Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1258 PM EST sun Dec 8 2013
high pressure slides northeast of the region today. Low pressure
will develop off of Cape Hatteras tonight...and track east of Montauk
on Monday. High pressure moves overhead tonight...and then
offshore on Sunday as low pressure approaches from the west. That
low will move across the region Sunday night and Monday. Another
weak low will pass to the south on Tuesday...followed by a series
of cold frontal passages during the middle to late week.
Near term /until 6 PM this evening/...
before 21z...lowered probability of precipitation slightly with dry conditions and strong
banding of precipitation staying south and west of the region. Temperatures were
lowered again with otherwise no remarkable changes. Thinking here
that the main band stays south of the region but more precipitation would
develop within the County Warning Area and near it over the next 2-3 hours. Radar
returns will convey more filling in. This is similar to 12z GFS
and CMC with NAM notably too north with precipitation.
Strong high across central PA and western New York state will translate
northeast of the area today. All models are conveying in their
mslp signature a sharp curving pattern just east of the
Appalachians...a sign of cold air damming. A northeast flow
developing and staying through the early evening along with warm
air advection aloft with positive vorticity advection...points
towards an earlier onset of precipitation. Models are showing this
and usually this occurs with warm air advection aloft scenarios.
With wet bulb cooling in the boundary layer...this will easily
make 33-36 degrees f readings drop to near 30 degrees f within a
short period of time. New 12z NAM showing higher quantitative precipitation forecast along with
earlier onset time.
Monitoring upstream observation closely to see their quantitative precipitation forecast over the next few
hours to see if snow amount forecast needs to be increased. There
is possibility for forecast snow amounts to increase 1-2 inches
with subsequently a possible expansion of Winter Weather Advisory.
Already noted and increased clouds in forecast...with higher to
lower clouds moving and increasing potential for seeder feeder
mechanism. Temperatures and dewpoints were pretty well in tolerance so far
but did lower temperatures a few degrees in afternoon with earlier onset
Short term /6 PM this evening through 6 PM Monday/...
precipitation spreads northward during the evening.
Precipitation still expected to be all snow with evap cooling the bl at the
start. The pattern and model data continue to suggest fairly rapid
middle level warming so after about an inch of snow at the
coasts...expect a quick transition to rain. Ely winds will be
picking up and warming the bl...so do not anticipate any
significant freezing rain at the coasts at this time.
Inland however is a different story...where surface temperatures will stay
blw freezing as the middle levels warm. As a result...expect some ice
accretion overnight into Monday morning. The freezing rain/rain line transitions
northward Monday morning...with all areas rain during the day on Monday.
Total snow/ice/qpf graphics are posted.
Rain tapers off Monday afternoon as the low tracks southeast of kmtk.
Long term /Monday night through Saturday/...
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 US ushering in shots of Arctic air
for the middle to late week.
Precipitation should taper off quickly Monday evening as low pressure passes
east of New England and a cold front drops to the south.
Tuesday continues to pose some uncertainty on whether the region is
affected by a light snow event. The players are the next is 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 a light snow event to a near
miss...lending to maintaining chance probability of precipitation for southern zones to
slight chance northern zones.
Thereafter...models continue to point to shots of an Arctic airmass
building over Canada spilling into the northern US. Uncertainty
remains on how much of this airmass sinks south and timing...which
will be dependent on the evolution of the hudsons Bay polar vortex
through the end of the week/weekend. Wednesday through Friday continue
to look anomalously cold...with high struggling to get above
freezing for most of the region.
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 frigid this weekend...struggling to reach
the upper teens/lower 20s for highs this weekend. Based on the
uncertainty...have maintained continuity with previous forecast of a
slow moderation in temperatures (still 5 to 10 degrees below seasonable)
and potential for light wintry precipitation.
Aviation /18z Sunday through Friday/...
band of moderate-heavy snow across southern PA and southern New Jersey is
tracking to the east. Latest guidance keeps the heaviest of the
snow just south of knyc terminals...but the gradient will be very
tight...generally on the order of 10 miles or so will separate
visibilities from 1-3sm to 1/2sm or less. Do not think the heaviest will
make it to knyc terminals...but there is the chance. Will
therefore tempo 1/2sm visibility in moderate snow for a couple of hours
this evening for kjfk/klga/kewr/kisp. Confidence is low that the
band will make it that far north...and that band of 1/2sm visibility is
likely to impact kjfk than the other terminals.
Otherwise...snow...with 1-3" of accumulation at the terminals and
2-4" at kswf will develop by 20z. Snow then mixes with and changes
to sleet/freezing rain after 02z at southern terminals...and the changeover
will likely hold off until later tonight across interior
terminals. A trace to a couple of hundredths of ice is possible in
freezing rain...especially at kswf. A changeover to rain will happen
between 08-10z from south to north.
Generally IFR/LIFR conds on tap for tonight through Monday
morning. Rain and fog is likely through Monday morning. Low
stratus deck should hold tight through the day.
Outlook for 18z Monday through Friday...
Monday afternoon...IFR/LIFR in -ra/dz/fg/stratus. Winds shifting
from east...to southeast...then to northwest late in the day.
Monday night...conds improving to VFR. Northwest winds 10-20 knots.
Tuesday...MVFR or lower in -sn.
Tuesday night...improving conds. West winds 10-20 knots.
Wednesday...VFR. West-northwest winds 10-20 knots with gusts up to 25 knots.
hipres will result in light winds today. East winds will increase late
tonight ahead of low pressure from the S. A Small Craft Advisory has been issued for all
waters except for The Harbor. The wind decreases Monday afternoon as a low
pressure trough passes through. The Small Craft Advisory has therefore been set to expire at
18z. Seas on the ocean however will remain above Small Craft Advisory levels the
Small Craft Advisory conds likely Monday night after a cold frontal passage. Then
several periods of Small Craft Advisory conds are possible on all waters as shots of
Arctic air work into the region...likely Tuesday night into Wednesday and once
again Wednesday night into Thursday. Uncertainty increases thereafter.
around a half inch of liquid equivalent is expected tonight through Monday.
Flooding is not expected at this time.
Beyond 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 from 6 PM this evening to 8 am EST
Monday for ctz005>008.
New York...Winter Weather Advisory from 6 PM this evening to 8 am EST
Monday for nyz067>070.
New Jersey...Winter Weather Advisory from 6 PM this evening to 8 am EST
Monday for njz002-103.
Marine...Small Craft Advisory from 11 PM this evening to 1 PM EST
Monday for anz330-335-340-345.
Small Craft Advisory from 11 PM this evening to 6 PM EST
Monday for anz350-353-355.