NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Feb 1, 4:08 AM EST, 4 hours 52 minutes earlier.
Area forecast discussion, Feb 1, 4:08 AM EST, 4 hours 52 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
408 AM EST Mon Feb 1 2021
.SYNOPSIS...
Low pressure will slowly track up the Mid-Atlantic coast through
Tuesday, moving into the Canadian Maritimes on Wednesday. High
pressure will build in from the west Thursday, moving offshore
Friday. A cold front will cross the region Friday night into
Saturday. High pressure builds in on Saturday into Sunday. Low
pressure will develop along the southeastern coast and track up
along the Mid-Atlantic coast Sunday into Monday.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Summary: The significant winter storm will continue to impact the
area today with effects likely lingering into Tuesday.
The first round of primarily WAA driven precipitation performed
roughly as expected with widespread 2-5 inch totals, with isolated
totals of 6+ inches. The area now finds itself in a general lull in
heavier precipitation, and a myriad of light ptypes is being
observed...generally snow in the interior, sleet/FZRA near I-95, and
rain close to the coast.
This lull will only be temporarily for most of the area as the
coastal low is beginning to organize to our south and will intensify
and meander slowly northward today. A strong (60-70kt) 850mb ENE
jet will develop on the NW flank of the low, and low-lvl convergence
from this jet will promote robust FGEN over portions of our area.
This FGEN combined with increasing mid-lvl height falls, will
support a region of enhanced ascent which will manifest itself as an
intense band of heavy snowfall. Furthermore this band will only
pivot slowly cyclonically through the region and areas near the
pivot point will likely experience a prolonged period of heavy snow.
Unfortunately, particularly when considering it is only a 6-18 hour
lead time, AM guidance exhibits alarming levels of disagreement over
where the aforementioned band will set up and (very important for
the I-95 corridor) where the SE extent of the resultant snowfall
gradient ends up. Most of the CAMs depict a rather robust dry slot
enveloping the southern half or so of the forecast area, with
QPF/snowfall quite limited south of approximately I-195. Conversely
most of the globals/mesoscale models depict a broader shield of
precipitation with the axis of heaviest precipitation positioned
further south and west then the hi-res consensus.
The hi-res solutions make physical sense as regions of strong ascent
would typically be bordered by regions of strong subsidence.
However, at the same time the hi-res guidance appear to be
struggling in getting a handle on the coastal low's general
evolution and track, and these errors could result in incorrectly
placing the region of best FGEN. Consequently did my best to
compromise between the two disparate solutions, creating a tighter
gradient in snowfall, but it is still broader than what the CAMs
depict. The highest uncertainty in the snowfall forecast lies along
the I-95 corridor south of I-195, with additional uncertainty also
present in SE PA west of KABE. An evolution similar to what the hi-
res guidance depicts would result in fairly low amounts of snowfall
in this zone, with amounts potentially as meager as 1-3 additonal
inches. Conversely as much as 8-12 inches of additional snowfall
would be possible if the heavier band of precipitation sets up a bit
further south than the hi-res guidance depict.
The forecast is more straightforward for our northern areas, as the
band will almost certainly set up over them for an extended period
of times and new snow amounts in the 18-24 inch range are possible
if not probable. Additionally the forecast is pretty simple for
coastal areas and most of Delmarva (apart from New Castle county)
where precipitation will be rain for the balance of the day.
Additionally winds will be rather strong today due to the proximity
of the intensifying low. Widespread gusts of 35-40 mph are
expected, and gusts in excess of 50mph are possible along the
immediate coast (where wind headlines remain in effect). Blowing and
drifting of snow will be possible as well, particularly in northern
areas where the snow in general is of lower density.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
The low remains remains stalled just off the NJ coast through
Tuesday as the mid-lvl low amplifies and essentially becomes cut-off
just overhead. Lingering wrap-around precipitation will likely
continue through Tuesday. There are also hints in some of the
guidance of a TROWAL feature continuing to support light-moderate
precipitation on Tuesday aided by additional lift from vort maxes
pivoting around the mid-lvl low. If such a feature develops the
current forecast may be underplaying snow amounts in this timeframe,
but given the considerable uncertainty in the near term forecast
preferred to go the conservative route with snowfall accumulations on
Tuesday. Otherwise winds will decrease through the period as the
coastal low occludes and weakens (a tertiary low actually develops
near New England as it does so).
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
A relatively quiet start to the extended for Wednesday into Thursday,
before unsettled weather returns for the end of the week into the
weekend.
On Tuesday night, a series of low pressure systems will continue to
drift northward offshore of the northeast coast. As this happens,
there will continue to be several short waves embedded within the
cyclonic flow of the slow moving mid level low drifting across the
northeast as well. The lift associated with the short waves will
combine with some enhanced moisture and continue to the chance for
scattered showers into Tuesday night.
Wednesday is expected to be a breezy day as high pressure begins to
approach from the west with low pressure to the northeast. Winds are
expected to gust 25-35 mph at times through the day. There remains
some moisture around the area as well as some short wave/vorticity
impulses, so it would not be surprising to see some flurries around
the area, but chances are too small to include at this time.
High pressure will nose its way up the east coast into the Mid
Atlantic region late Wednesday night into Thursday, so dry weather
will continue through Thursday.
