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Area forecast discussion 
National Weather Service New York New York
420 PM EST sun Feb 1 2015

Synopsis...
low pressure approaches from the Ohio Valley tonight and passes
just south of Long Island Monday. The low tracks well to the east
Monday night. A series of cold fronts will move across the region
through the upcoming week...the first Wednesday night into
Thursday...and then another on Saturday. In between...cold...polar
high pressure will be across the area. Low pressure over the Gulf
Coast states late in the week still looks to take a track well
offshore.

&&

Near term /until 6 am Monday morning/...
models in good agreement with low pressure taking shape over the middle
Mississippi River valley this afternoon...tracking through the Ohio
Valley tonight...and beginning to redevelop just south of the tri-
state Monday morning.

Increasing and lowering clouds late this afternoon into this
evening...with increasing chance of light snow from west to east through
the evening.

Temperatures generally steady in lower 30s-35 along the coast for most of
the night...then wetbulbing to freezing with start of heavy
snow...then rising above freezing late across immediate south and
eastern coastal areas to above freezing towards daybreak. Just
interior of the immediate coast...across interior NE New Jersey...lower
Hudson Valley...and southern CT...temperatures should fall into the teens
and 20s with evaporational cooling once snow starts and hold
there into daybreak.

Based on approaching coupled jet structure...tight low/mid-level
thermal structure...and 60-70 knots low level jet feeding strong Gulf moisture
feed of 2-3 Standard precipitable waters up over the region late tonight...expecting
heavy snow initially to develop across the region from west to east after
2 to 4 am. Snowfall rates of 1 to 2 inches per hour possible.
This is supported by high probability of 1" per hour snowfall rates in
the sref.

A quick 2 to 5 along the city/coast is the most likely
(highest amounts across northern peripheries with locally 6
inches) before any changeover towards daybreak. A general 4 to 8
inches of snow by daybreak across interior NE New Jersey...lower Hudson
Valley...and SW CT. 3 to 5 inches across southeast CT. These ranges have
the potential to be shifted up or down by 1-2 inches...because a 1
hour difference in timing of changeover will mean the difference
in almost 2 inches of snow from the total! This variability issue
is illustrated well by the 10 and 90 percentile snow total graphics
on our web Page.

For the NYC/New Jersey metropolitan and coast...almost all of the snowfall for the
evening will be seen in the early morning hours. The early
morning commute will be heavily impacted for the entire area.

Thereafter...the forecast challenge remains in how quickly and far
north warm air rides in aloft as we approach daybreak Monday
morning...and where a coastal front sets up demarcating a tight
gradient between southeast winds and 40 degree temperatures to the southeast and
east-northeast/NE winds to the north with sub-freeing temperatures.

&&

Short term /6 am Monday morning through Monday night/...
model guidance has shifted bit farther north with the 12z
guidance...with general agreement in coastal low pressure re-
developing just south of the region Monday morning and skirted the
Li coast as it tracks east during the day.

00z sbu ensemble sensitivity guidance showed a nudge north in
ensemble means...with a bit of variance explained in faster speed
and a bit farther north track of low. This seemed to bearing out
in the 12 operational guidance with a bit warmer and quicker
movement of the low.

So with general consensus on a farther north track...uncertainty
still lies in the tightness of the thermal gradient aloft...speed
and northward extent of changeover from snow to liquid aloft. Then
at the surface...coastal front set-up will be critical...in
difference between plain rain to south (most likely south coastal
Li/nyc) and freezing rain to the north.

Highest confidence in remaining mainly snow through the event is
far interior lower Hudson Valley...an additional 3 to 5 inches of
snow likely here through the afternoon.

A mix of snow...sleet and freezing rain from after daybreak
through early afternoon likely for interior NE New Jersey...central lower
Hudson Valley and interior SW CT. An additional 1 to 3 inches of
snow and sleet likely here through the afternoon...with potential
for 1/4 to 1/2 inch of ice along southern/eastern boundaries. If
northward warming trend continues...the snow amounts would be
lower in the afternoon with increased potential to reach the 1/2
inch ice amounts.

