Allentown, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

535
FXUS61 KPHI 310034
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
834 PM EDT Sun Mar 30 2025

.SYNOPSIS...
A front that has stalled across the area will lift northeast
overnight and into early Monday. Following that, a more
powerful front moves into the region from the northwest Monday
night. High pressure returns Tuesday and Wednesday before a more
active weather pattern arrives for the end of the week into
next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Showers have recently developed across the southern Poconos,
Lehigh Valley and down into the northern Philly suburbs. Most of
the showers are rather light however. Pop/Wx grids adjusted for
this. Also, more adjustments in temps and dew points with the
front still draped across the area. readings are in the upper
60s/low 70s South and mid40 to low 50s North/West. Added fog to
the higher elevations NW.


Heading into the overnight, the frontal boundary will increase
the pace at which its lifting northward. This will be aided by a
strengthening southerly pressure gradient and an approaching
shortwave trough. Temperatures will cool into the early overnight
with the loss of daytime heating. Areas that have been north of
the boundary will then see temperatures that increase for much
of the overnight hours. Further south, temperatures will become
steady later overnight as WAA and overcast skies offset any
further radiational cooling. As a result, a very mild night is
expected with low temperatures south of the front near 60
degrees, and near 50 degrees north of the front. There will be
increasing chances for showers overnight with the approaching
trough, though nothing of any significance. Southerly winds
around 10 mph overnight, with some gusts near 20-25 mph
possible, but will be somewhat limited with the WAA leading to a
low-level inversion and limited mixing.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
A strong cold front will approach the area Monday afternoon and push
through Monday night, bringing a round of strong to severe
thunderstorms. Locally damaging wind gusts will be the main severe
weather threat, but an isolated tornado or two cannot be ruled out.
Heavy rain from these storms also bring the risk of flash flooding
across the region.

An upper level trough will pivot across the Great Lakes and Mid
Atlantic Monday before pushing offshore overnight Monday into
Tuesday morning. It will push a strong cold front across much of the
East Coast, moving through the greater Delaware Valley west to east
sometime in the evening into the overnight. Ahead of this front,
skies are expected to be mostly cloudy during the day Monday, but
temperatures are still forecast to warm into the low to mid 70s. The
cloudy skies will also helping limit daytime heating and overall
instability with MUCAPE values largely less than 1000 J/kg. However,
there will be very strong dynamics and shear in place, thus much of
the region remains in the SLIGHT risk for severe weather from the
Storm Prediction Center. Deep layer shear (0-6 km) will range in the
40-50 kt range, supporting the potential for severe thunderstorms
with damaging wind gusts. It is also worth noting that the 0-1 km
shear and helicity look to be quite high, in addition to 0-3 km bulk
shear around 30-35 kts with veering hodographs. As a result, an
isolated tornado or two will be possible.

The best chance for severe thunderstorms will come during the
afternoon through early evening timeframe. Better dynamics arrive
across the region to initiate convection sometime from 3-5 PM EDT,
mainly across eastern PA and western Delmarva. A few earlier showers
and perhaps an isolated thunderstorm may arrive in the morning/early
afternoon, but more zonal flow aloft supports drier conditions that
early in the day. As convection initiates, some thunderstorms could
start off more discrete in nature, maximizing any severe potential
there may be. These more discrete cells are expected to become more
numerous through the late afternoon and early evening before
coalescing into a more linear structure after sunset. Once this
occurs, the threat of flash flooding will begin to increase.

The heavy rain and flash flooding threat will be highest through the
mid to late evening into the early overnight hours as storms tend to
grow upscale and instability becomes more elevated. A strengthening
low- level jet during the evening and nighttime hours will support
PWAT values surging into the 1.5+ inch range, near the
climatological maximum for this time of year. As a result,
forecasted storm total rainfall has increased, with 0.75-2 inches
overall and highest amounts (1.5-2 inches) right over the I-95 urban
corridor. Despite our ongoing drought, there are localized flooding
concerns, especially due to potential rainfall rates causing
localized urban flooding.

The cold front will push offshore early Tuesday morning, giving way
to building high pressure for Tuesday. A surge of NW winds behind
the front can be expected after daybreak Tuesday with gusts 20-30
mph possible, before beginning to subside during the afternoon.
Increasingly sunny skies Tuesday with seasonable temperatures mainly
in the upper 40s to upper 50s for highs. A cold Canadian air mass
builds overhead for Tuesday night with reducing winds, so most areas
away from the coast and marine waters may be near or below freezing.
Depending on how it plays out, might need frost advisories or freeze
warnings for the Delmarva south of Wilmington, where the growing
season is defined to begin on April 1, though at this moment we are
still not forecasting temps to drop quite that much.

