Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 250254
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1054 PM EDT Wed May 24 2017

.SYNOPSIS...
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
through.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
An upper level low across the Ohio Valley will gradually move
toward the region overnight. An initial wave from this system
just clipped the Niagara Frontier earlier this evening. The
next (and more significant) wave of rain will continue to spread
across WNY overnight with high forecast confidence in rain
south and west of Rochester. 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. This is supported by a
consensus of model guidance and radar trends.

As the LLJ carries northward through the day Thursday, expect
the main slug of rain to into the North Country Thursday morning
and then northward into Canada in the afternoon. This will leave
just spotty showers across Western New York Thursday afternoon
and early 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
60s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
VFR conditions in place late this evening will gradually
deteriorate overnight as rain overspreads the region. CIGS will
lower 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 in a NE flow rather than an ENE one. 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.

Outlook...
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.

&&

.MARINE...
Low pressure will slowly track from he Ohio Valley to near the
lower Great Lakes and Western Pennsylvania through Thursday.
This will result in an increasing ENE flow to around 15 to 25
knots on the western end of Lake Ontario. These are not ideal
for building waves in the nearshores, but should be ample for
waves to reach 3 to 6 feet on the western U.S. shores, with the
highest waves in Canadian waters. There is a small craft
advisory in effect for western nearshores of Lake Ontario.

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

&&

.TIDES/COASTAL FLOODING...
A deepening low pressure system will move closer with an
increasing ENE flow on Lake Ontario. Winds will increase 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.
A Lakeshore Flood Warning 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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 8 AM Thursday to 2 AM EDT Friday
     for NYZ001>003.
     Beach Hazards Statement from 8 AM EDT Thursday through
     Thursday evening for NYZ001>003.
MARINE...Small Craft Advisory from 6 AM to 11 PM EDT Thursday for
         LOZ043.
         Small Craft Advisory from 6 AM Thursday to 2 AM EDT Friday
         for LOZ042.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...APFFEL/THOMAS
SHORT TERM...THOMAS
LONG TERM...CHURCH/WOOD
AVIATION...APFFEL
MARINE...APFFEL/THOMAS
TIDES/COASTAL FLOODING...HITCHCOCK/WOOD/APFFEL


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