366
FXUS61 KPHI 272008
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
308 PM EST Fri Dec 27 2024

.SYNOPSIS...
The next low pressure system arrives Friday night. Another
stronger system arrives Sunday, bringing mostly rain as
temperatures gradually moderate into the weekend. Unsettled and
warm weather lingers into early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
High pressure shifts offshore this afternoon, making room for
our next system tonight. Forecast will remain dry through the
rest of the afternoon and evening.

With the arrival of our next system, the biggest concern this
period is the freezing rain that is expected starting late
tonight and continuing into early Saturday morning.

Areas: Best chance for freezing rain remains generally along
and north of the Interstate 78 corridor. The Winter Weather Advisory
for NW NJ, Southern Poconos, Lehigh Valley, and upper Bucks
remains on track. Elsewhere in our region, the precipitation is
expected to start and continue as plain rain.

Timing: Latest high res and global guidance has slowed the
onset time of precipitation across our region to around 9pm to
midnight. Thus, have offset the timing of the Winter Weather
Advisory to being at 9pm Friday night and ending at 9am Saturday
morning.

Friday night temperatures at the surface will be in the upper
20s to mid 30s, southerly flow aloft will result in a rather
substantial warm nose, but calm winds at the surface will
limit how quickly temperatures rise at the surface. That being
said, we do expect temperatures to slowly rise after midnight or
so. Thus, expect most places will be above freezing by sunrise
Saturday morning (with the exception of portions of the southern
Poconos and Warren and Sussex Counties in NJ).

Impacts: Nighttime travel could become slippery and hazardous
as a result, especially along bridges, overpasses, other
untreated roadways, and untreated sidewalks.

After daybreak Saturday, most locations will have transitioned
over to rain. Temperatures will warm to the mid 40s to upper
50s. Total rainfall (non-frozen) amounts from this system will
range from 0.30 to 0.50 inches of rain across the northern half
of the region. Across the southern half of the region, around
0.10 to 0.30 inches.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
A significant warming trend is expected across the area after
the passage of the early Saturday system, with temperatures
warming into the low to mid 50s across portions of the Poconos,
to the mid 60s across the Delmarva.

Rain chances will continue across central and northern portions
of the forecast area into Saturday evening as a warm front
continues to advance northward. After the passage of this warm
front, many areas may have dry conditions during much of the day
on Sunday, especially east of the fall line.

Attention will then shift to our next system Sunday night into
the first half of the day on Monday. A strong h500 shortwave
will pivot through the area, with a strong surface cyclone
shifting northeast through portions of the Great Lakes and into
Quebec Monday with a surface cold front sweeping through our
region early in the day.

Showers will develop ahead of the cold front and push through
the area during this time period. In addition, forecast
soundings indicate that there will be some elevated instability,
so a few areas of thunder are possible. While there will be a
strong low-level jet that develops over the region Sunday night,
and impressive kinematic fields overall, the very limited
instability is expected to limit any potential for significant
winds mixing down to the surface.

Rainfall totals through the weekend of up to one inch are
possible across central and southern portions of the forecast
area, with one to two inches possible across portions of the
Lehigh Valley northward into the Poconos.

Precipitation can be expected to clear the area by Monday
afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
After the passage of the cold front, temperatures will remain
above seasonal normals, but again fall into the 30s areawide
Monday night.

The active pattern in place will continue on Tuesday into
Wednesday, with a low pressure system approaching the area from
the midwest. Rain chances will increase during the afternoon
hours on Tuesday. Again, models indicate some elevated
instability with the passage of this system, so some thunder
will be possible.

One thing to watch with this forecast will be the potential for
a coastal low to develop Wednesday into Wednesday night. While
models disagree on this, it is worth noting that should a
coastal low develop, there could be some snowfall across
portions of the Poconos. For now,have slight chance to low-end
chance PoPS across far northern areas Wednesday afternoon and
evening.

