Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 300736
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
336 AM EDT Tue May 30 2017

.SYNOPSIS...
A broad upper level low will meander across the region through the
rest of the week...bringing periodic opportunities for showers and
thunderstorms along with near to slightly below average temperatures.
Some of the storms could produce strong gusty winds and hail both
this afternoon and Wednesday afternoon...with the greatest potential
for the stronger storms found from interior portions of the Southern
Tier northeastward across the Finger Lakes and North Country.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 0730z...regional surface analysis shows broad low
pressure over northern Ontario Province...with an associated
secondary cold front draped southward across Lake Huron and
western Lake Erie. Out ahead of the front...scattered to
numerous showers and thunderstorms continue to develop across
nearby southern Ontario and Lake Erie...with the leading edge of
this activity currently working across extreme far western New
York.

Through the early morning hours the secondary front will continue
to slowly but steadily ease its way toward western New York...with
attendant shortwave energy and modest height falls spreading eastward
in a similar fashion. All of this should result in a continued uptick
in shower/thunderstorm coverage across areas from the Genesee Valley
westward...for which PoPs have been bumped all the way up to high
likely. While limited instability should keep any thunderstorms from
becoming all that strong...these will still be capable of some briefly
heavy downpours and brief/localized gusty winds. Further east across
the rest of the region - which will be further removed from the
encroaching frontal boundary - convective coverage should remain
considerably less through early this morning...though a few widely
scattered showers and storms will still be possible just about anywhere.

As today progresses...the secondary cold front will continue to slowly
push eastward across our region...reaching Central New York by the
end of the day. Concurrent with this...height falls will also continue
to overspread our region aloft...as a channelled mid level shortwave
impulse pushes into our region from the Central Great Lakes. With
renewed daytime heating leading to an increasingly unstable airmass
(CAPE values of 1000-1500 j/kg) out ahead of these features...it is
appearing increasingly likely that areas from about the Genesee Valley
eastward will see a round of stronger to potentially severe storms
between very late this morning and this afternoon...with 0-6 km bulk
shear values of 50-55 knots and relatively low (7-8 kft) freezing levels
supporting the potential for both strong gusty winds and hail.
With this in mind...SPC has upgraded the previous Marginal Risk
area for the above portions of our region to a Slight Risk of
severe storms...which looks very reasonable from this
perspective. On our end...we have added enhanced wording for
wind and hail (as well as locally heavy downpours) to the
forecast for the aforementioned areas for this afternoon...while
a mention of the severe threat continues within the HWO.

West of the Genesee Valley...the earlier timing of the frontal passage
will help to limit destabilization...and consequently just some "garden
variety" showers and storms are expected this morning across much of
the Niagara Frontier and portions of the Southern Tier closer to Lake
Erie...with these largely ending by midday/early afternoon as drier air
and subsidence arrives in the wake of the front...and strengthening lake
shadowing develops off Lake Erie. With respect to temperatures...
850 mb temps of +8C to +10C should allow for highs to range
from the upper 60s to mid 70s today...with the coolest temps
found across the North Country due to the aforementioned
convection...and the warmest readings found along the lake
plains from Niagara County over to about Rochester.

Tonight...any lingering showers/storms along our eastern periphery
should come to an end during the evening as the front moves east and
the atmosphere stabilizes...leaving behind quieter and mainly dry
weather for the second half of the night. With slightly cooler air
filtering in behind the front...overnight lows should mostly be in
the lower to mid 50s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
Well...I guess it could be worse. A high latitude omega block
featuring a persistent closed low over eastern Canada will keep a
deep cyclonic flow of conditionally unstable air over our region
during this period...and while there will be stretches of rain free
weather...this pattern will lend itself to supporting occasional
showers and thunderstorms. Meanwhile temperatures will average close
to...or just a bit below June 1st normals. Welcome to meteorological
summer! Now for the day to day details...

The persistent stacked low over northern Ontario will be in the
process of `reloading` and closing back off on Wednesday...while the
associated longwave trough will push across our forecast area. At
least one shortwave rounding the base of this transitional trough
will cross our region in the process...and this will combine with
low level convergence along a pronounced lake breeze boundary that
will push east from Lake Erie to generate midday and afternoon
thunderstorms east of a line from KART and KROC to KJHW. Some of the
storms could certainly get rather strong. SBCAPEs are forecast to
approach 1000 j/kg in the afternoon...and while this is not
particularly significant...the fact that the freezing level will
only be around 7000 ft is a bit of a concern. These ingredients are
conducive for storms that will have a higher probability of
producing small hail. There will also be 40 kts of bulk shear
(speed)...so there could be threat for some strong convective winds
as well. Will use some enhanced wording to mention gusty winds and
small hail with the likely pops. A higher chance for strong to
severe convection will be found further east across central New
York. Meanwhile...a well established lake breeze will shadow areas
from Lake Erie and the Niagara Frontier...to Rochester and beyond to
the Thousand Islands region. H85 temps averaging 6c will support max
temps that will generally be in the mid to upper 60s.

