Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230900

Area Forecast Discussion
National Weather Service Buffalo NY
500 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.


Persistent cold advection under northwest flow will occur across the
eastern Great Lakes through the first half of the week. This flow
will be directed between an anomalously deep surface low over
eastern Canada and a western Canadian sourced high pressure building
southeast across the Northern Plains, western Great Lakes and
Midwest states. This flow will largely feature dry continental air
but models/BUFKIT profiles do show some intermittent shallow plumes
of limited moisture tied to separate surface troughs sifting across
the eastern Great Lakes. These weak troughs will help drive some
weak/scattered lake effect showers through late Tuesday
night/Wednesday morning.

The persistent cold advection will cool our airmass from around -4C
at 850mb Monday to around -7C at 850mb. This will keep surface
temperatures running below normal along with driving up lake induced
instability over the lakes. One of the shallow plumes of moisture
mentioned above is forecast to shift over our area Monday night into
Tuesday morning. This should drive scattered/broken bands of lake
effect showers southeast of the lakes with the highest chance POPs
coming between about Midnight and Noon Tuesday. A 310-320 flow will
keep most of the lake effect showers limited to the southern shore
of Lake Ontario into the northern Finger Lakes off Lake Ontario and
across Chautauqua county off Lake Erie. Temps in the 40s by day will
equate ptype to rain showers but some wet snow could mix in across
the higher terrain Monday night as temps fall into the upper to mid
30s. The Canadian sourced surface high over the midwest region
Tuesday will build east toward our region Tuesday night. This will
drive down a capping inversion bringing an end to Lake Effect

High pressure will extend southeast across the Lower Great Lakes
Wednesday. This will support mainly fair dry weather with
temperatures within a few degrees of normal.


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. This storm will certainly lead to
an increase in cloud coverage with a chance of some rain showers
possible west of the Genesee Valley. While showers that arrive
should mainly be in the form of rain, there is a slight chance that
some wet snow could mix in across the higher terrain of the Southern
Tier into the Bristol Hills.

The storm system will track just northwest of our forecast area on
Thursday with a sharp shortwave trough aloft and strong 50kt low
level jet driving a likely probability of widespread rain showers.
While the track of this low fits the track of high wind events, we
are not expecting strong winds with this event. The 1008ish low will
not be deep enough to support mixing of strong winds within the low
level jet but some breezy winds will be likely post frontal.

Thursday night into 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 moisture
in place within a deep cyclonic flow. This will support scattered
showers with some lake enhancement possible as 850mb temps cool
back below freezing.

00z Guidance indicates high pressure will begin to shift back across
our region next Saturday as the storm system exits across eastern
Canada. This should help to taper off any lingering showers leading
to mainly dry conditions by the afternoon hours.


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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