Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 101825
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
125 PM EST Sat Dec 10 2016

.SYNOPSIS...
High pressure continues to settle over the region this weekend.
Low pressure then tracks across the Great Lakes Sunday night into
Monday, sending a warm front through the region. A cold front will
follow for Monday afternoon into Monday evening. High pressure
will then briefly build in for Tuesday before another southern
branch low possibly impacts the area for the mid week period. An
arctic cold front then follows behind the system Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Forecast generally on track with minor changes to high
temperatures as several locations near the city and on Long Island
have already reached previously forecast highs. Readings will only
rise a degree or so more from forecast as mid level clouds
continue to increase this afternoon with approach of shortwave.
Highs in the lower to middle 30s, around 10 degrees below normal
for this time of year. Isolated flurries are still possible this
afternoon with a bit better chance across Orange County.

For tonight, the atmosphere will become drier with more
subsidence as weak high pressure moves across the region. With
this high being weak, going into daybreak Sunday, there will be
mid to high level clouds moving in ahead of the next low pressure
system. Used a less vast spatial variance with lows consisting of
GFS MOS.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
High pressure slides offshore Sunday with an approaching warm
front. The warm front moves across Sunday night into Monday with a
subsequent cold front crossing Monday afternoon into early Monday
evening. Main upper level shortwave with more amplified pattern
and right rear quad of upper level jet moving in Sunday night into
Monday.

Dry conditions will be in place initially Sunday but the
precipitation chances will rapidly increase from afternoon into
evening. Initial precip type expected to be snow with cold airmass
in place and wet bulb cooling. Then a transition to rain will take
place from south to north Sunday night with some freezing rain across
the interior.

Monday the transition to rain continues for interior locations and
the rest of the event is expected to be mainly rain. The rain tapers
off Monday evening after the cold frontal passage. A more westerly
flow will advect in drier air.

Temperatures Sunday used the lower ECS and MAV guidance considering
limited vertical mixing. Used raw model temperatures of ECMWF and
NAM12 for Sunday night and Monday but for Monday blended it with
GFS MOS. GFS MOS was used for Monday Night. Expect non-diurnal
trend to temperatures Sunday night with temperatures slowly
rising.

Potential for interior locations to have 3-5 inches of snow and
some locations near interior NE NJ and Lower Hudson Valley could
see a period of freezing rain with light ice accumulations
possible of under a tenth of an inch. Elsewhere, looking at near 1
inch of snow or less with mostly rain anticipated. Bulk of precip
is Sunday night into Monday.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Upper air pattern will feature an anomalously high amplitude ridge
over Alaska, which will allow the polar vortex to drop southward
into central and eastern Canada by midweek. This will open the
door for the coldest airmass of the season for the second half of
the week.

High pressure will briefly follow for Tuesday with temperatures
just below seasonable levels. Another piece of Pacific shortwave
energy races across the country. Global models vary with the
amplitude of this feature with the nearly zonal flow in the
southern branch of the polar jet. The amount of phasing with the
northern branch looks to be the difference. Due to the fast flow,
there is likely to be uncertainty in the magnitude of this system
the next several days. For now. will run with a chance of
rain/snow Wednesday afternoon/night. Arctic air then spills
southward on the backside of the system Thursday into Friday with
daytime highs possibly not getting above freezing with overnight
lows in the single digits to teens. These values are 15 to 20
degrees below normal. To make matters worse, strong NW winds will
follow for Thursday producing very cold wind chill values.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
***HIGH IMPACT WEATHER LIKELY LATE SUNDAY NIGHT INTO MONDAY
 MORNING***

Upper level disturbance moving across the area this afternoon will
produce BKN VFR cigs 040-050 and scattered snow showers/flurries.
Any restrictions to vsby reduction will be brief. WNW flow left of
310 magnetic just over 10 kt with gusts 15-20 kt also expected.

High pressure approaches tonight with a diminishing WNW flow,
then moves offshore on Sunday with a return S/SW flow developing
by afternoon. Mid and high level clouds increase Sunday morning
ahead of an approaching warm front. Light snow is forecast to
develop Sunday afternoon with possible MVFR conditions. Confidence
in sub-VFR cigs and vsbys is low to moderate as it may take a long
period of time to saturate the low levels.

.OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY...

.Sunday afternoon...Mainly VFR. Chance of light snow in the
afternoon with possible MVFR.

.Sunday night...IFR/LIFR conditions developing, with snow mixing
with and changing to rain at most terminals. LLWS possible late
NYC metros/coast. S winds G25KT late at the NYC metros and KISP.

Here are the most likely precip types and snowfall accumulations:

KISP/KJFK/KLGA/KBDR/KGON: Snow changing to rain by midnight, with
a coating to an inch accumulation.

KEWR/KTEB/KHPN: Snow mixing with and changing to rain late, with
1-2 inches accumulation.

KSWF: Snow with accumulation 4-5 inches.

.Monday...IFR conditions. Snow mixing with/changing to rain in
the morning at KSWF, and rain elsewhere. LLWS possible in the
morning NYC metros/coast. SW winds G25KT at the NYC metros and
KISP, becoming W in the afternoon.

.Monday night-Tuesday...VFR.

.Wednesday...Low chance of snow. NW winds G25-30 KT after
midnight.

.Thursday...VFR with NW winds G30kt.

&&

.MARINE...
NW winds continue to gust on the ocean waters to 25 kt. Have
extended the SCA for Sandy Hook to Fire Island Inlet until 4 pm.
Winds should slowly fall below 25 kt this afternoon, but may last
a bit longer east of Moriches Inlet.

As a low pressure system approaches Sunday night, SW winds should
increase, with SCA conditions becoming likely, and gales possible
late at night into Mon morning. As the system passes, moderate W-NW
flow should bring at least SCA conditions to all waters on Mon.
Ocean seas will take longer to subside, and so SCA conds there
should last into Mon night and possibly tue morning out east.

Low pressure may develop over the Atlantic during mid week, which
could bring at least SCA conditions Wed night behind an arctic cold
front.

&&

.HYDROLOGY...
A half to an inch of liquid equivalent precipitation is possible
late Sunday through Monday.

&&

.EQUIPMENT...
New York City NOAA Weather Radio NWR transmitter KWO-35 is
experiencing intermittent outages.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for ANZ353-
     355.
     Small Craft Advisory until 6 PM EST this evening for ANZ350.

&&

$$
SYNOPSIS...JM
NEAR TERM...JM/DS
SHORT TERM...JM
LONG TERM...DW
AVIATION...DW
MARINE...Goodman/DS
HYDROLOGY...JM/DW
EQUIPMENT...


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