discussion on 2023-07-14

000
FXUS61 KOKX 142031 CCA
AFDOKX

Area Forecast Discussion...CORRECTED
National Weather Service New York NY
431 PM EDT Fri Jul 14 2023

.SYNOPSIS...
A frontal boundary stalled to the south will remain in close
proximity to the forecast area through this evening before
lifting back to the north or washing out by Saturday morning.
Another frontal system approaches from the west Saturday and
impacts the area on Sunday, followed by weak high pressure on
Monday. Unsettled weather is likely to continue through the rest
of the week with potential for a series of frontal boundaries.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Potential does exist for another round of showers and thunderstorms
late this afternoon through the first half of tonight. The combination
of a stalled front in close proximity to the NYC metro and LI
combined with a highly unstable airmass just to the south will
serve as the focus. The big question mark is that the cells
developing are struggling to get going. This may be due in part
to stability below 800 mb and weak low-level lift, despite the
front. The impetus may be an upstream convective complex over
central PA that may provide the extra lift needed to maintain
sustained convection. At the same time, it will be arriving
after max daytime heating. So there is clearly uncertainty in
the forecast with respect to the timing and coverage this
evening. However, with a highly unstable, moisture-laden
airmass, and a boundary in place, there is likely to be a least
some scattered convection. Thus, it seemed prudent to maintain
the watch with portions of the watch area having been beleaguered
by heavy rainfall and flooding over the past week. Once we get
through the first half of tonight the watch will likely be
dropped. Additional rainfall amounts on average look be a
quarter to half inch with pockets of localized higher amounts
exceeding an inch. There are portions of the Lower Hudson Valley
that need no more than an inch over an hour or 1.5 to 2 inches
in 3 hours. Areas over CT do need somewhat higher amounts and
may be less suspect to flooding tonight.

As for temperatures, very warm humid conditions will continue
with lows in the upper 60s to lower 70s, about 3 to 5 degrees
above normal. This will be in conjunction with similar dew
points.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Shortwave ridding on Saturday should keep airmass capped with
mid level warming and drying. However, there could be some
seabreeze enhanced convergence triggering convection during the
late morning into the afternoon hours. Coverage is forecast to
be sparse. Once gain, any rainfall will be capable of some heavy
downpours, but convection will be short-lived.

A very warm, humid airmass will remain in place with highs in
the mid to upper 80s Saturday and with lows in the lower to mid
70s Saturday night.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Persistent upper troughing will continue over the northeastern
portion of the CONUS through the long term. The most significant
ridging and heat will likely remain well to the south and west of
the area based on overall good agreement among the latest ensemble
means.

The main concern this period is on Sunday with another potential
heavy rain event. Concerns are elevated across portions of Orange
County and the interior where several rounds of heavy rains occurred
both this past Sunday and early Friday. Closed upper low near the
border of the Northern Plains and southern Canada will slowly push
east on Sunday. A fairly well defined shortwave will round the base
of the trough and approach on Sunday. There are also hints that the
region will lie within the right entrance region of a upper jet to
our north. There are also some hints of a second jet streak rounding
the base of the trough. These features could combine to enhance the
lift over the region on Sunday within a moist airmass with PWATs
averaging around 2 inches. One of the bigger uncertainties is the
exact placement of some of the surface boundaries. There does appear
to be potential for a warm front to lie nearby as the main frontal
system approaches from the west. The warm front placement could also
enhance rainfall. Flooding continues to be the main concern on
Sunday. WPC has the area in a slight risk for excessive rainfall,
with a moderate over Orange County where flooding has been
significant over the last week. Placement of the heaviest rainfall
is always difficult in convective season, but on average around 1-2
inches of rain is currently forecast. Heavy rainfall is also
possible and amounts could be locally higher. A flood watch may be
needed for portions of the area for Sunday with subsequent forecast
packages.

SPC has also has the region in a marginal risk for severe
thunderstorms on Sunday. Severe weather concerns are likely
dependent on if there is more significant destabilization. Bulk
shear values may end up around 30 kt. If more instability is
realized, then the threat for severe thunderstorms could be
increased.

The main forcing and moisture axis is progged to start moving
offshore Sunday evening with decreasing chances for convection
through the night.

