Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 100242
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
942 PM EST Fri Dec 9 2016

.SYNOPSIS...
Weak high pressure builds in through Saturday night and then
offshore Sunday as low pressure over the Midwest tracks northeast.
The low will track across the Great Lakes Sunday night into
Monday, sending a warm front through the region. High pressure
will then briefly follow 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 /UNTIL 6 AM SATURDAY MORNING/...
Forecast is on track. Only minor changes made to reflect current
observations.

High pressure will continue to build in tonight, allowing the
pressure gradient to weaken over the area. Therefore, winds are
expected to diminish.

Low temperatures will be well below normal for this time of year,
20s for much of the region. Some upper teens in the outlying
areas. Wind chill values will be in the teens region-wide.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
High pressure slowly builds into the region Saturday and Saturday
night. A weak shortwave and increasing low-mid level moisture could
trigger a few flurries mainly across the far NW portion of the
forecast area during the afternoon and evening hours. In general,
increasing afternoon clouds, then clouds diminish in the evening.
Temperatures through the short term are a blend of MAV/NAM MOS.

&&

.LONG TERM /SUNDAY 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. Prior to the time, an active southern branch of the jet
will take several pieces of energy from a shearing upper low
dropping southward across western Canada and into the Pacific
Northwest quickly eastward.

At the surface, this will be reflected as area of low pressure that
will track northeast across The Great Lakes and into eastern Canada
Sunday night into Monday. A warm front will approach from the
southwest during the same time, passing through the region on
Monday. This type of fast flow with the low tracking to the
northwest of the area is typically not conducive for a significant
snowfall event, especially at this time of year due to a return
flow developing off of warmer waters. The high is also transient
in nature and builds quickly off the coast on Sunday. There are
though differences amongst the models in how quickly the cold air
erodes over the region Sunday night into Monday morning, with the
operational NAM the most aggressive, and the GFS and ECMWF cold
enough to support several inches of snowfall across the interior.
There is also another potential wrinkle with weak low pressure
forming to the south along the warm front Monday morning. This
could potentially hold in the cold air a bit longer. The exact
timing of when the boundary layer warms sufficiently for a
changeover to rain is critical and allows for a fair amount of
uncertainty in the forecast. For the time, have taken a multi
model ensemble approach, discounting the warm NAM, for a Ptype
forecast. This results in a quick changeover to rain at the coast
Sunday night, and then a northward transition across the Lower
Hudson Valley and interior southern Connecticut near daybreak. A
deviation by 1-2 hours with strong overrunning precipitation can
have a significant consequence. At this time,the forecast calls
for 2 to 4 inches across northern portions of the Lower Hudson
Valley and interior southern Connecticut, with less than an inch
at the immediate coast. The trailing cold front passes through in
the late afternoon/early evening Monday with conditions drying
from west to east. Total liquid equivalent looks to be 0.50 to
0.75 inches.

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 /02Z SATURDAY THROUGH WEDNESDAY/...
High pressure builds in from the west through the TAF period.

VFR. Scattered snow showers/flurries with brief reductions in
cigs/vsby Saturday afternoon.

Gusty WNW-NW winds at NYC Metro terminals decreasing
overnight. WNW winds with gusts to 20 kt re-developing Saturday
morning for all terminals. Winds diminish Sat Evening.

.OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...
.Saturday Night...VFR. Diminishing winds..
.Sunday...Mainly VFR. Chance of light rain/snow near coast and
chance snow inland late.
.Sunday night and Monday...IFR in light snow Sunday night,
changing to rain/snow mix from south to north early Monday morning
becoming plain rain along coast thereafter.
.Monday night...Rain/snow mix ends becoming VFR.
.Tuesday...VFR.
.Wednesday...MVFR or IFR possible in chance rain/snow mix.

&&

.MARINE...
Gale Warnings have been allowed to expire on the ocean as wind
gusts are generally in SCA levels. There may be occasional gusts
to 35 kt or slightly higher over the next hour or so, but they
should not be frequent.

For the rest of the waters, SCA remains unchanged with the
western waters dropping below criteria by midnight, and the
eastern waters dropping by Saturday morning. Sub- SCA conditions
then expected Saturday afternoon and night.

There is a low chance for SCA conditions to develop Sunday night.
Seas on the ocean will build however on Monday as low pressure
passes through. Conditions improve on Tuesday with high pressure
building in. Low pressure may develop over the Atlantic during the
middle of the week, which could bring at least SCA conditions and
possibly gales Thursday behind an arctic cold front.

&&

.HYDROLOGY...
Up to an inch of rain and/or liquid equivalent is possible 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 midnight EST tonight for ANZ335-338-
     345.
     Small Craft Advisory until 6 AM EST Saturday for ANZ330-340.
     Small Craft Advisory until 10 AM EST Saturday for ANZ350-353-
     355.

&&

$$
SYNOPSIS...JC/DW
NEAR TERM...JC/JP
SHORT TERM...JC
LONG TERM...DW
AVIATION...NV
MARINE...JC/DW
HYDROLOGY...JC/DW
EQUIPMENT...


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