discussion on 2023-12-27

000
FXUS61 KOKX 270839
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
339 AM EST Wed Dec 27 2023

.SYNOPSIS...
-- Changed Discussion --High pressure continues to weaken and depart to the east through
this afternoon. Low pressure over the Middle Atlantic this evening
tracks northward towards Long Island by Thursday morning. The
low then slowly moves to the east later Thursday. A series of
weak lows or surface troughs will linger over the region
Thursday night through Friday night.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Dense fog is still the main concern early this morning.
Visibilities have not dropped as low across NE NJ and parts of
the NYC metro, but areas of dense fog continue across Long
Island and southern Connecticut. Given latest observation and
trends in webcams, will replace the Dense Fog Advisory over the
NYC metro and urban NE NJ corridor with an SPS. Will leave the
Dense Fog Advisory in place until 11 am across Long Island,
Westchester, and Southern Connecticut. Areas of drizzle are also
possible mainly across Long Island and Southern Connecticut.

A surface ridge axis remains over the area this morning. A
band of light rain is approaching from eastern PA and the
Middle Atlantic, but should begin diminishing in
coverage/weakening as it encounters the ridge axis. Some light
rain is possible this morning, mainly along and west of the
Hudson River corridor. This activity should help to keep any
dense fog from forming across these areas. However, areas of fog
may continue across Long Island and Southern Connecticut as the
surface ridging holds in place. There could be some areas of
dense fog into the afternoon, but confidence is not high enough
to extend any portion of the advisory at this time.

Warm advection will continue to increase through the day as a
frontal system approaches. Low pressure will also begin developing
over the Middle Atlantic late in the day and in the evening. These
features will help break down the surface ridge, but it could remain
in place through much of the afternoon. Recent runs of the HRRR only
indicate minimal rainfall amounts across the region through this
evening, likely due to the ridging preventing any steady rainfall
from occurring. Any rain that occurs before 00z should only amount
to a tenth or so at most and this would largely be west of the NYC
metro.

Highs today will be above normal in the upper 40s to lower 50s,
warmest near the coast.-- End Changed Discussion --

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
-- Changed Discussion --Low pressure along the Middle Atlantic coast will track northward
towards Long Island by Thursday morning and then shift towards
Cape Cod this evening. The low then slowly moves offshore, but
will leave behind several weaker lows or surface troughs through
Friday night.

...Key Messages...

*Rain will become widespread this evening and continue into early
Thursday morning. The bulk of the rain should be pushing east
of the NYC metro by day break Thursday with rain ongoing across
Long Island and southeast Connecticut. Coverage of rain
diminishes further into the afternoon.

*The rain will become moderate to locally heavy at times. Max
rainfall rates of around 0.50 in/hr are possible. Higher
probabilities for heavier rain exist across NE NJ, NYC metro,
and Long Island.

*Total rainfall amounts from this morning through Thursday
morning range from around an inch across the Lower Hudson
Valley and interior southern Connecticut to around 1.5 inches
across NE NJ, NYC metro, and Long Island. Locally higher
amounts around 2 inches are possible.

*Minor urban and poor drainage flooding is the main threat. A
few flashier rivers and streams in NE NJ could approach minor
flooding benchmarks.

There has been a growing signal in the guidance over the last
24 hours for a period of enhanced lift in the form of a coupled
jet structure and middle level frontogenesis. There will also
likely be enhanced moisture convergence along and north of the
track of the low pressure. The axis of the enhanced lift will
initially occur from the NYC metro on west the first half of the
night and then shift to the east across Long Island and
southern Connecticut towards the early morning hours. The low
should track south of Long Island Thursday morning with the axis
of moisture and lift shifting away from the region in the
afternoon.

HREF probabilities for seeing greater than 2 inches in a 6 hour
period tonight are low and under 5 percent. HREF probabilities
for seeing greater than 1 inch in a 6 hour period tonight are
about 50- 60 percent from around the NYC metro/urban NE NJ on
east into Long Island. Recent heavy rainfall brings a concern
for flooding along rivers and streams. Based on the latest
headwater guidance generally more than 2 inches is needed in 6
hours for minor flood stages to be reached on some of the main
stem rivers. 2 inches of rain in 6 hours seems like a worst case
scenario with this system. Have held off on a flood watch based
on collaboration with PHI. Any river flooding would more than
likely occur later on Thursday after the heaviest rain. Will let
the day shift reassess the latest guidance to see if a flood
watch will be needed for our NE NJ counties.

The main low will continue tracking east Thursday afternoon
and night. The main closed low will still be well to our west
near the Great Lakes and Ohio Valley. The closed low will then
shift towards the southeast Friday into Friday night. There will
likely be several spokes of energy aloft that could interact
with lingering lower pressure/surface troughs over the area for
periods of light rain at times. The modeling has not been
consistent on what time period this would be most likely. Have
elected to cap PoPs off at high chance late Thursday into Friday
night. It will not be a wash out, but periods of light rain are
possible at any time. Otherwise, mostly cloudy to overcast
conditions are likely to continue.

