Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 101439
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
939 AM EST Sat Dec 10 2016

.SYNOPSIS...
A flow of cold air will continue to generate areas of lake effect
snow east and southeast of the lakes today and into tonight. An area
of low pressure will then move through the Great Lakes region Sunday
and Monday and bring a widespread general snowfall to the
region...which may mix with a little rain or sleet before ending.
Bitterly cold air will build in behind this system for the latter
half of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Southern Erie county upgraded to a warning since a band of heavy
snow will continue to stream across far southern portions of the
county for the next several hours. One of several bands of moderate
to heavy snow off Lake Erie has edged north into the far southern
end of Erie County. This band is forecast to continue by most
mesoscale model guidance through this evening at varying
intensities.

Also added an advisory through this evening for Allegany and Wyoming
counties. A narrow band of moderate to heavy snow is extending inland
across central Allegany county this morning, with additional snow
clipping the southwest corner of Wyoming county. These areas may be
persistent through the morning, then become more intermittent this
afternoon and evening. Expect additional amounts of 3-6 inches in
localized areas in these two counties.

Areas along the immediate shoreline of Lake Ontario still may get
some lake effect snow today and into tonight. Radar shows snow
showers organizing across Western Lake Ontario and brushing the
Niagara and Orleans county shorelines. This may produce another 1-
2 inches of accumulation through midday. Another band of snow is
getting better organized over Wayne County near Sodus and will
remain in place through midday. Winds will initially be light, but
moisture from a shortwave and upstream lakes will enhance lake effect
activity this morning. Most mesoscale guidance develops a meso- low
over the lake which will drift east this afternoon and probably clip
the shorelines east and southeast of the lake. Lake effect headlines
associated with this are challenging since the progression of such a
system is difficult to pin point due to the weak flow. Using
consensus wind forecasts and mesoscale guidance, will carry Lake
Effect Snow Advisories east and southeast of the lake.

Things are more straightforward off Lake Erie, with a steady WNW
flow today forecast to shift to the WSW this evening. Snows off
Lake Erie will continue to take advantage of the significant lake
induced instability, and moisture from Lake Huron. Early this
morning, radar shows multiple bands with the most intense across
Northern Chautauqua/Cattaraugus and just clipping far Southern
Erie county. This band should continue through this morning. The
band may briefly disrupt late afternoon behind the shortwave, but
should reorganize this evening as a better aligned WSW flow
develops into a singular convergence band and lifts northward this
evening. The band will continue to lift toward the Buffalo metro
area late tonight, but should weaken as the flow becomes weaker.
This still may drop an inch or two of snow in downtown Buffalo,
but amounts will taper off quickly to the north of the city.

Outside of the lake effect snows, expect mostly cloudy skies this
morning, with a few snow showers or flurries with the shortwave.
After this, expect a few breaks of sunshine this afternoon, with
cloudy skies downwind of the lakes. Temperatures will continue to be
cold with highs in the mid 20s to around 30. Expect lows in the
teens to lower 20s tonight, largely depending on how long skies
clear out.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Sunday morning there will likely remain lake effect snow east of the
Eastern Great Lakes. A backing wind, but very weak flow aloft over
Lake Erie will likely limit lake snows to over the lake, and then
along the shoreline/and across northern Erie County. The wind field
will be a bit stronger east of Lake Ontario, and with backing winds
we should see a band of snow drift northward from near the Tug Hill
early Sunday morning, then weaken through the morning as snows carry
northward across Jefferson County, and across the Saint Lawrence
Valley.

Just as this long lived lake effect event winds down, we`ll turn our
attention to a synoptic system, one that may bring light snow to WNY
before lake effect snow finally ends across the CWA.

Water Vapor imagery this early Saturday morning displays an upper
level low near Vancouver Island, and this low will track across the
northern United States this weekend. An area of low pressure over
the Central Plains Sunday morning will begin to deepen and track
northeastward across the Central Great Lakes Sunday night, and then
just to our north Monday. Driven by isentropic upglide lift, this
system will bring an initial burst of light snow during the day
Sunday across Western New York. Snow will likely remain light
through the day, and will not pick up in intensity until later
Sunday afternoon and overnight.

