190
FXUS61 KOKX 220432
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
1132 PM EST Thu Nov 21 2024
.SYNOPSIS...
Low pressure retrogrades northwestward over the area tonight and
will linger nearby through Friday night. The surface low heads
into eastern Canada by Saturday afternoon as high pressure builds
in from the west Sunday and Monday. A fast moving, weaker low
pressure system then skirts to the north of the area late Monday
into Tuesday, before high pressure briefly builds back in on
Wednesday. Another low pressure system then potentially impacts
the area on Thursday.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --
The forecast remains on track with this update. Rain has
overspread pretty much the entire forecast region and become
moderate to locally heavy. Radar reflectivity has become more
whole indicating a widespread stratiform rain. Meanwhile, for
parts of interior NE NJ and Lower Hudson Valley, rain and snow
mix and some locations with pure snow have been reported.
Temperatures were slightly adjusted colder for parts of NE NJ.
POPs adjusted higher. Otherwise forecast mainly on track.
Low pressure deepening near the 40/70 benchmark just offshore
as an upper level low approaches from the west. The low will
continue to deepen tonight and track northwestward likely from
central Suffolk County up through southwestern CT and just north
of Putnam and Orange Counties. Light to moderate rain continues,
but as cold air gets wrapped into the area a changeover to a
rain/snow mix or all snow is expected for portions of northeast
NJ, the Lower Hudson Valley and southwest CT.
The Winter Weather Advisory remains in effect for western
Passaic and most of the Lower Hudson Valley. All global guidance
is showing a QPF max just southwest of the center of the low
and aligned with strong frontogenetic forcing as it passes
through. There are also hints of banding from the latest CAM
models. The thinking is there will be enough cold air wrapped in
for some of this moderate to heavy precipitation to fall as
snow for the Advisory areas. Although ground temps will be very
marginal (32 to 35 degrees), model soundings support snow, with
only a very shallow layer just above the surface being above
freezing. Tricky accumulation forecast given the marginal ground
temps, low SLRs (under 8:1), and also the uncertainty of the
intensity of snowfall. There is really only a 2-4 hours period
overnight sometime between 04z and 10z where moderate to heavy
snow is possible. The thinking is the higher elevations (above
500 feet) across the Advisory areas will see the most
accumulation, mainly 2-4 inches. Less confidence in lower
elevation areas where amounts could end up short of 3 inches and
be more widespread 1-2. Went with the Advisory given the
potential for brief heavy wet snow and the fact that it is the
first snowfall of the season and could produce hazardous travel
in the heaviest rates. Snowfall rates in heaviest banding could
reach .5 to 1 inches per hour.
Further east, over Long Island and southern CT, any heavy precip
will likely fall as rain. No flooding is expected. See Hydrology
section below.-- End Changed Discussion --
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
The upper-low to our west captures the surface low on Friday morning
leading to a stacked low that moves into central and eastern PA. The
stacked low then pushes back east and over our area Friday
afternoon. Skies remain cloudy with rain continuing through the day,
with some breaks. Snow or a rain snow mix is possible again Friday
night, but no accumulation is expected.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
**Key Points**
* Gusty NW flow and near normal temperatures behind the departing
storm system this weekend.
* A weak frontal system moves through late Monday into Tuesday.
Another area of low pressure potentially nears the region on
Thanksgiving.
The NBM was followed closely for this update with some lowering of
PoPs for Thanksgiving morning and afternoon based on the 12Z GEFS.
Potent upper low continues to pull away from the local area Saturday
with a midlevel shortwave on its heels into Sunday. Mid and upper
ridging then builds in from the Central Plains through Monday with
another upper low ejecting out of the Central Plains midweek.
At the surface, the pressure gradient begins to relax late Saturday
into Sunday AM as the surface low heads northeast. Saturday in
particular looks to remain blustery, with temperatures in the
mid 40s and northwest winds gusting 25-30mph. Any lingering
cloud cover and AM showers, especially for eastern LI and CT,
should depart by midday. Sunday and Monday look dry and more
seasonable temperature- wise, in the upper 40s to low 50s.
