Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 040000

Area Forecast Discussion
National Weather Service Buffalo NY
700 PM EST Sat Dec 3 2016

Nuisance lake effect rain and snow showers southeast of Lakes Erie
and Ontario will gradually diminish tonight as high pressure builds
across New York State. A few periods of rain and wet snow will then
follow Sunday night through the middle of next week as several weak
systems cross the area. Much colder air arrives late next week and
will bring an increasing potential for significant lake effect snow
downwind of the lakes.


Weak lake effect will continue southeast of Lake Erie early this
evening with slowly ending overnight. Diurnal cooling will support
any remaining showers falling mainly as wet snow from early to mid
evening through the overnight. A few spots across higher terrain
will see minor accumulations of less than an inch.

East of Lake Ontario, upslope will continue across Northern Oswego
and  Lewis Counties. Recent returns are very weak and may suggest
fine snow grains or some drizzle. All of this will slowly diminish
overnight. Expect little or no additional accumulation this evening.

Outside of lake effect areas, expect plenty of low stratus to remain
most of the night, with partial clearing possible late across the
North Country. Expect lows of around 30 on the lake plains of
Western NY, with mid 20s in the cooler Southern Tier valleys and
east of Lake Ontario.

Sunday...High pressure will build overhead with Pesky clouds hanging
tough in many areas. Weak northwest upslope flow and the low
December sun angle will offer little help in mixing out the low
level inversion responsible for trapping the low level moisture.
There may be some partial clearing briefly during the late morning
and early afternoon as the inversion weakens. This will be quickly
followed by more mid level clouds later in the day as warm advection
and isentropic upglide increase ahead of the next trough. Any precip
will hold off until Sunday evening across Western NY. High
temperatures will be around 40 on the lake plains of Western NY,
with mid 30s across the higher terrain of the Southern Tier. The
North Country will stay cooler with mid 30s at lower elevations and
upper 20s to around 30 across higher terrain.


Sunday night the weather will begin to deteriorate as a shortwave
over South Dakota this afternoon crests a ridge of high pressure
over the east coast Sunday night. This shortwave will carry Gulf of
Mexico moisture eastward this weekend, and with near saturation in
the favorable snow growth zone, combined with lift ahead of the
shortwave and good isentropic upglide, a period of light snow will
form from west to east across the CWA Sunday night and into Monday
morning. This shortwave will be quick moving thus overall snow
amounts will be light, generally an inch or two across the region
Sunday night through Monday morning.

Behind the shortwave we may see a brief lake response Monday, though
rapidly falling inversion heights, and loss of moisture within the
good dentritic snow growth zones will all but end any real threat
east of both lakes.

A brief ridge of high pressure will then bring fair weather later
Monday and into the first part of Tuesday. Later Tuesday a
shortwave, currently over the SW US will transverse the Plain States
and reach the Northeast by the afternoon hours. This shortwave will
again bring Gulf of Mexico moisture northward, and will also be a
several degrees warmer considering its source region. After a likely
dry start to Tuesday, this feature will bring a mix of rain and snow
to the region later Tuesday and Tuesday night.

Highs through the period will average a few degrees warmer than
normal, with afternoon temperatures reaching the upper 30s (higher
terrain) and lower 40s (lake plains). Overnight lows will be around
freezing, except for Tuesday night when the system from the
Southwest will keep most of the region at or above freezing.


A major pattern change will take place with a prolonged northerly
flow across the region bringing colder temperatures and periods of
snow. While there are still significant differences on the
specifics, there continues to be model agreement on the overall
pattern. Cold temperatures aloft will support persistent lake
effect snow in the Thursday through Saturday. Because of
uncertainty in wind direction, snowfall amounts cannot be
determined. This said, there is little doubt that there will be
accumulating snow at some locations during this time, some of
which could be significant. Now for the specifics...

A weak wave of low pressure will cross the region Wednesday, with
mostly rain showers which will end from west to east during the
day. Gradually colder air will build behind the low Wednesday
night, with some light rain or snow showers but no significant

Things get more complex later in the week as temperatures aloft
get plenty cold enough to support snow. Despite other differences,
model consensus pretty consistently drops 850mb temperatures down
to -12C to -14C. The key model difference can be seen between the
12Z operational GFS and ECMWF. The GFS develops a strong low near
Maine on Thursday while the ECMWF is much weaker and later with
this low. The GGEM and various GFS ensembles differ as well, also
with differences with the strength and track of the low. All of
this impacts moisture and wind direction which will ultimately
determine who gets the snow. The forecast uses a blend of model
guidance, providing more weight to the ECMWF model given both its
track record and that it is supported by many GFS ensemble members
which appear under- represented in the operational consensus.

Precipitation is likely on Thursday as the surface low develops
and with temperatures cold enough for most of this to fall as
snow. By Thursday night it will be cold enough for snow in all
locations with diminishing synoptic moisture, but still a cyclonic
flow which will provide ample moisture for lake effect snow. Lake
effect snow is likely at least through Friday night, with snow
showers continuing through Saturday but diminished areal
coverage. The mean flow during this time will most likely be WNW,
but variations in the flow will occur. This would put the
greatest amounts southeast of Lake Ontario, with significant
amounts also across the Western Southern Tier. However, this
pattern would bring snow to all areas at times, and a slight shift
in wind direction could easily shift the areas of greatest
concern. Details will come into better focus over the next couple
days as model guidance comes into better agreement.

Otherwise high temperatures will be mainly in the 30s Thursday,
with highs in the upper 20s to lower 30s on Friday and Saturday.
Lows should mainly be in the 20s, with some teens across the
interior. This favors raw model consensus over Superblend given
the widespread cloud cover and the persistent winds.


A cool northwest flow across the region will continue to produce
extensive stratus clouds through tonight with a mix of MVFR and
lower end VFR CIGS. The MVFR CIGS will be favored across higher
terrain and in any narrow bands of lingering lake effect showers.
Lake effect is showing up better southeast of Lake Erie where a
TEMPO group has been included for KJHW. East of Lake Ontario just
some fine snow grains or light drizzle may be found mainly inland
from KART.

Stratus will hang in through Sunday but mainly at VFR levels. KJHW
looks to be the only site which will see persistent MVFR CIGS
Sunday. Otherwise, mid level clouds will increasing from west to
east in advance of a weak warm front approaching the region.

Sunday night...IFR/MVFR with a period of light snow. Snow will mix
with rain across Western NY.
Monday...MVFR with a chance of rain and snow showers.
Tuesday...Mainly VFR.
Tuesday night and Wednesday...VFR deteriorating to MVFR with some
rain becoming likely.
Thursday...MVFR/IFR with snow likely.


Moderate northwesterlies will continue on Lakes Erie and Ontario
before slowly subsiding from west to east later overnight as high
pressure builds into the Lower Great Lakes. This will bring an end
to Small Craft Advisories overnight.

Winds will remain light Sunday and Sunday evening with high pressure
overhead. A trough will then cross the region Sunday night and
Monday. In the wake of this trough westerlies will increase again
Monday afternoon and produce choppy conditions on both lakes,
although conditions may remain just below Small Craft Advisory
levels. Relatively light winds will then continue through midweek
before increasing again late week as colder air moves back into the
Great Lakes.

Gales are possible late in the week as low pressure develops
across the Canadian Maritimes and establishes cold air advection
which will help mix winds aloft. Model guidance still differs on
the strength of this low.


MARINE...Small Craft Advisory until 4 AM EST Sunday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Sunday for



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