Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 290616

Area Forecast Discussion
National Weather Service Buffalo NY
216 AM EDT FRI JUL 29 2016

A weak cold front will slide southward across New York State
overnight with warm and humid conditions, then a wave of low
pressure will move south of the region today, bringing chances for
scattered showers and thunderstorms to the Southern Tier. Weak high
pressure on Saturday should limit shower activity to near the
Pennsylvania state line. The chances for scattered showers and
thunderstorms increase again Saturday night through Sunday night.


There will be little airmass change overnight as mild and humid
conditions will persist, low temperatures in the lower to mid 60s
inland and over higher terrain and to the upper 60s or lower 70s
near the Great Lakes and within urbanized areas. Patchy Southern
Tier valley fog will develop overnight with departing cirrus deck
allowing for optimal radiational cooling. Bradford and points south
into PA already reporting some fog early this morning, and expect
this area of fog will expand northward into our Southern Tier on the
heels of the clearing high cloud cover.

The forecast area remains caught between high pressure building into
the upper Great Lakes and a surface low tracking through the mid-
Atlantic early this morning. A weak frontal boundary sagging to our
south with surface pressure rises north of Lake Ontario dropping
southward along with increasing weak cold advection behind the front
will allow northeasterly winds to freshen early this morning. Winds
will pick up across Lake Ontario through daybreak with winds of 20
to 25 mph on the open waters, before these stronger winds taper off
this afternoon. Winds speeds across the lake plains will generally
remain around 10 mph today.

Northerly winds set up today will also bring slightly cooler and
less humid air to the region. Meanwhile, a wave of low pressure
passing eastward across Pennsylvania, on its way to becoming a
coastal low off the Mid-Atlantic states, will bring a few isolated
to scattered showers and thunderstorms to the Southern Tier this
afternoon. However, the rest of the forecast area should remain free
of any precipitation. High temperatures will be in the upper 70s to
lower 80s, which should feel more comfortable than it has been for
the past many days.


A broad midlevel trough and embedded vorticity maxima is forecast to
cross from the Midwest and Great Lakes to the Mid-Atlantic and New
England regions through the weekend. This trough will trigger a
surface low somewhere from the Ohio/Tennessee River Valleys shifting
east to the Mid-Atlantic region. Sufficient synoptic moisture will
be in place ahead of the trough and low to drive some showers and
possible thunderstorms mainly south of our forecast area on Saturday
then shifting north and east across our region on Sunday.

Large differences remain between the relatively dry 12z GFS and more
moist 12z ECMWF which leave a lower than normal confidence in a
forecast at this short range. While most of Friday night should be
dry, have introduced chance POPs across the Southern Tier later
Friday night. POPs have been increased some on Saturday while edging
them a little further north to hedge at least partially toward the
wetter EC model but still preserving a majority of continuity.

Higher confidence is found on Sunday where a sharper embedded
shortwave trough and higher level of instability looks to drive a
more widespread area of showers and thunderstorms. The highest POPs
over the weekend timeframe will be in place on Sunday. By Sunday
night the trough axis will shift east of the forecast area with POPs
tapering off as high pressure and mid-level ridging arrive from the
west. Temperatures over the weekend will be cooler than recent days
but still averaging a touch above mid-summer normals. Easterly winds
should prevent cooler temperatures from occuring on the eastern
shores of Lake Erie due to some downsloping.


During this period...surface-based ridging initially draped across
the Central Great Lakes will gradually push eastward and crest
across our region Tuesday and Tuesday night...before drifting off
the Atlantic coastline Wednesday and Thursday. Meanwhile aloft...
initial low-amplitude troughing will give way to a building upper
level ridge by the end of the period.

After a lingering chance of showers across southern and eastern
sections during the first half of Monday...the above evolutions in
the large-scale pattern will support a return to dry weather for
the remainder of the period...along with a steady day to day warming
trend thanks to a developing warm air advection regime and increasing
large-scale subsidence. While the exact degree of warming we can
expect still remains a bit unclear given continued differences in the
medium range guidance...a general consensus approach would suggest
daytime highs climbing from the lower half of the 80s on Monday to
the mid 80s to lower 90s by Thursday...with nighttime lows also
warming back into the mid 60s to lower 70s by the end of the period.
Accompanying the building heat will also be a return of more humid
conditions...with dewpoints climbing from around 60 on Monday to
the mid 60s by Thursday.


Expect mainly VFR conditions today. The exception is at KJHW where
valley fog should develop early this morning as high cloud cover
departs, with any fog that develops at KJHW largely breaking up by
around 11 to 12Z. A few isolated to widely scattered showers and
thunderstorms are possible across the Southern Tier this afternoon,
but chances are low enough and far enough east to exclude any VCSH
or VCTS from KJHW TAF.


Tonight through Sunday...VFR/MVFR with a chance of showers and
Monday and Tuesday...VFR.


Pressure rises and weak cold advection behind a frontal boundary
pushing south through NY state will help freshen northeasterly winds
on the lakes early this morning. Lake Ontario in particular will see
winds to around 20 knots and waves building to around 3 to 5 feet,
prompting small craft advisories through early afternoon. By this
afternoon winds and waves will subside as high pressure builds into
the region.


NY...Beach Hazards Statement from 8 AM this morning to 2 PM EDT
     this afternoon for NYZ001>004.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for



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