NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Dec 23, 9:19 AM EST, 41 minutes earlier.
Area forecast discussion, Dec 23, 9:19 AM EST, 41 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
919 AM EST Fri Dec 23 2022
.SYNOPSIS...
Low pressure will move across southern Canada today, dragging a
powerful cold front across our area. Arctic high pressure will
build over the region this weekend. This high will depart early
next week, followed by a milder Pacific high which will promote
a warming trend through the last week of 2022.
&&
.NEAR TERM /THROUGH TONIGHT/...
910 AM...Quick update just to say that we've issued an impact
based Winter Weather Advisory for conditions expected with the
sharp cold frontal passage today. This front will move through
west to east across the area through the latter part of the
morning into early this afternoon with rain showers changing to
a quick burst of snow before precipitation ends. Any snow
accumulation will be minor but the main concern will be sudden
reduced visibilities and a quick freezing of any wet surfaces
leading to icy conditions. It is for this reason, we issued the
Advisory.
***Significant, Impactful Storm Will Affect The Area Through
Today**
The overall forecast for he storm anticipated to affect our
region today remains on track. Latest analysis depict two areas
of low pressure that are beginning to consolidate into one. This
center of low pressure is expected to rapidly deepen as it
moves north through Ontario today. This will occur as a very
strong upper jet streak (wind max of 140-150+ knots) rounds the
base of the long wave trough along with an associated very
strong PV anomaly. By morning, the whole system will be taking
on a negative tilt (an upper trough oriented SE to NW) with
upper level diffluence noted ahead of the trough axis. This set
up is indicative of a very large amount of energy and lift, and
the best dynamics Friday morning look to be near the Mid-
Atlantic region.
In terms of what this means for impacts today, the main
concerns are coastal flooding, wind, then the passage of a very
strong cold front which will bring rain/a potential shot of snow
on its backside and a possible flash freeze. Wind Advisories
are in effect for the whole region through Friday evening as are
Wind Chill Warnings for Friday afternoon through early Saturday
morning. We also have concerns that coastal flooding could be
significant Friday morning and this is discussed further in the
coastal flood section.
The cold front will be approaching our western counties by
daybreak, though at this time there may still not be too much
going on precip- wise. A strong line of showers is expected to
accompany right along or just ahead of the front as it passes
through. Also, there will be another surge of southerly winds in
tandem with a 50-70 knot low level jet ahead of the front. All
of this will be in response to the incredible amount of forcing
and energy this system will have. Expect the front to move
through the area quickly with it likely arriving in our western
zones by around 8-9am, the I-95 metro around 10-11am, and then
clearing the coast in the early afternoon. Expect there will be
widespread winds gusting 40-50 mph through the day Friday, first
out of the south ahead of the front and then sharply turning
westerly behind it. The aforementioned line of showers along the
front may be able to tap into the accelerated winds not far off
the surface and mix down some higher gusts in the 50-60 mph
range increasing the threat for wind damage and power outages.
Right on the backside of the front, hi-res guidance and model
soundings are favoring a transition from rain to a quick burst
of snow as the temperatures plummet below freezing. Snow
accumulation should be confined mainly north and west of I-95
with totals up to a half an inch outside of the Poconos where an
inch is possible.
The other concern we ave associated with the rapid introduction
of a very cold airmass is the potential for a quick freezing of
wet surfaces causing widespread icy conditions. One factor we
may have in our favor to combat a significant flash freeze is
the few hours of precip-free conditions leading up to the
frontal passage, thus surfaces may not have a lot of antecedent
moisture. It is also possible that there may be a brief time lag
between the frontal passage/rain and when temperatures plunge
below freezing; a short time span between those two occurrences
coupled with elevated winds may allow some surfaces to dry and
limit freezing potential. But with all that said, the potential
for dangerous, icy conditions and slick surfaces is certainly
there and we will continue to closely monitor through the
morning. By late day, as temperatures continue to plunge,
dangerously cold conditions will become the primary hazard. So
all in all, still expecting a wild day weather-wise. It's worth
noting that the combined impacts of any power outages due to the
strong winds plus the extreme cold to follow could be
significant. Finally, there will be continuing rises on the
rivers continuing through late day Friday into the weekend and
this is discussed in the hydro section below.
