848
FXUS61 KOKX 201535
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
1035 AM EST Fri Dec 20 2024
.SYNOPSIS...
A coastal low and a clipper system approach the area today and
move by tonight. High pressure builds in from the west late
Saturday through early next week. A weak frontal system then
approaches move through the area Monday night into Tuesday. High
pressure builds back into the area for the middle the week.
&&
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
12z guidance has come in with the track of the offshore low a
bit closer to the coast and also some of the high res guidance
has been more expansive with the precipitation shield over the
area. No major changes to the forecast are needed at the moment,
but this trend will be monitored. It is also worth noting that high
res total snow depth products are still supporting the current
expected snowfall forecast.
The area remains in between a developing coastal low that is
poised to strengthen and move up the East Coast, but remain well
offshore this afternoon and into tonight and a clipper system
approaching from the west. The clipper system will be absorbed
into the strengthening coastal low and as the energy transfers
to the stronger low, the area may end up being a local minimum
of precipitation, but many complexities in the interaction
between these two lows make this forecast a particularly
uncertain one.
Rain and snow showers associated with the approaching offshore
low can be seen moving westward across the southern half of the
area as lighter returns are moving in from the west associated
with the upper level trough and weakening clipper system.
Updated PoPs to reflect this.
Some hi-res models have hinted at the development of a more
significant band of precipitation over the Lower Hudson Valley
and NE NJ as an inverted trough develops, but inconsistencies
among the extent of coverage and intensity reduce confidence in
the occurrence of this band. That being said, the possibility
of a more extended light to moderate snow or rain/snow mix this
afternoon and this evening over the western CWA can`t be ruled
out and if it does occur, snow totals may be a bit higher than
forecast in these areas.
For the remainder of the area, precipitation should be fairly
light and may become more scattered as the afternoon progresses.
By evening, much of the widespread precipitation shield from
the coastal low should be out of the area, but some mid-level
energy passing through the backside of the overhead trough
may result in the development of another more persistent band
of light snow that progresses from west to east. This area of
light snowfall has been consistent among models and will likely
be the best chance for coastal areas to see any snowfall or
minor accumulations of snow overnight and into Saturday
morning.
Overall, snow accumulations of an inch or less are expected with
the exception of portions of the Lower Hudson Valley and higher
elevations of NE NJ where 1-2.5 inches of snow are expected.-- End Changed Discussion --
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
By Saturday morning, any remaining snowfall over the coastal
areas should be largely coming to an end with high pressure
building in from the west. A tight pressure gradient will allow
gusty N/NW flow much of the day with strong CAA of a frigid
airmass expected. High temperatures on Saturday are expected to
be in the low to middle 30s. Gusts on Saturday of 20-25 mph are
possible.
Breezy conditions will continue into Saturday night and early
Sunday with continued advection of the arctic airmass. Lows on
Saturday will be in the teens along the coast with single
digits possible for interior portions of the area. Breezy
conditions may make the wind chill temperatures overnight
Saturday into Sunday morning feel like the low single digits or
near 0. Some interior locations may feel as cold as -5.
Clear skies but cold conditions continue Sunday with high
temperatures only in the 20s for the entire area. Interior
locations may not rise above the low 20s with coastal areas
topping out in the middle to possibly upper 20s. As the day
progresses and high pressure builds in, the pressure gradient
should relax and with it the winds. Sunday night will be colder
in terms of temperature, but a lighter wind should curb the
wind chill a bit more than Saturday night. Lows Sunday night
will be in the single digits for much of the interior areas with
the coastline dropping into the low to middle teens. Wind chill
temperatures should be closer to the actual temperature.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
Key Points:
* Unseasonably cold to start - then a gradual warmup to near normal
temperatures by the middle of next week.
* Potential for a light wintry precipitation event late Monday night
into Tuesday.
