Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1253 PM EST Tuesday Dec 10 2013
weak low pressure will move southeast of Long Island through this
afternoon. High pressure will then build from the west
tonight...followed by an approaching cold front on Wednesday. The
front will move across Wednesday night...with high pressure
building in from the south and west through the end of the week. A
coastal storm will likely impact the region this weekend...with
high pressure returning early next week.
Near term /until 6 PM this evening/...
first round of snow just about complete as the heaviest of snow
has exited southeast of Long Island. Snow is developing behind it
but it is not as organized and intensity appears less than snow
previously. It is more periodic with evident smaller and narrow
streaks in radar reflectivity. Even so...radar returns are
filling in within eastern PA and New Jersey so therefore snow is not done
yet. Additional accumulations of snow are expected mostly in the
1-2 inch range. Two areas of snow specifically are being
watched...one in south to central New Jersey streaming northeast and one
in eastern PA moving eastward. Expecting these to continue pushing
east. Dynamics are still present with the region being east of
upper level trough evident in the water vapor imagery. Tracking a
gradient of middle to high level moisture in this imagery and this
moves through western portions of the region a little after 20z
and the rest of the County Warning Area by 22z...which will mark an end to the
forcing for this snow.
Winter Weather Advisory remains in effect for entire forecast
region. One caveat is that temperatures have been more in the 32-34
degree range which is making if difficult for snow accumulation
right on the ground on lower non-grassy surfaces...so expect a
higher accumulation on grassy and elevated surfaces. Temperatures are
expected to lower this afternoon making for higher snow liquid
ratios and therefore more accumulation...giving more confidence in
keeping the Winter Weather Advisory up. In addition...untreated
roads will still be quite treacherous from the snow and slush.
Overall for storm total...snow amounts of 2 to 5 inches with
the higher amounts in NE New Jersey...NYC...southern lower Hudson
Valley...most of southern CT...and western Long Island. Thinking
that 5 inch amounts will be the peak of snowfall amounts at this
point and these should be localized.
Short term /6 PM this evening through 6 PM Wednesday/...
conditions quickly clear out across most of the area this evening as
the low pulls out with weak ridging building in aloft the exception
will be lake effect clouds setting up across far northwest areas. Blustery
winds tonight across all but western interior areas in the wake of
the storm...with gusts of 20-30 miles per hour. Used the minimum of mav/met/NAM
2-meter temperatures for lows - with values around 10 degrees below
normal. Did not undercut guidance with snow cover due to winds being
a limiting factor. Wind chills overnight will range from 5 to 15
degrees - coldest north of NYC and warmest over eastern Long Island.
Weak ridging exits to the east Wednesday with a west-southwest flow setting up
aloft. This should keep most if not all lake effect flurries/-shsn
to the north of the area. Mixing will be limited to around 925-900 hpa
so highs will struggle to reach the 30 degree mark in most
locations...with coastal southeast CT and the Twin Forks struggling to
reach freezing. These highs are consistent with a blend of mixing
down from 925 hpa...except 900 hpa well inland...with NAM 2-meter
temperatures and a blend of mav/met guidance...and are around 15
degrees below normal. Wind chills Wednesday will mainly be in the
teens...with some around 20 across coastal southeast CT and the Twin Forks.
Long term /Wednesday night through Monday/...
the 500 mb flow across the eastern US will start with a broad trough and
become zonal by the weekend. Meanwhile a split flow out west will
phase with time as the northern branch digs from the Pacific northwest to The
Rockies and plains states. This phasing energy will be the area to
watch through the remainder of the week as signals for a coastal
storm this weekend are apparent.
At the surface...a cold front will traverse the area Wednesday night. Deep
layered moisture is lacking...therefore expect it to pass dry. A Few
Lake effect flurries may make it into far northwest Orange County. Cold
weather will continue through the end of the week with highs
struggling to reach the freezing mark on Thursday (h85 temperatures around
-15c). Sided with the colder guidance with the snow pack expected to
remain on the ground. Lows Wednesday night will generally be in the lower
teens inland to around 20 in metropolitan NY/NJ. Thursday night will be a tad
colder with less cloud cover with teens at the coast and single
digits inland. Wind chills both nights will drop into the single
digits across the area...and could fall below zero Thursday night across
interior zones. Conds will remain dry through Friday with high pressure
nosing in from the S and west.