The introduction of somewhat drier air...low level ridging and most
importantly...nocturnal stabilization of the airmass will encourage
the convection to die off fairly quickly Wednesday evening. This
will leave fair weather for the remainder of the night with
temperatures falling to the lower 50s across the lake plains and 40s
anticipated across the Southern Tier and portions of the North
Country.

While a weakly cyclonic flow will still be in place over our region
on Thursday...high pressure nosing north from the Mid Atlantic
states will help to provide us with enjoyable...problem free
weather. Despite the wealth of sunshine though...it will still be on
the cool side of normal as we start the month of June. H85 temps
will still be in the vcnty of 6c...and like the day before...this
will lead to max temps in the mid to upper 60s.

Conditions will deteriorate late Thursday and Friday as the next
cold front will approach from the Upper Great Lakes. Showers and
scattered thunderstorms ahead of this front will become more
widespread during the course of the day...with the strongest forcing
coming late Friday afternoon when a 120 kt H25 jet will pass to our
north...placing our region under the right entrance region. As is
typically the case...it will be warmer ahead of this front on
Friday. H85 temps are forecast to climb to around 10c...so despite
the unsettled conditions...many areas should push to near 70 f.

While the cold front will push to our south Friday night...waves
along the front may keep it from advancing far enough for showers to
completely come to an end...especially across the Southern Tier
counties.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
Unfortunately...the forecast for the weekend into early next week
has turned decidedly more pessimistic. The operational ECMWF and a
fair number of GFS ensembles are now strongly suggesting that the
front from Friday/Friday night will stall across Pennsylvania...as
energy crossing the Canadian prairies will develop a fairly strong
wave along the frontal boundary back across the Upper Mississippi
Valley. This wave will then consolidate into a compact storm system
over the Great lakes region later in the weekend as the upper level
support likely evolves into yet another closed low.

The result of this updated scenario...
There will be some leftover showers across the Southern Tier counties
on Saturday with limited clearing elsewhere. Temperatures will top out
in the 60s for most areas.

Showers...or possibly even a period of steadier rain...will push north
across the region late Saturday night and Sunday as the aforementioned
surface low tracks east across Lake Erie.

As the stacked low drifts across our region Sunday night and MOnday...
the rain will become more showery.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Through the early morning hours...a secondary cold front will continue
to slowly but steadily ease its way toward western New York...resulting
in a continued uptick in shower/thunderstorm coverage across areas from
the Genesee Valley westward. While limited instability should keep any
thunderstorms from becoming all that strong...these will still be capable
of some locally gusty winds and brief/localized IFR/MVFR conditions in
heavy downpours. Further east across the rest of the region...convective
coverage should remain considerably less through early this morning with
VFR conditions generally continuing to prevail...though a few widely
scattered showers and storms will still be possible just about anywhere.

As today progresses...the secondary cold front will slowly push its way
eastward across our region and act as the primary focus for additional
showers and storms...particularly as daytime heating leads to increased
amounts of instability across central and eastern portions of the area
during the late morning and afternoon hours. It is appearing increasingly
likely that areas along and east of a rough KJHW-KROC axis will see a
round of stronger to potentially severe storms this afternoon...with these
capable of producing strong surface wind gusts...hail...and brief/localized
IFR to MVFR conditions. West of this axis...morning showers and storms
should tend to taper off through midday/early afternoon following the
passage of the front...with conditions improving to VFR by afternoon
under drier air and a developing Lake Erie lake shadow.

Tonight...any lingering showers/storms along our eastern periphery
should come to an end during the evening as the front moves east and
the atmosphere stabilizes...leaving behind mainly dry VFR conditions
for the second half of the night.

Outlook...
Wednesday through Saturday...Mainly VFR...with localized IFR/MVFR
possible in scattered to numerous showers and thunderstorms at times.

&&

.MARINE...
A secondary cold front will cross the region today...with another round
of showers and thunderstorms marking its passage...some of which could
be capable of strong wind gusts and hail across central and eastern
portions of Lake Ontario and portions of the Saint Lawrence River. In
the wake of the front...southwest winds will again freshen a bit across
the Lower Lakes region this afternoon...though at this point both winds
and waves are expected to remain below advisory levels.

During the middle and latter portions of the week a broad upper level
trough will continue to meander its way eastward across the region...while
maintaining a persistent general southwesterly to westerly flow across
Lakes Erie and Ontario. This said...at this point it appears that both
winds and waves will remain below advisory criteria.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JJR
MARINE...JJR



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