Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 270623
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
223 AM EDT Thu Apr 27 2017

.SYNOPSIS...
Weak low pressure slowly departs tonight and dissipates on
Thursday with weak high pressure building in. 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 THIS MORNING/...
Areas of dense fog were primarily confined across SE CT and
Eastern LI. There areas remain under a dense fog advisory.
Elsewhere, the fog is more patchy in nature and not as a dense.
It`s possible with the nearly saturated low-levels that the
dense fog could expand elsewhere. There seems to be a lot of
variability from hour to hour.

The upper level low and surface low both translate east of the
region, getting into the vicinity of coastal New England by
morning.

Overnight lows will be mild in the 50s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM 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 /06Z THURSDAY THROUGH MONDAY/...
Low pressure weakens as it drifts towards the Gulf of Maine this
morning. A weakening cold front then approaches from the west
into tonight.

Becoming IFR or lower at all terminals early this morning.
Conditions improve to MVFR around midday, except at KGON where
should improve to no better than IFR. VFR possible this
afternoon at KEWR/KTEB/KHPN/KSWF for a few hours. Return to IFR
or lower throughout this evening.

Light and variable winds become SSE-SE at under 10 KT inland
and around 10kt at coastal terminals from mid morning into early
afternoon. Winds become light and variable again this evening.

.OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY...
.Late tonight/Friday morning...IFR or lower probable. Isolated-
scattered showers possible with maybe a rumble of thunder. LLWS
possible late tonight at southern terminals.
.Friday afternoon-Sunday...Most likely VFR.
.Sunday night-Monday...MVFR or lower possible.

&&

.MARINE...
No changes to current forecast. Dense fog advsy is in effect
for all waters through 14z Thu due to a weak pressure gradient
and abundant low level moisture. 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.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 8 AM EDT this morning for CTZ008-012.
NY...Dense Fog Advisory until 8 AM EDT this morning for NYZ079-081.
NJ...None.
MARINE...Dense Fog Advisory until 10 AM EDT this morning for ANZ330-335-
     338-340-345-350-353-355.
     Small Craft Advisory for hazardous seas until 6 AM EDT Friday
     for ANZ350-353-355.

&&

$$

SYNOPSIS...Goodman/JM
NEAR TERM...JM/DW
SHORT TERM...JM
LONG TERM...Goodman
AVIATION...Maloit
MARINE...Goodman/JM
HYDROLOGY...Goodman/JM
TIDES/COASTAL FLOODING...



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