Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231742

Area Forecast Discussion
National Weather Service Buffalo NY
142 PM EDT FRI SEP 23 2016

A cold front move southeast and away from the area through this
evening with widely scattered showers ending from north to south.
This cold front will usher in a much cooler airmass for the weekend
with high pressure bringing a return to sunshine. Another cold front
will cross the region late Monday through Tuesday and bring the next
chance of rain.


Surface analysis early this afternoon showing the cold front pushing
southeast through PA and away from our region. This front has
anabatic characteristics, with the majority of the deeper moisture
and forcing for ascent on the cold side of the boundary. The last
band of scattered showers from Lake Ontario into the eastern Lake
Ontario region will drift southeast and across the region through
the rest of the afternoon. Temperatures are still in the 70s near
the PA state line, but elsewhere temperatures are falling in
moderate cold advection behind the cold front. Extensive stratus
supported by some contribution from lake effect moisture and
northerly upslope flow will maintain cloudy skies in most areas
through the rest of the afternoon.

A few scattered light showers may linger across the higher terrain
of the western Southern Tier and western Finger Lakes this evening,
otherwise the remainder of the night will be dry as mid level drying
advances south out of Canada. Despite the chilly airmass, a short
northerly fetch, extensive mid level dry air, and a stout inversion
near 5K feet will prevent any lake effect rain showers. The lakes
will be able to generate some cloud cover however, with north to
northeast low level flow favoring areas from the western Finger
Lakes westward across western NY for some lingering cloud cover
overnight, aided by upslope flow. The North Country and Central NY
will see at least partial clearing with no off-lake component.

Steady cold advection will bring much cooler temperatures overnight.
Expect lows in the upper 40s across most of the area, with lower 40s
east of Lake Ontario with no lake modification to the airmass. North
to northeast flow will keep areas within a few miles of the
lakeshores in the lower to mid 50s.

On Saturday surface high pressure over northwest Ontario province
will begin to nose into the Lower Great Lakes. Subsidence and drying
associated with the surface high will help to scour out any
remaining lake effect clouds south of the lakes by midday. A few
scattered diurnal cumulus will develop across the higher terrain of
the Southern Tier and Finger Lakes, with any clouds mixing out as
drier air continues to move in. The coolest airmass of the season
will settle into the area on Saturday. Expect highs in the mid 60s
in most locations, with lower 60s on the hills. The North Country
will be deeper into the cool air, with lower 60s at lower
elevations and mid 50s across the higher terrain.


This period will be dominated by delightful early Autumn weather as
a sharp...full latitude ridge will supply the region with abundant
sunshine and seasonable temperatures. As has been the case for the
past couple of days though...the various guidance packages have been
on different pages as to how this pattern will break down. Typically
when there is such a sharp ridge nestled between deep closed lows...
Pacific energy erodes the `base` (equatorward portion) of the ridge
to develop a `high over low` Rex block. This process can take days
to resolve itself before the mid latitude block weakens to allow for
a progressive pattern to become re established. In this case
though...the medium range ensembles are leaning towards keeping the
pinched ridge transitory in nature through its life cycle as several
vigorous shortwaves are forecast to feed into the western trough. We
can take a closer look at this in the long term section of this
discussion. For now...lets focus on the details of the nice weekend

As the aforementioned sharp ridge pushes east across the Upper Great
Lakes Saturday night...its associated surface high will extend from
Hudson Bay southward directly across our forecast area. Continued
drying in the low depicted by steadily falling dew
points from both the NAM and GFS...should lead to a
filled night. Very favorable conditions for radiational cooling will
allow temps to settle into the mid and upper 30s east of Lk Ontario
and across chunk of the Srn Tier...with both areas possibly
experiencing areas of frost. Will highlight this risk in the HWO
product. Elsewhere...mins Saturday night will range from 40 to 45.

The axis of the large...elongated Canadian surface high will remain
parked over our forecast area as we move through Sunday. This will
provide us with another glorious early Autumn day with generous
amounts of sun and afternoon temperatures that will once again top
out in the 60s...right at typical late September levels. It will be
another great day to get out and enjoy some early Fall foliage.

