NYC Office Forecast Discussion

204
FXUS61 KOKX 180133
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
833 PM EST Thu Jan 17 2019

.SYNOPSIS...
Low pressure passes south of the region 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 /THROUGH FRIDAY/...
A weak area of low pressure and associated upper level trough
will move across the area tonight and Friday morning. A light
snow event is expected from late this evening through the
overnight hours. This is a weak system with limited moisture
and weak lift. As such, QPF values will remain around a tenth
of an inch, which should yield snowfall amounts around an inch
or so, with the potential for 1.5 inches across the Lower Hudson
Valley.

As mentioned, snow overspreads the region sometime around
midnight and comes to an end between 6-8am. Areas east of NYC
may see precipitation linger in the late morning and possibly
even the early afternoon, however, temperatures should warm
during the morning hours, allowing any light snowfall to change
over to rain before ending. There is a very low chance for some
light freezing rain/drizzle as the precipitation comes to an end
Friday morning as moisture depth decreases, however that threat
appears too low at this time to include any freezing rain in
the forecast. A special weather statement has already been
issued.

As the precipitation comes to an end Friday morning/early
afternoon, expect clearing conditions and a light and variable
wind to become a bit more westerly with speeds 5-10 mph.

Lows tonight fall into the 20s, and highs on Friday climb into
the upper 30s and lower 40s.

&&

.SHORT TERM /FRIDAY NIGHT/...
High pressure will provide the region with dry conditions.
Mostly clear skies and light winds will allow temperatures to
fall into the 20s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
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 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 still
appears that the influence of the northern stream will not come into
play until the southern stream wave is near the east coast.

Regarding the track of the storm, some of the model guidance has
shifted closer to coast as compared to model runs 12 hours ago, and
others have shifted farther away. Better RAOB sampling should
occur with tonight`s model run, so hopefully a trend becomes
more established. With that said, changes in track forecast are
still possible in subsequent forecast packages. There is however
increasing confidence that an elevated warm layer will be
strong enough and push far north enough such that it encompasses
the entire area at some point, so it doesn`t appear to look
like an all-snow event anywhere at this point.

PCPN begins as snow everywhere, and becomes likely from around
NYC and points west by the end of Saturday afternoon. Snow will
then push west through the rest of the forecast area by
midnight. As the warm air aloft rushes in, sleet and freezing
rain is expected for most spots, and a changeover to plain rain
should occur for all coastal areas by sunrise on Sunday.
Meanwhile, primarily sleet and freezing rain for inland areas by
sunrise. The storm center shifts to our east Sunday morning,
with the warm nose aloft beginning to erode. This cooling aloft
and at the surface will be more pronounced in the afternoon, and
PCPN therefore eventually transitions back to all snow as it
comes to an end towards Sunday night. During this transition,
any standing water could quickly freeze, creating hazardous
travel conditions even where little wintry precipitation occurs.

A Winter Storm Watch has been issued for most of the forecast
area for the combination of snow/sleet accumulation and ice
accretion. Highest snow/sleet accumulations are expected mainly
NW of NYC where mostly 4 to 8 inches is currently forecast, and
possibly even higher towards Putnam and Orange Counties. Most
other areas are expected to see less than 6 inches of
snow/sleet, however with the potential of at up to around a
tenth or two of ice accretion in addition to snow/sleet,
hazardous conditions are possible for these locations as well.
The only areas not currently under a watch are parts of Long
Island where 1-3 inches of snow/sleet is expected and maybe at
least a trace of ice could occur. An advisory could eventually
be needed for this areas depending on the forecast trends.

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. 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. Timing and thermal
profiles with this next system are uncertain due to model
disagreement, so for the time being have in chances of rain/snow
primarily for Wednesday night, but PCPN could occur Weds afternoon
and Thurs afternoon.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Low pressure will pass to the south tonight into Friday morning,
followed by high pressure briefly building in late Friday.

High confidence in VFR through mid-evening. Conditions then
become MVFR, then IFR as light snow develops late this
evening/early overnight and continues into Friday morning. For
now appears should remain all snow across the region, except for
maybe mixing in some rain at KISP/KJFK right before ending late
Friday morning. Conditions improve to MVFR after the snow ends
mid Friday morning-early Friday afternoon from W to E.
Improvement to VFR expected late.

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: AMD possible to adjust timing of snow onset.

KLGA TAF Comments: AMD possible to adjust timing of snow onset.

KEWR TAF Comments: AMD possible to adjust timing of snow onset.

KTEB TAF Comments: AMD possible to adjust timing of snow onset.

KHPN TAF Comments: AMD possible to adjust timing of snow onset.

KISP TAF Comments: AMD possible to adjust timing of snow onset.

.OUTLOOK FOR 00Z SATURDAY THROUGH MONDAY...

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

.Friday night...VFR. NW-N winds G15-20KT possible.

.Saturday...VFR AM, then snow with IFR vsby developing in the
afternoon, especially from the NYC metros north/west.

.Saturday night...IFR or lower conds throughout. Snow changing
to rain after midnight at NYC/Long Island terminals, and to a
wintry mix at northern terminals. LLWS likely NYC metro/coastal
terminals.

.Sunday...IFR or lower likely. Precipitation changing to all
rain in the morning, except possible continued wintry mix for
Lower Hudson Valley Terminals, then changing back to all snow
throughout mid to late afternoon. LLWS possible in the morning.
N-NW winds G25-30kt and flash freeze likely in the afternoon.

.Sunday night and Monday...Chance of snow with IFR conds early
evening, then VFR. NW winds G25-35KT.

.Monday night...VFR. NW winds G25kt in the evening.

.Tuesday...VFR.

&&

.MARINE...
A weak low pressure system will move across the waters tonight
and Friday with sub SCA conditions on all waters. Tranquil
conditions will 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 tonight 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...Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for CTZ005>012.
NY...Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for NYZ067>075-078-176>179.
NJ...Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for NJZ002-004-006-103>108.
MARINE...None.

&&

$$

NWS OKX Office Area Forecast Discussion