Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 250020
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
820 PM EDT Mon Apr 24 2017

.SYNOPSIS...
Low pressure slowly tracks up along the eastern seaboard over
the next few days. It will eventually track from south of Long
Island to off of Nova Scotia by Friday morning. A weakening
frontal boundary then pushes into the region by Saturday, then
stalls out nearby into early next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Forecast is on track. Light returns on radar continue to stream
north. 00Z sounding shows that lower and middle levels are
still very dry. Also, there has been no limit to visibility in
any observations with rain reaching the ground, so anything that
does reach the ground will likely be in the form of sprinkles.

Low pressure over the Carolinas slowly moves up the coast tonight.
Levels below 850mb will be dry to start, so any rain that manages to
fall before midnight will likely be light. PoPs increase overnight
with deepening moisture and a weak low level jet approaching, but
again not expecting any rain to be heavy with some NVA progged below
700mb during this time. Will go with PoPs increasing to likely for
most areas by daybreak.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...
Low pressure continues to move up the east coast during Tuesday.
Moisture increases with a theta-e ridge shifting in from the south
and PWATs increasing to 1.25 to 1.50 inches. Isentropic and
shortwave lift will help push the likelihood of rainfall northward
through the rest of the CWA. Further lift will then be supplied by
another low level jet by late in the day.

Breezy conditions develop, especially along the coast with a
tightening pressure gradient increasing easterly winds. High
temperatures will be below normal.

With a stacked system, the coastal storm will slowly drift up the
Atlantic Seaboard Tuesday night and Wednesday while weakening as it
does so. Rain remains likely Tuesday night before chances lower
through the day on Wednesday. Models differ regarding the placement
of the axis of greatest qpf. With the low stacked, prefer a more
eastward track for the surface low - which would be closer to the
consensus track of the 500 mb low. This places the strongest lift
over the eastern zones. Will therefore continue with the idea from
the previous forecast and RFCs that the higher amounts of rain are
more likely to fall somewhere over the eastern half of the Tri-State
Area. No thunderstorms are anticipated as elevated instability is
progged to remain to our south, and it appears that the entire CWA
will fall short of flash flood and headwater guidance flooding for
this event. See the hydrology section below for more details. Went
closer to the cooler side of guidance for Wednesday`s high
temperatures.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A gradually filling cutoff low tracks from south of Long Island
Wednesday night to off of Nova Scotia by Friday morning.

The result should be spotty rain Wednesday evening, tapering of to
showers and patchy fog by Thursday morning. For now have gone dry
for the bulk of Thursday and Thursday night, but cannot rule out a
stray shower on the backside of the departing low during this time
frame. Given abundant low level moisture and an inversion forecast
to set up around 850 hPa, do expect some cloud cover, for now going
partly sunny/mostly cloudy however do have possibility of partly
cloudy (optimistic) to overcast (pessimistic). As a result have
decreased the diurnal range in this time frame.

A 700-500 hPa shortwave passes on Friday, with isolated to scattered
showers and thunderstorms (best chance basically area to the N/W of
NYC - where highest CAPES are expected).

Ridging builds in from the South From Friday night into Sunday -
however should also have a frontal boundary stalled out near the
area. The models differ on the strength and orientation of the
ridge, so the amount of precipitation. if any, received during this
time frame is in question.

It will be a balance between increasing subsidence under the
building ridge and vs. lift with the front - for now going dry
Friday night/Saturday then slight chance pops Saturday night-Sunday.

For now have chance pops Sunday night/Monday as shortwaves approach
ahead of a full latitude trough (with a cutoff low at its head).
This might be a little on the aggressive side, especially if ECMWF
idea of a stronger ridge plays out.

Temperatures Wednesday night through Thursday are a blend of MOS and
NAM 2-meter temperatures (with a mix down from 975-950 hPa blended
in for highs on Thursday) and should be around 10 degrees above
normal then 5-10 degrees above normal respectively. Temperatures
Thursday night-Monday were based on the Superblend, and are
forecast to remain above normal.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Low pressure slowly moves up the Mid-Atlantic coastline through
Tuesday night.

MVFR and IFR cigs expected to develop in bands of rain late
tonight. Vsby will likely be slower to come down...perhaps not
until Tuesday morning. Expecting IFR/LIFR cigs on Tuesday...with
vsby potentially lowering to these levels as well...as rain
continues. Increasing potential for LIFR conds Late Tuesday into
Tuesday evening...with potentially heavy rain.

