Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241103

Area Forecast Discussion
National Weather Service Buffalo NY
703 AM EDT SAT SEP 24 2016

An expansive area of high pressure crossing from Ontario to Quebec
will provide our region with fine early Fall weather this weekend...
as mostly sunny days will be accompanied by seasonable temperatures
in the 60s. Our next chance for rain will come late Monday and
Monday night when a cold front will push across the Lower Great
Lakes. A stationary storm system over the Upper Great Lakes will
then generate scattered lake effect rain showers for parts of the
region Tuesday and Wednesday.


While there will be some lingering low clouds early this morning
across parts of western New York...we can look forward to a
beautiful early Autumn day across the region. Lets set the stage.

Expansive high pressure centered over Ontario today will extend
south to the Gulf Coast. A wealth of dry air associated with this
fair weather giant will provide the bulk of the region with sun
filled skies...but there are a couple factors that will keep some
stubborn cloud cover in place over the far western counties.

To start with...there is still enough low level moisture in place
beneath a strong subsidence inversion to be lifted into cloud cover
by an upslope flow. While 11-3.9u imagery is showing that this area
of cloud coverage is shrinking...steep 10 deg c/km lapse rates
beneath the capping inversion should result in some `self destruct`
sun for areas west of the Finger Lakes that experience pre dawn
clearing. Will continue the trend of dragging the feet when it comes
to completely clearing out the far western counties this morning.
For much of the Finger Lakes region and certainly the Eastern Lake
Ontario region will be sunny and delightful.

In terms of will be the coolest day in months.
H85 temps in the single digits C will only support afternoon mercury
readings in the mid 60s F for most areas. While this may feel colder
than normal...these readings will actually be exactly where they
should be for this point in September.

Tonight...the axis of the large Canadian high will pass over our
forecast area. This will provide our region with nearly ideal
radiational cooling conditions...and given the Canadian origin of
the should come as no surprise that it will be the
chilliest nights in quite some time. Temperatures under star filled
skies will drop off into the low to mid 40s for most areas...with
readings bottoming out in the 30s across much of the Western
Southern Tier and Eastern Lake Ontario regions where there will be
some scattered frost. The frost is not expected to be widespread
enough across the Western Southern Tier to warrant an advisory...
however with temps forecast to drop to arnd 35 for a large portion
of Lewis County...have decided to issue a frost advisory for that
area. The dayshift can re-examine later today to see if the areas
under an advisory have to be expanded.


This period will open with a splendiferous day on strong
surface-based ridging will be draped directly across New York State.
This will promote mostly sunny skies and light to modest northerly
to northeasterly winds...with 850 mb temps of +2C to +8C allowing
temperatures to recover into the mid to upper 60s in most locations
after a chilly start to the day. This said...the North Country will
remain a bit cooler overall...with readings only peaking in the upper
50s to lower 60s there.

Sunday night...fair and dry weather will continue across our region as
the axis of the surface ridge slides eastward into New England. The
developing warm air advection regime on its backside will allow some
mid and high cloud cover to spill southeastward across New York State...
which will eventually help to render skies partly cloudy for all but
the North Country. The combination of the increasing cloud cover and
a developing southeasterly low level return flow should result in a
milder night for areas from the Genesee Valley westward...where lows
should range between the mid 40s and lower 50s. Further east...a close
facsimile of the previous night`s low temperatures is expected given
lesser amounts of cloud cover and lighter winds...with readings again
dipping into the mid 30s across the North Country...where some patchy
frost will again be possible. Accordingly...have retained a mention of
such in both the ZFP and HWO.

Monday and Monday night...our weather will deteriorate again as the
aforementioned ridge gives way to a rather deep mid and upper level
trough digging southeastward across Ontario Province and the Great
Lakes...with this feature eventually morphing into a deep closed
upper low over Central Ontario by Tuesday morning. At the surface...
an attendant surface wave will slide along a similar path...and will
eventually swing its trailing cold front through our region. The
00z/24 guidance suite continues to universally speed up the timing
of this feature...and now brings it through our area between later
Monday afternoon and Monday night. With this in mind...have sped up
the frontal timing some 3-6 hours from our previous continuity...
while maintaining an attendant swath of likely PoPs given favorable
moisture pooling and a band of narrow but deep lift accompanying
the frontal passage. At this point instability looks limited enough
for the bulk of the precip to be in the form of plain rain showers...
though cannot rule out an isolated thunderstorm or two approaching or
reaching extreme far WNY later on Monday afternoon. Following the
passage of the front...strong dry slotting should build into the
region Monday night...while bringing a temporary return to mainly dry
weather for many areas.

