Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

281
FXUS61 KPHI 030110
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
910 PM EDT Wed Apr 2 2025

.SYNOPSIS...
High pressure over eastern Canada moves out to sea tonight.
Meanwhile, strong low pressure over the Midwest lifts into the
Great Lakes, and a warm front extending out from that low lifts
north through the region tonight through Thursday morning. A
cold front passes through Thursday night and then gets hung up
over the area through the weekend. This front will oscillate
back and forth as several waves of low pressure pass through the
region. A stronger cold front passes through Sunday night,
followed by another cold front Monday night. High pressure
returns for the rest of next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
Into the overnight, temps will remain on the mild side thanks
to the abundance of cloud cover and the warm front that will
surge northward after midnight. This will cause an increase in
overall warm air and moisture advection, so lows in the 40s
should occur mostly before or around midnight. We`ll likely see
a lull in activity once this initial round moves out before
midnight ahead of a second round of shower activity approaches
late tonight into early Thursday morning. This second round will
be in association with a remnant/decaying MCS tracking out of
the Tennessee/Ohio Valley overnight. Fortunately, this MCS
should be weakening as it approaches Thursday morning, so not
expecting anything severe, however rumbles of thunder and heavy
downpours may be possible.

For Thursday, an area of low pressure will track up into Quebec
as a frontal boundary trails back to the southwest. With the
warm front lifting up well into interior New England, our entire
area will be settled well into the warm sector. Despite mostly
cloudy to overcast skies, high temps will be mild in the upper
60s to upper 70s with a few spots approaching 80 degrees across
the Delmarva. We`ll also have a very moist airmass in place,
with dew points rising into the low to mid 60s, so it`ll feel a
bit more like early summer than early spring. With the front
approaching from the west in the afternoon (and into Thursday
night) and the moist airmass in place, there is expected to be
at least some shower/storm activity around in the afternoon.
Best chances appear to be south of the I-78 corridor where there
is more moisture available to tap into. In fact, a few of these
storms may be strong to borderline severe, however there is
quite a bit of uncertainty even now, as it is one of those low
CAPE/high shear environments with limited to no sunshine. This
lies with the general thinking by the Storm Prediction Center
which has the majority of our forecast area in a MARGINAL Risk
(Level 1/5) for severe weather on Thursday with only the western
most portion of Berks County in a SLIGHT Risk (Level 2/5).
Damaging wind gusts will be the main threat, but with the
abundance of shear, an isolated tornado threat cannot be ruled
out.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
The cold front works its way through the region Thursday night
through Friday morning. Weak low pressure passes through the
region along that front and departs by midday Friday. Showers
and scattered thunderstorms develop Thursday evening and become
more widespread through the overnight hours, ending Friday
morning. With dew points in the 60s, there will be abundant low
level moisture over the area for locally heavy rain to develop.
There is a lack of forcing and instability due to lack of
daytime heating since it will be at night, so the severe threat
will be minimal. But there still could be some thunderstorms.
SPC has a Marginal Risk (1 out of 5) for severe weather during
this time.

Conditions dry out Friday afternoon and a cooler and drier air
mass builds down into the region. Surface dew points drop into
the 40s and 50s Friday afternoon and night. Highs will generally
be in the low to mid 60s, though it will be warmer in Delmarva,
as it should be south of the cold front.

Low pressure approaches from the west and passes north of New
York State Friday night through Saturday. This will pull the
frontal boundary back north as a warm front. Another round of
showers will develop Friday night and continue into Saturday
morning. Onshore flow will keep the area cloudy. Uncertain as to
how far north the warm front will get, so it will be uncertain
as to how warm the entire area will get. Based on latest
guidance, it should get into the 70s in Delmarva, in the low to
mid 60s south of the I-195 corridor, and in the mid and upper
50s in the southern Poconos, northern New Jersey, and the Lehigh
Valley. Though those temperatures will be highly dependent on
how far north the front gets.

Another low pressure system approaches from the west, and
another round of showers is possible A few showers or an
isolated thunderstorm will be possible early this evening in
association with the thunderstorm activity currently over
western PA that will track toward the northern third of our
area.late Saturday afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Unsettled conditions on tap through the weekend as a frontal
boundary will remain over the area and several waves of low
pressure will ride along this boundary.

