Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1100 PM EDT Friday Mar 27 2015
a deep upper trough will push across the region tonight through
Saturday. Meanwhile...low pressure over the middle-Atlantic will
track towards the Canadian Maritimes on Saturday. High pressure
then builds into the region Saturday night into Sunday...followed
by a series of frontal systems that will impact the area through
the upcoming week.
Near term /until 6 am Saturday morning/...
forecast overall is still mainly on track. Made some minor
adjustments to temperatures...dewpoints and probability of precipitation for showers
according to latest observed trends. Main area of rain still
about 15 to 40 miles southeast of Long Island. This will pivot
gradually back towards the region overnight with further
shower development across eastern portions of the forecast
Some middle-level shortwave energy...as well as a surface low pressure east
of the 40/70 benchmark...will track to the northeast tonight.
Meanwhile...a deep upper trough with several strong 500 mb shortwaves
will continue to slowly pushing into the Ohio Valley and track to
the east. Another surface low...currently over the Carolinas...will
begin to track to the northeast...and this interaction will
produce showers across the region late tonight. Prior to
midnight...temperatures will be warm enough for precipitation to be rain. After
midnight...thermal profiles fall below freezing across the
County Warning Area...and precipitation will mix with and change to snow. The bulk of the
snow will fall over extreme southeast CT and the Twin Forks of
Long Island... where the best forcing will occur...and 1/4 to 1/2
inch snow possible by daybreak Saturday.
Lows tonight will range from the upper 20s to low 30s.
Short term /6 am Saturday morning through Saturday night/...
unseasonably cold airmass spreads east for the weekend. With 850
mb temperatures from -10c to -12c and 1000-500 mb thicknesses will fall
to 515-520 dam during the day Saturday. This will set up conds
for wintry weather for most of the day.
Upper trough slowly moves east during the day Saturday...and then
a closed upper low will cut off over the northeast by Saturday
evening. Meanwhile...surface low offshore will continue to track
towards the Canadian Maritimes during the day...and departs by
Saturday evening. As the low passes east of Cape Cod...it will
form an inverted trough that will extend back towards eastern CT
and eastern Long Island. Operational models are in good agreement
with this occurring...and are indicating some banding there. Will
go ahead and bump up probability of precipitation to likely/categorical for the far
eastern zones...and currently expecting about 1-3 inches of snow
by Saturday evening. Do not think a Winter Weather Advisory is
needed...but some spots could pick up close to 3 inches across New
London County. Otherwise...snowfall totals should average 1-2
Precipitation tapers off Saturday evening as inverted trough moves into
the open Atlantic waters and closed low/upper trough track east.
Most precipitation should be over by daybreak Sunday...and any additional
precipitation over eastern zones Saturday evening will be light.
Temperatures will be about 15 degrees below normal with highs
generally in the middle 30s to around 40. Lows Saturday night will be
quite cold...ranging from the middle teens inland to the middle 20s near
Long term /Sunday through Friday/...
a progressive...yet amplified flow is being advertised by the global
models through next week. Initially...a series of fast moving Pacific
systems ride over top the ridge over western North America...
dropping southeast across central Canada and into the NE quarter of the
nation. However...toward the end of the week...there are timing and
magnitude differences with Pacific energy moving into the West Coast of
the lower 48. The 12z European model (ecmwf) focuses on a trailing second piece of
energy...thus slowing down the frontal system at the end of next
week. For the time...will maintain a low chance of rain showers Thursday
and Friday with the possibility that this system may be slower than
The other system that may be noteworthy is a clipper low that the
12z GFS takes just north of NYC and Li Tuesday night...while the European model (ecmwf)
is significantly farther south emerging off the middle Atlantic coast.
The latter scenario has some support from the gefs. This could raise
concerns for some wintry weather...especially inland. For now...going
with an all rain forecast based on climatology and model uncertainty.
A much weaker cold front will move across the area Monday with
perhaps a few showers.
After an unseasonably cold start on sun with highs 40 to 45...both
highs and lows will rebound to near seasonable levels. The one
caveat is a farther south storm track Tuesday night into Wednesday.
