Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 251020
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
620 AM EDT Fri Jun 25 2021

.SYNOPSIS...
Weak low pressure passes through Eastern Long Island today. High
pressure over the western Atlantic will then remain the
dominant weather feature through the first half of next week,
allowing a warm, humid airmass to build into the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
The forecast is mostly on track with little change with this
update.

A weak low pressure center heads north through the forecast area
today, passing over or nearby Eastern Long Island during the second
half of the morning or near noontime. Associated clouds and light
rain/drizzle will be focused toward Long Island and CT, then
drying conditions for the afternoon with lower clouds moving
out, and perhaps some cirrus moving in. Although warmer and more
humid than the past couple of days, high temperatures likely
fall short of seasonal norms.

A trough of low pressure remains nearby tonight. Moisture
convergence along this boundary along with weak shortwave lift after
midnight could produce some showers. Models seem to favor the
western half of the forecast area - closer to better moisture
convergence and lift, but thinking is that there will be a chance
even over eastern areas where some isentropic lift will be present.
High dewpoints could lead to patchy fog, but with decent turbulent
mixing right above the low level inversion, any fog that manages to
develop is not expected to become dense.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
High pressure remains anchored over the western Atlantic this
weekend with heights aloft generally rising through the period. A
relatively weak and low-amplitude approaching shortwave will however
move along the western periphery of the longwave ridge and weaken by
late Saturday. This combined with increasing daytime instability
could trigger showers and thunderstorms until early evening, then
mainly dry for the rest of the night. High temperatures on Saturday
near normal with Saturday night`s lows above normal.

Due to warming aloft, there will be more of a lid on the convective
potential for Sunday. Any convection will be diurnally driven, and
mainly from around NYC to points north and west due to differential
heating and thermal trough development.

850mb temps rise to around 17C in the afternoon. It could start out
cloudy in the morning for some areas, but it should turn out partly
to mostly sunny in afternoon, so expecting highs in the low 90s for
parts of NE NJ and NYC away from the marine influence. Most areas
end up in the middle to upper 80s, with around 80 for south-facing
shorelines. Based on progged boundary layer RH values, surface
dewpoints away from the marine influence might be able to mix out
slightly in the afternoon in spite of SW flow. Heat indices
therefore are expected to remain below 95 across the entire forecast
area.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Upper level high will remain stationary centered just off the East
Coast, while a surface high remains over the western Atlantic
through the long term period. A cold front will remain nearly
stationary to our west, over the Great Lakes region. During this
time frame, thermal troughs will develop over the Northeast, which
will be the focus for diurnally driven convection, mainly north and
west of New York City. The upper level high and associated ridge
looks to very gradually weaken late Tuesday into Thursday, with a
possible change in airmass.

Uncertainty still remains toward the end of the period of how
quickly the western periphery of the ridge breaks down, with the
potential for an upper low cutting off somewhere in the vicinity of
the Great Lakes at the end of the period, could make for a slow
eastward frontal progression with active convection. This looks to
be the most active period in terms of convection.

There remains high confidence of a hot, humid airmass building in
from Monday through mid-week. This has the markings of a heat wave,
defined as at least 3 consecutive days of high temperatures of 90 or
higher. Highs will rise into the upper 80s/lower 90s by Monday from
NYC and points north and west, with the lower to mid 80s closer to
the coast. The warmest days with potential record heat will be
Monday through Wednesday, with highs in the lower to middle 90s
across away from the coast. Much of the area during this time will
have heat indices of 95 or higher with dew points close to 70, so
heat advisories are seeming likely at this time.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
Low pressure slowly lifts through the area today before lifting
north and dissipating tonight.

Conditions are generally MVFR to IFR (mainly for ceilings) across
most terminals, except KSWF. LIFR ceilings are possible, but the
most likely places to see that will be eastern terminals such
as KISP and KGON. Showers and some drizzle are possible,
especially across eastern most terminals. A return to VFR is
expected by late this morning into the early afternoon, however
there is some uncertainty with timing.

Light NE winds today will become south at mainly 5 to 10 kt
during the afternoon.

 ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Amendments also possible for categorical changes this morning
into the early afternoon.

.OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY...
.Friday night...VFR conditions gives way to MVFR conditions, with
IFR and possibly LIFR becoming more likely late with fog possible.
.Saturday-Tuesday...VFR. A chance of afternoon showers/tstms,
mainly NW of the NYC terminals each day.

Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90

&&

.MARINE...
Winds and seas remain below SCA levels today.  Although winds and
waves are expected to remain below SCA criteria, a prolonged period
of southerly flow will produce near SCA conditions for the ocean
waters Sat night through Tue. Seas may briefly reach 5 ft
Monday night. Elsewhere, non-SCA conditions can be expected.

&&

.HYDROLOGY...
No hydrologic impacts are expected through the period.

&&

.TIDES/COASTAL FLOODING...
There is a moderate rip current risk for today and Saturday.

&&

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

&&

$$
SYNOPSIS...JC
NEAR TERM...JC
SHORT TERM...JC
LONG TERM...JP
AVIATION...JP
MARINE...JC/JP
HYDROLOGY...JC/JP
TIDES/COASTAL FLOODING...JC/JP


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