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Area forecast discussion 
National Weather Service New York New York
1209 am EST Thursday Feb 11 2016

Synopsis...
low pressure east of New England this evening will gradually lift
northeast across the Canadian Maritimes through Thursday...while
polar high pressure builds east from the Midwest. A weak trough of
low pressure will pass through the area Thursday afternoon. A
strong Arctic cold front will then approach Friday night and pass
through Saturday morning as a developing ocean storm passes by to
the southeast. Strong Arctic high pressure will build across later
Saturday into Sunday night...then retreat to the northeast Monday
into Monday night. A low pressure system follows for the middle-week
period.

&&

Near term /until 6 am this morning/...
minor adjustments made to forecast based on current conditions.
Light snow is falling across western/central PA in associated with the
the approaching upper trough. There is some uncertainty as to how
much of this activity will make it east of the ridges later
tonight with a moderate westerly.

Short wave ridging aloft will briefly build across the area this
evening which will result in partial clearing. The upper trough
axis to the west though will approach later tonight with decent
lift in the low to middle levels and a nearly saturated 850-700 mb
layer. This should produce scattered snow showers and/or flurries
across the region during the overnight. A dusting is possible
across the region.

Gradual cold advection will continue through the night with the
upper trough moving across the area. Overnight lows will be in
the upper teens to the lower 20s. Wind chill values will drop to
around 10.

&&

Short term /6 am this morning through 6 PM Friday/...
upper trough axis lifts NE across the region on Thursday and passes to
the NE by evening. Deep-layered cyclonic flow and steep middle-
level lapse rates will result in scattered snow showers through the day.
The most likely time would be during the late morning and
afternoon when surface based instability is the greatest.

A tight pressure gradient between departing low pressure over the
Canadian Maritimes and high pressure building east from the
Midwest will result in wind gusts up to 30 miles per hour...possibly higher
during the early evening hours with the passage of a surface trough.
Cold advection will continue with 850 mb temperatures approaching -20 degree c
by evening. Winds begin to relax late Thursday night as high pressure
builds over the Middle Atlantic States. Skies will clear Thursday evening.

Highs Thursday will be 25 to 30...and lows Thursday night will be in the
single digits inland and in the lower to middle teens at the coast.
These readings will be 10-15 degrees below normal.

&&

Long term /Friday night through Wednesday/...
Friday begins with fair conditions with weak surface ridging and a
zonal flow aloft. The atmospheric column begins to moisten aloft
ahead of shortwave energy rounding the periphery of a deep upper
trough/polar vortex. With the lack of combined lift and sufficient
moisture...will go with a dry forecast. A mav/NAM MOS blend looked
good for high temperatures...which will be below normal.

An Arctic cold front then approaches Friday night along with the
shortwave from the north. At the same time...shortwave energy moves
off the middle Atlantic coast. The combined energy should initiate surface
cyclogenesis along a baroclinic zone to our south with the low
passing well southeast of the 40n/70w benchmark late at night. Looks like
any chance of snow directly associated with this low looks
low...however...with the Arctic front and decreasing stability due
to cyclonic flow aloft...scattered snow showers expected. Will cap probability of precipitation at
chance for now.

An anomalously cold air mass then pours in behind the cold front for
the weekend. Another shortwave arrives alongside the core of cold
air aloft during Sat/Sat evening. The atmospheric column
dries...however there is still at least a chance of flurries during
this period.

As for temperatures Sat and Sat night...the calendar day high temperature on
Saturday will probably occur during the pre-dawn hours as strong
cold advection drops temperatures throughout the day. By noon...temperatures
are probably in the teens area-wide with wind chill values below
zero. Record to near-record cold temperatures for Sat night in spite of
gusty northwest flow. Both GFS and European model (ecmwf) show 850mb temperatures dropping to -29c
to -30c during the night before rising a few degrees toward
daybreak. Based on temperatures that occurred during a similar synoptic
setup last February with warmer temperatures aloft...went slightly below
the low temperatures that had occurred...which are close to what European model (ecmwf) MOS
has been showing for the past few runs. See the climate section
below for more details. The cold air combined with winds would
produce wind chills that would warrant an advisory during Sat night
into Sunday morning...possibly even a warning for some of the
northern suburbs.

