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Area forecast discussion 
National Weather Service New York New York
745 am EST Wednesday Mar 4 2015

Synopsis...
deepening low pressure tracks across eastern Canada today with a
cold frontal boundary approaching as a wave of low pressure
develops along it southwest of the region. The cold front slides to
the southeast tonight...with waves of low pressure tracking along
it into Thursday. Canadian high pressure then builds in through
Thursday night...then slides to our south through Friday night. A
series of weak cold fronts cross the region this weekend into
early next week.

&&

Near term /until 6 PM this evening/...
forecast mainly on track. Increased probability of precipitation for rain across northern
parts of the region.

A west-southwest flow remains across the region through the day today. Pretty
much a steady state environment with temperatures only rising a few
degrees and intermittent rain. This should be mostly light.

The upper level jet streak of around 200 knots will be approaching
through the day. Temperatures remain generally in the middle to upper 30s to
keep precipitation in the form of plain rain. The intensity will
be rather light due to the area not being in a favorable region of
lift relative to the jet streak placement but increased divergence
aloft should allow for rain field to expand.

Temperatures used were a combination of gmos...nam12 and
gfs40...holding within the upper 30s for most locations.

&&

Short term /6 PM this evening through Friday/...
models in good agreement with northern stream energy digging down
the Front Range of The Rockies into northern plains/upper Great
Lakes today...interacting with a SW US low...and then gradually
lifting across the US to East Coast by Thursday night.

Have stayed close to ensemble means...with a reinforcing cold front
moving south of the region this evening with falling temperatures tonight. A
series of waves will develop along a stationary front to the south
tracking NE through the middle Atlantic...ahead of approaching upper
trough axis and as the region falls under favorable entrance
region of a 175-200kt upper jet.

Biggest uncertainty exists in quantitative precipitation forecast...with models wobbling back and
forth from run to run on northern extent of heavier quantitative precipitation forecast axis.
There will likely be a sharp cutoff from several inches of
accumulating snow under frontogenetic banding...and quickly
tapering to a dusting to the north (30 mile range). Have relied on
an ensemble approach to quantitative precipitation forecast...with 1/4 to 3/4 inch of quantitative precipitation forecast across
the region as the synoptic setup taps into a moist SW flow all the
way from the subtropical Pacific. Ensemble indicating highest probability of
5 inches or greater after transition to snow for southern
portions of NYC/New Jersey metropolitan and Li.

Models in general agreement with thermal profiles cooling through
the overnight...with a changeover of precipitation from rain in the early
evening to wintry mix then snow from northwest to southeast. All areas appear to be
mainly snow by 06z. Modest frontogenetic forcing appears to work
into southern zones...with potential for snow to be heavy at
times late tonight through Thursday morning there...coupled with strong
jet dynamics. Snow should gradually taper off in intensity and
coverage from northwest to southeast Thursday afternoon as shortwave trough
approaches and offshore stationary front slides well offshore.

Highest confidence in 6+ inch amounts is for Li and southern
portions of NYC/New Jersey metropolitan. Will upgrade to warning in this area after
collab with phi and box...for a 4 to 8 inch snowfall. 00z ensemble
runs have reduced probability of 1/2 inch quantitative precipitation forecast slightly across southern
areas...so if this trend continues this are may fall on the lower
end of range.

Lower confidence in snowfall forecast across southern CT and lower
Hudson Valley...with potential for snowfall amounts to rapidly
decrease working northward. With low potential for 6 inches for
coastal southern CT...the rest of NE New Jersey...and southern portions of
lower Hudson Valley will leave watch up in this area...but higher
likelihood of advisory level or lower. For areas far n&w of
NYC...between a dusting to 4 inches is possible...so not enough
confidence for an advisory at this time.

Drying conditions Thursday night...with temperatures dropping into the
single digits...lower teens NYC metropolitan...on gusty northwest winds.
Windchills likely dropping to around zero to 5 below zero for much
of the region by Friday morning.

&&

Long term /Friday night through Tuesday/...
thereafter...mean troughing continues into early next week.
Unseasonably cold conds (about 20 degrees below seasonable) continue
Thursday night into Friday night as Canadian high pressure builds into the
region.

