Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 210009
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
709 PM EST Fri Jan 20 2017

.SYNOPSIS...
An upper level disturbance weakens tonight as the disturbance
moves through the region. High pressure briefly returns on
Saturday. Deepening low pressure moving across the southern states
on Sunday will reach the southern Mid Atlantic region by Monday
morning, while high pressure builds southeast into the Canadian
Maritimes. The low will intensify into a significant coastal storm
as it moves up the coast toward the area Monday through Tuesday.
High pressure builds for Wednesday as the coastal low departs
towards New England. A cold front slowly approaches the area from
the west, moving through late Thursday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
With the weakening upper level disturbance the precipitation
associated with the shortwave has been also weakening and
diminishing in areal extent. Latest guidance has heights beginning
to rise across New Jersey and into the western portion of the
forecast area 01Z to 03Z and the precipitation ending a couple of
hours sooner across the western half of the area. Guidance seems
to handling the trends well and updated the probabilities through
tonight. Temperatures, dew points, and winds remain mostly
unchanged, with just minor adjustments across eastern Long Island
where temperatures remain in the lower 40s.

Low-level ridging is still lingering, and with added moisture
from the rain expect stratus, possibly areas of light drizzle and
some patchy fog, will continue through the night. Extensive cloud
cover and weak warm advection will support low temperatures in the
mid 30s to lower 40s, 15-20 degrees above climatological normals.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
High pressure briefly builds across the area for Saturday. Light
drizzle and patchy fog will gradually end by morning as the flow
strengthens from the west-southwest. Subtle downslope flow and
subsidence will support high temperatures in the 50s, well above
normal for this time of year. With the low-level inversion
remaining in place, stratus will linger once again. If clouds do
eventually erode with the subsidence, then temperatures may
potentially be a few degrees warmer than forecast. Similar
conditions are expected overnight with cloud cover and weak warm
advection once again leading to well above normal lows around 40.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Significant coastal storm likely Sunday Night into Tuesday with
potential high wind...heavy rain...and coastal impacts.

Main focus is on this storm forecast to take shape as strong
Pacific jet energy is currently crashing onshore the California
coast...allowing an upper level system to close off over the
southern plains this weekend and then negatively tilt up the east
coast Monday into Tuesday. The result will be strong low pressure
tracking through the southern states this weekend...and then
tracking up the coastal plain towards the area Mon/Tue. Models in
general agreement with the synoptic fields...but considerable
spread exists in timing/track/intensity of the closed upper low as
it moves up the coast...which is playing out in model spread on
track/speed of the surface low Mon/Tue. This is particularly seen
in the timing of coastal low development and eventual development
into the primary low. SBU ensemble sensitivity still pointing
towards a strong wave packet emanating from shortwave energy that
came off the eastern Asia coast last night. Have stayed close to
an ensemble mean with forecast...with general agreement in low
pressure tracking over or just se of Li Late Monday Night/Tue.

Potential exists for multiple impacts of strong winds, heavy rain
(wintry mix NW) and minor to locally moderate coastal flooding, with
likelihood of occurrence in that general order.

In terms of winds...GEFS signaling an easterly llj 5-6 std above
climo. EPS probabilities for wind gusts over 50 kt have increased
to categorical for Mon/Mon night for the immediate coastline, and
the extended 00z/12Z GFS/ECMWF MOS guidance indicate sustained
winds 30-35 kt along the coast. This signals a high potential for
wind advisory conditions for the coast and low potential for high
wind...peaking Mon aft/eve.

See coastal flood sections for potential coastal flood impacts.

In terms of heavy precip...PWATs of 3-4 stds above climo continue
to be signaled as the system taps into tropical connection to the
Caribbean and Eastern Pacific. Coastal front development and
orographic lift over western terrain should come into better focus
over the next 48 hrs to pinpoint potential high end rainfall
amounts and locations. Embedded convection not out of the question
late Monday/Mon eve ahead of approaching closed low and with warm
conveyor belt feeding into the region. Based on
ensemble/operational output...likelihood for 1 to 3 inches of qpf
with higher swaths possible.

Based on strong dynamics and consensus storm track over or just se
of LI...potential for thermal profiles to diabatically cool to near
freezing and result in a period of rain/sleet/snow mix well N&W of
NYC Late Sun Night into Mon night...with even a period of heavy wet
snow across NW hills. A light snow/sleet accumulation is possible
across interior portions of NE NJ...Lower Hud...and Southern
Ct...with potential for an advisory level wet snow for the NW hills.

