Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 221513

Area Forecast Discussion
National Weather Service Buffalo NY
1113 AM EDT Tue Aug 22 2017

A strong cold front will cross the region later today and tonight
with several bands of strong to severe thunderstorms crossing the
region. Some storms may contain damaging winds and torrential
rainfall. Rain will end from west to east this evening following the
cold front. Much cooler weather will then build into the region for
Wednesday through next weekend with a few spotty showers possible
Wednesday and Thursday. High pressure will then bring dry weather
Friday through the weekend.


Western and North-central NY is firmly within the warm sector of a
storm system centered over southwest Quebec near midday with gusty
southwest winds and dewpoints into the upper 60s to lower 70s. A
cold front to our west extends southwest from the low to the western
end of Lake Erie with the warm front lifting into southern Quebec.
Satellite imagery showing increasing low and mid cloud cover ahead
of the front but still enough break to allow for further surface
heating and destabilization. Radar near 11am shows some scattered to
isolated cells from near Erie PA and across the eastern end of Lake
Erie north to over Lake Ontario and east of Toronto. These storms
are being triggered along a prefrontal trough which is expected to
bring the first wave of severe weather starting early this

Synoptic Pattern...

A mid level trough will sharpen and dig across Ontario and Quebec
into tonight, with mid level height falls and DPVA overspreading our
region this afternoon and evening, providing strong large scale
ascent. The surface low will deepen across southwestern Quebec with
a strengthening cold front surging southeast late today and tonight.
As is often the case, most of our thunderstorms will develop along a
pre-frontal trough as it interacts with our local lake breeze
boundaries, well ahead of the actual cold front.

Expect storms to initiate along the southern edge of the Lake Erie
lake breeze from NW PA into SW NY around midday. A cluster of
showers and storms may also develop over or near Lake Erie and
spread into the Niagara Frontier around midday in response to the
increasing large scale forcing and prior to the stable lake shadow
becoming established. The lake breeze storms will then rapidly
expand and move northeastward across the rest of the area, reaching
the Genesee Valley during the early afternoon before moving to the
eastern Lake Ontario region by mid to late afternoon.

High resolution model guidance suggests a second round of storms may
develop across NW PA and SW NY during the mid to late afternoon,
spreading through the western Southern Tier and into the western
Finger Lakes. Meanwhile, strong southwest winds will force a stable
lake shadow to develop northeast of Lake Erie, likely bringing a
period of dry weather to the Niagara Frontier following the midday

This evening the actual cold front will sweep east across the region
with a few more scattered showers and thunderstorms, which will end
through the late evening and early overnight as the cold front
clears east of the area. A strong push of subsidence and drying
behind the cold front will bring clearing overnight.

Severe Weather Potential...

Moderate instability is beginning to develop inland from the lakes
with surface temperatures climbing into the low to mid 80s and
surface dewpoints approaching 70. SPC Mesoanalysis shows 1500 j/kg
of SBCAPE with the 14z analysis. Severe weather will be further
supported by strengthening large scale forcing, which will aid in
deep layer ascent and deep convective overturning. The low and mid
level wind field will become quite strong in the warm sector this
afternoon, with 0-6KM effective bulk shear increasing to 40-50 knots
along the leading edge of the front. The combination of instability
and shear become quite favorable for the organized severe weather
developing early this afternoon.

Parameter phase/space and strong linear synoptic forcing suggest the
initial storms will quickly grow upscale into bowing line segments,
with damaging winds being the primary risk. These bowing segments
will move very rapidly, with forward speed likely to exceed 50 mph
once they become organized. Large hail risk will be fairly low given
the weaker mid level lapse rates, but a few of the initial discrete
cores may produce isolated marginal large hail. Tornado potential is
fairly low with SPC expanding the 2% threat area westward late this
morning to include all regions inland of the lake breezes. Further
east, low level flow locally backed ahead of the line especially
across Central and Eastern NY could pose some risk of a brief QLCS
type spin-up, especially where any discrete cells merge with the
advancing line of storms.

Heavy Rainfall Potential...

PWAT rises to around 2 inches ahead of the cold front and warm cloud
depth is very deep, suggesting that storms will be efficient
torrential rain producers. Storm motion will be very fast and linear
however, which should prevent any organized risk of flash flooding.

Synoptic Scale Winds...

Outside of the severe weather potential, southwest winds will become
quite strong today, especially in the normally windy spots northeast
of Lake Erie. Following the pre-frontal trough and initial
convective line, winds of 40-45 knots just off the deck will develop
over and northeast of Lake Erie. Lapse rates should steepen
sufficiently to allow some of this to mix down during the afternoon
and early evening, with typical funnelling down Lake Erie aiding in
stronger winds. This will likely produce some gusts of 45-50 mph
across the Niagara Frontier. These winds will rapidly drop off this
evening with the loss of daytime mixing and passage of the cold


Wednesday and Thursday a large upper-level low will meander slowly
eastward across Quebec, while a couple of shortwave embedded in the
cyclonic flow will move across the region.

