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442
FXUS61 KOKX 201709
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
Issued by National Weather Service Boston/Norton MA
109 PM EDT Tue Apr 20 2021

.SYNOPSIS...
High pressure settles to the south today as a cold front
approaches from the west. Low pressure develops along this
front 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. Another frontal system potentially impacts the
area on Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
950AM Update:
No major changes to the near term forecast. The latest visible
shows any minor fog has burned off and wispy high cirrus clouds
have moved in from the west. Temperatures are also warming up
nicely into the the mid and upper 50s. We remain on track to
reach the low and middle 70s away from the coast. Forecast
remains on track. See previous discussion below.

-------------------------------------------------------------

Patchy fog across eastern Long Island and interior southwest CT
and interior Lower Hudson Valley should quickly diminish shortly
after sunrise.

An upper ridge axis moves offshore today as high pressure builds
to the south and west. A cold front will also approach from the
north and west. It is possible that this boundary reaches the
interior Lower Hudson Valley this afternoon as a strong northern
stream shortwave traverses across southeast Canada. The frontal
boundary should have no impact to sensible weather as any lift
resides well north of the area. There will be a gusty southwest
flow ahead of this front, with gusts 20-25 mph. Otherwise, it
will be warm, dry and mostly sunny today. High temperatures are
above most guidance and closer to the 50th percentile of the
NBM. Have also made adjustments upward a few degrees in the
typical warmer urban NE NJ and NYC metro away from the influence
of the sea breeze. Highs away from the coast should be in the
lower 70s with middle 70s possible in the warmer spots. Across
Long Island and coastal Connecticut, highs will be a bit cooler
in the middle and upper 60s.

A much stronger shortwave digs across the Great Lakes and midwest
tonight, amplifying the flow over the eastern states. The
amplifying flow and frontal boundary may be enough to develop an
isolated shower across the interior this evening or tonight.
The frontal boundary should begin to lift to the north
overnight. This is due to the flow amplifying aloft as the
shortwave trough approaches. Low pressure will also develop
along the front across the Middle Atlantic. Otherwise, it should
remain dry with increasing clouds towards morning.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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. The 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 early to mid afternoon along and west of
the Hudson River, and mid to late afternoon east of the Hudson
River. 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 J/kg of SBCAPE from around the NYC
metro on north and west coinciding with about 35-50 kt of low
level flow. SPC continues to highlight a marginal risk of
severe thunderstorms with the main threat from isolated damaging
wind gusts. 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. 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 temperatures may hit the freezing mark early
Thursday. The strong winds will prevent any frost development.

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.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
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 /18Z TUESDAY THROUGH SUNDAY/...
Mainly VFR conditions are expected through the TAF period.
Gusty winds diminish around 22z-23z this evening, then become
light for the overnight period. Ceilings should remain VFR.

VFR conditions continue for the first half of Wednesday. A cold
front will move across the region providing showers and isolated
thunder showers as well between 19z and 21z Wednesday, ceilings
may briefly drop to MVFR/IFR. Ahead of the front S winds will
be breezy, sustained 10 to 15 knots and gusts to 25 knots.
Shortly after the frontal passage wind will become WNW with
gusts to 35 knots. Ceilings rebound to VFR conditions overnight
into Thursday morning.


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

Chance of low clouds and patchy fog tonight.

.OUTLOOK FOR 0Z THURSDAY THROUGH SUNDAY....
.Thursday...VFR. WNW gusts 25-30kt.
.Friday...VFR. WNW gusts 20-25kt.
.Saturday...Mainly VFR, chance of MVFR in rain at night.
.Sunday... MVFR/IFR possible with rain likely.

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

&&

.MARINE...
High pressure settles south of the waters today. S-SW flow
increases into the afternoon and gusts could reach around 20
kt. Otherwise, sub-SCA conditions continue through tonight. S
flow increases ahead of a strong cold front on Wednesday, with
SCA conditions likely on all waters in the afternoon. The cold
front moves across the waters by evening. Gales are possible on
the ocean behind the front and may continue into Thursday. Have
issued an SCA on all waters Wednesday afternoon and have issued
a gale watch Wednesday night into Thursday on the ocean. The SCA
on the non ocean waters continues Wednesday night and will
likely need to be extended 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.

&&

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

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from noon Wednesday to 6 AM EDT Thursday
     for ANZ331-332-335-338-340-345.
     Gale Watch from Wednesday evening through Thursday afternoon
     for ANZ350-353-355.
     Small Craft Advisory from noon to 6 PM EDT Wednesday for
     ANZ350-353-355.

&&

$$
Gaucher