Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 262134
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
534 PM EDT Wed Apr 26 2017

.SYNOPSIS...
Weak low pressure moves into coastal New England tonight into
Thursday. The low eventually dissipates altogether, leaving the
region with weak high pressure briefly Thursday afternoon into
Thursday evening. A cold front approaches late Thursday night
and moves into the region Friday but will also weaken with time.
A cold front will slowly approach from the north late Friday
night into Saturday, and pass through Saturday evening. High
pressure will briefly build in its wake from southeast Canada on
Sunday. A warm front will approach Sunday night and lift north
on Monday, followed by a trailing cold front late Monday in to
Monday night. Weak high pressure will pass to the south from
Tuesday into Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The main story tonight will be the low clouds and fog. The upper
level low and surface low both translate east of the region,
getting into the vicinity of coastal New England by early
Thursday. With atmospheric flow staying below 15kt below 10kft
and a low level inversion at around 1-2 kft, the low level
moisture stays in place. There could be some drizzle or very
light showers but most moisture probably is manifested as fog.
Most susceptible areas will be where relatively more rain has
fallen, Eastern Long Island and Southeast Connecticut where just
a little cooling this evening with light easterly flow will
help advect and further develop the fog, and it will eventually
become dense. Dense fog advisory for Eastern Long Island and New
London County Connecticut was issued for late this evening into
early Thursday morning. Other areas farther west will also get
fog but not as much dense fog. Took relatively warmer MAV
guidance for lows, upper 40s to upper 50s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
Fog burns off in the morning with daytime heating and as more
westerly flow develops in the atmosphere. The upper level low
moves farther east of the region as a surface low dissipates.
More of a return W-SW flow develops in the region thereafter.
Models agree on a substantially warmer day Thursday, getting
well into the 60s for a majority of the region for highs. Weak
high pressure will briefly reside in the region with dry
conditions during the day and through the first half of Thursday
night.

The next low pressure system and associated upper level trough
will be approaching late Thursday night.The upper level flow
remains SW and the parent low with the system moves northward
Friday within Southeast Canada while its cold front moves in and
dissipates with time. There will initially be enough vertical
lift late Thursday night into early Friday along with some
elevated instability to give the region some showers and
thunderstorms. However, this looks to be brief without producing
much rain. Outside of the rain with the flow ahead of the cold
front turning more southerly, the region will see a return of at
least patchy fog Thursday night into early Friday with more
onshore flow and inherent moisture advection. Dry conditions
return later Friday.

The overall shift will be one of a gradually warming airmass.
Temperatures trend several degrees warmer for both lows
Thursday night and highs on Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Big picture shows an amplified patter developing over the eastern
half of the lower 48, with a building upper ridge over the East and
a closed low moving from the Plains states through the Midwest and
into southeast Canada. At first the area will be under zonal flow
aloft between the ridge to the south and an upper trough moving
across southeast Canada, that will send a back door cold front
toward the area late Friday night into Saturday. A shortwave
embedded in the flow aloft could trigger a shower or tstm late Fri
night or early Sat morning, then Sat should be a partly sunny to
mostly cloudy day with temps on the warm side, with highs 80-85 from
NYC north/west and in the 70s across Long Island and southern CT.
Low levels look capped just above the boundary layer until late day
Sat, so do not expect any precip until late day Sat with the cold
fropa, and only and isolated shower or tstm at most.

Cooler air returns for Sat night into Sunday night, with lows in the
40s and 50s, and highs in the 60s to near 70. As the flow aloft
amplifies, a leading warm front well in advance of the surface low
over the Midwest will approach, and move through some time on
Monday, The front should lift through NYC metro and points
north/west by afternoon, nut could take longer across Long Island
and southern CT. Then as upper ridging moves east, cold front
should pass through late day Monday into Monday night, with showers
and a few tstms. Do not expect strong convection with the cold fropa
attm, but a faster timing per 12Z ECMWF could yield a brief window
for this to occur late day Monday from NYC north/west.

Dry wx with near to slightly above seasonable temps expected for Tue
into Wed, with the weakening low passing well north, weak surface
high pressure passing to the south. Zonal flow aloft will also
become re-established by Wed, that could lead to late week precip
chances just beyond the forecast period.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
Low pressure will slowly shift east this afternoon and evening.