With respect to temperatures Monday and Monday night...a strengthening
southerly downslope flow and the overall warm air advection regime out
in advance of the cold front will allow temperatures to rebound back
into the upper 60s across the North Country and to the lower to mid 70s
across far western New York. The warmest overall temps will be found
across the favored downslope flow regions along the Lake Erie shoreline
and across the lake plains from Buffalo over to Rochester...where we
have accordingly continued to aim some 5 degrees above current guidance.
Developing cool air advection in the wake of the cold front will then
send readings tumbling back into the upper 40s to mid 50s Monday night.

After that...the remainder of this period will then feature the large
closed upper low slowly meandering its way southward/southeastward
across the Great Lakes. The deep cool pool and region of deeper
wraparound moisture attendant to this feature will result in a return
to cooler temperatures along with a general opportunity for some
scattered showers...with some bands of more concentrated lake effect
rain showers also possible downwind of the lakes. Given the many model
permutations noted in both the evolution of the closed low and its
consequent influence on the orientation of the low level wind field
over the past few this point it remains difficult to pin
down exactly where the lake enhanced/driven showers might for
now have just indicated some very broad areas of mid range chance PoPs
to the lee of both Lakes Erie and Ontario. Temperature-wise...850 mb
temps of +4C to +6C should translate into daytime highs in the lower
to mid 60s on Tuesday...with lows in the mid 40s to lower 50s then
following for Tuesday night.


In the longer term portion of the forecast...the medium range models
remain in loose agreement on the closed upper low eventually exiting
our region and expansive surface-based ridging building into our area
in its wake...though some differences in the exact details of all this
still persist. This is most notably the case with the 00z/24 ECMWF...
which sharply broke continuity with its previous runs and the other
guidance packages and now takes the closed low due south rather than
due east Wednesday and Thursday...before slowly lifting this feature
back northward toward our area on Friday. Given the outlier nature of
this solution...feel it best to stick to our continuity of lingering
scattered showers Wednesday giving way to a return to fair and dry
weather Thursday and Friday...along with temperatures climbing back
to near or slightly above normal levels by the end of the work week.


11-3.9 imagery depicts a wealth of stratus and low strato-cu across
the western counties early this morning...while clearing has already
taken place for the Eastern Lake Ontario region. Cigs associated
with the low cloud cover will be just above MVFR levels for the main
TAF sites such as KIAG and KBUF...while MVFR cigs will be found
across the bulk of the Southern Tier and also at KROC. IFR cigs will
be possible through 12z for KJHW.

The low clouds will slowly thin and clear out over the western
counties after daybreak. This will leave VFR conditions across the
entire region by mid morning. The fine weather for flying will
remain in place through tonight as Canadian based high pressure will
remain stretched across our region.


Sunday through Monday...VFR...except 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.


Small craft advisories will remain in place this morning for the
western portion of Lake Ontario and the New York nearshore waters of
Lake expansive high pressure over eastern Canada will keep
a northeast flow in place across the Lower Great Lakes. The gradient
will weaken while backing to the north during the midday and
afternoon...and this should allow winds and waves to subside as we
work through the day. Waters will also be fairly choppy in the Lower
Niagara River.

The large Canadian surface high will move by to our north tonight
and Sunday. This will produce gentle to moderate northerlies across
the Lower Great Lakes for the remainder of the weekend...with waters
being choppy at times along the south shore of Lake Ontario and also
southwest of Dunkirk.

Winds will veer to the southeast and freshen Sunday night and Monday
ahead of an approaching frontal system. While the offshore winds
will keep the highest waves in Canadian waters...small craft
advisories may be needed by Monday afternoon for the stronger winds.


NY...Frost Advisory from 2 AM to 9 AM EDT Sunday for NYZ008.
MARINE...Small Craft Advisory until 11 AM EDT this morning for LEZ040.
         Small Craft Advisory until 11 AM EDT this morning for



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