Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 130205
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
905 PM EST Mon Nov 12 2018

.SYNOPSIS...
Conditions will deteriorate across much of the region later tonight
and Tuesday as a storm system passing to our south and east will
generate some accumulating snow. While most areas should pick up a
coating to an inch of snow, the higher terrain of the Southern Tier
and Eastern Lake Ontario region could receive 3 to 5 inches of
accumulation. Accumulating lake effect snow can then be expected
southeast of both lakes late Tuesday into Wednesday.

&&

.NEAR TERM /THROUGH TUESDAY/...
Radar imagery showing plenty of returns overhead this evening, and
the precipitation has finally started reaching the ground across the
western Southern Tier. Precipitation is mainly light snow across the
higher terrain, with some rain mixing in at lower elevations and in
Chautauqua County. Precipitation will mainly be relegated to the
western Southern Tier and western Finger Lakes through late evening,
with most other areas staying dry due to extensive sub-cloud
evaporation.

High pressure centered just off the New England coast this evening
will push further out to sea during the overnight. This will allow
disorganized low pressure within a broad inverted trough over the
Tennessee and Ohio valleys to consolidate and deepen over the Mid
Atlantic region. While not a perfect textbook example, this could be
categorized as Miller A type of cyclogenesis.

As the surface low becomes better organized over the Mid Atlantic
region, a strengthening baroclinic zone will set up across
Pennsylvania and southeast New York, and to a lesser extent back
across our forecast area. This developing boundary will then be
acted upon by a south to southwest flow beneath H85 that will
obliquely force a deepening moisture field to produce fairly strong
frontogentic lift. Some assistance will be given to the deep layer
of ascent by the right entrance region of an incredibly strong
185kt H25 jet.

Light snow will break out across the Southern Tier region after
about 02z, with the precipitation spreading northeast and filling
back in to the west during the course of the night. The most
widespread pcpn should be experienced between about 08Z and 13z.
While the bulk of the pcpn tonight should be in the form of snow,
there could be some rain mixing in, especially for sites north of
the NYS Thruway between BUF and SYR. Its worth noting that guidance
is `colder` than previous model runs...and point soundings suggest a
fair amount of evaporational cooling at the onset...both pointing
towards more snow and less rain. Snowfall amounts tonight will range
from a coating to less than an inch across the bulk of the lake
plains...to 2 to 3 inches across the higher terrain of the Srn Tier
and also for the Tug Hill. Have expanded the winter weather advisory
for Lewis County to also include Wyoming, Cattaraugus, and Allegany
counties...as 24 amounts could reach as high 5 inches and also
because it is still relatively early in the season.

The fairly widespread rain/snow mix early Tuesday morning will then
taper off to scattered snow showers in most areas, with some rain
still mixing in through mid afternoon close to the lakes...as the
supporting storm system will exit up the New England coast. This
will effectively remove the H925-70 frontogenetic forcing from our
area...but while synoptic forcing will dramatically weaken...
deepening cold air will set the stage for lake effect to take over.

As we progress through the afternoon...H85 temps over the lakes will
tumble to -12c. Northwest flow will direct some initial lake effect
snow showers into the western Southern Tier off Lake Erie, and
southeast of Lake Ontario. Mesoscale model guidance such as the NMM,
ARW, and Canadian GEM suggest a multitude of squally snow showers
during the afternoon across much of the area from a combination of
some lake effect bands from Lake Huron and our local lakes, steep
low level lapse rates, and large scale forcing from the incoming mid
level trough. These brief bursts of snow showers may bring low
visibility and fresh coatings of slushy snow to many areas during
the afternoon. Surface temperatures will also begin to fall during
the afternoon, affording these snow showers a better opportunity of
sticking after 2-3PM.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Lake effect snow which begins to develop Tuesday afternoon/evening
continues to strengthen during the early overnight hours as cold air
continues to build into the region. This event will be short lived
as drier air and less favorable flows develop on Wednesday.
Temperatures will remain below normal this period...with highs
Wednesday remaining below freezing for much of the region.

Off Lake Erie...the northwest flow will produce multibanded lake
effect snows downwind of the lake with accumulations of a few inches
before the drier air starts building in with diminishing activity
Wednesday morning.

Off Lake Ontario...the longer fetch combined with upstream
connection will produce a moderate to heavier snowfall likely
targeting Wayne, Northern Cayuga and Oswego counties. Will continue
to highlight the potential for heavier snowfall -- half a foot or so
over a 24 hour period -- in the HWO with headlines still not out of
the question. As drier air builds in during the day Wednesday will
look for diminishing snows through the afternoon and evening
hours...with lingering snow showers into the early overnight hours
of Wednesday night.

