591
FXUS61 KBUF 291533
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1133 AM EDT Sat Jun 29 2024

.SYNOPSIS...
It will be quite unsettled the first half of the weekend...as a passing
warm front this morning will be the first of several boundaries that
will generate widespread showers and possibly some gusty...drenching
thunderstorms into tonight. Our sub tropical airmass will then give way
to less humid conditions in the wake of a cold front on Sunday...
although some showers will still be possible...especially east of
Rochester. High pressure will then guarantee PERFECT weather for
outdoor activities Monday and Tuesday.

&&

.NEAR TERM /THROUGH SUNDAY/...
...Torrential Downpours and Possibly Severe Weather Today...

A large swath of moderate to heavy rain working through the CWA with
the warm front. Some areas (S. Tier) have  already exceeded 1.0 to
1.5 inches of rainfall with this first batch of precipitation. While
welcome precipitation...areas that have been worked over will become
susceptible to flash flooding. More on this below...

In the wake of the warm front a sub tropical air will flood
northwards across our forecast area within the associated warm
sector. Tds will surge into the lower 70s with PWAT values swelling
to over 2 inches. The latter is more than 2 STD above normal for
late June and represent values that are outside of 30 year
climatology return intervals. This warm plume of deep moisture will
include high freezing levels that will result in warm cloud depths
in excess of 13k ft...maximizing the efficiency of rainfall rates
within the showers and thunderstorms. This will elevate the risk for
torrential downpours...and with short MBE vectors expected...these
downpours could be slow moving or even build back to the southwest
during their progression.

The forcing for the increasingly widespread showers and likely
thunderstorms today will be a pre-frontal trough that will trudge
through the area several hours behind the aforementioned warm front.
All of this has led to a slight risk for excessive rainfall...
especially across the western Southern Tier and Eastern Lake Ontario
region where CAMs and high-res guidance is favoring the most widespread
convection. Its worth noting that flash flood guidance suggests that it
would take roughly 1.5 to 2 inches of rain in an hour to induce
localized flooding concerns. A Marginal Risk of excessive rainfall will
be found elsewhere.

In regards to the risk of severe weather today...it will largely come
down to how much diurnally induced instability we can achieve. While a
few hundred joules/kg will be in the environment already...any breaks
in the cloud cover will potentially allow as much as 1000 j/kg of
SBCAPE to build. Meanwhile...a 40-45kt low level jet will offer PLENTY
of shear for any true convection to become better organized. 6km bulk
shear values of 40kts or better will include 0-1km SRH that will exceed
200 m2/s2...favoring the development of supercells...both in advance of
any line segments or within the convective clusters themselves. Given
poor lapse rates though...this threat will heavily depend on added
diurnal instability. The greatest chance for this will be across the
western Southern Tier...and especially SOUTH of the border...with the
highest risk of severe weather coming in the form of damaging straight
line winds along with isolated tornadoes. Large hail is NOT anticipated
given the poor lapse rates and likely lack of SIGNIFICANT instability.

The pre frontal sfc trough and deep plume of sub tropical moisture will
push east of our forecast area early tonight. While there can still be
some torrential downpours east of Lake Ontario early...the showers will
taper off from west to east within the shrinking column of moisture. It
will remain rather mild and somewhat humid though with the airmass yet
to change ahead of a cold front.

While Sunday will prove to be a nicer day...the passage of the initial
cold front during the morning may provide a short lived uptick in
shower coverage. The most widespread showers will remain east of Lake
Ontario. Otherwise...it will be quite breezy in the wake of the
aforementioned cold front with increasingly comfortable conditions due
to the tumbling Td`s. Interestingly...our high temperatures in the low
to mid 70s will occur by midday/early afternoon with slowly falling
mercury readings thereafter. This is unusual for this time of year...
so this gives you a semblance of how strong the cold advection will be
in the wake of the first cold front.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
Sunday night the core of the upper level trough and secondary cold
front will slide south across our region. Coupled with upsloping and
lake influences (the latter owing to rather cool 850 mb temps
falling to around +5C to +6C)..the above should generate a fair
amount of cloud cover along with some scattered showers...with the
greatest pcpn potential lying east and southeast of Lake Ontario.
With this in mind have increased both PoPs and cloud cover notably
from blended guidance...which appears to be handling these rather
poorly. Otherwise it will be a much more comfortable night for
sleeping...with lows ranging from around 50 across the interior
Southern Tier and North Country to the mid 50s across the lake
plains.

