Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250233

Area Forecast Discussion
National Weather Service Buffalo NY
1033 PM EDT SUN JUL 24 2016

An upper level trough will slowly cross the region late tonight
and Monday while producing scattered showers and thunderstorms. A
trailing cold front will pass through our region Monday evening...
followed by slightly cooler and less humid weather Tuesday before
temperatures and eventually humidity levels trend upward again
Wednesday and Thursday. A weak area of low pressure will then
cross the region Friday and Saturday along while bringing the next
chance of showers and thunderstorms.


As of 0230Z...regional satellite imagery shows that the first batch
of mid and high clouds continues to make steady eastward progress...
with its back edge now situated from eastern Lake Ontario to the Upper
Genesee Valley. Behind this lies a substantial break in the cloud cover
that stretches all the way back to Southern Ontario and southeast
Lower Michigan...with more clouds and developing scattered convection
situated to the west of this...along a prefrontal trough over west-
central Michigan.

Have updated the forecast to account for recent satellite trends...
which suggest that the region will see varying amounts of mid and
high clouds for much of the overnight hours...before clouds and
convective chances both increase late tonight with the approach of
the aforementioned prefrontal is discussed below.
Otherwise expect a warm and increasingly humid night as increasing
amounts of warmth and moisture are advected into our region in
advance of the prefrontal trough...with overnight lows ranging
between the upper 60s and mid 70s.

Late tonight a weak mid level trough and pre-frontal surface trough
will approach western NY. Mesoscale model guidance continues to
struggle with the details of timing and placement for convection,
but in general expect scattered convection that develops this
evening across lower Michigan to spread ESE across southern Ontario
and reach western NY late tonight. The convection will have some
large scale support, with ascent and deeper moisture increasing
ahead of the mid level trough. A modest 30+ knot low level jet will
also support an increase in low level convergence and moisture
transport across western NY late tonight. Even so, given the ongoing
drought and lack of model consensus have kept PoPs in the high
chance range for late tonight and early Friday.

On Friday the morning convection associated with the pre-frontal
trough and first mid level trough will continue to move ESE across
the area. Following the morning convection, if enough breaks in the
clouds are realized, moderate to strong instability will develop
with very warm surface temperatures and high boundary layer
moisture, while mid level height falls begin to overspread the lower
Great Lakes. A stronger mid level trough will approach in the
afternoon, with the actual surface cold front not crossing the area
until the evening. The main focus for afternoon convection will be
along the lake breeze convergence zones, and possibly along residual
outflow boundaries from morning convection. Expect coverage to be
scattered in nature, with the best coverage from the Southern Tier
across the Finger lakes to central NY.

If the greater instability values suggested by some operational
models are realized, there may be at least some severe weather
potential as deep layer shear increases into the 35-40 knot range by
mid to late afternoon. By this time much of the convection will
likely be east of our area, but a few storms may linger along lake
breeze boundaries farther west from the Southern Tier into the
Finger Lakes to southern Tug Hill region. The area will be situated
in the right entrance region of a 90+ knot upper level jet which
will provide upper level divergence and aid in storm

Highs on Monday will reach 85-90 depending on how much sun develops
in the afternoon.


Monday night through Wednesday night will feature dry and warm
conditions as high pressure builds across the region and lingers
through mid-week. An upper level trough will exit to our east Monday
night giving way to mainly zonal flow with some weak ridging Tuesday
into Wednesday. A surface high will build across the Ohio valley
Tuesday and remain stalled there through Wednesday. 850 mb
temperatures will take a small step back to around +16C on Tuesday
behind the departing wave, allowing high temperatures to run near
seasonal values, while drier northwesterly flow will cut dew points
back into the mid to upper 50s, making the warmth more comfortable.
By Wednesday, the modifying airmass under the surface high will push
850 mb temperatures to about +18C, resulting in afternoon
temperatures back into in the upper 80s. However, humidity will
remain low as the dry high pressure remains in control and dew
points again drop into the mid 50s for the afternoon. Overnight lows
will run in the mid to upper 60s near the lake plains. Mainly clear
skies and light winds allow radiational cooling to drop interior
valleys into the mid to upper 50s.


While drought busting rains are not anticipated during this
period...there is relatively high confidence that the pattern will
be more many areas should pick up at least a little
rainfall. This will be due to a subtle shift in the dominant ridge
that has been in firm control of the country.

Unlike the past couple weeks when an expansive sub-tropical ridge
either flexed its muscles with anomalously high heights over the
nations mid section...or stretched from ocean to ocean across the
southern half of the Conus...this time frame will feature low
amplitude troughing over the Great Lakes region. Meanwhile...the
heart of the aforementioned ridge will have retrograded to the
Desert Southwest. This upper level transition will encourage a
little more baroclinicity across the Great Lakes region...which
should support a more active storm track.

At the surface...the period will open with a wavy frontal boundary
that will be stalled in the vcnty of the Mason Dixon Line. It is
interesting in that all of the real baroclinicity...lift and moisture
will be found a few hundred miles north of the sfc front. This
should initially keep the bulk of any showers and thunderstorms
north of the international border...but as push into Friday...a
fairly well organized wave will develop over the Mid West and slowly
track east along the front. The ensembles are all over the place
with the location...speed and track of this wave...but all are in
general agreement that the system will move close enough to our
region to help generate more widespread rainfall. The best
opportunity for some rain would be Friday and Friday evening with
basin average rainfall averaging under a quarter inch...but locally
up to three quarters of an inch.

Confidence drops off for the weekend as a second wave could bring
another round of beneficial showers and thunderstorms to the
forecast area. This will largely depend on the strength of the first
system will only use relatively low pops to express this

In terms of temperatures...while mercury levels will generally be
lower than those of the past few weeks...there is high confidence
that they will remain close to...if not still a few degrees above


Through the early overnight hours...largely dry VFR conditions should
prevail underneath varying amounts of mid and high cloud cover.

Late tonight and Monday morning...a trough will cross the lower Great
Lakes region and bring an increasing chance of scattered showers and
thunderstorms. With the exact timing and coverage of any convection
still remaining very much in question, have stuck with VCSH/VCTS
qualifiers in the TAFs until the evolution of the expected convection
becomes more clear. By Monday afternoon most of the scattered showers/
thunderstorms should be confined from the Southern Tier northeastward
across central NY and the North Country...with an increasing southwest
flow off Lake Erie driving an expanding stable lake shadow and reducing
the chance of convection across much of western New York.

Monday night through Wednesday...Mainly VFR.
Thursday...Mainly VFR with a chance of showers and thunderstorms.
Friday...VFR/MVFR with a chance of showers and thunderstorms.


A cold front will move east across the lower Great Lakes on Monday.
Southwest winds will increase along and ahead of the cold front,
especially on Lake Erie where winds and waves may approach Small
Craft Advisory criteria in the afternoon. Winds will diminish Monday
night following the passage of the weak front, with winds and waves
then expected to remain below Small Craft Advisory levels through midweek.





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