Area Forecast Discussion
Issued by NWS Upton, NY-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KOKX 271906
Area Forecast Discussion
National Weather Service New York NY
306 PM EDT Tue Sep 27 2016
A weakening cold front offshore going into tonight will slowly
move farther offshore. This boundary remains southeast of Long
Island during Wednesday and Wednesday night while weak high
pressure builds in from the Canadian Maritimes. However there will
be an approaching area of low pressure along with a warm front by
Wednesday night. This low pressure over the Ohio Valley and Mid
Atlantic states will meander about this region into the weekend
bringing an extended period of unsettled weather. The low will
gradually lift through New England early next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Any showers remain southeast of Long Island with the weakening
cold front and will diminish altogether by late this afternoon.
The front further weakens this afternoon as it remains southeast
of Long Island. Winds at the surface will be light out of a
general southwest direction.
The forecast is generally on track this afternoon with dry
conditions still anticipated. Clouds are thinning out from NW to
SE going into the afternoon as drier air works in with the more
High temperatures will be near normal but perhaps slightly above
normal for the western half of the CWA with more sun.
There is a moderate risk of rip current development at the ocean
beaches for today.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
The weather will become more unsettled during this timeframe.
Starting aloft with tonight, there will be some ridging taking
place across the region. This will allow for subsidence. The
local region will actually be between a large cutoff upper level
low in the Ohio Valley and an elongating upper level trough in
the Canadian Maritimes as it becomes more of an open wave.
At the surface, the front will further weaken and move farther
offshore as high pressure builds into the Canadian Maritimes.
Mainly dry conditions should prevail but there could be a few
showers southeast of Long Island, closer to the lingering frontal
Lows were taken from the ECS guidance which was relatively warmer
and exhibited less spatial range between temperatures.
For Wednesday through Wednesday Night, the region will remain
between a southward shifting large cutoff upper level low going
towards the Tennessee Valley and the upper level shortwave in the
Canadian Maritimes. There will be continued ridging between the
two upper level features. However, at the surface, the center of
high pressure remains strong and centered more towards Southeast
Canada. There will be a low pressure area well southwest of the
region that will be approaching. There is evident too from the
model MSLP fields an inverted trough that will be approaching
ahead of the surface low. Aloft, there will be increasing
isentropic lift especially Wednesday afternoon through Wednesday
night. This goes along with the SW flow in the mid to upper levels
setting up warm air advection aloft.
At the surface, a persistent pattern with high pressure in Southeast
Canada and the local region being on the SW periphery of this
high. This will give the region increasing NE flow and with the
high being strong centered in the Canadian Maritimes, a steep
pressure gradient will setup, resulting in winds becoming gusty.
Model precipitation fields are showing some very light
precipitation amounts across the region Wednesday and increasing
towards the western portions of the region Wednesday night. This
all conveys here a situation with moisture getting trapped under
an inversion. This low level moisture will increase Wednesday and
eventually materialize as drizzle or light rain to start with a
higher chance of rain Wednesday night when it will increase in
intensity, coverage, and become more steady. At that time, the
atmospheric column becomes more moist as well.
Regarding temperatures Wednesday, used the ECS guidance and
slightly adjusted downward. NE flow and increasing clouds points
to a cooler than normal day on average out east while farther west
highs are forecast to be near normal. Wednesday night features
lows from a MAV/MET blend with again not much of a spatial range,
mostly mid 50s to near 60 across the area.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
NWP guidance and ensembles are in good agreement with the overall
H5 pattern across North America through the first half of the
weekend...then solutions begin to diverge with the next
trough/cutoff low entering the PacNW although this should not
impact the local area until early next week.
The long term period starts with cutoff low pres over the Ohio
Valley trapped between ridging to the east and west. This will
result in the system meandering about this area into the weekend
before the ridge to the east finally begins to break down allowing
it to track through the eastern Great Lakes and New England early
next week. Confidence decreases in the finer details...although a
frontal boundary extending from the sfc low in combination with
strengthening isentropic lift will result in much needed overrunning
rainfall Wed night into Fri morning. While the periods of heavier
rainfall remain uncertain there is a signal that Thu night could
be one timeframe where heavier pcpn does occur with mid level vort
energy passing through.
Unsettled pattern will continue into the weekend with abundant
cloud cover and perhaps a transition to more showery pcpn with mid
level ridging trying to build in from the east. Moisture transport
will still be originating from the Gulf of Mexico under this
pattern. Warm front may push through on Sun as the system begins
to lift through the Great Lakes. This will also push the heaviest
rainfall to the north as well...resulting in decreasing PoPs
The EC remains the western outlier...hanging tough with this soln
for the past 3 runs...although it has moved somewhat closer to
consensus. Based on the location of the system...heaviest rainfall
is expected to fall west of the area. See hydro section for more
information on expected totals locally.
Removed thunder as the lower heights associated with the deep low
are too far west...thus it remains too warm aloft for any elevated
.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
VFR at most terminals but pockets of MVFR remain especially KISP
and KGON. Little change is expected the remainder of this
afternoon but continued improvement expected from west to east.
Light wind mainly W 10 kt or less this afternoon may briefly become
S-SW around city terminals. Winds become light and variable this
evening before becoming NE around 5 kt early Wednesday morning. By
midday...ne winds increase to near 15 kt and become gusty at times
near 20-25 kt.
...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: Amendments possible to adjust wind direction
KLGA TAF Comments: Amendments possible to adjust wind direction
KEWR TAF Comments: Amendments possible to adjust wind direction
KTEB TAF Comments: Amendments possible to adjust wind direction
KHPN TAF Comments: Amendments possible to adjust wind direction
KISP TAF Comments: Amendments possible to adjust wind direction
.Outlook for 18Z Wednesday through Saturday...
.WED...Becoming MVFR late morning/early afternoon. NE gusts to 25 kt
possible in the afternoon.
.THU-SAT...IFR/MVFR in showers. NE winds 15-20 kt with gusts
25-30 kt possible THU-FRI.
.SUN...Mainly VFR but MVFR possible with a chance of showers. N winds
Sub SCA initially but with a weak wind field, there will not be
much to resist incoming swells from the south. Thinking there will
be some higher seas eventually getting back into the ocean zones
that may meet SCA criteria tonight with otherwise sub SCA
conditions across all other waters. Then Wednesday into Wednesday
Night, SCA looks more probable across all waters with ocean having
a higher probability of both winds and seas getting to SCA levels.
There will be a tight pressure gradient setting up between a
Southeast Canada high and low pressure southwest of the region.
The rough conditions continue into at least Thu night due to a
tight pres gradient across the waters. There still remains a low
probability of marginal gale force gusts during this time...thus
will continue the mention in the HWO. It may only be confined to
the ocean waters however. The GFS is indicating gusts into the
40`s but feel this is overdone. NAM looks more reasonable...but
perhaps a tad light. Have used a compromise of the 2 weighted more
towards the NAM.
Winds subside on Fri as the gradient weakens...although seas on
the ocean will remain elevated...possibly into Sat.
Dry weather expected through tonight and any rain Wednesday
through Wednesday night will be light with rainfall totals less
than a quarter of an inch.
The proximity of a low pressure system late in the week looks to
be too far west at the current time for the local area to fall in
the axis of heaviest QPF. Currently between 1/2 and 1 1/2 inches of
rainfall is forecast between Wed night through Sat. This is not
expected to cause any hydrologic impacts.
A persistent moderate easterly flow during mid to late week may
combine with increasing astronomical high tides associated with
the new moon on Friday to cause minor to locally moderate coastal
flooding late this week.