlook...

Thursday...Primarily VFR, though MVFR/IFR conditions possible
(20-40%) as some showers and thunderstorms develop in the
afternoon, with the highest probability for restrictions coming
for KABE/KRDG.

Thursday Night...VFR. No significant weather.

Friday...Primarily VFR, though restrictions possible (15-30%)
with scattered showers and thunderstorms around in the
afternoon.

Friday Night...VFR. No significant weather.

Saturday through Saturday Night...Primarily VFR. Isolated
showers around in the afternoon and early evening.

Sunday...Primarily VFR but restrictions possible (50-70%) with
showers and thunderstorms developing in the afternoon.

&&

.MARINE...
No marine headlines are in effect through tonight. South-
southwest winds around 5-10 kt and seas around 2 feet this
morning. Winds increase to around 10-20 kt this afternoon and
evening with building seas of 3-4 feet. Scattered showers and
thunderstorms possible this afternoon into tonight, which may
cause locally gusty winds in excess of 34 kt.

Outlook...

Thursday...Sub-SCA conditions expected, though cannot rule out
a few gusts near 25 kt. 15% chance an SCA is needed. Seas 2 to 4
feet. 20% chance of a thunderstorm late.

Friday through Sunday...No marine headlines expected. Periods
of showers and thunderstorms possible, mainly in the afternoon
and evening most days.

Rip Currents...

For today, south-southwest winds around 5-10 mph with breaking
waves around 1-2 feet and a southerly swell around 7-8 seconds.
As a result, have maintained a LOW risk for the development of
dangerous rip currents all beaches.

For Thursday, southwest winds increase to 10-20 mph with
breaking waves around 1-3 feet and a building southerly 3-4 foot
swell around 7 seconds. As a result, have upgraded Cape May and
Atlantic County beaches to MODERATE due to more perpendicular
swell and have maintained a LOW risk for rip currents for the
remainder of the Jersey Shore and Delaware Beaches.

Rip currents occur often in the vicinities of jetties and piers
and the speed of the currents are generally maximized at low
tides.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM to 8 PM EDT Thursday for PAZ060>062-
     070-071-101>106.
NJ...Heat Advisory from 10 AM to 8 PM EDT Thursday for NJZ001-
     007>010-012>027.
     Flood Watch from 3 PM EDT this afternoon through late tonight
     for NJZ001-007>010-012-015.
DE...Heat Advisory from 10 AM to 8 PM EDT Thursday for DEZ001>004.
MD...Heat Advisory from 10 AM to 8 PM EDT Thursday for MDZ012-015-
     019-020.
MARINE...None.

&&

$$

SYNOPSIS...Staarmann
NEAR TERM...DeSilva
SHORT TERM...Staarmann
LONG TERM...Staarmann
AVIATION...DeSilva/Hoeflich/Staarmann
MARINE...DeSilva/Hoeflich/Staarmann