-- Discussion containing changed information from previous version are highlighted. --
914
FXUS61 KBUF 210450
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1250 AM EDT Sat Sep 21 2024

.SYNOPSIS...
Little by little...our prolonged stretch of outstanding weather will
come to an end. A vigorous mid level disturbance will dive across
the region on Saturday to generate some showers and thunderstorms
over the western counties...then after a fine day on Sunday...a wavy
frontal boundary will set up over our area to support scattered
showers and potentially some thunderstorms through much of the
upcoming week. The change to unsettled weather will be accompanied
by cooler...more seasonable conditions.

&&

.NEAR TERM /THROUGH TODAY/...
High pressure extending from the Canadian maritimes to the
Lower Great Lakes will maintain rain-free weather through late
tonight. Satellite imagery shows high clouds gradually spreading
from west to east across the region late this evening. The
increased cloud cover will portend more unsettled weather for
the start of the weekend...at least across the western counties.
Otherwise it will be mild tonight with the mercury only
dropping off into the mid 50s (Srn Tier/Lewis county) to lower
60s (most elsewhere).

A vigorous shortwave...seen in WV imagery crossing the upper-most
portion of the Mississippi valley this afternoon...will make its way
across the Upper Great Lakes tonight before diving southeastward
across our western counties on Saturday. Fairly strong low level
convergence with the passing of this feature will be accompanied by
some added lift from a 100kt jet to our west...and this will result
in showers and possible thunderstorms over the western counties...
mainly during the afternoon. A tenth to a quarter inch of rain is
forecast for this area...while increased cloud cover but mainly dry
conditions will be found east of Lake Ontario. It will remain warm
though...as max temps will range from 75 to 80.

The aforementioned shortwave will exit across Pennsylvania Saturday
night...stripping away the mid level moisture and taking the
associated shower activity with it in the process. Meanwhile...mid
level ridging will quickly build in from the Upper Great Lakes. This
will aid in at least partially clearing the skies with the most
stubborn cloud cover expected to be over the Finger Lakes region.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
After the mid-level shortwave trough passage on Saturday, a brief
ridge will slide across the lower Great Lakes Sunday. At the surface
this will support surface high pressure over the Canadian maritimes
to extend southwestward across the Northeast and into the lower
Great Lakes. This will support one last day of dry weather across
western and northcentral New York Sunday.

The mid-level pattern will then shift Monday initiating a period of
active weather. This being said, surface low pressure will lift
northeast across the central Great Lakes, dragging a cold front
across the area Monday and Monday night. Starting late Sunday night,
the first of the showers will move into far Western New York. Then
as the cold front sweeps across the area, showers and thunderstorms
will gradually move from west to east across the area.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Unsettled weather continues through the much of the work week
as the longwave pattern across North America becomes
increasingly amplified. By Tuesday, a strong ridge will be
building across the much of the western CONUS as northern and
southern stream upper level troughs move downstream across the
Canadian Prairies and central Plains. While these will initially
be partially phased, as a strong 250mb jet streak on the
eastern periphery of the ridge digs south into the central
Plains, it will likely cause the southern stream trough to
deepen.

Uncertainty in the sensible weather forecast is high especially
beyond Tuesday given the very chaotic nature of the longwave
pattern. A number of vastly different scenarios is being advertised
by deterministic guidance over the past couple of model
runs...Including the southern stream trough completely closing off
and stalling out over the Mississippi Valley which keeps us in a
warmer pattern (20/00z CMCNH, 20/00z and 12z GFS), the northern
stream trough becoming dominant and closing off over the Great Lakes
putting us in a much cooler pattern (19/12z and 20/00z ECMWF), and a
variety of solutions in between. Will need to keep an eye on trends
as we move closer to next week.

At this juncture, confidence is highest in widespread showers and
possibly a few elevated thunderstorms between Tuesday evening and
Tuesday night as low pressure under the troughing to the west lifts
a warm front into the eastern Great Lakes. Thereafter, have greatly
undercut NBM`s PoPs Wednesday through Wednesday night with generally
decreasing chances for showers into Friday. While this somewhat
reflects the uncertainties stated above, it also takes into the
account the possibility of mid-level dry air and upper level ridging
moving back into the region later in the week, which is being
depicted in some capacity among much of the otherwise poorly aligned
guidance solutions.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
A mid level shortwave will cross the eastern Great Lakes today,
bringing with it a period of cloudiness with VFR bases and scattered
showers. The scattered showers will start to enter Western NY by mid
to late morning, then reach as far eastward as the Finger Lakes
later this afternoon before tapering off and ending tonight.
Overall, coverage of the rain showers will stay scattered to widely
scattered, with the best chance of a more organized cluster of
showers across the Genesee Valley and Southern Tier for a few hours
late afternoon/early evening. There may be a few isolated
thunderstorms as well in this area later this afternoon. Given the
expected scattered nature of showers, and even more sparse coverage
of thunder, used VCSH in the TAFs for now.

Tonight, any remaining showers will taper off and end, and skies
will partially clear. The light winds and clearing skies will allow
areas of fog and local IFR to develop, especially across the
Southern Tier and Finger Lakes valleys and in any locations that
receive rainfall today. KJHW is the most likely terminal to
experience fog overnight through Sunday morning.

Outlook...

Sunday...Patchy fog and local IFR through mid morning, then
mainly VFR.
Monday through Wednesday...VFR/MVFR with showers likely and a chance
of thunderstorms at times.
-- End Changed Discussion --

&&

.MARINE...
High pressure will remain over eastern Quebec and the Canadian
Maritimes through the weekend. The pressure gradient to the west of
this high will start to increase east to northeast winds on Lake
Ontario over the weekend with a moderate chop developing. Winds
will generally be lighter on Lake Erie through the weekend.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

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