Area Forecast Discussion
Issued by NWS Upton, NY

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397
FXUS61 KOKX 231423
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1023 AM EDT Fri Jun 23 2017

.SYNOPSIS...
A warm front will be well north of the region today. A cold
front approaches tonight and moves across the area Saturday. A
series of frontal boundaries will move across the Tri-State area
Sunday through Tuesday. A large area of high pressure builds in
thereafter.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Adjusted POPs for showers late this morning into start of
the afternoon to be more confined with the higher coverage
towards NYC and to the north and west. This is consistent with
the mesoscale models forecast of reflectivity in the same time
window. To the east, expecting mainly dry conditions to
continue. Temperatures were adjusted slightly higher to better
match observed trends this morning. Otherwise, no other
remarkable changes made to the forecast database.

The region will be between Bermuda ridging and deepening
northern stream longwave trough across the north Central US
today...with one distinct southern stream shortwave riding
northeast this morning and then several weaker vorts riding
northeast later today. At the surface...a warm front washes
out/pushes north of the region this morning...with likely pre-
frontal trough development in the lee of the appalachians this
afternoon.

Deep southwest flow with sub-tropical connection will result in
an increasingly moist and humid airmass working into the region
today.

The initial shortwave rides north through the region this morning
into early afternoon. LLJ forcing weakens as this activity works
towards the region...but a marginally unstable and moist airmass in
place should support scattered shower and isolated thunderstorm
activity to work northeast through the region. Overall appears
to be a marginal instability with moderate shear
situation...which presents only a low probability of an
isolated strong to severe storm.

In the wake of this shortwave...potential for partial clearing and
additional destabilization late this afternoon/early evening across
NYC metro and points N&W. Although moderate instability/uni-
directional shear levels could exists during this time...appears to
be lack of a distinct focus or trigger for convection until the
evening. In fact...subsidence and weak mid-level capping may
limit convective activity across the region until late. Based on
instability/shear environment there is a threat for isolated
strong to severe storms during this time...conditional on
sufficient heating and development along any differential
heating boundaries or elevation.

Otherwise...considerable cloudiness and convective debris today
will keep temps in the lower to mid 80s for most of the region.
If enough breaks in the clouds materialize...temps could rise
into the upper 80s across NYC metro and points N&W.

There is a moderate risk of rip current development today, due
to building southerly winds waves and a 2 ft long period SE
swell.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Northern stream longwave trough continues to deepen into the
Upper Mississippi River Valley and Great lakes through the
period...with the shortwave remnants of Cindy shearing northeast
towards the region late tonight into Saturday morning. At the
surface...a cold front over the Great Lakes will slide east
towards the region tonight...with the remnant circulation of
Cindy riding NE towards the region along the front.

Leading edge of southern stream shortwave energy and pre-
frontal trough approach the region this evening. Will have to
watch for convection developing over Central/Eastern PA this
afternoon...and whether line segments can translate east in the
moderate mid- level flow into the Lower Hudson Valley/NE NJ
before instability begins to wane. A conditional low threat for
severe winds gusts exists mainly NW & W of NYC if this activity
survives.

The parade of shortwaves late evening into the overnight and
tropical airmass will keep a threat for iso convection with
heavy downpours overnight. Coastal stratus/fog development
possible with high dewpoint airmass advecting across E LI/SE
CT late today/this evening.

Main concern during this period will be approach of cold front
and remnant low of Cindy late tonight/Saturday morning.
Environment presents a threat for flash flooding along and just
to the south of the path of this low...with PWATS in excess of
2+ inches and Corfidi vectors indicating potential for slow
moving or back building convective elements. Also can`t rule out
an isolated severe wind/tornado threat if any MCS type activity
develops in a weak instability but high shear/helicity and low-
LCL environment.

745am Update...06z guidance is indicating that this feature may
track to the south of the region. If 12z guidance continues
with this theme...the above mentioned severe/flash flood threat
may end up south of the region.

Drying conditions in the wake of the cold front and Cindy
circulation Saturday afternoon...with highs in the mid to upper
80s.

A high risk of rip current is likely Saturday with building
southerly swells and wind waves.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
NWP is in agreement that a broad upper level trough will remain east
of the Rockies into early next week. The H5 flow then flattens from
west to east as a cutoff low pres system moves through the western
Canadian provinces...eventually consolidating with a vortex over
northern Quebec. This will sharpen the trough with its axis passing
through Tue night followed by weak ridging for the remainder of the
forecast period.

