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fxus61 kokx 110548 
afdokx

Area forecast discussion
National Weather Service New York New York
1248 am EST sun Dec 11 2016

Synopsis...
high pressure settles over the region overnight into Sunday
morning and then moves offshore Sunday afternoon. 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 today/...
slight adjustments were made to temperatures, dewpoints, and cloud
coverage to better match observed trends. Overall, the forecast is
on track.

Mostly clear skies and light winds the first half of the overnight
should allow temps to drop well down into the lower to middle
teens across interior and Pine barrens of Li. Generally lower 20s
at the coast...except mid 20s NYC/NJ Metro. Temps likely stabilize
or even rise a bit towards daybreak as cloud cover increases.

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 positive vorticity advection as shortwave energy races eastward ahead of an upper
trough across the Great Lakes.

Increase in pops to high chance late in the day for much of the
area with likely across the far northwest 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 moderate.

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 /tonight through Monday night/...
initial surge of warm advection light snow moves off to the north
between 00z and 06z. 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 southeast 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
south to north. 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 northwest 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 northwest 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 /06z Sunday through Thursday/...
***high impact weather likely late tonight into Monday morning***

Light west-northwest flow and mostly clear skies early this morning as high
pressure builds in. High pressure moves offshore on today...with a
low pressure system approaching tonight. Light west-northwest winds turn S in
the afternoon. Light snow likely to develop Sunday afternoon into
early evening with moderate probability for MVFR conditions
likely...low probability for IFR. A brief break in precip possible
late Sunday evening...before steadier and heavier precip moves in
after midnight.

Outlook for 06z Monday through Thursday...

Late tonight...IFR/LIFR conditions developing, with snow mixing
with and changing to rain at most terminals. Brief freezing rain possible at
kswf. Low level wind shear 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 Monday 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. Wintry mix changing to rain in
the morning at kswf, and rain elsewhere. Low level wind shear possible in the
morning NYC metros/coast. S/SW winds g25kt in the morning at the
NYC metros and kisp, becoming west in the afternoon.

Monday night-Tuesday...VFR.

Wednesday...low chance of snow. Northwest winds g25-30 knots after
midnight.

Thursday...VFR with northwest winds g30kt.

&&

Marine...
winds and seas will continue to subside overnight...remaining
below Small Craft Advisory levels into 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 Small Craft Advisory levels after
midnight Sunday night and then on all waters Monday morning with
increasing southerly flow. Ocean seas will also increase above
Small Craft Advisory. It is not out of the question for a brief period of gale
conditions late Sunday night into Monday morning.

Winds and seas will gradually subside Monday night and conds should
fall below advsy levels on all waters by 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.

&&

Tides/coastal flooding...
with an approaching full moon...water levels will approach minor
flood levels across the most vulnerable coastal locales of SW CT
and the western Great South Bay during the Monday morning high
tide. Although southerly flow is not ideal...tidal departures of
less than 1 ft are needed to reach minor thresholds in some spots.

&&

Equipment...
New York City National oceanic and atmospheric administration weather radio NWR transmitter kwo-35 is
experiencing intermittent outages.

&&

Okx watches/warnings/advisories...
CT...none.
New York...Winter Weather Advisory from 4 PM this afternoon to 10 am EST
Monday for nyz067.
New Jersey...Winter Weather Advisory from 4 PM this afternoon to 10 am EST
Monday for njz002.
Marine...none.

&&

$$
Synopsis...24/ds
near term...24/jm/ds
short term...ds
long term...24

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