118
FXUS61 KBUF 171824
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
224 PM EDT Sat Aug 17 2024

.SYNOPSIS...
A large storm system over the Upper Great Lakes will slowly drift
eastward across our forecast area through Monday. This will result
in unsettled conditions with occasional showers and a chance of
thunderstorms...although there will also be periods of dry weather.
Some of the showers could be locally heavy...with a stronger storm
or two not also out of the question. Following the passage of this
system...Canadian high pressure will build across our region and
provide us a prolonged period of fair weather and cooler weather
that will last for most of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Broad and vertically stacked low pressure will slowly drift
east across Lower Michigan today and across southern Ontario
province tonight. The cyclonic flow aloft associated with this
trough and embedded disturbances will bring an unsettled pattern
which will last through the period.

This afternoon, a warm front exited to the east of the area,
and a brief period of subsidence behind this allowed for some
sunshine which increased instability. LAPS shows SB CAPE 1000 to
2000 J/Kg across Western New York, which will support
increasing areal coverage of storms this afternoon into early
evening. Limited agreement among mesoscale guidance that the
steadiest storms will develop along a weak boundary across far
Western NY this afternoon and then will gradually move eastward
across the Genesee Valley before weakening late this evening.
However, scattered showers and thunderstorms cannot be ruled out
anywhere during this time.

Wind profiles are modest from a severe weather perspective,
with only about 25 to 30 knots at 850mb and 700 mb winds not
much stronger. As a result there`s limited wind shear, but a few
strong to severe pulse storm cannot be ruled out, especially
considering the large scale lift provided by the shortwave. PWAT
values of 1.75 to 2 inches across Western NY also support
locally heavy rainfall, with a risk for flash flooding from
training or slow moving storms. This will have to be monitored,
especially through this evening.

After this, showers and storms will taper off some late tonight
as instability wanes, but at least a chance will persist during
the entire overnight period. Lows will range from the mid 60s to
around 70, with a risk of fog across higher terrain in the
Southern Tier late in the night.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
Unsettled weather will continue into the start of the work week,
with a cold front crossing the region from west to east early
Monday. We will hang onto showers and a few thunderstorms through
the day with still deep moisture, anabatic frontal precipitation,
and convergence along a 25 knot northerly LLJ ahead of the axis of
the mid level trough.

These showers will end through the evening hours towards the east,
with some clearing towards the west.

This northerly flow and steepening low level lapse rates will
encourage cloud reformation Tuesday, with partly to mostly cloudy
skies over the region...until a much drier airmass from the north
diminishes the strato-cu later through the day.

Clearing skies, light winds and mid single digit 850 hPa
temperatures will quickly drop temperatures in the evening...with
overnight lows Tuesday night dropping into the low to mid 40s inland
to mid 50s along the lake shorelines.

Highs Monday and Tuesday will largely remain in the 60s under cloud
cover and within an 850 hPa airmass that will be in the mid single
digits Celsius.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Sprawling surface high pressure will cross the region early this
period, with cool low humid conditions Wednesday through Thursday
morning giving way to day-to-day warming behind the surface high
through Saturday.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Approaching mid level trough and diurnal instability will
support increasing coverage of showers and thunderstorms this
afternoon into this evening. Greatest coverage will push into
far Western NY through 20Z then spread east to the Genesee River
and KROC late afternoon and evening before weakening.
Thunderstorms driven by subtle features, making exact timing
challenging so handled with tempo groups for most TAF sites.
Mainly VFR flight conditions outside of brief MVFR or lower due
to vsby in heavier rain.

Showers and thunderstorms taper off some after midnight, but
there still will remain a risk throughout the overnight hours.
Increasing low moisture with the approach of the trough will
result in expanding MVFR cigs with most sites MVFR by Sunday
morning. Chances for showers and thunderstorms will again
increase Sunday afternoon, but low confidence in exact timing
and location.


Outlook...

Sunday night...VFR/MVFR lowering to mainly IFR following the
wind shift. Showers and scattered thunderstorms with lowering
cigs with the northwesterly wind shift.

Monday...MVFR/IFR ceilings with showers likely and a
chance of thunderstorms.

Tuesday...Improvement to VFR.

Wednesday and Thursday...VFR.

&&

.MARINE...
Over the weekend expect a general southerly to southwesterly
flow on Lake Erie and a southerly to southeasterly flow on Lake
Ontario... with winds generally remaining at or below 15 knots.

The above said...there will be a period of slightly stronger
(15-20 knot) SSE flow on eastern Lake Ontario later tonight and
early Sunday. Fortunately...the offshore component of the flow
will direct the bulk of the greater wave action across Canadian
waters and should preclude the need for any Small Craft
Advisories during these time periods.

Of greater concern to marine interests this weekend will be the
potential for scattered thunderstorms...with locally higher winds
and waves possible in and near any such storms.

Following the passage of a cold front...northerly flow will develop
later Sunday night...then will strengthen across the Lower Great
Lakes Monday. This will at least bring some choppy conditions to
Lake Erie...with somewhat stronger winds across Lake Ontario
potentially leading to some advisory-level conditions along the
south shore of that lake Sunday night through Monday night.

Conditions should then gradually improve on Tuesday as Canadian
high pressure begins building into the region...with a
slackening pressure gradient allowing for winds and waves to
subside.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...JJR
NEAR TERM...Apffel/JJR
SHORT TERM...Thomas
LONG TERM...Thomas
AVIATION...Apffel/JJR
MARINE...Apffel/JJR