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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KOKX 171542
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1042 AM EST Thu Jan 17 2019

.SYNOPSIS...
High pressure settles in just north of the region today. Low
pressure and a weakening warm front passes through tonight into
Friday morning, followed by high pressure briefly building in
late Friday and Friday night. A significant winter storm impacts
the region late Saturday into Sunday and will be followed by
arctic high pressure Monday into Tuesday. The next frontal
system approaches the middle of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast on track with just a few minor adjustments to reflect
latest observations.

A strong polar high pressure system just north of the area will
be in control today providing dry and seasonably cold
conditions. Temperatures closer to the coast are expected to get
to, or near freezing. Temperatures inland and to the north will
only get into the upper 20s to around 30. Used a consensus
blend for today as there was general agreement amongst the
guidance with the best cold advection taking place during this
morning. Most of the numerical guidance is suggesting that
clouds begin to overspread the region from the WSW to the ENE
during the early afternoon, with lowering clouds into the
evening. South and southwestern areas will be in and out of high
clouds this morning, otherwise lots of sunshine to start, and
then the clouds for the afternoon from a fast moving system
approaching from the Tennessee Valley.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
A weak and broad area of low pressure will approach tonight
along with some troughing aloft and shortwave energy. The energy
in the southern branch of the jet stream is quite strung out and
not all that impressive. The model consensus is for
precipitation to start during the late evening, give or take a
couple of hours from west to east. Not an impressive system with
some of the BUFKIT profiles showing some gaps in the moisture,
with the mid level forcing weak to say the least. Due to weak
omega, in general snowfall amounts will not exceed two inches,
and that may even be pushing it. Snowfall amounts on average
should be around an inch, with very little for far southeastern
sections, and up to about 2 inches in the hills in interior
northwestern sections. POPs and QPF have backed down a bit with
latest package, with QPF amounts generally around a tenth of an
inch. With ground temperatures quite cold anything that falls
should stick to most surfaces, even at the coast, at least to
start. The low level profiles begin to warm getting closer to
11-12z Friday across southeastern coastal sections where a
change to plain rain is likely towards daybreak, with a
changeover to plain rain across the city likely during the mid
to late morning just before the precipitation ends. Due to the
timing of the snow, it will be a bit slick in spots, especially
on secondary roadways to begin the Friday morning commute. If
the snow does have any difficulty sticking it will be due to a
lack of intensity, and not temperatures during the overnight.

The back edge of the precipitation should clear the city by the
late morning on Friday, and the early afternoon the latest
across far eastern sections, with clearing setting up for late
Friday afternoon into Friday evening as high pressure briefly
sets up shop. West winds will blow slightly stronger behind the
system, and can`t rule out a few gusts far east late in the day
as the system attempts to intensify to some degree well
offshore. Temperatures for Friday afternoon will actually nudge
back to slightly above normal levels before the colder air
returns into Friday night.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The main concern in the long term is the significant winter storm
for late Saturday into Sunday. This storm will be followed by the
coldest air of the season. There is high confidence in a high liquid
equivalent event, but confidence in PTYPE is much lower.

Arctic high pressure will be located across southeast Canada and
ridge down into New England on Saturday. At the same time, a
southern stream shortwave spawns low pressure across the southeast.
The southern stream is progged to remain progressive and positively
tilted with little phasing from the polar jet to the north. It
appears that the influence of the northern stream will not come into
play until the southern stream wave is near the east coast. This has
led to a consensus of a colder solution and a track of the low
further south and east than the previous forecast package. Dprog/dt
on the recent deterministic runs shows this general trend well
except the GFS/GEFS which appear to be an outlier solution and
remain much warmer than the rest of the guidance. The main energy
with the southern stream wave will be coming onshore today. There is
also sensitivity as noted above with the how much the polar jet
interacts and phases with the southern stream, so changes in track
forecast are still possible in subsequent forecast packages.

Saturday will be dry through the afternoon then warm advection
quickly takes shape with snow overspreading the region in the
evening. The air mass in place at the onset will be supportive of
all snow. Strong warm advection and an increasing southeasterly low
level jet should bring in warmer air aloft to bring a transition
zone. How quickly this occurs will be important along the coast for
the amount of snow accumulation.

This warm nose aloft will gradually spread inland to encompass the
entire area Sunday morning. Even the colder model solutions still
show this warming aloft due to the broad middle level low center
tracking initially to our west Saturday night and then over the
region Sunday morning. Precipitation should transition to plain rain
for much of NYC, Long Island, and southeast Connecticut late
Saturday night into Sunday morning. PTYPE for the rest of the area
may transition to sleet and/or freezing rain depending on the depth
of the low level cold below the warm nose. The colder solutions of
the ECMWF and NAM out through 12z Sunday show potential for a
quite deep cold layer below the warm nose, which would mean more
sleet rather than freezing rain. It is too early to say for
sure how this aspect will evolve, so for now will show a mixture
of sleet and freezing rain for the interior Sunday morning.
Once the low tracks east of the area, colder air rapidly rushes
back in from the north and west and will bring a gradual
transition back to snow as the precip ends.

A significant snow and sleet accumulation of 6 plus inches appears
likely across portions of the NW interior. The 00z ECMWF EPS
probability of 6 inches or more is around 80 percent across this
region. Amounts will decrease as one nears the coast with a few
inches possible, but this will ultimately be dependent on how
quickly the precipitation changes to a mix or rain. Significant
freezing rain accretion is also possible Sunday morning, especially
north and west of NYC. Please note that small changes in track will
have significant implications for the type of precipitation and
amounts.

