discussion on 2024-01-18

000
FXUS61 KOKX 182039
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
339 PM EST Thu Jan 18 2024

.SYNOPSIS...
-- Changed Discussion --Low pressure develops along the Mid Atlantic coast tonight
and passes well southeast of the area on Friday. Arctic high
pressure then builds in through the weekend, with the center of
the high passing well south for the beginning of next week. A
frontal system may impact the area by the middle of next week.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --An upper level low over the Great Lakes will help send an
amplifying shortwave trough towards the east coast tonight.
This will help spin up a low pressure over the Middle Atlantic,
which quickly shifts well south and east of the area on Friday.

Energy rounding the base of the upper trough will start to
approach tonight, which keep conditions cloudy. A passing snow
flurry is possible this evening, but think conditions will
remain dry through the early morning hours. Lift begins to
increase towards day break, and some locations in NE NJ, and NYC
metro could see a very light snow or few flurries beginning by
6 am. Otherwise, lows will not be as cold as the last few
nights, generally low 20s inland and middle 20s near the coast.-- End Changed Discussion --

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
-- Changed Discussion --The expansive upper low over the Great Lakes and energy around
the base of the trough will help create an inverted trough as
an extension to the surface low well offshore. Model guidance
continues to place this inverted trough to our south, mainly
across central and southern NJ.

The energy rounding the base of the trough should help bring an
area of lift to its north Friday morning. There is also some
support from the region being located nearby to the left exit
region of an upper jet streak to our south. Lift appears to
maximize late morning through middle afternoon, especially for
the southern half of the area. As the offshore low organizes,
the flow will go northerly and help to bring in drier air from
north to south late afternoon through the evening.

Light snow may develop as early as 6am-8am, but should become
steadier through the morning. Impacts to the morning commute
look limited due to the overall light nature of the snowfall
and it could very well end up being flurries. The snow will
become more widespread and steady through middle to late morning
and continue into the afternoon before tapering off in the
early evening hours, 5pm-8pm. Some light snow could linger
across Long Island a few hours longer, but overall the drier air
and limited forcing will help bring an end to the snow.

This will be an all snow event with the main forecast challenge
revolving around amounts. The placement of the inverted trough
to our south favors heavier snowfall occurring south and west
of area. While models have trended south with the higher QPF and
higher snowfall potential, there is still a possibility that
the trough ends up slightly further north (as some guidance
hinted at the last few days). The other concern is it will
likely be snowing for much of the day across NE NJ, NYC metro,
and Long Island and even though it will be light overall,
impacts to the evening commute are very likely. A Winter
Weather Advisory has been issued for NE NJ, NYC Metro, Southern
Westchester, and Long Island from Friday morning into Friday
evening. The concern for slippery travel with the Friday
evening commute supports the issuance of an Advisory, even if
snowfall amounts do not reach 3 inches (Advisory criteria).
Will include mention of potential travel disruptions outside
the Advisory in the HWO.

Snowfall amounts generally 2-3 inches are forecast in the
Advisory area, and 1-2 inches to the north of the Advisory into
the Lower Hudson Valley and SW CT. Amounts may be even lower,
less than an inch across southeast CT given there may be a
battle with subsidence from confluent flow across New England.
This is another area the models have been fluctuating with, but
feel there is a decent chance the subsidence and less favorable
environment for snow will occur across portions of southeastern
CT. If this corridor ends up further south, then snow amounts
will end up lower than forecast.

Thicknesses are much lower than the previous event earlier
this week. The dendritic growth zone is lower in the atmosphere
which coincides with sufficient omega, especially late morning
into the afternoon. This appears to be more favored within the
corridor of the Advisory. The event looks to contain light QPF,
generally around 0.1 to 0.2. Snow to liquid ratios appear to be
relatively high (lighter/fluffier snow) compared to other snow
events typically observed in the area and have gone with a range
of 13:1-15:1.

Temperatures on Friday should remain below freezing and have
gone slightly below guidance given the snowfall. Highs will
reach the upper 20s to around 30 degrees.

The system moves away from the area Friday night, but the upper
low will settle over the northeast. Skies may remain mostly
cloudy for much of the night. N-NW winds will usher in colder
air with lows well into the teens. The wind will make it feel
much colder with wind chills around 0 inland and single digits
along the coast.-- End Changed Discussion --

.LONG TERM /SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --The long term starts off with the an upper level trough moving
through the Northeast on Saturday. This will allow for a partly
sunny start to the day to become mostly cloudy by late morning
into the early afternoon. Any lower level forcing for
precipitation in the form of a surface trough looks to weaken
during the day.

