721
FXUS61 KBUF 250543
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
143 AM EDT Wed Sep 25 2024

.SYNOPSIS...
Low pressure will move west of the eastern Great Lakes region
overnight, 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 TODAY/...
Regional radar shows showers and a few thunderstorms across Lake
Ontario and north central NY late tonight. Drier air is moving
into the forecast area as evident on water vapor imagery.
Showers will mainly be confined to the northern tier of the
forecast area overnight, however a few showers may develop
across the western Southern Tier in vicinity of a warm front.

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. 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 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 /TONIGHT 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 /06Z WEDNESDAY THROUGH SUNDAY/...
Low pressure will move northwest of the region overnight into
Wednesday. Showers and a few thunderstorms will move across
Lake Ontario and north central NY overnight. Drier air will
enter western NY decreasing the chance for showers through mid-
morning. A warm front is in vicinity of northwest Pennsylvania
which may result in a few showers developing near the western
Southern Tier into Wednesday morning.

A southeast flow has resulted in mainly VFR conditions across
the lower elevations with the exception of any showers or
thunderstorms. Low clouds/fog will hang onto the hill tops
across the region and result in sub-VFR, mainly IFR conditions
at KJHW/KOLE into Wednesday morning. Flight conditions do not
change much Wednesday with MVFR/low end VFR across most of the
TAF sites and IFR at KJHW. Showers and a few thunderstorms will
likely develop Wednesday afternoon. These may result in brief
periods of IFR at the TAF sites. A cold front will move across
the region Wednesday evening. Heavier showers and a few
thunderstorms will move through the region. MVFR/IFR conditions
will linger into Thursday morning.

Outlook...

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 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 until 8 AM EDT this morning for LEZ040-
         041.
         Small Craft Advisory until 2 AM EDT Thursday for
         LOZ045.

&&

$$

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