Temperatures will remain above normal Thursday and Friday with
highs in the upper 40s to low 50s.-- End Changed Discussion --

.LONG TERM /SATURDAY THROUGH TUESDAY/...
-- Changed Discussion --No significant changes made to the long term and stuck close to
the NBM for this update.

*Key Points*

* Rain chances now look to continue into Saturday, before drying out
on Sunday into New Year`s Day.

* A slight cooldown to more seasonable temperatures Saturday through
Tuesday.

Midlevel trough shears out as it heads east on Saturday morning
with the trough axis passing through the area by late in the
day. Attendant surface low heads to the northeast with moisture
wrapped around its western periphery, as surface ridging
approaches from the west. Have kept chance rain in for Saturday
morning through midday as the low slowly pulls away. Thermal
profiles suggest all rain on the backside of the system. Any
lingering precip will end from west to east by Saturday
afternoon.

Thereafter, mainly dry conditions look to prevail Sunday through
Tuesday. Weak upper ridging becomes more zonal by early next week.
A mid level trough ejects out of the Central Plains by late
Monday into Tuesday--there is some timing differences among the
global models on this. Nonetheless, guidance shows a surface low
developing out ahead of this across the Mid Atlantic by
Tuesday. At this time, the area remains on the north side of its
precip shield as the system remains south of the region.-- End Changed Discussion --

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --While vsbys have improved over the past few hours for NYC
terminals on west, LIFR cigs continue at all terminals except
KSWF which is MVFR. Expect the low conditions to continue
through the morning push and into the mid morning hours on
Wednesday. Conditions are expected to improve somewhat Wednesday
afternoon as precipitation approaches. Its possible that we
only improve to IFR or low end MVFR for just a few hours.
Conditions then fall back to IFR or lower Wednesday night in
rain, possibly heavy at times after 03Z.

Once again, winds will be light and variable through much of the
TAF period. Winds do become more easterly around 6-8kt late in
the TAF period.

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

Uncertainty on how much improvement occurs Wednesday afternoon.
Possibly conditions remain IFR but could also improve to MVFR.
Confidence on any timing of any improvement remains low.

OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY...

Wednesday night: Rain with IFR and pockets of LIFR conditions.

Thursday: MVFR possible with chance of showers. E winds G20kt
possible in the morning at the CT/Long Island terminals.

Friday: MVFR possible with chance of showers. N / NE winds.

Saturday: Mainly VFR. NW winds G20-25kt.

Sunday: VFR.

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

.MARINE...
-- Changed Discussion --Marine dense fog advisory remains in effect for all waters
through 11 am.

Conditions will remain below SCA levels through this evening.
E-SE winds increase tonight ahead of approaching low pressure.
Think winds will stay below SCA levels though as the low is
weak. The low passes near the waters Thursday morning and then
east Thursday afternoon leaving behind a weak pressure gradient
into Friday night. Ocean seas will build tonight into Thursday
with potential to see 5 ft seas late Thursday into Friday. Seas
should begin subsiding Friday afternoon into Friday night.

Marginal SCA conditions are expected on the ocean waters Saturday
morning. SCA conditions then become likely over the eastern ocean
zones with developing low pressure to the south late Saturday into
Sunday, with 5-7ft seas. Sub SCA conditions return by late
Sunday.-- End Changed Discussion --

.HYDROLOGY...
-- Changed Discussion --Storm total rainfall 1.0-1.5 inches is likely, mainly from this
evening through Thursday morning. Locally higher amounts are
possible around 2 inches. Due to recent heavy rainfall, minor
flooding along a few quick responding rivers in NE NJ is possible.
Otherwise, minor urban and poor drainage flooding should be the
main hydrologic impact.

There are no hydrologic impacts expected Thursday night through
early next week.-- End Changed Discussion --

.TIDES/COASTAL FLOODING...
The potential remains for minor coastal flood impacts for
vulnerable coastal communities on Thu with a passing low.
The threat exists for mainly the morning high tide,
particularly along the south shore of Nassau and Queens, and
possibly along the SW CT coastline on the Western Sound and NY
Harbor. Tidal departures of 1.25-1.50 ft are needed for minor
flooding, and 2.25-2.50 for moderate flooding during the morning
high tides. About 1 ft additional surge is needed for the
evening high tides.

The threat for dune erosion appears to be low and isolated with
this event.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...Dense Fog Advisory until 11 AM EST this morning for CTZ005>012.
NY...Dense Fog Advisory until 11 AM EST this morning for NYZ070-071-
078>081-177-179.
NJ...None.
MARINE...Dense Fog Advisory until 11 AM EST this morning for ANZ331-332-
335-338-340-345-350-353-355.-- End Changed Discussion --

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