943
FXUS61 KOKX 132300
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
600 PM EST Fri Dec 13 2024
.SYNOPSIS...
Strong high pressure gradually builds in through Saturday. The
strong high pressure area will move slowly north of the area
Saturday night and then into the Gulf of Maine for Sunday. A
weakening frontal system will approach Sunday night and move
across on Monday. A stronger frontal system will move across
Monday night into Tuesday, followed by high pressure Tuesday
night into Wednesday. A complex coastal low pressure system may
affect the region Wednesday Night into Friday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Main story for tonight, dry and very cold with strengthening
high pressure building in from the Great Lakes. Most forecast lows
in the teens to lower 20s.
Aloft a trough will move east of the region tonight with ridging
taking place across the local area behind this trough. The
confluence behind the trough will strengthen an approaching high
pressure area at the surface. This strengthening high pressure area
builds in from the Great Lakes tonight.
NAEFS showing negative anomalies of mainly between 1 to 2
standard deviations for temperatures throughout the atmospheric
column tonight. Model 850mb temperatures around -10 to -12
degrees C are forecast for tonight.
Mostly clear sky conditions along with light winds are in store
for tonight so expecting efficient radiational cooling. Used
relatively colder MET guidance for lows tonight, ranging from
near 10 across northern interior and rural locations to lower
20s for portions along the coast and within NYC. Some single
digit lows are forecast for parts of the interior.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
Main story remains the strong high pressure and colder than
normal temperatures. Core of cold airmass still in place to
start the weekend with some moderation of the airmass on Sunday.
Dry conditions continue.
Ridging continues aloft Saturday through early Sunday. Ridge axis
moves across late Sunday morning into early Sunday afternoon. Then,
some height falls thereafter as the ridge exits east of the region
and a trough approaches from the west.
At the surface, strong high pressure will be across the region
Saturday into Saturday night, with its center north of the region,
in the vicinity of Northern NY State and Northern New England near
the Canadian border. With generally light northerly flow expected
Saturday, anticipating highs again staying well below normal for
this time of year. Model 850mb temperatures near -8 to -11 degrees
C. The high pressure moving in with its magnitude potentially
getting to near 1050mb would be approaching record levels. See
the climate section for more details.
NAEFS continues to show negative anomalies of mainly between 1
to 2 standard deviations for temperatures throughout the
atmospheric column Saturday.
Used a blend of MAV/MET/NBM for high temperatures Saturday, ranging
from the low to mid 30s for much of the region, with some smaller
areas in the upper 30s. These are well below normal for this
time of year.
For Saturday night, even more efficient radiational cooling is
expected with lighter winds (some area winds becoming calm) and
mostly clear sky conditions. The forecast lows again used the
relatively colder MET guidance but more range compared to the
previous night from upper 20s within NYC to single digits for parts
of the interior.
Saturday night into Sunday, NAEFS negative anomalies remain at 200mb
but trend to slightly more positive anomalies (between 1 and 2
standard deviations) at levels 700 to 500mb. 850mb positive
anomalies appear Sunday afternoon also between 1 and 2 standard
deviations.
The strong high pressure area will move farther south Sunday, with
the center of this high eventually moving into the Gulf of Maine.
While the high pressure area will still be strong, the pressure
tendency will be negative with its center decreasing in pressure.
The approaching trough will be the converse of what was seen going
into early Saturday, there will be a diffluent pattern leading to
mass divergence aloft throughout the day Sunday. Clouds will be on
the increase during the day from west to east. However, with rising
trend to temperatures aloft, vertical mixing will allow for warmer
air to mix down to the surface adiabatically. Forecast high
temperatures again used a MAV/MET/NBM blend, several degrees warmer
than the previous day, reaching near 40 along much of the coast and
NYC but more in the 30s for Northeast NJ, Lower Hudson Valley and
Southern CT. Forecast highs are still below normal for this
year.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
-- Changed Discussion --
* Active and unsettled weather pattern next week
* Wintry mix likely for Monday morning commute N&W of NYC. Icy
conditions possible.
* Potential late week coastal storm
Active upper pattern setting up for next week with series of
vigorous shortwaves tracking from the Gulf of Alaska across the
northern tier of the CONUS, each successively deepening mean
troughing across the NE US.
