Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 170003

Area Forecast Discussion
National Weather Service New York NY
703 PM EST Sat Dec 16 2017

A cold front moves south of the area this evening and will be
followed by high pressure for Sunday. A series of weak frontal
systems then move through the region Sunday night through
midweek, before high pressure builds in for the late week. A
frontal system approaches by the start of the weekend.


A cold front across Central NY/New England will continue to
sink south through the evening hours as a shortwave and
associated vort max pass to our northeast.

To this point, many of the high-res models have been too
aggressive with depicted snow shower intensity. Mostly flurries
have been reported around the area, especially LI/CT. Somewhat
more organized reflectivity, is being seen with a band of very
light snow sinking south through Southern CT ahead of the cold
front. Will have to watch this band for some intensification as
it encounters the residual lake moisture plume extending
southeast through the Lower Hudson valley across LI through
around 9 pm. The extra surface convergence in combination with
the passing shortwave energy to our northeast may result in a
locally heavier burst of snow, which could put down a quick

Clearing skies should ensue late this evening into the
overnight behind the front passage, especially across the
eastern half of the region. Lingering moisture between 5 and 10
thousand feet may keep the western half of the region at least
partly cloudy. Lows will range from the teens inland to the
lower and middle 20s closer to the coast.


Another unseasonably chilly day is forecast on Sunday as high
pressure settles over the Tri-State. Shortwave energy will fast
approach from the west on Sunday within zonal flow aloft. This
energy currently resides over Mexico and will lift towards the
Plains tonight and get caught in the zonal flow on Sunday. The
shortwave energy will dampen out as it approaches, but there will be
enough moisture to increase clouds through day. No precipitation is
expected with highs in the lower and middle 30s.

The main concern on Sunday night will be surrounding any
precipitation that develops with warm advection as the weakening
shortwave energy moves overhead. Models differ in whether there
will be any measurable precipitation due to overall weak lift.
There will be a warm front approaching, which may be just enough
along with the warm advection to produce light precipitation.
Temperatures profiles are questionable, but there are signals of
a warm nose developing around 900-950 mb Sunday night. This may
be able to change any snow to freezing rain or rain. Surface
temperatures away from the NYC metro and coast will likely
remain below 32 degrees, so will need to watch for any freezing
rain. For now, PoPs are capped at 30 percent and will show a
chance for snow inland and a mix of snow, freezing rain, or rain
near the coast. Any snow inland could change to a mix towards
day break as the warm nose attempts to advance north.


Models continue in good agreement with a fairly progressive upper
pattern in place through the week, with a series of weak frontal
systems moving through the region Sunday Night through midweek as a
muted northern stream longwave trough slides from the Great Lakes
into the Northeast.

First system of note continues to be for Sunday Night into Monday
morning as the closed low currently over NW Mexico shears towards the
NE ahead of a developing Western US trough. General agreement in
this energy being significantly weakened as it approaches the region
with limited moisture, but potential exists for a light precip event
Sunday night into Monday morning. Thermal profiles suggest a start
as snow or wintry mix, quickly transitioning to rain for NYC/LI as
boundary layer sufficiently warms, but remaining a wintry mix to the
N and W of NYC/LI into Monday morning with a subtle warm nose but
likely freezing surface temps. Although precip amounts are expected
to be light, potential exists for hazardous (icy) travel N&NW of
NYC/LI for Monday morning commute.

Thereafter, models in fairly good agreement with the broad but
shallow northern stream trough approaching the NE on Tuesday and
sliding through during the midweek. At the surface, the primary low
pressure system rides through Quebec/Ontario with trailing cold
front approaching the region Tue, and crossing Tue Night. Not
expecting much precip during this time period, due to best forcing
north of the region, and limited moisture being drawn north in split
flow. Thermal profiles suggests precip would be mainly liquid, but
if anything develops in the waa pattern Monday Night into Tue
morning there would be a threat for freezing rain across interior as
cold air typically has a tough time scouring out in this setup.

Upper trough swings through the NE Tue Night into Wed with a
glancing shot of modifying arctic air in the wake of the cold front
for Wed. Upper flow flattens and even becomes a bit ridged for
Thursday ahead of the next northern stream trough digging into the
Upper Plains. At the surface, high pressure builds in from the west
Wed and across Thu, with dry and seasonably cold conditions.

Models in general agreement with a pattern shift to a more
longitudinally oriented upper flow heading into the weekend, as
several pieces of northern stream energy begin to dig a deep
longwave trough into the Western/Central US. This may bring the
coldest air of the season into the Central US by around Christmas.
Meanwhile, energy rounding this trough appears to send a frontal
system through the region during the Fri Night-Sat Night time


High pressure builds over the area into Sunday evening.

VFR through the TAF period. Isolated-scattered flurries possible
through around 1Z with ceilings around 5000 ft possible through
around midnight.

W winds veer to the NW this evening, with speeds falling below
10 KT throughout. Winds become light and variable throughout by
early Sunday afternoon.

.Sunday night-Monday morning...MVFR or lower possible in light
snow, transitioning to a wintry mix.
.Monday afternoon-night...VFR. Westerly flow developing.
.Tuesday-Tuesday night...VFR probable with MVFR or lower
possible. W-WSW winds G20-30KT possible.
.Wednesday-Thursday...VFR. NW winds G20-30KT probable
Wednesday/Wednesday night.


Small craft advisory remains in effect on the ocean into the
overnight as seas will lag winds falling below SCA. Seas may
remain above 5 ft east of Moriches inlet through Sunday morning.

A weak pressure gradient Sunday through Monday Night will lead
to sub- SCA conditions.

The next chance for SCA conditions will be late Tuesday/Tue eve in
SW flow ahead of approaching cold front, with high likelihood of
widespread SCA Tuesday Night through Wednesday with tight pressure
gradient and strong caa in wake of cold front. Marginal gale gusts
are possible during this time frame.

Conditions then should fall back below SCA heading into Thu as high
pressure builds towards the waters.


No significant hydrologic impacts expected.


NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the
air for an extended period of time.


MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ330-
     Small Craft Advisory until 1 AM EST Sunday for ANZ353-355.
     Small Craft Advisory until 6 AM EST Sunday for ANZ350.


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