Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 161726
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
1226 PM EST Sat Dec 16 2017

.SYNOPSIS...
Below normal temperatures will continue through the
weekend. Lake effect snow showers over the Adirondacks will
shift southward and diminish today, but light snow showers are
possible over much of the forecast area. Dry weather for Sunday,
but a chance of light snow will return Sunday night.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A Winter Weather Advisory remains in effect for the western
Adirondacks until 100 PM this afternoon.

Dominant Ontario lake effect band is shifting southward from the
advisory area toward the Mohawk Valley/Thruway corridor, but is
becoming less organized as it does so. Additional snow showers
enhanced by lake aggregate moisture and associated with deeper
moisture per IR imagery are located over central NY. Favored
location for seeing light accumulations with this activity is
the higher terrain of the western Adirondacks, Mohawk and
Schoharie Valleys, and Catskills. Some evidence that snow
showers can work their way into the Hudson Valley as well due to
the deeper moisture, upper level jet magnitudes increasing to
the south of the forecast area, and the development of weak
surface-based instability per model forecast soundings. Moist
upslope flow favors increasing snow shower activity in the
Berkshires and Greens as well. Updated PoPs and snow
accumulations to reflect the above. Additional accumulations of
1-2 inches are possible over westernmost portions of the Mohawk
Valley and Adirondacks, with an inch or less over the
Greens/Berkshires/Schoharie Valley/Catskills, and likely no more
than a dusting in the Hudson Valley. Will continue winter
weather advisory as snow showers are still occurring in the
advisory area. Any remaining snow showers across the forecast
area should quickly diminish after 21Z as upper flow becomes
confluent and high pressure noses in from the north.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
Quiet weather is expected tonight and Sunday as the ridge of
high pressure builds across the region and then shifts east by
late in the day on Sunday. It will be a chilly night tonight as
air from Canada flows into the region. Expect lows tonight to
generally range from 5 below to 15 above zero. Highs on Sunday
will be similar to Saturday generally ranging from the upper
teens to lower 30s.

Sunday night through Monday night will feature the chances for
some light snow or even rain showers on Monday as the forecast
area will be in a warm air advection pattern as a warm front
moves from the Ohio Valley Sunday evening through our region
Monday night. Lows Sunday night will be in the upper single
digits to mid 20s with highs on Monday in the upper 20s to lower
40s. Lows Monday night will be in the mid 20s to lower 30s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Much of the long term will be dominated by an increasingly zonal
northern stream flow, although there remains at least some potential
with some southern stream interaction at times.

To start the period, one PV anomaly is expected to move across the
northern Great Lakes into Quebec for Tuesday-Wednesday. Warm
advection should bring at least some light precipitation to northern
areas Tuesday-Tuesday evening, initially driven by some warm
advection. Forecast thermal profiles suggest some light snow, or a
light wintry mix may occur Tuesday morning, before changing to
mainly rain by afternoon, with precipitation chances greatest for
areas mainly north of I-90. Showers may expand south and east
Tuesday evening with a cold front. In the wake of the front, some
Lake Effect snow showers will be possible across the western
Adirondacks/Mohawk Valley later Tuesday night into Wednesday
morning. It should become quite windy Wednesday as a fairly tight
low level gradient develops. Tuesday highs should occur late in the
day, with 30s to lower 40s expected, warmest in valley areas. Some
temperatures could reach well into the 40s across portions of the
mid Hudson Valley. Temperatures will be cooling later Tuesday night,
with lows mainly in the 20s to lower 30s by daybreak Wednesday.
Wednesday highs should be mainly in the 20s to mid 30s, although
highs may occur in the morning before falling in the afternoon with
strengthening cold air advection.

High pressure may build across the region for Wednesday night into
Thursday. However, the one caveat is some southern stream energy,
which most 00Z/16 deterministic models and ensembles track from the
Gulf Coast region to the mid Atlantic coast. This track would keep
any associated precipitation well south/east of the region, however
will need to closely watch any northward trends as we approach, as
we have seen other southern stream systems track farther north and
west thus far this cold season than initially expected. Assuming the
more southern track occurs, expect cold and dry conditions, with
highs Thursday in the 20s to lower 30s, and overnight lows Wednesday
night/Thu morning in the single digits and teens.

For Thursday night-Friday, most 00Z/16 deterministic models and
ensembles track the next system developing over the southern Plains
northeast toward the Great Lakes. This may allow light precip,
mainly in the form of snow, to develop across the southern
Adirondacks and Mohawk Valley region later Thursday night, with more
widespread precipitation possible Friday, especially for areas north
of the I-90 corridor. Although there likely will be warming aloft
with this possible low track, shallow low level cold air may be
tough to dislodge across northern areas, so mixed precipitation
could occur in these areas, with a mix changing to rain farther
south. Lows Thursday night mainly in the 20s, although possibly
rising late; highs Friday potentially in the 30s for northern areas,
with some 40s possible across central and especially southern areas.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
Lake-enhanced light snow showers are ongoing downwind of Lake
Ontario and some may drift across the terminals from time to
time this afternoon. Not enough evidence to include a vsby
restriction at the terminals, except for KPSF where upslope
contributions may focus it a bit more. IFR vsby at KPSF cannot
be ruled out and will handle with amendments if it appears
likely. Elsewhere, have VCSH this afternoon. Drier air will
infiltrate from north to south, ending snow shower chances
between about 21-23Z. Outside of any heavier snow shower,
conditions are expected to remain VFR.

Tonight, high pressure builds in with clearing skies. Cannot
rule out a brief period of low stratus/freezing fog at KGFL as
was seen the last couple of mornings, and perhaps at KPOU as
well, toward 12Z Sun. Later TAF packages can assess this
potential for possible inclusion in the TAFs.

Winds this afternoon will be from the west to west-southwest
at around 10 kt with some gusts around 20 kt. Winds will become
light and variable overnight into Sunday morning.

Outlook...

Sunday Night: Moderate Operational Impact. Chance of SN.
Monday: Moderate Operational Impact. Chance of SHRA...SHSN.
Monday Night: Moderate Operational Impact. Chance of SHSN.
Tuesday: Moderate Operational Impact. Chance of SHRA...SHSN.
Tuesday Night: Moderate Operational Impact. Chance of SHRA...SHSN.
Wednesday: Low Operational Impact. Breezy NO SIG WX.
Wednesday Night: No Operational Impact. NO SIG WX.
Thursday: No Operational Impact. NO SIG WX.

&&

.HYDROLOGY...
No hydrologic problems are expected into early next weekend. Ice
will continue to form on areas lakes and streams. Any snowfall
will be light with the exception of moderate accumulations of
lake effect snow across portions of the western Adirondacks into
this morning.

For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Weather Advisory until 1 PM EST this afternoon for
     NYZ032-033.
MA...None.
VT...None.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...Thompson
SHORT TERM...11
LONG TERM...KL
AVIATION...Thompson
HYDROLOGY...IAA/11



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