316
FXUS61 KOKX 281948
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
348 PM EDT Fri Jun 28 2024

.SYNOPSIS...
High pressure pushes of the Northeast Coast this evening. A warm
front approaches Saturday and moves through late in the day. A cold
front approaches late Saturday night. A cold front passes late
on Sunday. High pressure follows it on Monday and lasts into
mid-week. Another frontal system may impact us Thursday into
Friday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Zonal flow aloft during this time frame, while at the surface, high
pressure pushes off the Northeast Coast this evening, or may already
be offshore to start off. This will mean a return southerly flow
develops across the forecast area, meaning an increase in humidity
levels through the night. Dew points are expected to rise from the
40s to lower 50s into the upper 50s to lower 60s by daybreak.
Additionally, low temperature will likely occur well before daybreak
as well as warm air advection and increasing clouds from the west
will mean temperatures rise overnight. Early lows should be in the
50s for many places, especially eastern outlying areas as this area
will see any increase in any clouds late in the this period, so they
will have time to radiate somewhat.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
The actual warm front is not expected to move through the area until
late in the day Saturday, so much of the morning will be dry, except
perhaps a passing shower or thunderstorm for Orange County. Better
chances for showers and thunderstorms occur in the afternoon and
overnight Saturday with the passage of the warm front and chances
for precipitation continue with the approach of the prefrontal
trough to the west.

Warm air advection continues through the period into Saturday night.
Low level jet increases during the day and into the first half of
the night, with 925 hPa wind speeds at around 2 am of 30 to 40 kt
and is then more limited to eastern areas of the forecast area
through 8 am Sunday. This will continue to bring in a moist air
mass, both at the surface and aloft. Dew points rise into the 70s
Saturday and Saturday night, leading to PWAT values in the 2.00" to
2.75" range. This does point to the possibility of flash flooding
with any thunderstorms that may move through. SPC HREF is showing a
10-20% chance for 1"+/hr rate from 2 am to 8 am Saturday night into
Sunday morning.

The potential for strong to severe is there as well, mainly N and W
of NYC. SPC has placed portions of NE NJ and the Lower Hudson Valley
in a marginal risk for severe storms for Saturday into Saturday
night. Surface based instability will be on the rise Saturday night,
mainly for western areas, where models show SBCAPE values of 500-
1500 J/kg north and west of NYC, while 0-6 km shear values rise to
35 to 40 kt. Models are also showing a lot of vertical lift during
this time frame. The main threat if severe storms develop would be
damaging winds.

Temperatures on Saturday will run at or slightly below normal, with
highs in the upper 70s to lower 80s, but transitions to warm
overnight with lows in the upper 60s to lower 70s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Sunday will see 2 rounds of showers and thunderstorms. One will
occur in the morning with a prefrontal trough. The other, will occur
with a late in the day cold front. All being driven in the upper-
levels by an amplifying trough over the Great Lakes.

Let`s discuss the showers and thunderstorms associated with the
prefrontal trough, first. A strong belt of moisture will set up
along the coast, helped being driven into the area by a 30-40 kt LLJ
(which quickly exits east Sunday morning). The latest model guidance
has PWATs peaking Sunday morning anywhere from 2.2 to 2.6 inches.
This is far above the max moving average of 2.03 inches per SPC`s
Sounding Climatology Page. Rainfall will occur aided by our location
in the right entrance region of a jet to our north, areas of mid-
level energy passing over, and a prefrontal trough at the surface.
Instability and SHear do not look very impressive, Sunday morning,
so any severe weather that occurs on Saturday may not transfer into
Sunday morning, but some heavy downpours could still occur, leading
to minor urban flooding or and isolated instance of localized
flashing flooding. The best timing of the showers and thunderstorms
with the prefrontal trough should have it cleared out and exiting
our area to the east by noon, if not an hour or two before this.

