Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 160541
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1241 AM EST Sat Dec 16 2017

.SYNOPSIS...
Low pressure departs offshore. A series of weak low pressure
and frontal systems will pass through the area this weekend
through mid week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Back edge of snowfall has pushed east of Long Island.

Generally 1 to 2 inches fell across the NYC/NJ metro,
Westchester and Fairfield CT, with 2 to 3 1/2 inches across
Nassau and Suffolk Counties and portions of coastal CT.

Otherwise...vigorous shortwave pivots east overnight with low
pressure departing out to sea. Clearing and increasing winds
are expected overnight as the pressure gradient tightens
between the strengthening departing low, and strong high
pressure over the SE US.

Cold night with lows ranging from upper teens well inland to
mid 20s at the coast.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Polar upper low pivots southeast into New England on Sat and
offshore Saturday Night. WNW caa low flow over the Great Lakes,
accompanied by shortwave lift and left front of 150 kt jet
streak, should be enough to extend light snow shower activity
into the region later Sat morning through Sat afternoon. A
dusting is possible in spots, particularly NW hills.

Otherwise, breezy and chilly on Sat with abundant cloud cover
and glancing caa. Temps will likely hold in the lower to mid 30s
for much of the region, with windchills in the 20s.

Shortwave slides east Sat night, with high pressure building in
from the west. This will have snow showers tapering from w to e
early in the evening, with potential for good radiational
cooling conds for outlying areas later Sat Night. Temps should
fall into the teens for outlying areas, with mid-upper 20s for
urban centers.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Models in good agreement with a fairly progressive upper
pattern in place through this period, 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 will be Sunday Night into Monday as the
closed low currently over Baja Mexico, shears towards the NE
ahead of a developing Western US trough. Models differing in
the strength of this energy and amounts of moisture drawn
northward, but potential exists for a light precip event Sunday
night into Monday morning. Thermal profiles suggest a start as
snow or wintry mix, transitioning to rain for NYC/LI, but
potentially remaining a wintry mix for the interior into Monday
morning. Too early for specific details on this light precip
event, but potential exists for hazardous travel conditions
N&NW of NYC/LI for Monday morning commute.

Thereafter, models in fairly good agreement with the broad bu
shallow northern stream trough approaching the region 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 Tuesday Night.
Overall, appears to be mainly a light qpf event for the Monday
night into Tuesday evening period, due to limited interaction
between northern and southern stream. Thermal profile suggests
precip would be mainly liquid, but could be dealing with
freezing rain across interior Monday night as cold air
typically has a tough time scouring our 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/Thu.

Upper flow flattens and even becomes a bit ridged for Thursday
ahead of the next northern stream trough digging into the Upper
Plains, which should allow for a moderation in temps ahead of
next potential frontal system.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Low pressure departs to the east overnight as a trough approaches
Saturday.

VFR conditions have returned as skies clear. Expect increasing
clouds during the day Saturday. Ceilings between 3-5 KFT expected
from late morning through the afternoon. Local MVFR or IFR
conditions cannot be ruled out in snow showers.

Westerly winds 5 to 10 kt increase continue early this morning.
Occasional gusts to around 20 kt are possible, mainly across NYC
metro terminals. After 12-14Z, westerly winds increase to 15 to 20
kt, with gusts 20 to 30 kt. Gusts become less frequent after 20-21Z.

By evening, winds turn to the NW and diminish.

.OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY...
.Late tonight...VFR.
.SUN...VFR during the day. Chance MVFR in a mix of -RA/-SN towards
midnight.
.MON...Low chance MVFR in -RA for coastal terminals, light wintry
mix inland. Improvement as the day progresses.
.TUE...MVFR possible with a slight chance of showers.
.WED...VFR. NW winds G20-30KT.

&&

.MARINE...
SCA conds will quickly develop from W to E overnight and
continue through Sat, with the potential for occasional gale
force gusts on mainly the ocean waters late tonight through
Saturday morning.

Winds and waves diminish below SCA Saturday night as high
pressure builds in.

Next chance for SCA conditions possibly as early as late
Tuesday/Tue eve ahead of approaching cold front, but higher
likelihood of widespread SCA Tuesday Night through Wednesday
night with tight pressure gradient and strong caa in wake of
cold front. Gales are possible during this time frame.

&&

.HYDROLOGY...
No significant hydrologic impacts expected.

&&

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

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ330-
     335-338-340-345.
     Small Craft Advisory until 1 AM EST Sunday for ANZ350-353-355.

&&

$$



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