Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240253

Area Forecast Discussion
National Weather Service Buffalo NY
1053 PM EDT Sun Oct 23 2016

An upper level disturbance dropping across the region will bring
some rain showers tonight, primarily to the Southern Tier.
Otherwise, cold northwesterly flow will persist into the middle of
the week, generating plenty of cloud cover, but little else in the
way of precipitation. Temperatures will continue to run below


Potent upper level wave currently seen on water vapor imagery
working across the eastern Great Lakes. Associated surface low will
move across the southern Great Lakes through the night and to the
south New England coast by Monday morning. Deep moisture will spread
into western New York from the northwest, producing a band of
showers to the north of the track of the low pressure. The highest
probabilities look to be along the Southern Tier closer to the
surface wave. There will be a few isolated thunderstorms through
midnight across the Western Southern Tier as deeper moisture and
warm air advection encounters colder air aloft.

Monday, the upper wave races east of the region, with the weak
surface reflection exiting to the east. Synoptically-forced
showers will end by morning. Northwest 1000-850 mb winds will
return cooler air to the region, with 850 mb temperatures tumbling
back to near -5c during the day. Inversions heights will also rise
toward 6k feet. That will return the threat of lake effect showers
for favored northwest flow areas. For the most part, high
temperatures will remain only in the 40s.


For the first 48 hours of this period...our weather will continue to
be dominated by persistent upper level troughing...the core of which
will only slowly drift from eastern Quebec Province to the Canadian
Maritimes. This feature will feed a continued northwesterly to northerly
flow of colder Canadian air across our region...which will result in
temperatures averaging solidly below normal right through midweek. More
specifically...expect daytime highs mostly in the lower to mid 40s both
Tuesday and Wednesday...while nighttime lows mostly ranging through the
30s Monday night will drop off into the upper 20s and lower 30s Tuesday
night...likely resulting in a killing freeze in most areas where the
growing season has not already ended.

Precipitation-wise...the persistent northwesterly to northerly flow
of Canadian air across our region will also lead to the potential for
some lake effect precipitation southeast and south of the lakes. This
stated...the combination of the shortening fetch...a fairly low (5-6 kft)
capping inversion...and less than impressive moisture below this level
should all help to keep any such activity fairly limited/scattered in
nature. As such...have kept PoPs confined to the 20-40 range...with the
highest values southeast of Lake Erie Monday night and early Tuesday...
where and when moisture will be a little bit more favorable. Ptype
with the lake effect precip will be predominantly rain showers by day...
mixing with or changing to snow each night/early morning as the boundary
layer cools. Any lake effect activity lingering into Tuesday night will
come to an end during the day on surface-based ridging
settles directly overhead along with increasing large-scale subsidence
and shear.

Wednesday night the axis of the surface ridge will grudgingly drift
east into New England...while a developing storm system over the Upper
Midwest slowly pushes into the western Great Lakes. The developing warm
air advection regime out ahead of this next system will initially drive
a west to east increase in cloud cover during the night...before leading
to the possibility of some showers across far western New York late.
While the bulk of these should be in the form of plain rain given the
strengthening warm air advection regime...interior sections of the
Southern Tier may well remain cold enough to support a brief mix at
the onset of the precipitation. Given the still somewhat-distant time
frame...have elected to keep this in the form of a general rain-snow
shower mix for now...though the degree of warming currently portrayed
aloft would ultimately be supportive of other precipitation types.

On Thursday...the surface low will continue to slowly deepen while
lifting northeastward into Southern Ontario...while pushing its
attendant warm front across areas south of Lake Ontario. Coupled
with height falls aloft and deepening synoptic-scale moisture...this
will lead to a likelihood of precipitation spreading across our
region from southwest to northeast...with the continued warm air
advection regime supporting rain showers as the predominant precip
type. This stated...high temperatures will remain a bit below average
thanks to thicker cloud cover and increasing precipitation coverage...
with readings generally remaining confined to between 45 and 50.


A progressive low amplitude flow will remain in place across the
country during this period. The center piece for this pattern will
be a 100kt H25 jet straddling the Canadian border....which will
effectively block any anomalously cold air to the north. This will
encourage temperatures across the Lower Great Lakes to average
within a couple degrees of normal.

As we open this period Thursday night...a compact area of low
pressure over Southern Ontario will start to push northeast away
from the region. In the process...this initial storm system will
start to transfer a bulk of its energy to a coastal low off New
England. We can anticipate rain showers as a result of this
scenario...particularly over the Eastern Lake Ontario region.

The negatively tilted H5 trough will deepen enough to generate a
stacked low in the vcnty of northern New England/Maine on Friday...
while weak sfc based ridging will extend from the Upper Great Lakes
to the Ohio Valley. This will place our region within a cyclonic
flow of moist chilly air so that scattered rain showers can be
expected. A minimal lake response should enhance the coverage and
possibly the intensity of these showers southeast of Lake Ontario.

The aforementioned weak ridging is forecast to push east across the
Lower Great Lakes Friday night and Saturday. This will enable our
weather to improve somewhat...but with low confidence in the
guidance and significant differences between the various
ensembles...will carry slight chc pops.

On Sunday...the weak ridging will exit across New England while the
next southern stream shortwave is forecast to approach from the Ohio
Valley. This would support the next round of precipitation...
although as mentioned...confidence will be lower than normal due to
significant discrepancies in the ensemble packages.


An upper level disturbance will cross the area tonight and trigger
rain showers across the region, most likely across the Southern
Tier, along with potentially reinvigorating lake-effect showers
southeast of Lake Ontario. IFR conditions associated with these
showers will be possible across the Southern Tier from 02Z-09Z, with
MVFR cigs possible farther north across the Niagara Frontier and
elsewhere south of Lake Ontario as the lake-effect clouds return,
with a few showers possible south of the lake. Clouds will linger
through much of Monday with only a chance of lake effect rain
showers southeast of the lakes, and low chance of MVFR cigs outside
of lake induced clouds.


Monday...VFR/MVFR with a chance of lake effect rain showers.
Tuesday...Mainly VFR.
Thursday...MVFR/IFR with rain showers likely.
Friday...MVFR with a chance of lake effect showers.


Brisk west-northwesterly flow continues across the lakes, as the
area remains with a tight pressure gradient between a deep low
pressure system centered to the north of Maine and high pressure
over the Ohio Valley and central Great Lakes.

Winds will relax somewhat tonight as a short wave trough moves
through. The downtime for the small craft advisory conditions will
likely be short lived as a northwest flow will increase behind the
system. Strong cold advection will assist in keeping winds up into
at least Monday night on Lake Erie and through Tuesday on Lake

High pressure will briefly ridge across the lake on later Tuesday
but another fast moving storm system will arrive Wednesday night
into Thursday.


MARINE...Small Craft Advisory until 9 AM EDT Tuesday for LEZ040-041.
         Small Craft Advisory until 6 PM EDT Tuesday for
         Small Craft Advisory until 9 AM EDT Tuesday for LOZ045.



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