Albany Office Forecast Discussion

000
FXUS61 KALY 172331
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
631 PM EST Sat Nov 17 2018

.SYNOPSIS...
A weak cold front will move south of the region tonight with
high pressure briefly building in with diminishing lake effect
activity. Mainly light snow will begin to overspread the region
Sunday afternoon into the night time period, as a disturbance
passing south of the region will be moving along the old frontal
boundary, as temperatures for mid November will continue below
normal.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 625 PM EST, Lake Effect moisture remains trapped below a
mid/upper dry layer and some isolated/scattered rain/snow
showers and patchy drizzle extending east through the southern
Adirondacks. A few sprinkles and flurries extend into the Lake
George area to northern Taconics and southern VT.

High clouds are streaming east from the midwest and Great Lakes
ahead of upper energy in the central U.S. that is timed to
affect our region later tomorrow and tomorrow night. Persistent
cloud cover and light winds will prevent temperatures from
falling as much as they could. So, siding on warmer side of
guidance with any lake effect scattered rain/snow showers
diminishing through the night. Lows in the 20s but near 30
southern areas and teens northern areas.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Ribbon of boundary layer moisture associated with low level flow
off lakes will interact with a ribbon of upper energy and
mid/upper moisture seen in satellite imagery. There is a decent
consensus in guidance/ensembles for the upper dynamics and low
level forcing along the leading edge of a quick burst of
boundary layer cold advection and low level wind convergence
across much of NY along and south of I-90 into southern VT and
the Berkshires. The southern periphery of the ribbon of
moisture, upper energy and boundary layer forcing looks to be in
the mid Hudson Valley and NW CT.

So, a narrow band of snow is expected to extend across the
western Mohawk Valley, Schoharie Valley and eastern Catskills
late Sunday afternoon, then build east through Sunday evening
across the Capital District, Lake George region, southern VT
and the Berkshires. There will be a mix of rain and snow in the
mid Hudson Valley and NW CT as boundary layer temperatures rise
to or just above freezing Sunday evening and night. Just
intermittent snow is expected along the northern periphery of
the precipitation in parts of the southern Adirondacks. Rain
and snow ends from west to east late Sunday night and early
Monday morning when coverage decreases and just some
isolated/scattered rain/snow showers linger Monday afternoon.

Snow amounts are expected to be 1 or 2 inches but maybe around 3
in higher elevations of the eastern Catskills, southern Green
Mountains and Berkshires. An inch or so is likely in the western
Mohawk Valley, southern Adirondacks, and a dusting at best in
the mid Hudson Valley and NW CT. Clouds will be slow to break
up Monday afternoon, so temperatures will not be able to rise
too much Monday afternoon, especially since another ribbon of
upper energy will begin to approach with associated mid/high
cloud cover later Monday afternoon.

Some lake effect cloudiness and snow shower activity should
continue in the western Mohawk Valley and southern Adirondacks
Monday night with the modified cold advection. However, snow
shower activity should become more organized and spread across
our region Monday night through Tuesday as the next trailing
upper energy interacts with the ribbon of moisture and
tightening of the boundary layer moisture gradient and
associated low level forcing. So, widespread clouds Tuesday with
scattered snow/rain showers over the entire region, with the
best coverage in higher terrain.

There is less consensus in sources of guidance/ensembles for the
timing and coverage of clouds and snow showers Monday night into
Tuesday. There are differences in where the best coverage of
precipitation sets up and whether there will be enough moisture
for measurable precipitation or just a lot of clouds and
flurries/sprinkles. So, again, indicating scattered snow/rain
showers Tuesday until guidance gives more confidence to either
reduce or increase chances for rain/snow showers.

Highs Sunday with the increasing cloud cover and onset of light
snow in the 30s but upper 20s northern areas. Highs Monday after
the steady snow ends in the 40s but 30s higher terrain. Highs
Tuesday in the 30s but near 40 southern areas and 20s northern
areas.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The main concern for the upcoming long term period will be a very
potent arctic cold front arriving Wednesday afternoon into Wednesday
evening which looks to bring a surge of very cold air and potential
for snow showers and snow squalls. This type of event would present
dangerous driving conditions for the evening commute and those
traveling Wednesday afternoon/night to Thanksgiving destinations.
After that, unseasonably cold air settles in Thursday giving us a
very cold Thanksgiving Day and night. Some areas could be near
record low maximum temperatures for the calendar day.

