Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 291812

Area Forecast Discussion
National Weather Service Buffalo NY
212 PM EDT FRI JUL 29 2016

Isolated showers and thunderstorms will be possible in the Southern
Tier this afternoon, near a weak stalled frontal boundary just to
the south across Pennsylvania and northern Ohio. Otherwise, it
should be quiet and dry today with seasonable temperatures. Weak
high pressure on Saturday should limit shower activity to near the
Pennsylvania state line. The chances for scattered showers and
thunderstorms increase again Saturday night through Sunday night as
a broad trough crosses the region.


Much of the forecast area is experiencing broad northerly anti-
cyclonic flow around high pressure centered over western Ontario and
the Arrowhead of Minnesota. This will help to moderate temperatures
across a good portion of the forecast area today, with most areas
topping out in the low to mid 80s. There is enough low-level
moisture hanging around that we should see a transition from
generally sunny skies this morning to partly to mostly cloudy skies
this afternoon, particularly across the higher terrain south and
east of Lake Ontario. In addition, a weak frontal boundary stalled
out near the NY/PA border should serve to aid in development of a
few isolated showers and thunderstorms in the western Southern
Tier this afternoon.

Tonight, surface high pressure will continue to nose into the region
from the north, with light northeast winds keeping a fetch of drier
air into the region. Overnight temperatures will be pleasant with
lows in the mid 60s near the lakes to the upper 50s in interior
valleys. Rain chances will increase toward the southwest corner of
the state by daybreak Saturday as a broad trough approaches the Ohio


A broad mid level trough will move from northern Indiana on Saturday
to Lake Erie Saturday night, then to western and central NY on
Sunday. Meanwhile at the surface a weak/diffuse area of low pressure
will ripple out of the Ohio Valley and eastward across Pennsylvania.
This system will bring some chances of beneficial rain over the
weekend, although the slow moving and diffuse nature of large scale
ascent will make timing and placement of more organized rainfall

On Saturday the first wave of deeper moisture will spread from
western NY into central NY. Forcing for ascent will be weak, with
just a subtle mid level shortwave and little in the way of enhanced
low/mid level flow. The best juxtaposition of forcing and moisture
will cross the Southern Tier where the majority of the scattered
showers will be found, with afternoon instability near the PA state
line also supporting a few scattered thunderstorms. Farther north,
expect only isolated showers from the Niagara Frontier eastward
across the Genesee Valley and central NY. The increase in cloud
cover will keep temperatures down somewhat, with lower 80s at lower
elevations and upper 70s on the hills.

The first half of Saturday night our region will be between waves,
with many areas becoming mainly dry. Scattered showers will linger
across the Southern Tier where deeper moisture and weak low/mid
level deformation will remain.

Late Saturday night and Sunday the mid level trough will slowly
cross the region, with several periods of DPVA supporting more
robust large scale ascent. A broad low/mid level deformation axis
will develop from Lake Erie to eastern NY to the north of the weak
surface low moving through PA, organizing deep layer moisture and
convergence. There continues to be some minor differences in the
details of this evolution amongst various operational models, but
enough confidence is there in the overall pattern to support
increasing POPS into the likely range in most areas Sunday. Some
limited instability will develop by afternoon, supporting scattered
thunderstorms as well. This system has potential to bring some
beneficial rain to the region, although the heavier amounts are
likely to remain unevenly distributed and tied to areas of
convection. The clouds and showers will keep temperatures down,
with upper 70s at lower elevations and mid 70s higher terrain.

Sunday night the mid level trough will meander slowly east into
eastern NY and western New England, while the surface low moves to
eastern PA and southeast NY. More organized showers and a few
scattered thunderstorms will focus on the eastern Lake Ontario
region overnight, with showers slowly tapering off from west to east
across the remainder of the area as better forcing and moisture
shift eastward.


During this period...surface-based ridging initially draped across
the Central Great Lakes will gradually push eastward and crest
across our region Tuesday and Tuesday night...before drifting off
the Atlantic coastline Wednesday and Thursday. Meanwhile aloft...
initial low-amplitude troughing will give way to a building upper
level ridge by the end of the period.

A few showers may linger on Monday across central NY and the North
Country as the slow moving mid/upper level low drifts east across
New England. High pressure will then build into the lower Great
Lakes Monday night and Tuesday with a return to dry weather. This
high will drift to the east coast and stall Wednesday and Thursday,
and remain in close enough proximity to keep our area dry.

Temperatures will steadily warm through the period as mid level
heights rise and southwesterly return flow becomes established by
midweek. Expect highs by Wednesday and Thursday to reach the mid to
upper 80s, with some potential for lower 90s if the warmer GFS based
solutions verify.


VFR conditions will persist through the next 24 hours. A few
disorganized showers and an isolated thunderstorm will be possible
across the Southern Tier this afternoon with activity tapering off
around sundown. Mid-level cigs will move in from the west later
tonight as an upper level trough approaches the region. This trough
will bring a chance of showers, with a few thunderstorms also
possible, to the forecast area on Saturday from 15Z onwards.
Activity should be mainly confined to the Southern Tier, in the
vicinity of a stalled frontal boundary.


Saturday Night through Monday...Mainly VFR with a chance of showers
and thunderstorms.
Tuesday and Wednesday...VFR.


Pressure rises and weak cold advection behind a frontal boundary
pushing south through NY state will help freshen northeasterly winds
on the lakes through this morning. Lake Ontario in particular will
see winds to around 20 knots and waves building to around 3 to 5
feet, prompting small craft advisories through early afternoon. By
this afternoon winds and waves will subside as high pressure builds
into the region.

Look ahead through the weekend, fairly persistent northeasterly winds
will remain in place as high pressure remains centered north of the
region and a few waves of low pressure track to our south. Winds and
wave Saturday should remain just below small craft level, while a
Sunday may see winds and waves meet small craft conditions.





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