NWS Forecast Discussion - New York City Area

Forecast Discussion for OKX NWS Office
000
FXUS61 KOKX 160524
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1224 AM EST Sun Dec 16 2018

.SYNOPSIS...
A series of weak low pressure systems pass to the south of the
area through the weekend while high pressure remains centered to
the north. Low pressure departs to the northeast Monday as a
Canadian cold front passes through the area. High pressure
builds mid week. Low pressure tracks to the west late in the
week, as a warm front passes.

&&

.NEAR TERM /THROUGH TODAY/...
Minor changes were made to reflect current conditions.

Analyzed all available datasets to determine temperatures
forecasts overnight, and feel advisory for freezing rain is
fine, with main concern those interior zones. Temperatures so
far are a few degrees warmer than some of the higher resolution
guidance, but still feel there is potential for temps to fall
to or just below freezing across the advisory area.

Per previous discussion, primary concern into Sunday is the
potential for freezing rain to develop across far northern NJ,
the lower Hudson Valley and portions of western Connecticut.
Cold air damming at the surface as the high builds to our north
will allow temperatures to lower to right around freezing in
these areas. Coincidentally as the upper low nears, low level
warm advection will strengthen in strong easterly flow above the
surface, allowing a warm layer to develop between around
875-600 mb. As always, there is significant uncertainty
regarding the extent of cold air damming, but it is typical for
model forecasts to underdo the cold air, and then erode it too
fast once established. Trended on the colder side, more towards
the operational NAM, on temperatures, keeping forecast readings
near freezing through much of the day where a Winter Weather
Advisory is now in effect. The Cooperative Institute for
Precipitation Systems (CIPS) historical analogs reflect high
probabilities for freezing rain across the aforementioned areas,
lending some confidence towards a colder surface solution. It
is possible that freezing rain continues well into the
afternoon.

There are certainly two potential scenarios in which the
forecast could develop differently as well:

1. The colder/below freezing solution does not materialize, and
while a cold rain falls, freezing upon contact at the surface
does not occur.
2. As the upper low passes, colder temperatures aloft lead to
weak elevated instability, which may locally enhance precipitation
rates and even mix a bit of graupel in with the freezing rain.
If instability can develop, ice accumulations may be greater
than the 0.10-0.25 inch currently forecast for the advisory
areas.

Outside the advisory, confidence is low in both temperatures and
the expected amount of ice. A Special Weather Statement is in
effect highlighting the potential for ice in those periphery
areas, and should forecast/model solutions trend colder, then an
advisory may be needed.

Elsewhere, a cloudy rainy day is expected as the upper trough
finally moves over the area, with the main concern being breezy
conditions that will develop overnight and persist into Sunday.
Temperatures will range from 5 to 10 degrees below climatological
normals.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM MONDAY/...
The upper low and an attendant coastal low quickly depart to the
northeast Sunday night in advance of a long wave trough,
allowing a cold front to move through the area. Any ongoing
precipitation may transition to snow as cold advection
strengthens, with quick but minimal accumulations primarily to
the north and west of the NYC area. Breezy conditions continue
behind the front, combining with lowering temperatures to make
it feel as though it is in the 20s overnight. Across the
interior - have extended the Winter Weather Advisory into Sunday
night to account for these additional potential accumulations.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Aloft, vigorous upper shortwave dives out of eastern Canada, quickly
passing across the northeast Monday into Tuesday. Ridge quickly
builds in for mid week. Next shortwave energy out of central Canada
will result in deepening longwave trough across the mid portion of
the country Thursday. This trough pivots east before lifting
northeast into eastern Canada by next weekend.

At the sfc, reasonable model agreement noted as deepening low
pressure moves northeast toward the Canadian Maritimes Monday. A
cold front passes late in the day. High pressure then builds Tuesday
and Wednesday.

By Thursday, low pressure develops over the Tennessee valley,
deepens and moves north across the Great Lakes region Friday into
Saturday. A warm front likely sweeps north Friday, followed by a
series of troughs Saturday.

As for sensible weather, any light wintry mix precip ends early
Monday morning. Do not foresee much precip with the upper shortwave
and associated cold front later Monday other than perhaps some
flurries. However, appears there is too much dry air to overcome.

