Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 281435 CCA

Area Forecast Discussion...CORRECTED
National Weather Service New York NY
935 AM EST Tue Feb 28 2017

A developing warm front well south of the area today, moves north
tonight. A strong cold front approaches Wednesday and moves
through Wednesday night as associated low pressure moves through
New England. Strengthening low pressure in the Canadian Maritimes
Thursday will be followed by an Alberta Clipper moving across the
local region Friday, moving offshore Friday night. High pressure
builds to the west, then moves over the region Saturday night,
and off the southeastern coast Sunday. Meanwhile for Sunday and
into early next week, low pressure will approach the region from
southeastern Canada.


Updated mainly for the cloud cover across Connecticut and Long
Island this morning in association of a short wave moving
through south of the area. This was producing showers and
isolated thunderstorms over the ocean waters.

Weak ridging aloft slides across the area today behind the
shortwave, another weak shortwave moves through the weak ridge
this afternoon. This along with very weak lift will result in a
slight chance of light rain.

A passing 700-500 hPa shortwave tonight coupled with persistent
moist SW flow aloft and a surface warm front lifting to the N
in response to a 60 kt 950 hPa jet passing just S of Long Island
overnight - should produce a more widespread rainfall tonight,
becoming more spotty after midnight as the low level jet exits
to the east. In addition have the potential for areas of fog
tonight, possibly becoming dense in areas after midnight.


The GFS remains a fast outlier with the 700-500 hPa northern
stream trough and associated sfc-850 hPa cold front
Wednesday/Wednesday night, so a non-GFS blend was generally
followed during this time frame.

Appears there could be a lull in the precipitation Wednesday
morning, then pops increase to likely to categorical across
western zones in response to a pre-frontal trough acting on
moist low level flow. With Showalter Indices below zero for most
if not all the day, have chance of thunder west and slight
chance thunder east (higher chance of thunder west due to more
surface instability).

Still looking at around 500-1000 J/KG of CAPE progged across
NYC/NE NJ/Lower Hudson Valley/SW CT and 60-70 kt of Bulk Shear.
Flow is fairly unidirectional - so would expect convective line
segments to be main mode. With a 70 kt 950 hPa Jet forecast to
track S of Long Island enhancing forcing, have the potential for
Strong to Severe Thunderstorms where surface based - basically
from New Haven County/NYC on west. SPC has most of NE NJ and
Western Portions of the Lower Hudson Valley + Staten Island in a
Slight Risk of Severe Thunderstorms with areas to the east in a
marginal risk. If there is any severe weather, the threat will
be primarily from damaging wind gusts where the storms are
surface based. The timing for any severe threat would be late
afternoon and early evening - right now, due to uncertainty only
have gusty winds with thunder in the forecast from New Haven
County/NYC on east during this time frame.

Wednesday should be very warm, with potential for record highs
with warm surge ahead of cold front. Depending on how fast
things cool off behind cold front, there could be some maximum
minimums set for the day as well (temperature at 1159pm might be
low for the day - especially out west). See the climate section
of the AFD for details.


The upper level jet will be situated south of the region Thursday
through Saturday along with there being a deep upper level trough
within the Northeast. The trough will begin to lift Saturday night
with ridging thereafter going into Monday. The upper level jet will
not be as strong and will be moving across the region and eventually
north of it early next week.

A much colder airmass will be on the way Thursday eventually
entering the region Thursday night and prevailing through Saturday
night. Colder than normal temperatures can be expected with cold air
advection from a gusty NW flow Thursday into Thursday evening. An
Alberta Clipper will be arriving Friday, providing a chance of snow
across the region with a conspicuous wet bulb cooling scenario.
Despite the highs being in the upper 30s to near 40 for locations
towards the coast, the falling snow aloft will cool the column down
to below freezing after a short time. Forecast POPs could go up
with subsequent forecasts as most GEFS members were showing
precipitation across the region on Friday. The liquid equivalent
amounts were mostly less than a quarter of an inch and with
temperatures being above freezing initially, not much in
accumulation is expected at this time, keeping snow generally
less than two inches.

Conditions dry out Friday night into Saturday with another
blast of cold air delivered on another round of gusty NW flow
with an area of high pressure building to the west of the
region. The flow aloft becomes more progressive with ridging
aloft and the airmass will moderate Sunday into Monday. The
winds decrease Saturday night along with continued dry
conditions as the ridge of high pressure moves across. The high
moves off the Southeast coast Sunday and further shifts south

Temperatures will return to being above normal. Concerning
precipitation Sunday into Monday, a low pressure area approaching
from the north and west will bring mainly rain, although north of
NYC there could be some snow as well depending on the timing of the


VFR conditions early this morning as high pressure builds
farther offshore and a warm front approaches from the SW. Have
updated TAFS to reflect prevailing VFR conditions for the late
morning and afternoon. Some periodic MVFR conditions cannot be
ruled out by the early afternoon, but confidence was not high
enough to put in TAFS.

