Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 221053

Area Forecast Discussion
National Weather Service Buffalo NY
653 AM EDT SUN MAY 22 2016

Scattered showers associated with a mid level trough will end by
midday for areas closer to the lakes, and by later this evening
across the higher terrain inland. High pressure will then bring a
return to dry weather for Monday and Tuesday with steadily warming
temperatures. A period of summer warmth will arrive for the second
half of the week along with higher humidity and a few scattered
showers and thunderstorms.


Radar imagery showing an area of steadier showers weakening and
shrinking in areal coverage across the Genesee Valley and western
Finger Lakes. These showers are within an axis of deformation on the
northwest periphery of a mid level circulation over north central
PA. Short term model guidance shows a region of mid level
deformation, upper level divergence, and 300-700mb Q-vector
convergence lingering in this area through the morning. The large
scale ascent will continue to support steadier showers through mid
morning from the Genesee Valley into the western Finger lakes, with
a few isolated showers at the far western end of the state.

Meanwhile the North Country will remain dry, being further removed
from deeper moisture and forcing associated with the mid level
circulation over PA. A weak surface cold front analyzed from the
Saint Lawrence Valley to the west end of Lake Ontario at 10Z will
drop south across the area early this morning and may also support a
few additional showers.

By this afternoon most of the large scale forcing for ascent will
exit the region and focus on the Mid Atlantic as the mid level
trough closes off and digs southward. Remaining moisture combined
with limited daytime heating will produce enough diurnal instability
to support a continuation of scattered showers into the afternoon
and evening, mainly across the higher terrain from the western
Southern Tier into the Finger Lakes and Tug Hill/western
Adirondacks. On the lake plains northerly flow will promote stable
lake shadows pushing inland during the afternoon and suppressing any
potential for diurnal showers, and even allowing for some breaks of

There will be very little airmass change behind the weak cold front,
so expect similar highs to yesterday with upper 60s across much of
western and central NY, and lower 70s across the Saint Lawrence
Valley. The higher terrain of the Southern Tier will again be cooler
with thicker/lower cloud cover yielding highs in the lower 60s. A
northerly flow will keep the lakeshores much cooler, with highs in
the upper 50s within a few miles of the Lake Erie and Lake Ontario

Any remaining diurnal showers across the higher terrain will taper
off by mid to late evening as the boundary layer stabilizes. The mid
level low will continue to move south across the Mid Atlantic
states, allowing deeper moisture to slowly pull away from our
region. This will allow for a slow clearing trend from north to
south overnight with the lake plains clearing first, and higher
terrain last. Expect lows in the lower 50s on the lake plains with
some mid 40s in the cooler Southern Tier Valleys and Tug Hill region.


Early next week will feature pleasant spring weather with fair
weather and above normal temperatures. A closed upper level low
across the Mid-Atlantic states on Monday will gradually lift into
the Gulf of Maine by Tuesday night which will promote a surface
ridge to the west of this which will build across our region. An
ensemble of model guidance is in good agreement on this pattern
which provides above average forecast confidence during the period.

The majority of model guidance keeps our area dry throughout the
entire short term period, however the 00Z GFS/12Z ECMWF forecast
some light and diurnally driven QPF across far Eastern portions.
Model guidance is often too high with afternoon dew points. With
BUFKIT soundings showing very small values of `thin` CAPE lower dew
points would effectively suppress any showers so will leave out any
mention at this time. Near lakes an afternoon lake breeze should
suppress most diurnal cloud cover resulting in sunny skies and
virtually no chance for any precipitation through Tuesday. A weak
vorticity ripple from upstream convection will cross the ridge late
Tuesday night with a slight chance for showers late.

Temperatures will be above normal during the period with daytime
highs mainly in the 70s on Monday and Tuesday. The exception will be
the immediate lakeshores which will only reach the 60s. A
Northwesterly gradient flow on Monday will help suppress the typical
Southwest lake breeze at Buffalo and Watertown. On Tuesday there
will be minimal gradient flow with typical afternoon lake breezes
expected. In general expect slightly greater diurnal temperature
ranges than consensus temperature guidance due to the dry regime.


An upper level ridge will remain across the region resulting in a
summer-like pattern with a prolonged period of above normal
temperatures. As the upper ridge axis approaches the region during
midweek, so will the opportunity for late day and evening
convection. There will be an opportunity for late day through
evening thunderstorms on Wednesday and Wednesday night as a couple
ripples of vorticity move across the upper ridge, from southern
Ontario to the North Country and spreading into western NY during
Wednesday evening and night.

Subtle shortwaves will continue to encounter the ridge axis with
periodic chances for mainly diurnally driven showers and
thunderstorms. These shortwaves will be hard to time with POPs
reflecting a diurnal trend. Otherwise a consensus of 00Z runs of the
GFS/GGEM/ECMWF suggests the best chance for showers or thunderstorms
is Thursday even though they cannot be ruled out any day. These
would tend to develop along and inland of the lake breeze.

The ridge will strengthen with consensus 850 hPa temperatures
gradually warming from from +14C to +17C during the period. Highs on
Wednesday will range from the mid 70s to lower 80s. These will
gradually warm to the upper 70s to mid 80s by Saturday corresponding
to the warmest air aloft. A weak flow will result in typical
afternoon lake breeze development which will cool areas near the
lakeshores, including the cities of Buffalo and Watertown.

The weak southerly flow will also build the humidity through this
period with uncomfortable levels reached by the end of the week. Dew
points will climb into the lower 60s which will also provide a
rough proxy for overnight lows.


An area of steadier showers will continue to weaken through mid
morning across portions of the western Finger Lakes, Genesee Valley,
and inland areas of the western Southern Tier including areas from
KROC to KDSV to KELZ. Most of the rain will be light, so CIGS/VSBY
will remain VFR across most of the area through this morning. The
one exception will be found across the western Southern Tier where
patchy fog and stratus in more abundant low level moisture will
produce some local MVFR/IFR conditions.

Later this morning any patchy fog and low stratus across the western
Southern Tier will burn off. This will leave VFR to prevail for the
bulk of the area, although some MVFR CIGS may linger across the
higher terrain of the Southern Tier as surface flow becomes
northerly and allows for a period of upslope flow. Expect some
additional scattered showers as a mid level trough slowly crosses
the region, with most of the showers found across the higher terrain
well inland from the lakes from late morning through the afternoon.

Monday through Wednesday...VFR.
Thursday...Mainly VFR with a chance of showers and thunderstorms.


A weak cold front will cross the lower lakes this morning with winds
becoming northerly at around 10 knots behind the front today. High
pressure will then build into the central and eastern Great Lakes
Monday and Tuesday with light winds and flat wave action. Relatively
light winds will continue for the second half of the week, although
there will be a few scattered thunderstorms as summer warmth and
humidity build into the region.





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