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fxus61 kokx 201353 
afdokx

Area forecast discussion
National Weather Service New York New York
953 am EDT Thu Jul 20 2017

Synopsis...
hot and humid weather will continue across the tri-state area
today. A weak cold front will pass across the area tonight into
Friday. This cold front will stall south of the area late
Friday and remain around through the weekend before finally
moving south as a cold front early next week. High pressure
follows through mid week.

&&

Near term /until 6 PM this evening/...
a batch of high clouds was pushing south across the lower
Hudson Valley and Long Island so sky grids were tweaked in the
next few hours. Otherwise any adjustments made were to hourly
temps and dewpoints based on recent trends. Given the flow is
shown to be more westerly across coastal Fairfield County, CT
highs were tweaked up here a bit which put them closer to
observed values yesterday since I don't see any reason they will
run much cooler. Some tweaks were also made to bump up highs a
bit along the Highway 25 corridor of Suffolk County as well as
at Montauk based on high temperatures from yesterday in addition
to the latest observations. The rest of the forecast looks
reasonable at this time and no other changes were made. Very
juicy air will continue to flow off nearly 75 degree ocean water
right into south facing shoreline areas as evidenced by the 77
degree dewpoint reached at JFK this morning. Heat headlines
continue and look justified.

A deep west-northwest upper flow zonal flow existing today around an
anomalously strong polar low moving across Hudson Bay. At the
surface weak diurnal surface/thermal troughing will develop over
the region.

Although marginal to moderate instability development is
expected today...there is a lack of a distinct trigger to
initiate convection. Highest instability/dewpoints are expected
along the coast once again today...where the thermal trough/sea
breeze could act as focus for isolated pulse convection across
NYC/Li this afternoon if any weak vort energy tracks through. A
localized strong wet downburst is possible.

Otherwise...main story will be heat today. Deep mixing and warm
temps aloft should have temps rising into the lower to mid 90s
for much of the region. A few upper 90s possible for NYC/New Jersey
Metro. As was the case yesterday, deep mixing and subsidence will
likely promote dewpoints to mix out into at least the the lower
to mid 60s in the afternoon across areas n&w of the sea
breeze (nyc/New Jersey Metro and interior). Meanwhile...south coastal
areas will likely see dewpoints hold in the lower to possibly
mid 70s with sea breeze development off 75 degree ocean. Based
on 95-100 heat indices being reached across the New York/New Jersey Metro
area as well as coastal SW CT and the eastern 2/3rd of Li for a
second day, have continued/expanded heat advisory into these
areas.

There is a low risk of rip current development this morning,
which may become moderate for the beaches of Queens and Nassau
County late today with coastal jet development.

&&

Short term /6 PM this evening through 6 PM Friday/...
an active near zonal flow will develop as a anomalously strong
polar low tracks through northern Ontario/Quebec.

A weak cold front approaches tonight as the first in a series
of shortwaves tracks through the NE in the developing zonal
flow.

Main forecast challenge and concern for tonight into early
Friday morning is progression of any mesoscale convective system activity into the
region. The shortwave energy emanating from the activity
currently occurring over the upper Mississippi River
valley/Great Lakes this morning will likely provide trigger for
upstream convection (eastern great lakes) this
afternoon/evening which could track over the region tonight.
Considerable model spread exists on the track and intensity of
any activity across the region tonight. This is due to
differences in the favorability of the environment (particularly
mid-level lapse rates) and the unpredictability of the
interaction of a yet to form convective complex with this
environment. So overall the threat for a strong mesoscale convective system passing
through the region tonight into early Friday morning, with an
associated flash flood and damaging wind threat, is low.

Higher probability is for scattered shower and embedded
thunderstorm activity as shortwave energy moves through the
region and interacts with a moist and marginally unstable
airmass over the area. An isolated strong storm is possible in
this scenario, with a low chance for minor urban flooding.

Pretty good agreement that any shortwave energy and convective
activity pushes east by Friday morning. In its wake, deep west/northwest
flow and subsidence will favor a hot and dry day. Temps across
the coastal plain will likely rise into the lower 90s to 95,
with upper 80s to lower 90s interior. Deep mixing and subsident
northwest flow should promote lower dewpoints area wide. At this time,
it appears that heat indices could marginally reach 95 degrees
across the NYC/mj Metro and Li, but not enough confidence to
extend advisory at this time as dewpoints may mix out more than
forecasted.