As for the weekend system...the initial surface low associated with the
southern branch of the jet stream is forecast to develop in the Lee
of The Rockies and move across the Southern Plains Friday and Friday
night. As the northern stream energy phases with it and moves
towards the middle Atlantic coast...the system will strengthen and
track from the middle Atlantic coast just S and east of Li before lifting
towards Nova Scotia.
The devil is in the details and there is a 6-12 hour difference in
the timing between the operational ec...CMC and GFS. The track is
the most consistent aspect of the system and with a decent high to
the NE it should be cold enough at the onset for snow with a gradual
warming of the atmosphere. The timing and extent of the changeover
still needs to be resolved. The GFS is much warmer than the ec to
start which is a known bias of the model. It is likely eroding the
cold air too quickly. This will ultimately have impacts on
p-type...so have low confidence in the details of the current
High pressure then builds towards the area for the start of the new work
week with dry but cold and potentially gusty conds.
Aviation /17z Tuesday through Saturday/...
low pressure passing to the south will bring varying conditions
through midday...with improving conditions late this afternoon
Heaviest snow band has exited the region...with light snow with
IFR ceilings/visible now expected through the afternoon...ending west to east
between 20-22z. Could see ceilings/visible improve +1-2 hours sooner than
in taf over entire area.
Additional snow totals...mainly NYC and east could amount to 1-2
Clearing skies and VFR conditions after 21z.
Winds increase from the west-northwest after 21z...with gusts between 20-25
kts lasting into tonight. Gust diminish for a period overnight
before increasing again tomorrow morning after 12z.
New York 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: low confidence of brief period of moderate snow
with LIFR conditions possible between 18-19z.
Klga fcster comments: winds will shift between 300 and 330 through
21z. Moderate confidence conditions drop between 18-19z to IFR.
Kewr fcster comments: moderate confidence ceilings drop between 18-19z to IFR.
Kteb fcster comments: IFR conditions may linger +1 hour than in
Khpn fcster comments: moderate confidence conditions drop between
Kisp fcster comments: IFR ceilings may end +1 hour sooner than in taf.
Outlook for 18z Wednesday through sun...
Wednesday...VFR. West winds g20-25kt.
Thursday...VFR. West-northwest g20kt.
Sat-sun...MVFR or lower conditions with mixed wintry precipitation.
after a lull with sub-Small Craft Advisory conditions...wind gusts increase late
this afternoon to Small Craft Advisory levels on the coastal ocean waters late this
afternoon. Since this should be only a couple of hours before the
Gale Warning starts...it will not be of long enough duration to
warrant an Small Craft Advisory. Gusts to gale force are expected tonight on the
coastal ocean waters...with gusts to Small Craft Advisory levels elsewhere in the
wake of the departing low. The Small Craft Advisory level gusts will likely
continue on all waters Wednesday.
Gale Warning in effect for the coastal ocean waters for tonight
and a Small Craft Advisory for the remainder of the waters. With
confidence not quite at 80 percent...opted not to extend the Small Craft Advisory
into Wednesday on the non-ocean zones.
Small Craft Advisory may need to be continued into part of Wednesday night with winds and
seas diminishing. After a brief lull on Thursday/Thursday night...cold air advection is
expected to bring winds and seas back up with Small Craft Advisory likely need on at
least the ocean waters Friday. Conds then should remain at sub-advisory
levels until the coastal system this weekend although timing is
uncertain at this time. Strong gales are possible on the backside of
will receive from .1 to .4 inches of liquid equivalent
today...almost all of it in the form of snow. No hydrologic issues
are expected. It should then be dry through Friday.
There is the potential for significant precipitation this weekend in
association with a coastal low pressure system.
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 5 PM EST this afternoon for
New York...Winter Weather Advisory until 5 PM EST this afternoon for
Winter Weather Advisory until 4 PM EST this afternoon for
New Jersey...Winter Weather Advisory until 4 PM EST this afternoon for
Marine...Small Craft Advisory from 6 PM this evening to 6 am EST
Wednesday for anz330-335-338-340-345.
Gale Warning from 6 PM this evening to 6 am EST Wednesday for