Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252353

Area Forecast Discussion
National Weather Service Buffalo NY
753 PM EDT THU AUG 25 2016

A mid-level trough and weak cold front will bring scattered showers
and thunderstorms across the region through the first half of
tonight before rain tapers off from west to east overnight. High
pressure will then build into the region for Friday and Saturday
with a return to dry weather while temperatures remain above normal.
A weak cold front may produce a few isolated showers and
thunderstorms late Sunday before high pressure returns for early
next week.


Radar imagery showing scattered to numerous showers and
thunderstorms increasing in coverage across western NY early this
evening as ascent from an approaching mid level trough interacts
with moderate instability, and also increasing convergence with the
approach of a pre-frontal trough, and the remaining convergence from
the remnants of the Lake Erie lake breeze boundary. These showers
and scattered storms will move east towards the Genesee Valley and
western Finger Lakes through mid evening.

Given the increase in coverage of showers and storms over the last
hour or so, and well defined mid level trough apparent on water
vapor imagery, have increased POPS a little more into the high
likely range for much of the area from western NY into the Finger
Lakes for this evening.

With regard to any severe weather potential, deep layer shear has
increased to around 30-35 knots this evening with the approaching
front and storm motions will be a quick 30 to 40 knots off to the
east. The best mix of instability, shear and forcing appears to move
across northeast OH and northwest PA, however our western Southern
Tier will be on the edge of these prime conditions and thus would
not rule out a few strong to severe thunderstorms producing strong
to damaging wind gusts. A few storms over the past hour have briefly
developed strong elevated cores, but quickly weakened after reaching
marginal severe limits given the relatively weak shear environment.
As these storms evolve eastward toward the Genesee Valley and Finger
Lakes region they should slowly weaken with time as we get later
into the evening and lose instability.

Overnight, showers will diminish in coverage and track eastward out
of the forecast area. With plentiful low-level moisture remaining in
place behind the frontal passage, especially across western NY
(particularly Buffalo) which received rainfall last night, in
addition to any new rainfall this evening, expect patchy to areas of
fog to develop overnight. Temperatures will be slow to fall
overnight only reaching the upper 60s to low 70s by morning.

A few showers may linger in the North Country by Friday morning with
mainly dry but overcast conditions behind the frontal boundary for
the rest of the forecast area. We will then see clearing from
northwest to southeast from mid to late morning through the early
afternoon as drier air and subsidence behind the wave accompany
diurnal mixing to help skies clear out. High temperatures won`t be
dramatically cooler, in the low to mid 80s, but it will be less
humid than today as dew points fall into the low 60s with a few
upper 50s readings in the higher terrain.


Shortwave ridging building over the region will allow surface high
pressure to build over Western and North Central New York at the
beginning of the period. Larger-scale subsidence will keep the area
dry with mainly clear skies expected Friday night and mostly sunny
conditions for Saturday. The mostly clear skies will allow for
cooler temperatures Friday night with lows in the upper 50s to lower
60s, perhaps a few lower to mid 50s in the normally cooler locations
across the Southern Tier and east of Lake Ontario. Seasonal
temperatures in the upper 70 to mid 80s expected for Saturday.

A weak shortwave riding the periphery of the upper high centered
over the southern U.S. will lift up though Michigan into southern
Ontario Saturday night into Sunday. This should allow for an
increase in mid/high level cloudiness, with the latest model
forecast soundings keeping lower levels dry.

A warm front will lift through the eastern Great Lakes Sunday in
advance of a stronger upper trough working through the Upper Midwest
and western Great Lakes. This will bring the risk for a few
diurnally driven showers and thunderstorms for inland areas Sunday
afternoon. Sunday should be the hottest day of the period with 850
mb temperatures nearing +20C. This will translate into highs in the
upper 80s across the higher terrain to the lower 90s across the lake

By Sunday night the approaching upper trough, favorable right
entrance region forcing, and associated cold front working through
will expand the risk for convection across the entire area.


As we move into the new week, the aforementioned upper trough and
associated cold front cross the forecast area Monday. We will see
chances for showers and thunderstorms taper off from west to east
through the day as nominally cooler but considerably drier air
filters in from Canada and surface high pressure moves overhead.

After Monday night, a decent amount of uncertainity creeps into the
forecast, as the next shortwave upstream scrapes along the top of
the mid-level ridging parked over the Ohio Valley and Mid-Atlantic
states. Global models differ on the strength both of this ridging
and the shortwave and the associated surface cold front...but in
either case given the prevailing WNW flow across the Great Lakes,
this feature will not have a lot of moisture to work with and as
such will stick with just a slight chance of showers for Tuesday.
The slight chance of showers forecast will continue into Wednesday,
as global models once again suggest potential for showers, but for
very different reasons, with the ECMWF suggesting lingering showers
along the slower cold front, while the GFS is quicker to swing a
warm front northwards towards the area by midweek.

Regarding temperatures, with the cool front moving through Sunday
night/Monday, we should see readings drop back closer to normal on
Monday, with highs in the lower 80s. However, with a generally flat
upper level pattern in place across the country and a jet stream
solidly confined to north of the border for the foreseeable future,
temperatures are likely to remain above average well into next week,
with highs in the low to mid 80s and lows in the low to mid 60s, or
around 5 degrees above average, through much of the week.


Scattered to numerous showers and thunderstorms across Western NY
this evening will move east across the Finger Lakes towards Central
NY through the first half of the night. Conditions will be mainly
VFR, but any of the heavier showers will produce brief/local MVFR
and IFR conditions. Later tonight the showers and scattered
thunderstorms will taper off and end from west to east as the mid
level disturbance moves east of the area.

Behind the rainfall, model guidance suggests a significant amount of
low level moisture will be left behind. As surface winds become
light, expect fog and low stratus to become more widespread from 06Z-
12Z across Western NY, especially where heavier rainfall occurred
today. This will produce areas of IFR VSBY and CIGS, which may last
into the morning push at KJHW and KBUF.

The fog and low stratus will burn off by mid morning Friday, with
skies clearing across the lake plains first, and higher terrain by
midday. This will leave VFR to prevail for the afternoon.


Friday night thru Sunday...Mainly VFR.
Monday... Mainly VFR with a chance of showers and thunderstorms.


A cold front will ease its way across the Lower Lakes tonight. This
feature will bring a few rounds of scattered showers and
thunderstorms through tonight, which may produce locally higher
winds and waves.

After this high pressure will build across the region with
fair weather and fine boating conditions expected for Friday and





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