Winds start off light and gradually pick up through the day, but
generally less than 10KT. A strong SW low-level jet approaches late
Tuesday night with low-level wind shear likely at the coastal
terminals with 40-50KT winds at 2000 ft.

The greatest uncertainty is with how quickly cigs lower, eventually
to widespread IFR/LIFR Tuesday evening. Timing could change and
will continue to monitor latest trends.

     NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component forecasts,
can be found at: http:/

KJFK TAF Comments: Timing of IFR conditions low confidence and
may be off by up 2 hrs.

KLGA TAF Comments: Timing of IFR conditions low confidence and may
be off by 2 hrs. Winds may shift to SE +/- 1 hour of forecast.

KEWR TAF Comments: Timing of IFR conditions low confidence and may
be off by 2 hrs.

The afternoon KEWR haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: Timing of IFR conditions low confidence and may
be off by 2 hrs.

KHPN TAF Comments: Timing of IFR conditions low confidence and may
be off by 2 hrs. Winds may shift to SE +/- 1 hour of forecast.

KISP TAF Comments: Timing of IFR conditions low confidence and may
be off by 2 hrs.

Wednesday morning...Areas of fog, then rain. MVFR/IFR and
possibly lower. LLWS possible with SW winds 45-55 kt at 2kft
early. SW winds G15-20KT possible Wednesday morning.
.Wednesday afternoon-Wednesday night...Showers and a chance of
thunderstorms. MVFR or lower possible. SW winds G20-30KT. Winds
become westerly late Wednesday night.
.Thursday...VFR. W-NW winds G25-35KT.
.Friday...MVFR/IFR possible with a chance of light snow. NW
winds G20-25KT.
.Saturday...VFR. NW G20-25KT.


A shortwave passing over the ocean waters this morning was
producing showers and isolated thunderstorms. Updated the
probabilities and weather for this. Otherwise the wind and the
seas forecast remains on track.

A weak pressure gradient force will keep winds well under small
craft advisory levels through this afternoon.

Areas of fog, quite possibly dense, likely will form on the
waters tonight.

Winds increase late tonight as the pressure gradient tightens,
building seas to SCA levels on southern portions of the coastal
ocean waters.

Winds Wednesday/Wednesday night are a bit tricky. While
soundings show limited if any potential for strong winds
(60-70kt) at around 2000 ft to mix down, there is some potential
that sustained winds over the coastal ocean waters could reach
gale levels. For now it appears the most likely outcome is Small
Craft Conditions on all waters, with a small (less than 50
percent) chance of gales.

As a result, have an issued an SCA for the coastal ocean waters
from 3am tonight-6am Thursday and for the remainder of the
coastal ocean waters from 6am Wednesday-6am Thursday.

The ocean seas will stay at minimal SCA levels for much of the long
term period from Thursday through Saturday. The highest of the ocean
seas will be Thursday from leftover swell, with forecast ocean seas
of 8 to 11 ft. Also on Thursday, Central and Eastern Long Island
Sound will build seas to 5 ft from a more gusty westerly fetch
developing. Gales will be possible for all waters, but more probable
for the ocean Thursday. Those winds will decrease Thursday night
initially to SCA levels for the ocean and then below that by
overnight Thursday night. Non-ocean waters will have sub SCA winds
Thursday night. Another round of gales possible for the ocean Friday
through Saturday with SCA winds for non-ocean waters. Winds then
subside below SCA levels Saturday night.


Rainfall from this afternoon through Wednesday night should run
from 1/2 to 3/4 of inch, with locally higher amounts possible.
While the possibility is low, stronger convection could cause
isolated minor flooding of poor drainage/urban areas.

No hydrologic impacts expected from any precipitation late this week
through Monday.

Release from spring snow melt is occurring down the Connecticut
and Housatonic Rivers.


Record highs for Wednesday March 1

Location.......Record High/Year Set.....Forecast High

Central Park............73/1972...............71
J F Kennedy.............58/2004*..............66

* = and in previous years

Record high minimum temperatures for Wednesday March 1

Location....Record High Min/Year Set.....Lowest Temperature during 24 hour day

Central Park............45/2004...............54
J F Kennedy.............42/1974*..............51

* = and in previous years


MARINE...Small Craft Advisory from 6 AM Wednesday to 6 AM EST Thursday
     for ANZ330-335-338-340-345.
     Small Craft Advisory from 3 AM Wednesday to 6 AM EST Thursday
     for ANZ350-353-355.


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