While forecast amounts of snow, sleet, and freezing rain are of
lower confidence, there is higher confidence in a liquid equivalent
of 2 to 3 inches.

Temperatures rise into the upper 30s and low 40s along Long Island
and southeast Connecticut Sunday morning, but will rapidly drop back
below freezing in the afternoon and evening, any standing water
could quickly freeze, creating hazardous travel conditions even
where little wintry precipitation occurs.

Temperatures will continue to plummet through the overnight hours,
with lows Monday morning ranging from the single digits to near 10
degrees. Gusty northwest winds will result in wind chills around 5
to 15 degrees below zero. The lowest wind chills are most likely to
occur across the interior.

The arctic air remains in place on Monday as high pressure builds
into the region. Highs will only be in the teens with wind chills
staying 0 to 10 below. Temperatures should warm into to the 20s and
low 30s on Tuesday and then potentially above normal on Wednesday
ahead of the next system approaching the area.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
High pressure gradually retreats into the Canadian Maritimes
through tonight, as a weak coastal low approaches from the Mid
Atlantic.

High confidence in VFR through the evening push, then light
snow and MVFR conditions developing W-E late this evening and
into the overnight. IFR expected for at least a couple of hours
late tonight. Warmer air in the low levels will result in a
transition to a mix of snow and rain at coastal terminals near
the end of the TAF period, although there could be a few hours
of FZRA/FZDZ at NYC/LI terminals depending on how quickly
surface temperatures rise. Timing of this could be a few hours
off from current forecast.

Light winds (less than 10 kt) through the TAF period.

     NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component fcsts, can
be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

The afternoon KJFK haze potential forecast is GREEN, which implies
slant range visibility P6SM outside of cloud.

KLGA TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

The afternoon KLGA haze potential forecast is GREEN, which implies
slant range visibility P6SM outside of cloud.

KEWR TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

The afternoon KEWR haze potential forecast is GREEN, which implies
slant range visibility P6SM outside of cloud.

KTEB TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

KHPN TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

KISP TAF Comments: Timing in changes in wind direction could be
off +/- 1-2 hours.

.OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY...

*** HIGH IMPACT WEATHER LIKELY SATURDAY NIGHT INTO SUNDAY NIGHT***

.Friday morning...IFR becoming VFR late morning. Light snow
changing to rain at coastal terminals (FZRA/FZDZ possible early)
before ending. KSWF/KHPN should remain all snow. Runway
accumulations of about 2 inches at KSWF, and around an inch
elsewhere.
.Friday afternoon-Saturday morning...VFR. NW-N winds G15-20KT
possible at night.
.Saturday afternoon/evening...Becoming IFR or lower with snow
developing from W to E. LLWS possible late.
.Late Saturday night...IFR or lower conditions likely. Snow changing
to rain at City/Long Island terminals and to a wintry mix at
northern terminals. LLWS likely.
.Sunday-Sunday night...IFR. Precipitation changing to all rain
Sunday morning except possible continued wintry mix for Lower Hudson
Valley Terminals. Precipitation changing back to all snow Sunday
afternoon/evening before ending later Sunday night. LLWS possible in
the morning. Flash freeze possible Sunday afternoon/evening. NW
winds G30-35+KT probable Sunday afternoon/night.
.Monday...Most likely VFR, low chance of MVFR in any snow showers.
NW winds G25-35KT possible.

&&

.MARINE...
High pressure builds over the coastal waters today with sub SCA
conditions with lowering seas and winds. A weak frontal system
moves through the waters Thursday night and Friday with sub SCA
conditions continuing. Tranquil conditions continue over the
waters through the day on Saturday before an approaching low
results in deteriorating conditions Saturday night. SCA
conditions are expected to develop beginning Saturday night and
continue through the day on Monday, with gale force gusts on the
ocean water and potentially the near shore waters Sunday
afternoon into Monday. Winds should begin to subside below SCA
levels Monday night, but ocean seas may remain elevated.

&&

.HYDROLOGY...
For Thursday night into Friday morning light precipitation is
expected with liquid amounts under a quarter inch.

Two to three inches of liquid equivalent precipitation is
likely Saturday night through the day on Sunday. Frozen
precipitation may be predominate across the interior. Liquid
rain is probable closer to the coast Sunday morning into early
Sunday afternoon where minor urban and poor drainage flooding is
possible in any periods of heavier rain.

&&

.TIDES/COASTAL FLOODING...
Minor to locally moderate coastal flood impacts are possible during
the Sunday morning high tide cycle. Departures of one to one and
a half feet, locally two feet, are needed for minor benchmarks
to be reached and two and a half to three feet are needed for
moderate benchmarks to be reached.

&&

.EQUIPMENT...
NYC Central Park winds are out of service until further notice.
Loss of data is due to a severed cable. Parts are on order.

NYC NOAA Weather Radio Station KWO35 (162.55 MHz) will remain off
the air for an extended period of time.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$

SYNOPSIS...JE/DS
NEAR TERM...BC/JE
SHORT TERM...JE
LONG TERM...DS
AVIATION...Maloit/DS
MARINE...JE/DS
HYDROLOGY...JE/DS
TIDES/COASTAL FLOODING...
EQUIPMENT...