-- Discussion containing changed information from previous version are highlighted. --
965
FXUS61 KBUF 211745
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
145 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 /UNTIL 6 AM SATURDAY MORNING/...
This morning convective activity is focused along and north of a
surface frontal boundary that is draped across Lake Ontario and
points eastward. Convection, along an instability boundary, is
occurring across Jefferson and Oswego County, drifting towards Lewis.
MUCAPE of 1K J/KG is only expected to increase through the morning
hours and as convection deepens, don`t see a lot of dry air
entrainment aloft, maintaining the potential for these heavy
downpours into the afternoon hours. With the slow movement, and
moist lower atmosphere (PWATS 1.71 inches on the Buffalo 12Z
sounding this morning), heavy downpours of rain are likely within
any convection through the afternoon, that will likely become
focused towards southern regions as this frontal boundary sags
southward.

While there will be some measure of showers and thunderstorms with
this boundary, overall coverage appears to be limited right now.
That said...have placed the best coverage for the afternoon (higher
PoPs > 50%) across the S. Tier (closer to the NY/PA line) and into
the Genesee Valley/western Finger Lakes region. This is supported by
most Hi-res guidance. It is also highlighted by SPC with a MRGL risk
for severe storms. We should see most of the activity today occur
with peak heating. Highs today (a few degrees cooler) will be found
in the 80s to near 90F in spots.

Tonight...most convection should slowly wane with the loss of
daytime heating. The weak east to west frontal boundary to our south
is also advertised to return back north as a warm front. We
could see a few showers or even a thunderstorm as it returns.
Otherwise...mild and muggy night with lows in the 60s to low
70s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
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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.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR across all terminals this morning. A weak frontal boundary will
sag south through the region today and potentially support some
showers and thunderstorms. This will mainly be the case for areas
south of Buffalo and Rochester during the midday and afternoon.

Tonight...mainly VFR but there may be some fog/low status across the
S. Tier at KJHW. Low confidence, so didn`t include it in the TAF.

Outlook...

Saturday...Mainly VFR. A chance for afternoon and 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.

&&

.MARINE...
Light winds and minimal wave action is expected to continue across
the Lower lakes through Saturday. 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.

&&

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

&&

$$

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