Allentown, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

175
FXUS61 KPHI 040804
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
304 AM EST Wed Dec 4 2024

.SYNOPSIS...
High pressure centered over the Appalachians early this morning
will continue to dominate our weather through the first part of
the day before sliding off to the south and east late day as
low pressure moves into the Great Lakes region. This
strengthening low will track to our north tonight and Thursday,
pushing a strong cold front across our area early Thursday. Cold
and dry high pressure will build into the Ohio Valley Friday
through Saturday before weakening into our area through Sunday.
The next low pressure system looks to affect the area early next
week.

&&

.NEAR TERM /THROUGH TODAY/...
It remains mainly clear but cold early this morning as high pressure
continues to dominate. Lows by morning should range from the teens
over portions of NE PA into NW NJ with low to mid 20s for most areas
farther south.

As we head into the day today, it will be sort of like a
`transition` day as high pressure will still maintain control of our
weather through much of the day. Upper level flow will gradually
back and briefly become zonal ahead of an advancing strong trough
over the Great Lakes. Although the airmass will be moderating, highs
will mainly be in the upper 30s to mid 40s across the area with
increasing clouds throughout the day. As a whole, most of Wednesday
will remain dry. The exception is across northeast PA or northern NJ
late in the afternoon as some energy in advance of the trough
streams into the north portions of the area. This may result in a
passing snow shower or two, otherwise, the bulk of the precip holds
off until Wednesday night. Finally worth noting, it will also become
quite breezy in the afternoon with S/SW winds 10 to 15 gusting as
high as 20 to 30 mph.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
A strong storm system will impact the region Wednesday night through
Thursday night, bringing some rain and snow showers, strong winds,
and continued below normal temperatures. A Wind Advisory remains in
effect for Thursday from 6 AM until 10 PM for strong westerly winds
near 20-35 mph, with gusts around 40-55 mph. Greatest impacts are
expected Thursday morning when strong winds and scattered snow
showers, mainly north, could impact the morning commute with
slippery road conditions.

Synoptic Overview...A deep positively tilted trough approaches the
Great Lakes tonight. The trough axis will dive quickly southeastward
across the Mid Atlantic early Thursday while becoming negatively
tilted as it shifts offshore. Height falls quickly spread across the
area tonight into Thursday morning. At the surface, a strengthening
low pressure system will pass just north of the Great Lakes today,
reaching the Canadian Maritimes late Thursday. A strengthening
pressure gradient will result beginning today, remaining in place
through Thursday night. A strong cold front will sweep through the
area Thursday morning, likely offshore by noon. The frontal passage
will yield very strong cold advection in its wake, with 850 mb
temperatures upstream around -10C to -15C. Post frontal surface
pressure rises will be near 1 mb/hour. This is not a clipper system,
to be sure.

Tonight...As stronger forcing for ascent arrives overnight,
precipitation, mainly in the form of scattered showers, should
develop within the region, with the greatest chances (60-70%)
residing mainly north and east of the Philly metro. Within the
Philly metro and south, less forcing may result in little to no
precipitation until the arrival of the front Thursday morning. Areas
along and north of the I-78 corridor will likely see mostly snow
with this activity, with a rain/snow mix farther south and mainly
rain near the coast. QPF is light, largely less than 0.10". Any
snowfall accumulation outside of the Poconos and higher elevations
of northwest New Jersey will remain less than 1", a brief dusting at
best. The higher elevations and southern Poconos could see about an
inch or two of snow tonight.

A southwest breeze will be strengthening overnight as the cold front
approaches, and especially toward daybreak to around 15-20 mph, with
gusts near 25-30 mph possible. The winds, mixed boundary layer, WAA,
and cloud cover will keep temperatures relatively mild, perhaps even
rising a few degrees overnight. Forecast low temperatures are mainly
in the 30s.

Thursday through Thursday night...The strong cold front will quickly
approach and begin passing through the forecast area near or just
after daybreak Thursday, and should be offshore by around noon. If
moisture is sufficient, some snow showers or snow squalls could
develop along or just ahead of the frontal boundary following the
diminishing overnight precipitation. Moisture is expected to be
limited though, so it will probably be a struggle to get anything of
significance farther south. The limiting factor for any impacts from
this activity will be surface temperatures, as most areas south of I-
78 will be above freezing with above freezing roadway temperatures.
Nevertheless, a quick dusting a snowfall could result in grassy and
elevated surfaces as far south as the coastal plain, and may cause
some slippery travel during the morning rush hour. An additional
inch or two of snowfall is forecast for the southern Poconos, and a
Winter Weather Advisory may need to be considered in a future update
for this area given event totals of 1-3". However, any impacts from
the snow could be more short fused in nature, and may be covered by
Snow Squall Warnings instead. Temperatures will likely reach their
daytime maximum in the mid 30s to low 40s in the morning, then
gradually fall into the afternoon.

