Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
117 am EST Monday Dec 9 2013
low pressure will move north to a position off the southern New
Jersey coast early this morning...then pass slowly southeast of
Long Island on Monday. The low will then move into the Canadian
Maritimes Monday night...with high pressure building in from the
west late. Another weak low will pass to the south on
Tuesday...followed by a series of cold frontal passages during the
middle to late week...and another weak low passing to the south this
Near term /until 6 am this morning/...
main precipitation shield only making slow progress northward early this
morning...as low pressure drifts northward. Based on latest model
guidance/radar/Sat trends...should see light precipitation become more
widespread through the early morning hours...but with heaviest
precipitation likely staying across southern zones.
Colder cloud tops moving aloft allowing for seeder- feeder ice
nucleation and light snow to re-develop. Expectation is for
transition to sleet and then freezing rain through through the
next several hours from south to north as warmer air moves in
aloft. So only expecting up to an inch of additional snow/sleet
accumulate across interior...lesser along the coast.
Ice accretion sensors at knyc and kmgj picked up a few hundredths
of an inch of ice in an hour. With temperatures still in the upper 20s
across interior and only a slow creep up through daybreak...and a
couple tenths of quantitative precipitation forecast before that...have bumped up ice accumulate to 1
to 2 tenths for this morning for NE New Jersey...lower Hudson Valley...and
coastal CT. Temperatures across southern Li/NYC are now creeping above
freezing...but a few more hundredths of an inch likely across
northern coast of Li and NYC.
Do not expect snowfall much more than an inch overnight and a
glaze of ice.
Short term /6 am this morning through 6 PM Tuesday/...
extended advisories through the morning in many areas as cold air
across interior sections will be slower to erode due to NE flow
between offshore low pressure and cold air damming still in
place...with freezing rain inland and rain along the coast.
Rain lingers through the afternoon especially eastern regions of
the area with temperatures overall increasing into the 40s for much of
the region. Far interior portions of the area may stay in the
Rain tapers off and becomes more of showers in precipitation Mode Monday
night. It will be cold enough across some portions of the lower
Hudson Valley and interior southwest Connecticut for these to be
The upper level jet approaches slowly Monday and Monday night
while picking up in strength with maximum winds increasing back to
about 170-190 knots. 500mb heights lower through the day Monday and
Monday night. At a larger scale...the ridging across the southeast
becomes flatter as the west-southwest to east-northeast trough continues eastward
progress. Tight gradient aloft will convey a fast steering flow.
At the surface...the weak low moves across the region Monday and
to the northeast of the region Monday night. High pressure from
the south and west will build in late.
Long term /Tuesday night through Sunday/...
no major changes to the forecast during this time period as the
polar vortex over Hudson Bay continues to rotate a series of
shortwaves through the northern states...ushering in shots of Arctic
air for the middle to late week.
Tuesday continues to pose some uncertainty on whether the region is
affected by a light snow event. The players are the next in a series
of northern stream shortwaves and a bit of southern stream energy
approaching the region Tuesday...inducing a weak wave of low pressure
along a cold front stalled to the south. The key will lie in the
amount of southern stream interaction...which always poses some
predictability issues. Latest operational models/ensemble solutions
continue to show spread between an advisory level snow event for
NYC/Long Island to a near miss...lending to maintaining chance probability of precipitation
for southern zones to slight chance northern zones. However...with
the area falling under the right rear quadrant of an upper jet
streak to the northwest and a stripe of 700 mb-5 frontogenesis predicted just
south of NYC/Long Island...think NYC/Long Island/coastal southeast CT have
a good shot at seeing some light snow...so bumped pop there to
likely...with amts up to an inch possible.
Will note that the 18z GFS/NAM have come in snowier...suggesting
a 2-5 inch snowfall from north to south. However...the 12z gefs
mean and 15z sref show about half that...so until the European model (ecmwf) trends
toward a snowier solution still feel it is best to play a middle
ground between ensemble means and the mainly dry European model (ecmwf)...so no
forecast changes planned as of yet.
Thereafter...models continue to point to shots of Arctic air
building over Canada and spilling into the northern states.