Winds should fall off rather quickly Mon Night from sw to e as
llj moves ne...with rain becoming more showery in nature overnight.

Gradually improving conditions Tue into Tue Night as the upper low
pivots ne and low pressure tracks up the New England coast.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
A wave of low pressure will move across the area tonight with
weak high pressure returning for Saturday.

Light rain continues through the evening with MVFR conditions
going to IFR conditions due to lowering ceilings. The light rain
will taper to drizzle. Localized LIFR is possible.

Some forecast guidance is hinting at residual low level moisture,
which could result in areas of fog early Saturday morning.

Winds remain light through the period at less than 10 kt. Wind
directions will be Southeast, then South overnight. Some locations
may become variable overnight. Winds then become southwest to west
during Saturday. Conditions are expected to improve during the
late morning into the afternoon. Some locations may hold on to
MVFR into the afternoon.

 ...NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component forecasts,
can be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: Timing of lower CIGs may be off by an hour or
two.

KLGA TAF Comments: Timing of lower CIGs may be off by an hour or
two.

KEWR TAF Comments: Timing of lower CIGs may be off by an hour or
two.

KTEB TAF Comments: Timing of lower CIGs may be off by an hour or
two.

KHPN TAF Comments: Timing of lower CIGs may be off by an hour or
two.

KISP TAF Comments: Timing of lower CIGs may be off by an hour or
two.

.OUTLOOK FOR 0Z SUNDAY THROUGH WEDNESDAY...
.Saturday night... MVFR conditions will give way to IFR, with
possible LIFR conditions, with possible fog for some locations
after 0z.
.Sunday-Sunday Night...MVFR or lower in light rain, then moderate
rain at night. NE winds G20-30KT by late day, and G30-40KT later
at night.
.Monday-Monday Night...IFR conditions. Snow and rain for the
interior including KSWF, and moderate-heavy rain elsewhere.
ENE winds 25-30KT with G40-45KT.
.Tuesday-Tuesday night...Rain tapering off in the
afternoon and evening with improving ceilings. NW winds G25-35KT,
highest in the morning.
.Wednesday...VFR.

&&

.MARINE...
Seas will remain below SCA levels through Saturday night under a
relaxed pressure gradient.

An intensifying storm moving up the coast early next week will
likely bring storm force gusts to the ocean and LI Sound...with
potential for gusts even on nearshore waters Sunday night into
Monday night. These winds have the potential to build seas to as
high as 20 ft on the ocean waters, and 5-10 ft on LI Sound.

&&

.HYDROLOGY...
Likelihood of 1 to 3 inches, with locally higher amounts with a
coastal storm Sun NIght into Monday...with heaviest rainfall Mon
aft/eve. If high end rainfall amounts are realized...this will bring
a threat for moderate urban flooding and minor small stream
flooding in NE NJ/Lower Hud Valley. This would be exacerbated by
coincidence of high tide with the heavy rain Mon eve. Rises on
larger rivers would be likely...but at this point the potential
for minor flooding appears slight.

&&

.TIDES/COASTAL FLOODING...
A strong coastal storm will likely cause 3 successive high tide
cycles of minor coastal flooding Sunday Night into Monday
Night...with potential for locally moderate coastal flooding with
the Monday evening high tide. This moderate threat could
linger into the early Tue morning high tide cycle.

An ensemble of guidances is showing potential for surge building to
3 1/2 to 4 1/2 ft by Monday evening.

The highest threat for coastal impacts will be for flood prone
locales along the south shore bays of Li/NYC...eastern bays of
LI...lower NY/NJ harbor including tidally affected rivers...and
western Li Sound.

The other concern will be for widespread dune erosion and localized
washovers at Atlantic ocean beaches from long period easterly
swells of 15-20+ ft Mon into Tue.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Storm Watch from late Sunday night through late Monday night
     for ANZ330-335-338-340-345-350-353-355.

&&

$$
SYNOPSIS...MD/MET
NEAR TERM...MD/MET
SHORT TERM...MD
LONG TERM...NV
AVIATION...JC/JE
MARINE...MD/MET/NV
HYDROLOGY...MD/NV
TIDES/COASTAL FLOODING...



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