Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 020606

Area Forecast Discussion
National Weather Service Buffalo NY
106 AM EST Fri Dec 2 2016

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.


Through the rest of the night...lake effect rain and snow showers
will continue east of the lakes on a gradually veering westerly
flow...with primarily rain falling along and a bit inland from
the lakeshores...and wet snow tending to be more dominant across
the higher terrain. This will result in any slushy accumulations
being confined to the higher terrain away from the lakes...where
1 to 2 inches will be possible. Outside of the main lake effect
areas...conditions will be mostly cloudy and dry...with moderately
brisk west winds persisting. Overnight lows will generally range
from the lower 30s across interior portions of the Southern Tier
to the upper 30s and lower 40s across the lake plains and immediate

Friday winds will be almost westerly, favoring multi- banded
rain and snow showers across the Western Southern Tier and perhaps
the Boston Hills. Slightly drier air may build in Friday
afternoon, with lake effect showers a bit more patchy in nature,
but still likely to continue. Another 1 to 2 inches is possible,
mainly across higher terrain.

For Lake Ontario...radar shows precipitation is dominated by
upsloping, which is in line with most model guidance. Directional
wind shear is expected to continue overnight, which would prevent
a singular and more intense band from forming. 850mb temperatures
are slightly warmer here, running around -4C, so precipitation
will fall mostly as rain, with snow across higher terrain such as
the Tug Hill and far Northern Lewis county. Any snow accumulation
overnight should be confined to these areas, where 2 to 3 inches
of snow are expected, with little to no accumulation in most other

This will continue through most of Friday, until late in the day
when a shortwave is forecast to drop across the region. This will
enhance moisture and shift winds to the WNW late in the afternoon.
Before this shift, expect steadier precipitation, with slightly
cooler air advecting in. While mostly rain is expected near the
immediate lake shores, precipitation will change over to snow
across the interior with a few inches of snow possible in these
areas. Mesoscale guidance even hints at an upstream connection to
Georgian Bay may develop. This region probably will come closest
to advisory criteria snow amounts, however temperatures will be
very marginal which will limit accumulation.

Across the region, winds will remain gusty into the overnight hours,
but as the surface low to our north weakens, we should see a gradual
diminishment in the winds.


The main forecast concerns and challenges for the Friday night into
Saturday time frame revolve around lake induced rain/snow shower
activity. Pockets of deeper moisture will continue to pinwheel
around the western periphery of a broad mid level circulation
anchored over far eastern Quebec. Little change in thinking from the
prior shift in terms of this period with background synoptic support
aided by favorable over-lake instability as colder temperatures
aloft continue to move across the lower Great Lakes. Over-lake
instability, while sufficient to continue lake processes, are far
from outstanding. An additional limiting factor is that little
moisture is shown above the -10 C isotherm per model profiles.

While precipitation probabilities will be high Friday night into
Saturday in favored northwest flow areas as lake processes should
certainly be underway, the overall lake parameters should limit
intensity and snow accumulation. Best chance for some minor
snow accumulations during this time frame will be interior sections
of Chautauqua and Cattaraugus counties off Lake Erie and as well
as interior sections of Oswego, Northern Cayuga and eastern Wayne
counties. These areas should experience the coldest boundary layer

Broad ridging over the Upper Great Lakes Saturday will gradually
build eastward, while its associated surface high will become
centered over the Ohio Valley by Saturday night. Inversion heights
will gradual lower resulting in a slow diminishing trend to the
lake induced precipiation during the day Saturday and Saturday night.

By Sunday, ridging will build across our forecast area. While this
will finally bring an end to the prolonged nuisance lake supported
precipitation, the period of associated fair weather looks to be
short lived. A potent shortwave within a negatively tilted trough
will push across the Lower Great Lakes Sunday night. This will
produce a round of mixed rain/wet snow showers.


The big story during this period will be the phasing and subsequent
amplification of the longwave pattern over the continent. A very
strong shortwave will dive south from British Columbia on Sunday...
and this will eventually lead to a deep closed low over the Northern
Plains early in the week. Meanwhile...a strong downstream ridge will
amplify over the east. This pattern will direct a surge of cold air
southward across the Inter-Mountain west...but the opposite will be
true for the eastern third of the country where temperatures should
once again climb to well above normal levels.

The medium range ensembles are in general agreement with this
scenario...although the ECMWF is slower and more pronounced with the
amplification and thus the anomalous nature of the temperatures
across the `Lower 48`.

Looking further down the road...the cold air over the western half
of the continent is forecast to make its way across the Great Plains
to the Great Lakes and Ohio Valley during the second half of the
week. There is relatively high confidence of this change to more
wintry weather... as 850mb temps are expected to finally drop into
the negative teens Celsius.

This cold air will likely be accompanied by plenty of synoptic
moisture by the end of the the stacked storm system from
the Northern Plains will cross by to our north. If this scenario
would hold true...then the stage would be set for a significant
winds followed by a strong lake effect snow event. The question
would then relate to the low level flow, as to which area downwind
of the lakes will be most affected...which at this time cannot be
answered with any degree of confidence. Stay tuned.


Through the rest of the overnight hours and much of Friday...a
general westerly flow will continue to focus lake effect rain and
and snow showers across areas east of Lakes Erie and Ontario.
Expect a mix of IFR/MVFR conditions within these...while the
remainder of the region should be predominantly VFR with just
some temporary fluctuations to MVFR at times in passing areas of
lower clouds.

After that...a shortwave and attendant secondary surface trough
will pass through the region between late Friday and Friday evening.
This will bring a more general chance of rain and snow showers/
associated MVFR to most areas...with lake effect rain and snow
showers and attendant IFR/MVFR shifting to areas southeast of the
lakes as the low level flow becomes more northwesterly.


Saturday 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...VFR with a chance of mainly rain showers.


Westerly winds up to 30 knots on the lakes will continue tonight and
through at least Friday night...with such winds and slight cold air
advection bringing waves greater than 4 foot to the lakes. As a
surface low weakens tonight to the north of Lake Ontario, winds over
the rivers should relax enough such that the small craft advisories
will end as planned.


MARINE...Small Craft Advisory until 2 PM EST Saturday for LEZ040-041.
         Small Craft Advisory until 4 AM EST early this morning for
         Small Craft Advisory until 6 PM EST Saturday for
         Small Craft Advisory until 6 AM EST Saturday for LOZ042.



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