NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Jan 3, 4:29 AM EST, 1 hour 31 minutes earlier.
Area forecast discussion, Jan 3, 4:29 AM EST, 1 hour 31 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
429 AM EST Mon Jan 3 2022
.SYNOPSIS...
A surface low will move rapidly northeastward from the Carolinas
this morning to well off the Mid-Atlantic coast by this evening.
Migratory high pressure will dominate the eastern U.S. Tuesday.
A cold front will progress through the Northeast Wednesday and
Wednesday night. Another surface low will rapidly develop and
move northeastward near or through the Mid-Atlantic Thursday
night and Friday. High pressure will build into the region on
Saturday. Another system may affect the area on Sunday.
&&
.NEAR TERM /THROUGH TONIGHT/...
Spectacular satellite imagery over the East this morning as a strong
area of low pressure comes together to our southwest. Just a classic
eastern US winter storm presentation. A blossoming shield of
precipitation is now overspreading the local area. A major winter
storm will affect southern portions of the area over the next 18
hours.
The main change to the forecast overnight was an increase in QPF,
and by association, snowfall, for areas previously within and that
were just north of the previous Winter Storm Warning. The QPF
increase is almost unanimously supported by the last two cycles of
global and hi res guidance, and translates to an increase in snow
totals.
The most difficult portion of the forecast remains the northward
extent of precipitation shield. Even many of the recent model runs
which increased QPF across the south generally didn't move the
precipitation shield north much. The latest blend does bring amounts
up somewhat in the I-95 corridor. However, there is likely to be an
exceptionally sharp northern cutoff to accumulating snow, probably
even sharper than the latest forecast, which as it is has a much
sharper than normal gradient. Even across, for example, Philadelphia
County, it would not be surprising to see a significant difference
in totals. And for northern portions of the area, it will simply be
a cloudy and cold day with perhaps some flurries.
Confidence in snowfall is much greater for southern areas. It is
clear now that a swath of heavy precipitation will overspread the
region. Extreme frontogenetic forcing is allowing precipitation to
expand in coverage and intensity to our southwest, and this will
only continue today. While precipitation is beginning as rain in
some places, temperatures are continuing to cool behind yesterday's
front, and a flip to snow will occur. One possible exception is far
southeast Delaware, where rain or mix could hold on for longer.
Amounts were reduced a bit there. Otherwise, a large stripe of 8 to
12 inches of snow is now forecast, and can't rule out some localized
amounts a little over 12 inches. Snowfall to our southwest has
generally been over-performing, and this trend could continue into
our area. Snowfall rates could easily exceed 1 inch per hour at
times this morning, perhaps 2 inches per hour. While snow ratios
overall will be less than 10:1, these rates will quickly overwhelm
the warm ground conditions left by recent near record warmth. These
snowfall rates could persist for several hours this morning and
early afternoon. Banding features are certainly possible within the
heavy snow shield, leading to some local variations. Eventually,
precipitation will end from west to east late this afternoon and
this evening as the area of low pressure moves out to sea.
Northeast winds will become strong near the coast today, gusting in
the 30 to 40 mph range for several hours. With heavy snow occurring
through this period, a period of near blizzard conditions is
possible for areas such as Sussex County DE and portions of Cape May
and Atlantic Counties. A Blizzard Warning was contemplated, but am
not confident enough in criteria being met for more than brief
periods. Also, don't want to confuse messaging, as it is only a
small area which could potentially see blizzard conditions, and a
blizzard headline would be more symbolic than anything.
Based on the new forecast, have added New Castle, Salem, Gloucester,
and Camden Counties to the Winter Storm Warning. The Winter Weather
Advisory was expanded to eastern Chester County. No other headline
changes were made.
As the snow moves away, frigid temperatures are expected tonight. It
will be the coldest night of the season so far, with all areas
dropping below 20 degrees. Fresh snowpack will exacerbate the
cooling in southern areas, and would not be shocked to see some
single digits over southern NJ by daybreak Tuesday.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
High pressure will translate through the eastern U.S. on
Tuesday, leading to our first sunny and dry day in quite some
time. However, it will also be cold despite the abundant
insolation, given the antecedent cold advection and weak mixing.
