Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 230800
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
400 AM EDT Wed Aug 23 2017

.SYNOPSIS...
In the wake of a strong cold front...much cooler and drier air will
build across the region for the rest of the week. A few spotty light
showers will remain possible at times through Friday morning...before
high pressure then brings dry weather from Friday afternoon right on
through the upcoming weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Area satellite imagery shows largely clear skies across the bulk of
the area early this morning...save for some very patchy cloud cover
across portions of the North Country and Southern Tier. The mainly
clear skies have allowed dewpoint depressions to greatly narrow across
interior portions of the Southern Tier...which in turn is leading to
the beginnings of some patchy valley fog as per GOES16 nighttime
microphysics composite imagery. This should continue to develop through
about sunrise this morning...before renewed daytime heating and mixing
leads to its eventual dissipation in the 8-9 am time frame.

Otherwise...our region will lie firmly within the grip of a deepening
upper level trough and its attendant pool of much cooler and drier air
right through this period. After a mostly sunny and dry start to this
morning...daytime heating of our much cooler airmass will lead to the
development of a broken cumulus/stratocumulus field during the late
morning and afternoon hours. By mid to late afternoon...some spotty
light showers will also become possible as a vorticity lobe and its
attendant weak secondary cold front push into our region...though both
the probability/coverage of these will remain rather limited in extent
thanks to both a lack of deep moisture and a cap around 10 kft. The
much bigger story of the day will be the return to much cooler and
more comfortable weather courtesy of the upper level trough...with
afternoon highs mostly ranging in the lower to mid 70s...and surface
dewpoints continuing to recede into the lower half of the 50s.

As we move into tonight...any diurnally-driven scattered light showers
from this afternoon will tend to die out with the loss of heating this
evening. This should leave behind partly cloudy and mainly dry weather
until very late tonight or early Thursday morning...when our slowly
cooling airmass and a subtle increase in background moisture may lead
to the development of some clouds and scattered light lake effect
showers along and a little inland from the south shore of Lake Ontario.
Otherwise we can expect a cool and comfortable late summer night with
overnight lows ranging from the upper 40s across interior portions of
the Southern Tier and North Country to the lower and mid 50s elsewhere.
As is usually the case at this time of year...such temps will likely
lead to the redevelopment of some patchy valley fog across the Southern
Tier overnight.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A much cooler, almost fall-like airmass will dominate the late week
period as a longwave trough becomes established from the Great Lakes
into New England. Much of the time will be rain free Thursday
through Friday morning, although a few weak synoptic systems and
lake effect potential may produce a few scattered showers.

On Thursday a weak low level trough will move slowly south across
Lake Ontario, ending up over Western and Central NY during the
afternoon. Colder air aloft will allow conditions to become a little
more favorable for some lake enhancement Thursday morning as the
trough crosses Lake Ontario, aiding in a few scattered showers along
the south shore of the lake. During the afternoon, expect most of
the scattered showers to favor inland areas away from the lakes as
the weak east/west oriented trough axis drifts south and away from
the lake. Expect a good deal of cloud cover as cold air aloft
supports lake effect, upslope, and diurnal cloudiness.

Thursday night the axis of the longwave trough crosses the Lower
Great Lakes, accompanied by a mid level shortwave and vorticity
maxima. Lake induced instability will peak during this period as the
pool of coldest 700mb air crosses the region, with lake induced
equilibrium levels rising to around 30K feet. The combination of
weak synoptic scale forcing and plenty of lake induced instability
will support a few lake effect rain showers southeast of the lakes
Thursday night. Even with the strong instability, the relatively dry
background synoptic environment and short northwest fetch will limit
the coverage and intensity of lake effect rain showers.

The lake effect rain showers southeast of Lake Erie should be done
by Friday morning as the trough axis shifts east and takes the
deeper moisture with it. A few showers may linger southeast of Lake
Ontario during the morning, but these should end as well by midday.
Extensive diurnal cumulus and leftover lake effect clouds will
initially build during the morning and midday, but a push of drier
air expanding southward out of Ontario should bring increasing
amounts of sunshine later in the day. Expect mainly clear skies
Friday night as surface high pressure builds into the eastern Great
Lakes.

