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Area forecast discussion
National Weather Service Buffalo New York
343 PM EST Tue Nov 13 2018

Synopsis...
cold air will filter into the region this evening behind a
system that's moving northeast along the New England coastline.
This will result in bands of lake effect snow downwind of Lake
Erie and Lake Ontario on a northwest flow. A stronger band setup
is likely southeast of Lake Ontario later tonight into
Wednesday, while the rest of western New York sees dry weather.
The next system will begin to impact the region late Thursday
and last through Friday.

&&

Near term /through Wednesday/...
for the remainder of this afternoon, there will be a brief
burst of snowfall behind a cold front which will exit eastward
into New England through this evening. Behind this will be a
brief period of ample lake enhanced moisture which will be
aided by upsloping. This will result in a quick dusting to an
inch of snow which will fall between 3 PM and 6 PM. Snow will
taper off from northwest to southeast during this time, but will
last a bit longer across higher terrain due to upsloping in the
northwesterly Post-frontal flow.

The main event through Wednesday will be the development of a
multi-lake connection snow band that affects areas southeast of Lake
Ontario. This band may have a tough time getting started this
evening, but confidence is high enough for a strong Single Lake
band or two separate bands moving across the region by late
tonight into Wednesday morning. A single band would be focused
squarely on an area from northern or NE Wayne County east to
western Oswego. All high res models pinpoint this area with peak
intensity between ~06-12z Wednesday, which is often a period of
intensification due to shoreline convergence and/or land
breezes. There is some disagreement to how stationary the band
will be though. If it wanders, then amounts may be more spread
out and a little lower than forecast. But with Peak Lake effect
season underway, plus a good triple lake connection signal, will
place amounts on the higher side with 3-6 hours of up to 2"
snow rates. Some models suggest two separate bands moving
through the region overnight while others create a single band.
With the former, parts of Monroe County could see some bursts of
snow, so have placed the Rochester area into an advisory. If a
single band results, then areas east of Rochester will have
higher amounts. Href amounts are a little on the light side
compared to the current forecast due to some differences between
the hrw nmmb member and the NAM nest being a little out of sync
with the hrw NSSL and arw. The duration of this event should be
relatively short which should keep amounts from getting out of
control. Still, expect a narrow swath of around a foot of snow
with the usual variability and localized higher/lower amounts.

Storm totals within the band may approach a narrow peak of 15"
bulls-eyed somewhere from about Wolcott to Fulton and/or
Phoenix, with far less 10-20 miles away from the peak. Areas on
the north side of the band, from about Mexico to Parish should
see only a few inches. Areas to the west toward Rochester should
see upwards of about 5" with amounts decreasing to the south
and/or southwest toward the thruway.

Outside of this, expect scattered rain-->snow showers as
temperatures slowly lower this afternoon and eve. There should
be a weaker Lake Erie multi-band with some upslope flow, but
with notably shorter fetch with only a weak short-fetch
connection to Lake Huron, amounts should be more spread out and
unimpressive when compared to neighboring Lake Ontario. Expect
variable accumulation as is often the case with multi-bands,
peaking around 2 inches or so, and mainly overnight.

By tomorrow afternoon, surface high pressure will be moving in
and weakening the Lake Ontario band. Like overnight, there is
some disagreement as to how the lake band will dissolve or move
in response to the approaching subsident and drying airmass. The
band may fall apart or slowly weaken as it moves east/northeast
in the afternoon.

&&

Short term /Wednesday night through Friday night/...
northwest flow over Lake Ontario will rapidly end on Wednesday
evening as flow turns southeasterly in advance of the next system
pushing toward the area. Warm advection will likewise be starting
off the deck concurrent with the wind shift, which should further
decrease instability, and thus allow for dissipation of snow shower
activity. A dry night and most of the early part of Thursday will
follow as clearing skies are replaced with high clouds on the heels
of increased isentropic ascent aloft in warm advection.