Guidance has trended downward over the past couple of days for
maximum temperatures, and given the snowpack for at least the
southeast half or more of the CWA, suspect highs will be lower
than consensus. Trended highs a degree or two lower, and it is
possible they remain a little too optimistic. That may be even
truer for Tuesday night's lows, though by this time, weak return
flow will become established (curtailing a more dramatic
temperature plunge). Nevertheless, it is possible lows are still
several degrees too high in more rural portions of Delmarva and
the Pine Barrens Tuesday night. Future forecasts may adjust
these values once the snowpack becomes established.
A fairly broad trough will be moving through the Midwest and
Great Lakes on Wednesday, with an attendant surface low expected
to move to the Saint Lawrence Valley by Wednesday night. Large-
scale ascent downstream of the trough will begin to generate
some precipitation along or near the East Coast on Wednesday.
Models have trended a little farther east with the development
of this precipitation, which seems reasonable given the
progressive nature of the trough and the moisture-starved
ambient conditions. Any precipitation in our area should be
very light (likely a tenth of an inch or less). Still some
question on the precipitation timing, with an earlier onset more
favorable for a light wintry mix. As stated yesterday, think
this is unlikely, with mostly light rain for our area.
Precipitation chances dwindle quickly by Wednesday night, with
the cold front sweeping through the area. The stronger cold
advection will probably hold off until Thursday, so lows on
Wednesday night will probably be slightly above seasonal
averages.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
Main forecast concern in the medium range is the potential for
snow Thursday night and Friday morning.
Thursday will likely be dry, as a weak surface high progresses
through the Mid-Atlantic, with highs near seasonal averages.
However, this break will be short-lived. A digging vort max in
the central Plains will make a pivot toward the east-northeast
Thursday night as it approaches the Ohio/Tennessee Valleys and
Appalachians. Downstream ridge amplification will have
commenced, leading to a favorable pattern for rapid negative
tilting of the trough. A coupled upper jet structure will
develop over the eastern U.S., with strong and deep ascent
aiding in quick cyclogenesis in the Mid-Atlantic region by
Friday morning. Deterministic models continue to exhibit typical
biases (particularly the GFS, which remains much more
progressive, suppressed, and weaker with the surface low).
However, the ECMWF and CMC appear to be converging, with a track
to the northwest of consensus the past few model cycles (as
expected). There is increasing concern that the result will be a
quick-hitting but potent snow event for portions of the CWA.
The tracks of the ECMWF/CMC would favor a pretty classic WFO PHI
evolution, with potentially heavy snow in the northwest third
to half of the CWA, rain-snow-line issues near the I-95
corridor, and mostly rain near the coast. The track of the GFS
would favor another southern CWA special.
Current thinking is that something closer to the former
scenario is more likely. For now, have mostly snow mentioned
late Thursday night for most of the CWA, with rain/snow and/or
just rain close to the coast (especially by Friday morning).
There has been a tendency for the models to trend later with the
rapid deepening of the system, suggesting that the most
substantial snowfall may be well to our north and east. However,
given the dynamic nature of the system, the potential for a
meaningful winter storm is apparent. Confidence remains lower
than average, given the continued large discrepancies in the
model solutions, so close monitoring of the forecast is advised
in the coming days.
Another aspect of this developing system will be strong winds on
the southwest periphery (i.e., mainly after the precipitation
exits the area). Have nudged forecast winds a little higher for
Friday and Friday night, though my guess is that these are
still under what we will end up observing. Strong cold advection
will bring temperatures to several degrees below average by
Saturday. Saturday night looks cold, as a progressive surface
ridge will likely be in our area.
