Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 160813

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

High pressure will build across the region through tonight. Patchy
fog this morning will give with to fantastic summer day with dry
conditions and lower humidity. A low pressure system will spread
showers and thunderstorms across the region late Thursday through


A cold 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
in the night is starting to clear. Otherwise, GOES-16 advanced
nighttime microphysics RGB reveals southern Tier valley fog
developing under the mostly clear skies there. Also, areas of fog
continue to develop along and ahead of the frontal boundary 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.

Tonight, high pressure will become centered over NY state promoting
ideal radiational cooling conditions. Southern Tier valley fog will
certainly develop again tonight. Temperatures and humidity will be
much more comfortable, as lows bottom out in the 50s to near 60
along the lake shores.


Consolidated mid level energy will lift from the upper midwest into
the upper great lakes during the period. Robust northward gulf
moisture transport will accompany a corresponding deepening of
southwest flow immediately downstream. This process will lift a warm
frontal boundary through the region Thursday and Thursday night. The
high degree of moisture advection tied to good system relative
isentropic ascent should provide a solid shot for rainfall late
Thursday and Thursday night. Locally very heavy downpours likely as
precipitable water values rise to near 2 inches.

Extent and residence time of warm frontal cloud debris/showers will
likely ultimately dictate the convective response with the trailing
cold front currently forecast to sweep through during the day Friday.

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.


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.


Southern Tier valley fog is developing per satellite imagery, 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/BUF/ROC are drying out in the wake a weak cold front passage,
and should be safe from any further fog this morning.

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 this afternoon with mostly sunny skies in the afternoon with
VFR prevailing.

Expect mainly VFR conditions tonight, with high pressure moving
across the area, except for IFR conditions in Southern Tier valley

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 night and Sunday...VFR with a chance of showers.


Winds will freshen early this morning in advance of a large surface
high. Winds will also veer to the choppy (but sub-
advisory) conditions can be expected in the nearshore waters of the
southern shore of Lake Ontario. 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





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