Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 201156

Area Forecast Discussion
National Weather Service Buffalo NY
656 AM EST Mon Nov 20 2017

While accumulating lake snows will persist east and southeast of the
lakes through at least midday...high pressure passing across the
deep south later today and tonight will signal a warm up for our
region with the lake snows ending. The clockwise circulation around
the large high will boost temperatures into the 50s throughout our
region on Tuesday...but the warm up will be short lived as the next
cold front will plow across the area Tuesday night.


The deep cyclonic flow of chilly air that has been in place for the
second half of the weekend will give way to ridging today...and this
will result in the start of a warm advective pattern. This will
bring an end to the accumulating lake snows southeast of both
lakes...but not before they deposit several more inches of

Starting with the multiple bands of lake snow off Lake Erie...a deep
westerly flow will keep these fingers of snow in place thorugh much
of this morning...keeping them focused on the Southern Tier with an
eastward extent to the ridges bordering the Genesee Valley. Fresh
accumulations from daybreak til noon will only range from a coating
in most areas to a couple inches across the higher terrain north of
Stockton...Cherry Creek and Ellicottville. As we progress from the
morning into the midday...these bands will weaken and drift to the
north towards central Erie county. By this time though...snow
accumulations will be negligible. This should allow the
corresponding winter weather advisory for these areas to expire on 18z (1 PM).

The limiting cap over Lake Erie will then drop below 5k ft during
the remainder of the the weak activity will move as
far north as the BUF metro area. The residual lake effect should
only consist of a few nuisance snow showers or flurries.

Meanwhile off Lake Ontario...a much more pronounced lake response
will support more significant snow accumulations over Wayne...
northern Cayuga and much of Oswego County. The main reasons for the
notably stronger response is three fold. The bulk of the `credit`
can be given to an upstream connection off Lake Huron...which is
priming an otherwise marginally moist environment. The other big
influences is a higher cap that will allow for a deeper dendritic
growth zone...and finally a slower northward advance of the band
during the course of the day. Breaking this down...

During the remaining pre dawn hours...a band of lake snow over Wayne
and northern Cayuga counties will deposit several more inches of
accumulation for sites north of Route 104. As we move past
daybreak...the 300 flow that had been in place for most of the night
will gradually back to around 280. The well organized single band
will push north across Oswego county in the process. Snow
accumulations will generally range from three to six inches across
the county with snowfall rates as high as 2 inches an hour...but a
slower movement of the band could add several inches to this

As we move through the late afternoon into the early evening...the
band which will be centered in the vcnty of the Tug Hill plateau
will push north across Jefferson and Lewis counties. Like its sister
lake six hours earlier...the band of lake snow will now weaken as
the cap will lower to under 5k ft. More this point
it will not have any upstream priming to help produce snow either.
The lake band will weaken over the North Country during the course
of the night as moderately strong warm advection will essentially
erase the leftover instability over the lake. will feature a wealth of clouds with the mercury
peaking a few degrees higher than those from Sunday. Winds gusting
to 35 mph at times will likely keep us from noticing the negligible
warm up wind chills will be in the 20s and lower 30s. As
our low level flow becomes more southwesterly late today and
tonight...drier air will advect into the region. This will lead to
clearing from the southwest that will end with mainly clear skies
over the western counties midnight. The strength of the warm
advection will support a non-diurnal temp trend our lows
should occur by midnight or so with gradually rising temperatures
thereafter through daybreak.


On Tuesday surface low pressure over Central Ontario Province will
slowly push northeastward into western Quebec...while slowly dragging
its trailing cold front in our direction. With our area remaining
well out ahead of the front...we can expect a dry day with fairly
plentiful sunshine through midday/early afternoon only giving way to
some increasing clouds during the mid to late afternoon hours. This
said...the tightening pressure gradient in place out ahead of the cold
front will also guarantee the development of another round of rather
breezy to windy conditions during the day...with the strongest winds
found across far WNY which will lie under an axis of stronger (40-50
knot) flow in the 925-850 mb layer. While the low level warm air advection
regime will help to prevent these stronger winds from totally mixing down
to the surface...the prevailing south-southwesterly low level flow will
still be supportive of some wind gusts approaching or potentially even
meeting low-end advisory levels across Niagara and portions of Northern
Erie Counties...for which a mention will be added to our Hazardous
Weather Outlook. Otherwise we can expect a rather mild day...with the
aforementioned breezy to windy conditions...fairly plentiful sunshine...
and 925 mb temps of +4C to +7C all leading to widespread high temps in
the lower to mid 50s...and a few spots in the Finger Lakes possibly
even reaching the upper 50s.

