Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240221

Area Forecast Discussion
National Weather Service Buffalo NY
1021 PM EDT Fri Jun 23 2017

Scattered showers associated with a cold front will end from
northwest to southeast overnight. An upper level trough will
then become established over the weekend with a brief shower or
thunderstorm possible both days, but the majority of the time
will be rain free. A better chance of showers will arrive Monday
as the trough sharpens over the Great Lakes. Temperatures will
drop to below normal over the weekend and early next week.


Radar imagery shows scattered showers along and just ahead of a
cold front which is entering Western New York this evening. The
steadiest showers, with a few embedded thunderstorms are across
the Eastern Lake Ontario region. All of this activity will end
from northwest to southeast overnight. Some of these showers
are still heavy, but moving quickly with additional rainfall
amounts expected to be less than a quarter inch.

The lake plains should see some clearing late tonight as a
push of dry air arrives out of Canada and subsidence increases
in the wake of the cold front. Low clouds will likely persist
across the higher terrain of the Southern Tier and Tug Hill
region in moist low level upslope flow. Cold advection will
increase behind the cold front and allow lows to drop to drop
into the lower 60s in most locations by daybreak.

On Saturday a weak surface ridge will build into the Ohio Valley and
eastern Great Lakes. Meanwhile, a broad/weak trough will become
established in the mid/upper levels across the Great Lakes. A mid
level shortwave will move through the mean longwave trough and cross
the eastern Great Lakes during the afternoon. Meanwhile, mesoscale
convergence zones will setup across our region as enhanced gradient
onshore SW flow develops downstream of Lake Erie, with more westerly
flow across Lake Ontario. This should allow a well defined surface
convergence zone to develop from Niagara Falls east to Rochester,
eventually building all the way east to Central NY. The convergence
along this feature combined with the weak large scale ascent from
the mid level shortwave may support a few widely scattered afternoon
showers and thunderstorms, mainly in the corridor between the NYS
Thruway and south shore of Lake Ontario. An isolated afternoon
thunderstorm also cannot be ruled out across the higher terrain from
the interior Southern Tier into the Finger Lakes. It will be less
humid on Saturday, with highs in the mid 70s in most locations, and
a few upper 70s from the Genesee Valley into Central NY.


Saturday night...The upper level pattern will feature a longwave
trough centered over the Great Lakes region with an upstream
intermountain ridge.  At the surface...a weak ridge will be in
place.  Thus any leftover scattered evening convection on lake
breezes, primarily S of Lake Ontario, should quickly dissipate
during the evening with a dry and cool remainder of the night - low
should be mostly in the 50s.

Sunday and Sunday night...Sunday should start out nice, but expect
the eventual development of scattered to possibly numerous showers
and thunderstorms developing on lake breeze boundaries.  Additional
development may form along a weak cold front moving SE into WNY
during the afternoon. Similar to Saturday night, expect convection
to dissipate fairly quickly with the loss of daytime heating.

Monday...The upstream cold pool aloft corresponding to the upper
level trough will pass overhead.  Strong insolation and resultant
mixing, together with plenty of moisture and cool air aloft without
any signs of a cap will result in fairly quick development of
showers and some thunderstorms, although CAPE values will be
unimpressive with a skinny profile seen in point forecast soundings.
Still, with a freezing level somewhere near 8000-10000ft, cells
could easily support small hail. As noted earlier, there may
even be a hint of a lake response with a dry adabatic lapse
rates over the 65-70+F waters. Once again, expect showers to be
on the decrease during the evening with little or no showers


Tuesday a final upper level shortwave will round a longwave trough
over the Northeast, bringing additional chances for showers and
thunderstorms through the day.

The upper level trough will push eastward Tuesday night and
Wednesday, with just a small chance for a lingering shower across
the North Country. Surface high pressure will drift across the
eastern US, south of our region Wednesday, providing for some
clearing skies. Southerly winds behind this surface high Thursday
will bring increasing temperatures, along with an increase in
humidity levels. A shortwave rippling across the northern US may
trigger a few showers and thunderstorms later Thursday and Friday,
though timing at this point remains a bit uncertain.

Temperatures under the upper level trough Tuesday and Wednesday will
remain below normal. Southerly winds Thursday and Friday should push
temperatures into the upper 70s to lower 80s across the region.


Scattered showers will linger through the remainder of the
evening hours, but should be done by 06Z. There will be areas of
low cigs and fog just ahead of the front, but these will be
localized and patchy. These are likely to last longest at
JHW/ART. Expect improving conditions behind the front as drier
boundary layer air moves in.

On Saturday a weak/broad mid level trough will become established
across the Great Lakes. While most of the time will be rain free, a
few isolated showers and thunderstorms may develop along lake breeze
boundaries, most notably along the KIAG to KROC corridor. Any
lingering IFR CIGS across higher terrain will improve, leaving VFR
to prevail Saturday outside of any isolated thunderstorms.

Sunday through Tuesday...Mainly VFR with a chance of
mainly afternoon showers and isolated thunderstorms.
Wednesday...Mainly VFR.


Funneling has helped enhance the southwesterly flow on Lake Erie
just enough to require a brief and low-end Small Craft headline
southwest of Dunkirk. 3 to 5 foot waves will diminish late this
evening. Winds will pick up on Lake Ontario ahead of the front
later this evening, but without the funneling of the Chautauqua
Ridge these are not expected to get as strong.

West to southwest winds are likely to increase on Sunday on Lake
Erie as the pressure gradient increases ahead of a secondary cold
front crossing the eastern Great Lakes. The increase in winds is
less certain on Lake Ontario with considerable model differences
showing up. At least moderate westerlies will continue with choppy
conditions, and there is a chance of stronger Small Craft Advisory
conditions if the stronger GFS based guidance verifies.


MARINE...Small Craft Advisory until 2 AM EDT Saturday for LEZ040.



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