Area Forecast Discussion
Issued by NWS Upton, NY-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KOKX 240231
Area Forecast Discussion
National Weather Service New York NY
1031 PM EDT Thu Mar 23 2017
A warm front approaches tonight and moves across the region on
Friday. An unsettled weather pattern then sets up this weekend
and continues into the middle of next week. A back door cold
front moves through Saturday afternoon and night. Low pressure
gradually approaches from the west Sunday, and moves across on
Monday. Another frontal system may impact the region Tuesday
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --With the surface ridge axis moving across the area late this
evening, winds at the coast have either become SW or light and
variable. This has resulted in significant differences in
temperatures, due to radiational cooling, and dew points in a
matter of hours have risen from zero into the lower 20s at some
locations. As the southerly flow gradually increase late
tonight, the airmass will become more homogeneous with temperatures
leveling off or even rising.
Clear to start, then clouds begin to increase late at night
ahead of an approaching warm front. Models agree that it remains
dry through the night. Clouds arrive too late to make much of
an impact on low temperatures, which will be below normal.
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.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Isentropic lift and low-mid level shortwave energy pass through
along with the surface warm front during Friday morning. The best
combination of moisture and lift will be north and west of the city.
It will then be dry by mid afternoon across the CWA. Have scaled
back on PoPs somewhat from the previous forecast, but did not have
enough confidence to drop it below likely over the far NW zones.
Regarding PCPN types, expecting a short period of mixed PCPN before
changing to plain rain as temps aloft warm up quickly. For the NW
zones this mix starts out as mostly snow, and near the coast there
could be a brief rain/sleet mix at the onset before changing to all
rain. There is the potential of up to an inch of snow/sleet
accumulation NW of the city before the changeover. There is also the
chance that there`s freezing rain in the mix for a couple of hours
for Orange and Putnam Counties and areas right near their borders.
Thinking is that the changeover to plain rain will be too quick for
a widespread freezing rain event, especially without an ideal
cold air damming setup. Will therefore not issue any advisories
at this time. High temperatures will be a little below normal.
Dry during the nighttime with the warm front still to the north.
This plus mostly cloudy conditions will lead to above normal
low temperatures Friday night.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Unsettled weather pattern sets up across the region through the long
On Saturday, a split flow jet stream with polar jet running across
the New England southern Canada border and southern stream cut-off
across the south central United States. Weak ridging attempts to set
up between these two streams. Surface high pressure across the
western Atlantic pumps unseasonably warm air into the area under
southwesterly flow. At the same time, a back door front will
gradually sink south from New England. Deterministic models and
ensembles all indicate strong high pressure pushing south out of
southeast Canada, forcing the boundary south through the day on
Saturday. The main question is with the timing. The ECMWF, NAM, and
NAM-3km all bring the boundary south of Long Island by early
afternoon. The GFS and CMC are a bit slower, bringing the boundary
south by early evening. There is notable spread in the 15z SREF as
The timing of the back door front will have be important with
regards to temperatures. The slower timing will allow temperatures
to warm well into the 50s, and possibly lower 60s.
Faster timing will hold highs down, more in the 40s and 50s.
Spread in the 15z SREF at BDR for high temperatures ranges from 44
to 60 degrees. Have generally sided with a consensus for this
forecast, with the boundary moving south in the afternoon, allowing
temperatures to warm into the middle and upper 50s.
Upper level cutoff low opens Sunday night into Monday as the
remaining shortwave passes near or just to our north. PoPs increase
to likely this period with rain. Parent low will likely pass to the
north, with possible secondary development along nearly stationary
front near or just south of Long Island. High temperatures will
ultimately be determined by where this boundary sets up. Current
forecast shows readings in the 50s near the coast, and upper 40s
Shortwave passes east Monday night followed by weak ridging aloft.
Progressive flow pattern leads to the continuation of unsettled
conditions with models and ensembles signaling another frontal
system approaching Tuesday, passing Tuesday night into Wednesday.
Continued chances for rain and near seasonable temperatures are
forecast. High pressure should follow for next Thursday.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --High pressure slides offshore tonight. A warm front them lifts
to the north from Friday morning into Friday afternoon.
VFR through the TAF period. There is the potential for some
light precipitation on Friday morning. At this time confidence
high enough for prevailing at KHPN and KSWF which should see a
wintry mix, with KSWF also seeing MVFR cigs. Any accumulation
at those two terminals should be less than 1 inch. Elsewhere
address with PROB30 - with rain possibly mixed with sleet at
Winds have turned southerly at KJFK, and should do the same
earlier at KLGA/KISP as well. Otherwise winds should become
light/variable tonight, the increase out of the S-SSW Friday
morning to around or just over 10 kt. Gusts just over 20 kt
likely Fri afternoon at KISP/KGON and possibly elsewhere.
.OUTLOOK FOR 00Z SATURDAY THROUGH MONDAY...
.Friday night-Saturday morning...VFR.
.Saturday afternoon-Monday...MVFR/IFR probable, possibly LIFR.
.Monday night-Tuesday...MVFR or lower possible.
-- End Changed Discussion --
Tranquil conditions on all waters tonight into Friday morning
with a high pressure ridge passing through. Winds and seas then
increase Friday afternoon with the pressure gradient tightening.
Expecting all but NY Harbor to see SCA conds in the afternoon,
with advisory conds continuing into the night for the ocean,
Eastern Sound and Eastern Bays.
Lingering seas around 5 ft are possible east of Moriches inlet
Saturday morning. Otherwise, winds and seas are expected to be below
SCA levels on Saturday. Increasing easterly flow Saturday night into
Sunday brings wind gusts near 25 kt on the ocean, with ocean seas
approaching 5 ft. SCA winds are possible on LI Sound, LI Bays, and
The pressure gradient weakens Sunday night into Monday. Sub-SCA
conditions are forecast on all waters through Monday night. The
approach of a frontal system may build seas around 5 ft Tuesday
Unsettled weather this weekend into early next week may result in an
inch or more of precipitation. However, this would occur over a
prolonged period, so no hydrologic concerns are anticipated. Snow
melt across interior sections continues at a slow rate with a more
significant snow melt on Saturday as temperatures rise to above
MARINE...Small Craft Advisory from 10 AM Friday to midnight EDT Friday
night for ANZ330-340.
Small Craft Advisory from noon to 6 PM EDT Friday for ANZ335-
Small Craft Advisory from 10 AM Friday to 6 AM EDT Saturday