There is very good agreement in the global models this period. A
large dome of high pressure from eastern Canada south into the
southeast U.S. will work offshore late Monday as a fast moving area
of low pressure moves into the Great Lakes. The low takes a track to
the north of the area late Monday night into Tuesday, sending a weak
frontal system through the area. Light precipitation is expected at
this time with snow, possibly mixed with rain at the coast. Any
accumulation at this time looks to be minor. High pressure then
returns for the middle of the week. Due to the good agreement of the
00Z guidance and noted trends, stayed dry Wednesday and Thursday.
NBM has an endless period of chance low PoPs during this time.
As for temperatures, the NBM deterministic forecast for much of this
period resides near the 75th percentile. This may be more reflective
of the recent bias calculations. Decided to blend with a model
consensus (CONSALL) which nudges temperatures down slightly from the
NBM. Temperatures on Monday will be about 10 degrees below normal,
but will approach normal values by midweek as air mass having some
Pacific origin move into the area.
&&
.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
High pressure to the north lifts further up into Eastern Canada this
afternoon, while a clipper low moves across the Ohio Valley and
another low deepens off the Mid Atlantic coast. The latter of which
will pass well east of the area tonight and up into the Canadian
maritimes on Saturday.
NE winds have increased, especially for the more eastern terminals
which include KJFK and KLGA this morning to 10-15kt, with some gusts
at or just above 20 kt. These wind speeds and gusts should continue
through the afternoon and into the beginning of the evening push.
Latest amendments account now for wind gusts at the aforementioned
terminals. Winds will then gradually back to the N into tonight,
with G20-25kt developing after 12Z Saturday.
Primarily MVFR conditions going into this afternoon. Chance of IFR
this afternoon with light precipitation. Expect -RA or -RASN or -SN
for the NYC metros, mainly -RA at the eastern terminals with the
chance of -SN mixing in, and -SN at KSWF and KHPN. This looks to be
intermittent for the most part.
Potential for 1-3 inches of snowfall at KSWF through Saturday
morning, with less than inch elsewhere. NYC terminals generally stay
above freezing with runway accumulation unlikely at this time.
...NY Metro (KEWR/KLGA/KJFK/KTEB)TAF Uncertainty...
Amendments likely with lowering flight categories and precipitation
types with regard to -RA versus -SN.
Changeover to all snow late this afternoon into this evening,
earlier further west. Precipitation is expected to intermittent.
Runway accumulation unlikely at this time.
OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
Saturday: Chance of MVFR or IFR in light snow AM, becoming VFR late
morning into the afternoon. NW winds G25-30kt, strongest in the
afternoon/evening.
Sunday: VFR. NW winds G20kt.
Monday: VFR.
Monday Night-Tuesday: Chance of MVFR in light sow or a light
rain/snow mix.
Tuesday: Mainly VFR.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
SCA in effect for ocean waters this afternoon through at least
Saturday night. SCA in effect for Peconic and Gardiners Bay and
the Eastern LIS this afternoon through late tonight.
Weak pressure gradient will keep below SCA conditions across all
forecast waters through this morning. Then, winds and seas will
increase with the approach of coastal low pressure. SCA
conditions expected to develop on the ocean zones this
afternoon and maintain SCA conditions through Saturday. For non-
ocean zones, for Friday afternoon through Friday night, wind
gusts will be marginal for SCA, with more confidence in eastern
waters. Some occasional 25 kt gusts are forecast but most gusts
are expected to be near 20 kt. For Saturday, all waters are
likely to see 25 kt gusts and SCA conditions.
Winds will be slowly diminishing Saturday night through Sunday, but
gusts to 25kt will still be likely on all waters through Saturday
night, and probably continuing on the ocean all the way through
Sunday afternoon.
High pressure builds across the waters on Monday with a weak frontal
system passing through the area late Monday night into Tuesday.
Winds and seas during this time will remain below SCA criteria.
&&
.HYDROLOGY...
There are no hydrologic concerns through the middle of next
week.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ331-332-
335-340-345.
Small Craft Advisory until 6 AM EST Sunday for ANZ350-353-355.-- End Changed Discussion --
&&
$$
SYNOPSIS...DW/MW
NEAR TERM...JT/MW
SHORT TERM...MW
LONG TERM...DW
AVIATION...JE
MARINE...DW/MW
HYDROLOGY...DW/MW