000
FXUS61 KOKX 211357
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
957 AM EDT Fri Jul 21 2023
.SYNOPSIS...
Low pressure tracks through the Northeast today, with an attendant
cold front moving through the region tonight. Weak high pressure
gradually pushes into the region for the weekend and settles
nearby through mid week.
&&
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
A line of showers and thunderstorms continues to advance east
through the region and weaken, pushing through the NYC metro and
the lower Hudson Valley as of 10z. Fortunately, the line is running
into a less favorable environment as it does so, and should continue
to weaken, if not dissipate, as it tracks into southern CT and Long
Island. After this initial line, there may be a respite until later
in the morning or the afternoon ahead of the trailing cold front.
Forecast remains on track and previous discussion follows.
Broad upper troughing remains over the Northeast and Great Lakes
regions today while a shortwave swings through to our north. At the
surface, low pressure tracks along the Saint Lawrence River Valley,
with a weak secondary to our south along the Mid-Atlantic coast.
The first round of showers and thunderstorms should limit additional
convective development, at least initially, before daytime heating
and some clearing help to recharge surface instability ahead of the
cold front. Toward late morning or early afternoon, scattered
showers and thunderstorms are expected to re-fire over the same
areas impacted by the first line. The main concern with this
system will be the potential for flooding, especially with
antecedent moist soil conditions from the recent rounds of
rainfall. 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
divergence 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.
Overall QPF should average between 0.5 to 1.5 inches for most, with
lesser amounts across SE CT and eastern Long Island. Given the
convective nature, locally higher amounts are expected, with the 00z
HREF highlighting localized pockets of 2 to 3 inches possible in
areas of convective maxima. WPC has kept a slight risk for excessive
rainfall for all except far eastern areas, indicating the potential
for scattered areas of flash flooding. Given recent rains, it will
not take much to cause issues, particularly over the lower Hudson
Valley, as well as NE NJ and the urban centers.
In addition to the heavy rainfall threat, isolated strong to severe
thunderstorms will be possible, though this appears to be a
secondary threat to the hydro concerns. There will however be a
veering profile through the mid-levels with 0-6 km bulk shear of 25-
35 kt, supporting updraft maintenance and the threat of supercell
development. Areas of enhanced updraft helicity may also come into
play with the triple point and offshore low centers nearby. SPC has
maintained a marginal risk for the region, primarily for isolated
damaging winds, though a brief tornado or large hail cannot be
entirely ruled out either.
The cold front looks to moves through in the evening hours, around
00z for NYC and the metro, and through eastern areas by 6z, bringing
an end to the threat of showers and thunderstorms as it moves east.
Conditions dry out overnight as the flow turns WNW behind the fropa.
Temperatures bottom out in the 60s by daybreak Saturday. Largely
followed a consensus of short-term guidance for this update, with
subtle adjustments.-- End Changed Discussion --
&&
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Upper troughing lingers but drier conditions greet us to start the
weekend, as weak surface high pressure builds in from the west
behind the fropa.
Dew points should drop a tad from previous days with the light WNW
flow, though likely still in the low to mid 60s, with afternoon
highs close to seasonal normals, in the low to mid 80s. Sunshine
prevails with a bit of mid-level cu at times.
Mostly clear skies and light winds Saturday night may allow some of
the far interior and LI Pine Barrens to drop into the 50s overnight,
with the remainder of the region in the 60s.
&&
.LONG TERM /SUNDAY 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 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 1000 J/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 /14Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A warm front will move through this morning, followed by a cold
front this evening. Weak high pressure will follow thereafter
into Saturday morning.
Mainly VFR into early afternoon as a band of mostly light
showers moving across Long Island and SW CT attm. Tstm chances
this afternoon look less clear cut especially for the NYC metros
and may end up being more likely for the CT and Long Island
terminals, but still can`t rule out scattered afternoon
activity at the metros after about 18Z, and then with the
actual cold front this evening. So for now have backed off on
specific terminal impacts for the NYC metros but still mention
possible vicinity impact.
Winds should be mostly out of the S initially, then shift SW
this afternoon at the Hudson Valley and NJ terminals, possibly
also KLGA. Winds may then go light/variable this evening with
the cold front moving through, then pick up N-NW 5-10 kt after
06Z tonight.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Backed off on direct tstm impact for now. AMD possible this
afternoon should that situation change.
The afternoon KJFK/KLGA/KEWR haze potential forecast is YELLOW,
which implies slant range visibility 4-6SM outside of cloud.
OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
Saturday and Sunday: VFR.
Monday: Mainly VFR. Slight chance of an afternoon shower/tstm.
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 prevail through the weekend and into early next
week with a weak pressure gradient in place.
&&
.HYDROLOGY...
A frontal system is expected to produce between 0.5 to 1.5 inches of
rainfall across much of the area through this evening, with locally
higher amounts expected. Flash flood guidance thresholds are
lower than normal due to recent rains, with 1-hour thresholds
being most susceptible of being met. The main limiting factors
appear the forward motion of storms and low confidence in cell
training. WPC has maintained a slight risk of excessive rainfall
for all but SE CT and eastern LI, indicating isolated to
scattered areas of flash flooding possible.
No significant widespread rainfall is expected from Saturday through
mid next week.
&&
.TIDES/COASTAL FLOODING...
NYC and Nassau Co beaches have a low risk for rip current
development today, with Suffolk Co beaches in a moderate risk.
The moderate risk remains in effect for only eastern Suffolk on
Saturday, with a low rip risk elsewhere.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...DR
NEAR TERM...DR
SHORT TERM...DR
LONG TERM...DBR
AVIATION...JE/BG
MARINE...DBR/DR
HYDROLOGY...DBR/DR
TIDES/COASTAL FLOODING...