discussion on 2023-11-19

000
FXUS61 KOKX 191739
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1239 PM EST Sun Nov 19 2023

.SYNOPSIS...
A cold front approaches today and moves across tonight. Strong
high pressure from the Great Lakes then builds in through
Monday night. High pressure moves offshore Tuesday, followed by
a complex frontal system and associated low pressure for
Tuesday night into early Wednesday. High pressure builds for
Wednesday night through Friday. Low pressure may approach next
weekend.

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --The forecast remains mostly on track. Made minor adjustments to
hourly temperatures.

A cold front will approach from the northwest today. Ahead of
the cold front, vertical mixing is expected to be efficient,
resulting in a breezy day. Temperatures will be climbing well
into the 50s along the coast and within NYC as well as Northeast
NJ with relatively cooler temperatures across the interior.
Downsloping with the NW flow will allow for this temperature
gradient between coast and more inland locations.

Clouds increase late day ahead of the cold front but did not
mention rain showers as sounding profiles show much dry air.
Also, the latest HRRR has been trending weaker with rainfall
showers associated with the cold front. Earlier runs of
mesoscale weather forecast models also indicate some rain
shower activity across mainly SE Connecticut and Eastern Long
Island.

Most of the forcing indicated by the large scale weather
forecast models is conveyed to be across central and northern
New England where the positive vorticity advection will be much
greater with approaching mid level trough axis.

There will be not enough forcing to sustain the rain showers
and too much dry air, such that rain will likely evaporate
before reaching the ground. Have some minimal POPs of near 5 to
10 percent for rain showers, and this is not enough to warrant
mention in the forecast.-- End Changed Discussion --

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
A cold front moves across this evening. Gusty winds continue
with increased cold air advection behind the cold front. As
mentioned in the near term, the limited forcing and moisture
will keep this frontal passage mainly dry. There will be extra
clouds the first half of tonight with this frontal passage.

The large scale weather forecast models indicate mid level
ridging overnight into early Monday morning as a mid level ridge
approaches from the west. This will give subsidence with
clearing sky conditions.

The pressure gradient however will still be steep enough to keep
boundary layer winds up overnight with some occasional gusts
quite possible, especially along the coast. For low temperatures
forecast late tonight, used the MET guidance with temperatures
ranging from the mid 20s to upper 30s. This guidance keeps
coastal locations relatively warmer with lows compared to
farther inland.

Strong high pressure builds in for Monday and Monday night. Much
cooler temperatures expected Monday and Monday night with cold
air mass within the region.

Forecast high temperatures Monday range mainly in the low to mid
40s with some upper 40s for portions of NYC and portions of
Northeast NJ. This will be about 10 degrees colder than high
temperatures the previous day.

Winds will be on a decreasing trend Monday into Monday night with
eventually light to calm winds Monday night as the pressure
gradient weakens. There is some uncertainty in the forecast
Monday night with the cloud cover. The large scale weather
forecast models have the center of the high pressure north of
the region with an approaching frontal system from the west.
Some have widespread cirrus moving in Monday into Monday night
with some indicating the cirrus not moving until late Monday
night.

The current forecast sides with bringing in cirrus later
Monday night. This will make for more uncertainty in the low
temperature forecast and the differences in radiational cooling.
Used a combination of MAV, MET, and NBM for lows forecast,
ranging from the lower 20s to mid 30s. Some parts of the area
where growing season is still active, within NYC, Hudson NJ, and
Southern Nassau NY are forecast to have lows around freezing but
with the uncertainty and potential for at least several degrees
temperature change in subsequent forecasts, did not want to put
up any freeze watch or frost advisories at this time.

.LONG TERM /TUESDAY THROUGH SATURDAY/...
The main feature of the long term period will be a complex
frontal system and associated low pressure that is expected to
impact the region late Tuesday and Tuesday night, into early
Wednesday.

On Tuesday an upper ridge will be moving off the east coast as
a deep upper trough moves through the Upper Midwest and
Tennessee Valley. The upper trough will be progressive and swing
across the eastern states Tuesday night into Wednesday morning.
The biggest uncertainty is the energy in the SW states and how
much of that energy gets involved in the trough as it swings
east and into our area. The GFS gets more of the SW US energy
involved, while some of the other global guidance does not and
hangs much of the SW energy back to the west, and thus the
system deamplifies as it progresses through towards mid week.
These details will be important in ultimately determining how
potent this storm system will be, and the impacts for our area.

Meanwhile, the primary low will lift northeast and up the
Tennessee and Ohio Valleys, while a secondary will form likely
in the Mid Atlantic towards the Delmarva and track nearby and
just south or east of the region. With the high pushing offshore
and a return flow out of the SE and off the warmer ocean,
expect precip to be mainly plain rain at the onset, although a
few wet flakes at the start cannot be ruled out well N and NW. A
strong surge of warm advection in the lower and mid levels is
expected with the NAM and GFS suggestive of a strong LLJ and
frontogenetic forcing. The LLJ at 925 mb may reach 50 to 60 kts
with strong isentropic lift along the warm front and PWATs
increasing to around over an inch Tuesday night, with periods of
moderate to heavy rainfall possible. While the system will be
progressive, 1 to 1.5 inches of rainfall is a good possibility,
with locally higher amounts of up to 2 inches. Progs show
little elevated CAPE and little instability however at this
time. WPC has placed SW portions of the area in a marginal risk
of excessive rainfall.

