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Area forecast discussion
National Weather Service Buffalo New York
703 am EDT Fri Aug 23 2019

Synopsis...
aside from a few diurnally driven showers this afternoon and a Few
Lake enhanced showers south of Lake Ontario tonight into Saturday
morning, a comfortably cool and dry weather pattern will be over
western and central New York right through the weekend. There will
be some typical inland valley fog during the overnight and early
morning hours. The next chance of rain along with warmer weather
won't return until next Tuesday or Wednesday.

&&

Near term /through tonight/...
aside from leftover valley fog across the southern tier and Black
River valleys through mid morning, high pressure will continue to
build across the area from the northwest. Expect some morning sunshine,
followed by fairly rapid upslope induced inland stratocumulus.
Appears now that diurnal heating and just enough low level moisture
will combine with some added lift courtesy of a fairly sharp upper
trough just upstream, to possibly produce a few light
showers/sprinkles this afternoon across the higher terrain south of
Lake Ontario. Otherwise, expect a dry and comfortably cool August
day with a mix of sun and clouds elsewhere, with the most sunshine
seen across the lower terrain and along the lakeshores. High
temperatures will range from the upper 60s across the higher terrain
to the lower 70s elsewhere.

Tonight, a weak surface trough will push south across the lower
Great Lakes, with a reinforcing push of cooler air right behind it.
Winds will strengthen some and shift to north-northeasterly while
850mb temps drop a couple more degrees, bottoming out around +5c
overnight. Meanwhile, a fairly potent shortwave rotating through the
base of the mean upper trough will push south over the area. Despite
low level anticyclonic flow and dry air in the low levels, may be
just enough lake enhanced moisture/instability, that when combined
with the potent shortwave energy aloft, may produce a few showers
downwind of Lake Ontario on a north-northeasterly fetch. Any showers
would be mainly focused across the higher terrain of the western
Finger Lakes and the interior southern tier. Otherwise, expect some
lake clouds to develop south of Lake Ontario, and the typical valley
fog to form where skies remain clear to partly cloudy late tonight.
Expect a dry and quite cool night elsewhere. Temperatures will
indeed be chilly by latter August standards. Lows will bottom out in
the low to mid 40s across the higher terrain, with lower to mid 50s
elsewhere.

&&

Short term /Saturday through Monday night/...
additional shortwave trough drifts across region on Saturday. This
wave along with residual low-level moisture and continual cool air
aloft and resulting over-water instability (h85 temps as low as
+4c in the morning) will allow for the any isolated light lake
effect showers that may develop tonight to persist into at least
mid morning Saturday before diminishing. Otherwise, the
residual moisture with daytime heating should result in
expansion of fair weather stratocu and cu late morning into the
afternoon especially over the southern tier and east of Lake
Ontario thanks to upslope NNE flow. High pressure at sfc then
begins to build in during the afternoon which will diminish NE
winds closer to Lake Ontario. Should see high temps pretty
similar to values today, upper 60s higher terrain of southern
tier and east of lk Ontario, with low 70s elsewhere. On Saturday
night, center of high pressure settles across southern Quebec
to New Brunswick and Prince Edward Island. Light winds and dry
air tied to the high will allow another chilly night with some
fog for the valleys of the southern tier and for areas east of
Lake Ontario while mostly clear skies and temps in the mid 50s
should cover things elsewhere.

Into Sunday, as shortwave trough that drops across Saturday, slowly
exits off the East Coast will begin to see light low-level return
flow develop. Looks like we'll gain a couple degrees at 850 mb compared
to Saturday, so should see aftn highs on Sunday rebound into the low
70s in the southern tier and east of Lake Ontario, to the upper 70s
elsewhere.

