Area Forecast Discussion
Issued by NWS Upton, NY

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252
FXUS61 KOKX 191153
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
653 AM EST Thu Jan 19 2017

.SYNOPSIS...
Weak high pressure will be in control through Friday morning.
An upper level disturbance approaches from the south Friday and
weakens as it moves across Friday night. High pressure briefly
returns Saturday. Deepening low pressure moving across the
southern states on Sunday will reach the southern Mid Atlantic
region by Monday morning, while high pressure builds southeast
into the Canadian Maritimes. The low will intensify into a
significant coastal storm as it moves up the coast toward the
area Monday through Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Temperatures continue to be largely above freezing except across
the interior where several mesonets and MGJ are at or a few
degrees below. Ground temperatures are also near freezing. Patchy
fog continues so there is likely some mist in spots which could
lead to some icy conditions from black ice across the higher
elevations. Have expanded the SPS to include all of the interior.
Visibilities have generally stayed above 1 mile and actually have
seen some improvement over the last few hours so do not think
dense fog will occur.

Northern stream shortwave passes early this morning with overcast
skies at sunrise. Clouds will begin to clear through the morning
as NW downslope flow dries out the lower levels of the atmosphere
behind the shortwave. Mostly sunny skies are forecast thereafter
with temperatures rising to around 10 degrees above normal.
Readings range from the upper 40s inland to the low 50s in NYC/NJ
metro and Long Island. It would not be out of the question for
readings to be a bit higher based on the anomalously mild pattern
we are currently seeing across the country.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Middle and upper level ridging builds overhead tonight with surface
high pressure in control at the surface. Some hints at returning
stratus deck overnight on the 00Z NAM12. However, this appears
aggressive and will go with a mostly clear forecast. Time heights
from the 4-km nam and GFS show some increase in moisture around
2kft, but not enough to warrant a broken or overcast deck of
stratus. Lows will range from the upper 20s inland to the lower and
middle 30s near the coast and NYC metro.

Southern branch shortwave energy across the midwest will eject
eastward and shear out as it approaches on Friday. The ridge axis
moves overhead Friday and weakens in response to the approaching
energy. Frontal boundary associated with this system likely stays to
the south, but with the energy approaching clouds increase from
south to north through the day. Much of the daytime on Friday will
be dry with pops increasing to likely in the late afternoon and
early evening for mainly the NYC metro and NE NJ tapering to chance
into the Hudson Valley and western Long Island. There is good
agreement among the 00z GFS, GEFS, ECMWF, CMC, NAM, RGEM, and SREF
in an average of a tenth of an inch of liquid between 21z Fri and
00z Sat where likely pops are forecast.

High temperatures on Friday continue about 5 degrees above normal in
the lower and middle 40s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Likely PoP in the forecast for Friday night for NYC metro, the lower
Hudson Valley, and western Long Island as a weakening frontal system
moves across. With the upper level support plowing into a longer
wave ridge and shearing out, chances for rain appear lower across
most of southern CT and eastern Long Island. Another trailing
shortwave may produce a few sprinkles or showers Saturday afternoon,
with the bulk of the day being dry and on the mild side, with
highs 50-55.

Attention focuses thereafter on a storm forecast to take shape as
Pacific upper jet energy crashing onshore the California coast
later this week consolidates over the southern states this
weekend, then intensifies over the Mid Atlantic region as the
upper level system closes off and becomes negatively tilted, and
as it picks up significant moisture aloft from a tropical
connection to the Caribbean and Eastern pacific and interacts with
a vertically stacked high moving into the Canadian Maritimes. For
us this spells potential for multiple impacts including strong
winds, heavy rain and coastal flooding, with likelihood of
occurrence in that general order. EPS probabilities for wind gusts
over 50 kt have been as high as 60-80 percent for the immediate
coastline for two successive cycles, and the extended 00Z
GFS/ECMWF MOS guidance predicts sustained winds 25-30 kt along the
coast and in the higher interior elevations. Most of the rain
should fall over a fairly long period of time, but there is
potential for a period of heavy rain and some rumbles of thunder
late day Monday into Monday evening as the low moves up the coast,
with low level moisture convergence becoming maximized via a 60-70
kt easterly LLJ and lessening static stability, with TT indices
approaching 50 and Showalter indices dropping to about 1C.

