FXUS61 KBUF 271058

Area Forecast Discussion
National Weather Service Buffalo NY
658 AM EDT Sat May 27 2017

Weak high pressure will cross the Lower Great Lakes to start this
Memorial Day weekend...so generally fair weather can be expected
through at least Sunday morning. Conditions will then deteriorate
Sunday afternoon as an approaching warm front will present the
threat for some showers and thunderstorms for the western counties.
The unsettled weather will become more widespread Sunday night when
a cold front will push across the region.


While weak high pressure moving across the Lower Great Lakes will
encourage the return of fair dry weather today...we will have a
wealth of leftover cloud cover to deal into at least the midday
hours. The reason for the slow return of any sunshine will be three
fold. Winds to help remove our low level moisture will remain very
weak...a distinct subsidence inversion around 7k ft will help to
keep the moisture trapped in the low levels...and there will be lack
of significant drying upstream. That being said...there should be
enough diurnally induced mixing to help poke some holes in the cloud
cover for the midday and afternoon so that we should be able to at
least experience a little sun after two days of gloomy weather.

Also adding to the cloud cover over the Southern Tier will be some
blow off from a weakening convective complex over northeast Ohio/
western Pennsylvania. Its not out of the question that could even be
a morning shower or two over the Southern Tier from this dying

Temperatures today will climb well into the 60s...with some lower
70s possible in some of the Southern Tier valleys or in the Genesee

As the weak surface high moves east across New England tonight... a
progressive mid level ridge will ease across our forecast area. This
will provide us with fair weather and more pronounced clearing. The
mercury tonight will generally settle into the lower 50s...with some
40s possible east of Lake Ontario.


During the first 24 hours of this period...yet another in a series
of closed upper level lows will dig from the Canadian Prairies into
the Upper Great Lakes...with an associated broad surface reflection
tracking from Illinois to the Ontario-Quebec border. In the process...
this system will push a warm front across our region between late
Sunday and Sunday evening...before swinging its trailing cold front
into far western New York later Sunday night.

Over the past two days...all models have continued to trend slower
and slower with the arrival of this next system...with the 27/00z
suite of guidance no exception. As a result...Sunday continues to
look progressively better for outdoor activities...with all areas now
appearing likely to remain rain free through at least mid afternoon...
before the aforementioned warm front brings slowly increasing chances of
convection to areas from the Genesee Valley west late Sunday afternoon.
Owing to the slower arrival of the warm front and its attendant cloud
cover and convection...there will also be a greater window for sunshine
and consequently better daytime heating. In tandem with 850 mb temps
warming to between +10C and +14C...this should be enough for most areas
to see highs in the mid to upper 70s...with a few of our normally
warmer spots potentially reaching the 80 degree mark.

As we move into Sunday night...the combination of continued warm air
advection across our region...increasing height falls aloft...and the
arrival of the above mentioned surface boundaries will provide ample
lift in the presence of an increasingly moist airmass (PWATs climbing
to around 1.5 inches)...resulting in widespread showers developing
across our region from west to east. There will also likely be some
embedded thunderstorms as well given the presence of some weak to
modest instability...though the relatively limited nature of the
instability and the unfavorable nocturnal timing should result in any
storms remaining on the tame side. Otherwise we can expect a rather
mild night...with the general warm air advection regime and southeasterly
to southerly surface flow both helping to keep temps from falling below
the upper 50s to lower 60s...resulting in overnight lows that will be
some 10 to 15 degrees above late May normals.

By sunrise Monday the trailing cold front will be situated over far
western New York...with this feature then pushing east across the
rest of our region through the midday/early afternoon hours. Fairly
widespread showers and embedded storms out ahead of the front will
tend to diminish pretty sharply from west to east as strong drying
and subsidence overspread the region in its wake...with the much drier
air and increasing lake shadowing only allowing for a low chance of
some secondary lake breeze-driven afternoon convection across interior
portions of the Southern Tier and Finger Lakes. Otherwise...weak to
modest cool air advection in the wake of the cold front will only
result in a small drop in temps from Sunday...with most areas seeing
highs range in the lower to mid 70s. The coolest overall readings
will be found northeast of the lakes...where a stiffening southwesterly
breeze off the cooler lake waters will be in place.

Monday night the closed upper level low will continue to slowly meander
its way across Ontario Province...while maintaining a general cyclonic
flow across our region. Any leftover diurnally-driven convection should
come to a fairly quick end during the evening hours...with the above
mentioned cyclonic flow then supporting a general low chance of some
widely scattered light showers overnight. Temperature-wise...cooler
air continuing to filter into our region will allow overnight lows
to settle back into the lower to mid 50s.


Moving on into the extended portion of the forecast...the massive upper
level low will only slowly meander its way across the Great Lakes and
southeastern Canada through the middle portions of next week...with its
associated pool of cooler air slowly filtering across our region. This
will result in highs in the upper 60s to lower 70s Tuesday pulling back
into the mid to upper 60s for both Wednesday and Thursday...while
nighttime lows gradually settle back to between 45 and 50.

With respect to precipitation potential...numerous shortwave impulses
rotating around the upper low will result in frequent opportunities
for showers across our region...with some embedded thunderstorms also
possible Tuesday and Wednesday with diurnal heating/destabilization of
our slowly cooling airmass. While timing such waves remains a difficult
exercise this far in advance...in general precipitation chances should
tend to peak each afternoon across areas away from the lakes owing to
diurnal heating...before diminishing each night with nocturnal
stabilization of the boundary layer.

Late in the period...the upper level low will begin to lift out into
the Canadian Maritimes...while allowing surface high pressure to build
eastward into our region. This should finally bring a return to drier
weather to close out the work week...though temperatures will probably
remain a bit below normal with highs remaining confined to the mid
and upper 60s on Friday.


A deep cyclonic flow of very moist air will keep the region shrouded
under clouds into at least the midday hours with spotty MVFR cigs
gradually lifting to VFR levels. VFR weather with light winds can
then be anticipated this afternoon through tonight...as weak high
pressure will pass over the region.

Sunday...VFR but with a chance of afternoon showers and
thunderstorms west of the Genesee Valley.
Sunday night...Areas of MVFR with fairly widespread showers and
Monday...Mainly VFR but with leftover showers and thunderstorms...
mainly over the Finger Lakes and Eastern Lake Ontario regions.
Tuesday and Wednesday...Mainly VFR with scattered afternoon showers
and thunderstorms.


Weak high pressure will cross the Lower Great Lakes today and early
tonight. This will maintain a weak surface pressure gradient that
will keep light winds in place along with negligible waves.

As a warm front approaches on Sunday...east to southeast winds will
freshen a bit...but will remain well below small craft advisory
levels. The only ill effects will be choppy conditions on the
western end of Lake Ontario...and particularly near the mouth of the
Niagara River where the winds will oppose the outflow from the
river. The main concern though will come from thunderstorm activity
that could develop during the afternoon. This threat will be
greatest over Lake Erie.

Showers and thunderstorms will become widespread over the Lower
Great Lakes Sunday night...gradually spreading across the St
Lawrence Valley late Sunday night and Monday. Meanwhile...winds will
continue to freshen Sunday night as they veer to the south in the
wake of the passing of a pair of frontal boundaries...including the
aforementioned warm front.

For Memorial Day...the showers and thunderstorms will push east...
clearing Lake Erie by mid morning and eventually clearing Lake
Ontario by mid afternoon. Moderate southwesterlies will be found on
both lakes...but winds and waves should remain below small craft
advisory levels.





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