Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 232013
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
413 PM EDT Tue May 23 2017

.SYNOPSIS...
Weak high pressure moves east of the waters tonight. A low
pressure system tracks southeast of Long Island late tonight
into Wednesday morning. Weak high pressure builds in later
Wednesday, followed by a slow moving low pressure system
affecting the area Thursday into Friday. Weak high pressure
returns for Saturday. Another frontal system affects the area
for the latter half of the holiday weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Anomalously large and deep upper trough and associated upper
low digs into the the Central US tonight...with jet streak and
shortwave riding up the coast late tonight into Wednesday
morning. In response...southern low pressure tracks to the Mid-
Atlantic coast tonight and then quickly near of just se of the
40/70 lat/lon Wed morning.

Still quite a bit of spread in terms of areal coverage of
rainfall between models. A rather tight gradient of heavier
rainfall from frontogenetic zone to the N/NW of the low...which
should mainly stay se of LI. With region in briefly favorable
left front quad of approaching upper jet streak...have leaned
towards higher likelihood of light rain for city/coast late
tonight/early Wed morning...with decreasing chances for
measurable rain to the North and West. Gusty N/NE winds develop
along the coast late tonight and continue into Wed morning in
response tot he low as well.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Anomalously large and deep Central US upper trough and associated
upper low gradually slides east into the Ohio/Tennessee River
Valleys Wed into Wed night.

Initial shortwave/jet streak and resultant coastal low pressure
departs Wed aft...with brief high pressure building in Wed aft/eve.
Any rain pushes east early Wed morning...with gusty N/NE winds Wed
morning gradually subsiding into the afternoon. At least partial
afternoon clearing should allow temps to rise to near seasonable
levels...upper 60s/lower 70s.

Models in good agreement with increasing potential for rain
development late Wed Night into Thu morning ahead of approaching
deep closed low with deep layered lift of sub- tropical
moisture tap. Easterly winds will be increasing as well...with
tightening gradient between warm front/low pressure to the S/SW
and Canadian Maritimes high. See TIDES/COASTAL FLOODING for
associated impacts.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Unsettled pattern for much of the long term.

High amplitude upper level trough over the eastern two-thirds of the
country, with its axis stretching from the Central Great Lakes
region to the Gulf Coast Thursday morning will push east and become
negatively tilted through the day. This is indicative of a mature
system.

At the surface, a warm front will approach from the south. However,
this front looks to remain south of the region, but should provide a
lifting mechanism. A moist airmass, with dewpoints rising into the
upper 50s, with some 60 degree dewpoints not out of the question,
will already be in place. As the upper low with the system moves
closer to the area, cooler air aloft will provide some elevated
instability. MUCAPE values of up to 500 J/kg noted in some of the
models. A period of moderate to briefly heavy rain is possible
Thursday morning. Right now, just some general thunderstorms are
possible.

Although precipitation fields are not currently indicating a high
rainfall event for Thursday with flash flooding, there is a low
probability, given local climatology. The potential for embedded
convection, PWATS near 1.50", and low pressure moving into the area
from the west all point to this potential. Although, winds will be
east, a shift more to the southeast on Thursday would be another
ingredient favoring excess rainfall. Again, would be more confident
in flash flooding if QPF was higher and occurring later in the warm
season, but for now, minor urban and poor drainage flooding seems
most likely.

Surface low pressure moves over the area Thursday night, then heads
northeast, into the Gulf of Maine Friday morning. Light showers will
continue for Friday on the back side of the low.

Weak high pressure builds in for Saturday, with another frontal
system impacting the area Sunday into Memorial Day.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
VFR this evening.  Low pressure passes to the southeast late tonight
but close enough to impact coastal terminals with a short period of
MVFR in late tonight and early Wednesday. Patches of light rain are
expected 07-14z Wednesday morning, mainly near the coast.

Winds becoming light and variable early this evening...mainly SE
then N-NE wind increases late tonight and Wednesday morning 10-15KT.
Gusts 15-20KT possible coastal terminals early Wednesday as the low
passes east.

     NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component fcsts,
can be found at:
http:/www.weather.gov/zny/n90

KJFK TAF Comments: Amendments possible with timing of MVFR
conditions overnight and Wednesday morning.

KLGA TAF Comments: Amendments possible with timing of MVFR
conditions overnight and Wednesday morning.

KEWR TAF Comments: Low chance of MVFR conditions overnight and
Wednesday morning.

KTEB TAF Comments: Low chance of MVFR conditions overnight and
Wednesday morning.

KHPN TAF Comments: Low chance of MVFR conditions overnight and
Wednesday morning.

KISP TAF Comments: Amendments possible with timing of MVFR
conditions overnight and Wednesday morning.

.OUTLOOK FOR 21Z WEDNESDAY THROUGH SUNDAY...
.21z Wednesday...Becoming VFR. NE wind near 10KT becoming SE near
10KT late.
.Wednesday night-Friday night...MVFR or lower possible. Slight
chance of thunderstorms Thursday. E winds G20kt with LLWS
possible.
.Saturday...VFR.
.Sunday...MVFR/IFR developing.


&&

.MARINE...
Winds and seas are expected to remain below small craft levels
through tonight. Overnight, an initially weak pressure gradient
will tighten as an area of low pressure moves up the coast. As
such, marginal NE SCA winds and seas are likely to develop on the
ocean late tonight into Wednesday morning. Winds will become light
by Wednesday afternoon...but seas may remain elevated on the ocean
through Wednesday night.

Low pressure will approach the waters Wed Night into Thursday
Morning with easterly SCA winds likely developing across all
waters...with a low probability for gale gusts. Winds likely
begin to diminish late Thu into Thu eve. Ocean seas building to
5 to 7 ft Thursday and remain Friday, then diminish to less
than 5 ft for Saturday and the remainder of the weekend.

&&

.HYDROLOGY...
0.75" to 1.00" of rain is currently forecast from Thursday
through the day on Friday. Higher amounts are possible in any
thunderstorms that develop on Thursday. The potential for flash
flooding is low given local climatology (see Long Term section)
and the most likely scenario is minor urban and small stream
flooding given antecedent wet conditions.

Another round of light to moderate rainfall is possible for
beginning of next week.

&&

.TIDES/COASTAL FLOODING...
Increasing threat for successive rounds of minor coastal
flooding for the Wed Night, Thu Morning and Thu Night high tide
cycles. Greatest threat for widespread minor and potentially
moderate coastal flooding appears to be with the Thursday
eve/night high tide cycle as a slow moving low pressure system
approaches the region...and with less than 1/2 ft of surge
needed in many places to reach minor flood thresholds and 1 to 2
ft for moderate.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 6 AM Wednesday to 8 AM EDT Thursday
     for ANZ350-353-355.

&&

$$
SYNOPSIS...JP/NV
NEAR TERM...NV
SHORT TERM...NV
LONG TERM...JP
AVIATION...IRD
MARINE...JP/NV
HYDROLOGY...JP/NV
TIDES/COASTAL FLOODING...NV



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