-- Discussion containing changed information from previous version are highlighted. --
791
FXUS61 KOKX 050213
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1013 PM EDT Thu Jul 4 2024

.SYNOPSIS...
A trough of low pressure stalls over the area tonight with a warm
front lifting through the region during Friday into Friday night. A
cold front then approaches on Saturday, slowly moving through the
area Saturday night. The front stalls just southeast of the area
Sunday into Monday as weak high pressure builds into the area. The
front may then lift back to the north Monday night into Tuesday
ahead of another frontal system working east across the Great Lakes
and Ohio Valley states.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Some further adjustments were made to the forecast in terms of
POPs for showers and thunderstorms as well as temperatures and
dewpoints to better match with observed trends. More stable
marine layer has resulted in showers weakening as they move east
across western parts of the region this evening. Increased POPs
for showers to likely for western areas but reduced the
probabilities of thunderstorms to slight chance for most
locations for much of the rest of the night. Still think there
will be a relatively higher chance of thunderstorms for south of
Long Island late this evening and overnight.

A trough of low pressure stalls over us tonight with shortwave
lift slowly shifting through. The showers will move across the
rest of the forecast region heading into overnight with
thunderstorms staying mainly isolated although more scattered
thunderstorms are possible south of Long Island overnight.

Minor/poor drainage flooding will be possible with thunderstorms as
they move fairly slowly with a weak flow aloft. Still can`t
completely rule out flash flooding due to the slow motion of storm
cells with plenty of moisture as PWATs average around 2 inches.

Warm and muggy conditions tonight otherwise, with potential for
overnight stratus/fog development in a moist and weak flow
environment.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Broad upper troughing across southeastern Canada retreats northward
Friday into Saturday, with a low over the Great Lakes Friday
shearing into Ontario/Quebec on Saturday. A weak shortwave moves
east of the region Friday morning, with another weak shortwave
approaching Friday afternoon.

It appears that the surface trough that will be across the forecast
area will lift as a warm front during the day, aided by afternoon
seabreeze development. Subsidence and mid-level drying in the wake
of the departing shortwave should allow for a window for good
heating after morning stratus/fog dissipates, leading to very warm
and humid conditions (lower to mid 80s coast, to upper 80s to around
90 for NE NJ and LoHud). There`s potential for isolated to scattered
afternoon/eve convection in a marginally unstable and modestly
sheared environment with the approach of the next shortwave, and in
the vicinity of the warm front/seabreeze. This will be mainly for
areas N&W of NYC. Lack of focus and a stabilizing marine layer to
the east across the coast should limit shra/tsra activity thru early
Friday evening. Strong storms possible with severe storm chances
still limited by relatively weak 0-6km bulk shear, but perhaps a
little stronger than today`s shear. CAPEs will also probably be
higher on Friday, so trends will need to be monitored for the severe
threat.

An increasing threat for heavy downpours sliding west to east across
the entire area for Friday night through Saturday morning. There
will be strengthening mid/upper support ahead of shearing low to the
west. There will also be a strengthening a low-level jet ahead of an
advancing cold front and pre-frontal trough, advecting in an
increasingly sub-tropical environment with weak instability, deep
moisture with 2"+ PWATS, and a warm cloud layer.

The pre-frontal trough appears to stall over the area Saturday, with
potential for scattered afternoon convection ahead/along it in the
afternoon and evening. This appears to be the best chance of a few
strong to severe thunderstorms, roughly over the NW half of the
forecast area, based on moderate deep layer shear and SBCAPEs
potentially around 2000 J/kg. The exact location of the trough will
determine possible focus for training convection and a localized
flash flood threat as the flow parallels the stalled boundary. More
clarity on this part of the forecast in the next 24 to 36 hrs.
Activity should weaken in intensity as it translates to the coast
with waning instability and a deepening coastal stable layer
Saturday evening. The cold front will slowly move through the area
during the night with the end of the shower/thunderstorm threat.

Finally, a hot and humid airmass brings the likelihood of heat
advisory criteria being met for most of NE NJ for the Friday-
Saturday period. A heat advisory has therefore been issued here for
this period. Not enough confidence to include portions of the Lower
Hudson Valley or Western Passaic County at this point, but it may be
a close call. Surface dewpoints will have a tough time mixing out
during peak heating with surface troughs in the vicinity both days a
relatively moist boundary layer, and southerly-component surface
winds. 850mb temps progged at 18-19C both days, perhaps slightly
cooler Saturday vs Friday, and Saturday has more cloud potential.
Heat indices of 95-100 expected both days.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
At the onset of the period, a weak cold front will pass just
southeast of the area early Sunday morning with high pressure
building in from the west into Monday. With the exception of some
lingering showers for the south fork of Long Island and extreme
southeast New London, Sunday should be dry, but will need to watch
how far offshore the boundary gets. Shortwave energy embedded within
the longwave trough to the west will then send a frontal system east
across the Great Lakes and Ohio Valley states Monday night into
Tuesday. his will bring increasing chance of convection Tuesday into
Thursday.

