Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 152354
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
754 PM EDT Tue Aug 15 2017

.SYNOPSIS...
High pressure over the Upper Great Lakes this evening will gradually
build across our forecast area during the upcoming 36 hours. This
will guarantee a scintillating day across our region on Wednesday
before more unsettled weather arrives late Thursday into Friday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Early this evening, radar shows a few scattered showers
remaining across portions of Western New York and the North
Country. These should taper off over the next couple hours,
leaving mainly dry weather.

A robust shortwave passing to the north will push a weak cool
front through the region tonight. The overnight hours will then
feature gradually clearing skies...although some fog will be
likely in the Southern Tier valleys and in areas that picked up
significant rains from the afternoon convection. Since most of
the forecast area (exception North Country) will not experience
an airmass change in the wake of the front...temperatures
tonight are expected to drop to within a few degrees of 60.

On Wednesday...a large area of high pressure will supply us with an
absolutely beautiful late summer day. Some patchy stratus may
develop south of Lake Ontario in the northerly post-frontal flow during
the morning hours, but these should quickly mix out by the
afternoon. We can look forward to bountiful sunshine and light
winds with temperatures generally climbing into the mid and
upper 70s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
Surface high pressure will be overhead Wednesday night with clear or
mostly clear conditions, at least through the evening.  Toward
Thursday morning, some cirrus should be moving in with slowly
increasing clouds as the next system starts to move into the
Northern Great Lakes.

Thursday and Thursday night...the next feature of interest is
readily visible via satellite, with a clearly defined upper level
trough over the Western US.  As this feature moves off the
intermountain region and into the Central Plains, it will draw
moisture northward from the Gulf of Mexico...primed to move into
Western NY either late Thursday or Thursday night.  Will forecast a
categorical rain showers/chance of thunderstorms for Thursday night
for all but the Eastern Lake Ontario region.  Model QPF seems a
little on the low side considering high moisture content
(precipitable water near 2.0"), so will lean toward the higher side
with basin averages probably near/above 0.5" with of course higher
amounts in heavier showers.

A cold front sweeps across western New York Friday. This will
maintain chances for scattered showers and possible thunderstorms,
especially east of Lake Ontario.

While a mid level cyclonic flow will be in place across the Great
Lakes, weak surface ridging in the wake of the front will combine
with a dry slot to provide a mainly dry Friday night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
On Saturday...the GFS/ECMWF are in reasonable agreement that the
surface low responsible for the unsettled conditions late in the
work week will lift northeastward across Quebec Province...while
slowly pushing its attendant weak cool front from central/eastern
New York into New England. Meanwhile the Canadian GEM exhibits a
similar pattern...though with the low/cold front substantially
further to the south and west initially. For now...have opted to
disregard this latter (and more pessimistic) solution as it appears
to be an outlier...and instead indicate a mainly dry day for
Saturday...with just a chance of showers lingering across our far
eastern zones associated with the slowly departing cool front.
Otherwise we can expect less humid conditions and seasonable
temperatures to prevail...with afternoon highs mostly in the mid
to upper 70s.

Moving into the latter half of the weekend...some model disagreement
also continues into Sunday as well...with the GFS considerably more
amplified and slower with the passage of the next longwave trough
axis than the other guidance...which if realized would support
another general chance of showers and thunderstorms. Meanwhile...
the GEM/ECMWF would suggest a much faster/weaker trough passage
Saturday night with high pressure and dry weather then building in
for Sunday...which is much more in line with our existing continuity.
Given all this...have elected to hold PoPs below chance levels for
Sunday...with another mainly dry forecast. Meanwhile...850 mb temps
will recover a little from Saturday...which should allow highs to
climb back into the upper 70s to lower 80s.

After that there is much better agreement that Monday will feature
surface high pressure situated squarely over our region...which
should translate into a dry day and near ideal sky conditions for
viewing of the solar eclipse...while continued slow warming of our
airmass supports afternoon highs mostly in the lower to mid 80s. The
GFS/ECMWF then remain in lockstep agreement that fair and dry
weather should then continue through Monday night...before the next
mid-level trough and attendant cold front arrive on Tuesday along
with the next general chance for some showers and thunderstorms.
With warmer and more humid air advecting into our region out ahead
of this system...expect highs on Tuesday to surge into the mid to
upper 80s...while dewpoints climb back to moderately humid levels in
the lower to mid 60s.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Expect widespread VFR conditions to start the 00Z TAF cycle. A
weak cold front will drop southward across the region tonight,
resulting in a modest NNE post-frontal flow. Patchy stratus may
develop behind the front late tonight and into Wednesday morning
with few hours of MVFR conditions possible south of Lake
Ontario. Any clouds that do develop should mix out relatively
quickly Wednesday afternoon with mostly sunny skies in the
afternoon. The only other issue is fog which is likely to
develop in the typical Southern Tier river valleys which will
probably result in a few hours of IFR conditions at JHW.

Outlook...
Thursday...VFR deteriorating to MVFR as showers and thunderstorms
increase later in the day and at night.
Friday...Mainly VFR with a chance of showers and thunderstorms.
Saturday...VFR.
Saturday night and Sunday...VFR with a chance of showers.

&&

.MARINE...
Winds will freshen late tonight and early Wednesday in advance
of a large surface high. Winds will also veer to the
northeast...so choppy (but sub-advisory) conditions can be
expected in the nearshore waters west of Irondequoit Bay
Wednesday morning. During the afternoon as the large surface
high builds over the lake...winds and waves will subside.

Conditions will deteriorate over the Lower Great Lakes late Thursday
and Thursday night as a series of frontal boundaries will cross the
region. While winds and waves will remain below small craft advisory
levels during this period...there will be a heightened risk for
special marine warnings from an increasing coverage of
thunderstorms.

&&

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

&&

$$

SYNOPSIS...RSH
NEAR TERM...APFFEL/RSH
SHORT TERM...ZAFF
LONG TERM...JJR
AVIATION...APFFEL
MARINE...RSH/APFFEL



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