Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

611
FXUS61 KPHI 230555
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1255 AM EST Tue Dec 23 2025

.SYNOPSIS...
High pressure will move offshore tonight, then a clipper system
will impact the region early Tuesday with a warm front lifting
north. A cold front will push offshore Tuesday night, followed
by weak high pressure building on Wednesday. Another weak
clipper may impact the area with light precipitation on
Christmas Day, then a stronger system looks to impact the region
on Friday. Unsettled weather may persist into the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
1 AM Update: The Winter Weather Advisory was expanded to include
Morris, Warren, Northampton, and Lehigh Counties based on the
latest guidance and trends. These areas have a decent chance of
experiencing a light glaze from light freezing rain or freezing
drizzle before precip ends around midday, in addition to seeing
1-3 inches of snow. Details below...

Current analysis places cold high pressure just south of our
region over the southern Chesapeake and Delmarva. Meanwhile, a
clipper system is pushing southeast across the Canadian
prairies, heading towards the Great Lakes tonight and towards
Montreal on Tuesday. While the tap isn`t great, there is just
enough of a feed off the Gulf ahead of the system to bring our
region a bit of wintry weather as it passes.

For this evening, clouds will increase, but temps should manage
to drop below freezing beforehand in just about the whole
region, save possibly the immediate coast and warmest urban
centers. Clouds should prevent temps from dropping much below
freezing, with most areas ending up in the mid-upper 20s,
possibly even starting to rebound overnight as the clouds
thicken and wind starts shifting more southerly. However, warm
advection aloft will beat the surface warming for much of the
region, resulting in the outbreak of precipitation across
northern and central areas before dawn and across the south
after daybreak. For northern areas, this will be mostly a wintry
system, with snow late tonight and tomorrow morning
transitioning to either a little freezing rain/drizzle or just
ending as mist towards midday/early afternoon. Further south,
from Philly southward, any snow early likely shifts to rain
before ending. With more marginal temps and a briefer period of
snow, accumulations near and south of Philly should be minimal
if any. However, near and especially north of I-78, an inch or
two of snow is more likely, with up to 3 or even perhaps 4
inches north of I-80. Areas north of I-80 also have a better
shot of getting that little glaze of ice at the end. Based on
this, have opted to issue winter weather advisories mainly near
and north of I-80 for tonight/Tuesday. The trend has been a
little wetter/snowier today, so if future guidance continues the
trend, its possible this may need a last-minute extension
further south, particularly for Morris County, but not feeling
the confidence here just yet. In any case, anyone planning to
commute or otherwise travel Tuesday morning near and especially
north of Philly should be prepared for slippery travel, and
delay until afternoon if possible. Temps will try to warm after
precip tapers off during the afternoon, with temps pushing into
the low 40s near Philly, but may struggle to reach freezing in
the Poconos. By contrast, southern Delaware may top 50.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
In the wake of our system, we trend drier Tuesday night. A cold
front will move offshore early which will usher in colder air
as our winds turn more out of the west to northwest. Winds will
increase Tuesday night with gusts for most between 20-30 mph and
upwards of 40 mph in the Poconos. Low temperatures are mostly
in the mid to upper 30s south of I-78, and close to 30 degrees
north of there. So any icy roads from refreezing snow melt
should be confined to untreated roads north of I-78.

A weak high pressure system will build into the area from the
Great Lakes region Christmas Eve and center itself over the area
Christmas Eve night into Christmas morning. We look to stay out
of the strong cold air advection this time around, so
temperatures should remain close to normal for late December.
However, it`ll be a bit breezy during the day with NW winds
gusting 25-30 mph for many with upwards of around 40 mph for the
Poconos. These winds become light to calm overnight as the high
pressure system moves overhead. High temperatures will be
mainly in the 40s on Christmas Eve, and lows mainly in the mid
20s to mid 30s for Santa during Christmas Eve night. A mostly
sunny sky for Christmas Eve, then increasing clouds overnight.

