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Area forecast discussion
National Weather Service Buffalo New York
118 am EST Tue Nov 12 2019

Synopsis...
the widespread snow will taper off from west to east overnight and
early Tuesday morning. This will be followed by local lake effect
snow southeast of lakes Erie and Ontario with minor accumulations
Tuesday through Wednesday. The well below normal temperatures will
continue through the end of the week before warmer weather arrives
next week.

&&

Near term /through today/...
the entire area being covered by moderate to occasional heavy
snow with snowfall rates of 0.5-1"/hr, with some rates still
near 1.5"/hr. Any mixed precipitation which was occurring along
the southeast fringe of the area during the evening has also
transitioned over to moderate/heavy snow.

Regional radars showing a rather distinct back edge to the snow,
progressing across southern Ontario from near Toronto to Long
Point. Nearly all hi-res guidance showing a rather rapid
diminishing trend to the snow from west to east between 09z and
12z.

After the synoptic snow diminishes, a cold northwest flow will
set the stage for some limited lake response. The very cold
airmass will bring Strong Lake induced instability, with
equilibrium levels rising to near 15k feet. Despite the strong
instability, the airmass is quite dry. The dry airmass and
unfavorable, short northwest fetch will limit the lake response
to some extent. Off Lake Erie, persistent upslope flow off the
lake will contribute to occasional snow showers across the
higher terrain of inland Chautauqua County and western
Cattaraugus County. This may add a few more inches locally
during the day Tuesday. Lake effect southeast of Lake Ontario
will also produce a few additional inches from Wayne to Oswego
counties on Tuesday, mostly in the morning while some synoptic
scale moisture is still in play.

Temperatures will stay in the lower to mid 20s through the day
today.

&&

Short term /tonight through Friday night/...
tonight a general northwesterly flow of cold air will continue
across the lower Great Lakes...with 850 mb temps settling into
the -15c to -20c range. An airmass this cold is almost unheard
of for this point in November...and at the surface will
translate to record low temperatures ranging from zero to five
above across the north country to 10 to 15 across the remainder
of the region...with record lows likely to be set for both
November 12th and 13th (see the climate section below for the
current records for these two dates). The record cold for this
time of year will be further exacerbated by winds of 5 to 15
mph...which will result in wind chills dipping into the single
digits above zero across the lake plains south of Lake
Ontario...and to subzero levels elsewhere.

With such a cold airmass crossing the much warmer waters of lakes
Erie and Ontario...there will also be some lake effect snow showers
to contend with southeast of the lakes. Off Lake Erie...the
combination of an initial short northwesterly to north-northwesterly
fetch and favorable orographics will lead to some initial mainly
light snow showers across the higher terrain of Chautauqua and
western Cattaraugus counties through the first part of the evening.
After that time...a gradual backing of the flow will then send a
weakening upstream connection to Lake Huron (previously extending
across Central Lake Erie and into northwest pennsylvania) northward
into Chautauqua County...western Cattaraugus County...and perhaps
extreme far southern Erie County. This should result in a in at
least a brief uptick in the snow showers for a few hours across the
above areas...before the combination of the weakening upstream
connection and a lowering cap results in the activity weakening
again overnight. At this point still feel we'll be looking at minor
total nighttime accumulations of 1-3 inches in the above areas...
though cannot completely rule out somewhat higher (including lower-
end advisory-type amounts) should the upstream connection hold on
longer than currently expected.

Meanwhile off Lake Ontario...an increase in background moisture and
a possible developing connection to Georgian Bay should help to
initially focus another area of lake effect snow showers across the
northeastern Monroe/Wayne/norther Cayuga/southern Oswego County
corridor early on. Subtle veering of the low level flow may then
help to push the lake snows a little further southwestward for the
balance of the night...with these focusing primarily from the
Rochester area eastward across Wayne and northern Cayuga counties...
though the edges of the lake snows could affect eastern Orleans and
far southern Oswego counties at times. During this time frame the
potential upstream connection to Georgian Bay could support a period
of at somewhat enhanced snowfall during the late evening and early
overnight hours...with the activity then weakening again late as the
capping inversion falls and the upstream connection weakens. Dependent
upon the development and strength of the upstream connection...some
lower-end advisory-type accumulations of 3-5 inches could be possible
within the most persistent lake snows...with lesser sub-advisory
amounts of a few inches more likely should the connection to Georgian
Bay not materialize. Needless to say...we'll continue to closely
monitor this potential over the next day or so.

By Wednesday morning strong surface-based ridging will be building
into our region...with attendant drying and sharp lowering of the
capping inversion (along with continued decay of any upstream
connections) resulting in the lake effect rapidly devolving into
some scattered light snow showers southeast of both lakes. The
subsequent passage and departure of the ridge axis off to our east
will then result in the low level flow weakening...backing...and
becoming increasingly sheared through the rest of the day...which in
turn will result in the snow showers further weakening and retracting
back closer to/over the lakes...before shifting northward and dying
out during the course of the afternoon. Outside of these the day
will be mainly dry...with the unseasonably cold airmass leading
to record or near-record low maximum temperatures largely in the
lower to mid 20s. Mainly dry weather should then continue to prevail
through at least the first half of Wednesday night...with just a
lower-end chance of snow showers reaching far western New York later
Wednesday night out ahead of an approaching mid level trough and
its associated weak warm front.

