Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 280218

Area Forecast Discussion
National Weather Service Buffalo NY
1018 PM EDT SAT AUG 27 2016

High pressure over the Saint Lawrence Valley will drift east
overnight. This will allow a weak warm front to lift across our
region overnight...followed by a prefrontal trough and trailing
weak cool front Sunday afternoon and evening. In the process...our
region can expect a couple rounds of scattered to numerous showers
and thunderstorms between tonight and Sunday. The next round of
fair weather will then move in for Monday and Tuesday when high
pressure builds in from the Upper Great Lakes.


Regional surface analysis at 02z shows sprawling surface high
pressure centered over the Saint Lawrence Valley...and weak/broad
surface low pressure over the western Great Lakes. This latter
feature is a reflection of several spokes of shortwave energy that
are in the process of lifting across the central Great Lakes...while
also generating some attendant clusters of showers and embedded

Through the course of tonight...the above shortwave energy will
continue to lift northeastward around the periphery of an
anomalously strong Bermuda High...a track that will take it across
nearby Southern Ontario and Lake Ontario. At the same time...a
pseudo-warm frontal boundary (really a dew point front) over
northeast Ohio/northwestern PA will also lift northeastward across
our region. As was pointed out Saturday afternoon... this boundary
separates the lingering drier air over our region (dewpoints in
the lower 60s) from considerably more humid air (dewpoints around
70) lying over the Ohio Valley.

As this airmass makes its way into our forecast area overnight
its leading edge will quickly destabilize our airmass...and this
in conjunction with the passing shortwave energy aloft will help
to trigger the development of some scattered showers and
thunderstorms...with the bulk of these likely to be found over the
far western counties in the vicinity of the mid level support and
corresponding 925-700mb frontogenesis. This scenario is identical
to what happened over our region just a few days ago.

By the start of Sunday morning the last of the shortwave energy
will be in the process of crossing Lake Ontario...with any
attendant convection making its way across parts of the Finger
Lakes and Eastern Lake Ontario regions...while also ending across
the far western counties.

After several hours of subsidence in the wake of this feature...
a second round of convection is expected to develop Sunday conjunction with both renewed daytime heating of
our warm and newly humid-again airmass...and the arrival of a
prefrontal trough and developing lake breeze boundaries. Expect
the bulk of this convection to focus along and inland from these
surface boundaries...which should result in the most numerous
activity extending from the Southern Tier northeastward across the
Finger Lakes and into interior portions of the North Country...
where likely PoPs remain intact from continuity. Meanwhile...
relatively lower chances for convection will be found over and
immediately northeast of the lakes...with a secondary maxima
extending from the Niagara Peninsula eastward across Niagara and
Orleans counties...within the lake breeze convergence zone and
in advance of the actual surface cold front...which will not
actually cross our region until sometime Sunday evening.

As was mentioned previously...this second round of convection
could become rather strong in areas away from the
SBCAPEs of 1500-2000 j/kg will be accompanied by impressive 10 deg
C/km low level lapse rates. This `fat CAPE` in the presence of
modest amounts (20-30 kts) of bulk shear should be supportive of
storms capable of producing some gusty winds and possibly some
small well as some heavy downpours given precipitable
water values pushing 2 inches. Given all this...have added some
enhanced wording to the forecast and HWO to better reflect this

As for temperatures...overnight lows will range from the lower
60s east of Lake Ontario to around 70 along the lakeshores of far
western New York... while temperatures on Sunday will climb to
between 85 and 90 along with increasingly uncomfortable humidity surface dewpoints will again reach into the mid and
upper 60s.


By Monday, a shortwave trough will track overhead and into New
England by the afternoon. Morning cloud cover will dissipate from
northwest to southeast as drier air and subsidence move into the
region through the afternoon. Temperatures will take a step back on
Monday, as 850 mb temperatures fall to +12 to +14C, thus highs will
be in the upper 70s to low 80s. Drier air will mix down in the
afternoon, allowing dew points to fall into the comfortable 50s.
High pressure will build across the region Monday night and Tuesday
leaving dry conditions and mostly clear skies. Monday night will
feature optimal radiational cooling with a dry airmass, and light
winds allowing temperatures to fall into the 50s for most locations,
except near the lake shores and urban locations. Tuesday will see a
warming trend as high pressure slights to slide east and the airmass
modifies with 850 mb temps to +17C, resulting in high temperatures
back into the mid 80s.

The upper level pattern across the CONUS starts to become more
interesting into Wednesday as a large Pacific trough craves out
across the western US which helps with downstream development of a
large ridge across the central plains. During the day Wednesday,
this will open the door for Canadian sourced airmass to dive from
the Hudson Bay region toward the northeast US. This airmass will be
on our doorstep by the second half of the day Wednesday. A warm,
humid and unstable airmass will be in place ahead of this front
across our region for the first half of Wednesday, and thus we
should see at least some scattered convection across the region
ahead of the frontal passage. However, with models trending quicker
on the arrival of the front, there may not be enough time
destabilize ahead of the frontal passage on Wednesday to develop
stronger thunderstorms across western NY.


An upper level trough axis will dig across Northern New England
through Friday. This will set up a persistent northwesterly flow
with cold air advection during this time. Model guidance is in
good agreement, with the 12Z GGEM/ECMWF/GFS all showing a similar
pattern. As such, model consensus will serve as a good starting
point, however some adjustments are still needed.

GFS BUFKIT shows moisture trapped beneath an inversion at about 5k
ft south of the lakes. Although deep layer mean RH largely misses
this, consensus 850 mb forecast to drop to +3C should support
some lake effect clouds during during the Wednesday through Friday
night period. Moisture is shallow and the flow is mostly
perpendicular to the lakes which will make lake effect rain
showers unlikely. However, because of this consensus guidance is
likely too warm for high temperatures on Thursday and Friday.
Daytime highs will be cooler than they have been for some time,
with many areas struggling to reach 70 on Friday.

For Friday night and Saturday, high pressure is forecast to build
across the region with dry and pleasant weather going into the
weekend. Good radiational cooling will result in chilly overnight
temperatures Friday night, followed by seasonable temperatures for


Overnight...a mid level disturbance will pass by just to our
northwest while bringing the risk of some scattered showers and
thunderstorms to our region. Outside of any convection...cigs and
vsbys should remain at VFR levels.

On Sunday...a period of subsidence in the wake of tonight`s
disturbance will allow for a period of relatively dry weather
between the late morning and very early afternoon hours...before a
prefrontal trough pushes through the region and (in conjunction
with developing lake breeze boundaries) triggers a second round of
scattered to numerous showers and thunderstorms...which will be
most numerous from the Southern Tier northeastward into the Finger
Lakes. Expect the risk of localized reductions to MVFR/IFR within
this convection...which could also present the risk for some gusty
winds and heavy downpours. Otherwise...general VFR conditions
should prevail.

Sunday night...Mainly VFR with some leftover evening showers and
Monday and Tuesday...VFR.
Tuesday night and Wednesday...Mainly VFR with a chance of showers and


High pressure over the St Lawrence Valley will move east
overnight... and this will allow the first of two frontal
boundaries to push across the region. While light winds and
negligible waves will remain in place... there will be an
increasing risk for thunderstorms as we progress through the

While winds will freshen somewhat across the Lower Great Lakes
on Sunday...the main concern will be the continued risk for
thunderstorm activity as a prefrontal trough and weak cool front
will both cross our region between Sunday afternoon and evening.

Fine weather for boating will then return late Sunday night and
Monday as the next Canadian surface high builds across the region.





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