-- Discussion containing changed information from previous version are highlighted. --
345
FXUS61 KBUF 051855
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
255 PM EDT Wed Jun 5 2024

.SYNOPSIS...
A slow moving cold front will press through the region later tonight
and Thursday...and while this will lead to increasingly widespread
showers and possibly some drenching thunderstorms...it will also
bring an end to our stretch of summery weather. In fact...
temperatures are slated to average below normal from Friday through
Monday of next week. The cooler weather will be accompanied by
fairly frequent shower activity.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
It will be warm and humid across the region this afternoon...as a
deepening southerly flow ahead of an approaching cold front will
allow a sub tropical airmass to move in from the Ohio valley. Td`s
will climb to the mid and even upper 60s for much of the forecast
area...and this will set the stage for some potentially drenching
thunderstorms.

As of midday...an area of nuisance showers was in the process of
moving across the far western counties. This activity is in the
vcnty of an elevated warm front. During the course of the
afternoon...the showers will continue to move northeast while
spreading over much of the rest of the western counties. The
environment is already unstable to the tune of 1500-2000 j/kg of
SBCAPE...so its only a matter of having any weak boundaries from the
aforementioned area of showers being able to initiate the
convection. If this were to occur...it would be over the Genesee
valley and Finger Lakes after 2 PM. DCAPE values in the vcnty of
1000 j/kg would then promote the risk for gusty storms for those
areas. Otherwise...locally heavy rain would be the only real
concern.

Meanwhile...areas east of Lake Ontario will continue to enjoy sun
filled skies with only some cirrus to contend with. This area will
be the warmest with highs in the upper 80s to near 90...which would
once again be record territory for Watertown (87 in 1973).

The deep plume of sub tropical moisture will be situated over our
region tonight...while a cold front will SLOWLY move through. Given
the moisture rich airmass that will be in place...the forcing from
the front will generate numerous showers and thunderstorms...some of
which will include pockets of heavy rain. The activity will be
scattered in nature through much of the evening...then it will
become more focused along and just ahead of a cold front over the
western counties after midnight. This timing is a little slower than
previous forecasts. Along with the `heavy rainers`...there will
still be the risk for localized gusty winds with some of the storms.

As we move through the wee hours of the morning towards daybreak...
the most concentrated areas of showers and possible thunderstorms
will make their way to the Eastern Lake Ontario region. The risk for
gusty winds with the convection should drop off by this point.
Otherwise...tonight will be a warm and muggy night with mins in
the more populated regions not falling below 65.

Thursday...the slow moving cold front will make its way across the
Eastern Lake Ontario during the morning hours. This will continue to
support cat pops for that area along with the potential for locally
heavy rain. The scenario will be far more convoluted over the
western counties.

While a negatively tilted mid level trough will continue to dig
over the Lower Great Lakes on Thursday...weak sfc based ridging will
develop over the western counties. This combination will work
against organized shower activity...except within a pronounced area
of low level convergence that will become established from KIAG past
KROC...basically just north of the NYS Thruway. Showers will be
likely in this particular corridor. For the immediate BUF area to
near KGVQ...a lake shadow is expected with gusts to near 30 mph.

The real airmass change though will take place Thursday night in the
wake of a secondary cold frontal passage. This will bring a
temporary end to the scattered shower activity...as Tds will drop
into the 50s. Towards daybreak though...deeper moisture on the
backside of a deep mid level low in the vcnty of the SOO will start
to circulate across the Lower Great Lakes. Lift underneath the front
left exit region of an 80-90kt H25 jet should be enough to restart
at least scattered shower activity over the far western counties...
and particularly across Chautauqua county and srn Erie co.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
-- Changed Discussion --
Opening the period Friday, deep troughing will be found across much
of southern Canada and the Great Lakes. Two broad yet distinct areas
of anticyclonic flow aloft will initially be embedded within this
trough: one over central MB/SK, and the other down across southern
ON and the Great Lakes. Through the course of the weekend the latter
will come to dominate the longwave pattern across much of the
eastern CONUS, with a single large closed low aloft gradually
sliding east to New England through the end of the weekend. This
pattern and its evolution will keep the core of the upper level jet
stream mainly to our south, allowing a continuous flow of cool,
moist Canadian air into the region while also periodically placing
the forecast area under regions of upper level divergence.