Lift in the 295-305k layer increases rapidly in the afternoon on
Thursday and into Thursday evening. Warm advection will be working
against evaporational cooling while achieving condensation pressure
deficits that fall below 10 mb with strong moisture transport from
the south in the layer. That said, isentropic omegas take a tad
longer to reach the southern tier in a coherent way such that
lighter precipitation rates will probably allow for some warmer air
off the deck to linger through the afternoon and evening hours. The
net result will be a chance of a wintry mix over western New York,
especially the southern tier, as precipitation spreads northward.
Deeper lifting profiles and some dynamical cooling should transition
everyone to snow overnight with a few inches of wet accumulation
likely in most spots given inefficient snow-to-liquid ratio
expectations.

On Friday, weakening moisture depth as the system that will have
been moving northward toward our area fills and a coastal low takes
over combined with a low-level seclusion of warm air west of
the appalachian chain that bulges northward toward our area will
result in a gradual changeover to rain in most spots as the
boundary layer warms. Further, the reduction in the lifting
profile will also mean a switch from steady rainfall to drizzle
at some point. That said, this will be short-lived, as the
coastal low takes over and flow turns westerly again and
strengthens into the weekend. This should allow for colder
Continental air to move back toward the area with some lake
effect showers.

&&

Long term /Saturday night through Tuesday/...
broad upper level troughing will continue to dominate the Great Lakes
and northeastern states in the extended portion of the forecast...
resulting in a certainty of continued well below normal temperatures.
Speaking more specifically...we can expect daily highs to mostly be in
the 30s...while nightly lows range from the upper teens/lower 20s across
the north country to the mid and upper 20s elsewhere. Such readings will
be more typical of mid-winter than the middle of November.

While below average temperatures remain a virtual lock in the long
term...the models have rather markedly diverged away from yesterday's
modest agreement on the path...timing...and strength of any migratory
surface troughs that might affect our region during this time frame...
and by extension the orientation and strength of the resultant low
level wind field across our region at any given point. As such...
forecast confidence in the timing/placement of both synoptically-
driven and lake-driven precipitation has significantly decreased...
and have therefore had to transition to the use of broadbrush chance
pops for the bulk of this period. Given current forecast temperatures...
the bulk of any precipitation will likely fall in the form of
snow.

&&

Aviation /21z Tuesday through Sunday/...
mainly MVFR ceilings with some IFR conditions over higher terrain
will continue into this evening as a low moves northeast along
the New England coast. There will be a 1-2 hour period of snow
with IFR/MVFR conditions mid to late afternoon. Conditions will
rapidly improve from northwest-southeast during this time as drier air builds
in.

There will be a slow transition to lake effect bands in the
evening. Later tonight, a concentrated band will eventually
develop between kroc and ksyr off Lake Ontario. Off Lake Erie,
some snow bands will continue variable conditions between IFR
and MVFR. Conditions will improve Wednesday but with IFR with a
Lake Ontario band through 18z.

Outlook...

Wednesday night and Thursday...mainly VFR.
Thursday night and Friday...MVFR/IFR possible in rain and/or
wet snow.
Saturday and Sunday...mainly VFR, but IFR possible
east of both lakes in lake rain and/or snow.

&&

Marine...
an area of low pressure off New England will rapidly deepen tonight
as it tracks towards Atlantic Canada. A northwest wind
developing around this area of low pressure will increase tonight,
bringing both winds and waves to Small Craft Advisory
thresholds. High pressure will then cross the lakes Wednesday
and bring diminishing winds and waves on the lakes, with scas
ending.

&&

Buf watches/warnings/advisories...
New York...Winter Storm Warning from 7 PM this evening to 6 PM EST
Wednesday for nyz004>006.
Winter Weather Advisory from 7 PM this evening to 6 PM EST
Wednesday for nyz003.
Marine...Small Craft Advisory until 4 PM EST Wednesday for lez040-041.
Small Craft Advisory until 4 am EST Wednesday for
loz030.
Small Craft Advisory until 10 PM EST Wednesday for
loz043>045.
Small Craft Advisory until 4 PM EST Wednesday for loz042.

&&

$$

Synopsis...zaff

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