A warm front is forecast to move into the area Thursday night,
before a cold front moves across the area on Friday and offshore
Friday night. This will bring our next chance of precipitation to
the area. Depending on when the precipitation beings, it may begin
as a brief period of snow, before changing to rain through the day
Friday, then back to snow as the precipitation ends Friday evening.
As we move into the weekend, models begin to diverge with their
forecasts. The GFS is faster developing a low pressure system and
moving to the northeast, offshore of the Mid Atlantic coast Saturday
into Saturday night. The ECMWF is slower, bringing it near the
area Sunday into Sunday night, as does the Canadian. Due to the
uncertainty of the models, we will keep a chance of
precipitation for Saturday through Sunday.
&&
.AVIATION /09Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today...IFR conditions likely through much of the day. Visibilities
will be variable. Mainly snow expected at KABE, KRDG, and KTTN.
FZRA/PL remain possible at KPNE, KPHL, and KILG through around 12Z
with a changeover back to snow, though a mix may remain through
as late as 15Z. Rain at KMIV and KACY may mix with or change
back over to snow this afternoon. Northeast winds around 15 to
25 knots with gusts around 30 to 40 knots. Low confidence on
intensity and timing of precipitation changes.
Tonight...Mainly IFR conditions expected in snow with varying
visibilities. Expect KMIV and KACY to change back over from rain to
snow. North winds 10 to 20 knots with gusts up to 30 knots.
Outlook...
Tuesday...Mainly IFR conditions expected. The snow continues into
Tuesday, though it will lighten and conditions will gradually
improve as the snow comes to an end. North to northwest winds around
10 to 15 knots with gusts of 25 to 30 knots. Moderate confidence.
Wednesday...VFR. Northwest winds 15 to 20 knots with gusts up to 30
knots, dropping off to around 10 knots at night. Moderate confidence.
Thursday...VFR. West winds 5 to 10 knots, becoming light southwest.
Moderate confidence.
Friday...MVFR or lower conditions possible in rain. Southwest winds
around 10 knots. Moderate confidence.
&&
.MARINE...
Needless to say it will be a bad day to be out on the waters as
winds will likely gust to storm force off the NJ coast with gale
force gusts off the DE coast and over DE Bay. Additionally seas in
the 15-20 ft range look likely over the northern ocean waters this
afternoon.
Winds as seas will begin to come down tonight, but likely remain
above SCA criteria for some time as the coastal low remains in our
vicinity.
Outlook....
Tuesday night-Wednesday night...Small Craft Advisory conditions are
expected from Tuesday night through Wednesday night, although winds
could approach Gale force Tuesday night into Wednesday.
Thursday...Conditions likely fall below advisory levels Thursday.
Thursday night-Friday...Winds may increase back to Small Craft
Advisory levels.
&&
.TIDES/COASTAL FLOODING...
Strong onshore, east to northeast winds will continue today through
tonight, before winds begin to shift more offshore in some areas by
Tuesday. Guidance continues to indicate widespread Moderate coastal
flooding with the high tide today and tonight, with widespread minor
to moderate coastal flooding on Tuesday on the Atlantic Ocean and
portions of Delaware Bay. The Coastal Flood Warning and Advisory
were left unchanged.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Storm Warning until 1 PM EST Tuesday for PAZ054-055-061-
062-105-106.
Winter Storm Warning until 10 AM EST Tuesday for PAZ060-070-
071-101>104.
NJ...Winter Storm Warning until 1 PM EST Tuesday for NJZ001-007>010-
012>015-020-027.
Winter Weather Advisory until 10 AM EST Tuesday for NJZ021>023-
025-026.
Coastal Flood Advisory from 10 AM this morning to 5 PM EST
Tuesday for NJZ021.
Coastal Flood Warning from 7 AM this morning to 5 PM EST
Tuesday for NJZ012>014-020-022>027.
High Wind Warning from 7 AM this morning to 10 PM EST this
evening for NJZ025-026.
Wind Advisory from 7 AM this morning to 7 PM EST this evening
for NJZ024.
Winter Storm Warning until 10 AM EST Tuesday for NJZ016>019.
DE...Winter Weather Advisory until 10 AM EST Tuesday for DEZ002.
Coastal Flood Warning from 7 AM this morning to 5 PM EST
Tuesday for DEZ003-004.
Wind Advisory from 7 AM this morning to 7 PM EST this evening
for DEZ004.
Winter Storm Warning until 10 AM EST Tuesday for DEZ001.
Coastal Flood Warning from 10 AM this morning to 5 PM EST
Tuesday for DEZ002.
MD...Winter Weather Advisory until 10 AM EST Tuesday for MDZ015.
Winter Storm Warning until 10 AM EST Tuesday for MDZ012.
MARINE...Storm Warning until 10 PM EST this evening for ANZ450>453.
Gale Warning until 6 AM EST Tuesday for ANZ454-455.
Gale Warning until 10 PM EST this evening for ANZ430-431.
&&
Synopsis...Meola
Near Term...Carr
Short Term...Carr
Long Term...Robertson
Aviation...Meola
Marine...Carr/Robertson
Tides/Coastal Flooding...Robertson