We start the long term period off with the shortwave from Tuesday
exiting out to sea with subsidence in its wake giving us partial
clearing. High pressure builds into the Northeast for Wednesday with
breaks of sun and temperatures warming in the mid-upper 30s.
However, an impressive 500mb cut off low in southern Canada looks to
dive southeastward into the Northeast Wednesday afternoon into
Wednesday evening ushering in a quick moving clipper and associated
arctic cold front. The GEFS show this arctic air mass to be 1 to 2
standard deviations below normal which helps illustrates just how
cold it is. With such a strong temperature gradient apparent at
850mb as this arctic front traverses the region, it is no surprise
that we also also see steepening lapse rates in the boundary layer
as the front moves through. This is a typical set-up for snow
squalls and the recently developed snow squall parameter highlights
Wednesday afternoon into Wednesday evening as a favorable period for
snow squalls, especially for areas near and north/west of the
Capital District. Since the boundary layer could mix up to 700mb
with 925mb winds near 35-45knots, strong winds could also occur
during any snow squalls. Temperatures initially could be in the mid-
30s but then drop quickly in the 20s during any snow squalls which
could allow snow, albeit low accumulations, to accumulate on
surfaces presenting a danger to drivers.

Strong Canadian high pressure near 1040mb quickly moves downstream
into the Northeast Wednesday night into the Thanksgiving holiday
with the strong pressure gradient likely keeping breezy conditions
in place. Very strong cold air advection continues overnight in the
wake of the arctic front with 850mb isotherms dropping impressively
to -18C to -20C by 12z Thursday. Even though we should see sunshine,
such a cold air mass will likely inhibit most locations across
eastern NY and western New England from rising out of the 20s for
the Thanksgiving holiday. This could challenge record low maximum
temperatures for the calendar day. Clear skies follow for Thursday
night with winds weakening. Radiational cooling under this arctic
air mass and a snow pack on the ground should allow temperatures to
plummet overnight into the low teens and even single digits.

High pressure remains firmly in place Friday giving us mostly sunny
skies with below normal temperatures continuing, although not as
cold as Thursday. Our high should shift into New England for
Saturday giving us southwesterly return flow and  temperatures
finally warming back to near seasonable levels in the upper 30s to
near 40. The next threat for precipitation then arrives Saturday
night into Sunday.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Weak high pressure will build across the TAF sites from the west
overnight into Sunday morning. An upper level disturbance and
wave of low pressure will approach from the Ohio Valley region
later Sunday afternoon into Sunday night.

BKN-OVC skies will persist across the terminals with a westerly
flow regime through this evening, with Cigs mainly in VFR
range, except for occasional MVFR cigs at KPSF. Lower level Cigs
should gradually erode after midnight, with valley sites
KPOU/KALB/KGFL scouring out first then eventually KPSF as high
pressure builds in.

High and mid level clouds will increase towards Sunday morning
ahead of a weak disturbance approaching from the south and west.
Clouds will thicken and lower through the afternoon, with areas
of light snow developing between 21Z-24Z/Sun from southwest to
northeast. Cigs should drop into the MVFR range once the snow
begins, with Vsbys trending to MVFR/IFR at KALB/KPSF, with
possible MVFR elsewhere. Some rain may be mixed in at KPOU when
the precipitation starts.

Winds tonight will be west to northwest at 5-10 KT this evening,
becoming light/variable after midnight into Sunday morning.
Winds will become south to southeast at 4-8 KT Sunday afternoon.

Outlook...

Sunday Night: Moderate Operational Impact. Likely SN.
Monday: Moderate Operational Impact. Scattered SHRA...SHSN...SN.
Monday Night: Low Operational Impact. Scattered SHSN.
Tuesday: Low Operational Impact. Scattered SHRA...SHSN.
Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: Moderate Operational Impact. Chance of SHSN...SN.
Wednesday Night: Moderate Operational Impact. Chance of SHSN.
Thanksgiving Day: No Operational Impact. NO SIG WX.

&&

.FIRE WEATHER...
A weak cold front will move south of the region tonight with
high pressure briefly building in with diminishing lake effect
activity. Mainly light snow will begin to overspread the region
Sunday afternoon into the night time period, as a disturbance
passing south of the region will be moving along the old frontal
boundary, as temperatures for mid November will continue below
normal.

&&

.HYDROLOGY...
Flows will continue to lower in the colder than normal
temperatures and mainly dry weather, except for lake effect
snow showers over the western Adirondacks into the western
Mohawk Valley.

A disturbance moving along a front south of the region will
bring some light snowfall amounting to light accumulations of a
few inches or less late Sunday afternoon through Monday. Another
disturbance and a cold front will bring chances of snow showers
on Tuesday and Wednesday with light QPF.

Colder than normal temperature persist into the Thanksgiving
holiday with flows continuing to recede.

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...NAS
NEAR TERM...KL/NAS
SHORT TERM...NAS
LONG TERM...Speciale
AVIATION...KL/JPV
FIRE WEATHER...NAS
HYDROLOGY...NAS

NWS ALY Office Area Forecast Discussion