&&

Long term /Friday night through Wednesday/...
although this period will start dry on Friday night, there is
an increasing chance of multiple rounds of heavy showers and
tstms from Saturday afternoon through Monday night.

The weather pattern favors the development of several meso
convective systems/mcss caused by short waves rotating southeast arnd a
Canadian polar vortex. There is considerable uncertainty
regarding their track and intensity, depending on where they
actually develop.

Adding to this complexity is where the approaching warm front stalls
late Saturday - Sunday, and the subsequent development of a low
pressure wave along the front late Sunday - Monday.

There is the potential for heavy showers, tstms, and strong gusty
winds during this time. Stay tuned.

Weather conditions will finally improve with the passage of a cold
front early Tuesday, bringing more comfortable late July
weather to the area next Tuesday through Thursday.

&&

Aviation /14z Thursday through Monday/...
a weak trough of low pressure gradually moves east of the region
this morning, before a weak cold front slowly approaches
later Thursday.

VFR conditions are forecast through Thursday.

After light and variable winds early this morning, a west-SW flow
redevelops for the late morning/afternoon. Wind speeds 10-15 kt
through the early evening with some gusts 15 to 20 kt with
otherwise 5-10 kt flow. Therefore a few terminals may gust for a
few hours for the late afternoon and early evening on Thursday.
There is a low chance for an isolated thunderstorm or two for
kisp and kbdr this afternoon, but confidence too low to put in
taf at this time.

New York Metro enhanced aviation weather support...

Detailed information, including hourly taf wind component forecasts,
can be found at: http:/www.Weather.Gov/zny/n90

Kjfk taf comments: amendments may be needed due to timing of
gusts this afternoon.

The afternoon kjfk haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Klga taf comments: amendments may be needed due to timing of
gusts this afternoon.

The afternoon klga haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.

Kewr taf comments: amendments may be needed due to timing of
gusts this afternoon.

The afternoon kewr haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.

Kteb taf comments: no unscheduled amendments expected.

Khpn taf comments: no unscheduled amendments expected.

Kisp taf comments: amendments may be needed due to timing of
gusts this afternoon, and for isolated thunderstorm chance this
afternoon.

Outlook for 06z Friday through Monday...
Thursday night...chance of thunderstorms with sub VFR
conditions, with improving conditions late.
Friday and Friday night...VFR.
Saturday...MVFR or lower possible with a chance of showers and
thunderstorms.
Sunday-Monday...MVFR or lower possible with a chance of
showers and thunderstorms.

&&

Marine...
a weak pressure gradient over the region will keep sub Small
Craft Advisory/Small Craft Advisory conditions through Friday.

Although winds and seas are forecast to remain below Small Craft Advisory levels
of 25 kt and 5 ft from Friday night through Monday, there will
be several rounds of showers and tstms starting Saturday
afternoon through Monday. Winds and waves may be briefly higher
in and around tstms. Stay tuned to possible marine weather
statements and/or special marine warnings during this time.

Note that areas of fog may temporarily reduce the visibility to near 1 nm
Saturday afternoon and night as a warm front moves north across the
coastal waters.

Depending on the exact track of the stalled front, southerly swells
may begin to increase through the weekend into early next week, with
a low probability for Small Craft Advisory conditions on the ocean by Monday.

Weather conditions will improve following the passage of a cold
front on Tuesday morning, when winds become offshore.

&&

Hydrology...
there is a low threat for a convective complex to track across
the area tonight into early Friday morning. The main threat if
this activity materializes would be minor urban flooding, with a
low threat for flash flooding.

There is a low chance for additional urban flooding from Saturday
afternoon through Monday night as a slow moving front interacts with
a moist and unstable airmass. This will bring a threat for periods
of heavy showers and thunderstorms.

&&

Okx watches/warnings/advisories...
CT...heat advisory until 6 PM EDT this evening for ctz009.
New York...heat advisory until 6 PM EDT this evening for nyz069>071-078-
080-177-179.
Heat advisory until 8 PM EDT this evening for nyz072>075-176-
178.
New Jersey...heat advisory until 6 PM EDT this evening for njz004-006-
103>108.
Marine...none.

&&

$$
Synopsis...gc/NV
near term...NV/cs
short term...Nevada

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