discussion on 2024-02-12

000
FXUS61 KOKX 130326
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1026 PM EST Mon Feb 12 2024

.SYNOPSIS...
-- Changed Discussion --Low pressure west of the Appalachians redevelops off the
Delmarva coast Tuesday morning, and intensifies quickly as it
passes south of Long Island Tuesday morning, then heads well
out to sea Tuesday afternoon and night. High pressure will then
return from Wednesday into Thursday before an Alberta Clipper
low passes through Thursday night into Friday. A series of weak
lows may pass across during the weekend before high pressure
returns Monday.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
-- Changed Discussion --Forecast on track and made only minor adjustments for the next
few hours. The adjustments mainly had to do with dewpoint
readings, as they have been coming in observed lower than
previous guidance.

Clouds are in the process of lowering from south to north across
the area with precip, mainly light rain knocking on the door to
the immediate south. Mid level and high end lower clouds over
the area attm will give way to pockets of light rain moving in
from the S and SW over So. NJ and the DC metro area into
Virginia. This precip will advance NE, reaching most places by
07z. P-type will likely start off rain at the coast with temps
falling thru the 30s and a weak elevated warm nose, then mix
with snow/sleet quickly within an hour or two of onset, then
mainly mostly snow towards daybreak as heavier precip starts to
arrive and the column cools, with stronger dynamic cooling to
ensue shortly thereafter. Inland the precip should be primarily
snow.-- End Changed Discussion --

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
* Winter storm to impact the area on Tuesday.

* Winter storm warnings issued for NYC metro and Long Island,
where there is higher confidence in at least 6 inches of
snowfall.

* Guidance continues to trend south. Forecast was originally
based on the 12Z GFS/NAM but made some last-minute changes
based on the 12Z ECMWF/NAM. This could put the metro area and
Long Island more under the axis of higher QPF, with lesser
amts north/west of NYC than originally anticipated.

Model guidance has continued to trend south, with the 18Z
ECMWF/NAM showing a tad less phasing with a northern stream
shortwave trough moving through the Great Lakes. This shift
should lead to lower snowfall amts quite a bit across the
interior, and put the axis of highest QPF either right over
the NYC metro area/Long Island or just south. At the last minute
blended the 12Z ECMWF with the 12Z GFS/NAM which were farther
north. Did not change headlines inland but lowered snowfall amts
to the 6-9 inches range across the interior, and if the
southward trend continues it is possible that northern areas may
less less than 6 inches of snowfall.

Meanwhile confidence has increased enough in higher snowfall
totals for the NYC metro and Long Island to upgrade watches to
warnings for those areas. Amts will be in the 4-7 inch range
around the NYC metro area were blyr temps will remain a little
warmer than areas to the NW and also across Long Island. Per
earlier forecasts of favorable deformation/frontogenetic
forcing near the coast and negative EPV* atop the frontogenetic
layer, there could be some slantwise instability and perhaps
some isolated thunder as the heaviest precip moves across in the
morning.

QPF of 1.00-1.25 inches expected only across the NYC metro area
and Long Island, with lesser amts of 3/4 to 1 inch to the north.

Snow ratios at the coast will likely be low at the onset, but
then increase as the snow becomes heavy (with rates at least
1-2 inches/hour) and low level winds become more northerly.

In addition, NE-N winds at the height of the storm will gust to
30-40 mph, strongest along the coast. This could further
restrict visibilities. However, with the wet nature of the
snow, blowing snow should be at a minimum and any blizzard-like
conditions should be short-lived.

NW winds on the back side of the low gradually subside Tuesday
night with clearing skies. Lows will be close to normal, in the
20s.

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
No major changes have been made to the long term Wednesday
through early next week.

Key Points:

* Temperatures look to be below normal through the weekend
before a slight warming trend early next week.

* A fast moving clipper system passes across the northeast
Thursday night followed by another potential fast moving
system early in the weekend.

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. The latest consensus takes the surface low
north of our area, which introduces slightly warmer air.
Moisture is still limited, but there is a brief window Thursday
night for enough lift to raise PoPs to high chance. NBM precip
probabilities continue support predominately snow showers
inland, but mainly rain with some wet snow mixed in 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. This is a fast moving system which limits the
amount of precip that could fall.

High pressure briefly returns Friday before modeling diverges
Friday night into the weekend. Another fast moving northern
stream shortwave approaches and could bring another clipper type
low. It is beginning to look like the northern stream will be
more suppressive and force any southern energy well south of the
area. It is still about 6 days out so the evolution could still
change. PoPs on the model consensus remain low with just a
chance of snow showers Friday night into Saturday. Uncertainty
increases further on Sunday as there could be another piece of
northern stream energy passing through, but moisture right now
looks very limited. High pressure may return early next week.

