Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 151414
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
914 AM EST Fri Dec 15 2017

.SYNOPSIS...
Seasonably cold temperatures will continue through the
weekend. Moderate accumulations of lake effect snow are likely in
the Western Adirondacks tonight into Saturday. Elsewhere, mainly
light snow showers will be possible Saturday as a cold front passes
through the region.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 900 am, updated forecast to refine PoPs this
afternoon/evening in advance of outer fringes of snowfall from
coastal low expected to impact southern zones. Latest guidance
suggests light snow will threaten areas mainly south of Albany
roughly 21-03Z. Accumulation still expected to be mainly half
inch or less, but possibly closer to an inch over Litchfield and
Dutchess Counties. Elsewhere, forecast remains on track.

Prev Disc...The area remains under mainly flat upper level flow
as the next upper impulse digs into the longwave trough. At the
surface, weak high pressure will nose into the area this
morning and quickly exit by the afternoon as the next wave of
low pressure shifts eastward across the Great Lakes and as a
coastal low develops off of the Carolinas. This coastal low is
expected to stay far enough offshore such that it will limit the
impacts to just some snow showers south and east of the Greater
Capital District (mainly in Litchfield and Berkshire counties).
As these weather makers shift towards the region today, low
level moisture and cloud cover will increase, leading to another
chilly and cloudy day with highs in the upper teens and lower
20s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
A Winter Weather Advisory has been issued for northern
Herkimer county and northern Hamilton county, mainly along Route
20 and west of Route 30 from 10 PM this evening through 1 PM
Saturday...

The next upper level shortwave will approach and pivot through
the region tonight with an attendant surface low tracking
eastward north of the St. Lawrence Valley.This should allow
winds to back such that they align with the long axis of Lake
Ontario for a time late tonight into early Saturday. Surface to
850 mb delta-Ts will range from 20-25 C, and deeper moisture
associated with the upper level wave will enhance lake effect
processes, resulting in a period of moderate to heavy lake
effect snow for portions of the western Adirondacks. Therefore,
have issued a winter weather advisory for northern Herkimer and
Hamilton counties from 10 PM this evening through 1 PM Saturday.
It looks like the lake effect band will shift south as the low
level winds veer northwesterly late Saturday morning. This
should allow for the dominant lake effect band to break up and
shift southward. Current forecast accumulations of 3 to 6
inches, with locally higher amounts possible support an
advisory for now but will monitor conditions to see if a warning
is needed.

Upslope snow showers may begin to occur across the higher
terrain of western New England tonight as well. Elsewhere,
clouds and a moderate wind will keep temps from falling as much
tonight compared to early this morning, although lows will
likely be below normal. Some lingering snow showers will
possibly spread toward the I-90 corridor and into the valleys
Saturday as the lake effect band shifts southward, but minimal
accumulation is expected as there is no midlevel forcing with
the height rises. A cold and dry night is expected Saturday
night with diminishing winds as high pressure builds into the
region.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Many differences between the various operational deterministic model
guidance and ensemble solutions, the extended period remains a
rather low confidence forecast at this time.

We begin this long term period with a cut-off low across the four
corners region with a short wave ejecting out of this system across
the Plains and through the Ohio Valley then into the northeast
corridor Sunday night.  The upper flow will be rather confluent as
broad isentropic lift and overrunning evolves through the evening
hours.  A period of light snow is expected overnight which could
make a tricky morning commute Monday morning.

This aforementioned wave departs off the New England coastline
Monday morning with perhaps a narrow ridge of high pressure tracking
across the region before the next upstream disturbance approaches.
This is when models diverge a bit as waves across Canada will
eventually dictate the synoptic pattern through most of next week.

All global models suggest a deepening surface low across central
Canada but differ significantly on placement and intensity.  Its
downstream impacts will be the approach of a cold front for tuesday
into Tuesday night.  The GFS is quite aggressive with the GGEM the
least aggressive but all suggest frontal passage to occur by Tuesday
evening.  So the chance of rain/snow showers as H850 temperatures
moderate to near or above 0C before returning below freezing Tuesday
night.

This system and its cyclonic flow regime will quickly depart through
Wednesday before the next warm front and overrunning situation sets
up for the second half of the week with light precipitation chances
on the increase Thursday.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
VFR conditions are in place this morning with light and variable
winds. Per GOES 16 data, seems some of the Lake Effect clouds
were making into the KALB-KPSF with sct-bkn VFR decks. As this
band lifts northward, we will keep some of these restrictions
into the TAFs at this time. For KPOU and KGFL, should remain VFR
due to upstream higher terrain blocking some of these CIGS from
progressing eastward. Winds will become S-SW around 5 kts. Mid
level clouds will increase during the afternoon hours, with all
sites seeing bkn cigs around 7-12 kft by late in the day.

Some lake effect snow may brush into the KALB-KPSF this evening
with upslope areas of KPSF the higher chance where we will place
a TEMPO group at this time.

Outlook...

Friday Night: Low Operational Impact. Slight Chance of SHSN.
Saturday: Moderate Operational Impact. Breezy Chance of SHSN.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: Moderate Operational Impact. Chance of SHSN.
Monday: Low Operational Impact. Slight Chance of SHRA...SHSN.
Monday Night: Moderate Operational Impact. Chance of SHRA...SHSN.
Tuesday: Moderate Operational Impact. Chance of RA...SN.

&&

.HYDROLOGY...
No hydrologic problems are expected through the weekend.

Temperatures will largely remain below freezing into the
weekend, promoting ice formation on areas lakes and streams.
Any snowfall is mainly expected to be light, although moderate
accumulation of lake effect snow is expected over the western
Adirondacks tonight into Saturday morning, and light to
moderate accumulation is possible over the higher terrain of
western New England as well.

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 from 10 PM this evening to 1 PM EST
     Saturday for NYZ032-033.
MA...None.
VT...None.

&&

$$
SYNOPSIS...Thompson/JVM
NEAR TERM...Thompson/JVM
SHORT TERM...Thompson/JVM
LONG TERM...BGM
AVIATION...Frugis/BGM
HYDROLOGY...Thompson/JVM


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