discussion on 2023-08-12

000
FXUS61 KOKX 121517
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1117 AM EDT Sat Aug 12 2023

.SYNOPSIS...
Low pressure north of the Great Lakes tracks across eastern Canada
through Sunday, pushing a warm front through during today, then
slowly dragging a cold front across the region Sunday into Sunday
night. High pressure then settles in before another frontal
system impacts the area Monday night and Tuesday. High pressure
returns for Wednesday and Thursday. A cold front approaches the
region Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --Forecast mainly on track. Made some adjustments with respect to
POPs for showers, thunderstorm chances, cloud coverage and
temperatures. Showers are moving across parts of the region
within Lower Hudson Valley, Northeast NJ, and NYC late this
morning. Thunderstorms just slight chance late this morning into
the first hour of this afternoon with higher chances thereafter
for the rest of this afternoon. Temperatures a few degrees
cooler than forecast with shower activity for western parts of
the region but still think once these showers exit going into
early this afternoon, more breaks of sun will compensate the
daytime warming with resulting highs the same as previously
forecast. Forecast highs still mainly in the low to mid 80s with
some upper 80s for parts of Northeast NJ and NYC.

The main focus will be on the potential for strong and/or severe
convection, mainly during this afternoon into tonight. Before this,
a warm front currently in the vicinity of the forecast area will be
lifting north as the morning progresses. Isentropic lift along with
a weak shortwave may create just enough upward forcing to squeeze
out a few showers this morning.

We will then be in the warm sector this afternoon and tonight with a
pre-frontal trough and PVA aloft approaching from the west. 0-6km
bulk shear during the afternoon is forecast to be 25-35kt, with
MLCAPES mostly 1000-1500 J/kg mostly over the NW half of the
forecast area. This is where CAMs show the best chances of showers
and thunderstorms this afternoon. Then late in the day into the
evening, the shear increases to 35-50kt with shortwave energy
shifting through and a pre-frontal trough in the vicinity. This
along with low level backing of winds ahead of the trough will serve
to enhance low-level helicity. This will pose a low threat of a
tornado NW of the city where the elements will best overlap. Biggest
threat however will be potentially damaging winds with even a chance
of large hail. The wind and hail threat is then expected shift east
as the night progresses as shear, MUCAPEs and CAPEs in the -10 to
-30C region will still be sufficient. Best overall chance of
thunderstorms and impacts will be over the Lower Hudson Valley and
Southern CT, however chances will exist everywhere at some point by
the end of the night. SPC continues to have most of the area under a
slight risk for severe weather.

As for flooding, WPC has the northern half of the area under a
slight risk for excessive rainfall and a marginal risk elsewhere.
The main limiting factor for widespread flash flooding will be the
forward speed of storm cells due to increasing wind speed aloft.
Nevertheless, PWATs increase to 1.75 to 2.00 inches so cannot
 rule out that 1-hr or 3-hr flash flood guidance thresholds
are met anywhere in the forecast area. Thinking is that the
probability of a widespread enough flash flooding event is too
unlikely to warrant a Flood Watch at this time.-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
A cold front will be trailing the trough, but will slowly progress
east and weaken Sunday into Sunday evening as the flow aloft
flattens. After a lingering threat of morning showers and
thunderstorms over CT and LI, likely dry for the rest of the day
with highs in the 80s for most spots, but around 90 in NE NJ and
parts of NYC.

Weak surface ridging holds on long enough during the daytime on
Monday to keep any showers from moving in from the west as the next
storm system approaches from the Ohio Valley and Great Lakes. Highs
near normal at 80-85.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Another shortwave will be approaching from the Great Lakes region
Monday night, and moves through Tuesday into Tuesday night. A wave
of low pressure will track along a nearly stationary cold front
south of the region Monday. This will bring a warm front near or
into the region late Monday night into Tuesday. Precipitable water
values will be increasing to 2 to nearly 2 1/3 inches Monday night,
and with forcing, instability, and surface CAPE increasing with the
front,  convection is expected to develop with periods of moderate to
heavy rainfall possible. The 90% percentile from SPC`s sounding
climatology page is 1.75 inches. The WPC currently has the region
under a marginal risk for excessive rainfall. There is uncertainty
as to where the warm front will be, and a track farther to the north
could bring the heavier rainfall into the region.

The frontal system will be progressive as the upper trough weakens
and passes to the east Tuesday night. A mid-level ridge continues to
build into the area Wednesday into Thursday.
Then another shortwave digs into the Great Lakes and upper midwest
Thursday night into Friday before becoming negative during Friday.
At this time there are minimal chance for precipitation Friday.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --A warm front is lifting through this morning, followed by a pre
frontal trough this afternoon and into tonight. A cold front will
track into the region toward Sunday morning, moving through early in
the day. Mainly VFR, except MVFR or lower possible in thunderstorms.

Light E/SE winds this morning increases to around 10 to 15 kt from
the S late morning into the afternoon.

A few widely scattered showers around late morning into early
afternoon as the warm front is nearby, mainly in the NYC vicinity.
Coverage and chances increase later this afternoon with additional
showers and thunderstorms. A few thunderstorms may produce heavy
rainfall and gusty winds, however, coverage and timing are low
confidence. Another round of showers and thunderstorms will be
possible late this evening into the overnight, and these storms will
have a better chance of producing locally higher winds and heavy
rain.

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

Potential for a few showers late this morning with a warm frontal
passage. There is a higher probability of shra/tsra activity in the
late afternoon/early eve. Uncertainty on coverage of and timing of
activity in aft/eve. There is the chance of another round of
convection late evening into the overnight with the potentially for
strong gusty winds.

The afternoon KJFK, KLGA, and KEWR haze potential forecast is
YELLOW, which implies slant range visibility 4-6SM outside of cloud.

OUTLOOK FOR 12Z SUNDAY THROUGH WEDNESDAY...

Sunday: VFR.

Monday through Tuesday: VFR Monday, then a chance of showers and
thunderstorms Monday night and Tuesday with MVFR.

Wednesday: VFR.

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

&&

.MARINE...
Winds increase from the south on today ahead of a cold front which
will pass through during Sunday into Sunday night. Sub-advisory
conditions will prevail, and are expected to persist through
at least the daytime on Monday. With a persistent southerly
flow Monday night into Tuesday, ahead of a cold, ocean seas
likely build to around 5 feet Tuesday. Then with a southwest to
west flow behind the front late Tuesday into Tuesday night ocean
seas will gradually subside below SCA levels Tuesday night from
west to east, with marginal seas possible into Wednesday east
of Moriches Inlet.

&&

.HYDROLOGY...
Most of the area is expected to receive less than an inch of
rainfall today into tonight, however 0.75 to 1.50 inches of rain is
forecast for the Lower Hudson Valley into parts of southern CT. Due
to the anticipated quick forward motion of the rain with limited
chances of training storm cells and only isolated higher rain
amounts possible, only a low chance of flash flooding is
anticipated. Minor urban/poor drainage flooding and perhaps small
stream flooding would be more likely to occur.

Monday night into Tuesday, brief periods of moderate to heavy
rainfall may produce isolated nuisance flooding. From Tuesday night
through the end of the week no hydrologic impacts are expected.

&&

.TIDES/COASTAL FLOODING...
There is a moderate risk for rip currents on ocean beaches through
Monday.

&&

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

&&

$$
SYNOPSIS...JC/MET
NEAR TERM...JC/JM
SHORT TERM...JC
LONG TERM...MET
AVIATION...DR/MET
MARINE...JC/MET
HYDROLOGY...JC/MET
TIDES/COASTAL FLOODING...