Tuesday night the surface low will gradually lift toward the Ungava
Peninsula while dragging its trailing cold front across our region.
While the main surface low will thus remain far to our north...the
boundary will still have the robust support of a fairly sharp mid
level trough to work with...and this combined with low level convergence
and moisture pooling along the boundary should be more than sufficient
to generate a fairly solid band of rain showers as the front crosses
our region...for which PoPs have been further bumped up into the high
likely range. In the wake of the frontal passage...modest cold air
advection may then lead to the frontal precipitation briefly mixing with
or changing over to wet snow before quickly ending overnight...with only
very minimal snowfall accums of under a half inch possible across the
higher terrain. Otherwise...the cold advection regime behind the front
will result in low temperatures falling back to the lower to mid 30s.

Following Tuesday night`s frontal passage...high pressure with colder
and much drier air will build across the region Wednesday and Wednesday
night. While this fresh airmass will be plenty cold enough to support a
lake response east and/or southeast of the lakes...its rather dry nature
should limit this to just some scattered light snow showers east-southeast
of the lakes Wednesday...with these then likely falling apart altogether
Wednesday night as the ridge crests overhead. Otherwise conditions will
be mainly dry...and thus favorable for pre-Thanksgiving travel across
our region. With regard to temperatures...the colder airmass will result
in high temps remaining confined to the mid and upper 30s on Wednesday...
with lows then ranging through the 20s Wednesday night.

On Thanksgiving Day fair/dry weather should largely continue with the
aforementioned surface ridge remaining in place a little to our south...
with just a few scattered lake effect snow showers possible across the
North Country as the next cold front approaches from the northwest...
and leads to an increase in moisture across Lake Ontario. Otherwise high
temperatures will again generally range between 35 and 40 degrees...
albeit with a gradually freshening southwest wind as the pressure
gradient tightens some out ahead of the approaching cold front.

Finally for Thanksgiving night...the various guidance packages have
come into better agreement that the next cold front will quickly slide
southeastward across our region...though the bulk of its effects still
look to remain largely confined to the North Country...where scattered
frontally-driven snow showers may at least become briefly enhanced by
Lake Ontario and lead to some minor accumulations. Meanwhile...the rest
of the area should be drier with much more widely scattered snow showers.
Temperature-wise...we can expect more of the same with overnight lows
ranging in the mid to upper 20s.


On Friday...mainly dry and uneventful weather will return as another
narrow ridge of high pressure quickly traverses the region in the wake
of Thursday night`s cold front. As the axis of this ridge departs to
our east...developing warm air advection will help afternoon highs
to largely climb back into the lower 40s south of Lake Ontario...and
into the mid to upper 30s across the North Country.

After still appears that the rest of this period will feature
a return to more unsettled weather courtesy of a another area of low
pressure that the medium range guidance packages all track eastward
across Ontario and Quebec Provinces Friday night through Saturday
night. Out ahead of this system...continued warm air advection should
lead to a non-diurnal temperature trend and renewed chances for rain
and snow showers Friday night...followed by a relatively mild day and
some additional rain showers on Saturday as the low pivots its trailing
cold front into our region. Following the cold frontal passage...steady
cold air advection should result in lingering rain showers changing back
over to snow showers Saturday night...with a general northwesterly flow
of colder air then supporting scattered snow showers and areas of lake
effect snow southeast of the lakes on Sunday.


VFR conditions will be found across the majority of the region a large area of high pressure will nose north across our
region from the Deep South. The only issue will be continued lake
effect snow that will be found east-southeast of the lakes.

Disorganized...multiple bands of lake effect snow over the Southern
Tier this morning will produce MVFR conditions for sites between
KJHW and KBUF. During the midday and afternoon...this weakening
activity will push north toward Buffalo while weakening to just

More significant lake snows will be found southeast of Lake Ontario.
This activity will lift from the KSYR area northward during the
course of the midday...and particularly during the afternoon. The
snow will then weaken as it will move across and north of the Tug
Hill plateau tonight.

Elsewhere tonight...skies will clear so that VFR conditions can be

Finally...there will be the potential for low level wind shear
tonight. The greatest risk for this will come over the Western
Southern Tier and Finger lakes region.


Tuesday...Mainly VFR.
Wednesday...Rain and snow showers with a chance of MVFR/IFR.
Thursday...VFR, but MVFR in lake effect -SHSN E of the lakes.
Friday...Mainly VFR.


Small craft advisories will be in place for all of the New York
nearshore waters...including the BUF Harbor and IAG Upper IAG
River...for the bulk of the forecast period.

While the deep storm system from the weekend continues to move away
across the Canadian maritimes...strong high pressure over the Deep
South will Keep a relatively strong surface pressure in place over
the region. This will keep moderately strong winds in place...
although there will be times when winds will subside to under 15


NY...Lake Effect Snow Warning until 6 PM EST this evening for
     Winter Weather Advisory until 10 AM EST this morning for
MARINE...Small Craft Advisory until 6 PM EST Tuesday for LEZ020-040-041.
         Small Craft Advisory until 6 PM EST Tuesday for



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