Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 232109

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

Occasional showers and scattered thunderstorms associated with a
cold front will continue through this evening before ending 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 showing numerous areas of showers crossing the region
this afternoon as several weak convectively augmented vorticity
maxima and associated small low level speed maxes cross the area,
bringing periods of enhanced ascent and moisture convergence. This
will continue to be the case through the late afternoon and early
evening, with a few rounds of showers expected in most locations.
There is been very little thunder so far given the extensive cloud
cover and showers limiting destabilization. There may be some
opportunity for limited instability to develop late this afternoon
with a few breaks in the showers, and this may support a few widely
scattered thunderstorms. PWAT is near 2 inches, so any storms that
develop may produce brief heavy downpours. Severe weather risk is
minimal given the anemic CAPE and poor lapse rates.

Showers and widely scattered thunderstorms will continue into this
evening along the pre-frontal trough and any remaining small scale
mid level perturbations. The rain will then end from northwest to
southeast overnight as the surface cold front crosses the area. 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

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 late.


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.


Periods of showers and a few widely scattered thunderstorms will
continue late this afternoon and evening ahead of a cold front
moving through the central Great Lakes. Some of the heavier
showers will produce areas of MVFR VSBY, with local IFR in the
heaviest downpours.

The showers and scattered thunderstorms will end from northwest to
southeast overnight with the passage of the cold front. There
may be a period of lower conditions (IFR or lower) just ahead
of the front when there will be lots of low level moisture.
These are likely to last longest at JHW, but may also briefly
impact BUF/IAG/ART through this evening.

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.
Thursday...Mainly VFR with a chance of a shower or thunderstorm.


Moderate west to southwest winds will develop on Lakes Erie and
Ontario overnight and Saturday in the wake of a cold front crossing
the area. This will bring choppy conditions with waves averaging 2-4
feet at the east end of both lakes, but conditions are expected to
remain just below Small Craft Advisory levels.

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.





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