While Thursday will start off dry across our region as lingering
surface-based ridging begrudgingly slides eastward and off the New
England coast...the fair weather will once again give way to
deteriorating conditions Thursday afternoon and especially Thursday
night as a another complex area of low pressure pushes northeastward
from the Southeastern states...and eventually evolves into yet
another deepening coastal low along the Mid-Atlantic coastline by
Friday morning. Plentiful moisture and lift attendant to this system
will spread increasing chances of precipitation into the area from
the south Thursday afternoon...with fairly widespread precipitation
then following for Thursday night...before diminishing from west to
east on Friday as the low departs into the Canadian Maritimes.
Thermal profiles continue to suggest that the atmospheric column
should be cold enough to allow for mainly snow with this event...
though marginal boundary layer temperatures will probably allow some
rain to mix in at the onset Thursday/Thursday evening and again on
Friday as the precip lightens and winds down. Otherwise...temperatures
through the latter half of the short term period will continue to
average solidly below normal...with lows in the mid 20s to lower
30s Thursday night sandwiched in between highs ranging through the
30s Thursday...and in the upper 30s to lower 40s on Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
In the wake of the late-week coastal system...broad upper level
troughing will once again dominate our weather through the long
term period. This will ensure a continuation of well below normal
temperatures through early next week...with daily highs averaging
close to 10 degrees below normal. At the same time...such an
environment will also lead to continued opportunities for lake
effect precipitation downwind of the lakes.

Digging a little more into the forecast details...a general west
to west-northwesterly flow will be in place across our region
through Friday night and early Saturday...before perhaps turning
a little more west-southwesterly to southwesterly on Saturday in
advance of an approaching surface trough. Meanwhile...850 mb temps
should drop off to the -3C to -6C range Friday night...before
remaining in this general range or perhaps warming a little on
Saturday out ahead of the aforementioned trough. While certainly
cold enough for a lake response...such temps aloft will likely
not be cold enough to support all snow...with boundary layer
temperatures the main determining factor for precipitation type.
With this in mind would expect more of a mix of rain and snow
Friday evening and again on Saturday when boundary layer temps
will be warmer...with snow more predominant during the second
half of Friday night. Meanwhile...precipitation should be much
more widely scattered outside of the main lake effect areas...
with mainly dry weather prevailing the majority of the time. As
for temps...we can expect lows in the lower to mid 30s Friday
night...followed by highs in the mid 30s to lower 40s on Saturday.

The surface trough then looks to cross our region Saturday night
along with a more general chance of snow showers...with a west-
northwesterly flow of much colder but also drier air in its wake
then supporting scattered lake effect snow showers southeast of
the lakes later Saturday night through Sunday. With 850 mb temps
falling to around -13C...Sunday will easily be the coldest day of
the period...with highs struggling to get above the upper 20s and
lower 30s areawide - readings that are much more typical of mid
to late January than November.

Surface-based ridging and drier air should build into the region
Sunday night...and this in concert with warming/subsidence aloft
should result in lingering lake effect snow showers weakening to
the southeast and east of the lakes. By Monday the medium range
guidance diverges markedly with the GFS/GEM suggesting the passage
of another trough...while the ECMWF keeps the area mainly dry.
Given the distant time frame...for now have elected to lean more
optimistic and follow the latter scenario...with a mainly dry and
somewhat milder day forecast.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Light snow is reaching the ground across the higher terrain of the
western Southern Tier with areas of IFR VSBY and MVFR CIGS. Some
rain is mixing in at lower elevations and at KJHW with better
visibility in these areas. The remainder of the area will stay dry
through late evening.

From late evening through the overnight precipitation will spread
from the western Southern Tier into the Finger Lakes and eastern
Lake Ontario region, and also build back to the north and west
eventually. Much of this will be in the form of snow, although some
rain may mix in at lower elevations near the Lake Erie and Ontario
shore. The most widespread precipitation will fall from roughly 08Z-
13Z, perhaps lasting a few more hours east of Lake Ontario. VSBY
will deteriorate to IFR in snow late tonight through early Tuesday,
with CIGS lowering to MVFR at lower elevations and IFR higher
terrain.

From mid morning through the afternoon Tuesday the steady,
widespread wet snow will transition to more intermittent snow
showers. These snow showers will continue to mix with some rain
through mid afternoon near the lakeshores. VSBY will be IFR in the
snow showers, with VFR between. Areas of MVFR CIGS will continue.

Outlook...

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

&&

.MARINE...
A relatively weak surface pressure gradient over the Lower Great
Lakes this evening will tighten on Tuesday...as a developing storm
will intensify while tracking up the coast of New England. The
corresponding winds will freshen in the process...likely leading to
Small Craft Advisory conditions for all of the NY nearshore waters
by late Tuesday and certainly Tuesday night.

Small Craft Advisory conditions will continue Wednesday with
moderate northwesterlies. As high pressure builds across the Lower
Great Lakes on Wednesday night, winds and waves will gradually
subside from west to east.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 6 PM EST Tuesday for NYZ012-020-
     021.
     Winter Weather Advisory from 1 AM to 6 PM EST Tuesday for
     NYZ008.
MARINE...None.

&&

$$

SYNOPSIS...Hitchcock/RSH
NEAR TERM...Hitchcock/RSH
SHORT TERM...JJR/Levan
LONG TERM...JJR
AVIATION...Hitchcock
MARINE...Hitchcock/RSH


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