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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBUF 172357
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
757 PM EDT Thu Aug 17 2017

.SYNOPSIS...
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Showers and thunderstorms associated with a well-organized low
pressure system over Upper Michigan will cross Western and North-
Central New York tonight, with more scattered activity possible
Friday afternoon as the low center slowly passes to our north. An
upper level disturbance will bring another chance for showers
Saturday before high pressure dries things out for the latter half
of the weekend into Monday. Temperatures will run near to slightly
above-normal through the weekend, with warmer temperatures in the
mid 80s possible next week.
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&&

.NEAR TERM /THROUGH FRIDAY/...
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Water vapor imagery showing a well defined circulation pushing into
Lake Superior this evening. A warm front associated with this
low is currently moving northeast across the lower Great Lakes.
Regional radars showing a broad area of rain with a few embedded
heavier convective elements tracking across western New York.
This activity will continue to move eastward through midnight.
Marginal instability will greatly limit any severe threat, but
could have brief very heavy downpours, especially along the
Southern Tier with precipitable water values in excess of 2
inches.

The low level jet axis fueling the band of precipitation will cross
the forecast area tonight, with the bulk of the precipitation
exiting the eastern edge of the forecast area Friday morning.
However, more scattered showers and thunderstorms are likely Friday
afternoon, as the region will remain under the influence of
troughing from the surface through the upper levels, as the large,
occluded low slowly tracks to our northwest from the UP of Michigan
into western Quebec. However, with the LLJ and associated moisture
passing to our east, it will not be quite as muggy, with highs in
the upper 70s, to lower 80s along the Lake Ontario plain, wheres
downsloping southwesterly flow will bump temps up a couple of
degrees.
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&&

.SHORT TERM /FRIDAY NIGHT THROUGH MONDAY NIGHT/...
By Friday night, a cold front will have passed through the region,
bringing in cold air advection behind it enough to drop 850mb
temperatures to around 10c. Combined with lake temperatures around
22c, this could produce showers overnight but will most likely
result in low clouds because of a low cap and very dry air above
850mb.

On Saturday, a secondary trough will bring another frontal boundary.
This combined with diurnal heating may produce showers inland during
the afternoon. Saturday will have the coolest temperatures of the
weekend, with highs in the mid 70s and lows in the low 60s.

A broad area of high pressure will build over the region Sunday,
accompanied by warm and dry air, bringing us back to seasonal
temperatures (near 80). High pressure will continue into Monday,
where temperatures will begin to climb back up to the low to mid
80s. Monday night, the ridge will still be over the Eastern United
States, with low temperatures near normal in the 60s.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
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 Tuesday...as 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. Will maintain high chc pops for
now...but can easily envision these pops being raised to at least
likely as model consistency and forecast confidence increases.

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.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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Conditions should remain VFR with area of rain and embedded
thunderstorms his evening, with brief periods of mvfr/ifr
possible in heavier -ra/tsra. As the atmosphere becomes more
saturated in the wake of the evening convection, we may see the
development of MVFR cigs, with IFR possible across the higher
terrain of the Southern Tier, after 06Z.

Conditions will improve to VFR after 12Z, as low level moisture
mixes out and slightly drier air moves into the region. However,
with troughing lingering across the region, expect more scattered -
shra/-tsra to develop Fri afternoon, especially inland from the
lakes.

Outlook...

Friday night...Mainly VFR with scattered showers and thunderstorms
tapering off in the evening.
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.
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&&

.MARINE...
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Winds will become southerly tonight as a warm front moves
northeast of the area, directing greater wave action into
Canadian waters. Low pressure will then move slowly from the
western Great Lakes Friday to southern Quebec by Saturday. This
will bring an increase in southwesterly winds to the eastern
Great Lakes, with Small Craft advisory conditions probable by
Friday afternoon for Lake Erie, and Saturday for Lake Ontario.
Winds and waves will decrease by Sunday as high pressure builds
into the Ohio Valley and eastern Great Lakes.
-- End Changed Discussion --

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...TMA/WOOD
NEAR TERM...TMA/WOOD
SHORT TERM.../RSH/ZAFF
LONG TERM...RSH
AVIATION...TMA/WOOD
MARINE...HITCHCOCK/TMA/WOOD