Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 181117
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
717 AM EDT Fri Aug 18 2017

.SYNOPSIS...
A warm front moves across today. The cold front with an area of
low pressure along it will slowly move across late tonight into
Saturday but will linger across the eastern end of Long Island
and Southeast Connecticut. The front will not totally clear the
region until Saturday night. High pressure will then build in
through the beginning of next week, followed by a midweek cold
frontal passage.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Line of heavy showers and embedded thunderstorms will move east
through the region this morning along a warm front. Main threat
is minor urban flooding.

Otherwise...the upper levels feature a ridge axis centered near
the region. Models at times can struggle with the precipitation
forecast with the departure of large mid level ridges above
580dm. So, forecast will adjust for this in situation where
there is more forcing and precip is too low and vice versa.

Lack of forcing without much height falls may signal here a lull
in shower and thunderstorm activity late this morning into early
afternoon. However, instability grows with daytime heating so
expecting this activity to pop up and develop and potentially
become more intense heading into the evening.

There is high precipitable waters close to 2 to 2.2 inches so
heavy rain will be possible as well as gusty winds with
thunderstorms. In addition, height contours are nearly parallel
from lower to upper levels. This signals potential for training
of showers thunderstorms, in which multiple showers and
thunderstorms move across the same area. Gusty winds are
mentioned because of increasing direction and magnitude of low
level shear. Forecast hodographs so increasing length in a
convex shape.

There is a moderate risk of rip currents at ocean beaches,
potentially becoming high this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
Models at times can struggle with the precipitation forecast
with the departure of large mid level ridges above 580dm. So,
forecast will adjust for this in situation where there is more
forcing and precip is too low and vice versa.

The upper level trough will be approaching the region tonight.
The height falls become more remarkable late tonight into
Saturday morning and this is when the trough moves eastward a
greater distance. The region will be getting closer to the right
entrance region of this jet. The trough amplifies and shortens
its wavelength during the day Saturday. 500mb heights lower
20-30 m from early morning until early evening. Vorticity still
increasing with height tonight and Sat looking at 925, 850, and
700mb levels.

Still have a threat of gusty winds and heavy rain with
thunderstorms tonight. High precipitable waters near 2 inches
still will be in place as will the vertical wind shear.

A cold front will continue to approach tonight. The cold front
moves into the region late tonight into Saturday but does not
totally clear the region until Saturday night.

However with aforementioned dynamics, pops still in place for
parts of the CWA during Sat evening with possibility for
isolated shower activity.

West to Northwest flow behind the cold front later Saturday
night and continued ridging will promote mainly dry conditions.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Shortwave trough pivots northeast of the region on Sunday, with
generally zonal upper flow over the region for early to mid of next
week, between southern ridging and a closed low moving into Hudson
Bay.

At the surface, high pressure builds into the region Sunday, and
then gradually sinks south and east of the region Monday into
Tuesday. The result will be dry and seasonably warm conditions on
Sunday, giving way to increasing heat and humidity Mon into Tue.
Perhaps some afternoon shower/tstm activity along a lee trough Tue
afternoon depending on any energy sliding through the upper flow
aloft, but low predictability at this point.

Decent model agreement with shortwave energy digging into the Great
lakes Tue into Tue Night and then towards the NE US on Wed. An
associated frontal system will bring the next chance for organized
shower and tstm activity late Tue into Wed.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
A warm front lifts north through the area into this morning. A
cold front approaches late today.

Showers and thunderstorms working their way into the city
terminals as of 11Z. There could be a period of heavy showers
between 12-14Z. Gusty winds are possible in any heavier shower
or thunderstorm. Thinking a period of VFR late this morning
into this afternoon, however MVFR could prevail. Another round
of showers and thunderstorms likely this evening with the cold
front approaching.

Southerly winds will increase today, mainly between 10 to 15
kts. Gusts to 25 kt possible across much of the region this
afternoon, but especially along the coast. Higher gusts possible
with any thunderstorm.

For tonight, MVFR or lower possible in showers/tstms with gusty
winds possible during the evening. Fog/stratus with MVFR or
lower conds may linger through the 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: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
morning.

The afternoon KJFK haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KLGA TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
morning.

The afternoon KLGA haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KEWR TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
morning.

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

KTEB TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
morning.

KHPN TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
morning.

.OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY...
.Saturday-Monday...VFR. light NW wind becoming SW by Late
Sunday and Monday.
.Tuesday...Iso shra/tstms possible with MVFR or lower
conds...otherwise VFR.

&&

.MARINE...
SCA on ocean today through tonight with sub SCA on other waters.
Overall sub SCA conditions expected Sat and Sat night with
offshore flow developing behind cold front.

Winds and seas are expected to remain blw sca lvls on all waters
Sun thru Wed as high pressure builds across the waters.

&&

.HYDROLOGY...
One round of showers and embedded thunderstorms will produce
moderate to heavy rain this morning. Another round of heavy
showers and thunderstorms will be possible this evening ahead of
the cold front. Rainfall accumulations are expected to be
around a half an inch to an inch, with locally higher amounts
possible in thunderstorms. It still remains difficult to
pinpoint where heavier showers and thunderstorms will develop.
There is a slim chance of flash flooding with the more likely
flooding hazard being minor flooding of poor drainage and urban
areas especially tonight with places that received heavy rain
during the morning.

Impacts from potential showers and thunderstorms Tuesday into
Wednesday are uncertain at this point.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ350-353-
     355.

&&

$$
SYNOPSIS...JM/NV
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...NV
AVIATION...CB
MARINE...JM/NV
HYDROLOGY...JM/NV



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