Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 250637
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
237 AM EDT Thu May 25 2017

.SYNOPSIS...
A storm system over Ohio early this morning will remain nearly
stationary through midday before drifting to the east across
Pennsylvania. This will produce widespread rain across our area
through the midday hours...with some areas over the far western
counties picking up more than an inch of rain. While there may be
some scattered showers in the area on Friday...weak high pressure
will produce fair weather for Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As has been advertised for several days now...most of the region
will experience a soaking rain today. Rainfall amounts through this
evening are forecast to range from an inch over the far western
counties to a half to three quarters of an inch east of the Genesee
Valley.

The widespread rain can be attributed to a stacked area of low
pressure that...early this morning...was found over Ohio. While this
mature storm system will remain nearly stationary during the course
of the morning...it will push an occluded sfc front northward across
our forecast area. Deep lift associated with the combined forcing
from a 40kt easterly low level jet and the left exit region of a
125kt H25 jet will interact with a very moist environment to produce
a swath of moderate rain. The moisture laden airmass can be seen in
WV imagery early this morning...with a plume of sub tropical
moisture being directed northward along the eastern seaboard. While
the richest moisture will remain to our east...an axis of PWAT
values averaging 1.25 inches will accompany the strongest dynamics
through midday. This will support the rainfall amounts outlined
above.

As we push through the midday and into the afternoon...the storm
system will slowly move east across Pennsylvania while transferring
much of its upper level energy to the coast. Meanwhile...the
accompanying 40kt low level jet will propagate north across Ontario
and Quebec with the H25 jet axis pushing north across New England.
The removal of the deep source of lift will be accompanied by fairly
significant mid level drying in the wake of the surface occlusion...
so any rain this afternoon over the western counties will be showery
and spotty in nature.

Temperatures today will average some 5 to 10 deg below normal late
May values...as the mercury will top out in the low to mid 60s.
Relatively high humidity values will probably help to take some of
the edge off the cooler air this afternoon though.

Tonight...the mature storm will complete its reorganization off the
East Coast...while a deep cyclonic flow rich in low level moisture
will remain in place across our forecast area. This will keep
overcast and damp conditions in place...with weak shortwaves around
the periphery of the exiting storm generating some spotty light
showers. The most widespread pcpn tonight should be found east of
Lake Ontario where there will still be a fair amount of moisture in
the mid levels.

Temperatures tonight will settle into the low to mid 50s...which is
right where they should be for this time of year.

&&

.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 /07Z THURSDAY THROUGH MONDAY/...
Deteriorating conditions will be found across all of western and
north central New York today...as a nearly stationary storm system
over Ohio will spread steady rain across the region. The rain will
be accompanied by lowering cigs...which by daybreak will range from
IFR levels across the Southern Tier and MVFR for KBUF and KIAG...
to VFR levels from the Finger Lakes to the North Country.

Cigs will deteriorate across all of the region during the course of
the upcoming day...with IFR level cigs anticipated for most of the
taf sites by early afternoon. The exception will be east of Lake
Ontario where MVFR conditions will be in place. Meanwhile...the
widespread rain from the morning will taper off to scattered light
showers from south to north during the afternoon and evening.

For Thursday night...IFR to MVFR cigs are anticipated regionwide
with only the chance for some light showers.

Outlook...
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 later today...allowing waves to build to 3 to 6 ft
by the 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 this morning to 2 AM EDT
     Friday for NYZ001>003.
     Beach Hazards Statement from 8 AM EDT this morning through
     this evening for NYZ001>003.
MARINE...Small Craft Advisory from 6 AM this morning to 11 PM EDT this
         evening for LOZ043.
         Small Craft Advisory from 6 AM this morning to 2 AM EDT
         Friday for LOZ042.

&&

$$

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



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