000
FXUS61 KOKX 202335
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
735 PM EDT Thu Jul 20 2023
.SYNOPSIS...
A broad area of low pressure approaches from the south and west
tonight, then shifts through on Friday. An associated cold front
passes through Friday night. High pressure builds into the region
from the northwest from Saturday through Monday. A weak frontal
system may then impact the area on Tuesday followed by high
pressure Wednesday and Thursday.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --
The forecast is on track this hour with only minor changes made
to the database based on current observations. Previous
discussion follows.
Partly cloudy this evening, then more in the way of
clouds later tonight. This will be associated with the approach
of a broad area of low pressure stretching from the Great Lakes
through Mid Atlantic Regions. Rain chances begin after midnight,
with rain becoming likely for some spots west of the Hudson
River towards daybreak.-- End Changed Discussion --
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Longwave trough axis at 500mb will be pivoting across the Northeast.
At the surface, two progged centers embedded within the broad area
of low pressure - one moving along the Saint Lawrence River Valley
to our north, and another passing not too far to our south as it
emerges off the Mid-Atlantic Coast. Additionally, a triple-point low
in between may pass just to our north.
Rain becomes likely for all but eastern LI and SE CT during the
daytime, where where at least moderate chances of rain will still
exist. The main concern with this storm system will be the potential
for flooding, especially with antecedent moist soil conditions from
the recent rounds of moderate to heavy rainfall we`ve had for the
past week or so. Moisture deepens with PWATs increasing on the order
of 1.75 to 2.00 inches. Upward forcing to help maximize the rainfall
amount potential will come in the form of upper level as a the left-
exit region of a jet streak moves in, shortwave lift in the mid-
levels, and low level forcing/moisture convergence along the nearby
frontal boundaries and low centers. Areas of enhanced updraft
helicity may also come into play with the triple point and offshore
low centers nearby. Less certain is the convective element as the
first round of rainfall in the morning may hinder CAPE potential in
the afternoon, robbing some energy and preventing more from building
with convective debris clouds. Additional limiting factors for
flooding, more so in the morning, will be the forward motion of
storms and lower potential for training cells. WPC keeps most of the
area under a slight risk for excessive rainfall for Friday into
Friday night. There is currently not enough confidence to place any
portion of the forecast area in a Flood Watch. See the hydrology
section below for more details.
A lesser concern is the threat of severe thunderstorms. As stated
earlier, CAPE will be somewhat uncertain. There will however be a
veering profile through the mid-levels with 0-6km bulk shear of 25-
35 kt, supporting updraft maintenance and the threat of marginal
supercell development. Main severe wx threats would be wind gusts
and hail, but a non-zero threat for tornadic development may exist
over southern zones and wherever the triple-point ends up as lower-
level storm relative helicity would be enhanced by the proximity of
the nearby low centers. SPC has expanded the area of marginal risk
of severe wx to include almost all of the forecast area.
A trailing cold front moving during the night will end the threat of
showers and thunderstorms west to east.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Ensemble means continue to depict an eventual breakdown of the
northeastern trough by the end of the period. A mean trough
associated with a closed low over eastern Canada slowly weakens from
the weekend through Tuesday. Heights begin to rise thereafter, with
mean ridging building in from the middle toward the end of next week.
In terms of sensible weather, a mainly dry extended looks to be in
store. Surface high pressure builds in from the northwest for
Saturday, Sunday and into early Monday. Dewpoints will drop a bit
over the weekend under the weak northwest flow, allowing apparent
temperatures to be close to the actual temperatures, with highs in
the mid and upper 80s, which is near normal. By Monday afternoon,
weak shortwave energy may trigger an afternoon shower or
thunderstorm, especially across interior areas. Model soundings are
showing very weak shear (>25 kts) and CAPE (~500J/kg) so not
expecting much in the way of organized convection. A mid level
shortwave trough then approaches by Tuesday along with a weak cold
front, providing another potential for afternoon showers and
thunderstorms. CAPE/shear profiles look a bit better for the
convective potential on Tuesday, with 30-35kts of bulk shear and
SBCAPE near 1000J/kg. PWATS also start to approach 1.75" by the
afternoon. So have maintained NBM chance PoPs and thunder for the
afternoon across much of the CWA.
