okx-afd on 2025-01-19

401
FXUS61 KOKX 192112
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
412 PM EST Sun Jan 19 2025

.SYNOPSIS...
-- Changed Discussion --Deepening low pressure off the Mid Atlantic coast will quickly
pass to the east of the area tonight and up into the Canadian
Maritimes by daybreak Monday. An arctic airmass will then build
in through mid week with high pressure building in from the west.
High pressure moves overhead Wednesday night into Thursday and
then offshore thereafter. A frontal system passes offshore Friday
before another high builds in from the west for next weekend.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Steadiest precipitation remains north and west of the NYC metro
in association with the upper trough. This will begin to expand
east over the next couple of hours across NYC, LI, and CT as
low pressure continues to deepen off the Mid Atlantic. The
latter of which will pass quickly to the east this evening and
up into the Canadian Maritimes by daybreak Monday. Much of the
area will see about a 6-8hr window of mainly snow, with 2 to 4
hours of it possibly falling in the moderate to occasionally
heavy intensity. 12Z HREF has 50 to 80 percent probabilities of
inch per hour rates this evening, but only for an hour or two.
Also, portions of eastern LI will initially mix with rain at the
start. The key to snowfall amounts will be how quickly temperatures
drop as a strengthening northerly flow draws colder air down
into the region. This will especially be critical along the
coast where temperatures topped out around 40 this afternoon.
Liquid equivalent amounts on average area expected to range from
0.4 to 0.5" with some localized enhancements. Ratios will vary
quite a bit at the start with temperatures in 30s, but at some
point should get into the 15-10:1 range as temperatures fall.
Expect snowfall amounts of 3 to 5 inches along the coast and 5
to 7 inches across the interior. This is slight adjustment down
(1/2-1"). Thus, no changes are planned to the hazards at this
time. The snow will become light and end around midnight for NYC
and points north and west and 3 to 4 am far eastern areas.

Temperatures will tumble into the upper teens to around 20 by
daybreak with N-NW winds gusting 20 to 25 mph, possibly up to
30 mph. Wind Chill values fall into the single digits overnight
and possibly as low as zero for the interior. These values fall
short of Cold Weather Advisory (-5F at the coast and -10F
inland).

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
-- Changed Discussion --Low pressure strengthens as it moves northeast into the Canadian
Maritimes with strong high pressure moving in from the west. This
tight pressure gradient will keep a gusty westerly flow, with cold
aid advection increasing.

Weather will be dry and very cold. Temperatures expected to be well
below normal.

Arctic airmass encompasses the area with NW winds ushering in colder
air. There will be strong cold air advection. Any leftover snowmelt
will refreeze and lead to slippery conditions for any untreated
surfaces. Temperatures forecast in single digits to lower teens
for morning with wind chills several degrees colder. Max temperatures
forecast only in the low to upper 20s. Went below MOS for the
high temperatures. With gusty westerly flow continuing, wind
chills will be at most, mainly within the lower teens on Monday.

For Monday night, the cold air advection continues. The westerly
gusty flow continues as well. Forecast lows are in the single digits
to lower teens for much of the area. The minimum wind chills are
mostly below zero with some locations near -5 to -10 degrees
towards early Tuesday morning.-- End Changed Discussion --

.LONG TERM /TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --Main upper jet remains south of the region Tuesday through Friday,
with then a return to more zonal flow. Main trough in mid levels
remains over the Northeast Tuesday into Wednesday and then another
trough develops, moves in latter half of the week but more zonal for
next weekend.

Looks like the core of this arctic airmass will be across the local
region Tuesday through Wednesday. Strong high pressure will continue
to slowly build in from the west and move overhead Wednesday night
into Thursday. Gusty westerly flow Tuesday will subside Tuesday
night into Wednesday. Winds become nearly calm Wednesday night and
change direction to more SW.

Forecast highs are only in the teens Tuesday and get closer to 20
for Wednesday. Max wind chills Tuesday mostly in single digits and
then more in the teens for Wednesday. Lows Tuesday night mostly in
the single digits and then for Wednesday night interior is mostly in
single digits with coast mostly near 10. Minimum wind chills Tuesday
night below zero for most areas, and a greater fraction getting near
-5 to -10 degrees, locally near -15 degrees for isolated locations.

Low pressure system passes offshore Thursday night and then farther
out into the Atlantic Friday into next weekend. There could be some
snow across far southeastern sections of the region, just a slight
chance, with otherwise dry conditions continuing.

Across the local area, another high pressure area builds in from the
west for Friday into next weekend. Mainly dry weather conditions are
expected.

The airmass is forecast to moderate Thursday and thereafter into
next weekend. High temperatures forecast return to mostly mid to
upper 20s much of the area Thursday, but southeast sections lower
30s. Then forecast highs Friday lower 30s areawide and then rising
more within the 30s for next weekend.-- End Changed Discussion --

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
Low pressure develops along the Mid Atlantic coast, passing
southeast of the area tonight.

MVFR/VFR to start then conditions lower to IFR/LIFR in snow
late this afternoon and evening. The snow tapers off 03-06Z,
with VFR thereafter.

Winds veer to the N then NE today with speeds generally 10-12kt.
Winds become NW after 22-00Z. Gusts are expected tonight and
Monday with gusts in the lower and middle 20kt range.

Expected Snowfall Accumulations:

NYC terminals, BDR, ISP: 4-6" HPN: 4-8" SWF: 5-8"

...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Amendments possible for the timing on snow this
afternoon/evening. Occasional gusts possible late this
afternoon/evening and after midnight.

.OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY...

Monday afternoon: VFR. NW wind gusts 20-25 kt.

Tuesday: VFR. W wind gusts around 20 kt.

Wednesday: Chance of MVFR or lower in -SN, particularly coastal
terminals.

Thursday: VFR.

Friday: Mainly VFR, Chance of MVFR in light snow.

Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90

.MARINE...
-- Changed Discussion --Deepening low pressure passes to the east of the waters this
evening and then up into the Canadian Maritimes by daybreak.
Arctic high pressure will begin to build in from west. This will
is a strong N/NW flow overnight with gusts on all waters
25-30kt in Monday.

SCA conditions continue on the ocean Monday night. Wind gusts
will be marginal for SCA for non-ocean marine zones Monday
night. Some lingering SCA conditions possible on the ocean
Tuesday with otherwise mainly sub-SCA conditions Tuesday onward
through Friday. Some potential SCA gusts on the ocean Tuesday
night and Friday night.

Freezing spray potential for some of the waters Monday through
Monday night.-- End Changed Discussion --

.HYDROLOGY...
No hydrologic issues are anticipated through Saturday.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...Winter Storm Warning until 4 AM EST Monday for CTZ005>008.
Winter Weather Advisory until 4 AM EST Monday for CTZ009>012.
NY...Winter Storm Warning until 4 AM EST Monday for NYZ067>070.
Winter Weather Advisory until 4 AM EST Monday for NYZ071>075-
078>081-176>179.
NJ...Winter Storm Warning until 4 AM EST Monday for NJZ002-004-
103>105-107.
Winter Weather Advisory until 4 AM EST Monday for NJZ006-106-
108.
MARINE...Small Craft Advisory until 6 PM EST Monday for ANZ331-332-335-
338-340-345.
Small Craft Advisory until 7 AM EST Tuesday for ANZ350-353.
Small Craft Advisory until 7 AM EST Tuesday for ANZ355.-- End Changed Discussion --

SYNOPSIS...DW
NEAR TERM...DW
SHORT TERM...JM/DW
LONG TERM...JMC/JM
AVIATION...BC
MARINE...JM/DW
HYDROLOGY...JM/DW