In terms of sensible weather, this will translate to a rather
unsettled pattern Friday right through the weekend with temperatures
averaging below normal. While the nature of the convection will be a
bit different each day...Chances/coverage of showers and
thunderstorms will generally follow the diurnal insulation curve and
be maximized during peak heating in the afternoon hours, especially
inland from the lakes. Friday in particular will feature rather
widespread shower activity as robust shortwave energy pivots through
the eastern Great Lakes. Conversely, shower coverage should become
increasingly scattered through the evening hours with the loss of
daytime heating, though periodic upper level jet divergence and
quick hitting shortwave troughs will maintain Chc PoPs overnight and
through the morning hours. In fact, with 850H temps expected to
bottom out around +4C and recent lake temperature measurements in
Buffalo and Rochester between 61-63F...Not totally out of the
question we see some weak lake enhanced rain at times, especially
Friday night. Though, 850H temps are very marginal and the water
temperatures over the open waters of the lakes are likely much
cooler.

All this being said, while the expected showers and occasional
thunderstorms will certainly be a nuisance for those looking to plan
outdoor activities, PWATs will likely struggle to become elevated at
any given point, staying near or below 1" this period. Combined with
limited deep instability (peak MUCAPE values 100-200J/kg), the
threat of stronger storms should be limited.

For temperatures...Highs Friday through Sunday will average near 5
degrees below normal, only managing to reach the 60s in most areas,
perhaps a few low 70s across the interior valleys while the hilltops
may only reach the upper 50s. While the airmass will be abnormally
cool, a wealth of cloud cover is expected to hold nighttime lows
near normal in the low to mid 50s, possibly a few upper 40s across
the interior.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --
Eastern CONUS trough pattern will persist through the first part of
the  period, with the bulk of the unsettled weather Sunday night
into the start of the new work week, before the more highly
amplified pattern across the CONUS starts to relax a bit. This will
also be reflected in our temperatures as readings still below normal
on Monday, modify back to near normal levels for Tuesday and
Wednesday.

The catalyst for this modest change in the overall pattern will be a
robust shortwave diving south out of Canada through the base of the
mean longwave eastern trough, which will actually help to kick the
upper trough to our east sometime around the start of the work week.
There remains some disagreement in exactly when this feature will
pass across western and northcentral NY, thus will cap PoPs at
chance for Sunday night and Monday at this point, mainly due to
timing differences, as there will likely be a round of
showers/isolated storms along and ahead of the trough axis as it
passes through. PWATs at or below climatological means along with
decent movement, so not too concerned with any hydro issues at this
time.

As alluded to above, our airmass will start to modify for the second
half of the period as the overall upper level pattern somewhat
deamplifies across the CONUS. In fact, latest guidance continues to
trend drier for Tuesday and Wednesday with weak high pressure
surface and aloft building in over the region.
-- End Changed Discussion --

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Some showers will be found over the western counties during the
remainder of the afternoon...along with a few heavy rain producing
thunderstorms. While VFR conditions will persist...MVFR cigs will be
possible in the vcnty of the convection. Meanwhile...fair VFR
weather will be found east of Lake Ontario.

As a cold front approaches and moves through tonight...more
widespread showers can be expected...along with some gusty
thunderstorms. The onset of the more widespread pcpn will include a
change to MVFR Cigs. IFR conditions will set up across the Srn Tier.

MVFR to IFR cigs Thursday morning will then gradually give way to
VFR weather. The most widespread showers and possible thunderstorms
will be east of Lake Ontario through 15z.

Outlook...

Thursday night...Mainly VFR weather.
Friday through Monday...VFR/MVFR with mainly daytime showers likely
with possible thunderstorms.

&&

.MARINE...
A southerly flow will strengthen today into tonight ahead of a slow
moving cold front approaching from the west. With the flow being
mainly offshore, the main impact will just be a bit of an uptick in
light chop toward the open waters.

The cold front will cross the lower Great Lakes late tonight and
Thursday morning, however expect a threat for thunderstorms this
afternoon through Thursday. SW to WSW winds will freshen on both
Lakes Thursday and Friday in the wake of the cold frontal passage
with choppy waters developing. Conditions may possibly near Small
Craft Advisory criteria for a couple of brief periods Thursday and
Friday afternoon, especially across eastern Lake Erie.

&&

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

&&

$$

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