Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

918
FXUS61 KPHI 020110
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
910 PM EDT Tue Apr 1 2025

.SYNOPSIS...
High pressure will be in control through Wednesday. A warm front
will lift north across the area on Wednesday night as a strong low
tracks through Quebec on Thursday. The front will return on Friday
as it slowly drops south of the area by Friday night. Several waves
of low pressure will ride along this boundary causing it to fluctuate
north and south through the weekend yielding unsettled weather. High
pressure should return by early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Forecast on track. Only minor tweaks made to the grids.

Tonight, high pressure shifts east, which will lead to surface
winds becoming more northeasterly. Winds should remain elevated
enough on the outer periphery of the high around 5- 10 mph, but
the usual sheltered spots will likely go calm and radiate well
under mostly clear skies. This is noteworthy because the
Frost/Freeze program begins April 1 for our Delmarva counties.
With the dry airmass in place and a cool northeast breeze, this
should limit/prevent any frost development despite the low temps
in the mid to upper 30s. Further north, lows will be in the
upper 20s to mid 30s, but the growing season is not active yet
in these locations to warrant any freeze headlines.

For Wednesday, the high will continue to exit and shift off the
coast of New England. Should see mostly clear skies early in the
day, becoming more cloud-filled in the afternoon. Winds will become
southeasterly due to the positioning of the high, causing a more
onshore component. It will also become breezy on Wednesday with
winds increasing to 10-20 mph with gusts locally up to 30 mph. The
onshore flow will help keep a lid on temperatures across the north
and east portions of the region, with upper 40s to low 50s for areas
north of I-78 as well as the down the Jersey shore. Warmer
temperatures in the mid to upper 50s will be around for the Philly
metro, southeast Pennsylvania, inland South Jersey, and the
Delmarva. The next system will begin to approach late afternoon into
the early evening as a warm front extending from a strong low over
the Great Lakes. This warm front may bring in some warm air and
moisture advection to the region late afternoon, resulting in some
showers across the Lehigh Valley and Poconos before sunset.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Zonal flow aloft will persist through Wednesday night with upper
ridging building in for Thursday into Thursday night. At the
surface, departing high pressure will give way to a warm front that
lifts north across the area on Wednesday night before stalling
across New England on Thursday. Associated low pressure tracks up
through Quebec on Thursday as the "stalled" boundary begins to
slowly drop back south through the day on Friday.

For Wednesday night, the warm front eastward from the strong area of
low pressure tracking into the Great Lakes will surge northward
across our area on Wednesday night. This will result in a ramp up in
warm air and moisture advection. Still anticipate to see a few
isolated to scattered showers associated with the front, along with
some patchy fog especially north of the I-78 corridor. Overall any
QPF should be light. Lows will be in the upper 30s to upper 40s.

For Thursday and into Thursday night, the entire area will be within
the warm sector so expecting a mild day across the region with highs
in the upper 60s to upper 70s, with locales in the Delmarva pushing
80 degrees despite mostly cloudy skies. Some upper level energy will
be around as well as the stalled boundary across New England begins
to drop back to the south crossing back across our region on
Thursday night. As it does so, should see some showers and
thunderstorms develop in the late afternoon and evening hours. A few
of these storms could become severe as low level shear is quite high
and some forecast soundings depict a narrow corridor of instability
available to tap into. However, there remains a ton of variability
amongst guidance so the extent of the severe weather threat is
uncertain. This is 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 into
Thursday night. More details to come over the next few days.

For Friday, the boundary will be draped over the area in the morning
but should continue to drop south of the area through the afternoon.
Any shower activity should remained mostly confined to the Delmarva
region so have kept the mention of showers and thunderstorms there,
with drying conditions filtering in elsewhere north of the boundary.
Highs will vary from the low 60s north to mid 70s south.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The boundary that pushed south of the area on Friday will generally
remain south of the area through Saturday. However, several
disturbances will be riding along this boundary which will cause the
boundary to fluctuate north and south through the weekend. With this
in mind, there will be several rounds of showers around this
weekend. The first round appears to occur during the day on Saturday
where temperatures will be in the upper 40s to the north and mid 60s
to the south. A second round then looks to occur late Sunday into
Sunday night as the boundary lifts back north of the area where
temps on Sunday will be back in the 60s and 70s. Long story short,
the weekend period will present a period of relatively low
predictability but unsettled weather conditions. Should begin to see
rapid improvement by early next week as a cold front is on pace to
track across the region late Sunday night into Monday which will
shunt all precipitation east. High pressure will build back in from
the west and is expected to remain through Tuesday.

In terms of temperatures for next week, the pattern will support a
prolonged period of below normal temperatures. The Climate
Prediction Center projects a ~70% chance of below normal
temperatures for much of next week. This will present potential for
frost and freeze hazards across portions of the area, as the
Frost/Freeze program will begin on April 11th for areas south of I-
78 into PA and NJ. It begins today (April 1st) for Delmarva.

&&

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

Tonight..Remaining VFR with winds shifting to east/northeast
and diminishing to around 5 knots. High confidence.

Wednesday...VFR. Winds shift southeast 10-15 kts with gusts up to 20-
25 kts. High confidence.

Outlook...

Wednesday night through Thursday night...VFR early, with sub-VFR
conditions becoming more common by Thursday into Thursday night. A
chance for rain showers and fog on Wednesday night with showers and
thunderstorms possible on Thursday into Thursday night. Gusty winds
up to 25-30 kt possible on Thursday.

Friday through Friday night...Mainly VFR expected. A slight chance
for rain showers.

Saturday through Sunday...Sub-VFR conditions probable with rain
showers becoming more likely on Saturday and Sunday.

&&

.MARINE...
The Small Craft Advisory has been allowed to expire, with no
marine headlines on the waters through Wednesday. Winds turn NE
early tonight, before shifting SE by midday tomorrow, with gusts
up to 20 kt possible. Seas 3 to 4 feet.

Outlook...

Wednesday Night through Thursday...A Small Craft Advisory is in
effect for all ocean zones as seas build to around 5 feet with
wind gusts increasing to 25-30 kt out of the south. Winds will
be lesser on Delaware Bay, where no marine headlines are in
place.

Thursday Night...SCA conditions may linger into part of Thursday
Night, mainly with 5 foot seas. Some showers/thunderstorms
possible.

Friday through Saturday...No marine headlines expected. Rain
showers possible.

Saturday night through Sunday...SCA conditions possible mainly due
to seas building to 5-7 feet. Rain showers possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 8 PM Wednesday to 6 PM EDT Thursday
     for ANZ450-451.
     Small Craft Advisory from midnight Wednesday night to 6 PM EDT
     Thursday for ANZ452-453.
     Small Craft Advisory from 4 AM to 6 PM EDT Thursday for ANZ454-
     455.

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...Hoeflich/MJL
SHORT TERM...DeSilva
LONG TERM...DeSilva/Staarmann
AVIATION...DeSilva/Hoeflich/MJL
MARINE...DeSilva/Hoeflich/MJL