Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251101
AFDBUF

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

.SYNOPSIS...
A storm system over Ohio early this morning will remain nearly
stationary through midday before drifting 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 western counties
to a half to three quarters of an inch for the Eastern Lake Ontario
region.

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 SUNDAY NIGHT/...
On Friday vertically stacked low pressure over southern New England
will meander its way eastward to a position just offshore of Nova
Scotia. On its backside...a cooler northwesterly flow and plenty of
wraparound moisture will continue to circulate across our region...
supporting mostly cloudy skies and scattered rain showers that will
only slowly diminish in coverage from west to east. Expect high
temps to mostly range in the lower half of the 60s...though some of
our higher elevations will probably not make it out of the upper
50s.

Friday night and Saturday weak surface-based ridging will slide
eastward into our region from the Central Great Lakes and Ohio
Valley...while shortwave ridging results in slowly rising heights
aloft. This should allow for mainly dry weather to prevail...though
a few more stray showers still cannot be totally ruled out Friday
night and Saturday morning. After a mostly cloudy Friday night...
the increased ridging and arrival of somewhat drier air should allow
for the return of at least some partial sunshine during the day
Saturday...which in concert with weak warm air advection should
allow high temps to mostly recover into the upper 60s and lower 70s.

Saturday night the aforementioned surface ridge will slide eastward
and out to sea...while another developing wave of low pressure makes
its way across the Ohio Valley...in association with the next upper
level low dropping southeastward from the Canadian Prairies. Expect
dry and quiet weather to prevail for a good chunk of the night...
before lower-end shower chances return to far western sections late
with the approach of the next system. Otherwise temperatures will be
remain seasonably mild...with lows ranging through the 50s.

Sunday and Sunday night conditions will turn more unsettled again as
the upper level low digs southeastward across the Great Lakes...
while its attendant broad surface reflection pushes northeastward
across our region. While the timing of this system appears to be at
least a little bit slower in the 00z/25 guidance suite...the
combination of falling heights and warm air advection on its front
flank should nonetheless eventually allow for another round of fairly
widespread showers across our region Sunday and Sunday night...with
diurnal destabilization also allowing for the possibility of some
embedded thunderstorms Sunday and Sunday evening. As for temperatures...
these will remain above average with highs in the lower to mid 70s
Sunday followed by lows in the mid to upper 50s Sunday night.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
Moving on into next week...it appears that our region will remain
under the influence of the large upper level low...which will only
slowly meander its way across the Great Lakes and adjoining portions
of southern Canada through midweek. Numerous shortwave impulses
rotating around the large cyclonic gyre aloft will result in frequent
opportunities for showers across our region...with some embedded
thunderstorms again not out of the question each day with diurnal
heating/destabilization of our slowly cooling airmass.

Temperature-wise...highs in the lower to mid 70s on Monday should
pull back to the mid to upper 60s by midweek as progressively cooler
air filters into our region...while nighttime lows gradually settle
back through the 50s.

&&

.AVIATION /11Z 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.

Cigs will deteriorate across all of the region during the course of
this morning...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.

Tonight...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...
A nearly stationary storm system over Ohio early this morning will
generate moderate to fresh easterlies on Lake Ontario for the bulk
of today. Given the extended fetch...this will lead to small craft
advisory conditions for the nearshore waters west of Sodus Bay...
including the mouth of the Niagara River. Meanwhile on Lake Erie...
the offshore flow will direct the highest waves in international
waters with a weaker surface pressure gradient preventing winds from
climbing past 15 knots.

Tonight...the pressure gradient will gradually weaken across the
Lower Great Lakes as the core of the mature storm system will pass
across Pennsylvania to the New England coast. This will allow winds
and waves to subside during the course of the night.

Weak high pressure will build across the Lower Great Lakes Friday
into Saturday. Initially...this will lead to winds that will
continue to back to the northwest...but that will remain below small
craft advisory levels. Light winds and negligible waves can then be
anticipated Friday night and Saturday.

&&

.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 until 2 AM EDT Friday for NYZ001>003.
     Beach Hazards Statement through this evening for NYZ001>003.
MARINE...Small Craft Advisory until 9 PM EDT this evening for LOZ030.
         Small Craft Advisory until 11 PM EDT this evening for
         LOZ043.
         Small Craft Advisory until 2 AM EDT Friday for LOZ042.

&&

$$

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



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