Wednesday starts with some partial sun, then clouds increase as high
pressures shifts to our northeast and onshore flow returns. Another
backdoor front looks to keep temperatures cooler with upper 40s to
low 50s from the Poconos and Lehigh Valley through north and central
New Jersey, and even down the Jersey Shore. Slightly warmer
temperatures in the mid 50s to low 60s are expected for the Philly
Metro, inland South Jersey, and the Delmarva Peninsula.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
A more active weather pattern is expected for the latter half
of the week through next weekend. An initial low looks to move
by north of the area Thursday into Thursday night. The steadiest
precip with this system should stay to the north however there
still will be at least chances for some showers first with the
system`s warm front and then with its cold front. The cold front
with the system then looks to stall near or just south of the
area Friday which will keep chances of showers in the forecast.
One or more additional waves of low pressure then look to move
through along this front next weekend keeping things generally
unsettled with chances for rain/showers. As for temperatures,
Thursday looks to be quite warm with highs mainly in the 70s. It
will then trend cooler Friday into next weekend with highs next
weekend looking to be mainly in the upper 50s to low 60s.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Limited confidence fcst with lowering CIGS/VSBYs
KTTN/KABE and possibly other sites overnight. KMIV/KACY and
other Delaware Valley sites may remain VFR until dawn when CIGs
will drop to MVFR. Showers scattered KRDG/KABE. LLWS developing
all sites overnight with SW winds 40 to 45 kts at 020.

Monday and Monday night...Sub-VFR conditions developing in the
afternoon through the overnight with a frontal passage. Heavy rain
and thunderstorms likely. Gusty winds 20-25 kts.

Outlook...

Tuesday through Wednesday...VFR. Breezy early Tuesday morning.

Wednesday night through Friday...Mainly VFR but sub-VFR
conditions possible at times with chances for rain showers.
Most likely time frame for showers is Thursday night. Gusty
winds of 20-25 knots possible daytime Thursday.

&&

.MARINE...
SCA flag added to Delaware Bay where some recent gusts at the
(elevated) Brandywine station have reached 25 kts. Low-end SCA
conditions on the waters expected to develop as strong inversion
and steady SCA/Gale force winds freshening above it. These factors
make forecasting the surface winds challenging. Low clouds and
fog possible mostly across the Northern/central NJ coastal
waters.

SCA conditions prevailing Monday through Tuesday morning. Southerly
winds ramp up to 25-30 kts ahead of a cold front into Monday with
seas building to 5-7 feet. Winds shift to northwesterly behind the
front Monday night with gusts still around 25kts and seas 5-7 feet
early Tuesday. The Small Craft Advisory continues through this
period as a result.

Outlook...

Tuesday through Wednesday...Winds and seas diminish, falling
below SCA criteria late in the day Tuesday and staying below
criteria through Wednesday.

Wednesday night through Thursday...SCA conditions possible with
wind gusts around 20-25 knots and seas of 4-6 feet.

Friday...Sub-SCA conditions expected.

&&

.TIDES/COASTAL FLOODING...
For the high tide cycle tonight, many sites along the NJ Atlantic
Coast and southern shores of the Raritan Bay are likely to get
close to or over minor flood stage as astronomical tides remain
high. The biggest concern at this point is for tidal locations
in Middlesex and Monmouth Counties which will keep an onshore flow
through the high tide cycle. A coastal flood advisory remains in
effect for those locations. Elsewhere on the Atlantic coast, Delaware
Bay, and tidal Delaware River, tide levels are forecast to be near
but just below advisory thresholds.

On the northeastern Chesapeake Bay, tidal flooding isn`t expected
due to lower astronomical tides.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 2 AM EDT Monday for NJZ012>014.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM Monday to 6 AM EDT Tuesday for
     ANZ430-431.
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ450>455.

&&

$$

SYNOPSIS...AKL/Fitzsimmons/MJL
NEAR TERM...AKL/po
SHORT TERM...Fitzsimmons/MJL
LONG TERM...AKL/Fitzsimmons/MJL
AVIATION...AKL/Guzzo/MJL/po
MARINE...AKL/MJL/po
TIDES/COASTAL FLOODING...Johnson