Tonight the main theme is bitter cold. Winds likely stay upwards
of 20 mph much of the night with gusts over 30 mph at times,
with temperatures dropping into the single digits for much of
the area, and below zero on the Poconos. This will drop wind
chills down to near or below -10 for most, and below -20 in the
Poconos. Thus, wind chill advisories remain in place for the
entire area tonight. This looks to be one of the most brutally
cold night's we've seen in a long time, quite a few years for
sure.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Bitterly cold weekend ahead, with Saturday being the coldest and
windiest of the two days. Low pressure will be slowly retreating
northwards into Canada on Saturday, with a ridge of surface high
pressure extending straight north to south across the western
high plains. In between, the gradient will keep winds sustained
at 15-25 mph with gusts up to 35 mph, and temperatures will be
brutally cold, with readings struggling to reach 20. With
the upper trough still nearby, expect a decent amount of
stratocumulus to develop as well. The one perhaps good thing is
that it will be quite dry, with the only chance of perhaps a few
flurries being up in the Poconos, and even there, just flurries.
The high slowly starts shifting southeastward Saturday night as
the low stalls near James Bay. The gradient will relax a little
and cold advection will have ceased. In fact, temperatures look
likely to be a few degrees milder Saturday night, and with less
wind (10-15 mph with a few gusts up to 25 mph), wind chills
won't be as brutal as they will be tonight, either. Clouds
should start to clear out as the trough begins to lift. Lows for
most look like they'll stay in the teens Saturday night, vs the
single digits expected tonight, with wind chills staying about
10 degrees milder.
Sunday will see a notable moderating trend...still quite cold
for this time of year, but 5-10 degrees milder and a few mph
less of wind. This will be thanks to the high starting to
recenter over the deep south and the low pressure gradually
weakening to our north. Additionally, with the trough aloft
having lifted out a bit, we should see more sun than on
Saturday.
By Sunday night, the high will be solidly over the deep south,
and the low will start retreating again as it continues
weakening over eastern Canada. The gradient will relax further,
with winds dropping back to around 10 mph. Skies will also clear
out as the trough continues to lift away. However, this will
result in a better radiational cooling set up, so expect lows to
only be a degree or two milder than Saturday night, with
widespread low-mid teens. Wind chills will mostly stay above 0,
however.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
Moderation is name of the game in the final week of 2022. As the
week progresses, we look likely to see, on average, a 5 degree
gain in high temperatures each day, starting out Monday closer
to 30 but ending up Friday nearer to 50, with slow but steady
uptick each day.
The initial high pressure will be weakening and passing into the
Atlantic on Monday. This wil keep some sun around and help with
the moderation trend, but still expect most areas to stay below
freezing for one more day.
By Tuesday, a weak clipper system will pass by the region,
heralding the steadier warming trend as the flow shifts to a
more zonal one. Will have to watch for a few snow showers or
flurries as the system passes, but right now am keeping a dry
forecast.
Wednesday thru Friday, we'll have a Pacific high pressure
building eastward over us, and centering near the East Coast.
This will provide a milder west to southwest wind, but
relatively light, and it will also help usher in a seasonably
milder air mass. By late week we'll be notably back above
normal, but at least through Friday, the high should also keep
us dry.
&&
.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...IFR/lingering LIFR conditions early then improving
following the passage of a strong cold front. Expect the front
to impact KABE/KRDG around 15z, the I-95 terminals by 16z, then
to the coast by 17z. Expect RA with the frontal passage and a
possible burst of SHSN with immediate passage of the front.
