Area Forecast Discussion
Issued by NWS Buffalo, NY

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328
FXUS61 KBUF 020011
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
711 PM EST Thu Dec 1 2016

.SYNOPSIS...
Cold air will continue to flow over the eastern Great Lakes through
the end of the week, generating lake effect rain and snow showers to
the east and southeast of Lakes Erie and Ontario. These lake effect
bands of precipitation will begin to slowly weaken Saturday and
Sunday.

&&

.NEAR TERM /THROUGH FRIDAY/...
A vertically stacked low will remain across Western Quebec
tonight. In general, this will maintain a WSW flow across the
region overnight, resulting in only subtle changes to the current
conditions. Early this evening, radar shows lake effect rain and
snow showers off Lake Erie and Ontario.

For Lake Erie...early this evening the band is centered between
Dunkirk and Jamestown, and has become less organized over the past
couple hours. This is likely due to an increase in directional
shear as 850mb winds have become more westerly. Model guidance has
a fair handle on this, but consensus is a bit too far south.
Winds should gradually become more westerly which will push this
band slightly south and focused on the Western Southern Tier late
tonight. This band should extend well inland due to a 40 kt LLJ.

Temperature profiles, while cold enough to generate a lake effect
response are marginal for snow, and snowfall accumulation.
Gradually through the evening and overnight hours we should see an
increase in the amount of snow from the band of precipitation,
with accumulations of snow generally 1 to 3 inches across the
interior So. Tier, Boston Hills and southern Wyoming Hills.

Tomorrow winds will remain steady state bringing multi-banded in
nature rain/snow showers across SW NYS. The LLJ will begin to weaken
tomorrow, such that the inland extent to the precipitation should
diminish. The European Model suggests that there may be some
diminishment to the low level moisture midday tomorrow across Lake
Erie, and if this were to happen, there would be a brief
diminishment to the lake effect precipitation midday before low
level moisture again returns, enhancing the band of precipitation
late Friday afternoon. Snowfall totals tomorrow will range from an
inch or two, mainly across the higher terrain of Chautauqua and
Cattaraugus Counties.

For Lake Ontario...a broad but fairly disorganized band continues
east of the lake from the Tug Hill to Watertown. Radar shows some
upslope enhancement, which will continue overnight. This
precipiation should gradually shift south late tonight, with
directional shear likely to keep bands from getting to well
organized. Like off Lake Erie, temperatures will be marginal for
snow, with a mix of rain/snow through the evening hours. We should
see a transition to pure snow over the Tug Hill region tonight,
and also the western foothills of the Adirondack mountains. Here
there may be 2 to 4 inches of snowfall through the night. If
directional shear decreases and this precipitation becomes
organized into a band, then snowfall forecasts would need to be
increased for the Tug Hill where it will be just cold enough to
support a wet snow.

Tomorrow this band of precipitation should start the day across the
Tug Hill as a continual moist, westerly flow continues through the
night and morning hours. As the boundary layer warms slightly
through the day we should see a transition back to more rain than
snow from this band of precipitation. Towards the later afternoon
hours, and as the upper level low slides southeastward a subtle
shift to the winds will likely follow, such that winds will back to
more of a NW flow. This will push the band of precipitation from the
Tug Hill region early afternoon, down towards Wayne/Cayuga and
southern Oswego County by late afternoon/early evening. There is
even some hint that an upstream connection to Georgian Bay may
develop, and if this were to happen then enhanced rainfall southeast
of Lake Ontario. Temperature profiles suggest a mix of rain and
snow southeast of Lake Ontario through the afternoon hours.

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.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
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
temperatures.

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.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
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 week...as 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.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Most precipitation will be due to lake effect both tonight and
Friday. The WSW flow will keep this precipiation just out of
BUF/ART and more firmly out of IAG/ROC. For these terminals,
expect mainly VFR conditions, with periods of MVFR conditions as
lower clouds periodically pass through. At JHW, expect conditions
to lower to IFR as lake effect snow showers become more persistent
this evening. These may mix with rain at times, especially Friday
as temperatures rise slightly.

Outlook...

Friday night through Sunday...Mainly VFR with areas of MVFR/IFR
and rain/snow showers east of the lakes.
Monday...MVFR with a chance of rain and snow showers.
Tuesday...VFR with a chance of mainly rain showers.

&&

.MARINE...
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. Current SCA for the lakes may need to be
extended well into the weekend timeframe as continued cold air
flowing over the lakes maintains winds 20 to 25 knots.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 6 AM EST Saturday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Friday for LEZ020.
         Small Craft Advisory until 1 AM EST Friday for LOZ030.
         Small Craft Advisory until 6 AM EST Saturday for
         LOZ043>045.
         Small Craft Advisory until 1 AM EST Saturday for LOZ042.
         Small Craft Advisory until 1 AM EST Friday for SLZ022-
         024.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...APFFEL/THOMAS
SHORT TERM...TMA
LONG TERM...RSH/WCH
AVIATION...APFFEL
MARINE...APFFEL/THOMAS



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