Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 300218

Area Forecast Discussion
National Weather Service Buffalo NY
1018 PM EDT MON AUG 29 2016

High pressure over southern Ontario will settle southeastward
across the area overnight and to the Mid Atlantic coastline on
Tuesday... while maintaining fair weather and comfortable humidity
levels. A cold front will cross the region on Wednesday along with
some scattered showers and thunderstorms...then expansive high
pressure will build back over the Great Lakes and Northeast for
the remainder of the week and the long holiday weekend.


Overnight...high pressure centered over southern Ontario will
settle directly across New York State...while providing our region
with clear skies...comfortable temperatures and humidity
levels...and light winds. Under this regime...expect the usual
valley fog to develop across the Southern Tier overnight. Expect
lows to range from the upper 40s/lower 50s across interior
portions of the Southern Tier and North Country to the lower 60s
right along the lakeshores.

The high pressure center is expected to slide to the Mid Atlantic
coastline on Tuesday with another splendid day expected for western
and north-central NY. A developing west-southwesterly flow on the
backside of the ridge will allow temperatures to climb a bit higher
with highs likely reaching into the lower to mid 80s in most locations...
while dewpoints should remain in the comfortable mid to upper 50s.
After a sunny start to the day...a cold front sliding across central
Ontario and Quebec will bring a north to south increase in mid
and high clouds during the afternoon...with this most pronounced
across the North Country and Saint Lawrence Valley.


A potent shortwave in the vicinity of James Bay will push a pattern
changing cold front southward towards our region Tuesday night.
While this moisture starved frontal boundary could generate a few
showers near Lake Ontario and across the North Country before
daybreak...the overwhelming majority of the region will be rainfree
with only a gradual increase in cloud coverage.

The front will then pass through our forecast area during the day
Wednesday. Given the relative lack of moisture with the front...
there should be enough breaks in the associated cloud cover to allow
for SBCAPES to climb to 500-1000 j/kg. In order to support scattered
convection...this instability will certainly be needed to overcome
an otherwise paltry amount of synoptic lift advertised by most of
the guidance packages. Will thus keep low chc pops in place for the
bulk of the region...with only slightly higher chance found east of
Lake Ontario. Temperatures Wednesday afternoon should average within
a couple degrees of 80.

While the sfc front will push away to our south Wednesday night...
the supporting mid level trough will make its way across the Lower
Great Lakes. The resulting cyclonic flow aloft will combine with
limited low level moisture to keep skies from totally clearing
out...especially in the Finger Lakes region where a northerly
upslope flow in the low levels will be in place. It should be noted
that while it will be chilly enough aloft to support instability
over the lakes...the short fetch and limited environmental moisture
will greatly reduce any lake response.

On Thursday...a large...far-reaching area of Canadian high pressure
will extend southward across the Upper Great Lakes to the Southern
Plains while the aforementioned mid level trough will slowly cross
the St Lawrence Valley. This will generate a relatively deep
northerly flow of much cooler air over our forecast area with H85
temps settling to around 8c. Again...while this will keep
instability in place over the Lower Great Lakes...the overall regime
will be relatively dry. Will keep some clouds in place across the
Finger Lakes to account for the continued northerly upslope flow...
otherwise it will be a partly sunny and cool day with max temps
generally within a few degrees of 70.

It will become relatively cool for parts of our forecast area
Thursday night as the center of the expansive sfc high will make its
way across the Upper Great Lakes. Favorable radiational cooling
within a fresh Canadian airmass will allow the mercury to drop well
into the 50s away from the lakes...with parts of the Srn Tier likely
experiencing mins in the 40s.


While the start of this period will feature cool comfortable will be more noteworthy to point out the significant
day to day warming trend that will carry us into next week. The
ultimate factor leading to the return to above normal temperatures
will be the development of a strong jet across the Northern Pacific.
This jet will kick out persistent troughiness that will be in place
over British Columbia...a trough that we have not seen in a couple
months and at least partly responsible for the spell of cool
weather at the onset of this period.

In any case...the +120kt H25 jet will help to deamplify and broaden
the west coast trough...which in turn will lead to substantial
height rises downstream across the eastern half of the country.
Meanwhile...expansive high pressure will guarantee rain free weather
through the period. The details...

On Friday...a progressive upper-level trough with high-latitude
Canadian sourced air will pivot across New England. A dry...shallow
cool airmass will build across the region in its wake while a
sprawling surface high will move from the upper Great Lakes Friday
morning to over the forecast area Friday night into Saturday
morning. Despite 850 mb temperatures returning to around +10C Friday
afternoon...the shallow cool airmass will keep a low-level inversion
in place and thus high temperatures will remain in the lower 70s. We
will see much more sunshine however on Friday even drier
air will advect across the region.

Friday night will be the chillest period of the forecast package as
optimal radiational (minus the fresh snowpack) will encourage our
Canadian airmass to support mins in the low to mid 40s across the
majority of the Southern Tier as well as in Lewis County. The
mercury will flirt with the 40s elsewhere away from the lakes.

Temperatures will then recover Saturday into Sunday as the sprawling
high pressure system slides off the New England coast and allows the
airmass to moderate with 850s back into the mid teens C. This will
bring temperatures back into the upper 70s Saturday and low 80s
Sunday and possibly mid 80s by Labor Day. With high pressure
remaining in control this should remain a dry period with fair


High pressure sliding from southern Ontario to the Mid Atlantic
coastline will largely provide our region with VFR conditions
through the TAF period... with just some increase in mid and high
clouds expected Tuesday afternoon.

The only exception to the VFR conditions will be across the Southern
Tier...where developing valley fog will result in some IFR/MVFR
conditions between roughly 06z-13z Tuesday.

Tuesday night and Wednesday...Mainly VFR with a chance of
showers and thunderstorms.
Thursday through Saturday...VFR.


High pressure sliding from southern Ontario to the Mid Atlantic
coastline will keep light winds and minimal waves intact through

A cold front will cross the lakes Wednesday and Wednesday night and
this will kick up the winds and waves a bit Wednesday night and into
Thursday on the lakes...though conditions may remain just below small
craft advisory criteria. Fine boating conditons are then expected to
return for Friday and the Labor Day weekend as another expansive area
of high pressure builds across the Great Lakes region.





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