Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 102115
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
415 PM EST Sat Dec 10 2016

.SYNOPSIS...
High pressure settles over the region tonight and then moves
offshore Sunday. Low pressure then tracks across the Great Lakes
Sunday night into Monday, sending a warm front through the region.
A cold front then follows for Monday afternoon into Monday evening.
High pressure briefly builds in for Tuesday before another low
possibly impacts the area for the mid week period. An arctic cold
front then follows behind the system Thursday.

&&

.NEAR TERM /THROUGH SUNDAY/...
Shortwave trough swings across the the region this evening with
some lingering flurries. These will dissipate with loss of daytime
heating. High pressure then settles over the Tri- State. Clouds
should diminish overnight with mostly clear skies and winds
becoming light. Low temperatures range from the upper teens inland
to the lower and middle 20s at the coast.

Mid level ridge axis slides across the region Sunday morning with
a warm advection regime setting up as high pressure moves
offshore. Models are continuing to indicate a swath of light snow
potential along the initial surge of warm advection in the
afternoon and early evening moving from south to north. There is
also some support aloft from a strong upper jet to the north and
some PVA as shortwave energy races eastward ahead of an upper
trough across the Great Lakes.

Have shown an increase in PoPs to high chance late in the day for
much of the area with likely across the far NW interior. Thermodynamic
profiles show moistening slowly through the afternoon. A dusting
or a light coating of snow is possible within areas of light snow.
Dry subcloud layer may hinder the development of snow as dew
points may take some time to recover.

Followed a blend of guidance for highs as these seemed reasonable
with increasing clouds and little vertical mixing. Highs in the
lower to middle 30s are forecast.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Initial surge of warm advection light snow moves off to the north
between 00z and 03z. Models have been persistent in indicating mid
level dry air behind this initial surge so the precipitation may
end briefly before becoming widespread from west to east after
midnight.

Pattern recognition for the upcoming event Sunday night into
Monday is one that does not favor a significant snowfall across
the region. This is due to primary low moving through the Lakes
into SE Canada and surface high moving offshore. Low level winds
increase early Monday morning, surging temperatures upward. This
warm push will help to bring a transition from snow to rain from
north to south. Warmer air will begin to surge northward at the
surface overnight with locations near the coast warming into the
upper 30s and low 40s after midnight. This would be the majority
of the precipitation will fall as rain with the main warm
advection. Further inland across the NW interior, it will take a
little longer for the warm air to arrive so a short period of
accumulating snow is expected before transitioning to plain rain
around or just after sunrise. Within the transition zone across
the interior Lower Hudson Valley and NE NJ, a brief period of
freezing rain is possible. Do not expect this to last long as
temperatures will rise above freezing after sunrise with no
damming high to the north to lock in the cold surface air.

Models and ensembles have continued to come into better agreement
overall over the last several cycles. Followed a blend of the 12z
GFS/ECWMF for thicknesses and temperatures to formulate sensible
weather grids.

Through collaboration with neighboring offices, have issued a
winter weather advisory for Orange and western Passaic counties
Sunday evening into Monday morning. Confidence is highest in
these zones for advisory level snow and with the addition of a
brief period of freezing rain, the advisory was issued. Further
east across in the interior, confidence is lower and through
collaboration have decided to hold off on an advisory for now.

Total snow less than an inch across NYC and the coast increasing
to generally to 2 to 4 inches across the interior. Please see
latest winter weather graphics at www.weather.gov/okx/winter.

Plain rain is expected across the entire area from mid morning
into the afternoon. Temperatures may touch 50 degrees near the
coast and should be able to warm into the 40s even into Orange
County. Rain ends from west to east late as the trailing cold
front moves through.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Upper air pattern will feature an anomalously high amplitude ridge
over Alaska, which will allow the polar vortex to drop southward
into central and eastern Canada by midweek. This will open the door
for the coldest airmass of the season for the second half of the
week.