As far as temperatures go, highs on Thursday and Friday will likely
not reach 70, with upper 60s on the lake plains and low to mid 60s
across higher terrain. Lows Thursday night will range from the mid
50s near the lakes to the upper 40s across the interior Southern
Tier and Lewis County. Friday night will be cooler with less cloud
cover and lighter winds. Expect lower 50s near the lakes and mid 40s
across the interior Southern Tier and Lewis County.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
An extended period of dry weather will set up from this weekend into
early next week as high pressure remains parked over the Great Lakes
and New England. The upper level longwave trough will linger over
New England through the weekend before yielding to a building ridge
early next week. The slow retreat of the mid/upper level trough,
combined with airmass modification will allow temperatures to warm a
few degrees each day. This will bring highs back into the lower 70s
at lower elevations Saturday, and mid 70s by early next week. Nights
will still be cool with a dry airmass in place.

Dry weather should last through at least Tuesday, before increasing
moisture brings the next chance of showers by next Wednesday.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Area satellite imagery shows largely clear skies across the bulk of
the area early this morning...save for some very patchy cloud cover
across portions of the North Country and Southern Tier. The mainly
clear skies have allowed dewpoint depressions to greatly narrow across
interior portions of the Southern Tier...which in turn is leading to
the beginnings of some patchy valley fog. This should continue to develop
through about sunrise this morning and lead to areas of IFR/MVFR within
the Southern Tier valleys...before renewed daytime heating and mixing
leads to its eventual dissipation in the 12-13Z time frame.

Otherwise VFR conditions will continue to prevail through today...
albeit with an increase in cumulus/stratocu with diurnal heating of our
much cooler airmass. During the afternoon...some spotty light showers
will become possible as a disturbance aloft and associated weak secondary
cold front push into our region...however these are unlikely to have any
impact on aviation operations.

Any scattered light showers from this afternoon will then tend to die
out with the loss of heating this evening...leaving behind mainly dry
weather until some scattered light lake effect showers potentially
develop late along and a little inland from the south shore of Lake
Ontario. While flight conditions will remain predominantly VFR...some
spotty MVFR will become possible late along and a little inland from
the lakeshores...with some IFR/MVFR in valley fog also becoming possible
across the Southern Tier overnight.

Outlook...
Thursday...VFR/MVFR with a chance of showers.
Friday...A chance of morning showers southeast of the lakes...otherwise
VFR.
Saturday and Sunday...VFR.

&&

.MARINE...
In the wake of a strong cold front...a brisk westerly flow of cooler
air will persist across the Lower Great Lakes today...necessitating
continued Small Craft Advisories as outlined below. Winds and waves
will then diminish tonight and Thursday as the responsible low
pressure system pulls further away from our region...with high
pressure then building into our region and providing relatively
tranquil conditions for Friday and the upcoming weekend.

&&

.TIDES/COASTAL FLOODING...
A brisk westerly flow of cooler air will persist across Lake Ontario
today...before diminishing tonight. Coupled with already high lake
levels...the increased winds and wave action will continue to bring
increased shoreline erosion and lakeshore flooding to the east half
of Lake Ontario through today and into this evening. The static lake
levels have dropped since late spring/early summer, so the impacts of
this event are not likely to be as significant as earlier in the season,
but should still be enough to warrant a continued Lakeshore Flood
Warning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning until 11 PM EDT this evening for
     NYZ004>007.
     Beach Hazards Statement through this evening for NYZ004>007.
     Beach Hazards Statement through this evening for NYZ002-003.
     Beach Hazards Statement from 11 AM EDT this morning through
     this evening for NYZ019-085.
MARINE...Small Craft Advisory from 11 AM this morning to 8 PM EDT this
         evening for LEZ040-041.
         Small Craft Advisory until 5 AM EDT Thursday for
         LOZ043-044.
         Small Craft Advisory until 11 PM EDT this evening for
         LOZ042.
         Small Craft Advisory until 2 AM EDT Thursday for LOZ045.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...HITCHCOCK
LONG TERM...HITCHCOCK
AVIATION...JJR
MARINE...JJR
TIDES/COASTAL FLOODING...HITCHCOCK/JJR



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