Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 160537
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
137 AM EDT Wed Aug 16 2017

.SYNOPSIS...
High pressure over the Upper Great Lakes early this morning will
gradually build across our forecast area through Wednesday night.
This will guarantee a scintillating day across our region on
Wednesday before more unsettled weather arrives late Thursday into
Friday.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1 AM the frontal boundary has crossed the Niagara Frontier,
marked by a northerly wind shift and lower dew points spilling into
the region. As a result some of the lower visibility observed
earlier int the night is starting to clear there. Otherwise, GOES-16
advanced nighttime microphysics RGB reveals southern Tier valley fog
developing quickly under the mostly clear skies there. Also, patches
of fog continue to develop along and ahead of the frontal boundary
near Rochester and in the eastern Lake Ontario region. Expect areas
of fog to remain focused in the Southern Tier valleys through
morning. Meanwhile, east of Lake Ontario, areas of fog will likely
also linger through morning as northerly upslope flow develops in
the wake of the frontal passage, with little change in dew points
expected there behind based on upstream observations in southern
Ontario.

During the daytime today, 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 /TONIGHT 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 /06Z WEDNESDAY THROUGH SUNDAY/...
Southern Tier valley fog is developing and will bring MVFR to IFR
restricts to JHW early this morning. Also fog has developed in the
eastern Lake Ontario region and will likely prevail through sunrise,
bringing patchy areas of IFR conditions. IAG and BUF are drying out
in the wake a weak cold front passage, and should be safe from any
further fog this morning. ROC may see MVFR fog linger through 07 or
08Z as the weak cold front crosses the terminal, then expect mainly
VFR thereafter.

Patchy stratus may develop behind the front late tonight and into
mid-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 with VFR prevailing.

Expect mainly VFR conditions Wednesday night, with high
pressure moving across the area.

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 early this morning 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...CHURCH/RSH
NEAR TERM...CHURCH/RSH
SHORT TERM...ZAFF
LONG TERM...JJR
AVIATION...APFFEL/CHURCH
MARINE...CHURCH/RSH



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