Remaining cold but dry on Sunday as high pressure builds in with
highs only in the teens. Models then in disagreement with the timing
of the next system to potentially affect the region. High pressure
shifts offshore on Monday with the likelihood that the daytime hours
remain dry. A longwave trough then shifts through the eastern half
of the U.S. With its axis prognosticated to move through during Tuesday
night. This then helps strengthen a surface low moving up the
vicinity of the eastern Seaboard. Low confidence in the
evolution...track and timing of this system...and consequently precipitation
type. Have capped probability of precipitation at 50 percent for the rest of the long term
forecast for the time being and went with a general rain...snow or
mix of the two as precipitation type.

&&

Aviation /05z Thursday through Monday/...
mainly VFR across the terminals. Weak trough passes through the
region late tonight and into the morning...possibly touching
off some light snow showers and/or flurries with brief MVFR conds
around daybreak Thursday. However...probabilities are too low to
include these lower conds in the tafs.

Pressure gradient tightens overnight with winds/gusts increasing
through 12z...and strengthen further between 12z and 18z.

Outlook for 06z Thursday through Monday...
Thursday night...VFR. Diminishing northwest winds.
Friday...VFR.
Saturday...sub-VFR possible in brief -shsn. Northwest winds around 20 knots
with gusts up to 30 knots.
Sunday-Monday...VFR.

&&

Marine...
a Gale Warning is up for the ocean waters with a Small Craft Advisory elsewhere
for strengthening west/northwest winds tonight into Thursday night. Low pressure
east of New England this evening will track NE across the Canadian
Maritimes through Thursday night...while high pressure builds east from
the Midwest. This will produce a strong gradient wind. In
addition...cold air across the relatively warm waters will allow
mixing of gale force gusts down to the ocean surface.

Lingering Small Craft Advisory conds are possible Friday morning on the ocean waters.
Winds and seas otherwise subside for a brief period of sub-Small Craft Advisory
conds. Winds and seas then pick up again Friday night ahead of a
cold front which is expected to pass through late at night into
Saturday morning. After its passage...strong cold air advection
and a tight pressure gradient are expected to bring gale force
winds to most if not all waters. Gales could last into Saturday
evening for the ocean and eastern waters...otherwise...winds
gradually diminish through the night into Sunday. Small Craft Advisory conds all
waters on Sunday should quiet down again Sunday night as strong
high pressure builds overhead. The high shifts offshore on Monday
with increasing winds and seas...but probably remaining below Small Craft Advisory
criteria at least during the daytime.

&&

Hydrology...
scattered snow showers late tonight through Sat will result liquid
equivalents of less than a tenth of an inch.

A low pressure system impacting the area from Monday night through Tuesday
night could bring a liquid equivalent precipitation amount of an inch or greater.
Primary precipitation type is uncertain...so will need to monitor this system
for potential adverse hydrologic impacts.

&&

Climate...
with the extremely cold air mass forecast Saturday into
Sunday...record minimums and record low maximums may be reached.
Here are the records and forecasts...

Station......record/fcst minimum...record low maximum/forecast high
for 2/14 for 2/14

NYC...........2 (1916) / 1.............17 (1979) / 19
LGA...........1 (1979) / 2.............15 (1979) / 19
JFK...........4 (1979) / 2.............17 (1979) / 19
isp...........7 (2015) / 1.............26 (1987) / 18
ewr...........0 (1979) / 0.............15 (1979) / 19
bdr...........3 (2015*) / 0.............18 (1979) / 17

*in 1979 as well

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory from 6 am this morning to 6 am EST Friday
for anz330-335-338-340-345.
Small Craft Advisory until 6 am EST early this morning for
anz350-353-355.
Gale Warning from 6 am this morning to 1 am EST Friday for
anz350-353-355.

&&

$$
Synopsis...jc/dw
near term...dw
short term...dw
long term...jc
aviation...
marine...jc/dw
hydrology...jc/dw
climate...

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