Then a series of weak shortwave/cold fronts move through the
region this weekend into early next week...with temperatures moderating but
still remaining several degrees below seasonable. Some light rain/snow
shower activity possible with any of these disturbances.

&&

Aviation /13z Wednesday through Sunday/...
low pressure tracks across eastern Canada today...with its trailing
cold front crossing the area late this evening.

Periods of rain today with generally MVFR conds
expected...although the forecast is very challenging over the
next 24 hours. Several of the terminals have improved to VFR this
morning...but expect this to be short-lived. However...conds
could vary between MVFR and VFR through the day. Guidance is all
over the place.

Cold front will track through the area late this evening and
stall just S of Long Island. Soundings indicate a change over from
rain back to snow around 06z. However...model differences remain
with where the northern edge of the precipitation field will be tonight
which results in high uncertainty in conds.

SW flow expected to prevail until frontal passage this evening...between 02z and
06z...then becoming northwest. Gusts up to 20 knots possible late.

..NY metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts
can be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)

Kjfk fcster comments: flight category may vary between MVFR and
VFR.

Klga fcster comments: flight category may vary between MVFR and
VFR.

Kewr fcster comments: flight category may vary between MVFR and
VFR.

The afternoon kewr haze potential forecast is moderate...which
implies slant range visibility 4-6sm outside of cloud.

Kteb fcster comments: flight category may vary between MVFR and
VFR.

Khpn fcster comments: flight category may vary between MVFR and
VFR.

Kisp fcster comments: flight category may vary between MVFR and
VFR.

Outlook for 12z Thursday through Sunday...
Thursday...-sn with IFR to MVFR coastal terminals...MVFR to VFR
kswf. North gusts to 20 knots in the morning.
Thursday night-Friday...improving to VFR Thursday night. Northwest gusts
15-20kt possible Thursday night.
Sat/sun...VFR.

&&

Marine...
Small Craft Advisory conditions are expected to continue across the ocean with
other waters remaining below Small Craft Advisory. The Small Craft Advisory event will be more of a
marginal one and due mainly to seas but any rainfall will be of help
to transport momentum downward and give some higher gusts that
would reach Small Craft Advisory thresholds. Water temperatures are a few degrees warmer
on the ocean relative to other waters so it will be relatively
easier for higher gusts to be achieved on the ocean.

Small Craft Advisory conditions are likely on the coastal ocean
waters tonight into Thursday morning as a series of low pressure
waves tracks to the south of the waters. Some uncertainty if Small Craft Advisory
conds continue into Thursday afternoon...with higher confidence of re-
occurrence Thursday night. So for now have only run Small Craft Advisory until Thursday
morning.

Sub Small Craft Advisory conds return Friday as high pressure builds over the waters.

A series of weak cold fronts will move through the waters this
weekend into early next week...one Saturday night into Sunday
morning and another Monday night. Winds approach Small Craft Advisory criteria
Saturday into Saturday night and then again Monday night into
Tuesday on the ocean waters...but as of right now...they should
remain below. Waves remain below Small Craft Advisory criteria through the period.

&&

Hydrology...
around a quarter of an inch or less is expected with the rainfall
today. Low potential for flooding although some ponding of water
is expected with steady moderate rain that falls due to excess
runoff from melting snowpack.

1/4 to 3/4 inch liquid equivalent precipitation is likely Wednesday
night into Thursday. Most of this will be frozen...so hydrologic
impacts are not expected.

&&

Okx watches/warnings/advisories...
CT...Winter Storm Watch from 7 PM EST this evening through Thursday
evening for ctz008>012.
New York...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for nyz074-075-078>081-176>179.
Winter Storm Watch from 7 PM EST this evening through Thursday
evening for nyz071>073.
New Jersey...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for njz107-108.
Winter Storm Watch from 7 PM EST this evening through Thursday
evening for njz002-004-006-103>106.
Marine...Small Craft Advisory until noon EST Thursday for anz350-353-
355.

&&

$$
Synopsis...jm/NV
near term...jm
short term...Nevada
long term...jp
aviation...24
marine...jm/jp/NV
hydrology...jm/NV

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