Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 292313
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
713 PM EDT THU SEP 29 2016

.SYNOPSIS...
An upper level low, cut off from the main jet stream, will meander
over the Ohio Valley through the end of the week and upcoming
weekend. This low will keep unsettled weather through the weekend
with a few rounds of scattered showers from time to time.
Temperatures during the day will run near average, with above
average temperatures at night, thanks to the abundant cloud cover
expected.

&&

.NEAR TERM /THROUGH FRIDAY/...
Radar imagery early this evening showing a few areas of scattered
showers across the Genesee Valley and Western NY. The most
concentrated area of rain through mid evening will move northwest
across the Niagara Frontier. Elsewhere, any showers will be brief
and widely scattered.

Overnight, the vertically stacked cutoff low over the Ohio Valley
will complete a cyclonic loop back to the west, which will in
effect carry deeper moisture in our region westward. This will allow
showers to diminish in coverage, with areas from Rochester and
Canandaigua northeastward becoming dry overnight. Most of the
rain will end along the corridor from Dansville to the Niagara
Frontier as well, although a few more stray isolated showers cannot
be ruled out in this area overnight. The western Southern Tier will
remain close enough to the deeper moisture plume rotating around the
mid level closed low to keep more showers going overnight, with a
few subtle mid level vorticity maxima and associated small scale
speed maxes bringing periods of enhanced ascent and convergence.
With this in mind, have maintained likely POPS overnight for the
western Southern Tier.

Throughout the next 24 hours, the one area that will remain dry with
any certainty is the North Country, which will remain far enough
displaced from the upper low and moisture axis to remain dry through
the period.

Regarding temperatures, cool temperatures this afternoon will give
way to mild temperatures overnight as abundant cloud cover will
significantly dampen diurnal temperature ranges, with lows only
running a few degrees cooler than current readings, in the low to
mid 50s. Highs Friday will range from the mid 60s in the north to
the mid 50s in the higher terrain along the PA border, where it will
remain relatively cloudy and wet.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
A stalled upper-level low over the Ohio Valley will continue to
dominated the weather across the forecast area through the weekend
bringing a stretch of cloudy and mild weather with occasional
showers.

Looking at the day-to-day details, the stacked low pressure system
will be located near the Indiana/Kentucky state line Friday evening
and will slowly drift northward into central Indiana through the day
Saturday. Consequently, this will keep the mild and moist
southeasterly flow from the Mid Atlantic into the forecast area open
through the day Saturday. Friday night should feature little if any
precipitation across the region as there will be a lack of any
distinctive forcing mechanisms. Have maintained a low-chance (20 to
30%) PoP for any isolated to widely scattered showers across western
NY Friday night given the moist airmass, cyclonic flow and upper-
level divergence. Otherwise, it looks like the better chance for
more numerous showers across the forecast area will come during the
day on Saturday. As the stacked low pressure system inches
northward, a shortwave trough will rotate quickly from Tennessee
Saturday morning to Lake Erie by Saturday afternoon. This should act
to increase low-level jet and moisture advection from the Mid
Atlantic into the forecast area. Thus have raised PoPs for the
daytime on Saturday, mainly across WNY and the northern Finger Lakes
to the 60% to 70% range with lower chances (40% to 50%) in the North
Country, which will be farther removed from the forcing. This
however still does not mean Saturday will be a complete washout
across WNY and the northern Finger Lakes, but should certainly be
damp at times. Would also not rule out some rumbles of thunder
across WNY Saturday afternoon and evening with the passage of the
shortwave and attendant increased mid-level lapse rates.

By Saturday night, the aforementioned shortwave will quickly track
north of the forecast area and the stacked low pressure system
should track to the thumb of Michigan. This will result in a low-
level frontal passage as winds shift from southeast to southwest
across the region. This will direct the better Mid Atlantic moisture
into the North Country while some slightly drier air will make it in
across western NY. Thus precipitation chances should decrease
accordingly across WNY Saturday night, and have thus lower PoPs to
around 30% there, while the North Country may see scattered showers
overnight with a PoP around 50%.

