Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 310551

Area Forecast Discussion
National Weather Service Buffalo NY
151 AM EDT WED AUG 31 2016

A cold front will approach and cross New York late tonight and
Wednesday bringing scattered showers and thunderstorms. Cooler and
drier air moving in behind the front will usher in more comfortable
temperatures through the rest of the week as high pressure builds
across the region before summer heat returns for the Labor Day


Satellite imagery late this evening shows widespread mid and high
level debris clouds shifting over western and north-central NY from
remnant convection over Lake Huron and Southern Ontario Province.
The showers and storms are located just ahead of a cold front
stretching from James Bay, across Lake Huron, and southwest into
northern Illinois. These showers and thunderstorms will slowly make
their way towards our forecast area tonight as the front sags
southeast towards New York.

While forcing along the front is decent, deep moisture is lacking
and the late night timing is not ideal. That said, given synoptic
forcing, a few showers or thunderstorms developing over far Southern
Ontario well West of Buffalo may hold together long enough to impact
the Niagara Frontier late tonight. The scattered showers and
isolated thunderstorms north of Lake Ontario will shift southeast
across the Saint Lawrence Valley overnight.

The cold front will continue to drop southeast across the forecast
area on Wednesday. While we should see a chance of showers and
perhaps a thunderstorm in the region in the morning, best chances
for activity will be in the early afternoon, particularly if the
front slows up. Once again, while instability looks pretty decent
ahead of the front, with CAPE values getting up to around 1000 J/kg,
and with 0-6km shear approaching 30 kts, a couple of these storms
may end up being strong and approach severe limits, however activity
will likely be scattered in nature given the lack of a deep GOMEX
moisture tie-in. Regarding temperatures, we will see another warm
night with lows in the 60s as warmer air advects ahead of the front,
while clouds associated with the front should keep readings in the
upper 70s on Wednesday.


A progressive pattern will be in place across the country during
this longwave troughs centered over both coasts at the
start of this period will shift east by one wavelength by Saturday
night. This means that the corresponding ridge will make its way to
the Great Lakes region...prompting a relatively quick warm up from
the brief taste of Autumn like weather. Meanwhile...rain free
conditions during the period will exacerbate the drought conditions
found across the overwhelming majority of the region.

This time frame will open Wednesday night with a cold front exiting
to our southeast. Meanwhile...a robust shortwave digging into the
base of a longwave trough will push a secondary cold front over the
Lower Great Lakes. Cold advection associated with the frontal
boundaries will lower H85 temps to the upper single digits by
daybreak. While this will establish increasing instability over the
lakes...there will be several factors to greatly limit the resulting
lake response. This will include a relatively dry synoptic
environment...a short fetch...and a moderately sheared airmass.
While this should prevent any lake induced pcpn from developing...
some leftover showers will be possible during the first half of the
night in the wake of the initial cold front.

On Thursday...the aforementioned strong shortwave will cross the
region while a capacious area of high pressure will nose southward
across the Upper Great Lakes from Hudson Bay. The ensuing battle
between the large scale subsidence and the low level mesoscale lake
processes should be won by the the lake instability will
have a limited impact because of the already mentioned factors...not
to mention the presence of a lowering subsidence inversion and the
affects of a still relatively strong early Sept sun. All that being
said...a northerly flow should help to produce some upslope cloud
cover over the Finger Lakes region and portions of the Srn Tier.
Will only carry slgt chc pops. It will feel somewhat cool...with
afternoon temps in the lower 70s for most areas.

It will become relatively cool for parts of our forecast area
Thursday the center of the expansive surface high will
make its way to the Upper Great Lakes. This will set the stage for
favorable radiational cooling within a fresh Canadian airmass to
encourage the mercury to drop well into the 50s away from the lakes
with parts of Lewis County and the Southern Tier likely experiencing
lows in the 40s.

On Friday...broad ridging will be centered over the Mississippi
Valley while the associated sfc high will remain over the Upper
Great Lakes. This will ensure that cool dry weather will persist...
with H85 temps in the vcnty of 8-10c providing us with a second day
of max temps in the lower 70s.

As the sfc high drifts across the Lower Great Lakes Friday night...
we can anticipate the coolest night of the forecast period. Nearly
ideal radiational cooling under star filled skies will allow the
mercury to settle in the low to mid 40s across the majority of the
Southern Tier as well as in Lewis County...with mins found within a
couple degrees of 50 elsewhere.

Saturday will then feature absolutely beautiful weather across our ridging at levels will couple with a Canadian airmass to
produce sun filled skies and comfortable conditions. Temperatures
will top out in the upper 70s in most areas...while dew points will
remain within a few degrees of 50. Simply outstanding weather for
outdoor activities.


This period will feature a return to mid summer warmth as our
forecast area will be squarely under a ridge...sandwiched between a
broad based trough over the western half of the country and a
tropical system off the East Coast. This very high confidence
forecast will include dry weather as well. The dry and warm
conditions will only enhanced by strong subsidence that would be
found over our region if the medium range ensembles are correct in
their general position of the tropical system off the Northeast

Temperatures during this period will range from the mid and upper
80s for most areas by day to the mid and upper 60s most nights.

Looking further down the road at the remainder of next week...the
presence of a strong jet across the North Pacific should keep a low
amplitude trough in place over the western conus.  This will favor a
downstream ridge over the eastern seaboard with a persistent
southerly flow over the Lower Great Lakes. The strong zonal
Pacific flow will also help to block any attempt by chilly
Canadian air from making its way south of the border. The result
will be a continuation of above normal temperatures through the


VFR conditions will continue to prevail with increasing and lowering
mid and high level cigs. Showers and thunderstorms currently north
of Lake Ontario will track towards the Saint Lawrence Valley
overnight as a cold front sags south towards the region. Elsewhere,
we will see a chance of showers and perhaps an isolated thunderstorm
late tonight as the aforementioned front continues to progress into
Western/Central New York, however confidence remains low given the
late night timing and lack of deep moisture.

Moving into Wednesday, we will continue to see a chance of showers
and thunderstorms along the frontal boundary as it pushes southeast
across the forecast area, however prevailing conditions should
remain VFR outside of any cells. Any activity should be scattered in
nature so have only include VCSH/VCTS for now. Winds will retain a
west-southwest component throughout the day, with veering to the
west-northwest not taking place until after frontal passage late

Wednesday Night and Thursday...Mainly VFR with a slight
chance of showers.
Friday through Sunday...VFR.


A cold front will drop south across the lakes late tonight into
Wednesday, bringing a chance of showers and thunderstorms through
Wednesday morning. Otherwise, freshening northerly flow behind the
front will gradually build the chop on the south sides of the lakes
Wednesday night into Thursday.
By Thursday afternoon, waves may approach 4 feet, and a small craft
advisory may be required, particularly should the gradient tighten
as high pressure builds across the central Great Lakes. Waves should
subside as the high pressure moves overhead Friday.





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