The system is expected to get offshore by Wed afternoon as
drier air comes in. The GFS with its more robust and slightly
trailing upper level feature tries to spin up a double barrel
south to north low, but there is little support from the other
models camps. As low pressure moves away and deepens offshore a
northwest flow will usher in drier air. Afterwards, the
uncertainty increases for late in the week as most of the global
models indicate more southern branch energy into the Gulf and
SE states. The Canadian continues to advertise a system coming
out of the Gulf and deep south with low pressure bringing rain
to the region as the low tracks along the eastern slopes of the
Appalachians and hugs the coast on Friday. While the GFS and
German guidance continues to hold energy back until late Sat and
Sat night with possible low pressure emerging from off the SE
coast and it lifts north and offshore, with runs of the European
being in-between the Canadian and the GFS/German guidance.
These timing difference all have to do with the handling of
southern branch energy. The results are varying outcomes in
terms of the sensible weather for the tail end of the week.

In summary, after rain and wind for late Tue into early Wed,
look for clearing and drier conditions late Wed into the
Thanksgiving holiday. Uncertainty then increases for Friday into
Saturday. After above normal temperatures for late Tue into
Wed, look for temperatures to fall back to near normal on
Thanksgiving, and slightly below normal for late in the week.

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --A cold front passes this evening. High pressure will then
gradually build in from the north and west going into Monday.

VFR conditions expected to prevail through the TAF period. Very
low possibility of a rain shower towards KGON late today into
this evening but this is not included in TAF.

W winds become NW tngt behind the front. Peak gusts around 25
kt. Winds diminish overnight.

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

Timing of gusts could be 1-3 hours off from TAF.

OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY...

Mon: VFR with N winds. Ocnl gusts to 20 kt possible.

Tue: VFR to start, then MVFR and lower in rain. SE winds
10-20kt.

Tue night: IFR with rain. SE winds up to 25 kt. 2k ft winds
around 40kt with marginal llws.

Wed: MVFR possible with NW flow.

Thu: VFR with NW flow.

Fri: VFR with N flow.

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

.MARINE...
SCA continues on the ocean with sub-SCA conditions on non-ocean
waters today. The ocean SCA has been extended into Monday
morning. SCA is also in effect for non-ocean waters starting at
3PM this afternoon and going through tonight with 25 kt gusts
expected for much of the time period. For Monday, ocean SCA
could hold on into afternoon but confidence is low on wave
forecast and wave heights could be off by 1-2 ft so did not want
to extend too much with ocean SCA. SWAN guidance was
overestimating wave heights by about 1 ft overnight across parts
of the ocean. Otherwise, non-ocean waters expected to be below
SCA Monday. All waters expected to be below SCA Monday night.

A east flow becomes southeast and increases Tuesday in advance
of a complex frontal system and associated low pressure. Small
craft conditions will arrive either later in the day or by
evening and through at least Tuesday night, and likely into the
Wednesday. A period of gales cannot be ruled out, especially on
the ocean waters and eastern nearshore waters Tuesday night and
Wednesday morning. Behind the frontal system the winds will
switch to the northwest for Wednesday afternoon and Wednesday
night. The NW flow will continue into Thursday with marginal
small craft conditions likely persisting on the ocean, and
possibly for a portion of the nearshore waters.

.HYDROLOGY...
Mainly dry conditions are forecast through Tuesday with no
hydrologic impacts expected.

Moderate to heavy rain is likely Tuesday night into early
Wednesday morning, with minor and nuisance flooding possible.
There is the potential for 1 to 1.5 inches of rainfall, with
locally higher amounts up to 2 inches possible. WPC has placed
southwestern portions of the area in a marginal risk of
excessive rainfall for this system.

.TIDES/COASTAL FLOODING...
While astronomical tides remain relatively low into the beginning of
the week, an increasing southeast flow Tuesday afternoon and Tuesday
night ahead of a frontal system will allow forecast surge to
increase quickly. Local to widespread minor coastal flooding is
becoming more likely for portions of the coastline during the
Tuesday night/early Wednesday morning high tide cycle. Statements
and advisories will likely be needed for portions of the coast. The
highest likelihood of reaching minor coastal flood benchmarks are
for the south shore bays of Nassau and SW Suffolk, but also a good
portion of the CT coast along with Lower Westchester and some
sections of the north shore of Long Island, and possibly Peconic
Bay. The winds will switch quickly offshore during the day
Wednesday, thus at this time subsequent high tide cycles are
expected to fall short of minor coastal flood benchmarks.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ331-332-335-
338-340-345.
Small Craft Advisory until noon EST Monday for ANZ350-353-355.-- End Changed Discussion --

SYNOPSIS...JE/JM
NEAR TERM...JC/JM
SHORT TERM...JM
LONG TERM...JE
AVIATION...JMC
MARINE...JE/JM
HYDROLOGY...JE/JM
TIDES/COASTAL FLOODING...