Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 111515

Area Forecast Discussion
National Weather Service Buffalo NY
1115 AM EDT Fri Aug 11 2017

Low pressure will slowly move across the Great Lakes region before
exiting through Quebec on Sunday. While the weekend will not be a
washout, there is a chance of showers and thunderstorms through
Saturday, with warm yet seasonable temperatures. This will be
followed by mainly dry weather and slightly cooler temperatures
for Sunday and into next week.


A shortwave embedded in the cyclonic flow aloft will move across
Western New York late this afternoon and evening. Low level moisture
will increase in the southwesterly flow ahead of this, with
increasing surface based instability and PWATS increasing to around
1.5 inches. Scattered showers and thunderstorms will develop on the
nose of the low-level moisture advection which will be strongest
across the Finger Lakes and central NY, however lake breeze
boundaries will also help to force a few scattered showers and
thunderstorms across WNY.

There is a small chance for strong to severe storms and locally
heavy rainfall. Forecast wind profiles are quite weak through mid-
afternoon, with locally heavy rainfall possible due to slow storm
motion. After this, mid-level winds increase modestly in advance of
the shortwave with 30 kt 700 mb winds this evening. Although this is
far from impressive, when combined with adequate instability and
some directional shear, it may be ample to support a few strong
storms with gusty winds and hail possible. In each case, coverage is
not expected to be ample to justify enhanced wording. SPC has the
area in a marginal risk for severe weather.

Showers and thunderstorms will linger into the evening hours in
advance of the shortwave, but should taper off from west to east
behind the shortwave later tonight.

Temperatures today will be similar but slightly cooler than
yesterday. Highs will range from the mid 70s to lower 80s. Expansive
cloud cover will limit radiational cooling tonight with lows in the
lower to mid 60s.

On Saturday, the best moisture and instability axis ahead of the
upper level low will shift eastward across central and eastern NY,
which matches well with SPC`s marginal risk outline. Thus any
stronger thunderstorm activity will be most numerous mainly east of
the Finger Lakes and the North Country. However, isolated to
scattered showers will remain over WNY with the steeper mid-level
lapse rates in the vicinity of the trough axis. Cold air advection
behind the frontal passage will help steepen low-level lapse rates
from west to east Saturday afternoon and evening, which will help
winds mix down especially over the lower Great Lakes, with winds to
around 20 mph. This will make for a breezy afternoon as 850 mb
temperatures fall to around +10C. High temperatures will be limited
to the low to mid 70s.


Cooler air behind the cold front Saturday night will bring
cooler air temperatures and also some lake enhanced/upslope
precipitation chances. At 850 hPa temperatures will drop to
around +9C, which could initiate a few lake enhanced showers to
the east of the lakes. Chances for showers Saturday night will
be highest east of Lake Ontario where additional lift from a
secondary upper level trough axis may bring additional synoptic

Sunday behind the upper level trough, a drier airmass will flow
across the region. Outside of a shower early in the day towards the
east, fairer weather will increase across the region with clearing
skies. Temperatures this period will be near normal, with highs in
the 70s, and overnight lows in the mid 50s to lower 60s.


A persistent mid level low will continue to pinwheel over northern
Quebec through the first couple days of next week. A broad longwave
trough extending south across the Great Lakes with continue to keep
a slight threat for diurnal instability showers and thunderstorms
triggered on lake breeze boundaries inland from the lakes Monday.
General surface high pressure influencing our region below the trough
will contribute to prevailing dry weather outside of some isolated

12z model consensus shifts the longwave trough axis across the
eastern Great Lakes Monday night into Tuesday. Some limited synoptic
moisture with the weak synoptic scale lift will keep a slight chance
for some showers and thunderstorms on Tuesday as it passes east.
Wednesday and possibly through Thursday, dry high pressure will
cross the region, bringing abundant sunshine and fair weather. The
00Z ECMWF continues to hint of a few showers and thunderstorms
reaching the region Thursday, though the dry airmass that these
storms will be impinging upon will create just a very low chance for
activity at this time for Thursday.

Temperatures will average a few degrees below to near normal with
daytime highs in the low to mid 70s through the middle of next
week as the mid-level trough and associated cooler air passes
over the Great Lakes. Rising heights/warm advection will allow
for a return of some 80s for Thursday as southerly flow returns.
Dewpoints in the upper 50s to low 60s will provide a
comfortable to slightly humid airmass will keeping overnight
lows mild to slightly chilly.


Scattered showers and thunderstorms will develop this afternoon with
daytime heating. Expect VFR to prevail most of the time in the
afternoon, although some of the heavier showers and storms will
contain brief/local MVFR to IFR.

Expect mainly VFR conditions this evening as showers and storms
move to the east and taper off. Low moisture will build late
tonight, with MVFR or lower conditions possible late due to
lower clouds.


Saturday...VFR/MVFR with scattered to numerous showers and
Sunday through Tuesday...Mainly VFR.


A low pressure system will track north of the lower Great Lakes
through the weekend. Winds and waves will remain light through
Friday night with scattered showers and thunderstorms. A cold front
will cross the lower Great Lakes Saturday and Saturday night with
winds and wave possibly reaching small craft conditions Saturday
afternoon and night. High pressure will then build in Sunday through
Monday with decreasing wind and wave action.





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