Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210229

Area Forecast Discussion
National Weather Service Buffalo NY
1029 PM EDT Tue Jun 20 2017

A potent upper level disturbance will bring an hour or two of
rain and possibly a thunderstorm overnight. Then weak high
pressure and drier air will build into our region and bring a
return to mainly dry conditions for Wednesday and Wednesday
night. 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.


Late this evening, water vapor imagery shows a potent shortwave
across eastern Michigan. Showers and a few thunderstorms have
developed just ahead of this shortwave, with a surface trough
and wind shift. This will bring a brief period of rain to most
of the area, which will probably only last an hour or two in
most locations. Embedded thunderstorms are quite sparse, but are
still just worth chance mention in the forecast.

Drier weather and partial clearing will spread across the
region from west to east overnight as the potent shortwave and
its attendant surface cold front slide off 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.

On Wednesday...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 shortwave will move across the area between 03Z and 07Z with a
brief period of light (mainly VFR showers) and a chance of a
thunderstorm. Based on diminishing upstream convection, the
chance for thunderstorms appears to be small. Expect mainly VFR
conditions behind this wave, with a partial clearing toward
daybreak in most areas. The exception is across the Western
Southern tier, including JHW, where MVFR cigs may linger.

On Wednesday, expect diurnally driven cumulus to develop, but
bases should mainly be above 3k feet. A widely scattered shower
or thunderstorm cannot be ruled out near ART which will be
closest to a departing upper level trough.

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


Winds will continue to subside on Lake Erie overnight...but
moderate to fresh westerlies can be expected on Lake
Ontario...especially on the eastern half. Again...while waves
are forecast to remain below small craft advisory
criteria...conditions may become quite choppy at times.

High pressure will cross the Lower Great lakes on Wednesday. This
will result in light to occasionally moderate winds through midday...
with diminishing winds then following for Wednesday afternoon and





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