Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 251510

Area Forecast Discussion
National Weather Service New York NY
1010 AM EST Sun Feb 25 2018

A frontal system will move across the region today. High
pressure builds in from the west tonight and remains in control
through the middle of the week. A strong low pressure system
will likely affect the region for the end of the week.


Minor changes made this morning with the forecast mainly on
track. Phased sub-tropical and Pac jet energy will strengthen
through the Great Lakes into NE US this morning, with a strong
mid-level shortwave tracking NE from the Great Lakes and closing
off as it approaches James Bay. At the surface, strengthening
low pressure will take a similar track today, eventually
stacking under closing upper energy near James Bay late today.
Its trailing cold front will approach through this afternoon
with its warm front INVOF DelMarVa this morning, lifting
towards the region. Good model agreement on a wave of low
pressure developing along the warm front and tracking south of
NYC/LI this afternoon.

Moderate to locally heavy rain will continue to move across the
entire region this morning as warm conveyor belt and divergent upper
flow transport and lift a +3-4 std PW airmass into the region.

Rain and drizzle should taper off from w to e this afternoon with
low pressure and weak cold/occluded front pushing east. In its wake,
could be dealing with fog development, locally dense, for late
afternoon/evening with light winds and abundant moisture.

High temperatures will be mainly in the 40s. SE LI could flirt with
50 degrees if warm front can lift north.


Closed upper low over James Bay tonight slides east through Northern
Quebec Monday, with its associated trough axis approaching the
region through Monday. This will maintain a deep SW upper flow
over the region.

At the surface, low pressure moves offshore this evening with PAC
high building into the region from the west through Monday. This
should keep a southern low suppressed well south of the region
for Monday.

Stratus and fog likely this evening with light winds and
remnant moisture. Weak caa overnight should help in eroding
stratus, but patchy fog could linger until daybreak.

Fair and unseasonably mild conditions likely on Monday (10 to 15
degrees above normal), with an initially mild airmass in place and
only weak caa flow. Highs well into the 50s would be likely along
the coastal plain, near 60 NYC/NJ metro, based on current model
agreement for deep mixing and downslope flow.


The region remains on the top side of a deep layered ridge centered
over the N Caribbean Monday night-Wednesday night.
Associated subsidence should keep things dry, with minimal cloud
cover. The exception on cloud cover is on Wednesday and Wednesday
night, where should see a gradual increase in high then mid clouds
ahead of the next system, which tracks into the mid Mississippi
River Valley by Thursday morning. Temperatures Monday night through
Wednesday night will run several degrees above normal.

The models are in good agreement that the deep layered ridge axis
slides to the east on Thursday allowing a cutoff low to track into
the Great Lakes Thursday then into the northeastern States Thursday
night and Friday. The models then differ on how fast this cutoff low
exits to the east for the remainder of the week. This will
ultimately be dependent on the location/strength of blocking
downstream over the N Atlantic. As a result, while there is good
agreement that rain develops over the area by late Thursday, there
is not good agreement over when the precipitation ends (solutions
vary from Friday night through late Saturday at this point). There
also is not good agreement over how much, if any, wintry
precipitation the area sees with this system, with the best chance
over interior areas to the N/W of NYC and Long Island Sound.

In terms of sensible weather expect rain to develop from SW to NE
Thursday and continue through Friday, before tapering Saturday. Some
wintry mix possible over N/NW zones depending on evolution of this
system and with limited cold air to work with. Refer to the
hydrology and coastal flooding sections of the AFD for further
details on possible impacts from this storm.


A warm front will approach from the south today, followed by a
cold front tonight. Expect mainly IFR conditions to continue,
although locally conditions could occasionally be either LIFR or
MVFR. E winds gusting to 25-30 kt expected this morning along
the coast. Expecting also some marginal low level wind shear
1.5-2 kft of 100-120 degree 35-40kt flow through early
afternoon, mainly east of the city terminals.

After rain tapers off mid to late afternoon, areas of fog with
IFR conds should develop as winds lighten, and continue into at
least the first half of tonight. Conds should improve later
tonight with passage of the cold front. Exact timing is
uncertain, and the fog could even linger until past the end of
the TAF period especially out east.

.Monday through Wednesday...Chance of residual low clouds/fog
early Mon morning, otherwise VFR.
.Thursday...Rain likely with MVFR or IFR flight cat. E winds
G30kt and LLWS.


Widespread SCA conditions this morning, with brief period of
Gales developing on the eastern ocean waters. Ocean seas
expected to build to 6 to 9 ft, and 3 to 5 ft on LI Sound.

Winds subside below SCA this afternoon into evening from w to e as
easterly LLJ moves east. A period of SW gusts to 20 kt possible this
afternoon across eastern ocean waters in wake of low pressure. Winds
weaken further tonight into Monday with high pressure building in,
but SCA ocean seas will likely take till Monday morning to subside.

Sub SCA conds through midweek thereafter with high pressure moving
across the waters.

Next chance for SCA/Gale conditions will be with a potential strong
low pressure system Thursday through Sat.


Between 1/2 and 3/4 inch of rain has fallen across the region
as of 6am, with an additional rainfall of 1/2 to 3/4 inch
expected through the afternoon. There could be locally higher
amounts, especially in any areas of orographic lift with the
higher terrain. With saturated grounds, minor poor drainage
flooding is possible today. With 6hr FFG around one inch across
the fast reacting NE NJ small stream basins, there is a low prob
of localized minor flooding impacts.

It will be dry From Monday through Wednesday night, with no
significant hydrologic impacts expected.

There is the potential for a heavy rainfall (2 or more inches) from
late Thursday into Saturday. At this time it is too early to specify
exact impacts, but potential for minor flooding urban, poor drainage
and small stream flood impacts are possible.


A strong coastal low could be off the Mid Atlantic coast to the
SE of Long Island from Thu into the weekend, producing a
prolonged period of moderate to strong E-NE flow over the
region. With only around 1 ft surge needed for minor flooding
and 2 1/2 ft for moderate, there is the potential for minor to
moderate coastal flooding and beach erosion from late Thursday
into the weekend.

Monitor subsequent forecasts as the potential coastal impacts
will become better resolved with time.


NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the
air for an extended period of time.


MARINE...Small Craft Advisory until 2 PM EST this afternoon for ANZ335-
     Small Craft Advisory until 6 PM EST this evening for ANZ330-
     Gale Warning until 2 PM EST this afternoon for ANZ350-353.
     Small Craft Advisory until 7 AM EST Monday for ANZ355.


LONG TERM...Maloit
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