Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 271447

Area Forecast Discussion
National Weather Service Buffalo NY
1047 AM EDT Sat May 27 2017

Weak high pressure will cross the Lower Great Lakes to start this
Memorial Day 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.


Clouds continue to hound the forecast area this morning as moisture
remains trapped underneath a subsidence inversion, with additional
cloud cover being contributed by the remnant cloud debris from
dissipated convection passing to our south across PA. Latest visible
imagery does show some erosion occurring in the stratus layer to our
west and northwest...however GOES-16 imagery shows stratus is
quickly being replaced with rapidly developing stratocu where
clearing is occurring, most notably across NW PA.

With the above in mind, still expect that we will see denser cloud
cover continue to diminish, with some peeks of sunshine this
afternoon.  However, the mix of sun and clouds will most definitely
tilt more towards the cloudy end of the spectrum as we move through
the afternoon. As a result, have backed off on the temperature
forecast by a few degrees, going with low to mid 60s across most

We should see some clearing tonight, as upper level ridging moves
overhead and drier air in the mid-levels moves into the region. In
addition, with the loss of diurnal heating, afternoon stratocu
should dissipate. However, given lingering low level moisture,
should expected clearing materialize, we may see areas of fog
develop late tonight. Look for temperatures to fall into the lower
50s overnight, with upper 40s in the typically cooler North Country.


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 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.


IFR cigs have finally lifted into MVFR range this morning, low level
moisture is starting to mix out somewhat. Satellite imagery
indicates some clearing along the edges of the stratus layer, and we
should see this stratus layer continue to lift and eventually
scatter out this afternoon, towards 18Z. However, enough moisture
lingers that any clearing will result in the rapid development of
VFR/MVFR stratocu this afternoon, with cigs expected to persist
across most locations.

Expect clearing to take place tonight, with upper level ridging
moving overhead and somewhat drier air moving across the area.
However, low-level enough moisture should linger across the region
that, should expected clearing occur, fog development will be

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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