Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 242343

Area Forecast Discussion
National Weather Service Buffalo NY
743 PM EDT Wed May 24 2017

An upper level low will track across the region tonight and
tomorrow, spreading a period of rain late tonight and then through
Thursday across the region. This period will taper off to scattered
showers during the afternoon across Western New York, and then the
evening across the North Country. Temperatures will remain below
normal through Friday as the upper level low and trough pass


An upper level low across the Ohio Valley will gradually move
toward the region tonight. Several waves will pivot around this
low with the first just clipping the Niagara Frontier this
evening. Rain will be light with this, with dry boundary layer
air helping to evaporate some of this moisture before it reaches
the ground. Even so, a light shower or sprinkle is possible
across far Western New York.

The next (and more significant) wave rain will begin to spread
across WNY around midnight before reaching the North Country
late Thursday morning. Deep layer convergent lift from both the
leading edge of a 45 to 50 knot LLJ around 4K feet, and upper
level divergence from the left exit region of a 130 knot upper
level jet streaking along the eastern seaboard. This broad scale
lift ahead of the upper level low, within an environment with
PWAT values between 1.0 and 1.5 inches, will bring a period of
moderate rain across our region. As the LLJ carries northward
through the day Thursday, expect the main slug of rain to lift
northward towards Canada, leaving just spotty showers remaining
over the region during the afternoon and evening as the upper
level low tracks across the region.

Behind the upper level low Thursday night a westerly flow within an
inverted surface trough will bring scattered showers across the
region. Aloft there will still remain a trough, supporting the
showers. An upslope flow within a still saturated low level will
bring likely pops across the Chautauqua Ridge, and hills across SW
NYS. This lower saturated layer will also bring low clouds Thursday
night, of which some will produce patchy fog, mainly across the hill
tops of SW NYS.

Overall rainfall tonight through Thursday night will average around
an inch, slightly higher towards the Niagara Frontier where a
downslope SE flow slowing over northern Erie and Niagara County may
enhance rainfall totals, while slightly under an inch of rain is
expected across the North Country.

Temperatures at night will dip into the 50s, warmest tonight across
the lake plain where a southeast will maintain upper 50s. Highs
Thursday will remain below normal as the upper level low tracks
across the region, with temperatures rising into the lower to mid


Mid level low pushing through New England Friday. This will allow
shower activity to gradually diminish through the day, with only
some lingering shower activity in northwest upslope flow and wrap
around moisture. Friday will be a cool day with plenty of cloud
cover and scattered precipiation, with most highs in the upper 50s
to mid 60s.

Shortwave ridging should bring an end to the precipitation by early
Friday night. The shortwave ridge will crest across the forecast
during the day Saturday, providing for what should be a dry day for
Western and North-Central New York. Saturday will be a warmer day
under a weak warm air advection pattern and increased sunshine. Most
highs in the lower 70s.

Precipitation chances look to increase later Saturday night as upper
low level drops out of central Canada. The associated surface low
moves into the Ohio Valley by Sunday morning. Associated height
falls, forcing and moisture advection on the front flank of the
system will bring precipitation back into far western areas
beginning late Saturday night.


Precipitation chances look much more favorable on Sunday, as an
upper level trough 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 into the beginning of next
week. 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. Temperatures
will run in the upper 60s to low 70s Sunday into Monday. Cooler air
will filter into the region by Tuesday into Wednesday , as the axis
of the upper level trough begins to meander overhead.


Expect widespread VFR conditions for the start of the 00Z TAF
cycle, with mainly VFR conditions expected through the evening
hours. After this, rain will spread across the region ahead of
an upper level low, with CIGS lowering to MVFR (and IFR in
spots) as this rainfall persists and moistens the boundary
layer. The lowest conditions are likely to occur Thursday
morning with the steadiest rains and when the flow is ENE across
the area. This flow can result in IFR CIGS at BUF/IAG/ROC, but
only partially taps into upsloping which would be more
significant if the flow was NE instead of ENE. A period of IFR
conditions is also likely at JHW due to its higher elevation.

A modest improvement in CIGS is likely Thursday afternoon as
the steady rain tapers off. Even so, expect widespread MVFR
conditions with patchy IFR CIGS possible.

Thursday night and Friday...MVFR/IFR with scattered showers.
Saturday...Mainly VFR.
Sunday...MVFR/VFR with showers likely.
Monday...MVFR/VFR with a chance of showers.


As an upper level low tracks from the Lower Ohio Valley tonight
to near the eastern Great Lakes tomorrow, easterly winds will
increase more, to around 15 to 25 knots on the western end of
Lake Ontario. These winds will produce waves 3 to 6 feet on the
western shores, and will issue a Small Craft Advisory from the
Niagara River to Sodus Point for late tonight and through the
day Thursday.

As the upper level low crosses the lower lakes Thursday night the
winds and waves will diminish on both lakes.


A deepening low pressure system tracking out of the Ohio valley
will approach the lower Great Lakes over the next 12 to 24
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 6 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.
MARINE...Small Craft Advisory from 6 AM to 11 PM EDT Thursday for
         Small Craft Advisory from 6 AM Thursday to 2 AM EDT Friday
         for LOZ042.



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