Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 210848

Area Forecast Discussion
National Weather Service New York NY
348 AM EST Sun Jan 21 2018

Weak high pressure will move east through the region today. A
warm front will approach the region tonight, slowly working
north through the region late Monday into Monday Night. A strong
frontal system will cross the region on Tuesday, with high
pressure returning for the remainder of the week.


Zonal upper flow continues today, with confluence of Pacific
and polar jet to the north of the region, and southern stream
energy tracking through the deep south.

A glancing shot of Canadian air expected today in wake of a weak
cold frontal passage, with polar high pressure building into Quebec.
Weak high pressure moves across the region today, providing mostly
sunny and tranquil conditions. NAM has backed off stratus
working into the region for today, with the stratus shield
likely having trouble getting east of the Appalachians until
late day.

High temps will be several degrees cooler than yesterday, but
still several degrees above seasonable levels (mid to upper


Models in good agreement with the amplifying trough over the SW
states interacting with subtropical jet energy today. The
resultant deep closed upper low is then expected to track NE
across the Central Plains and Mid Mississippi valley tonight
through Mon. A large resultant low pressure system will take
similar track through the Central US.

Meanwhile the local region will remain under slight ridging, with
PAC/Polar jet confluence well to the north. At the surface, weak
high pressure moves offshore tonight, with a warm front
developing to the south of the region. Stratus and light
precip/drizzle appears likely to work into the region tonight
into Monday morning with strong theta-e advection ahead of the
approaching Central US system. Models have trended slightly
warmer with low-level temps tonight into Monday, with polar air
staying locked across northern New England. This has reduced
the threat for widespread freezing temps and icing across the
interior, but still potential for interior valley areas of the
Lower Hudson Valley and Southern CT to have temps hang around
freezing, resulting in a localized glaze of icing threat.

On Monday, the warm front will likely have trouble moving north
through the region until the llj works into the region Monday Night.
This based on position of the surface low well west of the
Appalachians on Monday and high-res models signaling a weak
cold air damming signal from high pressure nosing down the
coastal plain from SE Canada. This will spell chilly conditions
with stratus, drizzle, and light rain showers continuing Mon
into Mon eve. Patchy freezing rain/drizzle may linger across
interior through Monday morning, particularly in the CT River
Valley due to cold air drainage. Highs on Monday will likely
hold in the upper 30s interior to lower 40s city/coast.


Models continue in strong agreement with the closed upper low
tracking through the Great lakes Monday Night into Tuesday
before beginning to phase with northern stream energy as it
swings into the NE US Tuesday Night. At the surface, primary low
pressure tracks through the Great Lakes Monday Night into
Tuesday, while secondary low pressure develops in vicinity of
the region Tuesday and lifts into New England Tuesday Night.

Model-to-model and run-to-run consistency continues for a quick
moving moderate to heavy rain event for late Monday night into
Tuesday, in response to strong deep layered lift (region under
of nose of 65-70 kt LLJ and left front quad of a 125+ kt jet
streak in difluent upper flow) of a positive 2-3 STD above
normal PWAT moisture plume over the region, focused ahead of the
cold front/surface wave. Embedded thunder possible as well with
the strong forcing and weak elevated instability. Based on
SREF/GEFS ensemble model spread, a general 1/2 to 1 inches of
rain is likely across the region late tonight through Tuesday,
with locally 1 to 2 inches. Highest rain amounts will likely be
in path of surface wave and across interior hills due to
orographic enhancement.

Despite a low level inversion, a period of 30 to 40 mph gusts
appears likely for LI/SE CT Tue morn/aft ahead of cold front as
a 60-70 kt 950mb llj works over this region, with a low prob
for a few gusts of 40 to 50 mph being mixed down with
convection/heavy rain.

The frontal system pushes through by late Tuesday with drying
conditions Tuesday evening. A breezy NW flow will usher in a
cold and dry airmass for mid to late week, with Canadian high
pressure building in for the late week and east for the


High pressure remains centered to the south through today. A warm
front approaches from the south tonight. Initially VFR conditions
will gradually lowering to MVFR tonight with the approach of the
warm front. IFR conditions may be possible towards Monday morning.

Winds will generally be light WNW (left of 310) today, gradually
backing to the W-SW in the afternoon. Winds will then become light
and variable tonight as the warm front approaches.

Monday...MVFR/IFR possible. Chance of -RA. -FZRA possible at SWF
early Monday morning.
.Tuesday...IFR/LIFR in rain. LLWS. S winds G25KT morning, WSW winds
G30-35KT possible near the coast in the afternoon.
.Wednesday...VFR. WNW G25-30KT.
.Thursday...VFR. NW winds G20KT.


Winds and seas will remain tranquil through today as weak high
pressure shifts northeastward. A warm front then approaches tonight
and slowly moves through Monday, keeping winds light and seas
tranquil. As the warm front moves through Monday night into Tuesday,
southerly flow will rapidly strengthen, with at least SCA-level
winds on the waters. A strong low-level jet will lead to the
possibility of at least isolated gale-force winds on Tuesday,
despite an inversion that may hinder the strongest winds from
reaching the waters. Seas will rapidly build in response to the
strengthened flow.

Winds may then briefly decrease Tuesday evening as the cold front
moves through, before strengthening into Tuesday night in strong
cold advection. Expect SCA-level gusts Tuesday night into Thursday,
with seas remaining elevated on the ocean waters. High pressure then
begins to build across the area for the late week, with winds
decreasing and seas gradually subsiding.


A frontal system passing through late tonight through Tuesday
is likely to produce a widespread 1/2 to 1 inch of rain, with
locally 1 to 2 inches possible. No significant hydrologic issues
are anticipated at this time.


NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the
air for an extended period of time.




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