Winds will be mostly southerly ahead of the front then sharply
veering to southwesterly/westerly behind it. Winds 20-25 kts
with gusts to 40 kts expected, and potentially higher gusts
associated with the frontal passage. Moderate confidence
overall.
Tonight...Conditions improving to VFR by early evening.
Westerly winds 15-20 knots with gusts 30-35 knots. Moderate
confidence.
Outlook...
Saturday...VFR. Wind west to southwest 15-20 kts with 30 kt
gusts. High confidence.
Sunday...VFR. Wind west 10-15 kts with 20 kt gusts. High
confidence.
Monday...VFR. Wind west 5-10 kts. High confidence.
Tuesday...VFR. Wind west around 5 kts. High confidence.
&&
.MARINE...
Gale Warnings remain in effect for all coastal waters and the
Small Craft Advisory for the Delaware Bay continues. The Small
Craft Advisory will upgrade to a Gale Warning at 7AM. East to
Southeast winds will increase through the day with sustained
winds of 30-35 knots and gusts to 40-50 knots expected for the
ocean waters. Gusts will peak early afternoon around the time
of cold front passage when some brief storm force gusts are
possible with a sharp wind shift from southerly to westerly.
Temperatures will plummet late. Rain with a brief burst of snow
possible this afternoon.
Outlook...
Gales and much colder temps will continue tonight into Saturday.
Freezing spray advisories may be required for this period due to
the gusty winds and much colder air moving in. Winds likely drop
back to SCA levels Sunday, then probably sub-SCA Monday-Tuesday.
&&
.TIDES/COASTAL FLOODING...
The direct onshore flow was in the process of veering to the
south and southwest early this morning. The onshore flow caused
tidal departures to increase into the +2 to +3 foot range along
the coasts of New Jersey and Delaware, and into Delaware Bay and
the tidal Delaware River. The departures should remain nearly
steady or increase slightly before this morning's high tide (the
high tide occurs in the early afternoon on much of the tidal
Delaware River). We are on target to experience widespread
moderate tidal flooding and the Coastal Flood Warnings remain in
effect.
A southerly wind on the upper Chesapeake Bay early this morning
is forecast to shift to the west around mid morning with the
passage of a cold front. The water being pushed up the bay in
the southerly flow has caused tidal departure to increase to
around +2.5 feet early this morning. There is the potential for
localized minor flooding with the early morning high tide. The
west wind will likely shove the water against the upper eastern
shore this afternoon. As a result, that area is expected to
experience widespread minor tidal flooding at that time.
The west wind will begin to push water away from the Delaware
and New Jersey coasts this afternoon. Tidal departures should
begin to decrease at most locations. As a result, we are not
anticipating any additional tidal flooding after the high tide
cycles covered by the current warnings and advisories.
&&
.CLIMATE...
While the potential of a white Christmas has diminished
significantly, the potential of a very cold Christmas remains.
Highs are currently projected to get no higher than the 20s both
Christmas Eve and Christmas Day. This is a decent cold snap for
any December, as the last time we had two or more days in a row
with highs in the 20s at PHL was back in 2017, 5 years ago.
However, for Christmas Eve and Christmas Day itself, it's more
notable, as we've been on quite a stretch of warm Christmases of
late. The last time the high on Christmas Day itself stayed
below 30 was back in 2000, when the high was only 27. The last
time both Christmas Eve and Christmas Day stayed below 30 was
back in 1989, when the high Christmas Eve was only 21 and the
high Christmas Day was only 28. So, this year's Christmas
weekend has the potential to be the coldest in over 30 years.
Something to think about if you are planning any outdoor
services.
All this having been said, it will be be tough to match the
coldest Christmas eve and Christmas Days on record, which for
much of our area dates back to 1989 and 1983. Particularly in
1983, we had some of the coldest weather we ever see in our
region, with many areas below zero at night and not even
reaching 10 above during the day.
