discussion on 2024-02-12

000
FXUS61 KOKX 121845
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
145 PM EST Mon Feb 12 2024

.SYNOPSIS...
Weak high pressure across the area today will give way to a
storm system approaching from the southwest. Deepening low
pressure moves into the Tennessee Valley tonight with a
secondary forming near the Delmarva region Tuesday morning. The
coastal low will deepen while passing to the south and east of
Long Island during the day Tuesday. High pressure will return
from Wednesday into Thursday before an Alberta Clipper low
passes through Thursday night into Friday. Another low may
impact the region next weekend.

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Weak high pressure will remain across the area today as the
area resides on the northern edge of high clouds associated with
a storm system over the southern states. Skies may vary between
mostly cloudy across Long Island/NYC metro, to partly/mostly
sunny inland. It will be another mild day with highs in the
lower 50s in NE NJ, and mid/upper 40s elsewhere.-- End Changed Discussion --

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
* Major winter storm to impact area late tonight into Tuesday.

* Guidance has trended colder the last 24h with the potential
for 6+ inches across coastal locations. Winter storm warnings
remain in effect for all of southern CT, the lower Hudson
Valley, and adjacent portions of NE NJ. The urban corridor of
NE NJ, NYC, and Long Island remain in a Winter Storm Watch.

* Confidence is high across CT, the Lower Hudson Valley, and
interior NE NJ for 6+ inches of snow. There is medium
confidence for the watch area for 6+ inches, with high
confidence of 3+ inches.

* The greatest uncertainty is across the NYC metro area and Long
Island for the timing of rain changing over to snow. At this
time, this looks to be around 7-8 AM Tuesday at the latest.

Overall model guidance in recent says has been pretty good with
respect to the track of low pressure that will impact the area
late tonight into Tuesday, Where there has been uncertainty is
with the rain/snow line across the area with only a marginally
cold airmass in place. However, the last 24h specifically, from
the 11/18Z cycles and beyond, there has been enough of a
southward trend of the low to expand the potential for 6+ inches
down to the coast. The southward trend has also placed the area
in a favorable area for heavy banded snow to the north and west
of the low track, with favorable deformation/frontogenetic
forcing with the H8 and H5 lows to the south of the area, even
some negative EPV* atop the frontogenetic layer which could
lead to slantwise instability and even some isolated thunder.

There is good agreement with 1-1.25 inches of liquid equivalent
with the possibility of locally higher amounts. Interior
locations and even down to coastal CT may see some brief rain at
the onset, but this is largely an all snow event for these
locations. Even across Long Island and NYC, with the changeover
occurring near daybreak, there could be 0.75 to 1" of liquid
equivalent that is snow. Snow ratios at the coast will likely
be low at the onset, but then increase as the snow becomes heavy
and low- level winds become more northerly. For thermodynamic
profiles, used a blend between the colder NAM and warmer GFS.
This should result in temperatures at the height of the heaviest
snow in the lower 30s. For snowfall totals, expecting 8 to 12
inches in the warning area and the potential of 5 to 8 inches in
the watch area. SPC HREF showing high probabilities of more
than an inch an hour inland with even 50-60% probs some hours at
the coast. There could be some hours, especially inland of 2 to
3 inches an hour.

Much of the precipitation moves in during the early morning
hours Tuesday, becoming heaviest toward daybreak into early
afternoon. Snow ends from west to east in the afternoon. In
addition, NE to N winds at the height of the storm will gusts 25
to 35 mph, strongest along the coast. There could even be a few
higher gusts up to 40 mph. This will further restrict visibilities.
However, with the wet nature of the snow any blizzard-like
conditions are expected to be of short duration.

NW winds on the backside of the low gradually subside Tuesday
night with clearing skies. Lows will be close to normal and
mainly in the 20s.

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
There has not been too much change to the forecast thinking
Tuesday night into next weekend.

*Key Points*

* Temperatures look to be below normal with mainly dry
conditions this period.