High pressure briefly follows for Tuesday with temperatures near
seasonable levels. Another piece of Pacific shortwave energy races
across the country. Global models vary with the amplitude of this
feature with the nearly zonal flow in the southern branch of the
polar jet. The amount of phasing with the northern branch looks to
be the difference and 12z models have shifted towards a less
phased pattern with the energy passing well south of the area.
Have decreased pops to schc based on this trend. However...due to
the fast flow, there is likely to be uncertainty in the magnitude
of this system the next several days. Arctic air then spills
southward on the backside of the system Thursday into Friday with
daytime highs possibly not getting above freezing with overnight
lows in the single digits to teens. These values are 15 to 20
degrees below normal. To make matters worse, strong NW winds will
follow for Thursday producing very cold wind chill values.

Meanwhile...an upper level trough moves onshore from the Pacific
during the second half of the week. There are some differences
aloft by Sat...although confluent flow across the country and
developing low pres in the Plains could bring pcpn back to the
region during Sat. The cold airmass already in place should all
for pcpn to start in the frozen phase but will likely
mix/changeover with sly flow.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
***HIGH IMPACT WEATHER LIKELY LATE SUNDAY NIGHT INTO MONDAY
MORNING***

Upper level disturbance moving across the area will produce SCT-BKN
cigs 040-050 and scattered snow showers/flurries for the rest of this
afternoon. Any restrictions to vsby reduction will be brief. WNW flow
left of 310 magnetic just over 10 kt with gusts 15-20 kt.

High pressure approaches tonight with a diminishing WNW flow,
then moves offshore on Sunday with a return S/SW flow developing
by afternoon. Mid and high level clouds increase Sunday morning
ahead of an approaching warm front. Light snow is forecast to
develop Sunday afternoon with possible MVFR conditions. Confidence
in sub-VFR cigs and vsbys is low to moderate as it may take a long
period of time to saturate the low levels.

.OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY...

.Sunday afternoon...Mainly VFR. Chance of light snow in the
afternoon with possible MVFR.

.Sunday night...IFR/LIFR conditions developing, with snow mixing
with and changing to rain at most terminals. LLWS possible late
NYC metros/coast. S winds G25KT late at the NYC metros and KISP.

Here are the most likely precip types and snowfall accumulations:

KISP/KJFK/KLGA/KEWR/KTEB/KBDR/KGON: Snow changing to rain around
midnight, with a coating to an inch accumulation.

KHPN: Snow mixing with and changing rain to early Sunday morning,
with around an inch accumulation.

KSWF: Snow with accumulation 3-4 inches with a brief period of
freezing rain possible before going over to rain around daybreak.

.Monday...IFR conditions. Snow mixing with/changing to rain in
the morning at KSWF, and rain elsewhere. LLWS possible in the
morning NYC metros/coast. SW winds G25KT at the NYC metros and
KISP, becoming W in the afternoon.

.Monday night-Tuesday...VFR.

.Wednesday...Low chance of snow. NW winds G25-30 KT after
midnight.

.Thursday...VFR with NW winds G30kt.

&&

.MARINE...
SCA has been cancelled on the ocean. An occasional gust up to 25
kt is still possible on the waters east of Moriches inlet this
evening. Otherwise winds and seas will remain below SCA levels
through Sunday evening with high pressure in control.

A warm front crosses the waters late Sunday night with increasing
winds. Winds on the ocean should increase to SCA levels around day
break and then on all waters on Monday with increasing southerly
flow. Ocean seas will also increase above SCA. It is not out of
the question for an occasional gust to gale force on the ocean but
this should be short lived.

Winds and seas will gradually subside Monday night and conds should
fall below advsy levels on all waters Tue morning. Tranquil conds
then prevail through Wed...then sca or even gale force gusts are
possible behind an arctic front Wed night and Thu.

&&

.HYDROLOGY...
A half to three quarters of an inch of liquid equivalent precipitation
is forecast late Sunday through Monday. No significant pcpn
(greater than 1/2 inch) is then expected through the end of the
work week.

&&

.EQUIPMENT...
New York City NOAA Weather Radio NWR transmitter KWO-35 is
experiencing intermittent outages.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Weather Advisory from 4 PM Sunday to 10 AM EST Monday
     for NYZ067.
NJ...Winter Weather Advisory from 4 PM Sunday to 10 AM EST Monday
     for NJZ002.
MARINE...None.

&&

$$
SYNOPSIS...24/DS
NEAR TERM...DS
SHORT TERM...DS
LONG TERM...24
AVIATION...DW
MARINE...24/DS
HYDROLOGY...24/DS
EQUIPMENT...


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