Christmas Day should be a decent day overall with no
significant weather, but a weak clipper system passing through
could bring some brief light rain or sprinkles (flurries
possible up north) in the morning. PoPs remain around 20-30%.
Otherwise, it`ll be mostly cloudy to overcast with seasonable
temperatures (highs in the upper 30s and 40s). Christmas night
will remain cloudy with lows mainly in the upper 20s to upper
30s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Beyond Christmas Day, forecast uncertainty becomes very high.
Guidance indicates there will be a high over eastern or
southeastern Canada with low pressure moving eastward across the
Great Lakes and toward the Northeast or Mid Atlantic. This
setup will likely bring widespread precipitation to our area.
The more recent trends over the last few runs from guidance has
resulted in significant changes to the forecast. The main reason
is a much stronger high that suppresses a weaker low. This
trend keeps much of our area in a setup for colder air to remain
in place thanks to the stronger high to the north. A more
suppressed and southern track of this low keeps widespread
precipitation for the area but also prevents a lot of the warm
air advection from getting into the region. The updated forecast
now has highs on Friday in the mid to upper 30s for the I- 95
corridor and west with mid to upper 20s in the Poconos. Areas
south and east of the I-95 corridor have highs in the low to mid
40s. Wintry precipitation is now the result for much of the
area for at least part of the timeframe from daybreak Friday
into Saturday. Mixed precipitation may make it as far south as
parts of Delmarva. Warm air looks to gradually filter in through
this event which would cause a changeover to rain. Right now,
the best potential for this to be a mainly rain event looks to
be in parts of Delmarva and southern New Jersey.

There is a large amount of uncertainty with the forecast for
Friday into Saturday and trends will need to be monitored.
Uncertainty remains through the weekend but there are
indications that the forecast stays unsettled.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR initially, then ceilings lower toward MVFR after
09Z in SN at KRDG/KABE. Restrictions and precip likely hold off
until after 12Z at KTTN/KPNE/KPHL/KILG. Conditions should
remain VFR at KMIV/KACY. Light winds favoring a southerly
direction. Low confidence in timing of restrictions and
precipitation.

Tuesday...MVFR/IFR in SN at KRDG/KABE/KTTN through most of the
morning, and SN becoming RASN, then RA in the afternoon. For
KPNE/KPHL/KILG, the transition to RASN then RA will be several
hours earlier. For KMIV/KACY, all RA. Conditions should lift to
MVFR or even VFR prior to 00Z. Light S winds, becoming SW late.
Low confidence in timing details of restrictions, but high
confidence in at least MVFR conditions much of the day between
15-21Z at most sites.

Outlook...

Tuesday night through Wednesday night...VFR. Gusty NW winds
Wednesday.

Thursday through Saturday...Restrictions likely in low clouds
and potential for rain/snow. Gusty winds possible. Very low
confidence forecast for Friday into Saturday.

&&

.MARINE...
Sub-Small Craft Advisory through tonight, but south to
southwest winds expected to reach marginal SCA levels over the
ocean zones on Tuesday. Thus, issued for those zones only.

Outlook...

Tuesday night through Wednesday...Small Craft Advisory
conditions look probable with wind gusts increasing to 25-30 kts
with seas near 3-5 feet possible.

Thursday...No marine hazards expected. A chance of light rain
or sprinkles.

Friday through Saturday...Small Craft Advisory conditions
probable. Precipitation likely restricting visibility.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 4 PM EST this afternoon for
     PAZ054-055.
     Winter Weather Advisory until 1 PM EST this afternoon for
     PAZ061-062.
NJ...Winter Weather Advisory until 4 PM EST this afternoon for
     NJZ001-007-008.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM this morning to 6 PM EST this
     evening for ANZ450>455.

&&

$$

SYNOPSIS...Guzzo/Staarmann
NEAR TERM...RCM/Staarmann
SHORT TERM...Guzzo/Staarmann
LONG TERM...Guzzo
AVIATION...Guzzo/MPS/RCM/Staarmann
MARINE...Guzzo/RCM