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Area forecast discussion
National Weather Service Buffalo New York
650 PM EST Mon Nov 11 2019

Synopsis...
snow will increase in intensity this evening, with periods of
moderate to heavy snow across the entire area tonight. Some
sleet and freezing rain may mix in close to the Pennsylvania
state line, which will decrease snow accumulations locally. The
widespread snow will quickly taper off from west to east late
tonight 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 Tuesday/...
a mid level trough will sharpen and dig into the western Great Lakes
through tonight, with a well defined wave of low pressure moving across
central PA tonight, before exiting into New England Tuesday
morning. The frontal wave, sharpening trough, and associated
low/upper level jets will all support an extended period of
large scale ascent and frontogenetic forcing to the north of a
stalled frontal zone over central and northern PA.

Little change is expected for several hours this evening with a
stalled frontal boundary just south of the state line.
Temperatures are cool enough throughout the column for continued
light to moderate snow across most of wny and cny, although some
breaks in the weather continue near the PA/New York border followed by
a variety of mixed precipitation. This area should see an
increase in precipitation which will change over to snow as
colder air finally sinks into that region.

That area aside, the remainder of wny has seen an expected
uptick in snow rates. This is due to the above mentioned jets
(there are two: one centered over Quebec and the other centered
over in and lower mi, as depicted by dissecting amdar data),
which will be coupled as they pass overhead tonight ahead of the
sharping longwave upstream trough. This in turn will continue
to force the PA surface low to deepen slowly as it moves east
while the above mentioned frontogenesis continues.

The forcing and potential for mesoscale banding will peak
during the first half of tonight across western NY, and
overnight towards the east end of Lake Ontario. Snowfall rates
may reach 1-1.25" per hour during this time frame, lasting for a
few hours at any given location. Again, the exception may be
the extreme southern tier where profiles may be warm enough for
some sleet or freezing rain, primarily near the Pennsylvania
state line. Ice accumulations of up to a tenth of an inch are
possible, mainly across southern and eastern Allegany County and
far southern Cattaraugus County.

The steady snow will then taper off quickly from west to east late
tonight through early morning Tuesday. Initially, the airmass will
not cold enough in the boundary layer to support lake enhancement
with the favorable dendritic Crystal growth zone residing way up at
around 15k feet. This will change later tonight during the last few
hours of this event as the favorable dendritic Crystal growth zone
descends beneath the lake induced equilibrium level. This will bring
some added snowfall along the South Shore of Lake Ontario from
Niagara County eastward to Wayne County, including the Rochester
area.

A Winter Storm Warning remains with storm total accumulations of 7-
10 inches, with some local amounts of close to 12 inches where
mesoscale banding and/or lake enhancement develops. The bulk of this
accumulation will be this evening through the pre-dawn hours of
Tuesday, when travel conditions will be worst. Snowfall amounts
will be much lower across far southern Cattaraugus and southern
Allegany counties, where the wintry mix will hold snow amounts
to the 3-5 inch range.

The synoptic scale snow will quickly end Tuesday morning from west
to east. Cold northwest flow will then 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 fall through the 20s tonight. Temperatures
will then stay in the low to mid 20s through the day Tuesday.
The north country will be colder, 20s through this evening
falling to the teens overnight, then recovering only to the
upper teens to lower 20s on Tuesday.

&&

Short term /Tuesday night through Friday night/...
Tuesday night 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 /00z Tuesday through Saturday/...
snowfall will increase in intensity overnight, with peak
snowfall rates during the first half of tonight across western
NY, and overnight east of Lake Ontario. Visibility during this time
frame may approach airfield minimums at times at all the taf
sites. The one exception will be across the southern tier near
the PA state line. Here, a wintry mix will continue through the
evening, mainly east of kjhw. This area will change to all snow
later tonight as colder air arrives. Ceilings will be widespread IFR
to low end MVFR through the afternoon and tonight.

The widespread snow will quickly taper off from west to east late
tonight and early Tuesday morning. 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 11th-13th.

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

Monday November 11

Buffalo..........27f (1933)............19f (2017)
Rochester........29f (1933)............20f (1957)
Watertown........31f (2017)............12f (2017)

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 Tuesday for nyz003>008-013-
014.
Winter Storm Warning until 6 am EST Tuesday for nyz001-002-
010>012-019>021-085.
Marine...Small Craft Advisory until 10 am EST Tuesday for lez040-041.
Small Craft Advisory until 4 am EST Tuesday 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 Tuesday to 7 am EST
Wednesday for loz045.

&&

$$

Synopsis...Hitchcock
near term...Hitchcock/zaff

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