Area Forecast Discussion
Issued by NWS Buffalo, NY

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347
FXUS61 KBUF 221918
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
318 PM EDT Tue Aug 22 2017

.SYNOPSIS...
Several bands of strong to severe thunderstorms will continue to
cross the region this afternoon and evening ahead of a strong cold
front. Some storms may contain damaging winds and torrential
rainfall with an isolated tornado also possible. 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.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Severe weather event continues this afternoon across western and
north-central NY. Radar near 3pm shows the leading first round of
severe storms extending from the western Adirondacks southwest to
the Genesee Valley. A second line of severe thunderstorms is
extending from just south of Buffalo into the western Southern Tier.
Velocity/SRM signatures within radar scans show strong indication of
damaging wind and isolated tornado potential. A Tornado Watch
remains in effect for all of western and north-central NY through
9pm to cover for the severe storm and isolated tornado risk. Both
lines of storms have formed along prefrontal troughs with a
potential for even a third wave of storms possible along the
trailing cold front this evening. A strong lake breeze off Lake Erie
is likely hindering stronger convection across the Niagara Frontier
but this may be overcome synoptically later this afternoon when the
cold front arrives.

This evening the actual cold front will sweep east across the region
with a few more scattered, possible severe, 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.

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 have become
quite gusty today, especially in the normally windy spots northeast
of Lake Erie. Winds of 40-45 knots just off the deck over and
northeast of Lake Erie along with steep lapse rates should allow
some of this to mix down during the afternoon and early evening,
with typical funnelling down Lake Erie aiding in stronger winds.
This may 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 front.

Wednesday, 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 cool air aloft and some
added lake moisture as the attendant surface trough 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.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
The main feature of note during this period will be an upper level
trough that will be in place across the northeastern U.S. through
the period. A pair of shortwaves dropping out of Canada will
reinforce the troughing across the region, and with 850mb temps
falling to +6C generating a robust lake response, we can expect
fairly widespread cloud cover at least through Thursday. Shower
chances south/southeast of the lakes will only run to about 30
percent at best though, as there will be a dearth of moisture aloft.
It start to feel fall-like temperature-wise, with the trough causing
temperatures to fall into the upper 40s to mid 50s both Wednesday
night and Thursday night, with highs only reaching the upper 60s
Thursday.

Expect sunnier skies to end the work week on Friday, as the latest
shortwave passes to the east and surface high pressure begins to
build in from the upper Great Lakes. The corresponding
subsidence and very dry airmass, along with light winds aloft,
should outweigh lingering lake instability to provide for a
brighter end to the week, though it will remain on the cool
side, with highs in the upper 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A pleasant weather pattern is expected over the weekend and heading
into next week. Model consensus (ECMWF/GGEM/GFS) builds surface high
pressure across the region throughout the entire long term period.
This will result in a prolonged stretch of dry weather, with partly
to mostly clear skies. The back edge of an upper level trough will
pivot across the region Saturday night and Sunday. With 850 mb
temperatures falling to around +6C there may be some lake effect
clouds, and the shortwave may spark a stray shower.  This said, the
dry air mass will limit the potential for anything more than widely
scattered showers. Otherwise, the cool air mass will result in cool,
almost fall-like temperatures. Over the weekend highs will average
in the lower 70s with overnight lows falling well into the 40s
across the interior valleys. Temperatures will warm slightly early
next week, with highs in in the lower to mid 70s.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
VFR conditions will prevail through the bulk of today outside of any
convection with VFR then expected tonight and Wednesday following a
cold frontal passage.

Initial line of severe storms extends from just east of KART
southwest to near KDSV. A second line of severe storms extends from
just south of KBUF to KJHW. Both lines will spread very rapidly east
through this evening with a potential third line along the actual
cold front closer to 00z. Severe storms will produce a brief period
of heavy rain, gusty winds, and local IFR/MVFR 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.

VFR is expected Wednesday behind the cold front with breezy westerly
winds and sct/bkn stratocumulus clouds developing through the
afternoon. Scattered showers are also expected but should not bring
reduced flight categories.

Outlook...

Wednesday night and Thursday...VFR/MVFR with a chance of showers.
Friday through Sunday...VFR.

&&

.MARINE...
SW winds have increased this afternoon on both lakes Erie and
Ontario, bringing solid Small Craft Advisory conditions. Several
waves of strong to severe thunderstorms are also working across the
lower Great Lakes ahead of a cold front. These storms will bring
locally higher winds and waves and frequent cloud to lake lightning.

The 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.

&&

.TIDES/COASTAL FLOODING...
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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning until 11 PM EDT Wednesday for NYZ007.
     Beach Hazards Statement until 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
     NYZ010-019-085.
     Wind Advisory until 8 PM EDT this evening for NYZ001-002-010-
     011.
MARINE...Small Craft Advisory until 10 PM EDT this evening for LEZ020.
         Small Craft Advisory until 2 AM EDT Wednesday for LEZ040-
         041.
         Small Craft Advisory until 10 PM EDT this evening for
         LOZ030.
         Small Craft Advisory until 6 AM EDT Thursday for
         LOZ042>045.
         Small Craft Advisory until 11 PM EDT this evening for
         SLZ022-024.

&&

$$

SYNOPSIS...HITCHCOCK/SMITH
NEAR TERM...CHURCH/HITCHCOCK/SMITH
SHORT TERM...WOOD
LONG TERM...APFFEL
AVIATION...HITCHCOCK/SMITH
MARINE...HITCHCOCK/SMITH
TIDES/COASTAL FLOODING...HITCHCOCK



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