Area Forecast Discussion
Issued by NWS Upton, NY

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691
FXUS61 KOKX 171128
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
728 AM EDT Thu Aug 17 2017

.SYNOPSIS...
High pressure over the northeast and mid Atlantic states will
drift offshore today. A warm front will approach this evening
and move north late tonight into Friday morning. A cold front
approaches Friday, moving across the region late Friday night
into early Saturday. High pressure returns on Sunday into
Monday before a series of troughs and a cold front pass through
Tuesday into Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The forecast was updated mainly to account for mostly cloudy
conditions over some areas early this morning. The rest of the
forecast is still mainly on track.

An upper ridge axis will remain west of the region most of the
day, moving into the northeast around 00Z Friday. Meanwhile
surface high pressure centered over upstate New York will drift
to off the northeast and mid Atlantic coasts. The next shortwave
to affect he region will move into the Great Lakes region. The
upper flow will be somewhat blocky as the ridge builds and
moves slowly east. Will be dry with increasing clouds late in
the day as the ridge axis moves into the region.

There is a moderate risk for the development of rip currents at
the ocean beaches today.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
The upper ridge axis passes to the east and builds tonight into
Friday night as the upper pattern remains rather blocky as
heights rise as the ridge moves into the northern Atlantic.
This will keep the shortwave from moving east and lifts into
southern Canada and weakens as yet another moves into the upper
mid west and then into the Great Lakes region Friday night. At
the surface low pressure over the upper midwest will rotate
slowly into Ontario and western Quebec through Friday night.

A weak warm frontal boundary increases today and slow
approaches from the southwest this evening. Precipitation will
be delayed until late tonight as the warm front slowly pushes
into the region as the parent low remains well to the west. Best
chances or precipitation will be across northeastern New Jersey
into the Lower Hudson Valley. The region becomes warm sectored
Friday as the warm front lifts through. CAPE and surface based
instability increase during the day as the cold front slowly
approaches. There may be a break in the precipitation of a brief
time once the warm front lifts north, and until the cold front
nears later in the day. Best instability will be inland as a
deep southerly flow keeps a marine layer across Long Island and
into southern Connecticut. Best chances of thunderstorms,
possible strong, will be inland Friday afternoon into the
evening. Then the storms will weaken and move into Long Island
and southern Connecticut Friday night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Cold front moves through the area during Saturday with a chance
of lingering showers and thunderstorms in the morning. Models
then agree that the available moisture is probably too low for
consideration of afternoon showers and storms, especially since
a lagging upper trough and shortwave appear to be too late to
arrive for necessary lift and mid level instability. Will
therefore go with a dry forecast for the afternoon. Then with
stabilizing lower levels, the upper trough should pass through
dry during Saturday night. An even blend of MAV/NAM MOS looked
good for temperatures.

High pressure builds in on Sunday and lasts into Monday as the
upper flow becomes zonal to anticyclonic. Dry weather for both
days with highs mostly in the mid 80s.

For Tuesday into Wednesday, low pressure tracks across
southeastern Canada. This will bring a couple of pre-frontal
troughs here before a cold front eventually passes through
sometime most likely on Wednesday. Looks like the best
combination of moisture, lift and shear could be late day
Tuesday into Tuesday night. Will cap PoPs at chance Tuesday
through Wednesday for now given the timing uncertainty of the
surface features and sources of lift aloft. Highs generally in
the 80s both days.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
High pressure will slide offshore today before a warm front
approaches from the southwest tonight.

VFR through the TAF period.

Light northeasterly winds will veer to the southeast between
17-18Z as the high shifts offshore. KLGA may remain NE for a
bit longer before turning SE.

     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 of wind shift to SE could be off by
+/- 1 hour.

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

KLGA TAF Comments: Timing of wind shift to SE could be off by
+/- 1 hour.

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

KEWR TAF Comments: Timing of wind shift to SE could be off by
+/- 1 hour.No unscheduled amendments expected.

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

KTEB TAF Comments: Timing of wind shift to SE could be off by
+/- 1 hour.

KHPN TAF Comments: Timing of wind shift to SE could be off by
+/- 1 hour.

KISP TAF Comments: Timing of wind shift to SE could be off by
+/- 1 hour.

.OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY...
.Thursday night through Saturday night...MVFR or lower flight
cat possible in showers/tstms.
.Sunday And Monday...VFR.

&&

.MARINE...
Swells and seas have subsided on the ocean waters, and with
high pressure moving across the waters today, winds and seas
remain below small craft advisory levels. A warm front
approaches the waters today and moves north late tonight into
early Thursday morning. Southerly winds will be increasing ahead
of an approaching cold front Friday. And with the increased
winds, mainly west of Fire Island Inlet, and with the Ambrose
jet, ocean seas may briefly build to around 5 feet late Friday
afternoon into Friday evening. Will hold off on issuing an
advisory being late in the third period and with some
uncertainty.

Otherwise, winds and seas remain below advisory levels into
Friday night as a cold front moves into the forecast waters.
The cold front should cross the waters through the day on
Saturday with slowly subsiding seas and winds remaining below
SCA levels. Sub- SCA conditions then continue into Sunday and
Monday as high pressure builds in over the waters with a weak
pressure gradient.

&&

.HYDROLOGY...
A prolonged period of rainfall is likely from late Thursday
night into Saturday morning, with around 1 inch possible across
the region, with locally higher amounts. Locally heavy rainfall
is possible Friday and Friday evening. At this time it remains
difficult to pinpoint where heavier showers and thunderstorms
will develop. No significant hydrologic impacts are expected,
but some minor urban flooding is possible.

Impacts from potential showers and thunderstorms Tuesday into
Wednesday are uncertain at this point, however at least minor
nuisance flooding will remain a possibility.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$
SYNOPSIS...JC/MET
NEAR TERM...MET
SHORT TERM...MET
LONG TERM...JC
AVIATION...CB
MARINE...JC/MET
HYDROLOGY...JC/MET



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