666
FXUS61 KBUF 260547
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
147 AM EDT Thu Sep 26 2024

.SYNOPSIS...
A weak low pressure system will slowly drag a cold front through the
area with scattered showers overnight into Thursday. Areas east of
Rochester may experience some left over showers through mid morning
Thursday, otherwise high pressure will build across the lower Great
Lakes to support fair dry weather through at least Friday. Most, if
not all of the significant rains from Helene should stay to our
south.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
A weak low pressure system will ever so slowly lift north through
Quebec while dragging a wavy cold front into Thursday. Deep
rich moisture streaming forward along and ahead of this boundary
(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 bring once
again, after a brief lull, another round of 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 Wednesday
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 /06Z THURSDAY THROUGH MONDAY/...
A slow moving cold front will bring another round of showers through
the region overnight, with a mix of VFR/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...
Winds will gradually become southwest and then west overnight
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...None.

&&

$$

SYNOPSIS...AR/RSH/TMA
NEAR TERM...AR/RSH/TMA
SHORT TERM...PP
LONG TERM...PP
AVIATION...AR/RSH/TMA
MARINE...AR/TMA