Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 270800

Area Forecast Discussion
National Weather Service New York NY
400 AM EDT Tue Jun 27 2017

A cold frontal passage occurs tonight. A Bermuda high sets up
Wednesday night. Then a frontal system passes north of the
region Thursday through Friday night. A cold front approaches
Saturday and moves across Sunday into Sunday night. The front
may linger south of the region early next week with otherwise
weak high pressure returning.


Upr lvl low shows up on stlt e of Detroit this mrng. The system
will continue to track ewd today, then drift newd tngt. The
associated cool front tracking across OH will reach the cwa tngt
and pass offshore by sunrise Wed. All of the models are in good
agreement with this soln.

Radar indicates shwrs and tstms still firing from sern PA to NJ.
Water vapor suggests the dynamics are sufficient for this to
continue thru the mrng and expand into the swrn portion of the
fcst area thru 12z. The NAM, GFS and ECMWF all support this

After the first round of shwrs and embedded tstms this mrng,
lapse rates steepen as the h5 trof axis approaches, and with a
120kt jet streak passing thru, isold-sct shwrs and tstms are
fcst today before ending this eve as subsidence develops.

The nearly dry adiabatic lapse rates up to h85 indicate a
potential downburst scenario with the deepest convection. In
addition, around 1500 J/kg of sbcape progged by the NAM in
balanced by a brn around 35 and an el blw 30k ft could allow for
mini supercells. This would produce a hail threat, particularly
with any dry air intrusion abv h7 which the NAM predicts.

The limiting factor for tstm development this aftn, especially
the srn half of the cwa, is the amount of subsidence in the wake
of convection this mrng which could suppress later development.

Mainly clr in the wake of the upr trof tngt similar to the
current stlt over the midwest.

Temps were a blend of guidance which was in good agreement.

There is a mdt risk for rip current development today.


Despite very steep low lvl lapse rates, subsidence should keep
the area dry. There could be some flat cumulus, however with
condensation pres deficits around 40, even this may be
difficult, especially away from any terrain enhancement. Despite
the cool airmass aloft, deep mixing will allow for highs to be
only a few degrees blw average. A blend of guidance was used for


The jet lifts north of the region and stays north of the region
midweek going through much of the weekend. It starts to move farther
south into the region Sunday afternoon into Sunday night, before
lifting back north of the region early next week.

The mid and upper level flow transitions to more of a zonal flow mid
into late week and then transitions to more of a ridging pattern
going into the weekend. Shortwave approaches for second half of
weekend, presenting more of a trough pattern and SW flow aloft,
before returning to a quasi-zonal flow early next week.

High pressure moves off into the Western Atlantic, building
Wednesday night, and then slowly drifting farther out to sea through
Thursday night. Meanwhile, a warm front moves north of the Great
Lakes and into Northern New England Thursday into Thursday night.
There is a trailing cold front to the west that looks to weaken
Thursday night before moving northward as a warm front Friday into
Friday night. A cold front from the west approaches Saturday and
moves across Sunday into Sunday night. Possibly this could get
delayed as shown by the ECMWF, hence the longer time window
stated for its passage.

The frontal boundary of the weakening cold front Thursday night into
Friday is forecast to be close enough to warrant a chance of a
shower or thunderstorm. The chance continues into Friday night. The
next chance of showers and thunderstorms will be this weekend.
Another chance but only slight chance of showers and thunderstorms
is forecast for early next week with frontal boundary possibly
lingering not too far away to the south of the region.

Temperatures start off near normal Wednesday night and Thursday but
then trend warmer for the rest of the forecast period. It will be
getting warmer and more humid. The temperatures will average about 3-
5 degrees above normal.


VFR through the TAF period. A trough of low pressure passes
across the terminals early this morning, followed by another one
on Tuesday.

Winds are a bit uncertain through the middle morning hours.
However, speeds are expected to be less than 10 kt. Winds
should veer to the W or NW in the next few hours over the city
terminals with light and variable elsewhere. Winds will then
gradually become southerly into the morning 10 kt or less. Winds
veer to the SW into the afternoon and evening 10-15 kt, then to
the W-WNW overnight around 10 kt.

A few showers are possible early this morning, 08-11z over NYC
terminals, and 10-13z Long Island and southern Connecticut
terminals. An isolated shower/thunderstorm is also possible this

.Tuesday Night-Wednesday...VFR.
.Thursday...VFR. Chance of a late day shower/thunderstorm.
.Friday and Saturday...MVFR or lower possible in showers and


Winds and seas are progged to remain blw sca lvls thru Wed.

Sub SCA conditions are expected Wednesday night. Then SCA becomes
more probable Thursday through Friday night for the ocean with seas
reaching between 5-7 ft for much of the time. Wind gusts reach 25-30
kt much of the timeframe as well. Also during Thursday and Thursday
night, widespread for just about all waters, higher wind gusts near
25kt are forecast, with hence probable SCA conditions for all
waters. Ocean seas are forecast to linger in SCA range Saturday with
waves near 5 ft particularly east of Fire Island Inlet. Much of the
remainder of the weekend will have sub SCA conditions forecast.


No hydrologic impacts expected through the beginning of next


Astronomical tides are still running high with a low chance of
any minor coastal flooding across the south shore back bays of
Nassau county with the high tide cycle tngt. The water levels
would only be expected to touch the minor benchmarks at just a
couple of gages at most so no statement has been issued.


Observations from KFRG (Farmingdale, NY) are not available.
Observations from KHPN (White Plains NY) and KHVN (New Haven CT)
are being disseminated through backup methods. All is due to
an FAA communication line outage. Return to service time is




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