* A fast moving clipper system passes across the northeast
Thursday night.

* Forecast confidence lowers next weekend as there are some
indications of another low pressure moving near the region.

High pressure builds towards the eastern seaboard on Wednesday.
The ridge axis will be over the area Wednesday night before
shifting offshore on Thursday. The deterministic and ensemble
means are in good agreement on this scenario. A fast moving
Alberta Clipper low continues to be signaled on the guidance for
Thursday night. A general consensus has the surface low passing
over New England. Overall moisture is limited, but there should
be a brief period of lift to continue with chances of
precipitation. NBM precip probabilities support predominately
snow showers inland, but a mix of rain and snow showers to the
coast. The more northern track of the clipper low would
introduce slightly milder air towards the coast. If the low were
to trend further south, colder air and higher chances of a
period of snow showers could occur across the entire area. It is
important to note this is a fast moving system which limits the
amount of precip that could fall.

The modeling diverges Friday into the upcoming weekend. Another
fast moving northern stream shortwave may approach next Saturday
and could have some interaction with a southern stream system.
Other guidance hints that the northern stream may be suppressive
limiting any precip chances and low pressure development. It is
still much too early for any details on p-types and impacts as
each scenario seems plausible. For now NBM slight chance PoPs
Saturday into Saturday night look reasonable.

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --*Significant winter storm to impact the terminals on Tuesday

High pressure remains in control through this evening. Low
pressure approaches the region from the southwest tonight
passing south of the area on Tuesday.

VFR with light winds for the rest of today into early this
evening. Precip arrives generally 04-06z for most terminals with
MVFR following within an hour or two. Precip begins as rain or
a rain/snow mix at the coast, but changes to snow with IFR
conditions for all terminals by 11-13z. A low end chance
remains that some ice pellets mix in during the transition from
rain to snow, but this should be brief and confidence is not
high enough to include in the TAF. Snow then continues through
early Tues afternoon, and will be heavy at times during the
morning. Dry with VFR arriving late afternoon.

Winds under 10kt through around midnight. NE winds then increase
late tonight and will probably be strongest during the morning
push with sustained winds around 20kt and gusts around 30kt.
Winds back toward NW Tues aftn with gust still around 25kt.

Forecast Airport Snowfall Totals:

KJFK: 4-6 inches

KEWR/KLGA/KISP: 6-8 inches

KTEB/KHPN/KBDR/KGON/KSWF: 9-14 inches

...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

No unscheduled amendments expected through 03Z Tuesday.
Amendments may be needed to flight category changes and timing
of precip changes.

OUTLOOK FOR 18Z TUESDAY THROUGH SATURDAY...

Tuesday aftn...Snow ending and improving to VFR by late. NW
gusts around 25kt.

Tuesday night through Wednesday night...VFR. NW winds G20-25kt
during the nights and around 30kt Weds daytime.

Thursday: VFR.

Thursday night: Chance of MVFR and snow showers or mixed rain
and snow showers. NW gusts around 25kt late.

Friday: VFR. NW gusts 25-30kt.

Saturday: Chance of MVFR/IFR and snow showers.

Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --

.MARINE...
Quiet conditions today with weak high pressure across the
waters.

NE winds increase tonight ahead of an approaching deepening low
pressure system from the southwest. The low then passes just
south and east of the ocean waters on Tuesday. This will allow
winds to reach gale force on the ocean on Tuesday, with a gale
warning now in effect. A few gusts to 35 kt may also be possible
on the eastern Sound and the bays of Long Island, with SCA cond
elsewhere.

Winds on the waters will weaken somewhat Tuesday night as the
storm system departs. This will be short-lived as high
pressure builds in from the west Wednesday increasing the
pressure gradient. SCA winds are likely on all waters and there
is even a chance for gale force gusts on the ocean. Winds begin
to weaken on the non-ocean waters Wednesday night could remain
near SCA levels on the eastern Bays and eastern Long Island
Sound with ocean still 25-30 kt. Winds should fall below SCA
levels Thursday before potentially reach SCA levels Friday
behind a departing Clipper low pressure. Ocean seas will be
elevated Tuesday night through Wednesday night before briefly
subsiding below 5 ft Thursday. Elevated seas are possible to end
the week.

