Area Forecast Discussion
Issued by NWS Buffalo, NY

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767
FXUS61 KBUF 021758
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1258 PM EST Fri Dec 2 2016

.SYNOPSIS...
Cold air will continue to flow across the Lower Great Lakes through
the end of the week. This will result in lake effect rain and snow
showers persisting east and southeast of Lakes Erie and Ontario
right through Saturday...before falling apart Saturday night and
Sunday as high pressure builds across New York State.

&&

.NEAR TERM /THROUGH TONIGHT/...
Radars this early afternoon continue to show weak bands of lake
effect rain and snow showers falling east of the Lower Lakes. A
general westerly flow of sufficiently cold and moist air will
continue to support these bands of precipitation through the mid to
late afternoon.

Off Lake Erie...the bulk of the precipitation will be focused across
the western Southern Tier...while the Lake Ontario lake effect will
tend to linger in the vicinity of the southern Tug Hill Plateau.
With only a marginally cold airmass in place for rain versus
snow...the exact precip type(s) experienced at any given location
will be heavily dependent on both elevation and the time of the
diurnal cycle...with rain more favored across the lower
elevations/during the day and wet snow more favored across the
higher terrain/at night. With this in mind...any slushy snowfall
accumulations through much of today look to be largely confined to
the higher terrain away from the lakes...with a rough inch or two
possible across the Southern Tier...and up to 1 to 3 inches
potentially falling across the higher terrain of the Tug Hill and
western Adirondack foothills.

Outside of the aforementioned areas...the bulk of today will
largely be just mostly cloudy and dry...with breezy to windy
conditions again found everywhere in conjunction with the tight
pressure gradient still in place across the Lower Great Lakes.
Expect daytime highs to range from the mid to upper 30s across
the higher terrain of the Southern Tier and North Country to
the lower to mid 40s elsewhere...with brisk west winds of 15-25
mph and gusts to 30-40 mph again making the day feel chiller
than it actually will be.

Late this afternoon and this evening...a shortwave and attendant
secondary surface trough will quickly pass through the region
from northwest to southeast. These features will bring a general
chance of some rain and snow showers to the entire region as they
move through...while also ushering in further veering of the low
level wind field to a more northwesterly orientation. This change
in wind direction will result in the lake effect bands getting
shunted further southward to areas southeast of the lakes...while
possibly also becoming enhanced for a brief time due to the
potential development of one or more upstream connections to Lake
Huron. Following this shift...the lake effect should transition to
weaker multibanded lake effect activity southeast of the lakes for
the balance of the night given the shortening fetch across the
lakes.

During this second portion of the period...the thermal structure
of the atmosphere again looks to be very marginal for rain/snow
during the approach and passage of the aforementioned trough...
before turning more favorable for snow in its wake due to the
combination of modest cold air advection and nocturnal cooling.
Consequently...expect that a highly elevation-dependent mix of
rain and wet snow late this afternoon should trend toward more
snow as time progresses tonight...though any additional accums
out of this will again probably be minor and largely confined to
the higher terrain. At this point am expecting maybe another inch
or so across the Tug Hill before the lake effect gets shunted
further south...with up to another 1-3" of slushy accums possible
across the higher terrain of the Western Southern Tier. Otherwise...
expect a somewhat colder night tonight given the aforementioned
modest cold air advection...which will help push temps back down
into the lower to mid 30s areawide.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
This will be an uneventful period across our forecast area...as an
undulating low amplitude flow will remain in place across the
northern tier of the country...including the Great lakes region. It
is probably a wise idea to take advantage of this period...as a
serious buckling in the pattern will take place next week. This
could eventually lead to an impactful winter storm at the end of
this seven day forecast package. See the long term discussion below
for more details.

A nuisance lake effect event will be in the process of winding down
as we open this period on Saturday. While a low sheared northwest
flow will be in place over the unstable lakes...there will be very
little synoptic moisture to compliment the mesoscale process. In
fact...BUFKIT overviews indicate that there will be no moisture in
the dendritic growth zone. This will especially be the case over
Lake Erie...although an upstream connection to Lake Huron will
encourage this lake effect to be more focused than the activity off
Lake Ontario. In any case...an ever lowering subsidence cap will
also work against anything more than nuisance lake effect as the
limiting inversion is forecast to be in the vcnty of 5-6k ft by
early afternoon. This environment will only yield some rain
showers...possibly mixed with some wet snow early in the
morning...with the coverage of the pcpn gradually diminishing as we
work through the day. Will keep the cat to likely pops from
continuity in place for sites southeast of the lakes...but will drop
them off to just chc by evening.

Outside of the lake effect pcpn southeast of both lakes...generally
fair weather will be in place as a large surface high will push east
from the Ohio Valley and Upper Great Lakes. There will be a plenty
of low level moisture around though...enough to translate into a
mostly cloudy day. While the first weekend of December may not look
much winter for most areas...at least it will feel somewhat like the
season as H85 temps around -8c will produce afternoon temperatures
in the 30s to near 40. These readings will be right at typical 30
year normals.

The large surface high will advance to the east across the Lower
Great Lakes Saturday night. This will further strengthen the
lowering subsidence based cap and essentially squash the remaining
lake effect rain and limited snow showers. Otherwise...it will be
partly to mostly cloudy and uneventful.

On Sunday...the axis of the surface high will cross our forecast
area. We should experience at least some breaks of sunshine...
although temperatures will be similar to those of Saturday with
afternoon mercury readings in the 30s to lower 40s.

