Scientific Forecaster Discussion
fxus61 kokx 222009
Area forecast discussion
National Weather Service New York New York
409 PM EDT sun Oct 22 2017
dry and mild today as high pressure pulls away from the region.
A slow moving frontal system will impact the region Tuesday into
Wednesday with strong winds gusts and potentially heavy rain. A
frontal system slowly moves east Wednesday into Wednesday night.
An upper level disturbance passes Thursday before high pressure
returns for the end of the week.
Near term /until 6 am Monday morning/...
strong western Atlantic upper ridging will remain in control. At the
surface, high pressure slowly drifts east of the New England coast
with an increasingly moist S/se flow.
Moistening under a subsidence inversion should allow for patchy
stratus and fog development overnight. After early radiational
cooling across far outlying areas, where stratus develops it
would stabilize or raise temps late tonight into early Mon
morning. Lows generally in the 40s across far outlying areas,
50s coast, to around 60 for NYC Metro (close to normal highs for
this time of year).
Short term /6 am Monday morning through Tuesday night/...
models in good agreement with strong western Atlantic ridging slowly
shifting offshore, as vigorous Pacific shortwave/jet energy digs through
the central US Monday and all the way to the Gulf Coast by Tuesday
night/Wed. The resultant -3 to 4 Standard deep eastern US longwave trough
will then tilt towards the NE US for midweek.
Its associated frontal system will approach the region Monday night,
and then crawl across the region Tue into Wed in the longitudinally
oriented steering flow. Trend with this system has been slower based
on the upper pattern and dprog/dt.
Moisture remains relatively shallow on Monday afternoon into Monday
night, with lighter rain shower activity, as well as stratus/drizzle
development. Moisture and forcing increases Tuesday as the frontal
system approaches, presenting the following potential hazards
Tuesday into wednesday:
Heavy rain: the slow movement of the front, deep lift (potentially
right rear of 150+ kt jet streak), weak instability, and
interaction with an increasingly moist and tropical airmass (+3
to 4 std) signal potential for multiple bands of heavy rain as
weak waves lift north along the front. Lower resolution
ensembles continue to range between 1 1/2 to 3 inches of rain
Tue thru Wed. Higher res operational NAM/GFS and sbuwrf models
indicating potential for localized swaths of 3-4 inches, much of
which falls in a 6 hr period. This looks to be a credible
threat based on synoptic pattern, but location/timing is very
much uncertain based on front and frontal wave timing and
location. See hydrology section for associated flooding threat.
Strong winds: the other potential hazard is for strong winds during
the Tue into Tue night period as a 50-60 kt 950 hpa llj moves
overhead Tue afternoon into Tue night. NAM/GFS BUFKIT soundings
indicating a 12-15 hr period of southerly winds gusts of 30 to 40
mph, with potential for any low topped convective line/S ahead of
the cold front being able to drag down localized 45-55 mph wind
gusts to the surface.
Long term /Wednesday through Sunday/...
a deepening negative tilting trough will move into the region
Wednesday through Wednesday night. A stalled cold front in the
region Wednesday into Wednesday night will shift slowly eastward as
a wave of low pressure travels northeastward along it late Wednesday
night into Thursday, allowing the front to move across late
The trough axis moves across Thursday and well northeast of the
region Thursday night. The front moves slowly farther east of the
region Thursday into Thursday night. High pressure then moves in on
Friday and quickly GOES offshore, shifting eastward heading into the
start of next weekend before another frontal system approaches for
Thunderstorms chances will be slight Wednesday morning for eastern
sections of the region, highest Omega and elevated instability will
be shifting from southeast CT and eastern Long Island to east of the region
later Wednesday morning. Rain showers could still be heavy at times
Wednesday morning. The rain showers will linger the whole day across
much of the region and even into the night, but that will be mainly
for Long Island and southern CT. Winds will be trending down as the
frontal zone will be right across the region with the pressure
gradient being rather diffuse and weak.
Rain shower chances continue into Thursday behind the cold front but
coverage and probabilities will be lower than before as westerly
flow will promote more dry conditions. The factors still favoring a
chance of showers though will be the cold pool aloft and mid level
Omega associated with the upper level trough axis moving across.
Drier low level conditions will keep showers light without much quantitative precipitation forecast.
Dry weather will then return Thursday night through Saturday as
upper level ridging becomes strong as it quickly moves offshore. The
surface high pressure area quickly moves offshore as well and will
not be that strong, but should keep the dry weather along with
another warming trend with SW flow increasing in the atmospheric
Temperatures overall will continue to average at least few degrees
above normal for the rest of the week.
Aviation /20z Sunday through Friday/...
VFR through at least 06z Mon as high pres gradually moves east
S/southeast winds 8-12 kt late today from seabreeze enhancement at
Aft 06z tonight may start seeing indications of fog and/or
stratus development mainly away from the city terminals. Better
chance of stratus would hold off until Monday morning with
ceilings probably VFR or MVFR when it occurs.
Outlook for 18z Monday through Thursday...
Mon...VFR likely, chc MVFR cigs. S/southeast g20 kt Mon aftn.
Mon night-Tue...potential period of S/southeast g30-40 knots with low level wind shear
south-southwest 45-55kt@2kft for coastal terminals. MVFR/IFR developing in
-radz Mon night, continuing with rain showers and low prob/sparse thunderstorms and rain
Tue night-Wed...IFR possibly continues in rain showers Tue night, low
prob/sparse thunderstorms and rain early evening, improving to MVFR and possibly
VFR by late Wed.
Wed night-Thu...VFR, with iso-sct MVFR in rain showers.
quiet conds on all waters through Mon as high pressure over the
area slowly shifts east. The pressure gradient will begin to
tighten Mon night as low pressure strengthens over the Great Lakes.
Small Craft Advisory conds are expected to develop Mon night with the potential for
marginal gale force gusts Tue into Tue night on all waters. High
seas are expected to develop N the ocean. Will hold of on 4-5th
period gale watch...based on marginal potential and perhaps
more convectively correlated. Winds subside late tueday night
into Wednesday morning int the wake of the frontal system.
Small Craft Advisory conditions will still be probable across all ocean and eastern
waters Wednesday morning due to both winds and for the ocean, the
high seas as well. For Wednesday afternoon and thereafter, Small Craft Advisory
conditions will linger on the ocean mainly due to the high seas. The
non-ocean waters are forecast to have below Small Craft Advisory conditions.
a widespread 1 1/2 to 3 inches of rain is likely Tuesday into
Wednesday morning, with locally 3 to 4 inches. Concern is that
much of this rain could fall in a 6 hr period in slow moving
and/or training bands of low topped convection/heavy rain, but
the predicatability on location of where this occurs is low.
Despite antecedent dry conditions, these potential rainfall rates
present an areawide potential for minor urban and poor drainage,
with a localized threat for flash flooding. In addition, if the
heavier rain amounts occur over northeastern New Jersey and the
lower Hudson Valley, rapid rises in flashy small streams and minor
flood impacts to adjacent areas would be plausible.
Heavy rain threat diminishes Wednesday afternoon, with drying
conditions expected Thursday night through Saturday.
Marine...Small Craft Advisory from 3 am to 8 PM EDT Tuesday for anz330-
Small Craft Advisory from 10 PM Monday to 8 PM EDT Tuesday for