Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 200549
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
149 AM EDT Sun Aug 20 2017

.SYNOPSIS...
High pressure will build across the eastern Great Lakes overnight
and Sunday, moving east of the area on Monday. This will bring
gradually warming temperatures through Monday. A strong cold front
will cross the region Tuesday, with widespread showers and
thunderstorms. This will be followed by much cooler and less humid
conditions for the end of next week.

&&

.NEAR TERM /THROUGH TODAY/...
Increasing subsidence and drying will bring clearing skies from the
west in wake of the trough. Expect fog to develop in river valleys
across the Southern Tier as skies clear. Lows will range from the
lower 60s on the lake plains to the mid 50s across the interior
Southern Tier and Lewis County.

On Sunday, high pressure will ridge into the region with dry weather
and partly to mostly sunny skies. In the morning there may be some
lingering lake induced cloud cover, then in the afternoon diurnal
cumulus should develop inland of the lake breeze. In each case,
cloud coverage should be partial at most. Otherwise,
temperatures will be a bit warmer with highs ranging from the
mid 70s to lower 80s.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
Sunday night and Monday will be characterized by generally fair
weather as upper level ridging transits the region. Speaking of
transits, the ridging should provide for good viewing conditions for
the upcoming solar eclipse - while we may see some diurnal fair-
weather cu developing inland of the lakes during the afternoon,
skies will remain mostly clear during the early afternoon hours on
Monday. Skies will be clearest northeast of the lakes, where the
prevailing southwesterly flow should generate a lake shadow.

The aforementioned southwesterly flow will be the product of broad
return flow around a prominent western extension of the Bermuda High
that will be solidly in place across the southeastern U.S.. While
temperatures Sunday night will be seasonable, with clear skies and
light winds allowing for radiational cooling that will in turn cause
temperatures to drop into the upper 50s in the coolest Southern
Tier/North Country spots, with low to mid 60s elsewhere, readings
will climb into the mid 80s on Monday as the return flow advects
increasingly warm and moist air into the region, with 850mb temps
climbing to +18C by Monday afternoon. The southwesterly flow and
associated downsloping will tack on an additional couple of degrees
across the Genesee valley and the Lake Ontario plain, where highs
will reach the upper 80s.

The warm temperatures will be accompanied by increasing mugginess as
well, as GOMEX moisture is drawn across the Mississippi and Ohio
valleys and into the Great Lakes. Dewpoints will surge into the mid
to upper 60s Monday night, resulting in lows that will fail to dip
below 70 across much of the Lake Erie and Lake Ontario plains, while
the rest of the forecast area will only dip into the mid 60s, making
for a sticky night.

The hot and muggy weather will persist into Tuesday. The warm and
moist airmass will become increasingly unstable on Tuesday, with the
approach of a deep upper level trough tracking across the Great
Lakes. This will likely drive showers and thunderstorms that will
develop across the forecast area Tuesday afternoon ahead of a strong
cold front that will be crossing the region Tuesday night. An
anomalously strong 40+ LLJ ahead of the trough will advect
additional moisture and significantly increase low-level shear as
well, and latest 12Z runs are a little faster with the timing of the
trough driving the convection, with lift arriving during peak
diurnal heating Tuesday afternoon. Given the very warm and moist
airmass preceding the system, and the strength of the synoptic
system and associated vertical shear, severe weather is looking
increasingly likely Tuesday afternoon into Tuesday evening, as noted
in the SPC Day 4 Outlook. After another day in the mid to upper 80s,
readings will fall off into the low to mid 60s in the wake of the
cold frontal passage.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A much cooler airmass will flow over the region this period, behind
a strong cold front from Tuesday.

Initially Wednesday a few lake effect rain showers will be possible
east of the lakes as cool 850 hPa temperatures of +7 to +8C flow
over the lakes. As the upper level trough passes Wednesday
additional scattered showers will be possible across the region. In
addition winds will be brisk Wednesday especially over the lakes and
along the shoreline where WNW winds upwards to 25 knots and
increasing wave heights will be likely.

Thursday we will still have anticyclonic flow aloft, and with the
core of the cold air passing over the lakes, additional lake effect
showers and clouds will be possible...though with a thinner moisture
layer...expect the lake response to be more clouds than showers.

Both Wednesday and Thursday will be cool with highs in the upper 60s
to lower 70s.

Sprawling high pressure will then reach our region for Friday and
Saturday with abundant sunshine and temperatures around 70
Friday increasing to the lower 70s for Saturday.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Clearing skies overnight will lead to the development of valley fog
late tonight across the western Southern Tier with local IFR.

Any valley fog will quickly dissipate Sunday morning, with
mostly clear skies and VFR conditions during the day Sunday.

Outlook...

Sunday night and Monday...VFR except for late night and early
morning valley fog with local IFR.
Tuesday...Mainly VFR, with a chance of showers and
thunderstorms in the afternoon.
Tuesday Night...MVFR/IFR, with showers and thunderstorms
likely.
Wednesday and Thursday...VFR/MVFR with a chance of showers.

&&

.MARINE...
A moderate west-southwest flow will continue up to midnight
with choppy to small craft conditions on both lake Erie and
Ontario. Winds will then diminish from west to east overnight with
conditions on the lakes improving.

High pressure will bring a return to lighter winds Sunday and
Monday. Then a strong cold front will result in increasing winds
Tuesday which may require another round of small craft headlines
before and after the cold frontal passage. There also may be
strong thunderstorms along and ahead of the front.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 5 AM EDT early this morning for
         LOZ044-045.

&&

$$

SYNOPSIS...APFFEL/TMA
NEAR TERM...CHURCH/TMA
SHORT TERM...CHURCH
LONG TERM...THOMAS
AVIATION...CHURCH
MARINE...CHURCH/TMA



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