Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
441 am EST Wednesday Dec 11 2013
strong high pressure builds in from the south and west today. A
cold front will track across the area this evening followed by
another of high pressure for Thursday.
Near term /until 6 PM this evening/...
tranquil but cold conds expected today as high pressure builds in from
the SW. Strong subsidence aloft will allow for mostly sunny skies
today...with perhaps just a few-scattered strato cumulus around this afternoon.
Highs will only reach low to middle 30s this afternoon...which is a good
10 degrees below normal.
Short term /6 PM this evening through 6 PM Thursday/...
fairly benign conds will continue through Thursday...although it will
remain cold. A cold front will move across the area this
evening...although moisture is lacking and not expecting to see
any precipitation until perhaps it nears the coast and can tap into
Atlantic/sound moisture. Decent shortwave passing aloft...so this
may be enough lift for some flurries on Long Island.
A colder airmass will then filter into the region with 850 mb temperatures
only ranging between -16 to -18c on Thursday. Very cold tonight with
perhaps a period of gusty winds following the frontal passage. Winds should
remain high enough overnight to keep the bottom from falling out
towards morning. Expect lows in the teens inland to lower 20s at
the coast with wind chills in the single digits and teens
respectively. Highs on Thursday will struggle to reach 30 degrees at
the coast...with only middle to upper 20s inland and wind chills in
the teens across the area.
Long term /Thursday night through Tuesday/...
the models were in reasonable agreement Thursday night through
Friday night...so used a blend of the NAM/GFS/ecwmf/sref for the
forecast in that time frame.
A 700 hpa shortwave crosses the area Thursday night...however with
the low levels prognosticated to be dry - went with a dry forecast keeping
precipitation offshore (in this case favoring the NAM/sref over the
GFS/European model (ecmwf) which would suggest slight chance to chance probability of precipitation over southeast
zones). For lows Thursday night used a blend of mav/met guidance
with values around 5 degrees below normal. Wind chills late Thursday
night will run from the upper single digits to around 15 - coldest north
interior and Pine barrens - highest NYC metropolitan.
An Arctic front pushes through Friday afternoon/evening allowing for
a reinforcing shot of cold air to push into the region. Noting
continued dry low levels and no shortwaves forecast to pass aloft -
have kept the frontal passage dry...though cannot completely rule
out some flurries/localized -shsn as it GOES by and in its immediate
wake. For highs Friday used a blend of mav/met guidance with NAM
2-meter temperatures and a mix down from 950 hpa...except 925 hpa
well inland - expect readings to be around 15 degrees below
normal...with steady or falling temperatures in the afternoon. Wind
chills during the day should not get above the teens. For lows
Friday night used a blend of mex/men/ekd/ecm/ece/wpc guidance with
lows 5-10 degrees below normal and wind chills mainly from the middle
teens to lower 20s...except around 10 degrees over the eastern 2/3
of the County Warning Area where the wind will be a tad higher (around 10 miles per hour vice 5
miles per hour or less).
From Saturday through through Sunday night there are differences
between the models in their handling of a coastal storm. Because the
GFS historically has had a bias of being to weak with and to quick
to erode damming highs...and given that even it keeps the core of
the high to our north and does not have it retreating - another sign
that works against its idea of weakening the damming over the area.
Because of this...the GFS low track is too close to the coast as it
does not allow for sufficient blocking of its northward progress by
the high to the north. For this reason have leaned heavily towards the
European model (ecmwf) in this time frame - it also historically does fairly well
with damming highs in additions to generally being the better
performing model in this time frame.
Based on this model choice have the potential for a significant
winter storm to impact the area from mainly Saturday afternoon
through Sunday...with it passing near the 40n/70w Bench Mark during
the day on Sunday. More confident of all snow inland than at the
coast...with the surface wind forecast to go east-east-southeast Saturday
afternoon/night - usually this will bring most of Long Island and
NYC as well as at least coastal southeast CT to all rain. However...the
fact that an Arctic air mass will be in place and re-enforced to the
north means that if the flow is backed more than currently forecast due
to isallobaric influences - could end up staying mainly snow over
coastal areas as well. Still quite a bit of uncertainty on track of
the system so this forecast could very well change. For temperatures
Saturday-Sunday used a blend of all available guidance with European model (ecmwf)
2-meter temperatures - for now European model (ecmwf) 2-M temperatures appeared too
cold - so used other guidance to temper. Expect temperatures to be
below normal based on the above thinking.
In addition to the issues with precipitation...it could be quite
windy with this storm - too much uncertainty to specify if wind
related headlines could be needed - but it is reasonable to say that
possibility is within the reasonable realm of
possibilities...especially for coastal areas.
Reasonable model agreement returns from Monday into Tuesday so used
a European model (ecmwf)/GFS blend in this time frame.
For now expect precipitation to cutoff fairly rapidly as the storm
pulls away - so went dry Sunday night - and continued with that dry
forecast into Tuesday as 700-500 hpa northern stream ridge transits
the area. Used a blend of all available guidance for temperatures
with below normal values forecast.
Aviation /09z Wednesday through Sunday/...
high pressure will build to the south...with high confidence VFR
conditions. Forecast gusts in westerly flow could abate or be only occasional
through 14z...then become more frequent from 14z-19z.
..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: high confidence.
Klga fcster comments: high confidence.
Kewr fcster comments: gusts occasional before 14z.
The afternoon kewr haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: high confidence.
Khpn fcster comments: high confidence.
Kisp fcster comments: gusts occasional before 14z.
Outlook for 06z Thursday through Sunday...
late tonight...mainly broken VFR ceilings with approaching cold front.
MVFR conds possible with any snow flurries. Frontal passage toward daybreak.
Thursday...VFR. Northwest winds g20kt.
Sat-Sunday...IFR in wintry precipitation. Significant snowfall possible
inland...and a rain/snow mix at the coast. East-NE winds g30-35kt Sat
night into Sunday.
Small Craft Advisory continues on all waters through noon...with winds gradually
subsiding this morning. Seas on the eastern ocean waters will likely
remain at or above 5 feet for much if not all of the day and gusts will take
a bit longer to subside as well on the eastern waters. Small Craft Advisory conds
are expected to be met again this evening...therefore have opted for
simplicity and have extended the advsy for the eastern sound/bays
and ocean waters through tonight. Western Li sound...New York Harbor and
South Shore bays are marginal reaching Small Craft Advisory conds tonight and there
is also enough of a lull between events for it to be taken down
later this morning and afternoon.
Small Craft Advisory conds may linger into early Thursday morning on the ocean
waters...but are expected to subside by midday.
Small Craft Advisory conditions are likely on the coastal ocean waters Thursday night
through at least Friday...and possibly into Friday evening over
anz-353 and through Friday night (due to seas) over anz-350. For
the remainder of the waters...its likely Small Craft Advisory wind gusts will
return late Thursday night and continue through Friday...with sub-
Small Craft Advisory conditions Friday night.
All waters should experience sub-Small Craft Advisory conditions Saturday
morning...winds then increase with the approach/passing of a strong
coastal low Saturday night/Sunday. At least gale gusts are likely on
all waters by late Saturday night and should persist through Sunday.
Will highlight this potential in the severe weather potential statement. There is a small chance
for storm force winds late Saturday night/Sunday over mainly the
coastal ocean waters depending ont he exact track/strength of the
storm - but this potential is to low to mention in the severe weather potential statement at this
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.
Marine...Small Craft Advisory until noon EST today for anz335-338-345.
Small Craft Advisory until 6 am EST Thursday for anz330-340-