Scientific Forecaster Discussion
fxus61 kokx 230439
Area forecast discussion
National Weather Service New York New York
1139 PM EST Mon Jan 22 2018
a warm front lifts north through the region overnight and early
Tuesday morning. A cold front then crosses the tri-state
Tuesday afternoon and early evening, followed by a trough of low
pressure pushing through the remainder of Tuesday night. High
pressure then builds in for the rest of the work week, followed
by a frontal system over the weekend.
Near term /until 6 am Tuesday morning/...
SW flow aloft overnight, coupled with east-southeast flow at the surface,
and dry mid levels, will produce areas of drizzle and fog.
Visibilities across Long Island have reduced to generally 1/4
mile or less, so have issued a dense fog advisory there through
9z. Less than one mile at times. There is some potential this
may need to be extended in time, depending on exactly how fast
the warm front lifts to the north.
Elsewhere visibilities range from 0 to 5 miles at ASOS/AWOS
sites across the County Warning Area. There is the potential for the dense fog
advisory to be expanded to other portions of the County Warning Area. Will
continue to closely monitor overnight.
As low to mid level isentropic lift and saturation increases
overnight expect rain to develop from SW to NE after midnight.
Should see some improvement in visibilities late tonight as you
get increased low level lift and some rain, both of which should
create enough mixing to raise visibilities.
Lows tonight should occur this evening, then temperatures should
slowly rise overnight in response to low level warm advection.
Lows should be from the mid 30s to around 40, except lower 40s
in the immediate NYC Metro.
Short term /6 am Tuesday morning through Tuesday night/...
as a warm front continues to push north tonight and into
Tuesday a deep moisture airmass along with precipitable water
values of 1 to 1.25" will set the stage for periods of moderate
to locally heavy rainfall, as a cold front approaches late
tonight and moves across the area Tuesday morning. The front is
forecast to move through fast, so the heavy rainfall at this
time doesn't seem to be a significant threat.
There will be some good instability ahead of the approaching cold
front. Will continue the mention for an isolated thunderstorms as
the cold front makes its way across the area. There is also the
potential for strong winds above the surface to mix down in any
thunderstorms. Regardless, a tight pressure gradient will lead to
strong winds across the area through the day but at the moment it
appears winds will be brief and sporadic enough to preclude a Wind
Advisory for now.
The front will pull offshore by Tuesday evening. Northwest winds
behind the front will usher in more seasonable temperatures. Tuesday
nights low will be in the low to mid 30s.
Long term /Wednesday through Monday/...
not much change in the 12z data regarding the long term. High pres
builds in from the W on Wed, with WNW winds ushering in a colder
airmass. Deep mixing provides a high confidence in temps, so a blend
of the data was used. There could be a period of bkn-ovc aftn cu
which the model data is not picking up on attm, so an upgrade in
cloud cover is possible with subsequent updates.
With deep unidirectional flow, winds should keep the lowest lvls
mixed Wed ngt. Temps therefore not as cold as a pure MOS blend.
Still breezy on Thu but deep subsidence will produce a sunny day.
The superblend was used for temps.
Still in the cool regime Fri as return flow does not commence til
late in the day. The superblend again used for temps. Some mid clouds
may infiltrate the skies if the waa aloft develops fast enough.
A warming trend on Sat as a frontal sys approaches. The GFS and
European model (ecmwf) have diverged on timing however, with the European model (ecmwf) now about 24
hrs slower than the GFS, bringing the cdfnt and bulk of the rain in
on Mon. The fcst remains close to the more consistent timing of the
GFS, with pops focused on sun and sun ngt. Lower pops remain in
place for Mon, but again this could change if the European model (ecmwf) becomes a
trend. The superblend was used for temps.
Aviation /06z Tuesday through Saturday/...
a warm front just S of Long Island will push through late
tonight followed by a cold front Tue aftn.
Difficult forecast continues, especially for NYC and Long
Island terminals. IFR/LIFR with locally vlifr conds prevail at
all terminals. Although the depth of the low cloud deck is all
of around 500 ft, am starting to have doubts that conds improve
for a couple of hours NYC/Li overnight. Not completely out of
the question though with winds aloft increasing and dry air just
above this low cloud deck. Have moved the potential into a
tempo group since the improvement may not be for very long if it
occurs at all.
Otherwise, rain forecast to move in 09-13z. Any improvement
on Tue is forecast to be gradual and current forecast may even
be improving conds too early, especially in the morning.
Moderate to heavy rain showers and isolated thunderstorms will
impact the area from daybreak through the afternoon with the
approach of a cold front.
East/NE 5-10kt become light and vrb away from the coast overnight.
Winds veer to the southeast then S late tonight into Tue morning as
warm front pushes north of the region. Low level wind shear/compression likely
Tue with gusts up to 35 kt possible, strongest for kisp/kgon.
Cold frontal passage with wind shift to west will occur from mid
to late afternoon.
Outlook for 00z Tuesday through Saturday...
Tuesday night into Wednesday...VFR. West-northwest g20-25kt possible.
Saturday...showers possible with S-SW g20kt.
minor changes were made with this update to reflect the latest
trends in observations and guidance. The forecast appears on
With visibilities at ASOS/AWOS close to the coast generally less
than 1 mile, have issued a marine dense fog advisory through 9z.
There is some potential this may need to be extended in time,
depending on exactly how fast the warm front lifts to the north.
South to southwest flow will rapidly strengthen across the area
waters overnight, with at least Small Craft Advisory (sca)
level winds developing by morning. There probably will be some
occasional gusts to 25 kt on the coastal ocean waters late
overnight as well. Depending on the strength of the inversion,
there is potential for strong low- level jet winds to mix to the
surface, with at least occasional gale- force winds on Tuesday.
Occasional gale force winds will also be possible in any
thunderstorms that can develop. Seas will rapidly build in
response to the strengthened flow, remaining elevated even as
the cold front moves through Tuesday evening. Winds may briefly
drop off as the front moves through, before rapidly
strengthening again following its passage. Small Craft Advisory level winds in
the 25 to 30 kt range are expected Tuesday and Tuesday night on
all waters, so have an Small Craft Advisory up accordingly.
A Small Craft Advisory will be needed on the ocean Wednesday and Wednesday night.
Winds will be marginal elsewhere. Winds and seas will then
creep up towards sca levels again on Thursday as low pressure
deepens over the Atlantic. Winds and seas should be below Small Craft Advisory
levels on Friday, then SW flow increases over the weekend ahead
of a frontal system.
total rainfall through Tuesday is expected to range from around
1/2 to 1 inch, with locally up to 2 inches possible in any
stronger convection. There is a small chance for localized
ponding of water in any areas receiving locally heavy rainfall
due to convection, but no significant hydrologic issues are
anticipated at this time.
No significant hydrologic impacts are anticipated from Tuesday
night through early next weekend.
NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) is off the
air for an extended period of time.
New York...dense fog advisory until 4 am EST Tuesday for nyz078>081-177-
Marine...dense fog advisory until 4 am EST Tuesday for anz330-335-338-
Small Craft Advisory from 6 am Tuesday to 6 am EST Wednesday