Aloft Sunday night a 140 knot 300 hPa jet will be stretched across
the Central Great Lakes and towards northern New England, with the
core of the jet to our east. This will place our region within the
right entrance region of the upper level jet. In the lower levels a
60 knot low level jet will be crossing the mid-Atlantic states to
our east, with the core of the jet remaining across SE PA. This will
place our region within the left exit of the lower jet. Favorable
jet dynamic lift, in addition to increase convergence in the lower
levels as the surface low nears our region, and continued isentropic
upglide will bring large scale synoptic lift. Abundant moisture
lifted through a deep dentritic snow growth zone will bring high
confidence that precipitation will occur Sunday night, though
thermal profiles are a bit less confident in precipitation type
through the event. The NAM is more bullish with warmer air lifted
northward, bringing a wintry mix, and in some cases plain rain
across the CWA later Sunday night and into Monday.

A look at Ensemble Guidance, the 09/21Z SREF members favor more snow
than rain, with any freezing rain chances lying just to our east
across central PA/NY. The GEFS ensembles maintain snow through about
06Z, then transition the precipitation over to plain rain as warmer
air ridges northward ahead of an incoming cold front. Given that
track of this system to our west and north it is not out of the
question that warmer air aloft can reach our region. For now will
continue near previous thinking, and that is to bring snow across
the region Sunday night, transitioning to rain late Sunday night
across the Southern Tier, and then across the remainder of the CWA
Monday. Snow totals will likely fall within the advisory range with
a general 3 to 6 inches forecasted across the region. Given the
large scale lift there may be a few bursts of snow that give an inch
per hour snowfall rate, but this will be short lived. Greatest
snowfall totals may be across the southern Tug Hill region where
southern upslope flow may bring a half foot or slightly more over a
24-hr period. Still a good deal of uncertainty among the models in
both the characteristic of the storm with how deep it will become,
and also the thermal profiles...so at this point there is still to
much uncertainty to go with any winter storm watch across portions
of our CNY counties.

Monday we`ll lose the moisture within the snow growth zone as a
wedge of drier air aloft follows the cold front. Point soundings
suggest we`ll remain nearly saturated in the lower levels near the
surface through the day. This will likely bring some drizzle to the
area, and possibly light snow. Temperatures will likely be too warm
for lake effect early Monday morning, though some cooling through
the day may bring a little lake effect snow late in the day, this to
follow the light rain/drizzle/orographic lift precipitation earlier
in the day.

Behind the cold front Monday, winds will become gusty. Through the
day Monday the surface low will remain steady state- averaging
around 1010 mb and not overly deep. Mixing behind the cold front
will likely bring winds gusting within the 30-40 mph range across
the lake plains Monday and into early Monday evening.

Later Monday and Monday night cold air advection will lower the
dentritic snow growth layer, such that it will now cool to areas that
are with more moisture, leading to likely bands of lake effect snow
east of both lakes. Lapse rates will not be as great as with prior
lake effect events this season, with temperatures at 850 hPa dipping
to around -8 to -10C at 850 hPa...this over lake waters that are now
cooling to around +5C. Expect bands to remain weak...and for now
will have just a few inches in the forecast, with the higher totals
east of Lake Ontario.

Temperatures Monday and Tuesday will likely climb above the freezing
mark. Overnight lows will drop below freezing, with the coldest
night Tuesday night where temperatures will drop into the teens to
lower 20s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
The active and very wintry pattern will continue through the long
term, and even intensify by late next week. Looking at the longwave
pattern, a sharp upper level ridge will build over Alaska early next
week and allow for a period of cross polar flow, with Siberian air
making the trip across the Arctic and into northern Canada. The
Alaskan ridge will remain in place through much of the week and
force a deep longwave trough to develop over central and eastern
North America. A large piece of true arctic air will move south
through the Canadian Prairies and reach the Great Lakes and New
England later next week. This may set the stage for another round of
significant lake effect snow for Thursday and Friday. As the cold
air comes in, another baroclinic wave may bring some widespread
general snow Wednesday.

