Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 102055
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
355 PM EST Sat Dec 10 2016

.SYNOPSIS...
Low pressure tracking from the mid atlantic region Sunday will
strengthen as it tracks through southern New England and offshore
Sunday night and Monday. A widespread snowfall is expected late
Sunday afternoon into Monday, with the potential for moderate
accumulations over much of the area before transitioning to rain
and drizzle from the Capital Region south and east.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Northern periphery of high pressure will be over our region
tonight and winds will ease as some of the lake effect moisture
gets cut off. Some of the cloud cover should mix out as well with
the subsidence. Boundary layer moisture does seem to be increasing
over the OH valley and Great Lakes which could extend some of that
cloudiness into our area later tonight and toward daybreak. Areas
that see the most clearing and light winds should see temperatures
drop into the lower to mid teens but single numbers northern areas
and upper teens valleys.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Winter Weather Advisories issued for many areas for Sunday night
and Monday morning. Winter Storm Watches for the Southern
Adirondacks and southern Green Mountains. Since snow will arrive
latest in The Berkshires and Litchfield Hills, and a mix with rain
possible in the mid Hudson Valley, will let data and guidance
tonight determine what headlines are needed in those areas if
any.

Storm currently exiting the Rockies will track quickly east and
clouds will thicken through Sunday morning, with light snow
advancing to western areas around midday. Coverage of snow should
increase through the afternoon and by evening, most areas should
see snow but again light amounts through sunset, maybe an inch or
two in western areas and maybe a dusting to an inch eastern areas.

Sunday night, there is a good consensus on the strong low level
jet forcing, thermal gradient forcing and isentropic lift. The
bigger questions are how much moisture will contribute to liquid
equivalents across the region and how far north will warmer
boundary layer temperatures get Monday morning allowing for a mix
with sleet and rain in some areas? Some ensemble guidance and
mesoscale model data show totals of 5-10 inches of snow in higher
elevations of the southern Adirondacks, eastern Catskills and
southern Green Mountains, while other guidance is not as
aggressive with snow amounts.

There is a good consensus in guidance and run to run consistency
for advisory level snows in most areas, even the valleys, through
Monday morning. The dendritic growth zone is quite elevated but
some of the column of strongest upward motion extends through it.
Snow ratios should be near climo, so taking a blend of QPF
guidance and using those snow ratios around 12:1 supports the
current headlines.

Snow should increase in intensity Sunday night and by daybreak
Monday, many areas should see 3-6 inches of snow, with some
terrain upslope areas seeing 7 or more inches. These snowfall
predictions will likely be adjusted as newer data and guidance
arrive tonight and Sunday, so stay tuned, they may be raised or
lowered depending on how the storm evolves and where and when any
mixed precipitation occurs.

The system exits rapidly as does the deeper moisture Monday
morning. Precipitation should end by noon in most areas, with
just moisture through the boundary layer through the afternoon
contributing to light rain/snow and drizzle but quite light and
maybe very spotty. West boundary layer flow and the start of cold
advection may mix out some of the low level moisture and clouds
which would help temperatures warm well into the 30s to around
40. Southern areas may push the mid 40s depending on whether snow
cover anchors cold air at the surface or if the west flow helps
mixing since boundary layer temperatures could support surface
temperatures in the 40s. Temperatures on Monday are tricky and
just went a slight bit below guidance until mixing potential can
be better analyzed.

Monday night, cold advection increases as does isolated to scattered
lake effect snow shower activity. Isolated to scattered Lake
effect snow shower activity should be confined to the usual
southern Adirondacks, western Mohawk Valley, Schoharie Valley and
eastern catskills through Tuesday. Highs Tuesday in the mid to
upper 30s but 20s higher terrain.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A chilly pattern as polar vortex dives southward across central
Canada then eastward between the Great Lakes and James Bay through
the end of this week.  This will keep temperatures below normal with
lake effect potential continuing.

The 12Z NCEP Model Suite and international guidance are in rather
good agreement with the synoptic pattern evolving for the upcoming
week as increasing baroclinicity between I70 and I80 should take
most of the moisture and precipitation south of our local area
(compared to yesterday at this time).  However, any subtle wave not
resolved in the models could touch off additional snow showers and
flurries across the region.  The exception to this will be downwind
of Lake Ontario.  As lake temperatures were still well into the 40s
Fahrenheit per GLERL analysis and buoys still deployed, delta t/s
are expected to remain quite high through the week to keep the
threat for snow showers/squalls into portions of Herkimer and
Hamilton counties.  This is per the mean wind flow trajectories from
the westerly direction.

Then the coldest air of the season thus far is set to arrive
Thursday night into Friday.  While some timing differences remain,
seem the H850 temperatures are expected to drop well into the
negative 20s Celsius with even some hints as low as -30c Friday.
Potential for wind chill headlines do exist as we will monitor this
closely.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
While VFR conditions should prevail through the forecast cycle,
there is a chance for MVFR CIGS this afternoon as convective
temperature has been reached and some broken diurnally driven
clouds will result. Westerly winds will average near 10kts with
some occasionally higher gusts.

Clouds will continue to thicken overnight into Sunday with rather
light winds at the surface. There are some hints at another MVFR
CIG overnight around 2000 feet as warm advection gets underway.
For now, we will place a SCT deck and closely monitor trends.

Outlook...

Sunday Night: High Operational Impact. Definite SN.
Monday: High Operational Impact. Definite RA...SN.
Monday Night: Low Operational Impact. Slight Chance of SHSN.
Tuesday: No Operational Impact. NO SIG WX.
Tuesday Night: Low Operational Impact. Slight Chance of SN.
Wednesday: Low Operational Impact. Slight Chance of SN.
Wednesday Night: Moderate Operational Impact. Chance of SN.
Thursday: Low Operational Impact. Slight Chance of SN.

&&

.HYDROLOGY...
A substantial snowfall is possible Sunday night into Monday
night. At this time a moderate snowfall is possible with total QPF
currently forecasted in the one half to three quarters of an inch
range. The precipitation may change to rain from the Capital
Region south and east Monday late morning into the afternoon.

Flows will continue to lower in the cold air mass into the middle
of next week. No hydro problems are anticipated the next 5 to 7
days.

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 4 PM Sunday to noon EST Monday
     for NYZ038>043-047>054-058-059-063-064-083-084.
     Winter Storm Watch from Sunday afternoon through Monday
     morning for NYZ032-033-082.
MA...None.
VT...Winter Storm Watch from Sunday afternoon through Monday
     morning for VTZ013>015.

&&

$$
SYNOPSIS...NAS
NEAR TERM...NAS
SHORT TERM...NAS
LONG TERM...BGM
AVIATION...BGM
HYDROLOGY...NAS


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