Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 211438
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1038 AM EDT Fri Jul 21 2017

.SYNOPSIS...
Hot and dry conditions are expected through Saturday. A weak
cold front will settle south of the area tonight. This front
will remain nearly stationary across the area as waves of low
pressure move along it from Saturday night through early
Tuesday. High pressure will follow late Tuesday through
Thursday. A cold front will approach Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Temperatures, dewpoints and cloud coverage were slightly
adjusted to better match observed trends. Overall, the forecast
remains on track.

A near zonal upper flow today as a anomalously strong polar low
tracks east through Northern Ontario/Quebec. At the surface, a
weak surface cold front pushes south through the region today.

Lack of trigger and focus, subsidence and weak capping should
inhibit any convection development today.

Deep W/NW flow and subsidence today will favor a sunny, 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. A more comfortable
airmass expected later this morning into afternoon as deep mixing
and subsident NW flow should promote dewpoints at least falling into
the lower to mid 60s for much of the area.

Heat Advisory continues for the the NYC/NJ metro and LI, for 3rd day
with heat indices in the mid 90s...and have expanded to coastal
Westchester and Fairfield counties as well.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Active zonal upper flow continues during this period...with signal
for PAC/convective energy approaching the region late Sat/Sat Night.
At the surface, the weak cold front pushes se of the region
tonight with high pressure building in from the west on
Saturday.

Tranquil conditions expected tonight with warm but less humid
airmass than the last couple of nights.

Subsidence, deep mixing, and light offshore winds will spell another
mostly sunny (possibly filtered by high clouds), hot and dry day on
Saturday. Highs will generally be in the upper 80s to lower 90s
area wide. Dewpoints should mix down a bit more than Friday
based on lower 850 TD`s; into the upper 50s/lower 60s Sunday
afternoon across the interior. For coastal areas though,
dewpoints may creep back towards 70 degrees with afternoon sea
breeze development, while temps drop back into the 80s. It
appears that heat indices will generally top out in the upper
80s/lower 90s for much of the region, but a few spots in the
NYC/NJ metro could flirt with 95 degrees. Not enough confidence
to extend heat advisory at this time.

A this point it appears any MCS activity with the approaching
shortwave will hold off until Sat Eve/Night...but the evolution of
these complexes are always difficult to detail this far out. Will
gradually increase slight/low chance pops from w to e late day/eve
to cover timing uncertainty. Otherwise...dry conditions expected for
much of the day with subsidence and capping.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Prepare for unsettled weather from late Saturday through early Tuesday.

This portion of the extended forecast will be dominated by an unseasonably
south latitude polar jet orientation, with multiple short waves
moving through the Northeast in northwest flow, which is
typically a pattern that offers very little predictability.

Despite considerable uncertainty regarding the amplitude and timing of
the upper lvl short waves accompanied by their sfc reflections,
this pattern remains favorable for periods of heavy rainfall
and thunderstorms as multiple Mesoscale Convective Systems/MCS
move across the area in northwest flow. The greatest complexity
with the forecast remains on where frontal boundaries stall,
which have impacts on temperature, wind, instability, cloud
cover, etc, but most importantly on where exactly these systems
will track. The forecast will need to be monitored over the next
few days for potential heavy rain and flooding along with
severe weather.

An amplifying short wave is forecast to mv east of the area by
early Tuesday, bringing a refreshing air mass change to a dry
cool continental polar air mass during the mid week period
before another front approaches toward the end of the work week.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
VFR for today on a WNW flow, with coastal/eastern terminals
going more WSW later in the afternoon. Flow increases to around
10 kt late this morning and into the afternoon. For the mid to
late afternoon some occasional gusts at 15-20 kt possible for city
and southern coastal terminals.

     NY 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: Timing and duration of gusts may be off by an
hour or two for this afternoon.

The afternoon KJFK haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KLGA TAF Comments: Timing and duration of gusts may be off by an
hour or two for this afternoon.

The afternoon KLGA haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KEWR TAF Comments: Timing and duration of gusts may be off by an
hour or two for this afternoon.

The afternoon KEWR haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: Timing and duration of gusts may be off by an
hour or two for this afternoon.

KHPN TAF Comments: No unscheduled amendments expected.

KISP TAF Comments: Timing and duration of gusts may be off by an
hour or two for this afternoon.

.OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
.Saturday...VFR.
.Saturday Night-Tuesday AM...Episodes of showers and
thunderstorms with MVFR or lower conditions possible.
.Tuesday PM...Conditions improving to VFR.

&&

.MARINE...
Although winds and seas are forecast to remain below SCA (Small
Craft Advisory) levels of 25 kt and 5 ft from overnight through
Saturday night, there is the potential for thunderstorms
Saturday night that could result in higher waves and winds.
Marine Weather Statements and/or Special Marine Warnings are
possible during that time.

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 SCA conditions on the ocean by early
Monday. Conditions will gradually improve by mid to late week
as winds decrease in building high pressure, allowing any
lingering swells to slowly subside.

&&

.HYDROLOGY...
Chance of heavy rain causing flooding from Saturday night
through Monday as multiple waves of low pressure ride along a
nearly stationary front draped across the local area. Widespread
amounts of 1 to 2 inches likely; with isolated higher amounts.
Estimated maximum hourly rainfall rates of at least 1 inch.

&&

.TIDES/COASTAL FLOODING...
An approaching new moon (Sun) will have tides running high this
weekend into early next week. Positive tidal departures of 1/2
to 1 ft will be needed for minor flooding during the night time
high tides during this time.

Localized minor flooding is possible starting with the Saturday
Night high tide cycle, mainly in the western south shore bays of
LI. A bit more widespread minor flooding is possible Sunday
Night if an e/ne flow develops ahead of an approaching frontal
system. The threat for minor flooding could continue into
Monday.

Note: If any episodes of heavy rain coincide with the high
tides, coastal urban/poor drainage flooding would be
exacerbated.

&&

.CLIMATE...
Today will mark the 3rd consecutive day of 90+ degrees temps
for much of the NYC/NJ urban corridor, with a 4th day likely on
Saturday.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 6 PM EDT this evening for CTZ009.
NY...Heat Advisory until 6 PM EDT this evening for NYZ071>075-078-
     080-176>179.
NJ...Heat Advisory until 6 PM EDT this evening for NJZ004-006-
     104>108.
MARINE...None.

&&

$$

SYNOPSIS...GC/NV
NEAR TERM...JM/NV
SHORT TERM...NV
LONG TERM...GC
AVIATION...JE/DW
MARINE...GC/NV
HYDROLOGY...GC/NV
TIDES/COASTAL FLOODING...
CLIMATE...



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