Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 111755
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
1255 PM EST Tue Dec 11 2018

.SYNOPSIS...
Seasonably cool and mainly dry weather is expected through
Thursday, with a few light snow showers possible tonight and
again Thursday. A storm system may bring rain to the region
Friday night into Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1245 pm, stratus deck continues to expand eastward as
modest moisture advection continues beneath an inversion.
Current trends show the southern edge eroding while the eastern
edge continues to expand, so a somewhat low-confidence cloud
forecast. Broadly speaking, expect mostly cloudy skies
along/north of I-90, and mostly sunny to the south. Have
adjusted temps according to expected cloud trends. Have also
added flurries to portions of the Mohawk Valley, southern
Adirondacks, and Lake George Saratoga region with light echoes
on area radars and slightly lowered visibilities.

Tonight, moisture-starved northern stream wave will track
through the area. Weak ascent, augmented over the southern
Adirondacks and southern Greens by orographic lift, will allow
for some light snow showers, especially over the higher terrain
west of the Hudson this evening into early tonight. Snow showers
will shift southward a bit toward the western Mohawk Valley and
into the Schoharie Valley/eastern Catskills as a brief period of
lake effect occurs. This should be fairly brief as low-level
winds quickly veer to north-northwesterly toward sunrise
Wednesday, shifting any activity back west. Still expect any
accumulation to be less than an inch. Low temps in the teens and
20s are expected, which are near normal values. Possibly a bit
below normal for the Mid Hudson Valley and Litchfield Hills
where there is better probability that a period of clearing will
allow temps to drop a bit more.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Wednesday-
Wednesday night, another narrow ridge of high pressure builds
across the region. Initially, some clouds are expected Wednesday
morning, but increasing subsidence and drier air advecting
south and east should allow for mostly sunny skies by afternoon.
Wednesday highs should reach the lower/mid 30s for most valley
areas, and 20s across higher terrain. Clear skies and light to
calm winds are expected for Wednesday night, setting the stage
once again for excellent radiational cooling, especially across
the southern Adirondacks and higher terrain areas of southern VT
where a deep snowpack remains. Expect low temperatures to reach
the single digits above and below zero across the southern
Adirondacks and southern VT, with mainly teens to the south and
west.

Thursday, a weakening mid/upper level shortwave will be tracking
east from the southern Great Lakes region. There is some
uncertainty regarding the exact track of this feature, with some
models suggesting it tracks close to the I-80 corridor in PA/NJ,
while other models are further north. Depending on its ultimate
track, enough forcing combined with some low level moisture
could allow for spotty light snow or flurries to occur within
some deformation on its northern periphery. Have included slight
chance PoPs for snow showers from I-90 southward to account for
this possibility. Highs mainly in the lower/mid 30s, except 20s
across higher terrain and northern areas.

For Thursday night, the main upper level impulse should track
off the northern mid Atlantic coast. Expect partly to mostly
cloudy skies in its wake. The 00Z/11 NAM12 suggests additional
spotty light precipitation develops late at night in response to
low level warm advection and infusion of some Atlantic moisture
northward into the region. Should this occur, thermal profiles
suggest initially spotty light snow/snow grains, but warming
aloft could promote some sleet/freezing rain closer to Friday
daybreak. For now, since the NAM just started this trend and
remains among the only models thus far to indicate this
potential, have not included mention just yet and will await
future forecast cycles to reassess this possibility. Lows temps
mainly in the 20s, with temps possibly rising late at night due
to developing cloud cover.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Considerable spread in sources of guidance/ensembles for the period
of Friday through Monday. Some sets of guidance suggest an upper low
with southern stream origins tracks into our region through the
weekend with heavy precipitation, while other sets of guidance have
the main upper low track well south of our region as cooler northern
stream dominates our weather with less moisture and precipitation.

With such a spread in guidance, reality is likely to be somewhere
between the extremes, suggesting that even in the drier and cooler
scenario, some moisture and low level forcing associated with the
leading edge of cold advection should result in clouds and
precipitation Friday night through Saturday, with the best coverage
of precipitation in southern and eastern parts of our region.
Amounts should be light enough that any rain should not contribute
to flood potential and any snow in northern areas and higher terrain
should not be no more than advisory amounts, if they even get that
much snow.

Timing and track of upper energy, moisture and low level forcing so
uncertain, that keeping isolated to scattered rain/snow showers
through Sunday, then more confined to the southern Adirondacks by
Monday.  Details of when and where better chances for precipitation
and how much will have to wait until there is more of a consensus in
guidance/ensembles and systems get resolved better in data. Forecast
for Friday through Monday will likely change periodically until we
get that better consensus in guidance.

Highs Friday and Saturday in the 40s but upper 30s to around 40
higher terrain.  Highs Sunday in the lower 40s but mid 30s higher
terrain and some mid 40s southern areas. Highs Monday in the upper
30s to lower 40s but lower to mid 30s higher terrain.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Upper level disturbance is approaching from the Great Lakes. Stratus
and stratocu clouds have been approaching the area from the west and
cigs are becoming bkn-ovc at 3500-4500 ft for KGFL/KALB over the
next few hours.  KPSF has already seen a period of MVFR cigs around
2500 ft and these clouds will continue to become more widespread
through the afternoon hours.  Meanwhile, skies are still clear at
KPOU, but bkn cigs around 3500-4500 ft will move in by the evening
hours. Winds will be rather light and variable this afternoon into
this evening.

As the disturbance passes through the area, bkn-ovc cigs will
continue for the overnight hours. Flying conditions will generally
be VFR for the valley sites, although cannot totally rule out a
brief period of MVFR cigs.  Meanwhile, KPSF should mainly be MVFR
overnight with cigs around 2-3 kft there. Can`t totally rule out a
brief snow shower or flurry at KGFL or KPSF, but impacts on
visibility will be minimal.  Elsewhere, limited moisture should keep
any snow shower activity from occurring at KALB/KPOU.  Light and
variable winds will gradually become north to northwest by late in
the overnight hours and into Wednesday morning around 5 kt.

Ceilings  should start clearing out on Wednesday morning, with skies
becoming cleared out by afternoon.

Outlook...

Wednesday Night: No Operational Impact. NO SIG WX.
Thursday: Low Operational Impact. Slight Chance of SHSN.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: Low Operational Impact. Slight Chance of SHRA...SHSN.
Friday Night: Moderate Operational Impact. Chance of RA...SN.
Saturday: Moderate Operational Impact. Chance of SHRA...RA.

&&

.HYDROLOGY...
No hydrologically significant precipitation is expected through
at least Thursday. Temperatures averaging below normal, and
mainly below freezing, will support expansion and thickening of
ice on area waterways.

A warm-up appears possible Friday into the weekend ahead of a
strong low pressure system approaching from the southern US.
There is still considerable uncertainty on the track of this
system and resulting QPF, but moderate to locally heavy
precipitation appears possible Friday night into Saturday as
the system transports tropical moisture northward.

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...None.
MA...None.
VT...None.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...Thompson
SHORT TERM...KL
LONG TERM...NAS
AVIATION...Frugis
HYDROLOGY...KL/Thompson


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