As large-scale troughing becomes reestablished over eastern
Canada and the Great Lakes, another perturbation looks to move
into the Northeast by Sunday. Though the system overall looks
relatively weak, low-level temperatures will likely be cold
enough for at least the potential for a wintry mix; however,
most guidance indicates this system will be warmer than the one
expected on Friday.
Thanks for everything, VM, and best of luck to you.
&&
.AVIATION /09Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Through today...Starting VFR, however, precipitation and lower
ceilings will be moving into the region through 09Z. The lowest
conditions however are generally expected between 12 and 18Z.
Precipitation may start as a rain/snow mix, but should quickly
change to snow. KABE and KRDG are likely to stay northwest of
all of the precipitation, so should stay VFR through the period.
For the urban corridor TAF sites (KPHL, KPNE, KTTN, and KILG),
prevailing MVFR conditions are expected with temporary IFR
conditions likely during the heaviest periods of snow. For KMIV
and KACY, several hours of IFR, and periods of LIFR/VLIFR are
possible. Conditions should be improving to VFR as the precip
begins to move out of the region after 20Z. Winds starting out
of the NNW less than 10 kt. As the storm gets closer, winds will
shift to northeasterly and increase. Gusts near 30 kt possible
for the urban corridor and coastal plains. Winds should shift
back to northwesterly late this afternoon. Moderate confidence
on most aspects of the forecast including the winds and overall
pattern. Low confidence on timing and flight categories along
the urban corridor as this location will likely be on the edge
of the precipitation for this event.
Tonight...VFR conditions expected. Northwesterly winds near or below
10 kt. High confidence.
Outlook...
Tuesday and Tuesday night...VFR conditions expected. Winds will be
light (less than 10 kt) through out the period. The direction will
be northwesterly to start, becoming southwesterly and eventually
southerly. High confidence.
Wednesday...Starting VFR, but MVFR or lower conditions are possible
through the day as rain moves into the region. KRDG and KABE may be
west of most of the precipitation. South southwesterly wind 10 to 15
knots. Low confidence.
Wednesday night...Conditions should return to VFR through the
evening as the precipitation and low clouds move out of the region.
Southwesterly winds becoming westerly. Wind speeds 5 to 15 knots.
Moderate confidence on the overall pattern, but low confidence on
the timing of the return to VFR conditions.
Thursday...Mostly VFR conditions expected. Westerly winds 5 to 15
knots. Moderate confidence.
Thursday night through Friday...MVFR or lower with snow possible.
Light and variable winds Thursday night, becoming northwesterly 10
to 20 knots with higher gusts on Friday. Low confidence.
Friday night...Returning to VFR conditions with light (less than 10
kt) northwesterly winds. Low confidence.
&&
.MARINE...
Through today... A coastal storm will affect the region today,
bringing strong winds and increased seas to the local waters. With
the most recent forecast, a Storm Warning has been issued for the
Atlantic coastal waters of Delaware, where north-northeast winds
could gust close to 50 kt for a few hours. For all the other coastal
waters, with the exception of Upper Delaware Bay, a Gale Warning
will be in effect today. A stray storm force gust is also possible
for the Atlantic coastal waters of southern New Jersey. On Upper
Delaware Bay, winds will be a little lighter, remaining mostly at
SCA levels though a couple of gale force gusts are possible. Wind
direction will gradually shift from north-northeast to north-
northwest through the day. Seas building to 6 to 8 ft. Rain and snow
expected, which could be heavy.
Tonight... A fairly rapid drop in winds is expected, with winds
falling below gale force early in the night. Gale and Storm
headlines will be converted to SCA's as conditions allow. Seas
remaining 6 to 8 ft.
Outlook...
Tuesday...Seas may linger around 5 feet but should be lowering
with time. Winds are mostly expected to be sub-advisory.
Tuesday night...Sub-advisory conditions expected.
Wednesday through Thursday...Conditions may approach advisory
levels by Wednesday afternoon on the Atlantic waters, with seas
near 5 feet and southwest winds approaching 20 to 25 kt.
Conditions should improve on Thursday.
