Area Forecast Discussion
Issued by NWS Upton, NY-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KOKX 191300
Area Forecast Discussion
National Weather Service New York NY
800 AM EST Thu Jan 19 2017
Weak high pressure will be in control through Friday morning.
An upper level disturbance will approach from the south on
Friday, and weaken as it moves across Friday night. High pressure
will then briefly return on 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/...
Temps now at or just below freezing across a fair number of areas
outside NYC metro. Ground temperatures are also near freezing.
Patchy fog continues so there is likely some mist in spots which
could lead to some icy conditions, and have again expanded the SPS
to include all of the interior NW of NYC and Bridgeport, and
Suffolk. 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 mostly
cloudy skies in most places early. 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
.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
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 /13Z THURSDAY THROUGH MONDAY/...
High pressure builds in from the west through the TAF period.
Mainly VFR conditions are expected today into much of tonight,
although there are some areas of MVFR/IFR fog this morning. Also
another exception will be Friday when there will be another chance
of MVFR/IFR before and with the rain.
Winds will be generally W to 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
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
KLGA TAF Comments: Winds could be a few kts higher than forecast
KEWR TAF Comments: Winds could be a few kts higher than forecast
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
KHPN TAF Comments: Winds could be a few kts higher than forecast
KISP TAF Comments: Winds could be a few kts higher than forecast
this afternoon. MVFR/IFR end time could vary an hour from
.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
.Monday...Chance of IFR with moderate to heavy rain and strong E-NE
winds. NE gusts 35-45 kt.
SCA for Hazardous Seas remains in effect on the ocean waters
today. Easterly swell from an 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 tonight, mainly east.
Then winds and seas should be below SCA levels on all waters
through Sunday morning.
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.
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.
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
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.
MARINE...Small Craft Advisory for hazardous seas until 6 PM EST this
evening for ANZ350-353-355.