Beyond the shower potential with the front, the main story will the
the windy conditions expected in its wake. Hard pressed to find any
deterministic guidance showing anything less than widespread 35-45
kts of wind within the 925 to 850 mb layers during the post-frontal
regime. BUFKIT profiles indicate we`ll be mixing up to around the
800-850 mb layers post-frontal during the daytime, so it`s
reasonable to assume those winds speeds should translate to peak
gusts at the surface given extremely strong cold advection,
shortwave vort max pivoting through aloft with FROPA, and surface
pressure rises around 1 mb/hour. Long story short, we remain
confident that our area will experience widespread 40-55 mph wind
gusts for much of the daytime period Thursday. Expect westerly
sustained winds near 20-35 mph. A Wind Advisory remains in effect
for the entire area for Thursday. Some tree damage and isolated
power outages are possible.

Friday...The cold and dry high pressure will build into the Ohio
Valley Friday and Friday night. The pressure gradient and cold
advection will persist, though not nearly as strong as Thursday.
Expect highs in the 30s and lows in the 20s. A breezy northwest wind
will persist with wind gusts near 20-30 mph during the daytime.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure will dominate our weather through the weekend bringing
fair conditions. Saturday will continue to be quite chilly, with
highs in the 30s to low 40s, with temperatures warming back up to
more seasonable levels by Sunday as the high moves off the coast.

Monday and Tuesday...Long-term guidance suggests early next week
will become more unsettled with an amplified trough shifting across
the central US. That said, guidance remains in some disagreement
with the evolution of the system. However it does look like the
system will be warmer with less chances for any wintry precip. We
continue to carry chance/likely PoPs for the area during this
period. Temperatures by next Tuesday could reach into the upper 50s
to low 60s.


&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Overnight (to 11z Wed)...VFR with mostly clear skies and light winds
from the W/SW generally around 5 knots or less. High confidence.

Wednesday...VFR with increasing clouds and lowering ceilings
throughout the day. Southwest winds around 5-10 kt in the morning
will increase between 15z-17z to around 10-15 kt with gusts 18-22
kt, more out of the south/south-southwest. High confidence in
prevailing VFR, moderate confidence in timing of wind shift and
increase.

Wednesday night...Sub-VFR conditions likely developing overnight
along with rain or snow showers, especially at RDG/ABE. Southwest
winds 10-15 kts with gusts of 20-30 kts possible. LLWS possible.
Moderate confidence overall.


Outlook...

Thursday through Thursday Night...MVFR to IFR conditions early,
with improvement to VFR conditions by midday. Windy. West winds
increasing to around 20-25 kts with gusts 35-40 kts. Winds
lessen Thursday night.

Friday...VFR. West-northwest winds near 15 kts with gusts 20-30 kts,
diminishing in the evening.

Saturday through Sunday...VFR with no significant weather expected.

&&

.MARINE...
Winds ramp up once again as we head into the day Wednesday with a
Small Craft Advisory beginning for all waters at 1 PM. By late day
expect southwest winds 20 to 25 gusting up to 30 knots with seas 5
to 6 feet.

Outlook...

Tonight through Thursday night...Gale Warning now in effect.
Gale force winds arrive Wednesday night, peaking Thursday, then
gradually diminishing Thursday night. Wind gusts 35 to 45 kts
possible. The strong offshore winds could result in abnormally
low water during the Thursday late afternoon to evening low
tide, which could make navigation difficult in shallow waters.

Friday...Small Craft Advisory conditions abating into Friday
night.

Saturday through Sunday...Conditions look to be below Small
Craft Advisory levels with west to southwest winds generally 10
to 15 gusting up to 20 knots and seas 2 to 4 feet.


&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Advisory from 6 AM to 10 PM EST Thursday for PAZ054-055-
     060>062-070-071-101>106.
NJ...Wind Advisory from 6 AM to 10 PM EST Thursday for NJZ001-
     007>010-012>027.
DE...Wind Advisory from 6 AM to 10 PM EST Thursday for DEZ001>004.
MD...Wind Advisory from 6 AM to 10 PM EST Thursday for MDZ012-015-
     019-020.
MARINE...Small Craft Advisory from 1 PM this afternoon to 6 PM EST this
     evening for ANZ430-431-450>455.
     Gale Warning from 6 PM this evening to 6 AM EST Friday for
     ANZ430-431-450>455.

&&

$$

SYNOPSIS...Fitzsimmons
NEAR TERM...DeSilva/Fitzsimmons
SHORT TERM...Staarmann
LONG TERM...Fitzsimmons
AVIATION...Fitzsimmons/Staarmann
MARINE...Fitzsimmons/Staarmann