On Sunday into Sunday night, the stacked low will track slowly from
the thumb of Michigan to southern Ontario. Given the broad cyclonic
flow, attendant increased mid-level lapse rates, and moisture have
maintained at least low-chance (30%) PoPs across WNY while rain
chances increase (50% to 60%) in the North Country where the deeper
layer moisture and vorticity advection will be located. Some rumbles
of thunder will be possible especially from the northern Finger
Lakes to eastern Lake Ontario region where the steeper mid-level
lapse rates and forcing from the upper-low will be co-located.

Total precipitation amounts through this period won`t be very high
but should be beneficial, likely ranging between a third and three
quarters of an inch. Temperatures for the weekend will remain mild
with daytime highs in the mid 60s to low 70s and nighttime lows
mainly in the 50s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
The cut-off upper level low will slowly shift eastward Monday from
Lake Ontario to somewhere over New England with some slight model
differences in its exact position by Tuesday morning. This track
will continue the threat for scattered showers and potentially some
rumbles of thunder across western and north-central NY as lift
produced by the center of the low passing over New York continues to
interact with Atlantic moisture wrapping into and around the
circulation.

A return to dry and seasonable weather with a trend toward party to
mostly clear skies is then expected by Monday night through Thursday
day as the remnants of the upper low shift off the coast of New
England and a 500mb ridge builds over the eastern States. This
ridging is in response to a deep trough pushing across the western
states then becoming negatively tilted while lifting across the
Plains states. Daytime temperatures through the entire long term
period will exhibit day to day warming M/U 60s Monday warming to
U60s/L70s by midweek. Overnight temps will drop into the M/U 40s
across the interior locations with L/M 50s near the lake shores each
night.

Looking further out toward the end of next week we will be keeping a
close eye on model trends with Hurricane Matthew. 29/12z runs
continue to show wide variations in the northward push and track.
The faster GFS moves some of the outer bands of the system across
our forecast area on Friday while the slower ECMWF shifts a cold
front associated with the central US trough across western and
central NY.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
Scattered to occasionally numerous showers will continue across
Western NY this evening as Atlantic moisture continues to wrap
around an upper level low over the Ohio Valley. Showers will end
across most of the area overnight, with the exception of the
Southern Tier where closer proximity to deeper moisture will
maintain periods of showers. On Friday showers across the Southern
Tier in the morning will advance slowly north across the rest of the
area during the midday and afternoon as a disturbance wrapping
around the upper level low moves north across the region. VSBY
tonight and Friday will be VFR most of the time, but any of the
heavier showers will produce local/brief MVFR/IFR VSBY.

As far as CIGS go, widespread MVFR across Western NY with IFR across
higher terrain will continue through the evening hours. Overnight
CIGS will improve to VFR across the lower elevations, with areas of
MVFR and IFR lingering across the higher terrain near the PA state
line into Friday morning. Low level moisture will then increase again
from south to north Friday afternoon and evening, with CIGS
deteriorating to MVFR along the corridor from KBUF-KIAG-KROC during
the evening.

The North Country will miss all of the rain and lower CIGS, with VFR
dominating near KART.

Outlook...
Saturday through Monday...Areas of MVFR with scattered showers.
Tuesday...Mainly VFR.

&&

.MARINE...
A persistent upper level low will continue to spin across the
Ohio Valley over the next few days. Meanwhile strong high pressure
will remain parked over Quebec, with the pressure gradient between
the two maintaining brisk easterly flow. This will continue to bring
small craft advisory conditions on the west 2/3 of Lake Ontario
through Friday night and potentially as late as Saturday before winds
veer to the south as the low finally shifts northeast towards Ontario
province. Easterly flow is not expected to be strong enough to
warrant SCA headlines for the nearshore Lake Erie waters and St.
Lawrence River, and these advisories have been dropped.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 AM EDT Saturday for LOZ042-043.

&&

$$

SYNOPSIS...HITCHCOCK/WOOD
NEAR TERM...HITCHCOCK/WOOD
SHORT TERM...CHURCH
LONG TERM...SMITH
AVIATION...HITCHCOCK
MARINE...HITCHCOCK/WOOD



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