Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 071621
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
1121 AM EST Wed Dec 7 2016

.SYNOPSIS...
An occluded front will move across the region today as
the light snow and rain will end by the early afternoon.  High
pressure will briefly build in from the south.  However...a strong
upper level disturbance will move through tonight allowing heavy
lake effect snowfall to impact the western Adirondacks Thursday
into Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 1120 AM EST, the coverage of light snow and drizzle is
continuing to decrease, and there is some partial clearing in
western NY/PA. By mid afternoon, most of the spotty light snow
and drizzle should be gone. We could see some break up of the
clouds through the afternoon, especially across portions of the
western Mohawk Valley, but low clouds may be tough to dislodge
farther east, and therefore have trended afternoon forecast to a
cloudier scenario. Still, brightening of the sky and maybe a few
brief sightings of sun from time to time may occur by mid
afternoon, which may will help temperatures get into the lower to
mid 40s across portions of the mid Hudson Valley, with generally
mid 30s to lower 40s elsewhere.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
Lake Effect Snow Warning for northern Herkimer and Hamilton
Counties 9 am THU to 7 am Friday...

Tonight...Most of the forecast area will be under the influence of
the weak ridge of high pressure from the south and west. The
exception will be the western Adirondacks, where the leading edge
of much colder air approaches from the west especially after
midnight. Some snow showers tapping Great Lakes moisture will
begin to impact locations north of Rt 28 in the western
Adirondacks between 06Z-09Z. The H500 upper level low will move
over southwest Quebec. Pops were increased to chance to low likely
values for the snow showers ahead of the arctic front or sfc
trough prior to 12Z over the western Adirondacks. Lows will
generally be in the 20s.

Thursday-Thu night...An upper level disturbance and its
associated arctic front/sfc trough moves across the forecast area.
The flood gates open across Lake Ontario for an organized well-
defined lake band to form in the veering low-level flow to
a favorable 260-270 degree trajectory by the late morning into
the afternoon. The NAM shows little directional shear in the sfc
to H850 layer. The instability class goes to conditional to
moderate and occasionally extreme on neighboring BUFKIT
soundings, and the low-level capping inversion is not visible
below 10 KFT AGL. The avg lake temp is close to 7C. Favorable
delta T readings between the sfc to 850 or 700 hPa will favor a
heavy lake effect event for the western Adirondacks. A quick check
of the GFS and NAM sounding data with the KVIE inland extent
program /developed from past CSTAR research/ for KUCA and KALB
showed lake band extent possibly to 75-100 miles inland. This band
extent would be well into the western Adirondacks. Snow ratios of
20:1 were THU-THU night for that area. Confidence was moderate to
high to issue a lake effect snow warning for the northern Herkimer
and Hamilton Counties. Locations in the western portion of
Hamilton county will be most vulnerable for heavy lake effect
snow. Snow rates could reach 1-3" an hour especially late THU pm
into Thu night. Total snowfall of 8-14" is possible over northern
Herkimer CTY especially from Old Forge northward along Route 28.
North and west of Raquette Lake could have 6-10".
Elsewhere...isolated to scattered snow showers/squalls and
flurries will be possible with light snow accums along the western
spine of the southern Greens/Taconics/Berkshires. It will become
blustery and colder. H850 temps fall to -10C to -14C THU night.Highs
THU will only be in the upper 20s to mid 30s across the higher
terrain and mid 30s to around 40F in the valleys. Thu night will
feature brisk and cold conditions with the lake effect snowfall.
Lows will be in the teens to lower 20s over the mountains...and
lower to mid 20s in the valleys.

FRI-FRI night...The mid level trough axis moves across the region
Fri morning. The low and mid level flow will continue to veer and
take the lake effect activity further south and west of Albany in
the western Mohawk Valley...northern Catskills and Schoharie
Valley. We were not confident for a lake effect watch for southern
Herkimer County. We do think an advisory maybe be possible for 3-6
inches of snowfall or slightly more, but it is in the 4th to 5th
period. We will mention the possibility in the HWO for southern
Herkimer and Fulton and Montgomery. The flows veers quickly Friday
for lighter amounts further south across the Schoharie valley and
eastern Catskills. Light amounts would be 1-4". From the Hudson
Valley east drier and cold conditions are expected with H850
temps 1-2 standard deviations below normal...highs will only be in
the 20s outside the the Hudson River and CT River Valleys with
30-35F readings within them. Lows will be cold FRI night with
teens...and some single digit readings over the southern
Adirondacks.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Winds back somewhat to a more west-northwesterly direction
Saturday as a surface high builds to our south. With cold airmass in
place (850 mb temps around -15C) and moisture flux off the lake,
expect additional light to moderate lake effect snow showers to
continue, especially for the Western Adirondacks, Mohawk Valley, and
Schoharie Valley. High pressure appears to manage to build into our
area late Saturday/Saturday night as upper heights rise briefly,
resulting in and end to lake effect snow showers. Low temperatures
could be quite cold Saturday night if cloud cover can diminish.

Active pattern continues with fast quasi-zonal flow across the
CONUS. Medium-range deterministic models show a quick-moving wave of
Pacific origin amplifying over the eastern CONUS. Where and when
this amplification occurs is unclear, but significant consensus
exists among deterministic GFS/ECMWF/CMC and GEFS members to result
in precipitation likely forced by isentropic lift late Sunday/Sunday
night. With antecedent cold airmass, expect this would be mostly
snow. Likely PoPs for most of the CWA Sunday night.

Things become more muddled early next week, as ECMWF tracks another
wave through the region which would bring more widespread
precipitation, while GFS/CMC have a clean cold frontal passage which
would result in another cold snap and more lake-effect snow.
Regardless, fairly good agreement in a continuation of below-normal
temperatures next week.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
Deeper moisture has exited the area, leaving pockets of
drizzle/light rain showers. (L)IFR conditions prevail in a moist
boundary layer with light/calm flow. Expect poor aviation
conditions to persist into the daylight hours before gradually
improving during the late morning and early afternoon.

Tough call with whether MVFR-level clouds will scatter during the
evening and overnight as a ridge of high pressure builds in to our
south. Terminals look to be on the edge between the clearing now
noted over IN/OH and Great Lakes moisture further north. For this
TAF package, went with VFR conditions overnight but will continue
to monitor trends.

Light variable/easterly flow early becoming and south to
southeast during the late morning, veering to westerly during the
afternoon at less than 10kts.

Outlook...

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

&&

.HYDROLOGY...
Light precipitation amounts in the form of mainly snow occurred
last night into this morning with liquid equivalents of a tenth to
a quarter of an inch.

The active weather THU into FRI will be from lake effect snowfall
downwind of Lake Ontario. Precipitation will fall mainly as snow
through the weekend. Heavy lake effect snowfall is expected for
the western Adirondacks...and possible portions of the western
Mohawk Valley and Northern Catskills late in the week into the
early portion of the weekend.

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...Lake Effect Snow Warning from 9 AM Thursday to 7 AM EST Friday
     for NYZ032-033.
MA...None.
VT...None.

&&

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


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