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911
FXUS61 KBUF 280744
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
344 AM EDT Fri Jun 28 2024

.SYNOPSIS...
Beautiful weather will be in place today...as high pressure overhead
in the morning will drift off the coast of Long Island by this
evening. Conditions will then deteriorate tonight and particularly
on Saturday...as low pressure crossing the Upper Great Lakes will
push several frontal boundaries through the region. Scattered
showers late tonight will become much more numerous on Saturday when
a sub tropical airmass will support some heavy rain as well. Not a
good day at all for outdoor activities. Sunday will offer some
improvement...but a few showers will still be possible.

&&

.NEAR TERM /THROUGH SATURDAY/...
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...Severe Weather Threat and Torrential Downpours on Saturday...

High pressure overhead early this morning will gradually make its
way to the east during the course of the day...eventually moving off
Long Island by this evening. While some cirrus will stream across
the far western counties today and actually thicken somewhat during
the afternoon...beautiful weather can anticipated to end the work
week. It will be comfortable with continued low humidity...but warmer
by some 5 to 10 degrees...as afternoon temperatures will reach 75 to
80. The higher end of that range will be near Lake Erie and in the
downslope areas west of Rochester.

As the sfc high moves further off the East coast tonight...a
deepening southerly flow featuring a modest 30-35kt low level jet
will become established over our area ahead of a mid level shortwave
and attendant sfc warm front. Lift provided by the low level jet
over the sfc boundary will promote scattered shower activity after
midnight...mainly over the western counties. Elevated CAPE averaging
200 j/kg could be enough within a synoptically forced environment to
support a thunderstorm or two...with values as high as 500 j/kg over
the Southern Tier being the most favored area. It will be notably
warmer tonight than the past two...as the aforementioned deepening
southerly flow and associated pronounced warm advection only
allowing the mercury to drop to between 65 and 70 across the lake
plains to the lower 60s most elsewhere. Back to summer.

Saturday will then be quite unsettled...as a pair of boundaries will
support numerous showers along with some thunderstorms. While there
will be some dry time between the two rounds of pcpn...it will not
be the nicest day for outdoor activities. Quite the contrary.

First...a warm front will push northeast through the region during
the morning. A 40kt low level jet impinging upon this sloping
boundary will generate some showers and possible thunderstorms...
but more numerous showers and storms can be expected during the
midday and afternoon within a soupy sub tropical airmass in the wake
of the warm front. A pre frontal trough will plow through this
notably more humid airmass...and this will result in moderately
heavy showers with some areas picking up torrential downpours and
strong wind gusts within thunderstorms.

The potential for localized heavy rain will be supported by PWAT
values that will surge to nearly 2.25" and Td`s that will be within
a degree or so of 70. As was astutely pointed out in earlier
discussions...a measured PWAT value of 2.00 inches is uncommon for
late June on radiosondes launched from the Buffalo Airport. Only 7
instances (12Z or 00Z) of a PWAT of 2.00 inches or more have been
recorded since 1948. The exaggerated PWAT values will be a solid 2
standard deviations above normal...which for this time of year are
outside the climatology 30 year return interval. Impressive. Basin
average rainfall is forecast to range from a half inch or less over
the Finger Lakes to nearly an inch elsewhere...with localized
rainfall of 2 inches or more possible due to the sub tropical
airmass and short MBE vectors (slow moving/back building
convection).

In regards to the risk for severe thunderstorms on Saturday...the
advertised 40kt low level jet will promote an abundance of shear to the
tune of 40-50kts through 6km. While this high level of deep layer shear
could easily support organized convection...including some
supercells...the question will be how much instability will be
available given the forecast wealth of cloud cover. A minimum amount of
500 j/kg of MLCAPE should be expected with breaks of sun possibly
allowing for as much as 1000 j/kg of SBCAPE. The main severe weather
threat will be for damaging straight line winds...but the presence of
supercells will also introduce a non-zero risk for tornadoes...mainly
across the western Southern Tier. The greatest threat for any severe
weather will be during the midday and afternoon.

Otherwise...it will be a very breezy and muggy on Saturday with
winds gusting to 30 to 40 mph outside of the aforementioned
convection.
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&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
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Saturday evening a pre-cold frontal trough will push east across the
region. This boundary will act to effectively shunt the plume of
rich subtropical moisture (PWATs of 2 to 2.25 inches) eastward and
out of our area...thereby bringing an end to the threat for heavier
rain from west to east along with a commensurate decrease in
precipitation coverage. Prior to its passage...the presence of ample
deep-layer shear (0-6 km bulk shear values of 40-50 knots) could
also lead to a risk for some strong to severe storms early in
the evening...provided that sufficient instability can develop
during the preceding afternoon - a factor that remains highly
uncertain at this juncture. If realized...this risk would be
greatest from the Finger Lakes westward...as is advertised by
the Slight Risk area in SPC`s latest Day 2 Convective Outlook.
As mentioned in the near term section above...the main severe threat
would be for damaging wind gusts...though there would also be a
non-zero secondary risk of a tornado.

