Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 251421 CCA
AFDOKX

Area Forecast Discussion...CORRECTED
National Weather Service New York NY
1021 AM EDT Tue Apr 25 2017

.SYNOPSIS...
Low pressure slowly tracks up along the eastern seaboard through
Wednesday night. Weakening low pressure along the New England coast
Wednesday night tracks northeast and up into the Canadian
Maritimes by the end of the week. A weakening frontal boundary
dissipates across the area on Friday, followed by another weak
frontal boundary moving into the area Saturday into Saturday
night. The latter of which stalls out nearby into early next
week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pressure to the north and low pressure along the Carolina
coast has set up a maritime easterly flow. Warm front associated
with the low will gradually work northward today. As the upper
level low moves north along the eastern seaboard, moisture and
lift will increase through the day.

Stronger isentropic lift and deeper moisture work up the east
coast ahead of the low late this morning and into the afternoon.
The areas of rain have increased in coverage with some embedded
heavier rain moving across late this morning. The rain will still
be periodic in nature through today with some occasional lulls in
activity.

Fairly strong pressure gradient between the approaching low and high
to the north brings breezy easterly flow through the day with gusts
20-25 mph. Temperatures will be in the 50s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
Low level jet and a stacked coastal low will provide good lift
tonight for widespread moderate to locally heavy rainfall.
Precipitable waters increase to near 200% of normal with values 1.50
inches. Models have come into a little better agreement with
placement of heaviest QPF, but it is well known that QPF in models
can be erratic. A very moist airmass, slow moving stacked low, and
low level jet support around 0.50-0.75 inches of rain on average
across the area for the first half of the night. The low level jet
shifts to the east after 06z, which will focus the heaviest rain
across eastern Long Island and southern Connecticut.

Some hints at weak elevated instability on BUFKIT soundings, but
have left thunder out of the forecast for now. Better instability
still looks to remain to the south and east.

On Wednesday, the stacked low will be slowly moving south and east
of Long Island. Rain will continue across eastern Long Island and
southeastern Connecticut, tapering off into the afternoon. Due to
moisture wrapping around the low, cannot rule out light rain further
west as well.

The close proximity of the stacked low should keep low clouds
through the day and possibly some patchy fog, so have gone with
the cooler high temperatures in the lower 60s.

It still 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.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
A dissipating upper low lifts NE along the New England coast at
the onset of the period, otherwise a high amplitude upper ridge
will prevail along the east coast through early next week.

A series of weak frontal systems will converge upon the area,
the first on Friday, which likely dissipates across the area. A
backdoor cold front then may briefly drop south across the area
Saturday night with a confluent flow aloft and shortwave trough
moving over top the ridge across eastern Canada. 00Z ECMWF
support GFS with the backdoor cold front making it through, even
faster than the GFS on Saturday afternoon. Rain chances in both
cases are low with ridging aloft and a capping inversion in
place. Expect mainly showers, but an isolated thunderstorm is
not out of the question. Strong and/or severe convection is not
forecast at this time.

Front returns north as a warm front Sunday night into Monday
morning with a cold frontal passage Monday evening. There is the
potential for stronger convection along and ahead of the cold
front Monday.

Anomalous upper ridge off the east coast over the the weekend
into early next week will result in above normal temperatures
and muggy conditions, with readings generally in the 70s and
possibly the lower 80s, warmest across the interior. Conditions
will be cooler along the immediate coast. Sunday and Monday may
cool down a bit behind the backdoor cold front.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Low pressure slowly moves up along the Mid-Atlantic coastline today
and tonight.

Conditions gradually deteriorate through the TAF period.
Generally expect IFR cigs and visibilities, with LIFR possible
at times through tonight. Intermittent rain, locally moderate to
heavy at times today should lighten late tonight.

East/northeast winds prevail, with speeds in the 15 to 20 kt range.
Gusts will range 20 to 30 kt today and into tonight. Gusts
should become less frequent overnight tonight.

LLWS is possible this evening with SE winds 45-50 kt at 2kft, mainly
east of NYC 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: Rain will be more intermittent before 1630Z.
Visibilities at times will be a few miles higher than forecast.

KLGA TAF Comments: Rain will be more intermittent before 1630Z.
Visibilities at times will be a few miles higher than forecast.

KEWR TAF Comments: Rain will be more intermittent before 1630Z.
Visibilities at times will be a few miles higher than forecast.

The afternoon KEWR haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KTEB TAF Comments: Rain will be more intermittent before 1630Z.
Visibilities at times will be a few miles higher than forecast.
Fluctuation of MVFR/IFR ceilings before 1630Z.

KHPN TAF Comments: IFR visibilities possible before 1730Z.

KISP TAF Comments: IFR visibilities possible between 15 and 17Z.

.OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY...
.Wednesday-Wednesday Night...IFR in possible rain and fog. Potential
for IFR/LIFR in fog Wednesday night.
.Thursday...MVFR/IFR to start...with gradual improvement to VFR.
.Friday...Chance of MVFR in showers/thunderstorms.
.Saturday...VFR.

&&

.MARINE...
SCA conditions are expected today on all waters with a strong
pressure gradient. Gusts up to 25 kt remain possible on LI Sound, LI
Bays, and NY Harbor through the first part of tonight. Have
therefore extended the SCA on these near shore waters until 06z.
Winds diminish quickly on the ocean late tonight into Wednesday as
the low pressure moves of the waters. However, ocean seas will
remain elevated through Wednesday due to lingering swells so have
extended the SCA until 22z Wednesday.

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 around 3/4 to 2 inches is expected through
Wednesday. The highest amounts are most likely to occur across
Long Island and southern Connecticut where the best chances of
minor flooding of poor drainage and low lying areas will be. The
heaviest rainfall occurs late this afternoon and tonight.

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

&&

.TIDES/COASTAL FLOODING...
In response to a low pressure system moving northward along the
eastern seaboard, minor coastal flooding is expected across the
lower NY/NJ Harbor, the South Shore Bays of western Long Island
including Queens and Brooklyn, and locations along the western Long
Island Sound for the high tide this evening.

Localized moderate coastal flooding is possible along the south
shore bays of Nassau County. Only 1/2 to 1 foot of surge is needed
to reach minor flood thresholds this evening, and strong easterly
winds should pile water across these areas. A Coastal Flood Advisory
is now in effect.

Thereafter, minor coastal flooding thresholds will be approached in
the same areas once again with the lower Wed Am high tide, and
possibly briefly exceeded along the southern bays of Western Long
Island.

More widespread minor coastal flooding is possible with the higher
Wednesday night high tide cycle, with minor inundation likely along
the southern bays of LI. Only 1/3 to 3/4 of a foot of surge is
needed to reach minor flood thresholds Wed night.

In addition, the elevated water levels combined with a prolonged
period of 5 to 9 ft breaking surf Today into Thu will result in
beach erosion issues and may cause some localized dune toe erosion
during the high tides tonight into Wed night.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT
     Wednesday for CTZ009-010.
NY...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for
     NYZ074-075-178.
     Coastal Flood Advisory from 10 PM this evening to 1 AM EDT
     Wednesday for NYZ071-073-078-177.
     Coastal Flood Advisory from 6 PM to 11 PM EDT this evening for
     NYZ080-179.
NJ...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for
     NJZ006-106-108.
MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ330-335-
     338-340-345.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ350-353-
     355.

&&

$$
SYNOPSIS...DS/DW
NEAR TERM...DS/DW
SHORT TERM...DS
LONG TERM...DW
AVIATION...JM/PW
MARINE...DS/DW
HYDROLOGY...DS/DW
TIDES/COASTAL FLOODING...



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