After a mostly clear and still seasonably cool night on Sunday
night, developing upper troughing from south central Canada to the
western Great Lakes will aid in sfc troughing from northern plains
to the western Great Lakes. Monday should stay dry with a bit of
increase in mid to high clouds. By Monday night, there are
indications that shortwave drifting along base of primary trough
could be enhanced by convection and make its way toward the lower
Great Lakes overnight. Did not go as aggressive as GFS is in pushing
this feature into western NY, but have included low-end chances.
Better chances, at least through daybreak Tuesday, will probably
stay west closer to axis of elevated instability and stronger low-
level jet and upper-level jet. We'll solidly be within a stronger
SSE return low-level flow Monday into Monday night as high heads out
over the Atlantic and sfc troughing moves over western Great Lakes.
Majority of area will see highs upper 70s to near 80f on Monday
while lows on Monday night will stay warm in the 50s to lower 60s
with the stronger return flow. Only exception will be east of Lake
Ontario where readings could dip into toward 50f. Return flow could
turn gusty as pressure gradient tightens and pressure falls develop
north of region. Increased gusts some, especially closer to Lake
Ontario and Lake Erie.

&&

Long term /Tuesday through Thursday/...
broad longwave trough over central Canada will expand across the
Great Lakes and eastern Canada. Sfc flow will increase from the SSW
into the lower Great Lakes Tuesday into Wednesday as main sfc low
spins over northern Ontario toward the southern shore of Hudson Bay
sending a warm front across the lower Great Lakes into New England.
Expect temps to rise above normal with upper 70s to low 80s a good
Landing point for now.

Details remain murky about convection Tuesday with main issue
focusing on how expansive convection will be along warm front. GFS
continues to be more aggressive in eastward push of showers and
thunderstorms on Tuesday, showing qpf as far east as areas east of
Lake Ontario, while European model (ecmwf) and Canadian keep most of activity on
Tuesday over western New York closer to approaching strong SW-NE oriented
upper jet ahead of broad trough and also closer to axis of 1.75 to
2.0 inch pwats. Convective shortwave(s) riding into New York ahead of main
trough will have to be watched as it could boost pops earlier, but
going to go with slower idea from European model (ecmwf) and Canadian given strength
of incoming trough which will tend to amplify mid-upper level flow
and keep most widespread precip closer to larger scale features.

As initial cold front moves through Tuesday night into Wednesday,
should be a greater chance of seeing widespread convection. Though
mid to upper level winds will be brisk from the SW, any convection
will have potential to produce heavy rain as pwats reach 2 inches
and wbzero heights rise toward 14kft. Though it is pretty far out to
hone in on the details, seems that greatest chances for showers and
storms on Wednesday will be over our eastern areas toward Finger
Lakes and east of Lake Ontario as cold front arrives there during
the afternoon during peak heating/Max instability. If that timing
holds and sufficient instability is present, there would be at least
some risk of stronger storms given strong wind fields present.

High pressure is then forecast to build across the region later
Wednesday into Thursday behind the cold front. This will encourage
the return of fair weather along with more comfortable humidity
levels.

&&

Aviation /11z Friday through Tuesday/...
clear to partly cloudy skies will remain over the majority of our
area through the first part of the morning. Any River Valley fog
will burn off by mid morning.

Cold air aloft will promote efficient low level cloud development
today, especially across inland areas, where low VFR ceilings (isolated
MVFR interior southern tier this afternoon) will form late this
morning into this afternoon. Otherwise, expect VFR conditions with
few to scattered amounts of cloud coverage over the remainder of the
area today.

Low level clouds will scatter out during the evening with the loss
of daytime heating, leaving behind mainly VFR conditions across
the area through the late Evening. Lake induced clouds will
then form across areas south off Lake Ontario after midnight,
with low VFR ceilings possible across the Genesee Valley, Finger
Lakes and southern tier for the second half of tonight. Valley
fog will also be possible across the typical valley areas where
cloud coverage remains clear to partly cloudy.

Outlook...

Saturday through Monday...mainly VFR with nothing more than southern
tier valley fog producing local IFR conditions each late night and
morning.
Tuesday...MVFR possible with showers and thunderstorms.

&&

Marine...
expect some light chop on both lakes today before winds briefly
freshen out of the north-northeast later tonight through early
Saturday morning. This will bring another round of choppy conditions
on Lake Ontario, but again it looks like conditions will stay below
Small Craft Advisory criteria. Gradient flow will relax some later
Saturday afternoon into Sunday as high pressure builds closer the
lakes. This will promote light winds and diminishing waves.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...jm

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