968
FXUS61 KBUF 100218
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1018 PM EDT Tue Jul 9 2024

.SYNOPSIS...
Our stretch of fair dry weather will come crashing to an end later
tonight and Wednesday...as the remnants of Beryl will make its way
out of the Mid West. A soaking one to two inches of rain can be
expected in many areas by Thursday morning...with higher amounts
possible east of Lake Ontario and even moreso across the Adirondacks.
Along with tropical downpours on Wednesday...there will be the risk for
strong to severe thunderstorms...mainly across the western Southern
Tier and for portions of the Finger Lakes.

&&

.NEAR TERM /UNTIL 6 PM WEDNESDAY EVENING/...
...Significant Rains AND increased severe weather threat continues
from the Remnants of Beryl on Wednesday...

Late this evening, radar shows most of the showers have ended
across Western NY, with mainly rain-free conditions.

Conditions will significantly deteriorate during the course of
tonight though...as the remnants of Beryl over the Lower Ohio valley
will push northeast. A tropically enhanced warm front extending to the
east across Pennsylvania will approach our region in the process. A
modest 25 to 30kt low level jet impinging upon this boundary will
combine with forcing under the nose of an 80kt UL jet to lift a
deepening tropical airmass to generate increasingly widespread rain as
we progress through the overnight/wee hours Wednesday morning. PWAT
values will surge to 2.25" by daybreak...so some heavy rain will be
possible...particularly within any embedded thunderstorms. The focus of
the rain late tonight will be over the western counties with sites west
of the Finger Lakes most likely to experience the heavier downpours.

Wednesday will most certainly be the most unsettled day of the week...
as the center of whats left of Beryl will track across the far west end
of Lake Erie to southernmost Ontario. Meanwhile...the aforementioned
eastward extending warm front will gradually advance across our
forecast area. The deep tropical moisture will focus near and north of
the advancing warm front where widespread moderate to heavy rain is
expected. Daytime rainfall amounts are forecast to range from
around a half inch across the western Southern Tier to 1-1.5
inches most elsewhere. Embedded thunderstorm activity could
locally double that amount. The good news is that the threat for
excessive rains has diminished across the sloped terrain of the
Southern Tier...but on the flip side...the risk remains in
place for the more populated areas from Buffalo...Batavia and
Rochester to the Eastern Lake Ontario region. Six hour FFG
guidance for this particular area is in the vcnty of 2.25" and
this will limit the risk for widespread hydro concerns to some
extent. Rain will increase flow in most area tributaries, but
given recent dry weather and seasonably low current levels the
rises on larger rivers are likely to remain within bank.
However, localized heavy rains in this moist environment will
still have the potential to produce flash flooding or general
flooding. Updated WPC forecast clips Lewis county with a
moderate risk for excessive rainfall, leaving most of the
forecast area in a slight risk.

As for the potential for severe weather...the Storm Prediction
Center has outlined much of western New York within a slight
risk area. This aligns with the progression of the tropically
enhanced warm front where a notably enhanced amount of shear
will be present. Bulk shear values of 40-50 kts and veering low
level profiles will support supercells and a non-zero threat of
tornadoes...along with clusters that will include tropical rain
loaded downdrafts (ie localized straight line wind damage risk).
00Z HRRR shows convection developing early Wednesday afternoon
and moving from west to east across the area through around 8
p.m. This timeframe represents the greatest risk for severe
weather. There will be a frontal boundary near or just south of
the south shores of Lake Ontario, with areas in the northeast
flow on the cool side of the front at a much lower risk for
severe weather. However, non-convective northeast winds will be
quite breezy as the low passes by, with gusts to 35 mph and much
cooler weather. The boundary is likely to be near the I-90
corridor between Buffalo and Rochester but could meander some
during the day.

Wednesday night will remain very unsettled...particularly over
the Eastern Lake Ontario region. The center of the tropical
remnants will drift across the far western counties...while the
axis of deepest tropical moisture and associated will be slowly
exiting via the Thousand Islands and St Lawrence valley. This
could produce an additional inch to an inch and a half rain for
the Eastern Lake Ontario region...bringing 24 hour amounts to
nearly three inches. The highest amounts are expected to be over
Lewis county.

