Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231511
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1111 AM EDT Wed Aug 23 2017

.SYNOPSIS...
An large upper level trough over the Great Lakes will make for cool
and mainly dry weather across the region through 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/...
A deepening upper level low and its attendant pool of much cooler
and drier air is centered over central Quebec near midday. Satellite
imagery is showing mostly sunny skies near 11am with some
diurnal cumulus blossoming across the western Southern Tier and
eastern Lake Ontario regions. By mid to late afternoon...some
spotty light showers will also become possible as a vorticity
lobe and its attendant weak surface trough push southeast into
western New York. Both the probability/coverage of these showers
will remain rather limited in extent thanks to both a lack of
deep moisture and a cap around 10 kft. The more noticeable
feature of today will be the return to much cooler and more
comfortable weather courtesy of the upper level trough.
Afternoon highs will mostly ranging in the lower to mid 70s or
about 5 degrees below normal with 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 /15Z WEDNESDAY THROUGH SUNDAY/...
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
surface trough push southeast 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...
A brisk westerly flow of cooler air is in place today necessitating
continued Small Craft Advisories on both lakes. Winds and waves will
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.

All the above stated...there will also be the chance for a few
waterspouts over the next few days as a cool airmass crosses the
warmer lake waters.

&&

.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 until 11 PM EDT this evening for
     NYZ004>007.
     Beach Hazards Statement until 8 PM EDT this evening for NYZ002-
     003-019-085.
MARINE...Small Craft Advisory until 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/SMITH
NEAR TERM...JJR/SMITH
SHORT TERM...HITCHCOCK
LONG TERM...HITCHCOCK
AVIATION...JJR/SMITH
MARINE...JJR/SMITH
TIDES/COASTAL FLOODING...HITCHCOCK/JJR



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