022
FXUS61 KBUF 241911
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
311 PM EDT Tue Sep 24 2024

.SYNOPSIS...
Low pressure will move across the Great Lakes tonight,
spreading another round of rain across the region. A trailing
front will move slowly across the area Wednesday through
Wednesday night and support some additional rainfall. A few
showers may linger Thursday, especially east of Lake Ontario.
High pressure will then build into the Great Lakes region,
bringing a return to mainly dry weather Friday through the
weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
A deep longwave trough will dig across the Great Lakes and Ohio
Valley through Wednesday. Large scale forcing for ascent will
increase ahead of this trough through tonight. This lift will
be supported by DPVA, topped by mid/upper level diffluent flow,
and deep moisture transported northward by a 40 knot southerly
low level jet. As a result steady showers will continue to spread
from west to east across Western NY through this evening.
Terrain influences will play an important role in coverage of
rain and also rainfall amounts. Persistent south/southeast
downslope flow will result in shadows of lower rainfall amounts
and diminished rain coverage to the north of terrain and on the
lake plains. For these areas rainfall totals will average a
tenth to a quarter inch, with the greatest rainfall amounts east
of Lake Ontario where around a half inch of rain is expected.

Southerly downslope winds will continue Wednesday, and the lake
plains may see a period of completely dry weather Wednesday
morning due to a mid level dry slot and the drying influence of
downslope flow. However, the frontal zone will remain draped
from the Ohio Valley to Central NY, and this along with diurnal
heating/instability will support an uptick in showers Wednesday
afternoon.

While there will not be much surface based instability during
this event, there will be elevated instability which could
support some thunderstorms embedded in heavier showers this
afternoon through Wednesday evening.

The surface low will track to our north and into southern Quebec
Wednesday night, with a trailing cold front moving across our
region. This will bring another round of showers to the area,
especially east of Lake Ontario which will be closer to the
upper level trough. This will bring another half inch or so of
rainfall to that region.

During this time temperatures will average above normal,
especially overnight lows. The lake plains will be the warmest
locations due to warming from the southerly flow downsloping.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
By Thursday morning, the eastern Great Lakes will be sandwiched
between two upper level closed lows: one centered over far
southwestern Quebec, and another across the lower Mississippi
Valley. As the northern trough translates eastward towards the
Canadian Maritimes through Friday night, a flattening ridge of high
pressure and mid-level dry air will crest over the southern trough
and become wedged across the forecast area. This will allow the west-
to-east drying trend to continue through the day Thursday. While the
North Country will likely still be contending with showers and
possibly a thunderstorm or two Thursday morning, much of WNY should
already be drying out.

Dry weather should then be found areawide from Thursday evening
through at least Friday. Thereafter, much of the sensible weather
forecast across our region will depend upon the evolution of the
upper low over the Mississippi Valley. As TS Helene and its remnants
tracks northward out of the Gulf of Mexico Thursday night, it is
expected to rise along the eastern flank of the low and closely
interact with the upper level system. The details on how exactly
these features will interact remains a bit uncertain, though TS
Helene`s northward momentum and how it rearranges the orientation of
the southern branch of the jet stream is expected to allow its
remnants to track northward towards the forecast area. At this
juncture, the area of high pressure over the region is expected to
block much of this tropical-based moisture, though additional
showers reaching WNY by Friday night cannot be ruled out.

Temperatures Thursday through Friday night are expected to remain
above normal, with highs mainly in the 70s Thursday and Friday, a
few 60s lingering on the hilltops. Lows Thursday and Friday nights
will range from the upper 70s across the Tug/Western Dacks to the
upper 60s closer to Lake Erie, with 50s elsewhere.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
The evolution of the upper low over the Mississippi Valley will be
the large scale feature to watch during this period. As alluded to
in the short term, this system will be interacting with TS Helene
and its remnants late in the week, the details of which remain
uncertain at this time. Ensemble systems show the ridge across
the Great Lakes region remaining in place which should keep the
forecast mostly dry, however there are some signals from the
ensemble systems that draw the upper low further north and/or
open the low into a trough across the forecast area. This could
result in increasing moisture and therefore there are low
chances of showers across the forecast area over the weekend and
through early next week.

Temperatures remain above normal through the period, with highs well
into the 70s across the lower terrain each day and upper 60s/low 70s
across the hilltops. Lows will mostly range in the 50s, though there
could be a few upper 40s across the hilltops and low 60s near the
lakeshores.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
An upper level trough will slowly dig across the Great Lakes
through Wednesday. A round of steady rain showers with a few
embedded thunderstorms will move from west to east across the
area through tonight. Rain will be moderate at times, reducing
vsby to MVFR. Cigs will vary, with southerly downslope flow
helping to keep the lake plains mainly VFR/MVFR despite the
rain. This includes KBUF/KIAG/KROC/KART. Mainly IFR cigs at
KJHW, with fog possible tonight.

Expect a break in the showers for most locations Wednesday
morning as a LLJ exits to the east. However, showers and a few
thunderstorms will expand in coverage Wednesday afternoon due to
diurnal heating, especially from the Genesee River valley
eastward.

Outlook...

Wednesday night...MVFR/IFR with showers likely. A few widely
scattered thunderstorms possible.

Thursday...MVFR east of Lake Ontario with a chance of showers.
Becoming mainly VFR elsewhere.

Friday through Sunday...Mainly VFR. Local IFR in valley fog
across the Southern Tier possible overnight into the morning.

&&

.MARINE...
A moderate pressure gradient will remain in place over the eastern
Great Lakes through Wednesday between persistent high pressure over
the Canadian Maritimes and low pressure moving through the central
Great Lakes. This will maintain moderate southeasterly flow through
Wednesday, with the strongest winds on the east half of Lake
Ontario tonight through the first half of Wednesday. The
southeast wind direction will continue to push the greater wave
action into Canadian waters, but the offshore winds will become
strong enough to require a Small Craft advisory for the eastern
ends of Lake Ontario and Lake Erie.

Winds will gradually become southwest and then west Wednesday night
through Thursday as a trough crosses the eastern Great Lakes from
west to east, with wind speeds decreasing with the passage of the
trough. Northeast flow will then pick up Friday, possibly
requiring small craft headlines on Lake Erie and western Lake
Ontario.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 7 PM this evening to 8 AM EDT
         Wednesday for LEZ040-041.
         Small Craft Advisory from 10 PM this evening to 2 AM
         EDT Thursday for LOZ045.

&&

$$

SYNOPSIS...Apffel/Hitchcock
NEAR TERM...Apffel/Hitchcock
SHORT TERM...PP
LONG TERM...HSK/PP
AVIATION...Apffel
MARINE...Apffel/Hitchcock