The bigger concern for severe weather will be Sunday afternoon or
evening with the passage of a cold front. 12Z CAMs (NAM, FV3, RRFS)
have a line of showers and thunderstorms developing along a NE to SW
axis in the Lower Hudson Valley in the mid/late afternoon, then
moving southeast into the evening, sweeping much of the area. The
best chance for severe weather appears to be areas north and west of
NYC and around the NYC metro area. SPC currently places the entire
CWA in a Slight Risk area with CSU-MLP, concurring with this. The
main area of concern is showing strong signs of instability with
some models peaking SBCAPE`s at 4600 J/kg and Bulk Shear 45-50 kts.
Lapse rates do not appear very impressive, but after the morning
round of rain, more sunshine in the interior, could lead to better
surface heating compared the the coast and help aid in storm
intensity. The Energy Helicity Index (EHI) at both 0-3 km and 0-1 km
on some CAMs appears to signal a sufficient risk for rotating
updrafts both in the mid and low levels. The risk for tornadoes is
too hard to pinpoint, for now, but it is a risk that can not be
ruled out at this moment. The same goes for the risk for hail.
Strong to damaging winds associated with the thunderstorms will be
possible for areas both north and west of NYC and around the NYC
metro area. Whether this risk will translate further east and south
on Long Island and in eastern Connecticut, will really depend on how
the morning storms play out. If the morning storms don`t clear east
until after noon along with dewpoints getting into the mid-70s,
things could appear a little too "muddy" to hold the severe risk in
these areas. These risks will come into better view as more CAMs
bring the event into their sights over the next 24 hours.

Another brief note for Sunday: With high dewpoints expected to
coincide with warm temperatures (highs in the mid/upper-80s to
possibly low-90s) heat indices could peak around 95 to 100 in the
afternoon.

After the front exits, clearing is expected Sunday night into
Monday. The upper trough will swing through the region Monday and
will be followed by ridging into the middle of the week. Surface
high pressure starts to build in from the Great Lakes on Monday. The
high then settles overhead Tuesday before shifting south and east
into Wednesday. The latest modeling indicates a flatter shortwave
ridging around the periphery of the ridge, which may help lower
heights aloft. This may be able to bring a weaker frontal system
towards the area by next Thursday and/or Friday with most models now
depicting a return of rainfall.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
High pressure remains in control through tonight, before pushing
further offshore during Saturday.

Mainly VFR. MVFR ceilings become increasingly likely Saturday
morning.

The winds will be mostly S and SE with sea breezes pushing north
through the afternoon. SE winds lighten to 5 to 10 kt after 0z.
SE wind continues overnight into Saturday morning.

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

Amendments may be needed closer to 12z Saturday morning with
changing flight conditions. Arrival of MVFR ceilings may be off
up to 2 hours.

OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY...

Saturday afternoon: Mainly VFR with S gusts up to 20-25 kt for some
coastal terminals. Chance of showers later in the afternoon, mainly
west of NYC terminals. SE to S wind.

Saturday Night: MVFR or IFR possible in showers and thunderstorms.

Sunday: MVFR or lower possible with showers and thunderstorms.

Monday, Tuesday, Wednesday: VFR.

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

&&

.MARINE...
Conditions are expected to remain below SCA criteria through
Saturday as high pressure remains in control. With southerly flow
increasing over the waters, the ocean and south shore bays should
see winds gusts of 25 to 30 kt starting Saturday night. A SCA has
been issued for these waters. All other waters, confidence was not
high enough to issue SCA, but it is certainly possible. Waves will
increase over the ocean waters as well in response to the increased
southerly flow. 5 to 6 ft waves on the ocean is expected by daybreak
Sunday.

SCA gusts around 25 kt likely continue on Sunday on the ocean and
potentially the South Shore Bays. These winds will weaken below SCA
levels in the afternoon and evening as a cold front works across the
waters. Ocean seas should be around 5-6 ft on Sunday before
subsiding below 5 ft Sunday night. A relatively weak pressure
gradient early next week should then lead to conditions below SCA
levels.

&&

.HYDROLOGY...
With PWATS increasing to 2.00" to 2.75" and SPC HREF showing a 10-
20% chance for 1"+/hr rainfall rates within the forecast area late
Saturday night, there is the potential for flash flooding. The
only question is how fast the storm will be moving. Right now,
thinking is the most likely scenario is nuisance/minor urban and
poor drainage flooding. However, an isolated incident of flash
flooding cannot be ruled out.

&&

.TIDES/COASTAL FLOODING...
The rip current risk for today will range from low to moderate.
As for Saturday, the risk will be mostly moderate, but a high
risk is anticipated for the ocean beaches of Brooklyn and Queens
as well as eastern Suffolk County.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 6 PM Saturday to 6 AM EDT Sunday for
     ANZ345-350-353-355.

&&

$$

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