Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 040308
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1008 PM EST Sat Dec 3 2016

.SYNOPSIS...
High pressure will briefly build across New York State on Sunday
with widespread cloudiness lingering through much of the day. 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.

&&

.NEAR TERM /THROUGH SUNDAY/...
Radars are showing very isolated returns late this evening under
northwest flow. Have cut back POPs to slight chance as high pressure
centered over the Ohio Valley continues to build east lowering
inversion heights across the forecast area. Satellite imagery and
surface obs show lingering low clouds which should remained trapped
beneath the building high pressure through the remainder of the
overnight. This cloud cover is also keeping temperatures a little
warmer so bumped up overnight lows to a range of upper 20s to low
30s across western NY and low to mid 20s east of Lake Ontario.

Sunday...The high 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.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
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.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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
accumulations.

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.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
A cool northwest flow across the region will continue extensive
stratus clouds through the overnight with a mix of MVFR and lower
end VFR CIGS. Nearly all of the lake effect showers have ended as
surface high pressure over the Ohio Valley builds east.

Low 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.

Outlook...
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.

&&

.MARINE...
Northwesterlies have slackened late this evening with advisory level
winds and waves only lingering over the southeast Lake Ontario
nearshore waters. Expect winds and waves to continue to subside
overnight as high pressure over the Ohio Valley builds east. This
will yield light winds for Sunday and Sunday evening.

A trough will 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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 4 AM EST Sunday for LOZ043-044.

&&

$$

SYNOPSIS...HITCHCOCK/SMITH
NEAR TERM...HITCHCOCK/SMITH
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...HITCHCOCK/SMITH
MARINE...HITCHCOCK/SMITH



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