.HYDROLOGY...
There are no hydrologic issues expected at this time.

.TIDES/COASTAL FLOODING...
* Minor coastal flooding is likely during times of high tide
through tonight.

* Widespread minor and some moderate coastal flooding becoming
more likely with the Tuesday morning/midday high tides.

Forecast continues to be heavily based on Stevens NYHOPS
guidance, which has been performing reasonably well over the
past 24 hours.

Have decided to leave the coastal flood statement for coastal
Fairfield/Westchester running through early this afternoon
with the expectation of minor thresholds just being reached at
the Stamford and Bridgeport gauges. A better chance of more
widespread coastal flooding will be possible tonight, so have
gone ahead and issued a coastal flood advisory for tonight`s
high tide cycle.

A coastal flood advisory remains in effect for the south shore
of Nassau County for the high tide cycles today and tonight.
Further west, most of the guidance has the high tides falling
just short of reaching minor thresholds.

Depending on how some of the tides behave with todays high tide
cycles, a statement or advisory may be needed tonight. Areas
that might eventually need an advisory include southwestern
Suffolk, southern Queens, southern Brooklyn, Lower NY Harbor and
parts of western Long Island Sound. Nassau County already has
an advisory up.

Have not changed any headlines for Tuesday, there`s enough
confidence in moderate flooding to put up a coastal flood
watch for Southern Nassau County. Localized moderate coastal
flooding is possible for Southwestern Suffolk County. Otherwise,
widespread minor coastal flooding is looking more probable for
all but along the eastern Sound and along Peconic/Gardiners
Bays. Just like Monday night, there`s still time to gain more
confidence in the extent of minor flooding before issuing
headlines. Timing of a wind shift from NE to N on Tuesday brings
some uncertainty on how quickly some drainage help could occur
as well as the amount of time the north shore of Long Island is
exposed to a more direct onshore flow.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...Winter Storm Warning from 1 AM to 6 PM EST Tuesday for
CTZ005>012.
Coastal Flood Advisory from 11 PM this evening to 2 AM EST
Tuesday for CTZ009.
Coastal Flood Advisory from noon to 4 PM EST Tuesday for
CTZ009-010.
Coastal Flood Advisory from 11 AM to 4 PM EST Tuesday for
CTZ011-012.
NY...Winter Storm Warning from 1 AM to 6 PM EST Tuesday for
NYZ067>071.
Coastal Flood Advisory from 11 PM this evening to 2 AM EST
Tuesday for NYZ071.
Coastal Flood Advisory from noon to 4 PM EST Tuesday for
NYZ071-073-078-176-177.
Winter Storm Warning from 4 AM to 6 PM EST Tuesday for
NYZ072>075-078>081-176>179.
Coastal Flood Advisory from 8 AM to noon EST Tuesday for
NYZ072-074-075-178.
Coastal Flood Advisory from 8 AM to 5 PM EST Tuesday for
NYZ079>081.
Coastal Flood Advisory from 8 PM this evening to 2 AM EST
Tuesday for NYZ179.
Coastal Flood Warning from 8 AM to 3 PM EST Tuesday for NYZ179.
NJ...Winter Storm Warning from 1 AM to 6 PM EST Tuesday for NJZ002-
004-103>105.
Winter Storm Warning from 4 AM to 6 PM EST Tuesday for NJZ006-
106>108.
Coastal Flood Advisory from 8 AM to noon EST Tuesday for
NJZ006-106-108.
MARINE...Small Craft Advisory from 5 AM to 6 PM EST Tuesday for ANZ331-
332-335-338-340-345.
Gale Warning from 6 AM to 6 PM EST Tuesday for ANZ350-353-355.-- End Changed Discussion --

AVIATION...JC