E/NE winds increase tonight flow tonight...maximizing Tuesday
with speeds 15-25 kt and gusts 25-30 kt. Highest sustained winds
for coastal terminals.

     NY Metro Enhanced Aviation Weather Support...

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

KJFK TAF Comments: IFR cigs likely for morning push. E/NE wind
gusts around 25 kt likely...peak gusts to 30 kt possible.

KLGA TAF Comments: IFR cigs likely for morning push. E/NE wind
gusts around 25 kt likely...peak gusts to 30 kt possible.

KEWR TAF Comments: IFR cigs likely for morning push. E/NE wind
gusts 20-25 kt likely...peak gusts to 30 kt possible..

KTEB TAF Comments: IFR cigs likely for morning push. E/NE wind
gusts 20-25 kt likely...peak gusts to 30 kt possible..

KHPN TAF Comments: IFR cigs likely for morning push, possibly
LIFR. E/NE wind gusts 20-25 kt likely...peak gusts to 30 kt
possible.

KISP TAF Comments: IFR cigs likely for morning push. E/NE wind
gusts 20-25 kt. E/NE wind gusts around 25 kt likely...peak
gusts to 30 kt possible.

.OUTLOOK FOR 00Z WEDNESDAY THROUGH SATURDAY...
.Tuesday Night...IFR/LIFR in rain. NE gusts 20 to 25 KT. Winds
drop off late Tuesday night. LLWS possible Tuesday evening with
SE winds 45-50 kt at 2kft.
.Wednesday-Wednesday Night...IFR in rain. Potential for
IFR/LIFR in fog Wednesday night.
.Thursday...MVFR/IFR to start...with gradual improvement to
VFR.
.Friday...Chance of MVFR in showers.
.Saturday...VFR.

&&

.MARINE...
Have started the SCA on all waters a few hours earlier tonight than
what was previously posted with the expectation that winds will
increase more quickly than the previous forecast. Will still go with
the SCA ending Tuesday night after collaboration with the
surrounding offices, and although there could be a few gusts to gale
force on the ocean waters at some point Tuesday or Tues day evening,
confidence to go with a gale warning was not high enough at this
time.

A relatively relaxed pressure gradient over the region Wednesday
night through Saturday will limit winds to 15 KT or less during this
time frame. Sub-small craft conditions are expected on the non-ocean
waters as a result Wednesday night through Saturday. On the coastal
ocean waters, swells from the departing coastal low will keep seas
above SCA levels over at least part of each coastal water zone
Wednesday night through Friday. Seas should fall below 5 ft on all
coastal ocean zones by Saturday.

&&

.HYDROLOGY...
Total rainfall of 3/4 to 2 inches of rainfall is expected tonight
through Wednesday. The highest amounts are most likely to occur
across eastern Long Island and southeastern Connecticut where the
best chances of minor flooding of poor drainage and low lying areas
will be. The heaviest rainfall probably occurs during Tuesday
night.

No significant (0.5 inches or more) widespread rainfall is forecast
from Wednesday night through at least Sunday.

&&

.TIDES/COASTAL FLOODING...
There is the potential for widespread minor coastal flooding with
the Tuesday evening high tide cycle. The threat will be along the
southern bays of western Long Island/Queens/Brooklyn, western Long
Island Sound and NY Harbor. There is even a chance of locally
moderate coastal flooding along the south shore bays of Nassau
County. This is in response to a low pressure system moving
northward along the eastern seaboard. Only 1/2 to 1 foot of surge is
needed to reach minor flood thresholds Tuesday evening. Coastal
Flood Advisories might need to be issued tonight. Elsewhere, minor
coastal flooding threshold might be touched along parts of coastal
New Haven County.

Thereafter, minor widespread coastal flooding will be possible with
the high tide cycles during Wednesday morning and night primarily
across the south shore bays of western Long Island and the lower
half of NY Harbor.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Tuesday for ANZ330-
     335-338-340-345.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ350-353-
     355.

&&

$$
SYNOPSIS...JC/Maloit
NEAR TERM...JC
SHORT TERM...JC
LONG TERM...Maloit
AVIATION...NV
MARINE...JC
HYDROLOGY...JC/Maloit
TIDES/COASTAL FLOODING...



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