Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210613

Area Forecast Discussion
National Weather Service Buffalo NY
213 AM EDT Wed Jun 21 2017

Lingering showers will end overnight with weak high pressure and
drier air building into our region and bringing a return to mainly
dry conditions today and tonight. Broad low pressure will then slide
east across central and eastern Canada Thursday and Friday...while
bringing a return to increasingly unsettled weather to close out the
work week.


The main band of showers has shifted to the eastern Lake Ontario
region early this morning extending south into the eastern Finger
Lakes. This band of showers has been forced by a mid-level and
surface trough axis and is expected to continue to push east of the
forecast area before sunrise.

Drier weather and partial clearing is beginning to spread into the
Niagara Frontier and will further spread west to east overnight as
the trough exits to our east. With respect to temperatures...expect
overnight lows to mostly settle into the mid to upper 50s...though
areas along the immediate lakeshores may not drop below 60.

After sunrise...broad upper level troughing will remain in place
aloft... while weak surface-based high pressure and drier air will
slowly build east across our region. While daytime heating of our
still-cool airmass should once again result in the development of a
fair amount of cumulus away from any lake influences...the relative
absence of a noteworthy trigger for convection should result in a
mainly dry day for most areas... with forecast PoPs having
correspondingly been lowered below the chance threshold for most of
the area. The exception is across the Saint Lawrence Valley and
adjoining portions of the North Country... where the presence of a
lingering weak surface trough and approach of a weak shortwave may
produce a few afternoon showers and thunderstorms. There is also a
slight chance of a shower along the convergence of lake breeze
boundaries near the Niagara and Erie county
border.Otherwise...expect continued comfortable temperatures and
humidity levels...with 850 mb temps of +8C to +11C again supporting
afternoon highs mainly in the lower to mid 70s.


Weak high pressure will build over NY/PA Wednesday night. Any
leftover diurnal cumulus in the evening will dissipate and yield
mainly clear skies overnight. The airmass will remain fairly cool
and dry, which will allow for decent radiational cooling. Expect
lows in the mid 50s on the lake plains and upper 40s to around 50 in
the cooler Southern Tier valleys and Lewis County. The radiational
cooling may allow for some valley fog to develop in the typical
Southern Tier river valleys.

On Thursday a warm front and associated mid level shortwave will
move from Michigan to the eastern Great Lakes and de-amplify with
time. Associated moisture and warm advection will bring increasing
clouds from west to east. Model guidance continues to back off on
rain potential, but there may still be enough forcing and moisture
left to support a few showers along the advancing warm front by
midday in Western NY, and later in the afternoon east of Rochester.
Enough instability may develop to support a few isolated
thunderstorms by late afternoon, mainly across the western Southern
Tier. Temperatures will begin to move upward in the warm advection
regime, and humidity will increase. Expect highs around 80 in most
areas and mid 70s North Country.

Scattered showers and isolated thunderstorms will continue through
Thursday evening as the weakening wave and warm front cross the
region. Another, more notable mid level shortwave and warm frontal
segment will move into the region late Thursday night and Friday
morning. Deeper moisture and increasing isentropic upglide and DPVA
will support an increasing chance of showers and a few scattered
thunderstorms late Thursday night. The clouds, showers, and warm
advection will keep temperatures up, with lows in the mid 60s on the
lake plains and lower 60s interior Southern Tier and North Country.

On Friday the warm front and associated lead shortwave will continue
to move northeast across the area, with some additional showers and
scattered thunderstorms. Later Friday and Friday evening the cold
front and main mid level shortwave will cross the region, with
associated convergence and ascent supporting a few more rounds of
showers and scattered thunderstorms. Extensive clouds and showers
will likely limit destabilization and lapse rates, but if enough
breaks develop a few stronger storms may be supported by moderate
mid level shear, especially in eastern portions of the area.
Temperatures will climb into the lower 80s in many areas if enough
breaks in the rain develop as 850mb temps soar to around +16C.

The cold front will move across the area Friday night, with showers
and scattered thunderstorms ending from west to east with the cold
frontal passage. Fairly strong cold advection after midnight and the
arrival of a drier airmass will allow lows to drop to the upper 50s
to lower 60s in most areas by daybreak Saturday. On Saturday
subsidence in the wake of the cold front and mid level shortwave
should bring a mainly dry day with mid level drying supporting
increasing amounts of sun. A cooler airmass builds into the region
again, with highs in the mid 70s at lower elevations and around 70
on the hills.


Long range models are in good agreement on a overall broad troughing
pattern over the Hudson Bay through the weekend and into early next
week. The forecast area will be located on the southern periphery of
this broad low, and generally embedded within the west-southwesterly
flow aloft initially. This will allow for several fast-moving
Pacific sourced shortwaves embedded with the flow to cross near the
region. The day-to-day temperature trend will be generally cooler
through the weekend and into the start of next week as the trough
axis nears and crosses the region. Scattered showers and
thunderstorms are likely at times with the wave passages, with ample
dry time in-between.

Overall the weekend will be mainly dry with shower and thunderstorm
changes increasing through the day Sunday into Sunday night as a
cold front moves across the region. Cooler drier air will filter
into the region for the start of the work week behind a cold front
passage Sunday night. Latest model runs have trended cooler yet with
a more amplified trough for the beginning of next week. High
temperatures may well stay in the 60s Monday into Tuesday.


A band of showers is pushing across the eastern Lake Ontario region
as of 06z. Mainly VFR conditions are in place across the region but
some limited MVFR cigs/vis is found within the showers (KART) and
in some linger low clouds behind the showers (KBUF). Mainly clear
skies working across the Niagara Frontier will continue to spread
east overnight with most areas seeing clearing toward daybreak.

After sunrise, VFR should be widespread with clearing skies as high
pressure builds over the lower Great Lakes. Expect diurnally driven
cumulus to develop during the late morning/early afternoon, with VFR
bases around 5k feet. A widely scattered shower or thunderstorm
cannot be ruled out near ART which will be closest to a departing
upper level trough. VFR is expected under clear skies tonight
although some Southern Tier River Valley fog may develop after 22/06.

Thursday...Mainly VFR with a chance of showers and
Friday...VFR/MVFR with showers and thunderstorms likely.
Saturday...Mainly VFR.
Sunday...Mainly VFR with a chance of showers.


High pressure will cross the Lower Great lakes through today and
tonight. This will result in light to occasionally moderate winds
with waves 1-3 feet through midday, then diminishing winds and waves
will follow this afternoon and tonight.

Light winds and waves will continue on Thursday then increase again
Thursday night and Friday as a storm system passes across the
Central Great Lakes with its associated warm/cold fronts cross the
eastern Great Lakes. Expect conditions to be just below Advisory
criteria through Friday and Saturday.





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