A deep-layered SW flow during this time will maintain seasonably
warm conditions across the area along with increasing humidity
through Thursday. Daytime highs during this time will generally be
in the mid and upper 80s away from the immediate coast, along with
some lower 90s across metro NJ. Lows will mainly be in the upper 60s
to lower 70s, warmest across the NYC metro. Max heat indices at this
time look to fall just short of 95. Largely stayed close to national
blended guidance for this update.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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A weak cold front stalls near the area tonight into Friday
morning.

A line of showers and thunderstorms are beginning to weaken as
they move eastward towards NYC terminals. Any existing
thunderstorms are expected to weaken as they approach NYC
terminals. TEMPO for showers is in TAFs for 2Z-4Z with maybe
just an hour or two later for terminals east with all showers
possibly ending before getting to KGON. Confidence in this
scenario is low.

After showers exit tonight, dry conditions are expected until
showers and thunderstorms re-enter the TAFs Friday late
afternoon/evening.

Currently VFR at all terminals except KISP where they are IFR
due to low cigs. This will expand across most terminals tonight
into Friday morning with MVFR to IFR cigs and vsbys expected.
Some improvement is possible Friday afternoon before the chance
of MVFR to IFR return Friday evening/night.

MVFR/IFR conditions develop after 05z, primarily impacting the
coastal terminals. The low cigs will continue into Friday
morning with visibilities dropping. Slow improvement is expected
during the late morning into the early afternoon for becoming
MVFR to IFR again in the late afternoon/evening Friday.

South winds weaken tonight, becoming light and variable
overnight. Tomorrow winds will generally be around or below 10
kt from the south.

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

Amendments will be possible for the timing of showers and
thunderstorms tonight.

Amendments may be possible for cigs and visibilities overnight
and early tomorrow.

OUTLOOK FOR 03Z SATURDAY THROUGH TUESDAY...

Saturday: MVFR or lower conditions possible at times with
continued chance of showers/tstms.

Sunday and Monday: VFR.

Tuesday: Chance of showers and thunderstorms in the afternoon,
mainly west of NYC.

Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90
-- End Changed Discussion --

&&

.MARINE...
Sub-advisory conditions expected through the first half of Friday
night. The exceptions are occasional gusts up to around 25kt late
day/early evening near the entrance to NY Harbor eastward to western
Great South Bay today and tomorrow. Winds and seas pick up on Friday
night with SCA conds on the ocean mainly late at night. Being a late
3rd period start, will hold off on issuing a SCA for the ocean
waters. SCA otherwise potentially needed on the ocean late Friday
night through Saturday night.

Sub-SCA conditions expected Sunday into Tuesday with high pressure
over the region.

&&

.HYDROLOGY...
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Scattered heavy showers and some embedded thunderstorms with
heavy downpours producing 1-2"/hr rainfall rates are possible
through overnight into Friday. The primary threat is for
minor/poor drainage flooding.

Overall chances/coverage of showers and potential thunderstorm will
be higher late day Friday through Saturday evening. Total rainfall
amounts will vary greatly due to the convective nature, but an
average of a half inch to inch of rainfall is anticipated during
this period along with locally higher amounts. Once again, localized
1-2"/hr rainfall potential rates with scattered heavy downpours, but
this time across the entire area. The primary threat will be minor
urban/poor drainage flooding, but a localized flash flood threat
will exist in path of any training convection.

At this time, no widespread hydrologic concerns expected for Sunday
through Thursday. However, there is the threat for localized heavy
rain with any thunderstorms that may develop Tuesday into Thursday.
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&&

.TIDES/COASTAL FLOODING...
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For Friday, there is a moderate risk of rip current
development. For Saturday, there is a high risk of rip current
development. There is forecast to be a gradually building
onshore swell with surf height growing from around 3 ft Friday
to around 4 ft Saturday. Onshore winds will be increasing as
well Saturday giving more rip current development potential.
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&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None.
NY...None.
NJ...Heat Advisory from noon Friday to 8 PM EDT Saturday for NJZ004-
     006-103>108.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...JC/JP
NEAR TERM...JC/JM
SHORT TERM...JC
LONG TERM...JP
AVIATION...BR
MARINE...JC/JP
HYDROLOGY...JC/JP
TIDES/COASTAL FLOODING...JM