The first shortwave will dive southward out of Ontario province and
across the region Wednesday into Wednesday night. Marginal moisture
associated with this wave will combine with some added lake moisture
as the attendant surface front crosses the lower Great Lakes. This
will produce scattered showers across the region, which will be
locally enhanced by the northerly upslope flow into the Tug Hill,
and higher terrain from the western Southern Tier to the Finger
Lakes with the frontal passage. Outside of the scattered showers,
broken stratocumulus cloud deck will bring only spotty sunshine to
the region. 850 mb temperatures Wednesday will remain around +9 to
+10C, which will keep daytime highs in the low to mid 70s when
combined with the cloud cover. Showers will dissipate Wednesday
evening in the wake of the trough passage and with the loss of
heating. Overnight lows will bottom out in the upper 40s to mid 50s.

Cooler air will filter into the region Wednesday night and Thursday
in the wake of this frontal passage, with 850 mb temperatures
falling to around +5 to +6C for Thursday. This cooler air will
elicit a lake response, that will be mitigated by fairly dry air
and a stout inversion to start the day. Thus, this lake response
will mainly manifest as low cloudiness, which will help to keep
daytime highs limited to the mid to upper 60s. A sharper trough axis
will then move across Lake Erie Thursday late afternoon/evening.
Expect enough low level convergence with the attendant surface
boundary, along with some added lake moisture, to produce some
scattered showers and even perhaps thunderstorms as the mid-level
lapse rates steepen up. These will most likely be focused south of
Lake Ontario across the Niagara Frontier and Lake Erie late in the
day. As this trough moves over Lake Erie by late afternoon, any line
of showers and/or thunderstorms moving over the warmer lake waters
would be prone to produce waterspouts, and have included the chance
in the forecast. Showers and any thunderstorms will dissipate with
the loss of heating with clearing skies. Overnight lows will reach
the mid 40s to low 50s with the cooler airmass in place.


Friday through the weekend, the aforementioned upper level low will
make its exit eastward while a sprawling Canadian high pressure
system builds slowly eastward across the Great Lakes region. This
will bring a stretch of cooler and drier air more reminiscent of
fall, but with fairly light winds. There will be some day-to-day
warming as the airmass modifies with high temperatures slowly
building from the upper 60s Friday to the mid 70s by Monday. Nights
will be cool and crisp, with overnight lows ranging from the low
40s in inland valleys to the low 50s along the lake plains. The only
fly-in-ointment for the weekend will be a backdoor cool front
passage on Sunday. While the change in airmass will be fairly
minimal, there maybe just enough forcing and moisture with the front
to spark a few stray showers Sunday, mainly in the North Country.


VFR conditions will prevail through the bulk of today outside of any

Expect one or more lines of strong to severe thunderstorms to
develop across Western NY around midday or early afternoon, then
spread very rapidly northeast across the rest of the area through
late afternoon. These storms will produce a brief period of heavy
rain, gusty winds, and local IFR as they sweep across the area. A
few storms may be severe with surface wind gusts exceeding 50 knots.

In the wake of the line of storms, a few more widely scattered
showers and thunderstorms will develop from late afternoon through
evening, with VFR prevailing most of the time. These will end
overnight from west to east as a cold front crosses the area.

It will become quite windy today even away from the thunderstorms,
especially northeast of Lake Erie where gusts may peak at 35-40
knots during the afternoon and early evening near KBUF and KIAG.

Wednesday and Thursday...VFR/MVFR with a chance of showers.
Friday and Saturday...VFR.


SSW winds are increasing late this morning, expected to become
southwest and much stronger this afternoon on both lakes Erie and
Ontario, bringing solid Small Craft Advisory conditions. One or more
lines of strong to severe thunderstorms will likely cross the region
with locally higher winds and waves and frequent cloud to lake

A cold front will sweep east across the region this evening with
winds becoming northwest and diminishing on Lake Erie, with winds
and waves likely dropping below Small Craft Advisory criteria
overnight. Winds on Lake Erie will become west and likely increase
again Wednesday with another round of Small Craft Advisory
conditions. Winds will remain westerly and much stronger on Lake
Ontario overnight through Wednesday, with solid Small Craft Advisory
conditions continuing through Wednesday night before winds become
northwest and diminish by Thursday morning.


Strong southwest winds will develop over Lake Ontario late this
afternoon and early evening, then become westerly tonight
through Wednesday. The increase in winds and wave action will
bring and increase in shoreline erosion and lakeshore flooding
to the east half of Lake Ontario when combined with the already
high lake levels. The static lake levels have dropped since late
spring and early summer, so the impacts of this event are not
likely to be as significant as earlier in the season, but still
enough to warrant a Lakeshore Flood Warning.

In addition, the line of strong to severe storms expected to
cross Lake Ontario this afternoon may produce a seiche on the
lake, with a brief rise in water levels at the east end and a
sudden onset of stronger winds and higher wave action.


NY...Lakeshore Flood Warning from 5 PM this afternoon to 11 PM EDT
     Wednesday for NYZ007.
     Beach Hazards Statement from 5 PM this afternoon to 11 PM EDT
     this evening for NYZ007.
     Lakeshore Flood Warning from 10 PM this evening to 11 PM EDT
     Wednesday for NYZ004>006.
     Beach Hazards Statement until 11 PM EDT this evening for
     Wind Advisory until 8 PM EDT this evening for NYZ001-002-010-
MARINE...Small Craft Advisory until 10 PM EDT this evening for LEZ020.
         Small Craft Advisory until 2 AM EDT Wednesday for LEZ040-
         Small Craft Advisory until 10 PM EDT this evening for
         Small Craft Advisory until 6 AM EDT Thursday for
         Small Craft Advisory from 5 PM this afternoon to 11
        PM EDT this evening for SLZ022-024.



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