Record coldest high and low temperatures for Christmas Eve and
Christmas Day are listed below:
Record Coldest High Temperatures
12/24 12/25
Site Record/Year Record/Year
Allentown (ABE) 18/1960 8/1983
AC Airport (ACY) 21/1989 10/1983
AC Marina (55N) 19/1906 12/1983
Georgetown (GED) 27/1989 26/1983
Mount Pocono (MPO) 15/1935 & 1983 1/1983
Philadelphia (PHL) 21/1906 & 1989 10/1983
Reading (RDG) 16/1906 20/1983
Trenton (TTN) 18/1872 8/1983
Wilmington (ILG) 21/1989 10/1983
Record Coldest Low Temperatures
12/24 12/25
Site Record/Year Record/Year
Allentown (ABE) -5/1989 -2/1983
AC Airport (ACY) -1/1983 -2/1980 & 1983
AC Marina (55N) 6/1983 4/1983
Georgetown (GED) 9/1989 2/1989
Mount Pocono (MPO) -20/1989 -13/1980
Philadelphia (PHL) 3/1983 1/1980 & 1983
Reading (RDG) 4/1989 -2/1980
Trenton (TTN) -4/1983 -3/1983
Wilmington (ILG) -5/1983 -7/1983
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Advisory until 7 PM EST this evening for PAZ054-055-
060>062-070-071-101>106.
Winter Weather Advisory until 6 PM EST this evening for PAZ054-
055-060>062-070-071-101>106.
Wind Chill Advisory from 6 PM this evening to 10 AM EST
Saturday for PAZ070-071-101>106.
Wind Chill Advisory from 3 PM this afternoon to 1 PM EST
Saturday for PAZ054-055-060>062.
Coastal Flood Warning until 5 PM EST this afternoon for PAZ070-
071-106.
NJ...Coastal Flood Warning until 1 PM EST this afternoon for NJZ016.
Wind Advisory until 7 PM EST this evening for NJZ001-007>010-
012>027.
Winter Weather Advisory until 6 PM EST this evening for NJZ001-
007>010-012-015>019-021.
Wind Chill Advisory from 6 PM this evening to 10 AM EST
Saturday for NJZ009-010-012>027.
Coastal Flood Warning until noon EST today for NJZ012>014-
020>027.
Winter Weather Advisory until 6 PM EST this evening for NJZ013-
014-020-022>027.
Wind Chill Advisory from 3 PM this afternoon to 1 PM EST
Saturday for NJZ001-007-008.
Coastal Flood Warning until 5 PM EST this afternoon for NJZ015-
017>019.
DE...Coastal Flood Warning until 1 PM EST this afternoon for DEZ001.
Wind Advisory until 7 PM EST this evening for DEZ001>004.
Winter Weather Advisory until 6 PM EST this evening for
DEZ001>003.
Wind Chill Advisory from 6 PM this evening to 10 AM EST
Saturday for DEZ001>004.
Coastal Flood Warning until noon EST today for DEZ002>004.
Winter Weather Advisory until 6 PM EST this evening for DEZ004.
MD...Wind Advisory until 7 PM EST this evening for MDZ012-015-019-
020.
Winter Weather Advisory until 6 PM EST this evening for MDZ012-
015-019-020.
Wind Chill Advisory from 6 PM this evening to 10 AM EST
Saturday for MDZ012-015-019-020.
Coastal Flood Advisory until 9 PM EST this evening for MDZ012-
015-019-020.
MARINE...Gale Warning until 1 AM EST Saturday for ANZ430-431.
Gale Warning until 6 PM EST Saturday for ANZ450>454.
Gale Warning until 6 AM EST Saturday for ANZ455.
&&
SYNOPSIS...Brudy/Iovino/RCM
NEAR TERM...Brudy/Fitzsimmons
SHORT TERM...RCM
LONG TERM...RCM
AVIATION...Brudy/RCM
MARINE...Brudy/RCM
TIDES/COASTAL FLOODING...
CLIMATE...