Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 242305
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
705 PM EDT Thu May 24 2018

.SYNOPSIS...
A back door cold front lingering southeast Connecticut and
eastern Long Island will gradually dissipate overnight as high
pressure otherwise dominates. A weak low pressure trough will
develop over western portions of the region on Saturday. Another
back door cold front will pass through Saturday night into
Sunday morning, becoming nearly stationary just to the south and
west through Memorial Day. Another cold front will follow from
the west on Tuesday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Fog/low cloud bank over SE coastal CT and along the south fork
of Long Island on the cool side of the back door front has
remained nearly stationary early this evening. This fog bank
aided by onshore flow and evening cooling, but should dissipate
overnight as SW flow strengthens. Before then, the fog may
become locally dense right along shorelines.

Lows tonight will be in the lower/mid 60s in/near NYC, with 50s
elsewhere.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
A flat upper ridge will dominate aloft, with offshore sfc high
pressure and a week inland trough. With H8 temps increasing to
near 15C and H5-10 thicknesses near 570 dm, expect a very warm
day, with highs reaching 90 in NE NJ and in the valleys well NW
of NYC, with mid/upper 80s elsewhere away from south facing
shores. With a very dry air mass in place, heat index values
will actually be several deg lower than air temps.

Lows Fri night should be near 70 in NYC and in the 60s
elsewhere.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
A polar low over Greenland and associated trough across SE Canada
will slowly slide east through the weekend, while Bermuda ridging
builds off the SE coast. The local region will be in between these
two features, with broad but weak northern stream shortwave energy
over the US/Canadian plains gradually sliding/shearing east towards
the NE US through the weekend, as well as vort energy rotating
around the Bermuda ridge.

At the surface, lee trough development is expected on Saturday. A
modestly unstable and sheared environment, with increasing vort
energy in the mid/level flow, should lend to afternoon
shower/thunderstorm development west of the Hudson River. Main
threat will be torrential downpours in increasingly moist airmass,
but can`t rule out a few strong to severe storms in this regime as
well. Question is timing of trigger. Any convective/shower activity
should slide eastward through the late afternoon/evening but weaken
overnight with diminishing instability and maritime influence.
Temperatures should be quite warm on Saturday with increasing
humidity as well. Highs should be well into the 80s away from the
south coasts, and upper 70s to around 80 at the coast.

Then decent agreement on a backdoor cold front approaching Sat Eve
and then pressing across the region Saturday night into Sunday
morning. The front, interacting with the sub-tropical environment in
place, should increase the coverage of shower activity Sat Night
into Sun morning, but thunderstorm activity should decrease after
the evening hours as instability diminishes. Locally heavy downpours
are the main threat in this environment.

The region will then transition to a cooler Canadian maritime
airmass on Sunday into Monday, as high pressure builds southward
across New England. Subsidence and stable airmass may keep
shower/sprinkle activity rather limited by Sun afternoon and
continuing through Monday, but stratus will likely hang tough Sunday
into at least Monday morning with low-level inversion. Potential for
some breaks of sun heading into Monday afternoon as
northern/southern stream trough energy begins to slide east.

Fairly good agreement on next northern stream shortwave amplifying
into Quebec Monday Night into Tuesday, with ridging beginning to
build into the region through Midweek. At the surface, a cold front
crosses the region Tuesday morning with Canadian high pressure
building into the region in its wake. Forcing appears limited with
this frontal passage, but some uncertainty on instability, which
warrants a low chance for isolated shra/tsra. Otherwise, appears high
pressure builds into the region for midweek with dry and near to
above seasonable temps.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
High pressure dominates through Friday.

Mainly VFR conditions through the TAF period. The only exception is
LIFR or IFR conditions in stratus and fog across southeast
Connecticut at KGON and the forks of Long Island through around 06z.
Conditions should quickly improve to VFR at these locations after
06z.

SSW-S winds around 10 kt into this evening at most terminals. Winds
will diminish this evening and become light and variable outside of
city terminals.

SW winds increase to 10-15 kt with gusts 20-25 kt Friday morning
into Friday afternoon.

 ...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: Wind Speeds 10-15 kt through 01z.

KLGA TAF Comments: Wind direction may vary between 170 and 220 with
speeds 10-15 kt through 01z.

KEWR TAF Comments: Wind Speeds 10-15 kt through 01z.

KTEB TAF Comments: No unscheduled amendments expected.

KHPN TAF Comments: No unscheduled amendments expected.

KISP TAF Comments: No unscheduled amendments expected.

.OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY...
.Friday Night...VFR.
.Saturday...Mainly VFR. Chance of showers and thunderstorms near NYC
Metro terminals and to the N and W in the afternoon with possible
MVFR. Higher chance of showers and thunderstorms at night.
.Sunday-Monday...MVFR or lower at times with a chance of showers and
thunderstorms. Otherwise VFR.
.Tuesday...Mainly VFR.

&&

.MARINE...
A tightening pres gradient between low pres to the north and
high pres over the western Atlantic on Fri could bring marginal
SCA conds to the near shore ocean waters and the Long Island
south shore bays late day Friday, with gusts up to 25 kt, and
then to the ocean waters Fri night aftn/eve. A strengthening
sfc inversion will be developing over the waters, so despite
increasing winds aloft mixing potential will be limited. A 15-20
kt sustained flow could however bring ocean seas up to 5 ft Fri
night. No SCA at this time since the situation is either still
marginal or too far out in time.

Generally sub SCA conditions are expected Sat thru Tue in a weak
flow regime, but could see a period of 20-kt gusts, from the SW
Sat afternoon and then shifting E on Sunday.

&&

.HYDROLOGY...
Localized heavy rainfall is possible Sat night into Sunday
morning as a cold front passes through. Quite a bit of spread in
model guidance, with 1/4 to 3/4 inch of rain appearing likely,
but potential for locally 1 to 2 inches of rain. Minor urban and
poor drainage flooding appear to be the main issues.

&&

.TIDES/COASTAL FLOODING...
Water levels may reach minor flood thresholds along the south
shore back bays of Nassau County and in western Long Island
Sound with the Sunday afternoon/night high tide cycle. Forcing
for increased water levels will be increasing E-NE flow as a
front stalls to the south and strong high pressure sets up E of
New England, along with increasing astronomical high tides with
the full moon on Tue the 29th.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the
air for an extended period of time.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Dense Fog Advisory until 2 AM EDT Friday for ANZ350.

&&

$$
SYNOPSIS...Goodman
NEAR TERM...Goodman/PW
SHORT TERM...Goodman
LONG TERM...NV
AVIATION...DS
MARINE...Goodman/PW
HYDROLOGY...Goodman/NV
TIDES/COASTAL FLOODING...
EQUIPMENT...


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