211
FXUS61 KBUF 251855
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
255 PM EDT Wed Sep 25 2024

.SYNOPSIS...
Weak low pressure tracking by to our west and north today will drag
a wavy cold front through the region tonight. While scattered
showers will be found ahead of this front today...heavier...more
widespread showers can be expected tonight. Areas east of Rochester
may experience some left over showers Thursday morning...otherwise
high pressure will build across the Lower Great Lakes to support
fair dry weather Thursday afternoon through at least Friday. Most...
if not all...of the significant rains from Helene should stay to
our south.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
It will be damp and unsettled tonight...as a storm system pushing
north from Georgian Bay will drag a wavy cold front through our
region. In advance of this sfc front...a slug of deep moisture (PWAT
1.5") will be lifted by a combination of a 110kt H25 jet rotating
around the base of a vigorous northern stream shortwave and
convergence in the lower levels. This will result in fairly
widespread showers...some of which could be locally heavy. Rainfall
amounts tonight are forecast to range from a quarter to a half inch
in most basins...with the lesser amounts expected to be over the
Finger Lakes region. Elevated CAPE of 200-400 j/kg will be found
within this environment...so will maintain the chance for
thunderstorms. While the showers will taper off from west to east
late tonight as the mid level moisture gets stripped away...a wealth
of cloud cover will persist.

The slow moving front will certainly take its time exiting the
Eastern Lake Ontario Thursday morning...so likely to cat pops will
remain in place for the initial daylight hours. Meanwhile...s l o w
clearing will start to take place back across the IAG Frontier. As
we push through the midday and afternoon...the residual showers will
come to an end with more pronounced clearing taking place further
west due to more effective diurnal mixing and strengthening
subsidence from sfc based ridging.

High pressure centered to the north of Lake Ontario Thursday night
will then guarantee fair dry weather...although some cloudiness may
still linger near the Pennsylvania border. It will be notably
cooler...with mins forecast to be in the low to mid 50s...rather
than the 60s from the previous two nights.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
Friday through Saturday, the eastern Great Lakes will be sandwiched
between two areas of low pressure aloft: one closed moving east
across the Canadian Maritimes, and another meandering over the
Mississippi Valley. It is the latter that will need to be watched
for the potential for showers moving towards the end of the week. As
Helene`s remnants move northward across the Southeast states, a
Fujiwhara interaction will cause the tropical low to turn northwest
before becoming absorbed by the pre-existing closed low. Further
north, a flattening ridge of high pressure and mid-level dry air
will squeeze across our forecast area between this complex low to
the southwest and the departing trough to the northeast. The center
of the southern mid-level circulation is then expected to slowly
wobble northward towards the Ohio Valley, partially open into a
longwave trough, and progress eastward towards the Mid-Atlantic
states by Sunday night.

While the thin ridge of high pressure is expected to keep our region
entirely dry through at least Friday, there remains uncertainty in
the potential for showers Friday night and beyond. As the complex
low over the Mississippi Valley circulates a band of deeper moisture
northward towards the lower Great Lakes, it will run up against the
overhead area of high pressure, stall out, and become increasingly
removed from the stronger upper jet energy on the eastern periphery
of the low. The majority of the precipitation expected to approach
from the south with this system is therefore expected to fizzle out
as it nears the NY/PA border and moves across Lake Erie, though
there are enough signals from the latest guidance that suggest some
of this activity will survive the journey over the southern CWA
border. Low confidence in timing and overall coverage of showers at
this range so PoPs remain on the low side, though best chances for
precip look to be in the Southern Tier late Friday night and
Saturday afternoon, though can`t completely rule out the occasional
shower south of I-90 through Saturday night, while Sunday and Sunday
night look to be comparatively drier.

Outside of the chances for rain...Temperatures Friday and through
the weekend will continue to run on the warm side, with highs in the
low to mid 70s in most spots, a few readings in the 60s on the
hilltops. Lows will generally range from the low 60s close to the
Lake Erie shoreline to the upper 40s across the hilltops east of
Lake Ontario, with a range of 50s in between.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
The longwave pattern will continue to be dynamic through mid-week,
with more unsettled weather re-emerging. By Monday, the remnants
of Helene will be circulating within the partially open, positively
tilted wave over the Ohio Valley and Mid- Atlantic states. This
could lead to a few showers across the far Southern Tier Monday,
though high pressure ridging to the north should keep conditions
mostly dry. Meanwhile, a robust secondary mid-level trough will
be racing east across the Northern Plains and into the Upper
Midwest. As it does so, the two troughs will phase and deepen
over the Great Lakes. This will drive a strong cold front
through the forecast area sometime late Tuesday into Wednesday,
with the remnant moisture from Helene providing ample fuel for
widespread showers. Significant timing differences among the
models preclude higher PoPs this update but could see this
changing once the details come into better focus. Have stuck
close to NBM for now, with gradually increasing chances for
showers from west to east Monday night through Tuesday, then
tapering down some for Wednesday.

While temperatures are expected to continue to average above normal
Monday and Tuesday, much cooler air in the wake of the front will
finally give us a taste of true fall weather by Wednesday. Models
are far from lock and step with the depth of the cooler airmass,
though ensemble mean 850H temps are around +6C by Wednedsay which
should translate to highs in the 50s to low 60s. This will also
be plenty cold enough to potentially spur some additional lake
effect rain showers Wednesday, though the airmass may be
initially too dry for this to be realized.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
A slow moving cold front will produce fairly widespread showers
throughout the region tonight...with most areas experiencing MVFR to
IFR cigs...the latter of which will be focused across the Srn Tier.

While showers will persist east of Rochester Thursday morning...fair
dry weather will return to the region. Cigs will improve to VFR
levels by late morning/midday...then most areas will lose their cigs
altogether by the end of the day.

Outlook...

Thursday night...Mainly VFR.
Friday...Mainly VFR...but with a chance of showers across the
western Southern Tier.
Saturday through Monday...VFR.

&&

.MARINE...
A moderate pressure gradient will remain in place over the eastern
Great Lakes today through tonight between persistent high
pressure over the Canadian Maritimes and low pressure moving
through the central Great Lakes. This will maintain moderate
southeasterly flow today, with the strongest winds on the east
half of Lake Ontario today. 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 tonight 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 2 AM EDT Thursday for LOZ045.

&&

$$

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