Norristown, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

591
FXUS61 KPHI 231129
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
629 AM EST Sat Nov 23 2024

.SYNOPSIS...
Low pressure that was responsible for the rain on Friday will
gradually drift away from the region through the weekend.
Weak high pressure builds in Sunday into Monday. The next fast
moving cold front is expected to cross our region Tuesday. A coastal
low will be near our region Thanksgiving into Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low pressure has pivoted offshore and is currently located
southeast of Long Island. Precipitation has concluded across
our area with morning temperatures mainly in the 30s or low 40s.

The surface low will continue to depart and deepen as it lifts
toward the Gulf of Maine and Nova Scotia later today. As a result,
brisk northwest flow is anticipated as the pressure gradient
tightens over the region. Took a look at model soundings this
morning and looks like we should tap into some of the higher winds
aloft. With this in mind, expecting wind gusts upwards of 30 to 40
mph during the day. Should fall short of needing any wind headlines,
however wouldn`t completely rule out locally higher gusts along
ridge lines across the higher terrain. Skies will be mostly clear
during the day with highs in the 40s/50s; however it will feel more
like the 30s/40s when factoring in the wind.

Northwest flow should subside a bit this evening, however the
pressure gradient will remain elevated with gusts up to 25 mph
possible overnight. Lows will range from the mid 30s to low 40s
under partly cloudy skies.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
The main focus in the short term is on a Warm front that lifts
through on Monday followed closely behind by a cold front on
Tuesday.  This will bring another (albeit brief) chance for rain
across the region. Temperature profiles throughout this period
support that any precipitation will be rain. Of note, unlike the
system that just affected our region, this is a very fast moving
system, so the period of rain chances is only from Monday evening
through mid day Tuesday, and even that is a longer duration than
what any one model depicts, but there is uncertainty in exactly when
the front will arrive. Also due to the track of this system, rain
amounts should be light, generally less than a tenth of an inch.

As for temperatures, highs on Sunday will range from the lower 40s
to upper 50s. By Monday in the wake of the warm front, expect high
temperatures about 5 degrees warmer. For now, temperatures on
Tuesday are similar to Monday as the strongest cold air advection
isn`t expected until very late in the day, but if the front trends
faster then temperatures may trend lower.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
All eyes in the long term are on the Thanksgiving/Friday system.
This low looks like it is going to take a path similar to a Miller-
Type B system. However, how close it will track to our region, and
thus the ultimate impacts in our region, remain quite uncertain.

From the 00Z model runs, here is the range of possibilities. The
furthest south depictions show the system so far SE that most of our
region will stay dry with the exception of light snow or wintry mix
in Delmarva and far south Jersey (the main model depicting this is
the 00Z CMC). Furthest north depictions (notably in the 00Z ECMWF)
show the center of the low tracking over Delmarva and far SE Jersey,
which would result in widespread precipitation for our region, but
depending on the timing, would be almost all rain. The GFS appears
to be close to a middle of the road solution, with the low tracking
just SE of the coast. This would result in precip for most of the
region (possibly staying out of the southern Poconos), and as far as
precipitation type would probably be mostly rain with a transition
to wintry mix possible for areas from near the 95 corridor and
further west.

Of note, while most of the main deterministic models show the low
deepening and intensifying while it is tracking near our region,
none of them depict it slowing or stalling near our region, so this
may be a relatively fast moving coastal storm (relative to other
coastal storms).

All that being said, stayed close to a blend of guidance for the
forecast. Those with travel plans on Thursday and Friday should keep
an eye on the forecast as we get closer.

&&

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

Today...Lingering MVFR ceilings should improve to VFR by 13-14Z
and remain VFR through the afternoon. W to NW winds around
15-20 kt with occasional gusts up to 30 kt. Moderate confidence.

Tonight...VFR. W winds around 10-15 kt occasionally gusting up
to 20 kt. High confidence.

Outlook...

Sunday...VFR. W winds gusting up to 25 KT.

Monday...VFR.

Monday night and Tuesday...Brief period of MVFR possible with rain.
W winds gusting up to 30 KT Tuesday afternoon.

Wednesday...VFR.

&&

.MARINE...
A Gale Warning is in effect for all Atlantic coastal waters and the
Delaware Bay through this afternoon. Small Craft Advisory conditions
are then expected for tonight.

Northwest winds around 25 to 30 kt with gusts up to 35 to 38 kt
possible through this afternoon. Winds will gradually subside
tonight around 20 to 25 kt with gusts up to 30 kt. Seas of 4 to 7
feet.

Outlook...

Sunday...SCA conditions continue due to W winds gusting up to 30 kt.

Monday...Winds and seas should stay below SCA criteria.

Tuesday...Expect an abrupt shift to W winds behind a cold front
Tuesday morning. Wind gusts up to 30 kt possible behind the front.

Tuesday night/Wednesday...Winds should drop below 25 KT Tuesday
evening, though elevated seas near 5 feet may linger on the Atlantic
waters for a few hours longer. After seas and winds subside, no
additional SCA conditions are expected through Wednesday night.

&&

.CLIMATE...
Driest autumn (Sep-Nov) on record, and any 3-calendar month
period on record, plus current status:

                   9/1-11/22   Driest          Driest 3         Year/
Site              2024 precip  Autumn Year  Calendar months    months
Allentown (ABE)       2.86      3.81  1922      3.58        Oct-Dec 1928
A.C. Airport (ACY)    2.22      3.34  2001      2.35        Oct-Dec 1946
A.C. Marina (55N)     1.60      2.89  1941      2.52        Aug-Oct 1895
Georgetown (GED)      1.23      2.67  2001      2.20        Aug-Oct 2024
Mount Pocono (MPO)    4.25*     4.21  1931      3.36        Oct-Dec 1928
Philadelphia (PHL)    2.20      2.37  1922      2.37        Sep-Nov 1922
Reading (RDG)         2.34      2.89  1922      2.89        Sep-Nov 1922
Trenton (TTN)         2.12      3.18  1922      2.66        Jun-Aug 1966
Wilmington (ILG)      1.85      3.17  1922      3.17        Sep-Nov 1922

*Mount Pocono precipitation is only through 11/21. An updated total
through 11/22 will be available later today.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 6 PM EST this evening for ANZ430-431-
     450>455.

&&

$$

SYNOPSIS...Fitzsimmons/Johnson
NEAR TERM...DeSilva
SHORT TERM...Johnson
LONG TERM...Johnson
AVIATION...DeSilva/Johnson
MARINE...DeSilva/Johnson
CLIMATE...WFO PHI