Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 020313
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1013 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 Quebec tonight. In
general, this will maintain a WSW flow across the region
overnight, resulting in only subtle changes to the current
conditions. Late this evening, radar shows lake effect rain and
snow showers off Lake Erie and Ontario.

For Lake Erie...late this evening the band is centered across the
Western Southern Tier, with its northern fringe extending into the
Boston Hills. Model guidance has a fair handle on this band, but
consensus is a bit too far south with the band. Winds may become a
bit more westerly late tonight, which would push the band slightly
south from its current position, but for the most part expect
little change. 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. Precipitation will be all rain
near the lake shore, but will be mainly snow further inland where
elevations are a bit higher. Accumulations of snow will generally
be 1 to 3 inches across the interior So. Tier, Boston Hills and
southern Wyoming Hills.

Tomorrow 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
areas.

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.

&&

.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 /03Z 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 through FRiday morning.
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
persist overnight and into Friday.

A shortwave will drop across the region late Friday, which will
bring steadier precipitation to the Eastern Lake Ontario region
late in the day. This should fall as a mix of rain and snow at
ART with MVFR conditions.

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...
On the evening update, headlines were dropped for the St.
Lawrence and Lower Niagara rivers based on the latest obs.
Meanwhile, headlines were extended a bit longer on the lakes based
on the lastest wind/wave guidance which supported the adjustment.

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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 PM EST Saturday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Friday for LEZ020.
         Small Craft Advisory until 6 PM EST Saturday for
         LOZ043>045.
         Small Craft Advisory until 6 AM EST Saturday for LOZ042.

&&

$$

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



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