Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 152123
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
423 PM EST Fri Dec 15 2017

.SYNOPSIS...
Low pressure will move off the Middle Atlantic this evening and
offshore tonight. A series of weak low pressure and frontal
systems will pass through the area this weekend through mid
week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Snow continues to overspread the Tri-State area. Impacts to the
evening commute are anticipated, with potential for significant
impacts within the winter weather advisory area. No changes
were made to the headlines.

The only change made to the snowfall forecast was across
southern/coastal Long Island where some locations could approach
4 inches. This is due to increasing potential for moderate snow
banding in conjunction with best frontogenesis this evening.

There is a bit of uncertainty in how much snow will fall across
NE NJ and interior of the Lower Hudson Valley and southern
Connecticut. It is possible amounts could end up lower with
minimal impact since best lift appears to be setting up just
south, within the advisory area.

Divergence aloft is impressive as a 170-180 kt jet streak moves
across the Middle Atlantic. Our region will be located in the
favored left exit region for synoptic lift this evening. There
will also be interaction/phasing of the northern and southern
stream, which combined with the upper jet dynamics, will
continue to organize a surface low off the Middle Atlantic coast
this evening and then south and east of Long Island overnight.

Mesoscale models continue to indicate a swath of strong 850-700
mb frontogenesis across the southern portion of the area. The
lift coincides within the dendritic growth zone which may
enhance snowfall and produce banding, especially across Long
Island.

Thermodynamic profiles do not show much liquid water saturation
aloft for riming, so the snow will be a dry, high ratio type
similar to what we observed Thursday morning. Ratios may be
15-18:1. Surface temperatures will fall into the middle and
upper 20s as the snow begins continues to fall.

The snow tapers off around 7-9pm in NYC and around midnight on
the east end of Long Island. Liquid equivalent amounts around
0.05 inches inland and close to 0.20 inches are forecast across
Long Island.

Clearing and increasing winds are expected tonight behind the
departing low as the pressure gradient tightens between the
strengthening departing low, and strong high pressure over the
SE US. Another chilly night with lows in the ranging from upper
teens well inland to mid 20s at the coast.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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 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 /21Z FRIDAY THROUGH WEDNESDAY/...
***SNOW EXPECTED FOR EVENING PUSH***

Low pressure passes to the south this evening before quickly
ejecting eastward overnight.

Snow is already overspreading the area, and although initial
conditions are VFR, expect visibilities to quickly drop as snow
intensifies. Steadier snow will generally fall from around 20Z, then
quickly end from west to east between 02-05Z.

Expect a widespread 1-4 inches, with the highest totals across the
NYC terminals into KISP, KBDR and KGON.

Light and variable winds become westerly at 5-10 kt this evening.
Winds increase tonight with some gusts to 20kt after midnight.

     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: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 2-3 inches of
accumulation.

KLGA TAF Comments: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 2-3 inches of
accumulation.

KEWR TAF Comments: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 2-3 inches of
accumulation.

KTEB TAF Comments: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 2-3 inches of
accumulation.

KHPN TAF Comments: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 1-2 inches of
accumulation.

KISP TAF Comments: Best chance of steady snowfall with reduced
visibilities expected between 20z-02z with 2-4 inches of
accumulation.

.OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY...
.SAT...VFR. Chance MVFR after 18Z with isold -SHSN. WNW winds
G20-30KT daytime.
.SUN...VFR during the day. Chance MVFR in -RA/-SN towards
midnight.
.MON...Low chance MVFR in -RA for coastal terminals, light wintry
mix inland.
.TUE...MVFR possible. Slight chance of light -RA.
.WED...VFR. NW winds G20-30KT

&&

.MARINE...
The pressure gradient will tighten tonight as low pres passes S
and E of the waters. SCA conds are expected to develop late
this evening 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...Winter Weather Advisory until 1 AM EST Saturday for CTZ011-012.
     Winter Weather Advisory until 10 PM EST this evening for
     CTZ009-010.
NY...Winter Weather Advisory until 1 AM EST Saturday for NYZ079-081.
     Winter Weather Advisory until 10 PM EST this evening for
     NYZ071>075-078-080-176>179.
NJ...Winter Weather Advisory until 10 PM EST this evening for
     NJZ006.
MARINE...Small Craft Advisory from 10 PM this evening to 7 PM EST
     Saturday for ANZ330-335-338-340-345.
     Small Craft Advisory from 10 PM this evening to 1 AM EST
     Sunday for ANZ350-353-355.

&&

$$
SYNOPSIS...DS/NV
NEAR TERM...DS
SHORT TERM...NV
LONG TERM...NV
AVIATION...MD
MARINE...DS/NV
HYDROLOGY...DS/NV
EQUIPMENT...



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