Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 082107
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
507 PM EDT Sat Aug 8 2020

.SYNOPSIS...
High pressure will settle over the area through Sunday, then
merge with high pressure over the western Atlantic, which will
then dominate through mid week. A slow moving cold front will
begin to approach on Wednesday, move into the area Wednesday
night into Thursday, then stall to the south on Friday. The
front may sink farther south on Saturday as stronger high
pressure starts to build out of eastern Canada.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Sea breeze convergence across the interior may still develop a
shower or isolated thunderstorms early this evening. Otherwise, dry
conditions are forecast tonight as a weak shortwave ridge progresses
across the region. Surface high pressure will also build over the
area.

The only concern for the overnight is with potential of fog
development, especially for outlying areas across eastern Long
Island and southeast Connecticut. There is a chance that low clouds
will redevelop overnight as well, preventing any widespread fog
development. Due to the uncertainty, have mentioned patchy fog
across the entire region late tonight into early Sunday. Have also
indicated increasing clouds overnight as well to account for the
stratus development.

Lows will be in the 60s for most locations with lower 70s in the NYC
metro.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
The region will lie on the outer periphery of an upper ridge
across the central and southern states. Models are indicating
a shortwave traversing across New England during the afternoon.
This shortwave along with sea breeze convergence supports a 20
percent PoP across southern Connecticut. Have also extended this
PoP eastern Westchester and eastern Putnam as well as northern
Long Island. While there is a cap around 700 mb, convergence
along the sea breeze may be enough to develop some showers,
possibly a thunderstorm. This is something we have seen in
recent weeks where initially the flow is weak in the morning,
before onshore flow develops, converging with the weak flow to
the boundaries north.

Otherwise, a warming trend commences on Sunday as the air mass
moderates and warm air advects into the region from the west.
Highs will be in the middle and upper 80s for most, with lower
80s closer to the coast where the sea breeze holds temperatures
down a bit.

Upper ridging builds further behind the shortwave passage
Sunday night into Monday. The surface high will become a apart
of the larger Western Atlantic high pressure, with heat and
humidity expected to grow early this week. High temperatures
will reach the upper 80s to low 90s across the NYC metro and
interior, with middle and upper 80s elsewhere. Confidence in
heat indices reaching 95 degrees is not high at the moment due
to decent potential for dew points to mix out into the middle
60s during peak heating. The current forecast calls for heat
index values to come close to 95 across NE NJ, staying just
below in the NYC metro, with heat indices near 90 elsewhere.

There is some guidance hinting at convection Monday afternoon
and evening NW of NYC. With the ridge aloft and the possibility
of a stronger cap in the middle levels, elected to keep the
forecast dry for now.

Warm and humid conditions continue Monday night with the ridge over
the region.

There is moderate risk of rip current at the ocean beaches both
Sunday and Monday, via long period 2-ft swells Sunday and up to
3 ft at the eastern Suffolk beaches, plus afternoon sea breeze
development and late day low tides.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Weather features across the Northeast will be slow moving during
much of this time frame, with the area sandwiched between a slow
moving closed low moving from Ontario into Quebec, and an upper
ridge over the western Atlantic. A developing omega block over
Canada will further slow progression going into late this week.

Before a slow moving cold front begins to approach on Wed, we will
have to contend with heat relates issues Tue into Wed, with
widespread lower/mid 90s for highs on Tue, which along with
dewpoints in the upper 60s/lower 70s should yield heat index values
95-100 away from south facing shores. High temps and fcst heat index
values are more marginal on Wed despite higher dewpoints with the
approach of the front, but could be underdone if there is more
sunshine and/or positive low level theta-e advection ahead of the
front. Shower/tstm chances will be confined mostly to the
interior well NW of NYC.

The front will be slow to move through Thu into Fri, with less in
the way of heat issues (mid 90s heat index values only in urban NE
NJ) and more in the way of convection, with some potential for
flooding, See Hydrology section for details.

The front will take some time to clear the area. Because of
this it remain uncertain whether Sat will be dry despite high
pressure starting to build out of eastern Canada, so maintained
chance PoP for most of the area.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
A broad area of high pressure will remain over the area thru
Sun.

Mainly VFR today. Patches of stratus along the LI coast will bring
pockets of MVFR. Coverage of shwrs into the eve only expected to be
isold to widely sct, so they have not been included in the TAFs.
MVFR or lower cigs expected tngt, especially late. Potential for fog
as well. Improvement to VFR again on Sun.

Winds mainly lgt and vrb thru the TAF period. There is a sea breeze
component along the immediate s coastal arpts, resulting in speeds
up to 10 kt at times til about 00Z.

.OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY...
.Rest of Sun...VFR. MVFR or lower possible at ngt.
.Mon...VFR.
.Tue-Thu...VFR with periods of MVFR possible, primarily at ngt.
Chance for shwrs and tstms each day.

&&

.MARINE...
A weak pressure gradient in place through early next week will
lead to winds and seas below SCA criteria.

&&

.HYDROLOGY...
There appears to be some potential for flooding Thu into Fri,
with a slow moving cold front Thu into Fri. PW increasing to
over 2 inches and flow aloft aligning more with the approaching
front could lead to tstms capable of producing heavy rain, as
well as training cells especially Thu afternoon/evening. Still
lots of uncertainty here as frontal timing would have have to
coincide with peak daytime heating/instability to realize this
potential.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$
SYNOPSIS...Goodman/DS
NEAR TERM...DS
SHORT TERM...DS
LONG TERM...Goodman
AVIATION...
MARINE...Goodman/DS
HYDROLOGY...Goodman/DS



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