Colder air will continue to push into the area on Thursday and
into Friday. Temperatures areawide can be expected to be near or
slightly below seasonal normals, with mostly dry conditions
across the area.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of today...Primarily VFR conditions expected. Winds light
(5 kts or less) and favoring an easterly direction, but light
enough that wind direction could be variable at times. Some
patchy MVFR stratus across MIV/ACY this afternoon as well could
continue into the late afternoon hours. Moderate confidence.

Tonight...Starting VFR, but expecting lower ceilings to move in
through the overnight hours. Will likely quickly go from MVFR to
IFR ceilings once precipitation starts. Precipitation should be
all rain for most TAF sites, but a period of FZRA is likely at
KABE, and there is a small chance (less than 20%) that a brief
period could happen at KTTN and KRDG. Winds around 5 KT,
favoring an easterly or southeasterly direction. Starting around
06Z, a southwesterly low level jet is expected to develop over
the region. While the wind speeds with this low level jet will
only be 30 to 40 kt, there will be directional shear as well as
surface winds by that point should be favoring southeasterly.
Consequently, expect that low level wind shear will be a concern
for KPHL, KILG, KTTN, KPNE, KABE, and KRDG. For the coastal TAF
sites (KMIV and KACY), they may be far enough east that low
level wind shear won`t be as much of a problem.

Saturday...Sub-VFR conditions continue through the rest of the
day. Rain and low stratus is expected to bring IFR/LIFR
conditions through the day. Winds are also expected to be light
at the surface. LLWS concerns, mainly along the I-95 terminals
and northwest, will continue through the morning with a
possibility it may continue into the afternoon hours. Low
confidence.

Outlook...

Saturday night thru Sunday...Periods of MVFR and IFR due to low
ceilings and reduced visibility in rain. Small chance of
thunderstorms Sunday night. Winds gusting up to 30 kt Sunday.

Monday...Sub-VFR possible early with a chance of rain, then drying
out with VFR likely returning in the afternoon.

Tuesday...VFR early, then sub-VFR possible later as the next system
potentially brings rain back to the region late Tuesday into
Tuesday night.

Wednesday...MVFR early, then becoming VFR.

&&

.MARINE...
Winds and seas will stay below Small Craft Advisory conditions
through Saturday night. Some reduced visibility is possible
during this period due to rain and fog.

Outlook...

Sunday/Sunday night...SCA in effect with wind gusts above 25
kt, and elevated seas, especially on the Atlantic coastal
waters.

Monday...SCA in effect on the ocean with wind gusts 25 to 30 kt
and ocean wave heights 4 to 8 feet. Chance of rain in the
morning, ending by afternoon.

Monday night and Tuesday...Winds and seas subsiding Monday
night and remaining below SCA criteria Tuesday. However, the
chance of rain returns later Tuesday.

Wednesday...Winds and seas below SCA conditions.

&&

.CLIMATE...
Temperatures on Sunday will be up to 20 degrees above normal.
However, in general the forecast is still well below the record
highs for December 29. Currently only Reading and Georgetown
have a forecast within 5 degrees of the record high.

Record High Temperatures for December 29th

SITE...............RECORD...YEAR
Allentown (ABE)........72...1984
AC Airport (ACY).......75...1984
AC Marina (55N)........72...1984
Philadelphia (PHL).....72...1984
Wilmington (ILG).......74...1984
Reading (RDG)..........64...1982
Trenton (TTN)..........74...1984
Mount Pocono (MPO).....56...1982
Georgetown (GED).......69...1988

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 9 PM this evening to 9 AM EST
     Saturday for PAZ054-055-061-062-105.
NJ...Winter Weather Advisory from 9 PM this evening to 9 AM EST
     Saturday for NJZ001-007>010.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 10 AM Sunday to 7 AM EST Monday for
     ANZ430-431.
     Small Craft Advisory from 10 AM Sunday to 5 PM EST Monday for
     ANZ450>455.

&&

$$

SYNOPSIS...Johnson/MJL
NEAR TERM...Johnson/MJL
SHORT TERM...Cooper/Franklin
LONG TERM...Cooper/Franklin
AVIATION...Cooper/Franklin/MJL
MARINE...Cooper/Franklin/MJL
CLIMATE...