Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 221110
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
710 AM EDT FRI JUL 22 2016

.SYNOPSIS...
High pressure builds further offshore today as a cold front
approaches and moves through early Saturday. High pressure over
the area this weekend moves offshore early in the new week, and
then a cold front approaches on Monday and passes through the area
Monday night. High pressure returns for Tuesday through Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Morning forecast is on track, so no significant changes will be
made. Will update hourly grids based on latest surface obs and
satellite trends.

Mid level shortwave and associated sfc low pass well to the north
this morning. A SW flow will increase as the pressure gradient
tightens between high pressure off the Mid Atlantic Coast and the
aforementioned low. This will pump a hot and more humid airmass
into the region today. A Heat Advisory remains in effect for NYC
and most of NE NJ with max heat indices ranging from 95 to 100
degrees this afternoon. Heat indices for the rest of the region
will be into the 90s.

A pre-frontal trough will also develop over the area which could
be the trigger for showers and thunderstorms this afternoon,
although coverage is questionable due to the lack of upper level
support. Moderate instability will develop...but shear is lacking
until the next shortwave approaches this evening and tonight. A
few storms that develop late this afternoon could become severe
as the upper jet/vort move closer...although the disjointed nature
of the scenario has resulted in a low confidence forecast for a
widespread severe weather event. Models are in good agreement on
the timing of the better upper support coming tonight.

A high risk for rip current development at ocean beaches will be
also be developing this morning...and continuing to be high
through the evening due to southerly wind waves increasing to 3 to
5 ft and a residual 2 ft se swell.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Models are also in good agreement that the best dynamics from the
shortwave and jet streak approaching tonight will be closest to
eastern CT/LI with areas N of here in the sweet spot. Models are
still indicating moderate instability into the overnight hours as
a cold front approaches and while severe wx typically doesn`t
occur at night here...this could be an exception...especially
during the first half of the night.

Showers and thunderstorms taper off late tonight with the passage
of the cold front early Saturday.

Another hot day Saturday but relatively drier with the westerly
flow. This should allow for more vertical mixing and lower
dewpoints. Although the dewpoints are expected to be
lower...temperatures will be higher with heat indices well into
the 90s once again. The heat advsy continues for NYC on Sat and
may also be needed again in NE NJ with values near 100...but the
uncertainty in mixing down lower dewpoint air from the top of the
mixed layer could preclude this and keep it just below.
Therefore...do not have the confidence to extend NE NJ attm.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
High pressure builds back into the area from the west Saturday night
through Sunday. High temps on Sunday will top off in the upper 80s
to low 90s for most areas, but will be in the low to mid 90s for
NYC, portions of NE NJ, and southern portions of the Lower Hudson
Valley. With a W-NW flow, dewpoints should not be as high as
Saturday, generally in the upper 50s to low 60s. This results in
heat indices below 95 degrees.

The high moves offshore Sunday night, and return flow develops on
the back side of the high. Dewpoints will creep up into the mid and
upper 60s Sunday night through Monday as S flow increases ahead of
approaching cold front. Highs on Monday will top off in the low to
mid 90s, and heat indices will top off in the mid to upper 90s.

As cold front approaches on Monday, scattered showers and
thunderstorms will develop over western areas, and those storms will
continue to develop and spread east as that front advances and
pushes through the region Monday night. With deep S to SW flow, low
level moisture will increase throughout the region, and a very warm
and humid night on tap with lows near 80 in/around NYC, and in the
low to mid 70s elsewhere. Surface dewpoints will will be in the low
70s, resulting in overnight heat indices in the 80s for NYC and
urbanized portions of NE NJ. Areas of fog are likely as well.

Behind the cold front, surface dewpoints fall back into the 60s. It
will take some time for cooler and dryer air to build east. Highs on
Tuesday will climb back into the low to mid 90s, and with surface
dewpoints in the 60s, heat indices will once again top off in the
mid 90s.

High pressure continues to build in from the west for the midweek
period. Temperatures will top off in the upper 80s to low 90s on
Wednesday, and then will top off in the mid to upper 80s on
Thursday.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
High pressure remains offshore today. A cold front approaches
tonight and moves through early Saturday.

Generally VFR conditions expected through the day today, except
in any stronger thunderstorm that develops. Best chance from mid
afternoon through the evening for isolated to scattered
thunderstorm development. By late this evening and continuing
overnight, patchy fog and MVFR/local IFR vsbys are possible,
mainly outside NYC metro.

Southwest winds increase this morning, with speeds 15 to 20 KT
and gusts in excess of 20 KT this afternoon.

Gusts become less frequent after sunset, and speeds diminish
overnight.

...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: Gusts of 25 to 30 KT are possible this
afternoon. Amendments for thunderstorms late this afternoon and
evening are possible.

KLGA TAF Comments: Gusts of 25 to 30 KT are possible this
afternoon. Amendments for thunderstorms late this afternoon and
evening are possible.

KEWR TAF Comments: Gusts of 25 to 30 KT are possible this
afternoon. Amendments for thunderstorms late this afternoon and
evening are possible.

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

KTEB TAF Comments: Gusts of 25 KT are possible this afternoon.
Amendments for thunderstorms late this afternoon and evening are
possible.

KHPN TAF Comments: Gusts of 25 KT are possible this afternoon.
Amendments for thunderstorms late this afternoon and evening are
possible.

KISP TAF Comments: Gusts of 25 to 30 KT are possible this
afternoon. Amendments for thunderstorms this evening are possible.

.OUTLOOK FOR 12Z Saturday through Tuesday...
.Saturday through Sunday night...VFR.
.Monday-Monday night...Mainly VFR, except MVFR or lower possible in
scattered late day/evening thunderstorms.
.Tuesday...VFR.

&&

.MARINE...
SCA remains in effect for the ocean waters and the south shore
bays of Long Island due to an increasing SW flow today. Gusts up
to 30 kt are expected...especially late this aftn and eve as low
level winds peak. Seas on the ocean will also build to advsy
levels in response to the strong winds. Only change to the
headline was to pad the timing a few hours on the south shore
bays...which now expires at 11pm. A cold front moves across early
Saturday with conditions dropping below SCA levels.

High pressure will influence the waters from Saturday night through
Monday. A cold front passes through the waters Monday night, and
then high pressure returns for the middle of next week.

Sub-SCA conditions expected for the period.

&&

.HYDROLOGY...
Boundary layer winds increase today so any thunderstorms this
aftn and tonight will be faster moving, mitigating the flood
threat. Still though, some localized minor urban and small stream
flooding will be possible.

Scattered showers and thunderstorms will impact the region Monday
afternoon and Monday night. PWATs will range from 2-2.5 inches,
resulting in the potential for locally heavy rain. Localized minor
urban and small stream flooding is possible.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Heat Advisory from noon today to 7 PM EDT Saturday for
     NYZ072>075-176-178.
     High Rip Current Risk through this evening for NYZ075-080-081-
     178-179.
NJ...Heat Advisory from noon today to 7 PM EDT this evening for
     NJZ004-006-103>108.
MARINE...Small Craft Advisory from noon today to 6 AM EDT Saturday for
     ANZ350-353-355.
     Small Craft Advisory from noon today to 11 PM EDT this evening
     for ANZ345.

&&

$$
SYNOPSIS...24/MPS
NEAR TERM...24/MPS
SHORT TERM...24
LONG TERM...MPS
AVIATION...PW
MARINE...24/MPS
HYDROLOGY...24/MPS



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