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --*Significant winter storm to impact the terminals Tuesday.

Low pressure approaches from the southwest overnight, passing south
of the area on Tuesday, before moving away late Tuesday and Tuesday
evening.

The winds will be light initially, then begin to increase after 06z.
Precip arrives generally 05-06z for most terminals with MVFR
following within an hour or two. Precip begins as rain briefly, or a
rain/snow mix at coastal terminals, but changes to snow with IFR
conditions for all terminals by 9-12z. A low end chance remains that
some ice pellets mix in during the transition from rain to snow, but
confidence of occurrence is not high enough and duration not long
enough to warrant including in the TAF. Snow then continues through
early Tues afternoon, and will be heavy at times during the morning
with VLIFR conditions. The snow tapers in the afternoon, with dry
conditions and VFR returning by late afternoon.

Winds under 10kt to start, then NE winds increase overnight into the
Tuesday AM push, and will probably be strongest towards the tail end
of just after the AM push, with sustained winds around 20kt and
gusts around 30kt from 13z-17z from NE, then N. Winds back toward
the NW late Tues aftn with gust still 20-25kt.

Forecast Airport Snowfall Totals:

KJFK/KLGA/KEWR/KTEB/KSWF: 5-8 inches

KISP/KHPN/KBDR/KGON: 6-10 inches

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

Amendments will be needed for flight category changes and
probably precip type timing adjustments approaching the morning
push. Precip at onset may be all snow at some of the terminals
instead of a rain/snow mix or all rain.

OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY...

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

Thursday: VFR.

Thursday night: Chance of MVFR and snow showers or mixed rain/snow
showers. NW winds G25kt late.

Friday: VFR. NW winds G25-30kt.

Saturday: Chance of MVFR/IFR with snow showers.

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

.MARINE...
-- Changed Discussion --NE winds increase overnight 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 remaining in effect. SCA in effect elsewhere with gusts
mostly 25-30 kt, though a few gusts to 35 kt may be possible on
the eastern Sound and the bays of Long Island. Winds on the
waters will weaken somewhat Tuesday night as the storm departs,
with SCA cond continuing mainly on the ocean and ern waters.

A steepening pressure gradient Wednesday will lead to SCA
conditions on all waters with potential for gale force gusts on
the ocean. Winds begin to weaken on the waters Wednesday
night, falling below SCA levels Thursday before potentially
reach SCA levels Thursday night into Friday. Ocean seas will be
elevated through Wednesday night before briefly subsiding below
5 ft Thursday. Elevated seas are briefly possible Friday but
should be below SCA levels next Saturday.-- End Changed Discussion --

.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 to locally moderate coastal flooding with
the Tuesday morning/midday high tides.

* Minor coastal flooding likely Tuesday Night for the south
shore of Nassau County and coastal Westchester and Fairfield

Forecast is based on 50th percentile Stevens NYHOPS, ETSS, and
ESTOFS blend guidance, which tends to do well with these NE to N
system. PETSS guidance appears to be too high based on this
setup.

A coastal flood advisory remains in effect for the south shore
of Nassau County and coastal Westchester and Fairfield for the
high tide cycles tonight.

Winds quickly ramp up to NE gales early Tuesday morning,
backing to the N through the time of high tide. Widespread
moderate flooding (2 to 2 1/2 ft agl) expected for southern
Nassau Tue AM, with widespread minor elsewhere. Locally moderate
coastal flood impacts possible for Jamaica Bay and SW Suffolk
due to tidal piling accentuated on north facing shores, as well
as north facing shorelines of LI and twin forks due to 2 to 4
ft wave actions.,

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.

For the ocean beach front, 3 to 6 ft breaking surf will likely
cause beach flooding and beach escarpment during the Tuesday
morning and night high tides. Dune erosion impacts area expected
to be localized and minor.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...Winter Storm Warning until 6 PM EST Tuesday for CTZ005>012.
Coastal Flood Advisory until 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 until 6 PM EST Tuesday for NYZ067>071.
Coastal Flood Advisory until 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 until 2 AM EST Tuesday for NYZ179.
Coastal Flood Warning from 8 AM to 3 PM EST Tuesday for NYZ179.
NJ...Winter Storm Warning until 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 --

SYNOPSIS...BG/DS
NEAR TERM...JE/BG
SHORT TERM...BG
LONG TERM...DS
AVIATION...JE
MARINE...BG/DS
HYDROLOGY...BG/DS
TIDES/COASTAL FLOODING...