Dry weather persists mid week thanks to ridging and associated
subsidence, then rain chances increase Thursday as deep southerly
flow and WAA commence, enhancing lift. Steadier rain likely impacts
the area Thursday night into early Friday based on timing from 12Z
model suite, with mid level drying likely lowering coverage Friday
afternoon through Saturday.

Near normal temps Monday will fall below seasonable Monday night and
Tuesday due to CAA behind the front. This will be short lived as
ridge builds, followed by deep south flow ahead of amplifying trough
to the west. Temps rise back to above normal Thursday-Saturday.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
A series of lows track to the south of Long Island into Sunday
evening, as high pressure to the north retreats to the northeast
during Sunday.

The onset of steady and widespread precipitation may be delayed an
hour or two later than indicated in the forecast as the high
remains to the north, keeping drier air in the vicinity.

VFR conditions remain, possibly as late as 09Z, then lower to MVFR
as light rain becomes more widespread and steady.

With temperatures still above freezing across the lower Hudson
Valley at 05Z, the chance of light freezing rain at KSWF is reduced.
And with warmer air aloft a brief period of sleet will also be
possible at the onset of precipitation. Uncertainty remains with how
low surface temperatures across the lower Hudson Valley will fall.
If temperatures remain above freezing overnight at KSWF, then plain
rain will be likely.

IFR develops early Sunday morning, around 12Z, especially along the
coast. Periods of LIFR will be possible during Sunday with moderate
to briefly heavy rainfall. Conditions gradually improve to MVFR
Sunday evening, then to VFR late Sunday night.

NE winds 10-15kt increase overnight with sustained winds of 15 to
20kt, highest near the coast. Gusts have become frequent with gusts
25 to 30kt. LLWS likely Sunday morning with the strongest near the
Long Island south coast. As low pressure begins to move to the east,
winds will back to more northerly and then northwest late
Sunday night.

.OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY...
.Late Sunday night...MVFR/IFR in rain. There is the potential for
wintry mix across interior terminals as precipitation tapers off,
then becoming VFR toward 12Z. NE to N winds G20-30kt mainly across
the eastern terminals.
.Monday-Monday night...VFR. NW winds G20-30KT probable.
.Tuesday-Wednesday night...VFR. NW Wind G15-20kt possible Tuesday, W-
WSW winds G15-20KT possible Wednesday.
.Thursday...VFR, possibly becoming MVFR or lower late with rain.
LLWS possible late.

&&

.MARINE...
East-Northeast winds and gusts continue to increase tonight
into Sunday as low pressure deepens along the coast and high
pressure remains to the north. The strongest low-level winds are
expected into Sunday afternoon, where there is potential for
isolated storm-force winds to mix to the waters. A gale warning
is now in effect for all waters.

Although winds decrease somewhat Sunday night as the low passes
along the coast, it is likely SCA-level winds will continue, and
seas will remain elevated on the ocean waters.

Winds temporarily diminish early Monday as the low departs to
the Canadian Maritimes. A cold front passes across the waters
late Monday, and winds increase once again Monday night into
Tuesday. In fact, gale force winds are possible once again.
Winds will diminish Tuesday night through Wednesday as high
pressure builds. Winds shift around to the S/SE Thursday, and
will increase late in the day ahead of deepening low pressure to
the west.

Rough seas Monday and Tuesday are expected to subside mid week as
the winds diminish. Seas build late Thursday and Thursday night.

&&

.HYDROLOGY...
Between 0.50" and 1.25" of rainfall is then expected late
tonight through Sunday night. The highest rainfall amounts are
currently expected across portions of northeastern New Jersey,
NYC, and Long Island. A period of moderate to heavy rainfall
will be possible Sunday morning. Low chances of minor
nuisance/poor drainage flooding will be possible during the
daytime on Sunday.

Next chance for significant rainfall of at least a half an inch will
be late in the week. Too early to determine if there will be any
hydrologic concerns with this potential late week event.

&&

.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...Winter Weather Advisory until 6 AM EST Monday for NYZ067-068.
NJ...Winter Weather Advisory until 6 AM EST Monday for NJZ002.
MARINE...Gale Warning until midnight EST tonight for ANZ330-335-338-340-
     345-350-353-355.

&&

$$

NWS OKX Office Area Forecast Discussion