Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241807

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

An upper level trough will slowly cross the region tonight into
Monday which will produce a few 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 humidity trend upward again Wednesday and Thursday.
A weak area of low pressure will cross the region Friday and
Saturday bringing the next chance of showers and thunderstorms.


Visible satellite imagery showing thicker mid level clouds spreading
into western NY this afternoon. Central NY and the North Country are
still holding onto a good deal of sunshine, but clouds will increase
there as well through the mid to late afternoon. Temperatures are
rising efficiently despite the thicker cloud cover, with highs in
the upper 80s to around 90 this afternoon across lower elevations,
and low to mid 80s across the higher terrain and North Country. Lake
breezes will keep areas within a few miles of Lake Erie and Lake
Ontario cooler.

Upstream deep moist convection, and the remnants of earlier
convection, across southern Ontario and Northern Ohio will by in
large pass by to our south per latest radar trends and short term
mesoscale guidance. A few showers or an isolated thunderstorm may
clip Chautauqua and western Cattaraugus counties this evening as
more unstable air begins to spread into the southwest corner of the
state, but otherwise the rest of the area will stay dry through this

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

Temperatures will be very warm, with lows in the mid 70s on the lake
plains tonight along with steadily increasing dewpoints. Highs on
Monday will reach 85-90 depending on how much sun develops in the


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.


The pattern has the potential to become at least a little more
active from late week into the first half of next weekend. The
expansive mid/upper level ridge which has dominated the central and
eastern CONUS will be knocked back as the longwave pattern buckles
across North America, with a western ridge and eastern trough
pattern becoming established by next weekend. The developing
longwave trough in the Great Lakes and Northeast states will be
carved out by several mid level shortwaves, each of which will bring
a period of large scale ascent and increased deep layer moisture to
our region.

Looking at the details, the first relatively weak trough will
approach the Great Lakes Thursday afternoon and evening. This system
may touch off a few widely scattered showers and thunderstorms with
sparse coverage. Models begin to diverge on the timing details of
the finer scale features by Friday and Saturday, but most
operational and ensemble guidance show a more significant mid level
trough and associated surface wave moving through the Ohio Valley
and eastern Great Lakes either Friday or Saturday, with a better
chance of somewhat more widespread showers and thunderstorms.

Temperatures will continue to run hot through Thursday, with 850mb
temps of around +18C supporting highs around 90 at lower elevations
away from the lakeshores. More clouds and showers will bring
temperatures back closer to average by Friday and Saturday.


Extensive mid/high clouds from earlier upstream convection will
continue to spread from west to east across the area this afternoon
and evening with VFR prevailing. Several batches of showers and
thunderstorms upstream across northern Ohio will pass mostly to our
south, although an isolated shower or thunderstorm cannot be ruled
out this evening across the southwest corner of the state near KJHW.

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 timing and coverage of any thunderstorms
still in question, VCSH qualifiers have been used in the TAFs for
now until the timing can be refined. By Monday afternoon most of the
scattered thunderstorms should be confined from the Southern Tier
eastward across central NY and the North Country, with increasing
southwest flow off Lake Erie providing an expanding stable lake
shadow and reducing the chance of convection across much of western

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.


Light southwest winds will prevail through this evening on Lake Erie
with flat wave action. Northeast winds in the 10-15 knot range will
continue on Lake Ontario with waves up to 2 feet along the south
shore. 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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