344
FXUS61 KOKX 181800
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
100 PM EST Wed Dec 18 2024
.SYNOPSIS...
A frontal system approaches from the southwest today. The
frontal wave will then move across the area this evening,
passing to the east by midnight along with the associated cold
front. High pressure briefly returns on Thursday into early
Friday before a clipper low passes to the south and an offshore
low tracks well east Friday into Saturday. High pressure then
builds late in the weekend into early next week. A weak low may
pass Christmas Eve into Christmas Day.
&&
.NEAR TERM /THROUGH TONIGHT/...
Only minor updates needed to reflect current trends in
observations.
A quick change in weather is expected today as Pac jet energy
interacts with energy in the northern branch of the polar jet.
With no blocking over the North Atlantic, a frontal wave over
the Tennessee and Ohio Valleys will quickly track northeast and
into the area early this evening. Overrunning rains out ahead
will break out late this afternoon into early this evening. Much
of the guidance takes the low over or just south of LI. This
will make it tricky with wind direction and whether or not
coastal locations briefly get into the warm sector. The latter
of which could impact temperatures. Instability is weak though,
so not expecting any thunderstorms if we do indeed warm sector.
Due to the winds slackening this evening with the frontal wave,
expect a period of fog.
Rain will be moderate at times, but will get swept quickly
east with a cold frontal passage by midnight. Rainfall amounts
of 0.25-0.50" can be expected. Guidance has generally backed
off the last 24h with a little less amplification of the northern
branch shortwave. However, some of the guidance is pointing
toward a post-frontal band with the upper jet. This may add a
bit more rainfall. Thus, have maintained rain chances after
midnight.
As for temperatures, went with the warmer deterministic NBM for
highs today in the upper 40s to lower 50s, but then at or just
above for lows tonight due to the gusty NW flow and cloud
cover. Lows tonight will range from lower to mid 30s inland, to
the upper 30s to around 40 at the coast.
&&
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Behind the cold front, expect a gusty NW flow of 15 to 25 mph,
which will gradually weaken heading into Thursday afternoon as
high pressure builds in from the west. The next amplifying upper
trough will send a clipper low into the Ohio Valley Thursday
night. Cloud cover will likely begin to work into the area with
the upper trough as well as some strengthening low-level warm
advection. However, expect it to remain dry at this time.
Temperatures Thursday and Thursday night will return to normal
levels.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
* A light rain snow mix Friday into early Saturday.
* An arctic airmass follows the rest of the weekend into next
Monday with potential for several areas, especially inland,
not rising above freezing for at least 3 consecutive days.
* Christmas Eve (Tue) and Christmas Day (Wed) likely to stay dry
with more cloud cover and somewhat moderated temperatures,
though still below average. There is a possibility of a light
rain-snow mix.
Model guidance appears to be in good agreement on a solution for the
Friday-Saturday system we have been highlighting for the last
several days.
An Alberta Clipper low will be approaching the area early Thursday,
but is expected to rapidly weaken before arriving as its energy get
caught up in a deepening trough and transfers to a strengthening
offshore low which will pass to our southeast on Friday then
northeast into the Canadian Maritimes by early Saturday.
Light precip is possible with the approaching clipper system on
Friday. Nothing significant is expected due to the weak nature of
the clipper low. In fact, its entirely possible we could be mainly
dry on Friday with only isolated chances for showers. It will depend
on how weak the clipper low gets on its approach to the region.
Friday night into early Saturday, light precip is expected to remain
as we get impacted by the outskirts of the offshore low as it
passes. Most of the upper-level energy is expected to be offshore,
so not expecting much. The event will likely end up being a rain-
snow mix. Rain for coastal areas, with snow inland through the day
on Friday. Friday night rain will transition to snow along coastal
areas as cold air filters in behind the low as it exits to our
northeast and also aided by a deepening longwave trough over the
northeastern US. Precip will quickly end Saturday morning/midday as
dry air gets more entrenched as the low moves farther and farther
away. Only a few tenths of an inch worth of liquid QPF are expected
for the Friday-Saturday system. SNow accumulations may total a few
inches for far interior areas while coastal areas may only see a few
tenths accumulate, due to the rain transitioning to snow later
Friday night and the precip quickly ending.