Uncertainty remains on how much of this air mass sinks south and
timing...which will be dependent on the evolution of the Hudson
Bay polar vortex through the end of the week/weekend. The middle to
late week period continues to look anomalously cold...with highs
struggling to get above freezing for most of the region especially
from Thursday on.
Uncertainty increases in sensible weather for this weekend...with
model spread existing in the evolution of the polar vortex. If European model (ecmwf)
evolution of the polar vortex sinking into southeast Canada is
correct...temperatures would be very cold this weekend...struggling to
reach the upper teens/lower 20s especially on Sat. For now
maintained continuity with previous forecast of a slow moderation in
temperatures (still 5 to 10 degrees below seasonable) and potential for
light snow as an Arctic cold front approaches from the northwest and as
weak low pressure passes offshore.
Aviation /06z Monday through Friday/...
challenging forecast with low confidence in details/timing.
Low pressure approaches from the south overnight...then moves east
Atmosphere warming aloft...so any light snow begins to mix with
freezing rain and sleet. Within this light precipitation event...a gradual
changeover to plain rain is expected. NYC metropolitan and Li terminals
should be all rain by the morning push. Southern CT terminals will see a
changeover right around the morning push. And finally across
interior terminals...a changeover may not occur until after 6 am.
Well after at kswf.
Cloud decks have been lowering...and low stratus with ceilings under
1 kft are expected through the morning and into the afternoon hours.
Gradual clearing and return to VFR occurs by evening.
Minor snow accums possible...but the main weather impact will be
light icing due to sleet and freezing rain/drizzle this morning.
Winds will shift early in the afternoon Monday...eventually
turning toward the west as the low pressure center moves east late
in the afternoon.
Outlook for 06z Tuesday through Friday...
late Monday night...VFR.
Tuesday...MVFR or lower in -sn.
Tuesday night...improving conditions. West winds 10-20 knots.
Wednesday...VFR. West-northwest winds 10-20 knots with gusts up to 25 knots.
enough of a pressure gradient develops early this morning to give
wind gusts approaching 25-30 knots for most of the waters...ocean
earlier after midnight and into very early Monday morning for Long
Island Sound and the bays. This becomes more of a seas issue with
5-7 feet seas remaining on the ocean Monday afternoon.
Small Craft Advisory conds may continue into Monday night-Tuesday on the ocean on Tuesday as
weak low pressure passes to the south...then expect at least Small Craft Advisory
conds on all waters Tuesday night-Wed...with possibility of ocean
gales...as Arctic air pours in behind the low.
Marginal Small Craft Advisory conds could take place at any time thereafter through
Friday night on the ocean waters...but especially Thursday night-Friday after
another reinforcing shot of cold air.
additional liquid equivalent quantitative precipitation forecast of 2 to 4 tenths of an inch
expected through Monday. No hydrologic issues anticipated.
due to interference issues with the U.S. Coast Guard
emergency broadcast channel...the New York City National oceanic and atmospheric administration all hazards
weather radio station kwo35 remains out of service. The National
Weather Service is working with several U.S. Government agencies
to isolate and resolve this technical problem.
During this time...the transmitter may be returned to service
intermittently for use of the National oceanic and atmospheric administration all hazards weather radio
during potentially dangerous weather situations...for routine
weekly tests of the warning system...and to determine if the
interference issue has been resolved.
CT...Winter Weather Advisory until noon EST today for ctz005>008.
Winter Weather Advisory until 9 am EST this morning for
New York...Winter Weather Advisory until 5 am EST early this morning for
Winter Weather Advisory until noon EST today for nyz067>070.
Winter Weather Advisory until 9 am EST this morning for nyz071.
New Jersey...Winter Weather Advisory until 5 am EST early this morning for
Winter Weather Advisory until noon EST today for njz002-004-
Winter Weather Advisory until 9 am EST this morning for njz104-
Marine...Small Craft Advisory from 4 am early this morning to 1 PM EST
this afternoon for anz330-335-340-345.
Small Craft Advisory until 6 PM EST this evening for anz350-