The first feature being a closed upper low over the central US this
weekend, shearing to the eastern Great Lakes by Sunday Night and
then across the area Monday. This will be followed by a deeper
Central US trough pivoting through the Great Lakes Monday Night, and
then an even longitudinally deeper longwave trough approaching the
eastern US late week.
At the surface, the warm front of a weakening Great Lakes low
approaches Sunday Night into Monday as strong surface high pressure
gradually slides offshore. Tricky precip forecast late Sunday Night
into Monday AM, based on timing of precip onset with initially dry
airmass and strong surface high offshore, marginally cold thermal
profile with a developing 950mb warm layer across the interior, and
likely sub-freezing air and ground temps across the interior until
after daybreak. For the coast, including NYC/NJ metro, sufficient
boundary layer warming should allow precip to mainly fall as rain,
but can`t rule out some icy spots for any places that can radiate in
Sun eve. Thermal profiles should safely warm above freezing for the
entire area by mid to late morning for plain rain, but with weak
surface flow, interior valleys of LoHud and S CT could linger with
patchy freezing rain into the afternoon with in-situ cold air
damming.
Have leaned towards a blend of WPC WSE and NBM POWT to determine
potential footprint of freezing rain threat for Mon Am commute.
Primary concern for a glaze of freezing rain is across valley
locations of Orange, W Passaic, Putnam, and interior Fairfield and
New Haven counties, where 3 days of near or sub-freezing high temps
and early lows in the 20s Sunday Night with a transition to liquid
precip in the early AM could result in patchy ground icing. Will
address in HWO, with further refinement in the forecast through the
weekend.
Continued waa aloft should eventually end any lingering icing threat
through the afternoon. Light rain should gradually taper off in the
late aft/early eve as a shortwave aloft moves through with brief
shortwave ridging building in.
This drying will be very short-lived or non-existent as next quick
moving shortwave and associated frontal system brings a quick shot
of rain to the region later Monday Night into Tuesday morning.
Continued waa ahead of this feature will support an all rain event.
High pressure briefly builds in for Tue Night into Wed with
seasonable temps, before potential for a complex coastal system for
the late week period.
Considerable inherent model spread on evolution of the anomalously
deep trough for late week, manifesting in low pressure track and
timing differences, but potential exists for a heavy precip event.-- End Changed Discussion --
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Strong high pressure will persist the next few days.
VFR through the TAF period.
NW-N winds 10-15 Kt with gusts 15-20 kt, before diminishing
this evening. Winds shift to mainly N tonight but could become
variable at times. N winds 10 kt or less Saturday.
...NY Metro (KEWR/KLGA/KJFK/KTEB)TAF Uncertainty...
No unscheduled amendments are expected.
OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY...
18z Saturday: VFR.
Sunday: MVFR cigs likely at the NYC metro/coastal terminals in
the afternoon, spreading inland during the evening. Chance of
a wintry mix at KSWF and rain elsewhere, mainly after midnight.
Monday: Wintry mix still possible at KSWF early, otherwise light
rain likely with MVFR or lower cond expected. Fog may develop
at night with IFR cond possible.
Tuesday: Light rain likely with IFR or lower cond possible.
Wednesday: Mainly VFR.
Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
With strong high pressure in control, a weak enough pressure gradient
will be in place to keep conditions on all waters below SCA thresholds
through Sunday.
Sub SCA condition Sunday Night into Monday morning with a weak
pressure gradient. SE flow strengthens Monday Aft into Monday NIght,
with SCA ocean seas possible by late Mon. SCA conds likely on the
ocean Mon Night into Tue Night, possibly all waters for a period,
with strengthening southerly flow and building ocean waves ahead of a
cold frontal passage.
&&
.HYDROLOGY...
No hydrologic impacts are expected attm.
&&
.CLIMATE...
Very strong high pressure is forecast to settle over the
Northeast by Saturday. The potential high sea level pressure
(SLP) is close to the highest observed across the Northeast not
only in December but in any calendar month based on data from
WPC. The highest observed SLP in the Northeast ranges from
1052-1054 mb, which occurred on February 13, 1981. The highest
observed SLP at Central Park was 1052.5 mb, which also occurred
on February 13, 1981. The highest observed SLP in the Northeast
for December ranges from around 1049-1053 mb (1051.8 mb at
Central Park), which occurred on December 25, 1949.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...JM/NV
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...NV
AVIATION...IRD
MARINE...JM/NV
HYDROLOGY...JM/NV
CLIMATE...