Aviation /03z Saturday through Wednesday/...
surface low pressure developing off the middle Atlantic coast will
pass well to the south and east overnight and Sat. An upper level
disturbance and weak surface low pressure trough will move across
the region on Saturday.
VFR conds prevailing at all terminals except kgon where MVFR ceilings
are present. Expect MVFR to continue at kgon through around
09z...then drop to IFR with -sn. Onset is expected around 07z and
thermal profiles are marginal for snow...so start with a snow/rain
mix. Runway accumulation of 1-3 inches is forecast.
MVFR conds expected to develop sometime between 09z and 13z at
kisp and kbdr. Chc's for precipitation are lower here and further west so have
only included vcsh for now until timing can be narrowed further
from hi res model data. The rest of the terminals should remain
VFR through the taf period...although a brief period of MVFR is
not out of the question in any rain/snow showers on Sat.
Winds increase as the pressure gradient tightens with the offshore low
deepening and gusts should develop around 12z or so. NYC terminals
could see more than occasional gusts starting around 05z.
... 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: chance of MVFR conds in any rain/snow showers
Klga fcster comments: chance of MVFR conds in any rain/snow showers
Kewr fcster comments: chance of MVFR conds in any rain/snow showers
Kteb fcster comments: chance of MVFR conds in any rain/snow showers
Khpn fcster comments: chance of MVFR conds in any rain/snow showers
Kisp fcster comments: chance of MVFR conds in any rain/snow showers
Outlook for 00z sun through Wednesday...
Sat afternoon...chance of MVFR conds with any rain or snow
showers. Northwest winds g20kt.
Sat night...chance of MVFR conds with any snow or rain showers...
mainly in the evening. Northwest winds g20-25kt.
Monday...VFR. West winds g20kt.
Tuesday night...chance of MVFR conds with any rain showers.
rough seas will persist on the ocean waters tonight through
Saturday morning...and then as low pressure passes east of Cape Cod on
Saturday...the northwest gradient will tighten up...and can expect Small Craft Advisory
gusts to develop on the ocean on Saturday...and then on all waters
by Saturday evening. Will go ahead and hoist small craft
advisories for all non ocean waters by Saturday evening and
lasting through Saturday night.
Waves diminish to sub Small Craft Advisory on Sunday...but build to above Small Craft Advisory
criteria on a southerly flow late Sunday night into Monday ahead
of an approaching warm front. Winds mainly over the ocean waters
will gust to 25 knots late Sunday night into Monday night. Winds and
waves will diminish on Tuesday as the pressure gradient relaxes
with weak high pressure building in. There is the potential for
marginal Small Craft Advisory conditions Tuesday night into Wednesday morning depending on
the track and intensity of low pressure near the waters. Leaning
toward sub-Small Craft Advisory conditions at this time.
1/10 to 1/4 inch liquid equivalent possible tonight through
Saturday night...with eastern CT and eastern Long Island possibly
picking up close to 1/3 inch quantitative precipitation forecast. For most areas...precipitation will
fall either as snow or a rain/snow mix...and 1-3 inches of snow is
possible for eastern CT and eastern Long Island Saturday afternoon
No significant widespread precipitation is forecast Sunday into
Rivers and streams are expected to remain below bank full...but
increased river/stream flow across the lower Hudson Valley and
southern Connecticut will continue ice breakup and movement into
this weekend. Isolated ice jams are possible...which if they
occur...could result in localized flooding. Since ice jam flooding
is unpredictable and sudden...interests along ice covered rivers
should monitor National Weather Service forecasts for the latest information.
For details on specific area rivers and lakes...including
observed and forecast river stages and lake elevations...please
visit the advanced hydrologic prediction service /ahps/ graphs on
our web site.
Marine...Small Craft Advisory from 4 PM Saturday to 6 am EDT Sunday for
Small Craft Advisory from 6 PM Saturday to 6 am EDT Sunday for
Small Craft Advisory until 6 am EDT Sunday for anz350-353-355.