547
FXUS61 KBUF 241037
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
637 AM EDT Tue Sep 24 2024

.SYNOPSIS...
Low pressure will cross the Great Lakes this afternoon through
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, especially in
southern and eastern portions of the area. A few showers may linger
Thursday, especially east of Lake Ontario. High pressure will then
build into the Great Lakes region, supporting a return to mainly dry
weather Friday through next weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Radar imagery showing a few scattered showers across the Genesee
Valley and western Finger Lakes early this morning, including the
Rochester area. These showers are being driven by weak convergence
along an old frontal zone, and will likely persist through mid
morning before drifting north out over Lake Ontario.

A deep and complex longwave trough will carve out over the Great
Lakes and Ohio Valley today through Wednesday as northern and
southern stream shortwaves partially phase. The southern stream
shortwave will move northeast across the Ohio Valley and Central
Great Lakes this afternoon through tonight before reaching southern
Quebec by late Wednesday. A weak surface low will track from near
the southern tip of Lake Michigan today to Georgian Bay Wednesday
morning. Large scale forcing for ascent will increase ahead of the
trough later today through tonight as DPVA spreads into the eastern
Great Lakes, topped by mid/upper level diffluent flow ahead of the
digging trough. Deep moisture will be transported northward by a 40+
knot southerly low level jet.

The quality of moisture and forcing will support fairly widespread
showers moving into Western NY by early to mid afternoon, then
spreading to the Genesee Valley and western Finger Lakes late
afternoon and this evening, before reaching the eastern Lake Ontario
region overnight. 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. The highest rainfall totals will
track from southern Ontario over and north of Lake Ontario to the
Saint Lawrence Valley late today through early Wednesday, away from
the diminishing influence of downsloping.

Late tonight through Wednesday morning the best forcing and deepest
moisture will continue to move northeast into southern Quebec, with
rain tapering off across Western NY overnight, and by mid to late
morning east of Lake Ontario. Southerly downslope winds will
continue, so the lake plains may see a period of completely dry
weather supported by the mid level dry slot and drying influence of
downslope flow. The frontal zone will remain draped from the Ohio
Valley to Central NY, and model guidance continues to suggest a
baroclinic wave will ripple along the boundary starting Wednesday
afternoon. Differential temperature advection across the depth of
the boundary in response to the wave of low pressure will likely
allow for showers to expand in coverage again from south to north
Wednesday afternoon.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
An anomalously strong ridge will be across the Plains while a trough
resides across the Northeast Wednesday night. The trough will move
east while the ridge into the Great Lakes region through Friday.
During this time, a closed upper level low will remain centered near
the Ozarks while Potential Tropical Storm Nine moves into the
southeast U.S.

A mid-level trough axis and cold front near Michigan Wednesday
evening will move east across the forecast area overnight. A 35 kt
low level jet will be across western and north central NY with the
nose of the jet near north central/central NY. Theta-e advection
within a moist environment will result in medium to high chances for
showers and a few thunderstorms especially east of the Genesee
Valley. Rainfall amounts will average 0.1-0.30 inches east of the
Finger Lakes region and less than 0.1 inches west of the Finger
Lakes region. Mild overnight with lows in the upper 50s to low 60s.

Dry air filters into the region Thursday as the mid-level trough
axis moves east of the forecast area. The strong ridge will move
into the Great Lakes region while the potential tropical storm moves
into the southeast U.S. through Thursday night. A strong
southeasterly jet will transport moisture into the Mid-Atlantic
region and central Appalachians, however the strong ridge will
suppress moisture south of the forecast area. By Friday, the
remnants of any tropical storm will move northward while high
pressure extends into the forecast area from Quebec. Dry weather
will continue across the forecast area.

Temperatures will be slightly above normal with highs in the low to
mid 70s Thursday and Friday and lows in the 50s Thursday night.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
The evolution of the upper low over the Mississippi Valley will be
the large scale feature to watch during this period. Ensemble
systems show a ridge across the Great Lakes region 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 through the weekend and into Monday.

Temperatures remain above normal through the period.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Scattered showers will continue this morning across the Genesee
Valley and western Finger Lakes. CIGS have improved a mix of VFR and
MVFR across the lower elevations of Western NY thanks to increasing
southeast downslope flow. IFR remains solidly entrenched across the
higher terrain of the Southern Tier, with VFR east of Lake Ontario.
Expect this same pattern of CIGS to hold through midday or early
afternoon.

Surface low pressure and a strong upper level system will move from
near Lake Michigan this morning northeast across the central and
eastern Great Lakes later today through tonight. A broad area of
ascent ahead of this system will bring another round of widespread
rain showers, entering Western NY midday to mid afternoon, then
spreading east across the rest of the area later this afternoon
through tonight. Pockets of moderate rain may bring a few periods of
lower VSBY.

Expect widespread MVFR/IFR CIGS across Western NY this afternoon,
spreading east across the remainder of the area tonight. IFR will be
favored across higher elevations. S/SE downslope flow will try to
hold the CIGS higher across the lake plains including most of the
terminals. MVFR CIGS are still likely, but the downslope flow may
help to keep IFR at bay this afternoon through tonight.

Outlook...

Wednesday...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 Saturday...Mainly VFR. Local IFR in valley fog
across the Southern Tier each overnight and 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 today
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 end 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.

&&

.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...Hitchcock
NEAR TERM...Hitchcock
SHORT TERM...HSK
LONG TERM...HSK
AVIATION...Hitchcock
MARINE...Hitchcock