Thursday night...Mostly sub-advisory conditions expected. Rain
or a wintry mix likely.
Friday...Winds will rapidly increase as they become west to
northwest, with at least advisory conditions expected. Gales
are possible, if not probable, in the wake of the developing
low. Precipitation in the morning rapidly ending by afternoon.
&&
.TIDES/COASTAL FLOODING...
The morning astronomical high tides will remain elevated early
this week due to the new moon.
The wind has shifted to mostly a north direction early this
morning and is expected to remain so for much of the day. The
wind will strengthen as low pressure passes off the coasts of
North Carolina and Virginia on its way out to sea today. The
northerly wind and the associated Ekman transport should work to
push additional water toward the coast. Moderate tidal flooding
is likely this morning in the Delaware counties of Sussex and
Kent, and in the New Jersey counties of Cape May and Atlantic.
Those counties have been placed under a Coastal Flood Warning.
Widespread minor tidal flooding is likely in the other coastal
counties of New Jersey, as well as along the Delaware Bay
shoreline in New Jersey, and up the tidal Delaware River. Those
areas have been placed under a Coastal Flood Advisory for this
morning into the afternoon.
Models have trended upward with tidal levels for the high tides
this evening and Tuesday morning. It is likely that most tidal
areas on the Atlantic coast observe minor flooding with both
tides. We have extended the coastal flood advisory for the
northern New Jersey coast through Tuesday afternoon, as
confidence is high there will be three consecutive rounds of
minor flooding in these areas. Locally moderate flooding cannot
be ruled out, especially with this morning's high tide.
Advisories will likely be required elsewhere on the Atlantic
coast for the evening high tide as well. However, more moderate
flooding is possible on the southern New Jersey and Delaware
coast for the Tuesday morning high tide. Additional coastal
flood warnings may be required.
On upper Delaware Bay and the tidal Delaware River, the
overnight high tide tonight is not expected to produce flooding.
However, minor flooding is again expected for tomorrow's high
tide. Additional advisories may be required in these areas for
that high tide as well.
Widespread minor tidal flooding does not appear imminent on the
upper eastern shore of Chesapeake Bay during this event due to
the development of a brisk north to northwest wind.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 4 PM EST this afternoon for
PAZ070-071-102.
Coastal Flood Advisory from 11 AM this morning to 4 PM EST
this afternoon for PAZ070-071-106.
NJ...Winter Storm Warning until 4 PM EST this afternoon for
NJZ016>018-020>027.
Coastal Flood Advisory until 1 PM EST Tuesday for NJZ012>014-
020-026-027.
Coastal Flood Warning until 1 PM EST this afternoon for
NJZ022>025.
Coastal Flood Advisory from 9 AM this morning to 1 PM EST this
afternoon for NJZ016.
Winter Weather Advisory until 4 PM EST this afternoon for
NJZ013-014-019.
Coastal Flood Advisory from 11 AM this morning to 4 PM EST
this afternoon for NJZ017>019.
Coastal Flood Advisory until 1 PM EST this afternoon for
NJZ021.
DE...Winter Storm Warning until 4 PM EST this afternoon for
DEZ001>004.
Coastal Flood Warning until 1 PM EST this afternoon for
DEZ002>004.
Coastal Flood Advisory from 9 AM this morning to 1 PM EST this
afternoon for DEZ001.
MD...Winter Storm Warning until 4 PM EST this afternoon for MDZ012-
015-019-020.
MARINE...Small Craft Advisory until 6 AM EST early this morning for
ANZ431-450>455.
Gale Warning until 7 PM EST this evening for ANZ431-450>454.
Storm Warning until 6 PM EST this evening for ANZ455.
Small Craft Advisory until 1 AM EST Tuesday for ANZ430.
&&
Synopsis...CMS
Near Term...O'Brien
Short Term...CMS
Long Term...CMS
Aviation...Johnson
Marine...CMS/O'Brien
Tides/Coastal Flooding...CMS/Iovino