Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230829

Area Forecast Discussion
National Weather Service Buffalo NY
429 AM EDT Sun Oct 23 2016

Cold northwesterly flow off of the Great Lakes will keep plenty of
cloud cover hanging around Western New York today, while clouds
should clear across the North Country. An upper level disturbance
dropping across the region will bring more rain showers, primarily
to the Southern Tier, overnight. 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 apart from Sunday
night`s system. Temperatures will continue to run below average.


A peek at satellite imagery shows that the widespread cloud cover
south of Lake Ontario has rapidly dissolved over the last couple of
hours as low level flow has backed around to the west in response to
the continued northward track of a deep surface low now centered
north of Maine. However, the clearing is expected to be short-lived
as increasing warm advection and weak isentropic uplift ahead of an
approaching upper level shortwave will regenerate cloud cover across
the forecast area. This cloud cover is already blossoming across
Southern Ontario and Lake Erie and making its way into the western
Southern Tier at this time.

While clouds will build back in across the forecast area today, it
will remain a dry day as moisture associated with the clouds is very
shallow with very dry air noted above 850mb on model soundings. This
should change however as we move into the evening hours, as a
compact but potent shortwave currently positioned over Manitoba
rapidly drops across the upper Great Lakes today and across Western
New York tonight. This shortwave is expected to generate rain
showers across the Southern Tier tonight, while the increased
synoptic lift and moisture associated with the wave may also raise
inversion heights enough to generate a few lake-effect showers
elsewhere to the south of Lake Ontario overnight.

Regarding temperatures, the warm advection discussed above will
allow temperatures to rebound somewhat today, with readings rising
into the low to mid 50s, still several degrees below average.
Nonetheless, a persistent west-northwest breeze that will become
increasingly gusty as we move through the day will still make it
feel quite chilly outside. The increasing cloud cover and
precipitation will limit temperature falls tonight, with lows
running in the low to mid 40s, with the exception of the North
Country, where readings will fall into the mid 30s, thanks to
proximity to the departing upper level trough.


Our weather for the remainder of this period will be dominated by
persistent upper level troughing...the core of which will only
slowly drift from 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 temps
averaging solidly below normal through midweek. More
specifically... expect daytime highs mostly in the upper 40s to
lower 50s on Monday to pull back into the lower to mid 40s for
both Tuesday and Wednesday as our airmass cools...while nighttime
lows mostly ranging through the 30s Monday night will drop off
into the upper 20s and lower 30s Tuesday night...quite possibly
resulting in a killing freeze in those areas where the growing
season has not yet ended.

Precipitation-wise...the continual northwesterly to northerly flow of
Canadian air will also result in a potential for some lake effect
precipitation southeast and south of the lakes. This stated...the
combination of the short fetch...a fairly low (4-5 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 indicated southeast of Lake Erie Monday night/early Tuesday...
where and when moisture will be a little bit more favorable. The
predominant ptype with this should be rain...except at night and early
each morning when the boundary layer should be cool enough to support a
little wet snow inland from the lakes and/or across the higher terrain.
Any lake effect activity that does form should then come to an end
during the day on Wednesday...when surface-based ridging settles
directly overhead along with increasing large-scale subsidence and


A progressive sinusoidal flow over the country...dominated by Pacific
based air...will support a minimal day to day warming trend during
this time frame. While this will be accompanied by mainly unsettled
conditions...significant weather is not anticipated.

High pressure nosing south across the Lower Great Lakes Wednesday
evening will stubbornly give way to a deepening storm system over
the Mid West during the overnight. In the process...a tightening
baroclinic zone will advance across our western counties. This will
certainly lead to an increase in cloud coverage...with some rain
showers possible west of the Genesee Valley. The strengthening warm
advection ahead of the sfc low should encourage a non diurnal temp
trend...with the mins generally occuring around midnight. This will
especially be the case over the far western counties...assuring that
any pcpn that falls will be in the form of rain.

All of the guidance packages are in agreement that the storm system
will then track by to the west of our forecast area on Thursday...
while significant hgt falls will accompany the passage of an actual
warm front and relatively deep swath of moisture. Have bumped 50
pops to likely for the afternoon.

Thursday night...the associated cold front will make its way across
our region with more showers being generated as a result. Again...
all of the pcpn should be liquid as H85 temps in the single digits
will only drop to around zero c by daybreak.

On Friday...the core of the chilliest air will move across our
region as the base of the supporting negatively tilted trough will
make its way from the Lower Great Lakes to the Upper St Lawrence
Valley. There should also be plenty of `wrap around` synoptic
moisture in place within a deep cyclonic flow. This will support
scattered showers as midday temperatures will struggle to near 50f.

As we head into the start of the weekend...the medium range
ensembles diverge fairly significantly. While one `camp` suggests
that a weak shortwave ridge will cross our region on Saturday...
another favors the passing of a robust shortwave. Experience has
this forecaster leaning towards the former...with brief ridging
supporting a dry day on Saturday. Confidence with this Day 7
forecast is lower than normal.


Cold northwesterly flow is continuing to generate lake-effect clouds
south and east of the lakes, with ceilings mostly greater than 3kft.
Expect bkn stratocu to scatter out south and east of Lake Ontario
this morning as a shortwave ridge crosses the forecast area from the
northwest...however clouds should fill back in later this afternoon
as another upper level disturbance approaches the area.

The aforementioned disturbance will likely trigger rain showers
across the Southern Tier, along with potentially reinvigorating lake-
effect showers southeast of Lake Ontario, from 00Z onwards. IFR
conditions associated with these showers will be possible across
the Southern Tier after 02Z, 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.


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 this
morning, 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 on
central and southeastern Lake Ontario continue to flirt with gale
force and will leave the gale warning up for the time being, with
small craft advisories elsewhere throughout the day and into
tonight, as the gradient will remain fairly tight across the region.

Winds will relax somewhat tonight, as the main low weakens over
eastern Quebec and a weak trough associated with an upper level
disturbance moves through tonight, temporarily disrupting the west-
northwest flow. However, cold advection under northwesterly flow
will resume in the wake of this disturbance, with small craft
advisories likely being needed on Lake Ontario into Tuesday night.
The shorter fetch on Lake Erie as the flow veers to the north should
allow wave action to diminish below advisory levels Tuesday morning.


MARINE...Small Craft Advisory until 11 PM EDT this evening for LEZ040.
         Small Craft Advisory until 2 AM EDT Monday for LEZ041.
         Gale Warning until 11 AM EDT this morning for LOZ043-
         Small Craft Advisory until 11 PM EDT this evening for
         Small Craft Advisory until 5 AM EDT Monday for LOZ045.



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