Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 270517

Area Forecast Discussion
National Weather Service Buffalo NY
117 AM EDT SAT AUG 27 2016

Expansive high pressure over the Great Lakes will drift east to New
England on Saturday. A weak cold front will then produce a few showers
and thunderstorms on Sunday...before high pressure returns for early
next week.


Surface high pressure will expand across the Great Lakes region
overnight under building mid level heights. This will provide our
region with mainly clear skies and light winds...with just a little
bit of mid and high clouds spreading into far southwestern New York
late in advance of a weak shortwave lifting out of the Ohio Valley.
This will result in good radiational cooling conditions...which is
likely to allow temperatures to drop a bit cooler than consensus
model guidance. Lows will range from the mid to upper 50s within
interior valleys of the Southern Tier and North Country to the lower
to mid 60s across the lake plains. This also is likely to result in
the development of some patchy valley fog across the Western Southern

An influx of deep layer moisture and instability will be transported
into the Upper Mississippi Valley and western Great Lakes Saturday
as a result of strengthening southwest low level flow. This will
precede a mid level trough working though the northern plains. Low
level convergence and moisture transport is then forecast to shift
into the northern Great Lakes late in the day Saturday. Western and
north central New York will see more influence from the mid level
ridge parked over the Mid Atlantic, which will sustain low level dry
air through the day Saturday...though some mid and upper level moisture
may increase over the area. Weak warm air advection should help get
temperatures a few degrees warmer than today with most highs in the
lower to mid 80s, with a cooler regime close to the lakeshores.


After a mainly dry and warm night Saturday night, Sunday will
turn more unsettled as a shortwave trough moves into the Great
Lakes. This will slowly force a weak frontal boundary across the
forecast area on Sunday with a warm, humid and unstable airmass in
place. Frontal forcing and moisture advection don`t look very
impressive at the moment, and thus expect fairly scattered
convective coverage across the region that perhaps becomes
slightly more focused ahead of the frontal passage Sunday evening.
Sunday will be another fairly warm and sticky summer day, with
highs in the mid to upper 80s and dew points returning to the mid
to upper 60s. This will produce CAPE values around 1000 to 1500
J/k inland from the lake breeze boundaries, combined with deep
layer shear increasing to around 30 knots and storm motions of 25
to 30 knots could produce a few stronger storms with some gusty

By Monday, a shortwave trough will track overhead and into New
England by the afternoon. This may result in a few lingering
instability showers and cloud cover Monday morning that will both
decrease in coverage by the afternoon as drier air and subsidence
move into the region. Temperatures will take a subtle step back on
Monday, as 850 mb temperatures fall only a degree or two from
Sunday, thus highs will be in the low to mid 80s and dew points in
the lower 60s. High pressure will build across the region Tuesday
leaving dry conditions and slowly warming temperatures, a few
degrees warmer than Monday (mid 80s)


The longwave pattern will change, at least temporarily, during the
second half of next week and potentially allow for a brief push of
cooler air to enter the Great Lakes and New England. The North
Pacific wave train will amplify early next week, with a trough
moving into the Pacific Northwest. This will in turn force
downstream amplification across North America, with a ridge
centering on the high plains and a fairly deep downstream trough
developing across Quebec, forcing at least a temporary departure of
the strong, hot ridge dominating the east.

Looking at the details, a cold front associated with the deepening
Quebec trough will push southeast across the area Tuesday night and
early Wednesday. This frontal boundary will not have much moisture
to work with, as the Gulf of Mexico moisture will be largely cut off
from reaching this far north. The best large scale ascent will
remain north of the Canadian border in closer proximity to the
deepening trough. Given the relatively poor moisture and dynamics,
expect the cold front to only produce isolated to widely scattered
showers and thunderstorms.

High pressure will then build back into the Great Lakes Thursday and
Friday, bringing a return to mainly dry weather. Temperatures will
be notably cooler, with highs only in the lower to mid 70s by late
in the week with lows in the 50s.


Mainly clear skies and light winds will prevail through the
overnight hours, as high pressure expands across the Great Lakes,
with just a little bit of mid and high clouds spreading into western
New York in advance of a weak shortwave lifting out of the Ohio
Valley. Patchy valley fog could lead to brief MVFR/IFR conditions
across the Southern Tier, including at KJHW.

On Saturday...any early morning valley fog will quickly dissipate
after sunrise. This will leave behind widespread VFR conditions for
the balance of the day...with just some increase in mid and high
cloud cover expected.

Saturday night...Mainly VFR.
Sunday...VFR/MVFR with scattered to numerous showers and thunderstorms.
Sunday night and Monday...Mainly VFR with a chance of showers and
Wednesday...VFR with a chance of showers and thunderstorms.


Expansive high pressure over the Great Lakes will drift east to New
England on Saturday...while maintaining fair weather and fine boating
conditions. A weak cold front may then bring a few showers and
thunderstorms on Sunday...before high pressure returns for early
next week.





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