Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 281023

Area Forecast Discussion
National Weather Service Buffalo NY
623 AM EDT Sun May 28 2017

Quiet and dry weather will continue to prevail through this morning...
before an approaching low pressure system brings increasing chances
of showers and thunderstorms to western New York this afternoon...
followed by more widespread showers and embedded thunderstorms tonight.
After this system exits our region Monday...a large upper level trough
will then meander its way across the region through much of the upcoming
week...bringing a continuation of somewhat unsettled weather along with
near to slightly below average temperatures.


During the course of today...surface-based ridging over eastern New
York and New England will slide east and out to sea...with the axis of
its parent upper level ridge also sliding from western New York into
New England. Meanwhile...yet another upper level low will begin digging
across the Upper Great Lakes...with an attendant broad surface low over
Illinois gradually deepening and lifting northeastward to near Detroit.
In the process...this latter feature will push its associated warm front
into southwestern New York state this afternoon.

With our area remaining under the influence of the passing upper level
ridge through this morning...we can expect the first half of the day
to be quiet and dry...with a good deal of sunshine early giving way to
increasing diurnal cumulus by midday/early afternoon with strong diurnal
heating of the still-moist lower levels. This still appears
that any real chances for showers and thunderstorms will hold off until
the warm front approaches/arrives during the mid to late afternoon hours...
resulting in slowly increasing convective potential from about the western
Finger Lakes westward...with the greatest chances for this found over the
western Southern Tier. As for temperatures...the warm advection regime out
ahead of the approaching low will result in 850 mb temps climbing to the
+10C to +14C range this afternoon...which will be enough to support fairly
widespread highs in the mid to upper 70s...with a few of our normally
warmer spots potentially reaching the 80 degree mark. This said...areas
along the Lake Ontario shore from Niagara County over to Rochester will
be kept noticeably cooler by a modest east-northeast flow off the much
cooler lake waters.

As we move into tonight...the surface low will lift northeastward into
nearby southern Ontario and push its warm front across our region...before
swinging its trailing cold front into far western New York late. The
combination of continued warm air advection across our region...increasing
height falls aloft...and the aforementioned surface features 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 this 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 a 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.


An expansive...nearly stationary stacked upper level storm system
centered between Lake Superior and the heart of Ontario province
will be our dominant weather feature through this period...and
beyond to the end of the week. The resulting broad cyclonic flow of
relatively moist unstable air over the Great Lakes region will
support occasional shower activity...with the showers being enhanced
from time to time by shortwaves that will rotate through the base of
the broad cyclonic flow. Depending on the timing of these often
subtle impulses...diurnal instability will add fuel to this activity
as well. Interestingly...while the bulk of this period will be will be fair to say that the period will be
characterized by many as being unsettled. While temperatures will
average close to normal...there will be an almost imperceptible
day to day cooling trend. As for the day to details...

A cold front will be exiting our forecast area as we open this
period Monday morning. The bulk of the leftover convection
associated with the front will be focused on areas east of the
Genesee Valley and particularly over the eastern Lake Ontario
region. Meanwhile conditions will already be improving over the far
western counties. As the front pushes east across the Adirondacks to
western New England during the midday and afternoon...similar
improvement can then be expected for the remainder of the forecast
area. Temperatures for Memorial Day cook outs and other activities
will be reasonable for this of year...with H85 temps around 10c
supporting max temps in the low to mid 70s for most areas. Readings
will be a bit lower over the North Country as that region will get a
later start on any sunshine.

While fair weather should be in place Monday evening to close out
the holiday weekend...conditions will deteriorate during the
overnight. The first of several shortwaves during this period will
cross our region late Monday night...and it will be accompanied by a
cool front that will help to generate a passing line of showers and
possible thunderstorms. Will increase pops by 10 to 20 `points`

Subsidence behind the previous nights cool frontal passage should
offer us mainly dry weather for the first half of Tuesday. Diurnal
instability and the chance for another shortwave passage will then
hike up the risk for more showers and possible thunderstorms for the
afternoon. The exception would be in a corridor from the Niagara
Frontier to the North Country where lake shadowing should prevail.
Temperatures Tuesday should be a few degrees lower than those from
Monday...with max temps in most areas ranging from the upper 60s to
lower 70s.

Given the difficulty in timing the passages of the subtle
shortwaves...the short and medium range deterministic models
increasingly diverge as we move from Tuesday into Wednesday. Will
thus trend towards a more generic...ensemble approach at an earlier
stage in the forecast process. This will result in less more broad brushing of pops. That being said...

The daily shower activity may become a little more widespread on there is some suggestion that at least one shortwave
will cross the region...and possibly the base of the longwave trough
itself. Will thus maintain high chc pops outside of the influences
of the Lake Erie `shadow`. As will be the case with temperatures...
will aim a few degrees lower than the previous day...with highs
forecast to generally range from 65 to 70.


The persistent closed low centered over Ontario in the days leading
up to this period will slowly fill and push east as we end the week.
While our region could experience more scattered showers in the
process...shortwave ridging will build across the Lower Great lakes
in the wake of the exiting stacked low...and this should support
generally fair weather for the start of the weekend. It should be
noted though that model consistency remains forecast
confidence remains relatively low. That being to day
details will be limited.

On Thursday...low level ridging and somewhat drier air is expected
to promote mainly dry weather for our region. Will maintain slight
chc pops to account for the larger scale cyclonic flow and model
inconsistencies. Max temps will generally be in the 60s.

A greater number of ensemble members favor a frontal passage
sometime late Thursday night or have raised slgt chc
pops to chc to cover any possible showers. Again...afternoon highs
will largely be in the 60s.

A progressive shortwave ridge should build across the region in the
wake of the front on Saturday...and this would offer a brief
opportunity for some welcomed fair dry weather.


Any early morning patchy fog will quickly mix out after sunrise this
morning...leaving behind widespread VFR conditions for the balance
of the morning and early afternoon hours under a developing cumulus
field. An approaching warm front will then bring slowly increasing
chances for showers and thunderstorms to areas from about KROC-KDSV
westward during the mid to late afternoon hours...with some of these
capable of producing brief/localized reductions to MVFR.

Tonight surface low pressure will move into our region...along with
more widespread showers and embedded thunderstorms. This will result
in areas of MVFR and embedded pockets of IFR...which should tend to
become more widespread late as low level moisture increases.

Monday...Showers and thunderstorms tapering off from west to east...
with conditions improving back to VFR.
Tuesday through Thursday...Mainly VFR...with localized MVFR possible
in scattered (mainly afternoon) showers and thunderstorms.


As surface high pressure slides off to our east and a warm front
approaches from the Ohio Valley today...easterlies will freshen a bit
on Lake Ontario...though winds and waves will remain well below advisory
levels. The only real ill effects from this will be choppy conditions
on the western end of Lake Ontario and especially near the mouth of
the Niagara River...where the winds will oppose the outflow from the
river. Of greater concern will be an increasing potential for scattered
thunderstorms during the mid to late afternoon hours as the warm front
pushes into the area...with the threat of these greatest over Lake Erie.

Showers and thunderstorms will then become widespread over our region
tonight as surface low pressure slides eastward from the Central Great
Lakes. Meanwhile...winds will continue to freshen while veering to the
south following the passage of the aforementioned warm front.

On Memorial Day...the surface low will swing its trailing cold front
across the region during the morning...with the showers and storms
quickly winding down from west to east following its passage. In the
wake of the front...moderate southwesterlies will also develop across
the Lower Lakes...however winds and waves should remain below small
craft advisory levels.





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