Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
716 PM EST sun Mar 1 2015

a frontal system will approach from the west...then pass through
tonight as weak low pressure develops south of Long Island.
High pressure will briefly build in Monday into Monday night...
then pass to the east on Tuesday. Low pressure will track well
north of the area Tuesday night and Wednesday...with a warm front
lifting into the area Tuesday night...followed by a cold front
Wednesday and a reinforcing cold front Wednesday night.
High pressure will then build in for the remainder of the week.


Near term /until 6 am Monday morning/...
a band of moderate snow across the South Shore of Long
Island as of 00z...although think some of this is a mix of
snow...sleet and/or freezing rain. Lower correlation coefficient
values still remain just S of Long Island...but expect them to
come onshore shortly. Where it is still all snow towards the
central part of western Suffolk County...snowfall rates up to an
inch per hour are likely occurring...however...the higher
reflectivities will push to the east by 01z.

Snow totals forecast still looks on track with perhaps the
exception of southern Nassau County. Have bumped up totals a bit
there...and could see some locations in extreme southern parts of
the County end with around 6 inches...but have maintained the advsy.

Southern portions of NYC into southeast metropolitan New Jersey are a mix of
snow...sleet and/or freezing rain. Tough call how far north the
transition zone will get before precipitation ends...but received a report
as far north as East Rutherford of mixed precipitation. Regional radar imagery
indicates lighter returns already into the lower Hudson Valley
and NE New accumulating snow has generally ended here.

Areas in and S of the transition zone should see a glaze to a
tenth of an inch of ice before precipitation winds down around midnight or


Short term /6 am Monday morning through Monday night/...
high pressure approaches from the west on Monday...then builds
overhead on Tuesday. Highs on Monday will be in the middle and upper
30s...with a brisk northwest winds gusting to 25-35 miles per hour. Much colder air
will follow for Monday night...and undercut MOS guidance by 2-3 degree
given diminishing winds late at night and fresh snow cover...with
lows in the teens for NYC metropolitan and Long Island...and single
digits farther north/west.


Long term /Tuesday through Sunday/...
models are in decent agreement at 500 mb through the week...although
slight differences in heights begin to take shape during the latter
half from a digging trough in the middle of the country.

Ridging at the surface and aloft tracks moves offshore on Tuesday. Precipitation will
overspread the area late Tuesday afternoon as snow...but with increasing S-SW
winds and strong warm air advection temperatures will warm Tuesday evening/night with snow
changing to mixed precipitation then rain from S to north. Warm front lifts
towards the area Tuesday night...but there is some uncertainty if the
low level jet will be strong enough to push it through at the surface. Climatology
says no with the low so far to the northwest and very cold waters/
have gone below guidance with highs Wednesday...generally lower 40s with
middle 40s possible in NYC metropolitan.

The combination of these temperatures and rainfall will result in melting
snowpack which could lead to minor flooding across the area on Wednesday.
Cold front moves across Wednesday followed by a reinforcing cold front Wednesday
night. The northern edge of the precipitation shield of a southern stream
system riding along this secondary boundary could keep precipitation
lingering Wednesday night into Thursday. Models remain split on this...GFS is
further suppressed than ec so have kept chance probability of precipitation.

Cold air filters in behind the initial cold front on Wednesday. Thermal
profiles support a change back over to snow Wednesday night and Thursday with
any precipitation associated with the southern stream system. Another shot of
Arctic air infiltrates the area Thursday into Friday.

Strong Canadian high pressure then builds towards the area into the
weekend with dry weather. Temperatures will rebound around 5 degrees below
normal next weekend with warm air advection developing.


Aviation /00z Monday through Friday/...
a frontal system will pass through tonight as weak low pressure
develops south of Long Island. High pressure builds Monday.

A wintry mix of freezing rain...snow and sleet appears to be
lightening from west to east for NYC metropolitan and Li terminals.
Elsewhere...mainly snow is expected. Expect steady precipitation to wind
down by 2-4z. After midnight...precipitation should end altogether...except
a little longer at kisp and kgon. Even though precipitation ends...low end
MVFR or IFR ceilings should linger overnight.

Return to VFR Monday after 11-13z.

Winds will be light and variable...then will turn to the west 5 to
10 kts after midnight. Winds become west/northwest after 12z...10 to
15 kts. By 15z...frequent gusts 20 to 30 kts are expected. Winds
should remain to the left of 310 mag for the most part Monday...but
will be close.

Additional light snow accums are expected.
Most likely total runway accumulations: kgon/kisp...4-7 inches.
Kswf/khpn/kbdr/kteb/klga/kjfk/kewr...3-6 inches.

Outlook for 00z Tuesday through Friday...
Monday night-Tuesday morning...VFR.
Tuesday afternoon...chance MVFR or lower in snow.
Tuesday night...IFR or lower likely. Snow...changing to a wintry
mix after midnight...and then rain late at all terminals except kswf
and possibly CT terminals. Low level wind shear likely.
Wednesday...IFR or lower possible in any rain - with a brief period
of freezing rain possible in the morning at kswf. Low level wind shear possible in the morning.
Wednesday night-Thursday...MVFR or lower possible in any
precipitation...otherwise VFR. If there is precipitation...should
change to all snow Wednesday night and possibly continue into
Thursday. Northwest winds g15-20kt possible.
Thursday night-Friday...VFR. Northwest winds g15-20kt possible Thursday


tranquil tonight...then winds increase to Small Craft Advisory
levels Monday and gradually diminish Monday night. Expect sub-advisory conds
on Tuesday as high pressure builds across. Small Craft Advisory conds possible on the ocean
Tuesday night into Thursday behind the passage of two cold fronts...with a
tight pressure gradient. Sub-advisory conds then expected thereafter as
the pressure gradient weakens with another building high.


liquid equivalent quantitative precipitation forecast of 4-6 tenths of an inch expected tonight.
With all of this expected to be either frozen or freezing immediate hydrologic impact expected.

Between 1/2 to 1 inch of liquid equivalent precipitation is possible late
Tuesday through Wednesday. Some of this will fall as rain...therefore the
combination of this and melting snow pack could cause minor
flooding issues.

Ice will continue to develop on local area rivers and streams as
temperatures remain well below average.


Okx watches/warnings/advisories...
CT...Winter Storm Warning until 7 am EST Monday for ctz008-010>012.
Winter Weather Advisory until 7 am EST Monday for ctz005>007-
New York...Winter Storm Warning until 7 am EST Monday for nyz078>081.
Winter Weather Advisory until 7 am EST Monday for nyz067>075-
New Jersey...Winter Weather Advisory until 7 am EST Monday for njz002-004-
Marine...Small Craft Advisory from 6 am Monday to midnight EST Monday
night for anz330-335-338-340-345.
Small Craft Advisory from 6 am Monday to 6 am EST Tuesday for



National Weather Service Glossary of Abbreviations