Precipitation chances, rain at this point, looks to enter the
picture late Monday into Tuesday as a weak low pressure system
and associated fronts traverse New England. With increased
southwest flow on Tuesday, highs may be a bit above seasonable,
with upper 50s for most. After a dry and cooler day Wednesday a
more organized low pressure system approaches the area on
Thanksgiving from the southwest. Too early for sensible weather
specifics this far out with timing and strength differences,
with GEFS sfc low positioning anywhere from the Gulf coast to
eastern PA.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Low pressure strengthens as it passes north and eventually west of
the region through the TAF period.
Rain this evening will begin to become more intermittent from SE to
NW overnight into Friday. KHPN and KSWF likely maintaining rain
and for this rain to eventually mix with snow overnight into
Friday. KSWF going to pure snow for some time early Friday.
After a lull in the rain, rain returns late Friday through rest
of TAF period for all terminals.
IFR to MVFR forecast during the TAF period. Individual terminals
will likely have some variance between categories within the TAF
period. KSWF all IFR forecast with some LIFR forecast especially
during the pure snow with brief heavy snow potential there.
Only terminals with measurable snow in the forecast are KSWF
and KHPN. KSWF snow accumulation forecast of 1 to 2 inches snow
by early Friday afternoon. KHPN snow accumulation forecast of
near 0.5 inch by early Friday afternoon.
Winds will be more easterly initially for KISP and KGON and more
westerly for other terminals. All wind directions become more W to
SW late tonight through much of Friday. Wind directions become more
S-SE late Friday with more variability Friday night.
Wind speeds will be near 10-15 kt during much of the TAF period.
Gusts during much of the TAF period near 20-25 kt. These gusts
could be intermittent at times. Peak gusts to near 30 kt
possible at times tonight into early Friday.
...NY Metro (KEWR/KLGA/KJFK/KTEB)TAF Uncertainty...
Amendments expected for changing flight categories through the
TAF period.
Amendments likely for timing of wind shifts and wind gusts.
Additional amendments likely tonight due to timing of heavier
precipitation and turnover to mixed precipitation north and west of
city terminals.
OUTLOOK FOR 00Z FRIDAY THROUGH TUESDAY...
Friday night...Mainly MVFR with intermittent rain. Wet snow may
mix in N and W of the NYC metro. S-SW gusts 15-20kt possible
early. Winds becoming variable direction and light, under 10
kts, before becoming more NW late near 10 kt gusting to near 15-20
kt.
Saturday...MVFR possible. WNW winds gusting 20-30kt.
Sunday...VFR. WNW winds gusting to 20-30kt.
Monday...VFR.
Tuesday....MVFR with a chance of -SHRA.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
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Gale Warning remains in effect for the ocean waters as there
will likely be a period of 35 knot gusts tonight. A Small Craft
Advisory remains in effect elsewhere for 25 to 30 knot wind
gusts. Seas build on the ocean and likely peak around 10 ft late
tonight before lowering again. Winds fall below SCA criteria by
Friday afternoon. Seas remain elevated over the ocean waters so
a SCA will be needed once the Gale Warning is canceled or
expired.
Winds and waves remain elevated across the ocean waters Saturday
into Sunday. SCA seas are likely, with the potential for near Gale
force gusts Saturday through Sunday morning. Thereafter, high
pressure builds in from the west with decreasing winds and seas into
Monday.-- End Changed Discussion --
&&
.HYDROLOGY...
Additional liquid amounts of 1 to 1.5 inches can be expected. The
bulk of that will fall through early Friday morning, with the Lower
Hudson Valley and southwest CT seeing the higher end of totals.
There will likely be a period of moderate to locally heavy
precipitation overnight mainly across central Long Island and up
into the Lower Hudson Valley and southwest CT. There could be minor
flooding associated with clogged drains. Otherwise, no hydrologic
impacts are expected through the end of next week.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Weather Advisory until 10 AM EST Friday for NYZ067>070.
NJ...Winter Weather Advisory until 10 AM EST Friday for NJZ002.
MARINE...Small Craft Advisory until 1 PM EST Friday for ANZ331-332-335-
338-340-345.
Gale Warning until 6 AM EST Friday for ANZ350-353-355.
&&
$$
SYNOPSIS...DBR/JT
NEAR TERM...JM/DBR/JT
SHORT TERM...JT
LONG TERM...DBR
AVIATION...JM
MARINE...DBR/JT
HYDROLOGY...DBR/JT