Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240834

Area Forecast Discussion
National Weather Service Buffalo NY
434 AM EDT SUN JUL 24 2016

An upper level trough will slowly cross the region late today into
Monday which will produce some scattered showers and thunderstorms.
A trailing cold front will pass through our region Monday
evening...followed by slightly cooler weather Tuesday before
temperatures trend upward again Wednesday and Thursday.


An upper level ridge axis will move across the region this morning,
promoting surface high pressure and maintaining dry conditions through
this morning. There may be some patchy fog across the Eastern Lake
Ontario region where rain yesterday enhanced low level moisture.
Otherwise, high clouds from upstream convection will spill into
Western New York this morning.

After this, the forecast gets considerably more tricky. 00Z guidance
does a poor job initializing ongoing convection across the Central
Great Lakes with thunderstorms extending further south than model
consensus. It appears a mid-level wave along the leading edge of 700-
850mb warm air advection is providing the focus for this convection.
This features is shown by guidance and it is forecast to track into
Western New York late this afternoon, and weaken as it crosses the
cwa tonight. The HRRR appears to have the best handle on this, so
the forecast will heavily weight the HRRR through late afternoon,
then gradually blend to a model consensus for tonight. This keeps
the region dry through mid-afternoon with increasing chances for
showers and thunderstorms in far western areas late afternoon.
Temperatures will continue to be above normal, with highs in the mid
80s to around 90 in most areas with lower 80s across the North

This wave will move across the region tonight, with most guidance
suggesting activity along this boundary will weaken tonight. The 00Z
ECMWF is a notable exception, while the extended HRRR falls in line
with most other high resolution guidance. There is low forecast
confidence with chance POPS focusing on this mid-level wave as it
moves across Western New York from west to east tonight. It will be
another warm night, especially across the lake plains where an
increasing downslope SSW flow should keep temperatures from falling
below the mid 70s.


Monday our region will lie within a warm sector of a storm system,
with a warm front draped across CNY, and a cold front nearing from
the west. Aloft a shortwave over the central Great Lakes region will
be tracking eastward across northern U.S. and southern Canada.

There may be a few showers and rumbles of thunder early Monday
morning, this as a warm front completes its passage across the CWA.
Behind the front daytime heating will send instability values
upwards. As the upper level shortwave nears us from the west there
will be mid level height falls, and increasing mid level lapse
rates. There will also be a good amount of moisture as drier air
will not arrive till later in the day Monday and Monday night. This
will allow for PWATs to climb north of 1.5 inches.

There will be a concern for some of these thunderstorms to become
severe through the day Monday. Bulk shear values will be greater to
the northern portions of the CWA, which will be closer to the upper
level shortwave, with shear magnitudes of 35 to 40 knots. This
should be enough to support a few clusters of thunderstorms Monday,
with damaging wind gusts the greatest threat. WBZ in the 9 to 11k
foot range will be favorable for hail, and while not the greatest
threat there will be potential for some hail development within
stronger thunderstorms. Will go ahead and insert some enhanced
wording into the grids, for gusty winds and small hail...which will
line up well with SPC`s forecast of our region within a marginal
risk for severe thunderstorms.

Ahead of the cold front Monday a strong push of southwest winds over
Lake Erie will bring a stabilizing lake airmass across Metro
Buffalo. This will likely limit any shower and thunderstorm
development immediately downwind of Lake Erie by late morning, with
sunshine and a gusty SW wind instead likely through the afternoon.
Winds may gust upwards to 30 to 35 mph Monday afternoon across Metro

It will be muggy Monday as dewpoint values will rise into the lower
70s ahead of the cold front. Air temperatures will be very warm as
well with afternoon readings in the mid 80s to lower 90s. This will
bring apparent temperatures into the mid 90s south of Lake Ontario,
and through the Genesee Valley and Finger Lakes region.

The cold front will sweep across the region Monday afternoon with
scattered thunderstorms. There may be a few lingering storms early
Monday evening towards eastern zones, otherwise we should be drying
out behind the cold front. Overnight lows Monday night will drop
back into the 60s. Tuesday behind the cold front shall be dry with
air temperatures still above normal for afternoon highs. High
temperatures will reach into the low to mid 80s.

Continued dry Tuesday night as surface high pressure from the
central Great Lakes region advances eastward. Northwest flow ahead
of this high pressure should hold humidity levels comfortable with
dewpoints remaining in the mid 50s to around 60.


The pattern has the potential to become at least a little more
active from late week into the first half of next weekend. The
expansive mid/upper level ridge which has dominated the central and
eastern CONUS will be knocked back as the longwave pattern buckles
across North America, with a western ridge and eastern trough
pattern becoming established by next weekend. The developing
longwave trough in the Great Lakes and Northeast states will be
carved out by several mid level shortwaves, each of which will bring
a period of large scale ascent and increased deep layer moisture to
our region.

Looking at the details, the first relatively weak trough will
approach the Great Lakes Thursday afternoon and evening. This system
may touch off a few widely scattered showers and thunderstorms with
sparse coverage. Models begin to diverge on the timing details of
the finer scale features by Friday and Saturday, but most
operational and ensemble guidance show a more significant mid level
trough and associated surface wave moving through the Ohio Valley
and eastern Great Lakes either Friday or Saturday, with a better
chance of somewhat more widespread showers and thunderstorms.

Temperatures will continue to run hot through Thursday, with 850mb
temps of around +18C supporting highs around 90 at lower elevations
away from the lakeshores. More clouds and showers will bring
temperatures back closer to average by Friday and Saturday.


High pressure will remain across the region through this morning.
This will provide mainly VFR conditions, with fog the only concern
this morning. The best chance for this is at ART with a narrow temp-
dew point spread and additional radiational cooling expected through
daybreak. Fog is also possible at JHW, but with high clouds
spreading in have hedged more optimistic than guidance.

Convection across the Central Great Lakes region is roughly focused
along a mid-level wave which is forecast to gradually shift towards
Western New York later today. This should weaken considerably, with
activity expected to be sparse by the time the wave reaches late
this afternoon and into tonight. Expect mainly VFR conditions tonight
outside of a few showers or thunderstorms as this moves through.


Monday...Mainly VFR with scattered showers/thunderstorms and associated
brief MVFR/IFR.
Monday night...Mainly VFR with a chance of showers and thunderstorms
east of Lake Ontario in the evening.
Tuesday and Wednesday...VFR.
Thursday...Mainly VFR with a chance of showers and thunderstorms.


Generally quiet conditions should persist across Lakes Erie and
Ontario today. A weak trough/cold front will cross the region
tonight and Monday which will bring a chance of showers and
thunderstorms. Freshening southwesterlies out ahead of the front
will likely bring a period of advisory-worthy winds and waves to the
eastern end of Lake Erie Monday, before winds and waves diminish
Monday night. After that, we should see tranquil conditions return
to the lakes for much of the remaining week as a weak pressure
gradient will be in place across the region.





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