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

Synopsis...
a cold front moves across the area today as high pressure builds
to the north. 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. High pressure builds to the south and
east Tuesday and Tuesday night. An Arctic front approaches from
the northwest Wednesday...then pushes through the area Wednesday
night. Canadian high pressure builds in Thursday through
Friday...as low pressure tracks well to the southeast. This high
builds to the south Friday night. A cold front approaches from the
north on Saturday.

&&

Near term /until 6 PM this evening/...
weak ridging aloft ahead of upstream trough can be expected
today. Moisture increases ahead of an area of low pressure and
lift along the frontal boundary.

Surface high pressure moves to the south...with another area of high
pressure building north of the Great Lakes region. In
between...frontal boundary passes through and remains to the south
today.

Temperatures will rise into the upper 20s to lower 30s today per MOS
blend.

Most of the day will be dry...with light snow development possible
late for western sections of the tri-state ahead of the trough and
in response to weak lift in warm air advection.

&&

Short term /6 PM this evening through Monday night/...
challenging winter forecast...with mixed precipitation type to deal
with this time frame.

A slight northward trend to the surface low track is noted.

Strong lift ahead of trough...with plenty of moisture tapped in from
the south...will set the stage for a heavy precipitation event.
Analysis of 00z nwp suite indicates middle and upper level trough
moves quickly across the middle section of the country this
evening...tracking toward the East Coast by Monday afternoon.
Surface low along a frontal boundary over the Ohio Valley this
evening moves east tracking across southern PA toward the southern or
central New Jersey coast early Monday. The low tracks just south Monday
afternoon.

The middle/upper level trough moves through by Monday evening...with
surface low tracking well to the east.

Very tough forecast for multiple reasons. Models do indicate low
level warm air advection occurring as 800 mb low tracks over or just
north of NYC. At the surface...winds remain generally from the east
tonight ahead of the low and to the north of the frontal boundary.

By Monday...enough warm air aloft moves in...with NAM and European model (ecmwf)
fairly close with regard to temperatures aloft. GFS is slightly warmer.
Looking at surface and boundary layer...followed a gridded MOS...NAM
downscale blend for slow warming in east flow...mainly for eastern
Long Island and possibly into portions of southern Long Island and
southern portions of NYC.

Interestingly...high res arw and nmm track the low just
south...but forecast the coastal front across Long Island...which
sets up a large temperature gradient on either side of the front.
Temperatures in the 40s as winds turn south. This obviously would be
problematic and would require a huge shift in the forecast.
Again...will follow the NAM/GFS/ECMWF in keeping the low and coastal
front just south...but warming east end of Li and southern Li
sufficiently to result in rain. Across the interior...enough warm
air aloft for snow mixing with sleet and freezing
rain...stretching SW to NE across the area.

Given cold water temperatures...would believe temperatures do not rise much
above 32 for Long Island and into NYC. Will convert the watches to
warnings...except eastern Long Island...southern Suffolk and
southern Nassau. Given the high level of uncertainty...will allow
the day shift one more look to determine conversion to warnings or
to advisories. Any further north shift to surface low and 800 mb low would
result in more liquid.

In addition...freezing rain a concern for a good portion of the area.

The bottom line is...high impact for morning commute warrants a
warning for most of the area. Closer to the coast...snow to
rain/fzra/ip. Then back to snow before ending as deformation band
moves through on the back side as the low departs late in the day
Monday.

Interior...mainly snow...with possibly some sleet Monday morning.

Eastern/southern Long Island...snow to rain or freezing rain (depending
on those surface temps)...then possibly back to snow.

***It is important to note that many coastal area snow total
forecasts are for snow ahead of wintry mix transition...and after
wintry mix changes back to snow. However...any rain will likely
wash the snow away...leaving slushy conditions and lower totals as
a result***

So...morning commute will likely be a mess all County Warning Area. The afternoon
commute will likely be problematic as well for much of the area.
Any leftover slush will freeze as Arctic air rushes back in.
Expect icy conditions late in the day...especially for areas that
change to rain late morning/early afternoon.

Heaviest precipitation is late tonight (09-11z through 16-18z) when
greatest lift is realized.

Any lingering light snow Monday evening ends as the trough moves
east/ gusty northerly flow will usher in very cold air. Low temperatures
in the single digits to the teens.

&&

Long term /Tuesday through Saturday/...
zonal flow aloft should keep things dry Tuesday and Tuesday night. A
weak shortwave passes on Wednesday...with a stronger shortwave
approaching Wednesday night...just behind an Arctic cold front at
the surface. There should be enough forcing with the shortwaves and
the front to produce isolated-scattered -shsn Wednesday and Wednesday night.

There remain model differences from Thursday on. Both the European model (ecmwf) and
CMC suggest that the Arctic front become an anafront with snow
behind the front Thursday-Thursday night...and the CMC GOES farther
and brings a coastal low along it close enough to impact the area.
The GFS generally keep things dry Thursday/Thursday night. For now
went with chance probability of precipitation on Thursday...except slight chance far north
tier...then slight chance probability of precipitation Thursday night...except dry far north-northwest
tier of the County Warning Area.

All models agree should be dry Friday-Saturday on northwest flow aloft.

Main story of the extended will be bitterly cold air arriving
Wednesday night and lasting through Friday night. Highs will
struggle to reach the upper teens to lower 20s and lows will
generally be in the single digits Thursday and Friday night. Wind
chills should be below zero Thursday night/Friday morning...and
possibly be near advisory criteria over northwest interior zones.

&&

Aviation /19z 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-1/4"
ice during Monday morning and afternoon.

Khpn/kbdr/kgon: 4-8" of snow. Also...a trace-1/4" 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...
the region will be under a relatively relaxed pressure gradient
through this evening...so sub-small craft conditions are expected.

Winds increase to small craft levels on all waters after midnight
and persist through Monday...so a Small Craft Advisory has been
hoisted accordingly. Gusts to gale force are probable Monday night
on the coastal ocean waters...so a gale watch has been issued then
for those waters. For the non-ocean waters...small craft conditions
are expected to continue...so the Small Craft Advisory for these
waters last through then. There is a small chance for gale force
wind gusts on the non-ocean waters as well Monday night.

Small craft conditions will likely continue on all waters
Tuesday...and possibly gale force winds gusts in the morning on the
coastal ocean waters. Confidence in this is not quite high enough
for any headlines on Tuesday yet.

Sub-small craft conditions are expected on the non-ocean waters
Tuesday night-Thursday with winds 15 knots or less. On the ocean waters
small craft level seas are possible through the time frame...with
the best chance Wednesday-Thursday though a combination of winds
just under small craft levels and swells.

&&

Hydrology...
generally 1 to 1 1/2 inches of liquid forecast with the system
tonight through Monday. Most of this will be snow and sleet
across NE New Jersey...lower Hudson Valley and CT.

Across Li/NYC there is a potential for a period of heavy
rain. As such...urban flooding issues are possible...especially
due to clogged snow covered drains.

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 on Monday...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 Storm Watch from 7 PM EST this evening through Monday
afternoon 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 am EST Tuesday
for anz330-335-338-340-345.
Gale watch from Monday evening through late Monday night for
anz350-353-355.
Small Craft Advisory from midnight tonight to 6 PM EST Monday
for anz350-353-355.

&&

$$
Synopsis...maloit/pw
near term...precipitable water
short term...precipitable water
long term...maloit
aviation...jc
marine...maloit
hydrology...maloit/pw
tides/coastal flooding...

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