Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 131409
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
909 AM EST Thu Dec 13 2018

.SYNOPSIS...
High pressure shifts offshore today as a quick moving low pressure
system brings rain and snow to the region. A frontal system and
associated low pressure will impact the area this weekend. High
pressure returns through the middle of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
With high pressure remaining to the northeast and subsidence and
dry air at the lower levels across southeastern Connecticut and
the twin forks of Long Island, adjusted probabilities slightly
Precipitation remains all light snow and will transition to rain
as warmer air moves in this morning.

Precipitation should continue to overspread the area as the
morning progresses. Dew points are in the single digits across
much of southern Connecticut with a more northeasterly flow
noted. This may mean a more prolonged period of virga for this
area and may delay the onset of snow for this area. In fact, the
most recent run of the HRRR has much of the area dry through
much of the day, though it does seem a bit too dry.

A vigorous upper level low will approach from the Great Lakes
and track just to the north of the CWA today. While there won`t
be a lot of moisture with this feature, warm air advection via a
developing 20-25 kt S/SE LLJ will moisten the lower levels. The
onset time of the precipitation will be critical for snow
accumulation potential, especially along the coast. Models
continue to indicate temperature profiles will remain cold
enough for all snow across the interior, while a transition of
snow to rain is likely across the coast.

Increasing cloud cover already allowing temperatures to level off,
remaining above freezing across NYC and Long Island. Temperatures
could drop a degree or two, but onshore flow will raise temperatures
into the 30s fairly quickly this morning into early afternoon, while
temperatures will remain at or just below freezing across the
interior.

Expecting precipitation to move into the area after 8-9am, starting
as light snow. A dusting to around an inch is likely before a
changeover to rain fro the NYC metro area and northwestern Long
Island. A general 1-2 inches is likely across northwestern zones as
temperatures will remain below freezing. Southeastern CT and eastern
LI may see little to no snow accumulation as temperature
profiles will warm before precipitation develops.

Temperatures during the day will rise into the 30s to mid 40s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Despite mid level drying, lingering low level moisture across
the interior will bring the chance for spotty freezing drizzle
tonight. Not expecting much in the way of ice accumulation, so
have opted for no advisory at this time. Dry conditions are then
expected Friday morning before the next system arrives.

Low temperatures tonight will drop into the upper 20s to upper 30s,
with highs on Friday going above normal, in the mid 40s to
around 50.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
A more significant rainfall event is in store for the area Friday
night and potentially through the weekend. A frontal boundary will
be in the vicinity Friday night. A weak area of low pressure is
forecast to form along this boundary off the mid-Atlantic coast
Saturday morning and track northeast. A period of moderate to
briefly heavy rain is possible late Friday night into Saturday
morning for some portion of the forecast area. The details are still
uncertain at this time, given model spread, so did not add this to
the forecast due to uncertainty of where the axis of heavy rain
would be just yet.

Models further diverge on solutions Saturday night, mainly due to
the position of surface high pressure to our north that may dig far
enough south to cut off any precipitation Saturday night as per the
ECMWF.

As for precipitation type, plain rain is expected for the entire
area from Friday night through Saturday night. Enough cold air could
move into the far northern areas across the Lower Hudson Valley and
southwestern Connecticut to change rain to freezing rain or a mix to
freezing rain and sleet Sunday morning. However, this should be
brief as low level temperatures warm up enough to change it back to
rain.

Thereafter, the primary low over the southeast U.S. will push off
the mid-Atlantic coast and will reintroduce rain Sunday and Sunday
night, with the area drying out for Monday. There is the possibility
for some light precipitation to continue for Monday as a shortwave
moves through the Northeast, but right now, the thinking is that
precipitation will be limited to north of our area.

High pressure will keep the area dry through the middle of next
week, with temperatures at or below normal for this time of
year.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
A weak upper disturbance moves across the area today resulting in
light precipitation. This disturbance passes east tonight.

VFR will lower to MVFR and possibly IFR as light snow or
flurries develop across the NYC and Lower Hudson Terminals.
Coastal locations primarily KJFK and KISP are likely to see a
quick changeover to rain as the low-levels gradually warmup.

Any snow accumulations will be less than an inch, around one to
two inches interior.

MVFR/IFR ceilings persist tonight. Patchy freezing rain or
drizzle is possible NW of NYC.

NE-E winds 10-15 kt at the coast and 5 to 10 kt across the
interior will lighten tonight.

      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: Timing of lower clouds and wintry precip onset
may be off an hour or two.

The afternoon KJFK haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KLGA TAF Comments: Timing of lower clouds and wintry precip onset
may be off an hour or two. In addition, timing for transition to
rain may be off an hour or two as well.

The afternoon KLGA haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KEWR TAF Comments: Timing of lower clouds and wintry precip onset
may be off an hour or two.

The afternoon KEWR haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: Timing of lower clouds and wintry precip onset
may be off an hour or two.

KHPN TAF Comments: Timing of lower clouds and wintry precip onset
may be off an hour or two.

KISP TAF Comments: Timing of lower clouds and wintry precip onset
may be off an hour or two.

.OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY...
.Friday...MVFR to start, then MVFR/IFR conditions late in rain.
.Saturday...IFR likely in rain.
.Sunday and Monday...MVFR possible in a chance of rain.

&&

.MARINE...
Winds and seas will remain below SCA criteria through Friday.

An extended period of SCA is possible from Saturday night through
Monday as a complex frontal system and low pressure impacts the
area. Waves will increase Saturday night on the ocean zones, with 5
to 7 ft waves expected by late Saturday night, peaking to about 10
ft for extreme southeast portions of the eastern ocean zone Sunday
night. Waves diminish late Sunday night into Monday.

Winds will also increase during the same time frame, with 25 kt
possible on the ocean zones, Peconic and Gardiner Bays, and the
eastern sound Saturday night. At this time, gusts should remain
below gale force, but gusts into the lower 30 kt range is possible
for the first half of Sunday night for the ocean zones.

&&

.HYDROLOGY...
No significant widespread liquid equivalent amounts expected through
Friday.

Between 0.75" and 1.50" of rainfall is expected from Friday night
through Sunday, with more rainfall possible thereafter through at
least Sunday night. No widespread flooding is expected due to the
long duration and antecedent dry conditions. However, minor urban
and poor drainage flooding is possible.

&&

.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...CB/JP
NEAR TERM...CB/JP/19
SHORT TERM...CB
LONG TERM...JP
AVIATION...IRD/PW
MARINE...CB/JP/19
HYDROLOGY...CB/JP
EQUIPMENT...


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