These impacts could last into Tuesday if the storm slows down more than
model fcst, which is quite possible as it closes off aloft.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
High pressure builds in from the west through the TAF period. VFR
is expected to endure today into much of tonight, although there
will be a chance late going into Friday morning of MVFR/IFR
stratus before rain moves in.

Winds will be generally NW under 10 kt through early afternoon and
then NW near 10 kt for mid to late afternoon. Winds drop off again
tonight to a more northerly direction at near 5 kts or less.

     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: Winds could be a few kts higher than forecast
this afternoon.

KLGA TAF Comments: Winds could be a few kts higher than forecast
this afternoon.

KEWR TAF Comments: Winds could be a few kts higher than forecast
this afternoon.

The afternoon KEWR haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KTEB TAF Comments: Winds could be a few kts higher than forecast
this afternoon.

KHPN TAF Comments: Winds could be a few kts higher than forecast
this afternoon.

KISP TAF Comments: Winds could be a few kts higher than forecast
this afternoon.

.OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY...
.Friday-Friday night...MVFR or lower in -RA, mainly late Friday
afternoon through Friday evening.
.Saturday-Saturday night...Mainly VFR.
.Sunday-Sunday night...MVFR or lower in -RA, mainly late Sunday
afternoon through Sunday night. Moderate rain develops at night.
NE gusts 20-25 kt by end of Sunday afternoon. NE gusts 30-40 kt
Sunday night.
.Monday...Chance of IFR with moderate to heavy rain and strong E-NE
winds. NE gusts 35-45 kt.

&&

.MARINE...
Small craft advisory for hazardous seas remains in effect on the
ocean waters through 05z. Easterly swell from offshore low should
help keep seas above 5 ft through the day before subsiding this
evening. If the trend is slower than currently forecast, the SCA may
need to be extended into a portion of the overnight, mainly for the
eastern ocean waters.

Otherwise...A relaxed pressure gradient will keep winds and seas
below SCA levels on all waters through Saturday.

An intensifying storm moving up the coast early next week will
likely bring easterly gales to all waters from Sunday night into
Monday night, Storm force wind gusts may be possible on the ocean
and easternmost Long Island Sound.

&&

.HYDROLOGY...
No significant precipitation is expected through Saturday night.

Significant rainfall of 1.5 to 3 inches, with locally higher amounts
over 4 inches, is likely with a coastal storm early next week.
Highest rainfall amounts currently expected across Long Island and
coastal CT. This should be enough to cause at least minor areal
flooding. Current 24-hour FFG of 4 inches for the Yantic River in
eastern CT suggests small stream flooding may be likely, and minor
flooding of some larger rivers is not totally out of the question,
should the higher rainfall amounts materialize.

&&

.TIDES/COASTAL FLOODING...
A coastal storm may cause minor to locally moderate coastal flooding
if its highest surge coincides with the morning high tide cycle
either Mon or Tue, which is the higher of the two daily high tide
cycles.

Surge needed to cause minor coastal flooding is about 1.5-2.5 ft on
the Long Island South Shore back bays, and 2.5-3.0 ft elsewhere.

Surge needed to cause moderate coastal flooding is about 2.5-3.0 ft
on the Long Island South Shore back bays, and 3-4 ft elsewhere.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory for hazardous seas until 6 PM EST this
     evening for ANZ350-353-355.

&&

$$
SYNOPSIS...Goodman/DS
NEAR TERM...DS
SHORT TERM...DS
LONG TERM...Goodman
AVIATION...JM
MARINE...Goodman/DS
HYDROLOGY...Goodman/DS
TIDES/COASTAL FLOODING...



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