Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

670
FXUS61 KPHI 250758
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
358 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 compared to Thursday, especially into the afternoon.
Forecast high temperatures 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 0.25-0.5" 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 0.1-0.25",
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 /08Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...VFR. South to southwest winds 5 kts or less. High
confidence.

Today...VFR with ceilings increasing in coverage and lowering.
Southerly winds increasing to 10-12 kts, with gusts near 18-20 kts
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 kts
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 kts with
gusts up to 25 kts. 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 kts with gusts up to 25 kts possible at times
across the Atlantic coastal waters and seas building 4-6 feet. For
Delaware Bay, nearshore gusts near 25 kts 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...Staarmann
SHORT TERM...Deal
LONG TERM...Deal
AVIATION...Deal/Staarmann
MARINE...Deal/Staarmann
FIRE WEATHER...NWS PHI