The arctic high pressure will bring 850 hPa temperatures on
Saturday of -15 to -20 C range to the area. NBM may have a hard
time keying on just how cold the upcoming air mass will be, so
went slightly under NBM guidance for highs on Saturday. Have
high temperatures in the upper teens to lower 20s for Saturday,
with perhaps some middle 20s along the coast. Wind chill values
are expected to range from 0 to around 10 above during the
warmest part of the day. Overnight lows in the teens for much of
the area, with some single digits above 0 possible well inland.
These may end up being too warm if skies clear out quickly
enough as the upper shortwave pushes offshore. Minimum overnight
wind chill values of 10 below to just above 0 are forecast.

Conditions will be breezy due to the arctic high and the low off
shore strengthening on Saturday, increasing the pressure gradient
across the area. Northwest winds of 15 to around 20 mph along the
coast with gusts of 20 to 25 mph are expected. Isolated gusts of
around 30 mph is possible. Lighter winds are expected inland.

The upper level shortwave pushes off shore Saturday night, allowing
for some clearing. The high continues to build into the region
through the weekend, with the center of the high passing off the
Southeast US Coast on Monday. The next system to affect the region
may come by the middle of next week as a cold front approaches from
the north. There is too much uncertainty this far out with
precipitation types, but some areas may start off as snow or a
rain/snow mix Tuesday night before changing over to all rain by
Wednesday morning. One important player will be the position of
strong high pressure moving southeast across southern Canada into
northern New England Tuesday into Tuesday night.

Temperatures moderate Sunday into the middle of next week, with
highs on Sunday in the 20s inland to lower 30s along the coast.
Near normal temperatures are expected on Monday, with a return to
above normal temperatures by Tuesday.-- End Changed Discussion --

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --Low pressure approaches tonight and passes offshore Friday.

VFR through most of tonight. Lingering light snow and MVFR
conditions are possible through about 22Z for KSWF, KBDR and
KGON. Snow then develops in the 10-14Z Friday time period, with
IFR likely by around 14Z for the NYC terminals, KSWF and KHPN.
Snow is expected through the day on Friday.

WSW winds generally around 10kt. Winds will then go light and
variable for a time tonight before becoming NE less that 10kt
early Friday morning. Winds increase to around 10kt during the
day Friday.

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

Amendments likely with flight category changes early Friday
morning.

OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY...

Friday Afternoon...MVFR to IFR with snow ending in the evening.
Isolated NE-N wind gusts 20kt possible in the afternoon and at night.

Saturday-Sunday...Mainly VFR. N-NW wind gusts 25-30kt.

Monday...VFR.

Tuesday...VFR. Slight chance to chance of rain/snow.

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

.MARINE...
-- Changed Discussion --Have extended the SCA on the ocean east of Moriches inlet
through 7pm with lingering 5 ft seas. Conditions will then
remain below SCA levels through Friday. Winds on the ocean may
ramp up close to SCA levels Friday night as low pressure
intensifies as it moves well offshore. Seas may also build close
to 5 ft on the ocean by early Saturday morning.

SCA likely on all waters for Saturday with a strengthening
arctic high building into waters from the west. Northwest winds
could gust 25 to just under 35 kt. There is a low chance that
gale winds occur on the ocean waters during the day Saturday.
Winds diminish somewhat Saturday night, but moreso Sunday night.

Waves on the ocean stat off at 3 to 5 ft on Saturday, then
increase to 3 to 6 ft by Saturday night, then diminish to below
5 ft by Sunday night. Waves on the ocean may briefly build to 5
ft late Monday night, mainly on the eastern ocean zone, with a
return to sub SCA conditions by Tuesday morning.-- End Changed Discussion --

.HYDROLOGY...
-- Changed Discussion --No hydrologic impacts are expected through the middle of next
week.-- End Changed Discussion --

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...None.
NY...Winter Weather Advisory from 7 AM to 7 PM EST Friday for
NYZ071>075-176-178.
Winter Weather Advisory from 9 AM to 9 PM EST Friday for
NYZ078>081-177-179.
NJ...Winter Weather Advisory from 7 AM to 7 PM EST Friday for
NJZ002-004-006-103>108.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ350.-- End Changed Discussion --

SYNOPSIS...JP/DS
NEAR TERM...DS
SHORT TERM...DS
LONG TERM...JP
AVIATION...JT
MARINE...JP/DS
HYDROLOGY...JP/DS