Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 180215

Area Forecast Discussion
National Weather Service Buffalo NY
1015 PM EDT Sun Sep 17 2017

A weak cool front will stall over western New York Monday and
Tuesday...and this should promote the development of some scattered
afternoon showers both days. Otherwise...we can look forward to fair
warm weather through next weekend with temperatures averaging 10
degrees above normal.


Persistent high pressure will remain anchored over New England
overnight as a weakening cold front will limp in our direction
from Lower Michigan. This synoptic setup will guarantee that we
will experience another night of fair dry weather. With only patchy
clouds anticipated and a relatively `stale` airmass in place...we
can also expect patchy fog to redevelop through the course of the
night...with areas of fog forming in the Southern Tier valleys

Overnight low temps will be quite similar to those from Saturday
night with lows ranging from the upper 50s across the interior
of the Southern Tier and in parts of the North the
lower 60s elsewhere.

On Monday...the area of high pressure over New England will
grudgingly drift to the Canadian Maritimes. This will allow the
aforementioned cool front to slowly approach us from southern
Ontario and Lake Erie. Continued low level moisture advection from
the resulting south-southeast flow will help to finally destabilize
our airmass...and with minimal lift found in advance of the frontal
boundary...there could be some shower activity develop during the
midday and afternoon. Since guidance is suggesting that a weakened
subsidence cap may still be in place...with with only weak synoptic
forcing in place...have downplayed the potential for thunderstorms
by using only slgt chc wording. Otherwise chc pops will be used for
the bulk of the western counties...with likely pops used for parts
of the Southern Tier and Finger Lakes region where greater low level
instability will be in place.

It will continue to be warm on Monday with building humidity as
well. Sfc dew points will climb into the mid 60s for most areas...
and this will help to give us a little summer stickiness.


Monday night a weak cold front will move into Western NY and wash
out as it encounters subsidence and drying beneath a strong mid
level ridge over the Ohio Valley and eastern Great Lakes. An
associated weak mid level shortwave will drift northeast across
southern Ontario, with the southern end of this clipping Western NY.
Weak ascent from the mid level shortwave, and weak convergence from
the dissipating front may be enough to support a few isolated to
widely scattered showers Monday night across Western NY, but most of
the time will be rain free. It will remain dry east of the Genesee
Valley where the ridge remains more dominant. Lows will be mild, in
the low to mid 60s on the lake plains and upper 50s in the cooler
Southern Tier valleys and Lewis County.

Tuesday the cold front will have washed out, but the remnant
convergence zone will still be in place across Western NY. This will
combine with terrain and lake breeze boundaries to provide a weak
focus for a few more showers and isolated thunderstorms on Tuesday,
peaking during the afternoon with daytime heating. Drier air and
stronger subsidence will again keep areas east of the Genesee Valley
dry. Temperatures will continue to run a solid 10 degrees above
average with highs in the lower 80s across lower elevations away
from the lakeshores.

Tuesday evening any scattered showers and isolated thunderstorms
will end in Western NY with the loss of daytime heating, and as the
old convergence zone completely breaks down. Expect dry conditions
to then prevail through the rest of the night with partly cloudy
skies as patchy mid level clouds cross the region associated with a
weak mid level shortwave. Temperatures remain mild, with lows in the
lower to mid 60s on the lake plains and upper 50s in the Southern
Tier valleys and Lewis County.

Wednesday through Thursday a strong and dominant ridge surface and
aloft will build directly over the lower Great Lakes. This will
provide another stretch of dry weather with abundant sunshine both
days. Temperatures will continue to run a solid 10 degrees above
average, with highs in the lower 80s both days at lower elevations
away from the immediate lakeshores. Wednesday night lows will be in
the lower 60s on the lake plains and mid to upper 50s for the
interior Southern Tier and Lewis County.


A seasonally strong 500mb cut-off high is forecast to drift over the
eastern Great Lakes through next weekend in response to a deep
trough digging across the western states. This high should provide
summer-like temperatures for the start of Autumn. 850mb temps are
forecast to rise to between +16C and +18C which should easily allow
high temperatures to reach low to mid 80s if not warmer in many
spots. With perfect dry-adiabatic mixing upper 80s in many locations
may be possible. The subsidence brought on by the high will make for
dry and mainly cloud-free weather. Southerly low level flow should
also hold dewpoints in the 60s keeping a humid feel to the airmass.
Hurricane Jose or the remnants of, looks to loop around off the
southern New England coast which should not impact western and
central NY weather.


High pressure will remain in place across New England through
tonight...then it will drift east to the Canadian Maritimes on
Monday while a weak cool front will advance across southern Ontario.
While this scenario will keep fair VFR conditions in place for most
areas through the TAF period...there will be some exceptions.

Most notably...there will be another round of patchy fog tonight.
Given the `stale` nature of the airmass and subtle increase in low
level moisture within an environment of limited cloud cover...patchy
fog should once again develop...with areas of fog forming in the
Southern Tier river valleys. Expect conditions to lower to the
IFR/MVFR range within the fog...with LIFR/IFR developing within
the Southern Tier river valleys. At this point it appears that
KJHW/KART/KROC will be the most impacted TAF sites...while KBUF
may well remain VFR owing to a light southerly downslope (drying)
surface flow that will be in place.

Vsby restrictions due to fog at daybreak Monday will then give way to
VFR conditions regionwide by mid morning. While these VFR conditions
are then largely expected to continue through the rest of the day...
some showers could develop and produce some brief/localized MVFR
restrictions Monday afternoon...with the greatest chance of these
found from interior portions of the Southern Tier northeastward
across the middle/upper Genesee Valley...and into the western Finger

Monday night through Friday...VFR...but with IFR to MVFR conditions
possible each night (08-12z) at KJHW.


Stacked high pressure over New England will generally remain in place
overnight with a very weak sfc pressure gradient persisting over
the Lower Great Lakes...which will maintain light winds and negligible

While a weak cool front will limp across the Lower Great Lakes on
Monday...thunderstorms are not anticipated over the lakes and winds
should remain light.

Another area of high pressure will take up residence across eastern
Canada and the Lower Great Lakes for Tuesday through at least
Thursday. This will continue our stretch of fine weather with very
favorable conditions for recreational boating.





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