Our controlling surface high will drift east across Quebec and the
St Lawrence Valley Sunday an approaching dynamic trough
over the Upper Mississippi Valley will deepen into a closed low. As
described earlier...the continued pinching of the mid level ridge
should eventually lead to a high over low Rex block...but that is
looking to set up further to the north than originally expected.
This general scenario is also favored by the ECMWF. The result for
our region could be a stretch of unsettled weather in the long term
portion of the forecast. In any case...fair weather will persist
Sunday night with a bit of moderation in the overnight temperatures
across the far western counties. Meanwhile scattered frost may be an
issue again for the North Country.

Conditions across our region will start to deteriorate on Monday as
a very dynamic closed low will set up shop over the Upper
Mississippi Valley. This will continue to push the sharp...but
transitory ridge to the east across New England...thereby opening
the door for moisture to finally return from the Ohio Valley. The
mid level ridging should hold its ground long enough to keep rain
free conditions in place for the bulk of our region...but cannot
guarantee that some showers won`t make their way across the far
western counties ahead of a Pacific based cool front. The deepening
southerly flow ahead of the front will also support a warmer day...
with the mercury climbing into at lest the lower 70s for all but the
Eastern Lake Ontario region.

The closed low will stall over the Upper Great Lakes Monday night.
The vertically stacked low will drive its Pacific cold front across
our forecast area in the with increased consistency now
found between the operational GFS and ECMWF...will raise pops to chc
for the entire forecast area. While a 90kt H25 jet pushing north
across Lake Huron will coincide with the frontal passage...adding
upper level support and deepening the omega field for generating
pcpn...low level lapse rates are not impressive enough to include
any mention of thunder. There is also a marked lack of any elevated per the GFS BUFKIT profiles.


It will be somewhat unsettled for the bulk of this period...although
none of the days are expected to be a washout. That being said...

Confidence during this long range period has the
medium range ensembles have come into closer agreement in the
handling of a long wave trough over the Great Lakes. The discussed
Rex block that will develop as a result of the digging trough will
have its col/reflection point near James Bay rather than over
Southern this will mean that we can anticipate a higher
chance for scattered showers. Interestingly enough...the more
northward location of the Rex block will translate into lower
temperatures across our region in the vcnty of the cold core within
the heart of the trough...or persistent closed low (as per some of
the GFS ensemble members).

The scattered showers will be supported by a chilly cyclonic flow
over the Lower Great Lakes...but again...there will be stretches of
rain free weather that should dominate the period.

As we work through Wednesday into Thursday...ridging over the Upper
Great Lakes will build east to diminish the potential for showers.

Looking further ahead...the approaching ridge should provide our
region with fair dry weather along with above normal temperatures
for the end of the week into the first weekend of October.


A cold front will move southeast and away from the region through
the rest of the afternoon and evening with scattered light showers
ending from north to south. A widespread area of IFR and MVFR CIGS
in low stratus behind the front will continue through this evening,
supported by northeast upslope flow and some contribution from lake
effect moisture. CIGS will improve to MVFR across lower elevations
this evening, with IFR lasting longer across the higher terrain of
the western Southern Tier and western Finger Lakes. Overnight some
lake effect clouds may persist south of Lake Ontario with areas of
MVFR, with partial clearing and VFR elsewhere.

On Saturday any remaining lake effect clouds with local MVFR CIGS
will scatter out by mid to late morning. This will leave some
diurnal cumulus across higher terrain inland from the lakes
during the afternoon with mainly VFR for the afternoon.


Sunday through for some patchy overnight/
early morning valley fog with local IFR across the Southern Tier.
Monday Night and Tuesday...Areas of MVFR with a chance of showers.
Wednesday...VFR/MVFR with a chance of showers.


Moderate northeasterlies will continue on Lake Ontario through the
rest of the afternoon and tonight. This will continue to support
Small Craft Advisory conditions along the south shore of the lake.
Northeast winds will also increase on Lake Erie, with winds and
waves approaching Small Craft Advisory levels from Dunkirk to
Ripley. For now we have held off on a headline with the expectation
of conditions remaining just below Advisory levels.

High pressure begins to nose into the Lower Great Lakes Saturday
with winds starting to diminish. Winds and waves will subside
further Saturday night and Sunday as the surface high builds into
western Quebec and the Lower Great Lakes.


MARINE...Small Craft Advisory until 11 AM EDT Saturday for LOZ042>044.



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