Thereafter, the upper ridging begins to build in from the Central
Plains, with a gradual warm up and dry conditions Wednesday and
Thursday. NBM probabilities of >90F begin to increase into the 30-
50% range for Thursday for northeastern NJ and NYC. The trend in
probabilities of >90F have increased in magnitude, and coverage,
over the past few NBM cycles.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
Weak high pressure will be in control through most of tonight.
A slow moving warm front will approach late tonight into early
Friday morning, then a trailing cold front will approach Friday
afternoon.
VFR through most of tonight. Band of showers/tstms approaching
from the west early Friday should weaken as it approaches the
NYC metros and it is doubtful how far east they make it into the
area, for now kept TEMPO for thunder at KSWF/KHPN/KTEB/KEWR and
PROB30 farther east at KJFK/KLGA, at least to signify impacts
to western routes even if storms do not make it that far east.
MVFR cigs likely through the morning hours and early afternoon
for western terminals.
Scattered showers/thunderstorms then possible again in the
afternoon hours and have stuck with PROB30s for now with low
confidence in coverage.
KGON should see typical late summer fluctuating vsby late
tonight via onshore flow and increasing humidity.
Winds will become light tonight, and variable as the band of
showers arrives. SE flow 5-10 kt expected for the rest of the
24-hr TAF period.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Amendments possible as showers/thunderstorms approach from the
west early Friday morning.
OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY...
Saturday and Sunday: VFR.
Monday: Mainly VFR. Slight chance of showers/thunderstorms in
the afternoon.
Tuesday: Chance of afternoon showers/tstms with brief MVFR/IFR
vsby from the NYC metros north/west.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
A Marine Weather Statement is in effect for the Long Island
Sound. The National Weather Service in coordination with the
United States Coast Guard have received reports of a large
debris field across Long Island Sound, caused by recent flooding
across New England. This will create some hazards for boaters,
swimmers, and watercraft in the affected area. The debris vary
from trees, logs, coolers, and docks and may not be easily
visible.
Sub SCA conditions will prevail through the weekend into nearly next
week with a weak pressure gradient in place.
&&
.HYDROLOGY...
1 to 2 inches of rainfall is anticipated from Friday in to Friday
night with the potential of locally higher amounts. Flash flood
guidance thresholds are lower than normal due to recent rains, with
1-hour thresholds being most susceptible of being met. While the
threat of flash flooding will exist, there still isn`t enough
confidence that such flooding would be widespread enough to warrant
a Flood Watch at this time. The main limiting factors appear the
forward motion of storms and limited potential for cell training.
Additionally, there is still a good amount of uncertainty surrounding
the convective potential and location following the rainfall that
occurs Friday morning. The overall highest rainfall amounts are more
likely to occur from Nassau and Fairfield Counties to points west.
Should a Flood Watch eventually be needed, the most likely area that
would need one is northeast NJ where FFG values are the lowest.
No significant widespread rainfall is expected from Saturday through
mid next week.
&&
.TIDES/COASTAL FLOODING...
-- Changed Discussion --
For Friday, NYC and Nassau Co beaches have a low risk for rip
current with Suffolk Co beaches in a moderate risk given today`s
observations, the weak onshore flow and 6-7s wave period. The
moderate risk remains in effect for only eastern Suffolk on
Saturday, with a low rip risk elsewhere.-- End Changed Discussion --
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...JC/DBR
NEAR TERM...JC/DBR
SHORT TERM...JC
LONG TERM...DBR
AVIATION...JT
MARINE...JC
HYDROLOGY...JC/DBR
TIDES/COASTAL FLOODING...