Highs on Friday will be in the mid-30s in the northern interior, and
low.mid-40s for the remainder of the CWA. Temperatures will be
dropping Friday night, as low as the low-20s to near 30.
A strong Canadian high builds in from the Great Lakes region through
the weekend with a longwave trough aloft, that doesn`t make its exit
until Sunday night. Mainly dry weather and sunshine is expected
during this period with a very cold air mass in place. Highs on
Saturday will peak between 25 and 36 degrees north to south.
Saturday night is when the cold air will really begin to be felt
with lows dipping into the single digits in the northern interior.
The remainder of the CWA will drop into the teens. Given 5-10 mph NW
winds, wind chills Saturday night could drop near or below zero.
SUnday will be the coldest afternoon with highs in the mid/low-20s
area-wide. Lows Sunday night will again be in the teens to single
digits. Some areas of the interior of Orange county may near zero.
Surface high pressure centers over New England on Monday as heights
rise aloft under a mostly flat ridge. Highs on Monday will nudge
slightly warmer as a result in the mid-20s to low-30s. Monday night
lows will be in the teens to low-20s.
A weak low and associated mid-level shortwave approaches and passes
Tuesday (Christmas Eve) into Wednesday (Christmas Day). Most model
guidance either has a weak low passing or has high pressure stamping
out the low before it makes it here. Timing and strength of the
system still varies among the available 00Z global guidance. For
now, best guess is that we may see a mainly dry Christmas Eve and
Christmas Day with extra cloud cover. But the chance for light
precip remains. Model guidance also varies on temperatures so either
rain or snow or a rain-snow mix is still possible. But for now,
still looking to be on the lighter side of things. However, this far
out in the forecast, look for things to still change some.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
Weak high pressure slides east this afternoon as an area of low
pressure approaches and passes over the area tonight. The low
exits early Thursday morning with high pressure building in from
the west.
VFR. Becoming MVFR toward 22Z with light rain developing, then
lowering to IFR by 02Z, with the NYC metro terminals remaining
MVFR, with a chance of IFR. Returning to VFR after 10-13Z
Thursday.
Winds are still light and mainly out of the south, however as
the low approaches later this afternoon winds will shift to the
east to southeast. Depending on the track of low pressure,
winds may briefly become light and variable this evening. Then
with the low passing to the east, winds become northwest. Winds
increase as the rain ends 10-15 kts with gusts around 20 kts
possible early tomorrow morning into early tomorrow afternoon.
...NY Metro (KEWR/KLGA/KJFK/KTEB)TAF Uncertainty...
Amendments possible for changing flight categories as the rain
approaches the area.
Gusts on Wednesday may be occasional at times. Can not rule out
a few gusts higher than forecast.
OUTLOOK FOR 18Z THURSDAY THROUGH SUNDAY...
Thursday: VFR. NW gusts 15-20kt.
Friday: VFR, becoming MVFR, IFR at times, afternoon into night.
A chance of rain and/or snow during afternoon. A chance of snow at
night. NW gusts late at night 15-20 kt.
Saturday: MVFR to IFR with a slight chance of snow, ending late in
the afternoon. NW gusts 20-25 kt.
Sunday: VFR.
Monday: VFR.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
An approaching frontal wave today will bring a period of marginal
SCA conditions to the ocean waters tonight, both in the pre-
frontal SW flow and post-frontal NW flow. However, it does look
to be short-lived and should end by late Thursday morning. High
pressure will then build in from the west.
SCA conditions will not be met Friday. An offshore low passes
east of the waters Friday night into Saturday bringing the next
chance of SCA conditions, especially on the ocean. Winds look
marginal, but ocean seas should build to 5-6 ft. The marginal
SCA winds may continue on Sunday with seas near 5 ft.
&&
.HYDROLOGY...
There are no hydrologic concerns through the middle of next
week.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 10 PM this evening to 10 AM EST
Thursday for ANZ350-353.
Small Craft Advisory from 1 AM to 10 AM EST Thursday for
ANZ355.
&&
$$
SYNOPSIS...BR/DW
NEAR TERM...MD/DW
SHORT TERM...MD/DW
LONG TERM...BR
AVIATION...BC
MARINE...BR/DW
HYDROLOGY...BR/DW