As one wave of low pressure passes north of the region Saturday
night, it will pull a warm front through the Northeast and Mid-
Atlantic. The region will then be in the warm sector on Sunday.
Rain lifts from south to north and tapers off late Saturday
night, and then patchy fog develops late Saturday night as
southerly winds usher low level moisture in to the region and
surface dew points rise well into the 50s. Quite warm and humid
for the start of April on Sunday with highs well in the 70s and
even low 80s in Delmarva with dew points in the 50s and low 60s.

A deep upper trough will dig through the central U.S. and low
pressure will develop at the base of the trough over the
Southeast and Mid-Atlantic, and this low lifts north through the
region Sunday night. As it departs, the front over the area
will move through as a cold front late Sunday night through
Monday morning. Showers and isolated thunderstorms develop
Sunday afternoon and persist through the night, tapering off
from west to east Monday morning. Based on the setup, which
includes an airmass with 60 or so degree dew points ahead of the
front and 30 to 40 degree dew points behind it, there is the
potential for severe weather, but there will be a lack of
heating with the frontal passage occurring at night, so
instability may be limited.

Turning much cooler and dryer on Monday. Another cold front
passes through Monday night through Tuesday morning, resulting
in a reinforcing shot of colder and drier air into the region
for Tuesday and Wednesday. There may even be some rain and/or
snow showers with the passage of this front on Tuesday. High
pressure builds in from the west for the mid-week period.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR conditions early. Ceilings lower to MVFR between
03-06Z at all terminals. IFR ceilings probable after 09Z.
Southeast wind becoming south-southwest around 10 kt. LLWS
possible at all terminals after 06Z. High confidence in the
development of MVFR ceilings and winds overnight. Moderate
confidence otherwise.

Thursday...IFR conditions through 16-18Z with scattered light
showers and patchy fog expected. A gradual lift to MVFR during
the afternoon. Isolated to scattered thunderstorms possible in
the afternoon and evening. Southwest wind generally 10-15 kt
with gusts up to 25-30 kt. Moderate confidence.

Outlook...

Thursday night...Sub-VFR in SHRA and scattered TSRA.

Friday through Friday night...Improving conditions in the
morning, then sub-VFR in SHRA in the afternoon and at night.

Saturday through Saturday night...Sub-VFR conditions early,
then VFR for the middle of the day. RA develops in the afternoon
and evening with sub-VFR conditions. Sub-VFR in patchy fog and
low clouds Saturday night.

Sunday through Sunday night...Improving conditions from late
morning through the afternoon, then sub-VFR in SHRA and isolated
TSRA Sunday afternoon and night.

Monday...Sub-VFR in SHRA Monday morning, then VFR.

&&

.MARINE...
A Small Craft Advisory will be in effect beginning tonight for
the Atlantic coastal waters, with the Delaware Bay beginning
early Thursday morning. Southeast winds will become south winds
around 20-25 kt with gusts up to 25-30 kt through the day on
Thursday. Seas will also build to 5-7 feet. Fair weather
expected tonight with a chance for showers and thunderstorms on
Thursday. Dense marine fog is also possible beginning on
Thursday too.

Outlook...

Thursday night...SCA conditions continue on the ocean waters.
Winds will gust to 25 kt until midnight or so, and seas will
subside from 5 to 7 feet to 3 to 5 feet. VSBY restrictions in
showers and isolated thunderstorms.

Friday through Friday night...Sub-SCA conditions. Lingering
showers and thunderstorms in the morning, then another round of
showers possible Friday night.

Saturday through Saturday night...Generally sub-SCA conditions,
though seas may build to 5 feet late Saturday night. VSBY
restrictions in rain and fog in the morning, then again in the
afternoon and at night.

Sunday through Sunday night...SCA conditions possible for wind
gusts up to 25 kt and seas building to 5 to 7 feet. VSBY
restrictions in showers and isolated thunderstorms late in the
afternoon and at night.

Monday...SCA conditions possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Thursday for ANZ430-
     431.
     Small Craft Advisory until 6 AM EDT Friday for ANZ450-451.
     Small Craft Advisory until 6 AM EDT Friday for ANZ452>455.

&&

$$

SYNOPSIS...MPS
NEAR TERM...DeSilva/Hoeflich
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...Cooper/DeSilva/MPS
MARINE...DeSilva/Hoeflich/MPS