Thursday and Thursday night the aforementioned weak mid level trough
and its attendant surface trough will cross our region. While
weak...this system should still help to generate some scattered
light rain and snow showers as it crosses our region...with some
lake enhancement possible northeast of the lakes given sufficiently
cold-enough temperatures aloft. Otherwise...ongoing warm advection
should help thursday's highs to recover into the lower to mid 30s
east of Lake Ontario...and to the mid to upper 30s elsewhere.

Yet another (and stronger) mid-level trough will then pass by to our
north on Friday...with its attendant cold front pushing southward and
across our region. While the portion of this boundary crossing our
region will be relatively starved for moisture/upper level support
and therefore only capable of generating some widely separated rain
and snow showers...some modest lake enhancement will remain possible
east of the lakes given still-cold enough temperatures aloft. Following
the passage of this system...one last shot of colder but also rather
dry air should then follow for Friday night...with the dry nature of
the colder airmass and short northwesterly to northeasterly fetch
helping to confine any lake response to some scattered snow showers
southeast and south of the lakes. Otherwise...the incoming colder
airmass will result in nighttime lows settling back into the teens
in most locations.

&&

Long term /Saturday through Monday/...
in the long term portion of the forecast...strong high pressure will
crest across our region on Saturday. Its core will then slide eastward
to northern New England and the Canadian Maritimes on Sunday and remain
in place through Monday...with ridging still extending back across our
region through this period. This will result in mainly dry and uneventful
weather prevailing across our region this weekend and into early next week...
and more importantly one last day of well-below average temperatures on
Saturday giving way to a steady day-to-day warming trend for Sunday and
Monday as a southerly return flow of milder air develops on the backside
of the ridge axis. At this distant Vantage Point it appears that highs
in the mid 20s to lower 30s on Saturday will climb into the upper 30s
to mid 40s on Sunday...then to the mid and upper 40s on Monday...when
some portions of western New York could see readings approach or even
reach 50 degrees. Looking just beyond the end of the current forecast
period...this warming trend appears to be the beginning of a Switch Back
to a milder pattern that may last through most...if not all of next week.

&&

Aviation /06z Tuesday through Saturday/...
widespread IFR conditions will continue overnight. Wny
(kbuf/kiag/kjhw) have already seen peak snow rates with a
diminishing trend now underway. Peak snowfall rates of around
1"/hr expected to continue at kroc through about 08z, and
through about 10z toward kart. Following this, lighter snow is
expected into Tuesday morning.

By 12z, visibility will improve to VFR in most locations as the snow
ends. Some limited lake effect snow will develop southeast of
the lakes. Off Lake Erie, this may impact kjhw at times. Off
Lake Ontario, most of the snow will focus near or just southwest
of kfzy. Ceilings will improve to MVFR in the morning, with VFR
outside of lake effect areas in the afternoon.

Outlook...

Tuesday night and Wednesday...VFR/MVFR. A chance of snow showers.
Localized lake effect snow and IFR southeast of the lakes.
Thursday...MVFR/IFR with a chance of snow showers, especially east
of the lakes.
Friday and Saturday...VFR.

&&

Marine...
moderate northeast winds will continue through tonight as low
pressure passes by to the south of the lakes. On Lake Ontario,
the northeast winds will become northwest by Tuesday morning,
with moderate northwesterlies supporting Small Craft Advisory
conditions through Tuesday night. On Lake Erie, the northwest
winds will be somewhat lighter, with Small Craft Advisory
conditions ending by Tuesday morning.

High pressure will build into the eastern Great Lakes by Wednesday,
providing a brief period of lighter winds. Another trough will cross
the eastern Great Lakes Thursday, which may produce the next round
of Small Craft Advisory conditions as southwest winds increase.

&&

Climate...
a frigid airmass (for this time of year) will pass over the
region through midweek. The shot of sub Arctic air will support
near-record to record cold temperatures. Below are the record
low maximum temperature and record low minimum temperature for
our three climate sites of Buffalo, Rochester and Watertown
for November 12th-13th.

City.......record low maximum (year)...record low minimum (year)

Tuesday November 12

Buffalo..........31f (1983)............22f (1921)
Rochester........32f (1983)............21f (1983)
Watertown........32f (2013)............15f (1997)

Wednesday November 13

Buffalo..........24f (1911)............16f (1986)
Rochester........23f (1911)............17f (2013)
Watertown........24f (1983)............11f (1997)

&&

Buf watches/warnings/advisories...
New York...Winter Storm Warning until 9 am EST this morning for
nyz003>008-013-014.
Winter Storm Warning until 6 am EST early this morning for
nyz001-002-010>012-019>021-085.
Marine...Small Craft Advisory until 10 am EST this morning for lez040-
041.
Small Craft Advisory until 4 am EST early this
morning for loz030.
Small Craft Advisory until 10 am EST Wednesday for loz043-
044.
Small Craft Advisory until 1 am EST Wednesday for loz042.
Small Craft Advisory from 11 am this morning to 7 am EST
Wednesday for loz045.

&&

$$

Synopsis...Hitchcock/tma
near term...Hitchcock/tma/zaff
short term...jjr

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