Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 300549
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
149 AM EDT TUE AUG 30 2016

.SYNOPSIS...
An area of high pressure will cross the region this morning,
settling over the mid-Atlantic coastline tonight. Expect fair
weather with comfortable levels of humidity to continue through the
day today. A cold front will then cross the region on Wednesday with
some scattered showers and thunderstorms...to be followed by an area
of high pressure that will spell fair weather into the holiday
weekend.

&&

.NEAR TERM /THROUGH TODAY/...
Aside from some passing cirrus clouds, the region is mainly clear
this morning as high pressure centered over southern
Ontario settles directly across New York State. 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.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
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.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
While the start of this period will feature cool comfortable
weather...it 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 though...as 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
weather.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
For the 06z TAFS VFR flight conditions were found across the region,
though as the temperature cools under prime radiational cooling
conditions, we should see some river valley fog form across the
Southern Tier, while patches of fog are also likely to form across
the Northern Finger Lakes and Eastern Lake Ontario region.

There is still a fair amount of spread from the air temperature to
the dewpoint temperature this morning at KJHW and will only bring a
tempo IFR flight category across the airfield this morning, though
IFR flight conditions are likely just to the east through the river
valleys.

The other concern will be our eastern zones, where at Watertown
temperatures are nearing the dewpoint. Under light winds and clear
skies here too some periods of IFR flight conditions will be
possible.

Otherwise expect light winds with VFR flight conditions prevailing
through the end of the TAF period.

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

&&

.MARINE...
An area of high pressure over the Eastern Great Lakes this
morning is providing for light winds and near flat wave action on the
lakes. This area of high pressure will slide by to our east today,
and will allow for a light southerly wind to develop, though with
speeds still well below small craft criteria.

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.

Behind the cold front another area of high pressure will
influence the Great Lakes with fine boating conditons expected to
prevail into the holiday weekend.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...JJR/SMITH/THOMAS
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...THOMAS
MARINE...THOMAS


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