Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 240547
AFDBUF

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TODAY/...
11-3.9 satellite imagery is doing a beautiful job outlining the
extensive stratus and low strato-cu found across the western
counties. This moisture...leftover in the wake of this past
afternoons frontal passage...is trapped beneath a strong subsidence
inversion found ahead of a massive surface high that extends north
across Hudson Bay to the Canadian Archipelago. This moisture field
will be stubborn to thin and clear out...as a northeast upslope flow
will remain in place well past daybreak. There will also be modest
low level moisture enhancement from single digit H85 air passing
over the relatively warm waters of Lake Ontario.

Meanwhile...clearing has made its southward across the Eastern Lake
Ontario where both upslope and lake enhancement will not come into
play. Skies in this area should be clear to partly cloudy through
daybreak.

Temperatures overnight will settle into the 40s away from the
lakes...with some upper 30s not out of the question for sites from
the Black River Valley eastward to the foothills of the Adirondacks.

For Saturday...the expansive sfc high centered over Ontario will
continue to build south across the Lower Great Lakes. This will keep
a north to northeast flow in place through the morning hours...with
strato-cu remaining fairly persistent form the Finger Lakes to Lake
Erie. This cloud cover will gradually thin out as diurnally driven
low level mixing increases towards midday-early afternoon. Otherwise
it will be a beautiful early Autumn day with partly to mostly sunny
skies and pleasantly cool mercury readings. Temperatures Saturday
afternoon will generally be in the mid 60s.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...
High pressure will settle upon the region Saturday night, bringing
clear skies and light winds. A pool of cold air will be centered
near northern New England Saturday night, where sub-zero 850 hPa
temperatures will reside. We will still be on the western edge of
this pool of cold air through the night, with the cooler air aloft
over our eastern zones.

The combination of clear skies, light winds and cool air overhead
will bring favorable radiational cooling conditions, with many areas
dipping down into the 40s, and interior regions dropping down into
the mid to upper 30s. This will likely allow for frost formation,
across the interior So Tier, and North Country, with greater
confidence across the North Country which will lie closer to the
colder air aloft. Frost in these regions is near the norm, with the
average first frost here around the third week in September. Closer
to the rivers in the valleys frost will not be likely, but some
patches of fog will be possible.

A crisp, but sunny start to Sunday. As the surface high pressure
scoots eastward, and upper level ridge of high pressure bears upon
us, we should see afternoon temperatures warm nicely into the 60s
which is near normal. It will remain dry Sunday night though mid and
high level clouds will likely keep overnight lows a few degrees
warmer than the preceding night. There may still be additional frost
across North Country Sunday night, but not as great in coverage
area.

Our next system will be forming across the plains Sunday, as a deep
upper level shortwave trough of low pressure drops from the Northern
Rockies towards the Northern Plains. This system will be advancing a
Pacific based cold front across the lower 48-states. Meanwhile, a
steady flow of moisture from the Gulf of Mexico will be circulating
around a southeastern area of high pressure, with this plume of
moisture advecting northward up the lower Mississippi Valley and
eventually along and ahead of the cold front.

This system will bring a chance for rain Monday afternoon across the
western counties of NYS, with rain possibly reaching as far east as
the North Country. The likely period for rain showers will be Monday
night as a cold front crosses the region. Reasons for increasing the
Pops for Monday night will be upper level height falls, and
convergence along a low level jet, with the jet nose within a nearly
saturated layer from the surface up through 10K feet. The nocturnal
passage of the cold front and limited instability will reduce
chances for thunder, and for now will not include it in the
forecast.

There is still some timing differences on the passage of the surface
cold front, and will continue with chance pops Tuesday morning
across our eastern zones where shower along the cold front may still
reside, while allowing for a dry period Tuesday morning across WNY
where a dry slot behind the cold front will likely be found.

Scattered showers will again increase across the region Tuesday
afternoon as daytime heating combined with the passage of the upper
level trough axis and return of ambient moisture may bring a few
showers.

Highs on Monday will reach into the upper 60s to mid 70s. Warmest
areas will likely be along the Lake Erie shore, and the western lake
plain where southeast winds will downslope. Cooler Tuesday with
widespread 60s found.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Model consensus (GFS/GGEM/ECMWF) slowly brings an upper level trough
axis across the region on Tuesday night. Temperatures aloft will be
modestly cooler, dropping down to around +3C at 850mb. This will be
cold enough for some modest lake enhancement.  Lake enhancement
along with moisture from the trough and weak surface low will result
in some showers Tuesday night into Wednesday which will be most
prevalent downwind of the lakes. Considerable clouds and cooler air
aloft should keep high temperatures in the 60s on Wednesday.

The upper level trough will gradually exit east into New England on
Wednesday with a large ridge of high pressure forecast to build into
the area Thursday and Friday. This will bring pleasant fall weather
at the end of the week with quite a bit of sunshine, and gradually
warming temperatures. Because of the dry pattern, expect a slightly
wider diurnal range of temperatures with highs on Friday likely to
warm well into the 70s.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
11-3.9 imagery depicts a wealth of stratus and low strato-cu across
the western counties as of 06z...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...KBUF and KROC...while upslope flow and elevated
airfields across the Southern Tier will experience IFR to LIFR cigs.

The low clouds will be stubborn to clear after daybreak... but we
can expect a gradual improvement across the region with VFR
conditions anticipated for all sites by midday.

The VFR conditions from this coming afternoon will persist through
Saturday night.

Outlook...

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.

&&

.MARINE...
Moderate northeasterlies will continue on Lake Ontario and Lake Erie
through the rest of the overnight. This will continue to support
Small Craft Advisory conditions along the south shore of both lakes.

High pressure begins to nose into the Lower Great Lakes Saturday
with winds diminishing below advisory level through the morning
hours. Winds and waves will subside further Saturday night and
Sunday as the surface high builds into western Quebec and the Lower
Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for LEZ040.
         Small Craft Advisory until 11 AM EDT this morning for
         LOZ042>044.

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...RSH
MARINE...RSH


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