&&

.SHORT TERM /6 PM WEDNESDAY EVENING THROUGH FRIDAY NIGHT/...
By Thursday morning Beryl`s elongated remnant surface low will be
centered across the Lower Great Lakes and Upper Saint Lawrence
Valley...with this continuing to fill as it tracks into Southern
Quebec through the course of the day. While its attendant axis of
deep tropical moisture (and widespread moderate to heavy rains) will
be well to our east by this time...the continued close proximity of
the remnant low will keep clouds and at least some scattered lighter
showers going across the eastern Lake Ontario region through the
day...with upslope flow and wraparound moisture also producing a few
more of these across far western New York. In between...largely dry
weather should prevail across the Finger Lakes. This disparity in
cloud and pcpn coverage will also be reflected in the temperatures
we`ll experience...with highs ranging in the 70s across far western
New York and the North Country...and in the upper 70s to lower 80s
in between. It will also remain on the muggy side...with surface
dewpoints remaining in the mid to upper 60s.

Thursday night surface high pressure and drier air will ridge
northeastward into our region from the Ohio Valley. This will help
to bring an end to any lingering scattered showers...with fair dry
weather otherwise prevailing. Lows will dip into the upper 50s to
mid 60s as surface dewpoints drop back a little more...making for at
least somewhat more comfortable conditions compared to the preceding
few nights.

Friday and Friday night the aforementioned surface ridge will remain
draped across our region...while a weakening mid-level trough passes
by just to our north and west. In the process this latter feature
will brush our region...and this coupled with diurnal heating/
destabilization and developing lake/orographically-forced
circulations could be enough to pop some widely scattered convection
across the Southern Tier and interior Finger Lakes during Friday...
with this activity then weakening with the loss of heating and
sliding eastward Friday night. Have covered this potential with some
slight chance PoPs for now...with dry weather otherwise anticipated.
As for temps...highs on Friday will bounce back to the lower to mid
80s for the most part...with lows in the lower to mid 60s then
following for Friday night. It will also be at least somewhat
humid...as surface dewpoints will generally be in the lower to mid
60s.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
Guidance is starting to trend drier for Saturday as a shortwave
ridge moves into the area. A few showers can`t be ruled out for
eastern areas as a shortwave trough exits to the east.

The next trough tracks into the area on Sunday, bringing the next
potential for showers. Some timing issues still among the guidance
with shower onset time from early Sunday morning through Sunday
night. Thunderstorms will also be possible as instability increases
through the second half of the weekend.

Shower potential will continue into the new work week as a few
shortwave troughs track across the area within a quasi-zonal flow
over the region. Guidance is also slower with a cold front tracking
southeast across the Great Lakes and into the forecast area for the
first half of the work week. Again though, there is plenty of
uncertainty among guidance for timing and shower coverage. Per usual
certainty will start to increase closer to the period and as higher
resolution models start to cover any specific day.

Daytime temperatures will be some 5 to 10 degrees above normal for
the period. Depending on the actual cold frontal passage,
temperatures later in the period, on Monday and/or Tuesday may end
up being cooler.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
VFR flight conditions are in place late this evening, and will
last through around 09Z.

Later tonight and Wednesday the remnants of Beryl will approach
from the southwest. This will bring continued thickening and
lowering cloud cover...and eventually periods of moderate to
possibly heavy rain late tonight and Wednesday...along with some
scattered thunderstorms. This will result in flight conditions
lowering to MVFR/IFR. Wednesday afternoon and evening...enough
instability could develop to bring a risk of some strong to
severe thunderstorms...with this risk greatest south of a rough
KBUF-KROC-KFZY axis. The main threat with any such storms would
be strong wind gusts.

Outlook...

Wednesday night...MVFR/IFR with widespread rain diminishing.
Thursday...Improvement to MVFR/VFR with leftover scattered
showers.
Friday...Mainly VFR with a low chance of showers and thunderstorms
across the Southern Tier/Finger Lakes.
Saturday...Mainly VFR with a low chance of showers and
thunderstorms well inland from the lakes.
Sunday...Mainly VFR with a chance of showers and thunderstorms.

&&

.MARINE...
Low pressure associated with the tropical remnants of Beryl will
push into Ohio, and this combined with high pressure to the
north will result in a tightening pressure gradient.
Northeasterly winds will increase, especially on Lake Ontario
during Wednesday. Based on this, have issued small craft
headlines for the western two-thirds of the Lake Ontario waters,
and the Lower Niagara River.

There also will be several rounds of rain with embedded
thunderstorms moving through. Some storms may produce gusty
winds. The surface low will weaken and move across the eastern
Great Lakes with winds diminishing Wednesday night.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 11 AM to 11 PM EDT Wednesday for
         LOZ030.
         Small Craft Advisory from 8 AM Wednesday to 2 AM EDT
         Thursday for LOZ042-043.

&&

$$

SYNOPSIS...RSH
NEAR TERM...Apffel/RSH
SHORT TERM...JJR
LONG TERM...JM/SW
AVIATION...Apffel/JJR
MARINE...Apffel/RSH/TMA