Models depicting enough warming in the 800-950 layer across NYC/New Jersey
metropolitan...Li...coastal lower Hudson Valley...coastal SW CT...and southeast CT
for a complete transition from snow to liquid aloft Monday morning.
Coastal front set-up will be difference between freezing rain to the
north and plain rain to the south. Current track of surface low and
high res-guidance indicating coastal front lifting as far north as
North Shore of Li...N/NW periphery of New Jersey/NYC metropolitan...and southeast
coastal CT during the morning before sinking back southeast through the
afternoon. This would indicate potential for a 20-30 mile zone of
significant freezing rain (1/4 to 1/2 inch) just to the north.



While the 20-30 mile zone just to the southeast of the coastal front will
likely experience a period of plain rain as boundary layer warms
above freezing...before gradually changing to freezing rain (1/10
inch fzra)...sleet and then back to snow from around midday into
middle afternoon. This zone may include far northern portions of
NYC/New Jersey metropolitan...North Shore of western/central Li.

For southern Nassau County...eastern Li...southeast coastal CT and even
southern portions of NYC...fairly high probability of seeing snow
changing to plain rain after daybreak with boundary layer warming.
In fact temperatures could rise into the lower 40s across this areas in the
morning. Then a gradual change back to freezing rain/sleet and
eventually snow from northwest to southeast in the afternoon. A few hundredths to
a tenth of an inch of ice possible here in the afternoon.

For any area that does changeover from snow to rain/freezing
rain...urban flooding potential exists with 3/5 to 1 1/4 inches of
rain. See hydrology section for details.

Despite a changeover to rain...flash freeze potential for the evening
commute for the coast as the low pulls east...winds turn northerly
with temperatures likely dropping into the upper 20s with some light snow
banding.

Will maintain winter storm warnings as is for the impact to morning
and evening commutes for much of the region. Will change watch to
advisory for southern and eastern Li with less potential for
icing.

Snow tapers off in the evening from west to east as upper trough and
deformation band swing through. Windy and frigid conditions Monday
night in the wake of low pressure. Wind gusts of 35 to 40 miles per hour likely
Monday evening/night with low potential for Wind Advisory gusts up
to 50 miles per hour. Low temperatures falling into the teens coast and single
digits interior...with windchill of 10 to 15 below zero across
interior and around 5 below zero along the coast.

&&

Long term /Tuesday through Sunday/...
the main theme continues to be a progressive northwest flow across the northern
tier of the country with the mean upper trough situated from western
Canada southeast to the eastern Seaboard. This type of flow of late has
caused challenges with the amplification of Pacific shortwave energy
moving into the eastern U.S. This theme looks to continue through
the extended forecast.

For the most part...the 12z guidance is on board with a series of
polar cold fronts moving through the area...the first Wednesday night into
Thursday...and then another next Sat. In between...polar high pressure
and unseasonably cold conditions look to prevail. Once again...the
associated short wave energy with these fronts is in a constant
state of flux with the amount of amplification as the energy moves
in from western Canada. The 12z ggem and European model (ecmwf) are trending back
toward more amplification with the longwave trough on Thursday across the
eastern U.S. This is allowing a frontal wave off the southeast coast Thursday to
take a more western track...placing the forecast area on the northwest
periphery of light precipitation. Right now...will just maintain low chances
of snow with both cold frontal systems and see how future runs
handle the offshore low. Once again though...based on recent model
performance...this is something to still watch.

Tuesday and Friday look to to be the coldest days of the week with highs
likely not getting out of the 20s...with the warmest day coming
on Wednesday ahead of the next cold frontal system....in the low 30s
inland to the upper 30s at the coast. Vertical temperature profiles are
supportive of snow during the period.

&&

Aviation /21z Sunday through Friday/...
**high impact event tonight through monday**

Winds west-southwest 10kt becoming light and vrb this evening...then southeast-east towards
midnight.

High pressure south of the area weakens and moves offshore today. Low
pressure over the Midwest moves east today...and a warm front
extending ahead of the low pushes into the terminals from west to
east by this evening. Light snow is possible an hour or two as
indicated in tafs...but steady and more widespread snow
pushes into western terminals from 00-02z Monday and into eastern
terminals from 02-04z. Snow may be heavy at times during the
overnight hours.

