Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

500
FXUS61 KPHI 251408
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1008 AM EDT Fri Apr 25 2025

.SYNOPSIS...
A warm front will lift north across the Mid Atlantic this
evening followed by a cold front on Saturday. High pressure will
build in behind the low pressure system for Sunday and then
persist through much of next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Another warm, dry, and somewhat breezy day expected to close
out the week. A round of showers and storms is expected to pass
through the region overnight into Saturday morning, with
scattered showers and storms lingering through Saturday
afternoon ahead of a cold front.

Quasi zonal flow today will give way to an approaching
shortwave trough associated with upstream convection across the
Ohio Valley this afternoon. The shortwave will pass through
overnight, then a sharper trough axis will approach the area by
Saturday afternoon. At the surface, high pressure will remain
offshore through Saturday. A developing surface low will pass
from the southeastern Great Lakes tonight eastward into New
England by Saturday. An associated cold front will then push
into the local area by Saturday afternoon.

The high pressure retreating offshore, modest southerly flow
will result in another warm and dry day. Clouds will be
increasing in coverage, especially into the afternoon. Forecast
highs are mostly in the mid 70s to near 80 degrees (60s near
the coast). Southerly winds will increase by this afternoon to
around 10-15 mph, with some gusts near 20-25 mph at times.

Convective remnants from the Ohio Valley will approach the
region this evening and pass through overnight (after 10 PM or
so). This activity should be benign in nature. Some brief heavy
downpours possible along with some rumbles of thunder and
perhaps some locally gusty winds. Latest guidance has locked
onto the idea that the greatest coverage of activity overnight
will be focused mainly near and especially northwest of I-95,
although some scattered showers are certainly possible farther
southeast toward the coast. Highest PoPs are thus northwest of
I-95, gradually lessening toward the coast. This activity should
be moving out of the region by daybreak Saturday, though some
showers could linger through mid-morning or so. Generally
0.25-0.50" of rain is expected, though some areas could receive
locally more or less depending on the exact evolution of the
precip. The coastal plain will be looking at more like
0.10-0.25", and some areas northwest of I-95 could approach 1"
of rain.

Following the early morning activity departing, winds shift
southwest and increase ahead of the approaching cold front. With
skies breaking up some, we should destabilize a good bit into
the early afternoon. Anticipating some scattered showers and
storms to develop out ahead of and along the front. This
convection could morph into a broken line of sorts as it pushes
southeast across the coastal plain. Areas near and southeast of
I-95 have the highest PoPs in the afternoon. The afternoon
convection could be strong, though the severe threat appears to
be low. Instability should be less than 1,000 J/kg, though we`ll
have plenty of forcing. The limiting factor could be the mid
level dry air that it will have to overcome. Gusty winds, brief
heavy downpours, and small hail is possible though.

Aside form the afternoon convection, temperatures are forecast
to rise into the 70s ahead of the front. Southwest winds
increasing to 10-20 mph, with gusts up to 30 mph possible.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Lingering showers associated with the passage of a cold front
will be coming in an end through the overnight Saturday. The
upper level closed low will be tracking into New England through
the overnight as dry air pushes in to the Mid Atlantic. There
is strong PVA and so the synoptic lift earlier Sunday morning
may lead to a stray shower over the Poconos however most of the
area should remain dry Sunday.

Surface cold air advection on northwest flow will see temps
struggling to warm into the low to mid 60s. Broad subsidence
will then setup with building heights with high pressure setting
up. High pressure will then continue to build through Monday
with sunny skies and temps warming in the 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
High pressure continues to build through the middle of the week
ahead of the next system which consensus of the ensemble
guidance suggests will occur during the middle of next week. The
biggest item of note, is the persistence of forecast temps
warming into the low to mid 80s for Tuesday and Wednesday. While
the guidance has come down from its earlier peak towards the
mid to upper 80`s, there still is a 30-40% chance of seeing
temps above 85 for southern NJ and DelMarVa on Wednesday based
on NBM probs.

The frontal system then moves through and that will see a
return of more near normal temps for the end of the week.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR with ceilings increasing in coverage and lowering
after 18Z. Southerly winds increasing to 10-12 kt, with gusts
near 18-20 kt possible at times after 18Z. High confidence.

Tonight...MVFR ceilings likely developing, with potential for
IFR ceilings by 06Z. Scattered showers expected to develop
between 03-06Z. Heavier and more persistent showers likely at
RDG/ABE, including potential for visibility restrictions and
thunder as well. Thunder is possible (20% chance) at all
terminals, but confidence and coverage is too low to include a
TAF mention for now. Southerly winds remaining near 10 kts, with
some occasional gusts near 20 kt possible. LLWS for the I-95
terminals and south/east. High confidence in restrictions
developing by 06Z, but low confidence on timing details.

Outlook...

Saturday...MVFR to IFR restrictions lifting and scattering out
to VFR between 15-18Z. Scattered showers and thunderstorms
expected much of the day, with brief restrictions possible
associated with this activity. Southwest winds 10-15 kt with
gusts up to 25 kt. Winds shifting west or northwest after 18Z.

Sunday through Tuesday...VFR. Gusty NW winds likely on Sunday.

&&

.MARINE...
No marine hazards expected through today.

Southerly winds and seas will build after midnight tonight into
Saturday. Winds 15-20 kt with gusts up to 25 kt possible at
times across the Atlantic coastal waters and seas building 4-6
feet. For Delaware Bay, nearshore gusts near 25 kt possible on
Saturday. A Small Craft Advisory has been issued for these
periods, which extends through Sunday.

With dewpoints rising several degrees over the current water
temperatures, some areas of fog may develop tonight through
Saturday morning in addition to low clouds. Scattered showers
and thunderstorms expected from late tonight through Saturday
afternoon.

Outlook...

Saturday night through Sunday...SCA conditions as seas build to
5 feet. A period of 25 to 30 kt gusts possible Saturday night
and Sunday morning.

Monday through Tuesday...Sub-SCA conditions.

&&

.FIRE WEATHER...
Similar conditions are expected today compared to Thursday. The
lowest relative humidity values are expected across eastern
Pennsylvania and inland portions of New Jersey. In these areas,
minimum relative humidity values will be near 25-35%. Relative
humidity for Delaware, Maryland, as well as coastal portions of
New Jersey will likely see values in the 35-45% or greater
range. Based on coordination with our forest fire partners, a
Special Weather Statement is in effect through 7 PM for portions
of New Jersey and Pennsylvania for the increased danger of fire
spread.

Showers will impact the area tonight through Saturday evening.
Overall, between 1/4 and 1/2 inch of rain will fall across most
of the area, though up to an inch of rain is possible in the
southern Poconos and far northwest New Jersey, and 1/10 inch or
so is possible in Delmarva.

On Sunday, northwest winds will increase to 15 to 20 mph with
30 to 35 mph gusts possible. In addition, Min RH values on
Sunday will be 30 to 35 percent.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM Saturday to 6 PM EDT Sunday for
     ANZ430-431.
     Small Craft Advisory from midnight tonight to 6 PM EDT Sunday
     for ANZ450>455.

&&

$$

SYNOPSIS...Deal
NEAR TERM...DeSilva/Staarmann
SHORT TERM...Deal
LONG TERM...Deal
AVIATION...Deal/DeSilva/Staarmann
MARINE...Deal/DeSilva/Staarmann
FIRE WEATHER...PHI