Ceilings will continue to lower into tonight with fog
developing.

NE-N winds around 10 KT becoming a little lighter late this
aftn. Winds eventually bcmg light and variable this evening.

     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 vsbys lowering below 1SM might be off
by an hour or two, or may not happen at all.

KLGA TAF Comments: Timing of vsbys lowering below 1SM might be off
by an hour or two, or may not happen at all.

KEWR TAF Comments: Tempo or prevailing IFR cigs still possible
this aftn. Timing of return to prevailing IFR may be off by an
hour or two.

KTEB TAF Comments: Tempo or prevailing IFR cigs still possible this
aftn. Timing of return to prevailing IFR may be off by an hour or
two.

KHPN TAF Comments: Timing of vsbys lowering below 1SM might be off
by an hour or two, or may not happen at all.

KISP TAF Comments: Timing of vsby dropping below 3/4SM may be
off by a couple of hours or potentially might not happen at all
tonight.

.OUTLOOK FOR 18Z THURSDAY THROUGH SUNDAY...
.Thursday aftn...MVFR.
.Thursday night...MVFR with chc IFR.
.Friday...Chance showers/thunderstorms/MVFR AM, VFR PM.
.Saturday...Mainly VFR.
.Sunday...Mainly VFR.

&&

.MARINE...
Without much of a pressure gradient overall, light residual
easterly flow going into tonight will result in the fog
spreading farther west across the waters. The fog tonight across
the waters is expected to be dense. The marine dense fog will
quickly return this evening for eastern waters and will develop
eventually for more western waters late this evening. The dense
fog continues into early Thursday. The fog is expected to
gradually dissipate Thursday mid to late morning before
returning again Thursday night into early Friday.

Winds will stay below SCA through Friday but the higher ocean
seas will remain through Thursday night and perhaps into Friday
as well. Non-ocean waters stay below SCA. Ocean seas are more
marginal for SCA Friday, at near 5 ft, so left end time of 6am
Friday for SCA for hazardous seas on the ocean.

Ocean seas above 5 ft should linger into Fri night, and perhaps into
part of Sat into Sat night, depending partly on the strength of SW
flow ahead of a back door cold front that looks to move through Sat
night.

Advy level conditions are also possible on the ocean Mon afternoon
and night after a warm frontal passage and before/just after a cold
frontal passage, with S-SW flow gusting up to 25 kt and seas
building to 5-7 ft per combo of WaveWatch and wind/wave
climatology.

&&

.HYDROLOGY...
No significant rainfall expected through Friday. Rain amounts
through Friday are generally expected to remain below a quarter
of an inch. However, there may be isolated brief heavy
downpours in any thunderstorms that develop.

Combo of a warm frontal passage late Sunday night into Mon morning,
and a cold frontal passage late day Mon into Mon night, could bring
precip amounts of 1/2 to 1 inch, highest NW of NYC. Localized higher
amts possible that could cause typical nuisance ponding.

&&

.TIDES/COASTAL FLOODING...
Due to high astronomical tides and an easterly swell the next
couple of days, water levels may approach minor coastal flood
benchmarks, in particular across the south shore back bays of
western LI. Only 1/3 to 3/4 of a foot of surge is needed for
minor flooding. A coastal flood statement has been issued for
this evening`s high tide cycle for these locations.

In addition, the elevated water levels combined with a prolonged
period of 5-9 ft breaking surf tonight into Thu will result in
beach erosion issues and may cause some localized dune toe
erosion during the high tides.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 8 AM EDT Thursday for CTZ008-012.
NY...Dense Fog Advisory until 8 AM EDT Thursday for NYZ079-081.
NJ...None.
MARINE...Dense Fog Advisory from 10 PM this evening to 10 AM EDT
     Thursday for ANZ335-338-345-353-355.
     Dense Fog Advisory until 10 AM EDT Thursday for ANZ330-340-350.
     Small Craft Advisory for hazardous seas until 6 AM EDT Friday
     for ANZ350-353-355.

&&

$$
SYNOPSIS...Goodman/JM
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...Goodman
AVIATION...CB/JC
MARINE...Goodman/JM
HYDROLOGY...Goodman/JM
TIDES/COASTAL FLOODING...



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