Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 180751

Area Forecast Discussion
National Weather Service Buffalo NY
351 AM EDT Fri Aug 18 2017

A cold front will move across the area this afternoon and produce a
few more widely scattered showers and thunderstorms mainly southeast
of the lakes. Another weak front will cross the area Saturday with
widely scattered showers and thunderstorms, especially across the
Southern Tier. High pressure will then bring a return to dry weather
Sunday and Monday.


Radar imagery showing the most concentrated area of showers exiting
the eastern Lake Ontario region early this morning as the nose of
the supporting low level jet, and associated enhanced convergence
and isentropic upglide move east of the area. Behind this main area
of showers, expect isolated to widely scattered showers to continue,
mainly from the Genesee Valley eastward.

A mid level trough and associated surface low over the eastern
shores of Lake Superior this morning will move slowly east to the
Ontario/Quebec border by this evening, with a trailing cold front
approaching our region. The stronger large scale forcing for ascent
will remain well north of the Canadian border, leaving mesoscale
processes to dominate across our region. Enhanced southwest flow
will develop over and northeast of Lake Erie as the gradient wind
funnels down the lake, setting up a convergence zone from the
western Southern Tier through the Finger Lakes to the southern Tug
Hill region. This will act as a focus for widely scattered showers
and thunderstorms this afternoon and early evening as weak to
moderate instability develops across inland areas. Stable lake
shadows will expand northeast of the lakes and keep the Niagara
Frontier and Jefferson county dry with more sunshine.

The placement of better dynamics and convergence will keep most of
the stronger storms that develop east of our area, although a few of
the initial storms may produce locally heavy rainfall and gusty
winds across Oswego and southern Lewis counties.

Southwest winds will become quite gusty from midday into the
afternoon northeast of Lake Erie, with gusts of 30-35 mph across the
Niagara Frontier. 850mb temps around +16C will support highs in the
mid 80s across lower elevations away from lake influences, with
southwest winds keeping the Buffalo and Watertown areas a little

The diurnally driven widely scattered convection will mostly end by
mid evening as the boundary layer begins to cool and stabilize, and
the weak synoptic scale cold front moves east of the area. This will
leave mainly dry weather overnight, although cooling aloft
interacting with the warm lake waters may allow a few scattered
showers to develop late tonight over and east of Lakes Erie and
Ontario. Expect lows in the mid 60s on the lake plains, and around
60 across the interior Southern Tier and Tug Hill region. The
airmass will slowly become less muggy overnight as weak cool/dry
advection continues.


On Saturday, a progressive amplified trough will swing across the
forecast area. Weak warm advection ahead of the trough passage will
bring some modest instability back into the western Southern Tier
during the morning with increasing wind shear. A few stronger
thunderstorms may develop with the trough passage in the western
Southern Tier, with storms possibly being aided by the developing
Lake Erie lake breeze boundary. SPC has included this area in a
Marginal risk for severe weather. Otherwise, more widely scattered
showers and rumbles of thunder are possible Saturday afternoon and
early evening for the rest of the forecast area with the trough
passage. With slightly cooler air aloft under the trough and some
cloud cover, expect high temperatures will run just below normal in
the mid 70s. Showers and any thunder will diminish overnight in the
wake of the trough axis passage and loss of diurnal heating. Lows
Saturday night will be a bit cooler than previous nights, in the mid
50s to low 60s.

A broad surface high will build in across the upper Ohio Valley
Sunday bringing moderating temperatures and drier air. This will
result in high temperatures near normal values. As the surface high
slides off the mid-Atlantic coast Monday, return flow developing
will push high temperatures into the low to mid 80s. Skies will
remain mostly clear Sunday into Monday, which should provide prime
viewing conditions for the eclipse on Monday. Low temperatures
Sunday night and Monday will follow the same warming trend as the
high temperatures, with lows Monday night well into the 60s with
building humidity.


This period will be dominated by a steadily amplifying longwave
trough over eastern Canada and the Lower Great Lakes. This will lead
to notably lower day to day temperatures...although at the onset of
the time frame...our temperatures will be well above normal. As for
the day to day details...

Our region will find itself between systems on high
pressure anchored off the coast and a cold front approaching from
the Upper Great Lakes will support a very warm and increasingly
humid environment. Temperatures should easily climb into the mid to
upper 80s across the lake plains and in the valleys. This airmass
will also be increasingly unstable...and while the vast majority of
the day will be rain free...some showers and thunderstorms will be
possible later in the day. This will mainly be the case over the
western counties where lake breeze interactions and/or the presence
of a pre-frontal trough could focus convection.

A cold front will then push southeast across our forecast area
Tuesday night and early Wednesday, likely bringing widespread
showers and/or thunderstorms across the forecast area.

Expansive high pressure over the Upper Mississippi Valley Wednesday
afternoon will gradually settle to the southeast across the Lower
Great Lakes and Ohio Valley by Thursday. This will allow for
significant improvement in our weather with fair weather
returning...along with a pronounced turn to cooler and more
comfortable (lower dew points) conditions. Temperatures by Thursday
will average at least 5 deg f below normal.


Steady showers and a few scattered thunderstorms will exit the
eastern Lake Ontario region early this morning, with any associated
brief/local MVFR to IFR conditions ending. Behind the steadier
showers, a few isolated showers will continue. Areas of low stratus
will develop, with MVFR CIGS through mid morning across lower
elevations and IFR across higher terrain.

The low stratus will scatter out by mid to late morning, leaving
mainly VFR to prevail. The deeper moisture and ascent will move well
east of the area, but the passage of a cold front combined with lake
breeze boundaries will produce a few more widely scattered showers
and isolated thunderstorms during the afternoon, mainly from the
interior Southern Tier across the Finger Lakes to the southern Tug
Hill region. Otherwise expect VFR to prevail during the afternoon.
Southwest winds will become gusty over and northeast of Lake Erie,
with wind gusts approaching 30 knots at KBUF and KIAG.

Scattered showers and isolated thunderstorms will mostly end this
evening with the passage of the weak cold front, although a few
spotty showers may develop again over and east of Lakes Erie and
Ontario as cooler air aloft interacts with the warm lakes. Some low
stratus may develop again, with areas of MVFR and IFR developing
overnight especially across the higher terrain east of the lakes.


Saturday...Mainly VFR with a chance of showers.
Sunday and Monday...VFR except for late night and early morning
valley fog with local IFR.
Tuesday...Mainly VFR, with a chance of showers and thunderstorms late.


Low pressure will move from just east of Lake Superior today to west
central Quebec by Saturday, with a trailing cold front crossing the
eastern Great Lakes this afternoon. Southwest winds will become
quite strong on Lake Erie today as they funnel up the length of the
lake, with solid Small Craft Advisory conditions this afternoon and
evening. The southwest winds will be lighter at the east end of Lake
Ontario. West winds will slowly increase on Lake Ontario overnight
into Saturday, with Small Craft Advisory conditions probable on at
least the east half of the lake for Saturday, while winds remain a
little lighter on Erie.

High pressure will then bring a return to light winds Sunday and
Monday on both lakes.


NY...Beach Hazards Statement from noon EDT today through this
     evening for NYZ010-019-085.
MARINE...Small Craft Advisory from noon today to 2 AM EDT Saturday for
         Small Craft Advisory from noon today to 11 PM EDT this
         evening for LEZ020.



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