The model consensus is indicating the front from Sunday will be wash
out or weaken just offshore on Monday. Weak high pressure should
build into the region from the south and west with the region lying
between western Atlantic Ridging and the larger upper trough near
the Great Lakes. The upper trough then sharpens a bit into Tuesday
which will bring the next frontal system towards the area. The
shortwave may make its way across New England late Tuesday or
Tuesday night with another potential round of showers and
thunderstorms. Thereafter, it is a bit uncertain if the trough axis
will remain nearby or Wednesday or shift offshore. If the trough
axis remains closer to the area, then the front may slow down or
stall keeping the possibility of showers/storms at some point
Wednesday or Wednesday night. The guidance then hints at a continued
active pattern overall into the end of the week with weak impulses
moving around the continued upper troughing. Have followed the NBM
closely for the end of the week based on the uncertainty at this
time range. This yields potential of convection at some point
Thursday into Friday, but does not look to be a washout both days at
this point.

Temperatures in the long term overall look to be near seasonable
levels. However, there is chance for highs in the upper 80s to
around 90 degrees on both Monday and Tuesday. Heat indices look to
top out in the low 90s, but how much dew points mix out both days
will ultimately determine these values.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
A frontal boundary will remain in the vicinity of the terminals
this afternoon and tonight.

A chance of showers and thunderstorms for the rest of the
afternoon as breaks in the overcast allow for redevelopment
especially later in the afternoon and evening. Confidence of
timing and placement of any showers remains low. Will include a
TEMPO from about 21-01z for a TSRA, where highest confidence is
thunder development.

Categories of flight categories at any one terminal is low and
could vary VFR to MVFR depending on where the showers and
thunderstorms will occur. Some of the outlying terminals may
have MVFR or IFR fog/stratus develop late tonight.

Winds of variable direction this afternoon due to numerous
thunderstorm outflow boundaries however a return to S flow
around 10-15 kt expect into the evening. Winds become light and
variable once again late tonight into early Saturday morning.

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

Low confidence with the timing of showers and thunderstorms
into the evening hours. Low confidence in flight categories.

OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY...

Saturday: Becoming VFR with a chance of showers/thunderstorms
in the afternoon and evening.

Sunday: Showers and Thunderstorms with IFR or lower possible.

Monday: Morning MVFR possible in cigs/vsby becoming VFR.

Tuesday-Wednesday: Chance of showers/thunderstorms with MVFR or
lower especially inland.

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

&&

.MARINE...
Sub-SCA conditions are expected through early next week. However, an
increasing southerly swell Sunday into Monday may allow for ocean
seas to be near 5 feet at times Sunday night into Monday, especially
east of Moriches Inlet. Seas briefly subside Monday night before
potential of 5 ft seas returns on Tuesday.

&&

.HYDROLOGY...
-- Changed Discussion --A Flood Watch remains in effect for the Lower Hudson Valley and
Southern CT through this evening.

Locally heavy rain is possible from any shower or thunderstorm
through tonight. The main concern is from minor poor drainage
flooding and a low potential of small stream from reaching bankfull.
The Weather Prediction Center has kept the area in a slight
risk for flash flooding through tonight.

Flooding concerns continue on Sunday with potential for heavy
rainfall. Areas that have received heavy rainfall in the last week
are more prone to more impacts, but flash flooding is possible
anywhere across the region. Flashier small streams and rivers could
also reach bankfull. WPC currently has the region in a slight risk
for excessive rainfall with Orange County included in a moderate on
Sunday given recent significant flooding impacts.-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
There is a moderate risk of rip current development at all the ocean
beaches Saturday and Sunday. Increasing southerly swells on Sunday
could increase the risk to high.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch until midnight EDT tonight for CTZ005>012.
NY...Flood Watch until midnight EDT tonight for NYZ067>071.
NJ...None.
MARINE...None.

&&

$$

SYNOPSIS...DS/DW
NEAR TERM...DW
SHORT TERM...DW
LONG TERM...DS
AVIATION...IRD
MARINE...DS/DW
HYDROLOGY...DS/DW
TIDES/COASTAL FLOODING...//