Conditions will deteriorate Sunday night as a negatively tilted
trough...in the process of shearing out...will sweep northeast
across all of the Great Lakes region. While there will be some
lift provided by a diffluent upper level flow...the overall dynamics
with this feature do not look very impressive...as there should be a
lack of baroclinicity and our forecast area will also be in an
unfavorable left rear quadrant of a passing 150kt H25 jet. That
being said... there could be a little lake enhancement and with an
influx of synoptic moisture...any mixed pcpn should be able to turn
over to just a period of light snow for the overnight. Will increase
pops to high chc...but am not anticipating anything more than an
inch or so of accumulation.

As the shearing trough pushes away to our northeast on Monday...
drier mid level air will arrive in its wake while ridging will
become re-established over the region. This will encourage the light
snow from the previous night to taper off and end as a mix of rain
and wet snow showers by midday. While not significant...the mixed
showers will linger a bit longer east of both lakes due to a little
lake enhancement. Daytime snow accumulations will be unlikely.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
To say that this three day period will be active or unsettled could
be a gross understatement. For the past few weeks...a split flow
over the country has featured a low amplitude flow along the
Canadian border. This has resulted in a mild stretch of weather
across the Great Lakes with little measurable snow over our
forecast area. Mother Nature may be ready to finally change all of
that.

Energy over the north Pacific...indiscernible on satellite at this
point...will be the catalyst for the pattern change. This robust
feature is forecast to round the base of an Alaskan trough this
weekend before diving equatorward along the west coast and southern
Rockies. This will promote a phasing of the split flow over the
country while a deep longwave trough will dig across the western
states to the nations mid section. While several Pacific shortwaves
will eject out of this digging trough during the course of this
forecast period...the shortwave being discussed could initiate
significant cyclogenesis over the lower Mississippi Valley by
Thursday. It needs to emphasized though that the various medium
range ensembles are NOT in agreement with the timing and degree of
such a scenario. This means that there is a wide range of
possibilities as we head into the second half of the week...
including the risk of a high wind event and/or significant lake
snows. The models will not come into better alignment until they get
a handle on the shortwave over the north Pacific that should be the
major player in this transition.

A major pattern change is key to moving around large amounts of
anomalously warm or cold air. In this case...`home brewed` cold air
over Alaska and the Yukon will have the opportunity to break loose
and dive southward along the foothills of the Canadian Rockies to
the Lower 48. This airmass is not part of the frigid air that has
been parked on the other side of the pole in Siberia...but is part
of a nearly stationary airmass that will chill in place into the
first part of the weekend. The first real arctic airmass will make
its way across the Canadian Prairies to the Lower 48 by about mid
week...then will likely make its way to the Ohio Valley while
becoming somewhat more modified. A portion of this airmass could set
its sights on the Lower Great Lakes by the weekend of Dec 10.

In the meantime...there will be a leading shortwave that we will
have to contend with. This robust feature can be seen this morning
in WV imagery....churning its way across the Desert Southwest. By
Monday night it will be pushing across the Lower Mississippi Valley
and making a bee line for the Lower Great Lakes. As it makes its way
across the Ohio Valley on Tuesday...thickening clouds over our
region will yield a mix of rain and wet snow. The bulk of the pcpn
should be in the form of rain by late afternoon. A 40-50kt southerly
low level jet will accompany this feature as it moves across our
region Tuesday night...so much of the pcpn will remain in liquid
form. This will also lead to a non-diurnal temp trend for the
overnight hours.

The steadiest of the pcpn will exit the region for Wednesday as
ridging will temporarily become re-established over the Lower Great
Lakes. Any showers that we do experience should be light and
inconsequential with temperatures climbing into the 40s.

The main storm system in question will then develop in the vcnty of
the Lower Mississippi/Ohio Valley Wednesday night or Thursday. This
deepening storm will push northeast across our region sometime on
Thursday...with the likelihood of rain over the region. It is not out
of the question that there could be some snow on the front end of
this storm system...pending its exact track. There should also be
strong winds on the backside of this deepening cyclone...and
possibly some very significant lake effect snow. The fact that the
core of the coldest air will be approaching our region via the Ohio
valley is climatologically favorable for a big southwest flow event
off Lake Erie...but the majority of the ensembles are leaning more
towards a west to northwest flow event...so stay tuned.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
For the 18Z TAFs lake effect rain/snow has continued to drop
southward, now impacting the So. Tier of NYS including the KJHW
terminal. Activity here is broken in nature, likely lingering IFR
flight conditions for a few hours before an improvement back to MVFR
occurs.

East of Lake Ontario the band of precipitation has dropped well
south of the KART airport. Additional precipitation, this ahead of
an upper level shortwave is nearing the SLV, and will continue to
drop southward across not only the KART airfield, but also the
remaining 4 TAF sites this evening and early overnight.

After this activity pushes through, it will leave lake effect snow
in a weakened state, with mainly MVFR/VFR flight conditions across
the region for the last 6 to 12 hours of the TAF cycle.

Outlook...

Saturday afternoon through Sunday...Mainly VFR with
gradually diminishing lake effect rain/snow showers and attendant
areas of MVFR/IFR southeast of the lakes.

Monday...MVFR with a chance of rain and snow showers.

Tuesday and Wednesday...VFR with a chance of mainly rain showers.

&&

.MARINE...
A brisk general westerly flow (with winds to as high as 30 knots)
will continue across the Lower Lakes region today...before veering
to northwesterly and gradually diminishing tonight through Saturday
night. Accordingly...small craft advisories remain in effect as
outlined below.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 1 PM EST Saturday for LEZ040-041.
         Small Craft Advisory until 10 PM EST this evening for
         LEZ020.
         Small Craft Advisory until 4 AM EST Sunday for
         LOZ043>045.
         Small Craft Advisory until 1 PM EST Saturday for LOZ042.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR/THOMAS
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...THOMAS
MARINE...JJR



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