During the second half of Saturday night we can expect a continued
potential for some scattered showers (more numerous across the North
Country) and perhaps a couple more isolated thunderstorms as low
pressure tracks across central Quebec and pivots its initial
trailing cold front to our western doorstep. This being said...the
loss of the subtropical moisture plume and diminishing instability
should help to keep this activity of considerably lesser consequence
than that of Saturday afternoon and evening. Otherwise it will
remain very warm and muggy with the surface cold front remaining to
our west through the night...with overnight lows mostly ranging
between 65 and 70.

On Sunday the initial cold front will slide across our region during
the morning...with its passage marked by some additional scattered
showers and isolated storms. In its wake cooler and drier air will
overspread our region through the balance of the day and lead to
generally dry weather from the Finger Lakes westward...though the
approach of the supporting mid-upper level trough and an associated
secondary cold front should keep the potential for at least some
more scattered showers going right through the day east of Lake
Ontario. With 850 mb temps dropping into the mid to upper single
digits and surface dewpoints also falling through the 50s...both
temperatures and humidity levels will become much more pleasant...
with most areas seeing highs in the upper 60s to mid 70s.

Sunday night the core of the mid-upper level trough and secondary
cold front will slide south across our region...while supporting a
few more widely scattered to scattered showers. As was the case with
our last system...the potential for these will be greatest across
the North Country where forcing again looks to be the most
favorable. Otherwise the cool airmass (850 mb temps down to around
+5C to +6C) should prove sufficiently cool enough to generate a fair
amount of lake and orographically-induced cloud cover south and
southeast of the lakes...with the latter also likely helping to
preclude much in the way of river fog development across the
Southern Tier. 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.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
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Monday and Tuesday sprawling Canadian high pressure will slowly
meander its way from the Upper Great Lakes to the mid-Atlantic
coastline...while low-amplitude upper level ridging builds across
the region aloft. This will provide us with fine weather for the
first couple days of 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. This being said...surface dewpoints will remain
confined to the 50s even on Tuesday...so it will remain comfortable
in spite of the increasing warmth.

Wednesday and Thursday broad/flat troughing will develop aloft...
with associated surface low pressure passing by well to our north
and eventually easing a weak trailing cool front across our area.
This will lead to a renewed potential for at least some scattered
showers and thunderstorms during this time. Otherwise a continued
south to southwesterly flow out ahead of this boundary will pump
warmer and more humid air back into our region for Wednesday...when
high temps and surface dewpoints will likely climb back to between
85-90 and the mid-upper 60s respectively. Following the passage of
the weak cool front...slightly cooler highs in the lower to mid 80s
then look to follow for Independence Day...though humidity levels
will likely remain elevated.
-- End Changed Discussion --

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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While there may be some valley fog across parts of the Southern Tier
early this morning...fair VFR conditions with light winds will be in
place through the day...courtesy of high pressure that will move from
western New York to Long Island by this evening.

VFR weather will remain in place through the first half of tonight...
then an approaching warm front will help to generate scattered showers
late...mainly over the western counties. Alto-cu cigs this evening will
lower to VFR level strato-cu overnight in most areas...although MVFR
cigs will become likely towards daybreak Saturday across the Srn Tier.

There will be the potential for some low level wind shear late
tonight...especially across the Finger Lakes region.

Outlook...

Saturday...Localized restrictions in increasingly widespread showers
and scattered thunderstorms...some of which may produce locally heavy
rainfall.
Sunday...A chance of a leftover shower or two...otherwise mainly VFR.
Monday and Tuesday...VFR.
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&&

.MARINE...
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High pressure overhead early this morning will exit to Long Island by
late this afternoon. This will allow gentle southeast winds early today
to freshen a bit this afternoon while becoming more easterly. Wave
action will be negligible.

As the area of high moves off the coast tonight...a warm front will
approach the region from the south. Winds will respond by veering back
to the south and freshening overnight while remaining below small
craft advisory criteria.

It will then become quite unsettled on Saturday. Widespread showers and
possible strong thunderstorms will develop in the wake of the
aforementioned warm front during the course of the day...while fresh to
strong southerlies will generate more pronounced wave action.
Conditions may stay just below SCA levels...although conditions will
become choppy...particularly well offshore. The area that may
experience SCA conditions though will be the northeast corner of Lake
Ontario...north of Mexico Bay.

Fresh southwesterlies Saturday night will then freshen and become
westerly on Sunday when SCA`s will be more likely...especially on Lake
Ontario.
-- End Changed Discussion --

&&

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

&&

$$

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