Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 190252

Area Forecast Discussion
National Weather Service Buffalo NY
1052 PM EDT Tue Jul 18 2017

High pressure crossing the region will provide for fair weather
through tonight. The high will shift east on Wednesday, with warmer
and more humid weather returning by the afternoon, along with a
slight chance for an isolated shower or thunderstorm across a few
areas late in the day, as a disturbance approaches the region. More
scattered showers or thunderstorms are possible Thursday as a wave
of low pressure moves south of the region. High pressure then builds
in Friday brining dry weather. A frontal boundary will stall across
the region for the weekend brining more shower and thunderstorm


Clear skies continue to prevail across the forecast area this
evening, courtesy of a surface ridge that is parked overhead the
region. Expect another clear night with light winds that will
promote radiational cooling, with temperatures falling into the mid
to upper 50s well inland, with low 60s along the lake plains. The
cool temperatures and light winds will once again allow for the
development of fog in the river valleys of the Southern Tier.

After a beautiful start to the day on Wednesday, southwesterly winds
will pick up and temperatures will rise as the center of the high
moves off to the east. We will once again see some diurnal cu pop up
in the afternoon, though lake shadowing will likely keep areas east-
northeast of both lakes mostly clear through a good portion of the
day. Mid/high clouds will be increasing across the Niagara Frontier
later in the day as a shallow upper level trough and associated
convection approach the area. Depending on the timing of this
trough, we may see a few showers and perhaps an isolated
thunderstorm pop up late in the day in the Southern Tier or western
Finger Lakes, inland from the lake breeze, or across the Niagara
Frontier, should upstream convection from Canada survive long enough
to make it into the area. Overall though, the vast majority of the
forecast area can expect a dry day given the lack of moisture aloft
and modest mid-level lapse rates.

Regarding temperatures for Wednesday, as mentioned above, the
eastward shift in position of the surface high will allow for warmer
air to advect into the forecast area. This warming trend will be
further enhanced by strengthening southwesterly winds and associated
downsloping, particularly in the Genesee Valley and south of Lake
Ontario, where temperatures are expected to climb into the mid to
upper 80s. Elsewhere, look for readings to top out in the low 80s.
As mentioned previously, the southwesterly flow will also allow for
increasing low-level moisture across the area, with dewpoints once
again returning to the low to mid 60s by the afternoon, making it
feel considerably muggier than it has felt over the last couple of


A weak mid level trough across the area Wednesday evening will move
eastward to New England late Wednesday night. Some model guidance
shows a weak surface trough as well, with some light QPF while other
guidance has the surface trough and associated QPF washed out by
Wednesday night. Either way the areal coverage of any showers will
be sparse with this feature. Expect lows in the mid 60s for most
areas, and around 60 in the coolest Southern Tier valleys.

After this, a weak frontal boundary will develop roughly from Eastern
Michigan to northwestern Pennsylvania. This boundary will be
diffuse and meander at times, and also will serve as a focus for
subtle convection in the Thursday and Friday timeframe. Model
guidance is in poor agreement on the specifics of any convective
waves which may develop along this boundary. Although it is possible
convection along this boundary will be significant, there is low
confidence in timing these waves at this timeframe since they will
be convectively driven. Due to the sparse nature of this convection,
the forecast carries an extended period of chance PoPs which is
highest across southern portions of the cwa which is closest to the
consensus position of the boundary.

Temperatures for Thursday and Friday will be near to slightly above
normal with daytime highs in the lower to mid 80s. It also will be a
bit more humid with dew points climbing to the mid to upper 60s.


The region will remain southern edge of a cyclonic flow aloft which
will maintain a risk of showers and thunderstorms Friday night into
Saturday. Model guidance continues to differ on convective
development. After this there is some consensus on the pattern, but
overall low forecast confidence for PoPs during the long term
forecast period.

Model consensus suggests there will be a 12-24 hour period of dry
weather of the weekend with surface high pressure across Southern
Ontario ridging into the region. This will most likely occur late
Saturday into Saturday night. With this will be a northerly flow
with slightly drier air but still warm temperatures.

This ridge is likely to break down, with most model guidance
bringing a more significant wave across the region on Sunday as the
upper level trough starts to dig across the region. There is a good
chance of showers or thunderstorms with this wave Sunday and Sunday

Cooler air will build into the region early next week with the upper
level troughing and a northerly component flow. Surface high
pressure building to our north is likely to bring mainly dry
weather, especially across northern portions of the forecast area.
Meanwhile temperatures will be notably cooler, with highs in the 70s
on Monday and Tuesday.


Widespread VFR conditions will persist through the overnight period
for the bulk of the forecast area. The one exception will be in the
river valleys of the Southern Tier, where valley fog is expected to
develop again tonight underneath clear skies and light winds, after
06Z. This should once again bring IFR/LIFR conditions to KJHW.

Valley fog should dissipate rapidly after 12Z, with the forecast
area once again seeing widespread clear skies to start the day.
Mid/high clouds will move into the Niagara Frontier after 18Z as
upstream convection approaches the area, however convection should
be weakening, with only a very low chance of any occurring in the
forecast area through the forecast period, thanks to dry air aloft
and modest mid-level lapse rates. Otherwise, look for VFR conditions
to prevail with diurnal cu inland from the lakes during the
afternoon. Southwesterly winds will increase as the center of the
high moves off to the east, with winds gusting in excess of 20kts in
the afternoon NE of Lake Erie and Lake Ontario.

Wednesday night and Thursday...VFR/MVFR. A chance of
showers and thunderstorms with possible MVFR.
Friday...VFR. A chance of TSRA in the western Southern Tier.
Saturday and Sunday...a chance of showers and thunderstorms with
possible associated MVFR.


High pressure will maintain fine boating conditions through much of
Wednesday with light winds and little wave action. A weak cool front
will cross the lakes Wednesday afternoon into Wednesday night, with
only a low chance of a shower or thunderstorm. Several rounds of
scattered thunderstorms remain possible Thursday into the weekend
but no significant marine concerns are expected outside the storms.





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