-- Discussion containing changed information from previous version are highlighted. --
557
FXUS61 KBUF 211825
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
225 PM EDT Fri Jun 21 2024

.SYNOPSIS...
While it will still be uncomfortably warm and humid through this
weekend, a frontal boundary oscillating back and forth over our
region will support enough cloud cover and some thunderstorm
activity to suppress the dangerously high heat indices.
Unfortunately, the daily thunderstorms will carry the risk of
torrential downpours and even severe weather. Notably cooler and
more comfortable conditions can then be expected next week,
especially during the latter half.

&&

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
This afternoon a frontal boundary has dropped southward to around
Route 20A. Ahead of this front a still very warm and humid (PWATs
1.75") atmosphere is creating SBCAPE values of several thousand
J/KG, while behind the front instability is not as great.
Additionally ahead (south) of this front DCAPE values approaching
800 J/KG and lift along a lake breeze and frontal boundary will
support scattered to numerous thunderstorms, of which some may
become severe. Thinking most of this activity will be now through 8
pm, then some weakening to the instability will begin to diminish
coverage area of storms.

This evening subtle surface wave will bring a plume of deeper
moisture northward over Lake Erie, clipping NW Niagara Frontier.
This increase in moisture and lift near the surface low could fuel a
few evening storms across NW portions of our region. This low will
also begin to drag the frontal boundary northward.

Otherwise tonight will be fairly dry to the south, with potential
for fog formation, especially near areas that received afternoon
storms. To the north and near the frontal boundary and deeper
moisture a few showers and thunderstorms can not be ruled out.

It will be mild again tonight with overnight lows in the mid 60s to
lower 70s.

Saturday with this frontal boundary still wavering near northern
portions of our region, and plenty of instability showers and
thunderstorms will again blossom. Favored regions of lake breeze
boundrys and near the front will for storms. This will leave just
areas NE of Lake Erie with the lowest chances for storms. Highs
tomorrow will be in the mid to upper 80s, which with the humidity
will yield apparent temperatures 90 to 95F. Deeper moisture/cloud
cover east of Lake Ontario will likely keep this area in the mid 70s
for highs.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
An upper level trough will begin to dive across the upper Midwest
Saturday night, causing associated low pressure to strengthen across
the central Great Lakes and lift the warm front north of the region.
This will place the area beneath the warm sector, supporting ample
warm moist air advection. Overall the chances for showers and
thunderstorms will continue throughout Saturday night, with the best
likelihood for activity lying across the North Country due to its
close proximity to the front.

The now (roughly) 995mb surface low and associated trough will track
to the north of the area and result in a windy day Sunday, given the
850mb winds ramp up to nearly 45 knots. Overall this will support
the passage of a strong cold front across the area, likely producing
thunderstorms with its passage. Organized convection featuring
damaging winds will also be possible due to the ample wind shear
across the region. With this cold frontal passage, the arrival time
will play an important role with convection. There still are
significant differences in model guidance timing the frontal passage
and strength of the low. SPC has a portion of our area in a marginal
risk for severe weather. Even without thunderstorms, it will be a
windy day with wind gusts across the Niagara Frontier around 45 mph.

The cold front will then slide to the east of the area Sunday night,
supporting lingering showers and thunderstorms to taper off from
west to east.

The potent shortwave trough aloft will move across New England Monday
and bring increasing chances for showers and a few thunderstorms
across the North Country with lower chances elsewhere. After such a
warm and humid week, it will be notably cooler and drier Monday with
highs in the 70s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
An upper level trough over New England Monday night will shift into
the Canadian Maritimes by Tuesday, allowing a progressive mid-level
ridge to briefly become established across the eastern Great Lakes.
An attendant area of surface high pressure shifting southeast across
the Appalachians to the Mid-Atlantic coast will provide the forecast
area with a period of rain-free weather, while giving temperatures
an upwards nudge back into the low and mid 80s by Tuesday afternoon.

Shower and thunderstorm chances return from west to east late
Tuesday evening and through Tuesday night as the mid-level ridge
moves east, causing a warm front to lift out of the Ohio Valley and
into WNY. Confidence is low in timing and coverage of
showers/thunderstorms associated with this front as long range
guidance is in poor agreement on the evolution of a shortwave
expected to slide east across Southern Ontario and the Great Lakes
during this same timeframe. Greater chances for showers and
thunderstorms will arrive Wednesday as a ~982mb surface low tracks
across northern Quebec, sending its elongated cold front through the
Northeast. While timing of this front and its associated prefrontal
trough remain in question and thus lend lower confidence in how
convection will ultimately unfold Wednesday...The system is expected
to tap into a deeper plume of GOMEX-based moisture with PWATs
potentially climbing to near 2" as it approaches. Thus, any storms
that develop and move through the region should have the potential
to bring locally heavy rains.

The primary cold front should move through the region Wednesday
night, with increasing subsidence and a drier airmass allowing
shower/thunderstorm chances to decrease from west to east in its
wake. As much of the Northeast sits within the post-frontal airmass,
temperatures will be notably cooler Thursday and Thursday night,
with highs in the low/mid 70s and lows in the 50s and upper 40s
respectively. Dry weather should then last through the end of the
week with moderating temperatures as surface high pressure moves
over and east of the region.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
For the 18Z TAFS VFR flight conditions will largely rule, but there
will be two concerns.

First, afternoon and evening showers and thunderstorms. Greatest
instability and mid level lapse rates are found across interior WNY,
with convection along and out ahead of a lake breeze boundary.
Storms near KJHW early will push eastward. A frontal boundary,
roughly near route 20A will confine the deeper instability
southward, with KIAG, KROC and KART likely to remain dry through the
afternoon hours. KBUF, closer to the front, will likely stay dry,
but storms could near the TAF site late this afternoon.

The second concern will be the formation of fog and or low stratus.
Most likely areas for fog will be near areas where rain occurred
today, and will highlight the southern Tier, and towards the Finger
Lakes. This fog may expand towards KJHW tonight.

Tomorrow, with this frontal boundary still draped across our
region, additional showers and thunderstorms are likely, least
likely near KBUF where a lake breeze circulation will likely spread
a more stable layer inland.

Outlook...

Saturday night...Mainly VFR. A chance for evening thunderstorms
inland from the lakes.

Sunday...VFR/MVFR. Showers and thunderstorms likely.

Monday...Mainly VFR. A chance for afternoon and evening
thunderstorms inland from the lakes.

Tuesday...Mainly VFR conditions expected.

Tuesday night and Wednesday...MVFR/VFR with a chance for showers and
thunderstorms.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Light winds and minimal wave action is expected to continue across
the Lower lakes through tomorrow. There will be a chance of
afternoon showers and thunderstorms which could produce gusty winds
and higher wave action each day.

A cold front will approach the region Sunday with increasing southwest
winds which may bring a period of SCAs to area lakes. Northerly
flow behind the front will then bring continued choppy conditions
to the lakes through Monday. High pressure builds in late Monday with
diminishing winds and waves for Tuesday.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...AR/RSH/Thomas
NEAR TERM...Thomas
SHORT TERM...Apffel
LONG TERM...PP
AVIATION...Thomas
MARINE...AR/Thomas