000
FXUS61 KOKX 121010
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
610 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 --
The forecast is mainly on track so far. Main adjustments for
the next few hours were done to the cloud cover forecast.
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 /10Z SATURDAY THROUGH WEDNESDAY/...
Weak high pressure slides offshore overnight with a warm front
lifting through in the morning. A pre-frontal trough moves into the
region this afternoon and into Saturday night.
Light and variable winds overnight at all the terminals, becoming
light E/SE in the morning, and then S late morning into the
afternoon.
There is a low probability of a few showers early this morning
mainly in the NYC vicinity. A higher chance will be this afternoon
with showers and thunderstorms, especially by later in the
afternoon. A few thunderstorms may produce heavy rainfall and gusty
wind, however, coverage and timing are uncertain. Another round of
showers and thunderstorms will be possible later Saturday evening
into the overnight.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Potential for a few showers in the morning with a warm frontal
passage, 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 Saturday night.
The afternoon KJFK, KLGA, and KEWR haze potential forecast is
YELLOW, which implies slant range visibility 4-6SM outside of cloud.
OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY...
Late Saturday night: VFR with MVFR in showers and thunderstorms.
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
&&
.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
SHORT TERM...JC
LONG TERM...MET
AVIATION...MET
MARINE...JC/MET
HYDROLOGY...JC/MET
TIDES/COASTAL FLOODING...JC