361
FXUS61 KPHI 231949
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
249 PM EST Mon Dec 23 2024

.SYNOPSIS...
High pressure moves offshore tonight giving way to a weak
disturbance that will bring a light round of wintry precip to the
region on the morning of Christmas Eve. High pressure returns and
settles to our north on Christmas Day and persists through most of
Saturday. Another low pressure system then takes aim at the area on
Sunday into early next week.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of early this afternoon, high pressure is centered near Long
Island, while weak low pressure is west of Chicago. With the
high slowly retreating through tonight and warm advection
getting underway aloft ahead of the weak low pressure, expect
clear skies this evening to give way to thickening and lowering
clouds overnight. Temps likely bottom out in the upper teens and
low 20s this evening before starting to rise before dawn.

Precipitation with the associated weak low begins advancing into
the Poconos before dawn, but shouldn`t reach the I-95 corridor
until shortly after sunrise. Most areas start as snow showers,
but warm advection aloft will bring milder air into the Philly
metro, resulting in some mixed precip, with high potential for
freezing rain problems exacerbated by cold road temps. Thus,
even though amounts look very light, have expanded the
inherited winter weather advisory a few zones further north and
east, encompassing nearly the entire Philly metro. Further
north, precip should be mainly snow, and amounts should be
mostly under an inch. However, with cold road temps, even there
we could see slippery travel, so have issued an Special Weather
Statement for these areas highlighting the travel risks given
the holiday. Further south, any winter weather issues quickly
become more uncertain as latest guidance is mostly dissipating
precip while also warming temps, but potential does exist for a
bit of mixed precip south of the advisory, so for now have
issued another Special Weather Statement for these areas given
the possible mixed precip. Far southern areas should see little
precip, and what does fall is likely more plain rain than
anything else.

Warmer southerly winds should help bring temps up slowly but
surely through the day, and in fact skies likely start to clear
out later in the afternoon tomorrow. Highs for most should rise
above freezing, with 40s south of Philly and mid-upper 30s
north.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
Overall, the short term period will be relatively benign as weak
northwesterly flow aloft is situated over the region and surface
high pressure settles over southern Ontario. The only feature worth
monitoring is a shortwave that will track through the area on
Thursday.

As a result, fair weather conditions are anticipated across the
region for Christmas Eve night and Christmas Day featuring mostly
clear/sunny skies and light northerly winds. Heading into Christmas
night, tranquil conditions will continue, however there will be an
increase in cloud cover ahead of the approaching shortwave. As of
now, moisture profiles aloft are quite dry, so other than mostly
cloudy skies on Thursday, no precipitation is expected. Cannot rule
out a few passing flurries/sprinkles though, especially north and
west. Confidence is low in this occurrence though, so have opted to
not include this potential in the weather grids at this time.

In terms of temperatures, high temperatures on both Christmas Day
and Thursday will top out in the mid 30s to low 40s. Low
temperatures both nights will mainly be in the teens to mid 20s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Little changes were made to the long term forecast as an upper level
ridge begins to build over the region for the remainder of the week
into the start of the weekend. Overall, moderating and a gradual
increase in temperatures are expected, where temperatures may range
as much as 10 degrees above normal for the end of December. By
Sunday and into Monday, an upper level trough will approach the
Great Lakes and Mid-Atlantic region. Guidance differs significantly
with the timing of this feature, but it does appear it will be the
next potential threat to bring some widespread rainfall to the
area.

&&

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

Rest of Today...VFR. S winds around 5 kt. High confidence.

Tonight...VFR through 09Z, then MVFR or possibly IFR CIGs and
at least MVFR if not IFR vsby in light SN, mainly for KRDG/KABE,
after 09Z. Think precip mostly holds off until 12Z further
southeast. S winds less than 5 kt. Moderate confidence.

Tuesday...MVFR/IFR in SN at KRDG/KABE/KTTN, SN/FZRA at
KPNE/KPHL/KILG, mainly 12Z-16Z. Precip may not reach KMIV/KACY.
Precip ending from west to east and improving to VFR after 18Z.
W winds around 5 kt. Moderate confidence.

Outlook...

Tuesday night through Friday night...VFR. No significant weather
expected.

Saturday...VFR. A slight chance of a rain shower in the
afternoon.

&&

.MARINE...
Sub-Small Craft Advisory conditions through Tuesday. S winds
around 10 kt this afternoon and tonight. Winds turn W around 10
kt on Tuesday. Seas 2 to 3 feet. VSBY restrictions in rain
and/or snow Tuesday morning, ending Tuesday afternoon.

Outlook...

Tuesday night through Wednesday...No marine headlines expected.
Northerly winds around 10-20 kt and seas of 2-3 feet.

Wednesday night through Saturday...No marine headlines expected.
Winds generally around 15 kt or less and seas of 2-3 feet.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 5 AM to 1 PM EST Tuesday for
     PAZ070-071-101-102-104-106.
NJ...Winter Weather Advisory from 5 AM to 1 PM EST Tuesday for
     NJZ016>019.
DE...Winter Weather Advisory from 5 AM to 1 PM EST Tuesday for
     DEZ001.
MD...None.
MARINE...None.

&&

$$

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