Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240633

Area Forecast Discussion
National Weather Service Buffalo NY
233 AM EDT Mon Oct 24 2016

Cold northwesterly flow will persist into the middle of the week,
generating plenty of cloud cover, but only limited shower activity
southeast of the lakes. Temperatures will continue to run below


The shortwave that caused the rainfall across the Southern Tier
during the evening hours has moved off to the east early this
morning, taking with it the shower activity. However, as can be seen
on regional satellite imagery, cold cyclonic flow remains in place
across the region, and this is generating widespread lake effect
clouds downwind of the Great Lakes, with a few showers noted
upstream across northern Lower Michigan. While we should remain dry
through the rest of tonight, northwest 1000-850 mb winds will return
cooler air to the region, with 850 mb temperatures tumbling back to
near -5c during the day. This will cause equilibrium levels to rise
above 10kft, and as a result we should see at least some scattered
lake effect rain showers southeast of the lakes, mainly across areas
aligned with Georgian Bay and southern Lake Huron. The cold air
advection that will be responsible for the lake clouds and showers
will also serve to keep temperatures nearly steady through the day,
in the upper 40s to around 50.


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.


Shower activity has shifted south of the PA border with the passage
of last evening`s upper level disturbance and conditions have
returned to VFR across the forecast area. Persistent cold cyclonic
northwesterly  flow across the Great Lakes will continue to generate
plenty of VFR cigs across the forecast area through the TAF period,
and a few lake effect rain showers will be possible at times across
the far western Southern Tier, as well across areas south of Lake
Ontario. Cigs may drop to MVFR in these showers, but otherwise
cigs will remain VFR elsewhere through the TAF period.


Tuesday and Tuesday Night...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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