-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KOKX 210552
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
152 AM EDT Wed Apr 21 2021

.SYNOPSIS...
High pressure moves farther offshore tonight as a cold front
approaches from the west. Low pressure develops along this
front late tonight, which then strengthens on Wednesday as the
system moves across the region. The low then moves over the
Canadian Maritimes Thursday as high pressure builds to the south
and west. The high will then be in control into the first part
of the weekend. A coastal low pressure system brings in the next
chance for rain Sunday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Minor adjustments made to reflect latest observations and
trends.

Offshore high pressure gradually shifts east overnight and a
mid-level trough digs deep into the Great Lakes Region. Overnight,
temperatures in and around metro NYC fall to the mid 50s and
the outlying suburbs fall to the upper 40s and low 50s. Low
chances for showers toward daybreak, mainly north and west of
the NYC metro. CAMs shows spotty shower development at this
time. Breezy along the coastal areas.
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&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
The low pressure wave will lift across Southern New England on
Wednesday, dragging the cold front across the region. Strong
dynamics with the middle and upper level shortwave, divergence
aloft, and convergence along the front will provide deep layered
lift. The most organized forcing looks to lie along and just
ahead of the frontal boundary. While a few showers cannot be
ruled out in the morning, the bulk of the convection will move
across the region in the afternoon and evening. SPC has western
areas of the CWA in a marginal risk for severe storms. Higher
resolution models continue to signal the development of a line
of showers and embedded thunderstorms quickly moving across the
area from west to east from midday to mid afternoon along and
west of the Hudson River, and mid to late afternoon east of the
Hudson River. For the areas in the marginal risk have included
enhanced wording of gusty winds, as this will be the primary
threat. The line should be moving offshore in the early
evening. Have followed closely to the simulated reflectivity
fields for general PoP timing as the guidance seems to have a
relatively good handle the line. The major differences lie in
the exact timing.

The amount of destabilization is also a bit uncertain, but model
soundings indicate about 500 to 750 J/kg of SBCAPE from around
the NYC metro on north and west coinciding with about 35-50 kt
of low level flow. Surface based instability drops off to near
zero across much of southern Connecticut and central and eastern
Long Island due to a stronger maritime low level inversion.
However, have mentioned chance of thunder here as well due to
the strong dynamics and elevated instability. This should
however prevent any severe storms further east as the line
encounters the more stable low level air, and thus no enhanced
wording across this region. There are no flooding concerns with
the line as it will be moving fairly quickly across a given
area.

Southerly winds may gusts 20 to 30 mph ahead of the front
outside of the line of showers and embedded thunderstorms.
Strong cold and dry advection takes places behind the cold front
Wednesday evening and Wednesday night. Winds will shift to the
W and NW and could gust 25 to 35 mph at night with the strong
cold advection. Highs during the day on Wednesday should be in
the 60s. If clouds are not as extensive early in the day, the
locations away from the coast could warm a few degrees higher
than currently forecast.

Temperatures crash behind the front and should drop into the
lower to middle 30s by early Thursday morning. The growing
season does begin across the interior zones on April 21, and
average temperatures across some of these zones are forecast be
at freezing or below during this period. After collaboration,
have issued a freeze watch for these areas. For those areas
dropping to slightly above freezing, strong winds should prevent
any frost development, so no frost advisories planned at this
time.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Gusty winds continue on Thursday as the low pressure
strengthens while moving over the Canadian Maritimes. High
pressure also builds to our south and west, creating a strong
pressure gradient over the region. W-NW wind gusts 25 to 35 mph
are likely, and could reach 40 mph near the coast. There is a
low chance for a few gusts up to 45 mph, especially given the
deep mixed layer indicated by forecast soundings. Highs on
Thursday will be well below normal in the upper 40s inland to
the lower 50s near the coast. Winds weaken some Thursday night,
but should still remain gusty enough to preclude frost again.
Lows will be in the middle to upper 30s for most locations.

High pressure will build to the south and west through Friday and
then off the Mid Atlantic coast Saturday.

A progressive, yet amplifying upper trough over the Mississippi
Valley on Saturday will move across the area on Sunday. Global
models are in good agreement with a strong frontal wave developing
over the Carolinas Saturday and passing near or just south of Long
Island on Sunday. This would bring rain to the region Saturday night
into Sunday. High pressure will then follow early next week.

Temperatures will rebound to normal or even slightly higher
through Saturday. Sunday could be cooler depending on how much
interaction there is with the northern branch. Generally, stayed
close to the NBM, but leaned bit lower for Sunday.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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High pressure shifts farther offshore tonight. A strong cold
front crosses the area this afternoon.

VFR conditions expected through this morning. A few showers
could develop as early as 12-14Z ahead of the cold front, but
not expecting any ceiling/visibility impact from these. A line
of showers and thunderstorms then crosses the area between
17-23Z, with MVFR ceilings and IFR visibilities possible in any
thunderstorms. The best chance of thunderstorms will be between
19-21Z for the city terminals.

Southerly winds around 10 kt will continue at the coastal
terminals overnight, with light southerly or variable winds
inland. Winds then increase through the day as the front
approaches, with gusts 20-25 kt by mid-morning. Gusts to over 40
kt are possible in any thunderstorms. Winds then shift quickly
to the NW late in the day with G30-35 kt.

In addition, LLWS is possible through 12Z with winds at 2000 ft
remaining around 45 kt.


  ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

No unscheduled amendments expected through the overnight.
Amendments possible this afternoon for timing of
showers/thunderstorms.

.OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY....
.Thursday...VFR. WNW gusts 25-30kt.
.Friday...VFR. WNW gusts 20-25kt.
.Saturday...Mainly VFR, chance of MVFR/IFR in rain at night.
.Sunday... MVFR/IFR in rain.

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

.MARINE...
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Ocean buoys 44025 and 44017 around 5 ft with S winds around 20
kt. Thus, have begun the SCA on the ocean waters.

S flow increases ahead of a strong cold front on Wednesday,
with SCA conditions on the ocean waters and on all waters by
the afternoon. The cold front moves across the waters by
evening. Gale Warning on the ocean for frequent gusts over 34
knots Wednesday night into Thursday. The SCA on the non ocean
waters continues Wednesday night and will continue into
Thursday.

Lingering SCA conditions likely on Friday in a gradually
diminishing west flow, especially on the ocean. All areas will
briefly fall below SCA criteria on Saturday before a coastal low
impacts the area late saturday night into Sunday.
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&&

.HYDROLOGY...
No hydrologic impacts are expected through the week.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Freeze Watch from late tonight through Thursday morning for
     CTZ005-006.
NY...Freeze Watch from late tonight through Thursday morning for
     NYZ067-068.
NJ...Freeze Watch from late tonight through Thursday morning for
     NJZ002.
MARINE...Small Craft Advisory from noon today to 6 AM EDT Thursday for
     ANZ331-332-335-338-340-345.
     Small Craft Advisory until 6 PM EDT this evening for ANZ350-
     353-355.
     Gale Warning from 6 PM this evening to 6 PM EDT Thursday for
     ANZ350-353-355.
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&&

$$

UPDATE...DW
AVIATION...FEB/JC