Looking at the details, on Tuesday and Tuesday night a weak trough
will pass through the Great Lakes and may produce a few light snow
showers of little consequence. There may also be some limited lake
effect snow east of the lakes, but marginal instability will keep
this light.

On Wednesday the longwave trough will begin to dig into the Northern
Plains and Upper Great Lakes. Ahead of the trough, medium range
model guidance develops a baroclinic wave over the Ohio Valley and
Northeast. The GFS and most of it`s ensemble members along with the
Canadian GEM are more aggressive with this, and would produce a
general light to moderate snowfall across the entire area. The 12Z
ECMWF is much weaker with this feature. The ECMWF has shown a good
deal of inconsistency with this system, as previous runs looked more
similar to the current 12Z GFS. With this in mind, went closer to
GFS based guidance with snow likely for Wednesday.

In the wake of this system cold air will flood into the Great Lakes
Thursday and Friday. This will be the coldest air of the season,
with 850mb temps plummeting to -20C or colder. A look at sounding
climatology, values this cold would be close to record minimum at
850 hPa, with mid-December moving record-minimum average around -
20C. Given this, will keep temperatures below guidance for the
Thursday through Friday night period.

This will translate into highs in the teens and lows in the single
numbers away from the immediate lakeshores. There may also be a few
sub-zero readings within the traditionally colder interior spots. In
addition wind chills both days will likely fall below zero.

The deep cold air crossing the lakes and the overall pattern is
suggestive of more significant lake effect snow downwind of the
lakes for Thursday and Friday, however there are significant
differences in wind direction, not to be unexpected given this is
still 6-7 days out.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
Outside of lake effect snows, expect mainly VFR conditions. A WNW
flow will result in the most persistent snows across the Western
Southern Tier. Expect frequent IFR conditions, especially during
the day today when the steadiest band is expected to focus near
the JHW terminal. Lighter lake effect snows are possible
elsewhere, with periods of MVFR conditions today.

Winds will shift to the Southwest late tonight which will lift
bands northward. This will end the snows at JHW, but likely bring
a few hours of IFR conditions at BUF late tonight.

Outlook...
Sunday...Deterioration to MVFR/IFR with widespread light snow
developing.
Sunday night and Monday...MVFR/IFR in widespread light snow.
Tuesday...MVFR with a chance of snow showers.
Wednesday...MVFR/IFR with snow likely.

&&

.MARINE...
A moderate WNW flow will continue to require SCA headlines through
tonight for Lake Erie. Winds will briefly diminish on Lake Ontario,
but then slowly pick up again from west to east this afternoon and
evening. Winds may not ever pick up on far eastern portions of Lake
Ontario, but westerly winds on the rest of the lake should be ample
to build waves and eventually require small craft headlines for all
of the Lake Ontario nearshores.

Winds drop off on Sunday between systems, then increase ahead of the
next system Sunday night when more small craft headlines may be
needed.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lake Effect Snow Advisory from 1 PM this afternoon to 6 AM EST
     Sunday for NYZ006-007.
     Lake Effect Snow Advisory until 6 PM EST this evening for
     NYZ004-005.
     Lake Effect Snow Warning until 10 PM EST this evening for
     NYZ019-020.
     Lake Effect Snow Warning until 1 AM EST Sunday for NYZ085.
     Lake Effect Snow Advisory until 1 AM EST Sunday for NYZ012.
     Lake Effect Snow Advisory until 10 PM EST this evening for
     NYZ021.
MARINE...Small Craft Advisory until 7 AM EST Sunday for LEZ040-041.
         Small Craft Advisory from 6 PM this evening to 7 AM
         EST Sunday for LOZ043>045.
         Small Craft Advisory from 1 PM this afternoon to midnight
         EST tonight for LOZ042.

&&

$$

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



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