Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
655 PM EDT Monday Mar 30 2015
a cold front will pass this evening...followed by a quick moving
low passing to the south on Tuesday. High pressure will build
across the area on Wednesday ahead of a frontal system moving into
the plains. The frontal system will then progress slowly across
the area from late Thursday into early Saturday. High pressure
will return later this weekend.
Near term /until 6 am Tuesday morning/...
cold front had passed through central Long Island and south
central CT as of 22z and was moving into southeastern CT and the east end
of Long Island. Isolated shower activity will remain confined to
the interior...where slight chance probability of precipitation exist until about 00z.
Expect skies to become mostly clear...with west to west-northwest flow
diminishing overnight. Have continued to side with colder guidance
with clear skies and diminishing winds. This yields lows in the
upper 20s inland and in the Long Island Pine barrens...lower 30s
most elsewhere...and middle/upper 30s in vicinity of NYC.
Short term /6 am Tuesday morning through Tuesday night/...
Alberta clipper low now moving southeast across the northern plains will
continue southeast...reaching the northern middle Atlantic by Tuesday afternoon.
Expect Tuesday morning to be dry with increasing clouds...then precipitation
should overspread the area in the afternoon. Have likely/Cat pop
for nearly the entire County Warning Area...except for southern CT as there is
some uncertainty as to how far north the associated precipitation shield
will extend since nwp guidance shows best warm air advection and 500 mb forcing
passing mainly over NYC metropolitan/Long Island and points south.
Precipitation during the daylight hours should be mainly rain for NYC
metropolitan and Long Island...but inland there is some uncertainty as to
precipitation type. At this time expect an elevation-dependent snowfall...with a
cold rain or a rain/snow mix in the lower elevations...and mostly
snow in the highest elevations. P-type should trend more toward
snow throughout before ending as the boundary layer cools via
wet-bulb cooling and an increasing colder northerly flow. At this time
expect little to no accumulation in NYC metropolitan...no more than a
coating most elsewhere and up to an inch in the highest
elevations. The worst-case scenario would be a coating of
accumulation in NYC...up to an inch most elsewhere...and 1-2
inches in the higher elevations.
Long term /Wednesday through Monday/...
a progressive...yet somewhat amplified upper flow across the lower
48...will be featured during the period. This will result in
several swings in the temperature regime as we go from below normal at the
start of the period...to above normal ahead of an approaching
frontal system at the end of the week...followed by yet another shot
of unseasonably cold air at the end of next weekend. There are also
some timing issues...in particular with the frontal system at the
end of the week. The GFS is more aggressive with a rainfall with a
frontal wave...while the European model (ecmwf) has that wave displaced farther north
and west. Even so...both the 12z GFS and European model (ecmwf) dry conditions out
behind the cold frontal passage on Sat. The differences arise due to
the timing of the Pacific shortwave energy. The specifics of such can
not be worked out this early in the forecast process. Preference was
to take a middle ground approach with the timing of the late
Aviation /00z Tuesday through Saturday/...
a cold front continues to move across the terminals through early
this evening. Weak high pressure builds over the area tonight...and then
weak low pressure impacts the terminals late Tuesday and Tuesday night.
Winds have shifted to the west/northwest across the western terminals and will
shift from the west-SW to the west/northwest over eastern terminals by early this
evening as the cold front works its way east. Wind speeds will be
around 15 knots with 25 knots gusts after its passage...and then gusts end
and winds diminish to 8-12 knots this evening.
After midnight...west winds will average 5-8 knots...and then
increase by a few knots late Tuesday morning.
Broken deck around 4000 feet late this afternoon will scatter out this
evening...and then sky clear conds expected after midnight tonight. Middle-
deck increases Tuesday morning as low pressure approaches from the west.
VFR through 18z Tuesday.
For the 30-hour sites...kjfk/kewr/kswf...MVFR conds in rain for
kjfk/kewr and -sn for kswf after 21z Tuesday.
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: winds 270-290 mag with peak gusts 25-27 knots
Klga fcster comments: winds 280-300 mag with peak gusts 25 to 28 knots
Kewr fcster comments: winds 260-280 mag with peak gusts around 25
knots through 23z.
Kteb fcster comments: west-northwest winds with peak gusts up to 25 knots
Khpn fcster comments: west-northwest winds with peak gusts up to 25 knots
Kisp fcster comments: west-northwest winds with peak gusts around 25 knots
Outlook for 18z Tuesday through Saturday...
Tuesday afternoon...MVFR in developing rain/snow.
Tuesday night...conds improving to VFR by midnight Tuesday night.
Thursday night-Friday...MVFR in rain showers.
Saturday...MVFR in rain showers possible.
Small Craft Advisory on the New York Harbor remains in effect until 8pm. Gusts to 25 knots after
8pm on The Harbor should be more occasional. No changes made to
other Small Craft Advisory headlines.
Seas on the ocean are 4-6 feet and may increase another feet out east
as the flow shifts from SW to west after frontal passage tonight. Gusts out
east after frontal passage should reach Small Craft Advisory levels as well...but did not
issue Small Craft Advisory for the western sound or the South Shore bays as gusts to 25
knots look to be only brief/occasional in nature early this evening.
Small Craft Advisory conds could last on the ocean through Tuesday night...and also
return to the eastern waters Tuesday night...as low pressure passes to the
S and northerly flow increases in its wake. Then expect sub-small
craft level conditions Wednesday through Thursday as a weak pressure gradient
remains over the region. Wind gusts and waves increase to small
craft levels ahead of the next system approaching the ocean
waters Thursday night into Saturday.
quantitative precipitation forecast of 1/10 to 1/4 inch expected Tuesday afternoon and evening.
There is the potential for widespread rainfall at the
end of the week with a frontal wave along a slow moving frontal
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 until 8 PM EDT this evening for anz338.
Small Craft Advisory until noon EDT Tuesday for anz330-340.
Small Craft Advisory until noon EDT Tuesday for anz350-353-355.