Snow changes to a mixture of snow and freezing rain Monday morning
for kisp and the New Jersey/city terminals...before changing to plain rain
for part of the morning and afternoon. Rain then changes back to
freezing rain and snow. Brief sleet is also possible during the
times of change to liquid...and then back to frozen precipitation. See tafs
for timing. Other terminals will see more in the way of snow...but
still some mixed precipitation except kswf will be mainly snow.

Runway accumulations:
kteb/kewr/klga/kjfk/kisp: 2-5" of snow before changeover Monday morning
with up to another inch of snow possible Monday aftn-eve. Trace to one
quarter inch of ice during Monday morning and afternoon.

Khpn/kbdr: 4-8" of snow. Also...a quarter to half inch of ice during
Monday morning and afternoon.

Kgon:3-6" of snow. Also...a trace to a quarter inch of ice during
Monday morning and afternoon.

Kswf: 8-12" of snow. Possibly a little sleet mixed in late Monday
morning.

Outlook for 18z Monday through Friday...
Monday afternoon...mix precipitation changes back to snow. Northwest 15 g25kt
Monday night...any lingering snow showers end...and conds improve
to VFR. Northwest winds 15-20 knots with 25-35 knots gusts.
Tuesday...VFR.
Wednesday...VFR. A chance of snow showers Wednesday afternoon and
Wednesday night with locally MVFR to IFR conditions.
Thursday...VFR. Northwest gusts 20 knots.
Friday...VFR.

&&

Marine...
winds pick up from the southeast and east late tonight with Small Craft Advisory conds
developing across all waters. There is even a chance of a few gusts
up to gale force for a short period late tonight into early Monday
morning on the ocean waters. Thinking is that Small Craft Advisory is the best way to
go with this.

Low pressure center then passes through the waters Monday morning into
early afternoon with a lull in winds as well as a shift to north...then northwest on
the back side of the low. Winds increase through the afternoon and
evening with gales expected on all waters Monday night. In
addition...vessel icing is expected to moderate...so a freezing
spray advisory has been issued as well for Monday night.

Small craft conditions will likely continue on all waters into
the first half of Tuesday with improving conditions as high pressure
build across the waters. There is then the potential for Small Craft Advisory
conditions on the ocean waters in the SW flow ahead of a cold front
Wednesday into Wednesday night...and then Thursday into Thursday night in the Post-frontal
northerly flow. High pressure returns at the end of week.

&&

Hydrology...
generally 1 to 1 1/2 inches of liquid forecast with the system
tonight through Monday. Low potential for 2 inches across Li. Much
of this will be snow and sleet across interior northern NE
New Jersey...lower Hudson Valley and CT.

Across metropolitan NYC/NJ...Li...and even coastal CT/lower Hudson
Valley...a period of heavy rain/freezing rain likely with which would
cause some urban flooding issues due to snow clogged drainage. Rises
on flashy NE New Jersey...coastal lower Hudson Valley and SW CT small
streams closer to the coast are also possible.

No significant widespread precipitation is forecast for the remainder of the
period.

&&

Tides/coastal flooding...
at this time it appears that for the high tide Monday morning...that
departures will remain below the 1.5-2 feet required for minor
coastal flooding.

&&

Okx watches/warnings/advisories...
CT...Winter Storm Warning from 7 PM this evening to 6 PM EST Monday
for ctz005>012.
New York...Winter Weather Advisory from 7 PM this evening to 6 PM EST
Monday for nyz079>081-179.
Winter Storm Warning from 7 PM this evening to 6 PM EST Monday
for nyz067>075-078-176>178.
New Jersey...Winter Storm Warning from 7 PM this evening to 6 PM EST Monday
for njz002-004-006-103>108.
Marine...Small Craft Advisory from midnight tonight to 6 PM EST Monday
for anz330-335-338-340-345-350-353-355.
Freezing spray advisory from 10 PM Monday to 6 am EST Tuesday
for anz330-335-338-340-345-350-353-355.
Gale Warning from 6 PM Monday to 6 am EST Tuesday for anz330-
335-338-340-345-350-353-355.

&&

$$
Synopsis...NV/dw
near term...Nevada
short term...Nevada
long term...dw
aviation...jc
marine...jc/NV
hydrology...NV/dw
tides/coastal flooding...Nevada

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