In terms of sensible weather...not a whole lot to talk about. A
few cool frontal boundaries will pass through the local
area...the first Sunday aftn/eve with just a chance of isold
showers. Mid level warming will keep instability in check so no
tstms in the forecast.

The second boundary approaches on Monday and is very slow to
move through the area. It may become hung up...before pushing
east Tue night. Despite a decent shortwave and being in the RRQ
of a 120+ kt upper jet...moisture looks very meager...thus have
kept the forecast dry. Moisture is still limited on Tue...but
there could be enough for isold showers/tstms in the aftn.

Dry and seasonable weather then returns for the remainder of the
forecast period.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
A warm front moves well north of the region today establishing
a moist SW flow.

Mainly VFR. Areas of MVFR are possible later today with cigs around
2500 ft and SHRA moving through for the late morning and early
afternoon. There is also some potential for eastern terminals to
briefly go to MVFR in the late afternoon due to low stratus. For now
the tafs indicate VFR because coverage is in question and too
uncertain at this time. More widespread sub VFR conditions are
expected late in the TAF period.

There will be a chance of isold-sct shwrs thru the day (Friday),
with the best potential for thunderstorms after 19Z, particularly
in areas along and west of the Hudson River.

The sea breeze may attempt to back winds closer to the south
again after 16Z today for eastern terminals.

A chance at perhaps scattered thunderstorm coverage towards the
evening push for the city 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: Amendments may be needed to address scattered
showers and for any isolated thunderstorms that may develop.
Winds may become more southerly after 16z.

KLGA TAF Comments: Amendments may be needed to address scattered
showers and for any isolated thunderstorms that may develop.

KEWR TAF Comments: Amendments may be needed to address scattered
showers and for any isolated thunderstorms that may develop.

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

KTEB TAF Comments: Amendments may be needed to address scattered
showers and for any isolated thunderstorms that may develop.

KHPN TAF Comments: Amendments may be needed to address scattered
showers and for any isolated thunderstorms that may develop.

KISP TAF Comments: Winds may become more southerly after 16z.
Amendments may be needed to address possible low clouds /
ceilings that may develop after 18z.

.OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
.Saturday...MVFR or lower possible in shra/tsra.
.Saturday night-Sunday Night...VFR. NW winds...becoming W/SW.
.Monday-Tuesday...VFR. A chance of afternoon shra/tsra each
day.

&&

.MARINE...
Southerly winds increase to marginal SCA on the ocean this
afternoon...and likely continue into tonight. Occasional gusts
to 25 kt possible on nearshore waters this afternoon. Ocean
seas likely building to SCA levels this afternoon...and likely
further build to 4 to 7 ft tonight. Winds subside and
Saturday...but southerly swells are expected to keep ocean seas
at 4 to 7 ft on Sat.

The other hazards for mariners will be rounds of
showers/thunderstorms this today into Saturday morning, and
potential for dense fog development on the ocean waters and
eastern LI nearshore waters this afternoon and continuing into
tonight.

Seas begin to subside Sat night...but could take until Sun morning
to drop below SCA levels east of Moriches Inlet. A weak pressure
field is then expected to prevail through Tue...keeping conds at sub-
advsy levels.

&&

.HYDROLOGY...
Localized minor urban and poor drainage flooding is possible
with showers and thunderstorm activity this afternoon into the
first half of tonight.

There is a threat for flash flooding late tonight through
Saturday morning from a likely complex of showers and
thunderstorm associated with a frontal wave (remnants of Cindy)
moving through the areas. Uncertainty exists on the
exact track of this wave...which could be from the Northern Mid-
Atlantic to Southern New England.

745am Update...06z guidance is indicating that this feature may
track to the south of the region. If 12z guidance continues
with this theme...the above mentioned flash flood threat may
end up south of the region.

Otherwise, no other hydrologic concerns.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides are running very high, especially during the
evening high tide cycles today and Saturday.

Less than 1 ft of surge is needed during these evening high tide
cycles for minor flooding, and in some cases less then 1/2 ft.
The expected S/SW flow is not favorable for surge, but a
background anomaly will likely be enough for minor coastal
flooding of the most vulnerable coastal locales along the south
shore bays of Western Long Island, along Jamaica Bay, and along
western Long Island Sound during this time.

&&

.EQUIPMENT...
KOKX weather radar is scheduled for maintenance starting today June
23rd for a period of 3 days.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ350-353-355.

&&

$$
SYNOPSIS...24/NV
NEAR TERM...JM/NV
SHORT TERM...NV
LONG TERM...24
AVIATION...JE/MET
MARINE...24/NV
HYDROLOGY...24/NV
TIDES/COASTAL FLOODING...
EQUIPMENT...



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