Sprawling Canadian high pressure and plentiful dry air will then
slowly meander its way from the Upper Great Lakes to the mid-
Atlantic coastline Monday and Tuesday...while low-amplitude upper
level ridging builds across the region aloft. This will provide us
with fine weather to start off July...with highs in the upper 60s to
lower 70s Monday warming to the upper 70s and lower 80s on Tuesday
as a southerly return flow of warmer air develops around the
backside of the departing ridge. In between...ideal conditions for
radiational cooling will allow Monday night`s lows to range from the
mid-upper 40s across the interior of the Southern Tier/North Country
to the lower to mid 50s elsewhere. Humidity levels will also remain
comfortable throughout...with surface dewpoints only inching up into
the 55-60 range by later Tuesday.

Tuesday night the surface ridge will slip a little further
offshore...while the next mid/upper level trough and surface low
pivots across Manitoba and Ontario Provinces. With our region firmly
embedded within the deepening/strengthening southerly flow in
between these two systems...it will be a much warmer night than the
preceding two...with readings generally ranging through the 60s.
Meanwhile humidity levels will remain tolerable...as surface Td`s
will linger in the 55-60 range.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Wednesday and Thursday the aforementioned trough and surface low
will continue to make its way eastward to Labrador...and in the
process will ease a weak trailing cool front across our area
Wednesday night and early Thursday.

Out ahead of this boundary heat will build on Wednesday...with 850
mb temps surging into the upper teens...thereby supporting highs
climbing back to the mid 80s to lower 90s in most areas. Humidity
levels will also be on the increase...with surface dewpoints
climbing into the mid-upper 60s and lending a decidedly muggy feel
to the afternoon. As the cool front impinges upon this sultry
airmass later Wednesday afternoon and especially Wednesday
evening...it should help to set off at least some scattered
convection...which could prove problematic for any holiday fireworks
displays scheduled for Wednesday evening.

Convection should then tend to diminish in coverage from northwest
to southeast later Wednesday night and Thursday as the passing cool
front slips off to our south and ushers in a slightly cooler and
less humid airmass...though cannot rule out some spottier showers
and storms lingering into Thursday afternoon near the NY/PA border.
Otherwise slightly cooler highs in the lower to mid 80s are expected
for Independence Day...though humidity levels will likely remain
elevated.

The weak cool front then looks to stall out not far to our south
Thursday night and Friday...as a weak wave of low pressure develops
and ripples eastward along the boundary. While the medium range
guidance packages unsurprisingly exhibit differences on the timing
and strength of this wave...a rough consensus would currently
suggest a largely dry evening on July 4th...followed by a renewed
potential for scattered showers and storms later Thursday night into
Friday...with the latter greatest near the Pennsylvania border. This
being said it`s pretty early...with changes to this overall scenario
certainly possible over the coming days. Otherwise...it will likely
remain warm and on the humid side through the end of the week.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
MVFR to IFR within the moderate to at times heavy rain as a front
pushes through area terminals this afternoon.

A pre frontal trough pushing across the state will prompt additional
showers and possible strong thunderstorms within a very soupy sub
tropical airmass into this evening.

The heavy showers and thunderstorms will taper off from west to east
by this evening and night...MVFR to IFR cigs can be expected.

Outlook...

Sunday...VFR/MVFR with scattered showers.
Monday and Tuesday...VFR.
Wednesday...Mainly VFR.

&&

.MARINE...
It will be quite unsettled today...as a broad storm system centered
north of the SOO will push several frontal boundaries across the Lower
Great Lakes. This will result in widespread showers and possibly some
gusty thunderstorms. Meanwhile...moderate to fresh southerlies will
direct the greatest wave action into Canadian waters. The exception
will be the far east end of Lake Ontario where waves will be
significant enough to warrant a small craft advisory for sites north of
Mexico Bay. Otherwise...expect fairly choppy conditions...especially
well offshore.

Winds will weaken somewhat tonight while veering to the southwest. This
should allow the headline for eastern Lake Ontario to expire.

Fresh to strong westerlies can then be expected in the wake of a cold
front on Sunday. This will likely lead to a fresh round of headlines
for at least the eastern half of Lake Ontario...while choppy conditions
will be found elsewhere.

Looking further ahead...high pressure drifting across the region Monday
and Tuesday will offer fine conditions for recreational boating with
generally light winds and negligible waves.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for LOZ045.

&&

$$

SYNOPSIS...AR/RSH
NEAR TERM...AR/RSH
SHORT TERM...JJR
LONG TERM...JJR
AVIATION...AR/RSH
MARINE...AR/RSH