Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 240814
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
414 AM EDT Wed May 24 2017

.SYNOPSIS...
A weak disturbance may bring a few showers to the western Southern
Tier and possibly the North Country today...with fair and dry weather
otherwise continuing across the remainder of the region. Low pressure
will then produce a round of widespread rainfall as it works into our
region from the Ohio Valley later tonight and Thursday...with unsettled
conditions then persisting through Friday as this system slowly departs
off to our east.

&&

.NEAR TERM /THROUGH TONIGHT/...
During the course of today...a digging upper level low will gradually
settle across the mid-Mississippi Valley...with its attendant broad
surface low slowly getting better organized while drifting eastward
across the Tennessee and Ohio Valleys. Out ahead of this system...a
lead weak mid level shortwave will rotate northward into portions of
the Southern Tier this morning...then northwestward across Lake Erie
this afternoon. Coupled with increasing moisture...this feature should
produce some scattered light showers across portions of the Southern
Tier between this morning and early to mid this afternoon...with the
greatest chances for these focused across Chautauqua county. With diurnal
heating and the development of some weak to modest instability...a few
additional showers may also become possible across the higher terrain of
the North Country this afternoon...with the remainder of the area otherwise
remaining dry under a mix of mid and high clouds and some partial sunshine.
With 850 mb temps expected to run from about +9C to +11C...afternoon highs
should largely range from the lower 70s across the Southern Tier to the
mid and upper 70s elsewhere...though areas along the south shore of Lake
Ontario will be cooler thanks to an east to east-northeasterly flow off
the cooler lake waters.

Tonight the upper level low will make its way eastward across the Ohio
Valley...while becoming increasingly vertically stacked over its low
level counterpart. As the eastern flank of this system nears our region...
increasing moisture transport and large-scale forcing will result in
widespread rain developing/spreading northeastward across areas south of
Lake Ontario overnight...while the North Country remains more removed from
the deeper moisture/lift and thus largely dry. As for temps...we can expect
another mild night with lows ranging from the lower 50s across interior
portions of the Southern Tier/North Country to the mid and upper 50s
elsewhere.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The deep closed low over the middle Mississippi Valley Wednesday
evening will track slowly across the Central Appalachians Thursday
to the Gulf of Maine by Friday afternoon. A complex surface low
occlusion over the Ohio Valley Wednesday night will lift northeast
as secondary development takes place from the Mid Atlantic to the
New England coast by Friday. Despite some model differences in
track/placement of these feature there is agreement that the
Wednesday night into Thursday night time frame will be a wet one.
Plenty of deep layer moisture and forcing in the front flank of the
of the system will generate a solid period of soaking rain, with
most areas receiving a general half inch to an inch of rainfall.
While forcing with the incoming system is impressive, instability is
not. Therefore, thunder chances remain rather subdued.

Precipitation will transition to showers Thursday night into Friday,
as the low moves overhead and past the forecast area, though
scattered to numerous showers should linger thorugh much of the day
on Friday, thanks to continued troughing across the area, coupled
with wrap-around moisture. Shortwave ridging moving into the region
in the wake of the departing low pressure system Friday night should
put an end to the showers.

This will be a cool period as plenty of cloud cover and rainy
conditions will help to suppress temperatures with highs both
Thursday and Friday likely not getting out of the 60s, with lows in
the 50s during the nights.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Upper level ridging crossing the region should result in generally
dry conditions on Saturday, though moisture moving through the top
of the low-amplitude ridge just might generate a shower or two, so
have low slight chance pops in place for now. A northern stream wave
diving across the upper Midwest and Great Lakes out of Canada will
bring the next likely round of showers to the forecast area on
Sunday.

The location and timing of the various vorticity maxima
rotating around the upper low, in addition to additional upper level
energy moving thorugh the longwave trough that will be re-
established across the east will determine the specific timing of
rounds of showers as we move into next week, and it is too far out
to pinpoint these kinds of details. However, given aforementioned
longwave troughing becoming re-established across the Great Lakes
and Northeast, suffice it to say that the coming week will trend
towards the cool and showery.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Expect VFR conditions to prevail through today...with some scattered
light showers crossing the Southern Tier between this morning and early
to mid afternoon...and a few additional showers also becoming possible
across the North Country in the afternoon. Otherwise the remainder of
the area should remain dry under a mix of mid and high cloud cover.

Tonight low pressure will slowly make its way eastward across the Ohio
Valley. As this system approaches our region...clouds will thicken and
lower from southwest to northeast...with rain overspreading most areas
south of Lake Ontario between midnight and early Thursday morning. As a
result...VFR conditions will gradually deteriorate to MVFR across most
areas south of Lake Ontario...while ceilings gradually lower through the
VFR range across the North Country.

Outlook...
Thursday...Deterioration to MVFR/IFR in rain.
Friday...MVFR/IFR with scattered to numerous showers.
Saturday...Mainly VFR.
Sunday...MVFR/VFR with showers likely.

&&

.MARINE...
A general low level easterly to east-southeasterly flow will be on
a gradual increase through the course of today and tonight. This
said...conditions should remain below small craft advisory levels
through tonight.

On Thursday...east-northeasterlies will strengthen a bit more on
Lake Ontario as low pressure over the Ohio Valley pushes eastward
into Pennsylvania. This will likely lead to a period of advisory-
worthy winds and waves on the western half of Lake Ontario...while
lower wind speeds and waves continue to prevail elsewhere.

&&

.TIDES/COASTAL FLOODING...
ENE winds will increase somewhat Wednesday and Wednesday evening
on Lake Ontario into the 12-15 knot range, generating waves
averaging about 2 feet on the west end of the lake.

Low pressure will then move from the Ohio Valley to western Lake
Erie later Wednesday night and Thursday. Meanwhile weak high
pressure will remain across Quebec and northern New England. The
ageostrophic component between the two systems will support
increasing ENE winds on Thursday for Lake Ontario, with winds
possibly reaching 20 knots for a good part of the day. The
ageostrophic component also tends to force the winds to have a
little more NE component than model forecasts. With this in
mind, it appears another higher impact day of lakeshore flooding
and shoreline erosion is probable along the south shore of Lake
Ontario west of the Genesee River. A lakeshore flood watch has
been issued for Thursday for the Lake Ontario shore of Niagara,
Orleans, and Monroe counties.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 6 AM Thursday to 2 AM EDT Friday
     for NYZ001>003.
MARINE...None.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...TMA
LONG TERM...CHURCH
AVIATION...JJR
MARINE...JJR
TIDES/COASTAL FLOODING...HITCHCOCK



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