Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241004

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

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.


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 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


Steady rain will continue to spread east across the forecast area on
Thursday, as a vertically stacked low tracks from the Ohio valley
across the lower Great Lakes, en route to the Bay of Fundy, which it
should reach by Friday evening. Favorable upper level dynamics,
coupled with robust advection of Atlantic moisture across the region
on east-southeasterly flow will result in a solid soaking, with many
areas seeing upwards of an inch of rainfall from Wednesday evening
through the end of the day on Thursday. The steady rainfall of the
first half of the day should give way to more showery precipitation
by the afternoon across most areas, perhaps with the exception of
the St. Lawrence valley, as the low center moves overhead and the
main axis of moisture advection shifts away to the northeast.

Showers will linger through Thursday night, as the low continues to
track across the forecast area, with a gradual diminishment in
activity from west to east as we move through the day on Friday and
the low moves off into the Gulf of Maine, with only lingering upper
level troughing and vestiges of wrap-around moisture to support any
showers by the time we get to Friday evening. Shortwave ridging
should spell the end of virtually all of any remaining activity
Friday night.

Regarding temperatures, the abundant cloud cover associated with the
low pressure system will keep readings on the cool side Thursday, in
spite of a decent warm push ahead of the low. Look for highs in the
low to mid 60s. Plentiful moisture will limit temperature falls
Thursday night, with lows in the low to mid 50s. Friday and Friday
night will be near copies of Thursday, as slightly cooler air wraps
into the region behind the departing low.


Shortwave ridging will crest across the forecast area on Saturday,
providing for what should be a dry day for Western and North-Central
New York. However, given weak warm advection/isentropic uplift and
the presence of a multitude of weak impulses aloft making their way
through the low-amplitude upper-level flow regime, cannot completely
rule out an isolated shower or two.

Precipitation chances look much more favorable on Sunday, as upper
level energy over the central Rockies phases with a potent shortwave
dropping out of Saskatchewan, resulting in yet another broad low
pressure system that will move across the Great Lakes during the
latter half of the weekend. Falling heights and strong isentropic
uplift on the eastern flank of the approaching low should provide
for another widespread soaking rain Sunday, with showers once again
lingering through Monday and Tuesday as the large system
meanders across the region, with multiple upper level impulses
passing overhead. Strong warm advection ahead of this system
should push temperatures into the 70s Saturday, with upper 60s
to low 70s Sunday into Monday. Cooler air will filter into the
region by Tuesday, as the axis of the upper level trough begins
to move overhead.


Expect VFR conditions to prevail 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 this 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.

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


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.


A deepening low pressure system tracking out of the Ohio valley
will approach the lower Great Lakes over the next 24 to 36
hours. As this low moves closer, northeasterly flow on Lake
Ontario will freshen, with winds increasing to 15 to 25 knots on
Thursday, allowing waves to build to 3 to 5 ft by Thursday
afternoon. Given the high lake levels, this is expected to
generate lakeshore flooding from Monroe county west to the
Niagara River, with additional shoreline erosion likely. As
such, a Lakeshore Flood Warning has been issued and is in effect
from Thursday morning through Thursday evening.

The higher wave action and associated flooding risk should be
relatively short-lived, however. The low will move over head
Western New York by Thursday evening, resulting in sharply
diminishing winds, with waves subsiding shortly thereafter. A
baggy pressure gradient on the back side of the departing low
means that while northwesterly flow behind the low should
generate some choppy conditions Friday along the southern shores
of Lake Ontario, waves should remain in the 1-2 foot range, and
additional flooding issues are not expected.


NY...Lakeshore Flood Warning from 6 AM Thursday to 2 AM EDT Friday
     for NYZ001>003.



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