Tredyffrin, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

918
FXUS61 KPHI 221151
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
651 AM EST Sun Dec 22 2024

.SYNOPSIS...
Arctic high pressure centered over central Canada and the Great
Lakes will build east today until it is over New York State and
the Northeast tonight into Monday morning. This high departs
Monday night, and then weak low pressure passes through the
region on Christmas Eve. High pressure returns to close out the
week. A new system could approach by next Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
An arctic airmass in place through tonight will yield frigid
and very dry conditions.

Arctic high pressure across the eastern Great Lakes this
morning will shift gradually southeastward toward our region
today and into tonight. The attendant airmass will continue
advecting into the area through tonight as well. Today and
tonight will be the coldest period of this arctic outbreak with
temperatures ranging from 15-20 degrees below normal.

Following a cold start this morning with temperatures in the
10s (and some single digits north of I-78), temperatures will be
slow to climb to their afternoon highs in the 20s (10s in the
higher terrain) despite sunny skies. This will be owing to 850
mb temperatures ranging from -10C to -15C. The temperatures
today combined with a steady northwest breeze near 10-15 mph
will result in daytime wind chills only topping out in the 10s
across much of the area. Fortunately, the breeze is expected to
subside gradually into the afternoon. The Cold Weather Advisory
for the southern Poconos remains in effect for much of the
morning, with wind chills ranging from -10F to -15F.

Heading into this evening and tonight, temperatures will drop
off quickly as the surface high builds in overhead. Winds will
subside to nearly calm across much of the area, so the wind
chill will no longer be much of a factor in the very cold
conditions. While winds will be mostly calm, some moisture
(cirrus) moving in aloft could work to somewhat suppress the
otherwise ideal radiational cooling conditions. While wind chill
won`t be a factor, we`re expecting the coldest temperatures
since winter 2021-2022 across much of our area. Forecast low
temperatures by daybreak Monday morning range from near 0
degrees across the southern Poconos and northwest New Jersey, to
single digits across southeastern Pennsylvania and
central/southern New Jersey, to the low 10s in the Philly urban
corridor, Delmarva, and the immediate coast. Locally colder
temperatures are possible where ever deeper snowpack persists
following more sublimation today, including potential for
subzero minimum temperatures in the typical colder spots in
eastern Pennsylvania and northern New Jersey.

While unusually cold for this early in the season, the current
forecast high temperatures today are about 5-10 degrees shy of
record coldest high temperature values, and low temperatures for
Monday morning are about 5 degrees shy of record low values.
Most of the records were set during the December 1989 arctic
outbreak. See the Climate Section below for more details.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Arctic high pressure centered over New York State and covering
the Northeast and into the Mid-Atlantic Monday morning will
slide offshore during the day and departs Monday night. It will
remain cold with highs generally ranging from the 20s north and
west of the Fall Line to to the low to mid 30s across the
Delaware Valley, southern New Jersey, and Delmarva.

A clipper system then approaches from the west, passing through
the Great Lakes, then across northern New York State and
northern New England Monday night through Tuesday morning. Some
light snow will develop initially, but as winds shift to the
south, some warm air advection will develop, allowing for a
wintry mix of snow, sleet, and freezing rain to develop after
midnight Monday night mainly for areas south of the Fall Line.
Wintry precip looks to mix with and change to rain across
southern New Jersey and Delmarva. QPF looks to be minimal,
generally less than 0.05 inches, so any snowfall or ice
accretion will be minimal as well.

Although the surface low departs Tuesday morning, a mid-level
trough with shortwave energy passes through Tuesday afternoon,
possibly touching off another shot of light precipitation around
midday. Otherwise, conditions dry out and skies clear out as
high pressure builds in from the west. Highs will be some 10
degrees warmer on Tuesday compared to Monday, though still a few
degrees below normal, topping off in the upper 30s to low 40s.

Mostly clear Tuesday night with lows in the 20s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
High pressure will be centered north of New York State
Christmas morning, with the base of the high extending down into
the Mid-Atlantic. Dry and seasonably chilly on Christmas Day
with highs in the upper 30s to low 40s.

Although surface high pressure will be in control into the end
of the week, several weak upper level disturbances may touch off
some light precip from time to time into Friday. PoPs will be
capped at slight chance.

Another system approaches from the west on Saturday. Models
seem to be slowing the timing of its approach, but will carry
chance PoPs as some shortwave energy out ahead of the main
system may touch off some precip.

Going through the week, temperatures will be generally below
normal, warming back to and possibly just above normal levels by
this weekend.

&&

.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Northwest winds 10-15 kts early with gusts up to
20 kts possible, gradually diminishing after 18Z. High
confidence.

Tonight...VFR. Northwest to north winds near 5-10 kts early,
then diminishing and becoming locally calm. High confidence.

Outlook...

Monday...VFR.

Monday night through Tuesday...MVFR or IFR in SN initially,
possibly becoming a wintry mix before changing to rain and
ending late Tuesday morning.

Wednesday through Thursday...VFR.

&&

.MARINE...
Small Craft Advisory remains in effect through the remainder of
the morning for the Atlantic coastal waters, and was extended
through 10 AM for lower Delaware Bay due to winds remaining
elevated a little longer than previously forecast.

Northwest winds around 15-20 kts through much of the day,
gradually diminishing into the afternoon. Gusts up to 25 kts
remaining through this morning across the ocean waters, along
with seas 3-5 feet. Improving conditions into tonight with fair
weather. Slight chance of some freezing spray through this
morning, although water temperatures near 50 degrees should
preclude any mentionable threat from this.

Outlook...

Monday through Thursday...Sub-SCA conditions expected.

&&

.CLIMATE...
Near record breaking cold temperatures are forecast today and
tonight. Records for our climate sites are listed below:

Record Coldest High Temperatures
                      December 22
Site                  Record/Year
Allentown (ABE)           16/1989
AC Airport (ACY)          18/1989
AC Marina (55N)           19/1989
Georgetown (GED)          28/1980
Mount Pocono (MPO)        11/1989
Philadelphia (PHL)        19/1989
Reading (RDG)             19/1989
Trenton (TTN)             16/1989
Wilmington (ILG)          17/1989

Record Coldest Low Temperatures
                      December 23
Site                  Record/Year
Allentown (ABE)           -3/1960
AC Airport (ACY)           1/1989
AC Marina (55N)            6/1989
Georgetown (GED)           3/1989
Mount Pocono (MPO)        -6/1989
Philadelphia (PHL)         7/1989
Reading (RDG)              2/1989
Trenton (TTN)              2/1989
Wilmington (ILG)           4/1989

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Cold Weather Advisory until 11 AM EST this morning for PAZ054-
     055.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 10 AM EST this morning for
     ANZ431.
     Small Craft Advisory until 1 PM EST this afternoon for
     ANZ450>455.

&&

$$

SYNOPSIS...MPS
NEAR TERM...Staarmann
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...MPS/Staarmann
MARINE...MPS/Staarmann
CLIMATE...Staarmann