Area Forecast Discussion
Issued by NWS Buffalo, NY

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740
FXUS61 KBUF 231904
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
204 PM EST Thu Feb 23 2017

.SYNOPSIS...
Unseasonable warmth will continue through Saturday morning. A weak
frontal boundary is crossing the region this afternoon with some
widely scattered showers mainly east of the lakes. Late tonight into
Friday morning, a warm front will bring more widespread showers and
perhaps some thunder. A strong cold front will cross the region
Saturday, and may be accompanied by thunderstorms with gusty winds,
followed by windy conditions Saturday afternoon and evening. A quick
shot of colder air Sunday may bring some lake effect snows east of
the lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...
A slowly deepening surface low is tracking across Quebec this
afternoon with a trailing cold front expected to cross western and
central NY through this evening. As this trailing cold front shifts
across the region there will be some widely scattered rain showers
with the greatest chances across the North Country closer to better
moisture. Temperatures continue to remain extremely mild today, with
readings in the upper 50s to mid 60s. Behind the front some cooling
will occur with temperatures falling back into the mid 50s for the
afternoon.

Early tonight, the cold front will briefly stall just south of the
NY/PA border leaving mild temperatures mainly dipping into the 40s
with some patchy fog also possible as air temps fall to near
dewpoint temps. A developing storm system near Southwest KS this
afternoon will shift across Missouri through the overnight hours
with strong warm air advection ahead of the storm causing the
surface front running along the PA border to shift north as a warm
front. A very moist plume of moisture and strong low level jet will
accompany the warm front and drive widespread rain showers and
possible a few isolated thunderstorms lifting across western and
central NY during the second half of tonight into Friday morning.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
A sharp mid level trough will move from the mid section of the
nation Friday to the Great Lakes Saturday. Meanwhile a strong
Colorado low will eject eastward across the Plains and take a
similar track. This system will provide an active period of weather
for our region including several rounds of rainfall, strong winds,
and possibly even a few thunderstorms.

On Friday the deepening low will move from northern Missouri in the
morning to Lake Michigan by early evening. Downstream of the
deepening low, a warm front will push northeast across our region. A
period of isentropic ascent and deeper moisture associated with the
warm front will allow for an area of showers to move from southwest
to northeast across the area. Showalter Index values will be around
-2C, suggesting the potential for a few elevated, weak thunderstorms
along the warm front. Most of the rain will fall in the morning
across Western and Central NY, with showers tapering off and
possibly ending altogether as the warm sector builds northward.
Showers will last longer across the North Country with a slower and
later advance of the warm front, but even here showers should taper
off Friday evening.

Temperatures will be fascinating to watch on Friday with a dramatic
temperature gradient across the advancing warm front. Across the
Southern Tier expect temps to soar well into the 60s, with some low
70s possible as the warm sector arrives. Latest 00Z model guidance
progs the warm front near the NYS Thruway by late in the day, with
areas from Buffalo to Batavia and eastward to Ontario county surging
into the 60s by late afternoon, assuming the warm front moves north
of those areas. Farther north near the Lake Ontario shore and across
the Saint Lawrence Valley, northeast winds may persist through the
afternoon and keep high temperatures in the lower 40s, creating a
30+ degree temperature gradient across the forecast area. Friday
night the warm sector will continue to mix northward. Any areas that
stay cool on Friday will warm into the 50s and possibly lower 60s
Friday night with increasing southerly breezes. These overnight
temperatures are a solid 20-25 degrees above the normal high
temperature for late February!

Most of Friday night will be mainly dry in the warm sector. Very
late Friday night and Saturday morning the surface low will move
through the central Great Lakes, with a strong cold front surging
east across the area. The mid level trough will continue to sharpen,
and take on a negative tilt as it moves into Ontario and western
Quebec, further enhancing large scale ascent across the lower Great
Lakes. Expect a band of heavy showers along the cold front, with
Lifted Index values around -2C suggesting some potential for a few
thunderstorms as well. The strength and linear nature of the large
scale forcing, and strong wind fields aloft suggest the potential
for a line of gusty showers and possible thunderstorms along the
front. If this line becomes focused enough, some damaging wind gusts
cannot be ruled out.

Following the cold front, strong cold advection will spread east
across the area on Saturday. Temperatures in the 50s and 60s first
thing in the morning will fall sharply through the day. Strong post-
frontal winds will become a concern, especially in the typical areas
northeast of the lakes where winds are enhanced. The track of the
low is favorable, with a deepening low moving through the central
Great Lakes. Model guidance shows decent pressure rises and implied
subsidence in the cold advection regime behind the cold front. The
00Z GFS also shows a decent tropopause fold, with the 1.5 PVU
surface extending down to around 600mb within the mid level trough,
often a signal of deep mixing potential.

The main negative for damaging winds behind the cold front is the
relatively modest winds aloft behind the cold front, with 50-55
knots at 850mb. If these winds fully mix, damaging surface wind
gusts of 60 mph are possible, but partial mixing is more likely to
produce solid advisory gusts to around 50 mph. That said, the thawed
and wet ground may put the area at greater risk for tree damage even
if winds come in just below warning criteria. Given the somewhat
marginal winds aloft, there is not quite enough confidence for a
High Wind Watch yet, but the setup will continue to be monitored
closely.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Saturday night and Sunday a deep but transient trough will bring a
brief return to winter as 850mb temps plummet to -14C. The airmass
is fairly dry behind the cold front, so expect nothing more than a
few scattered snow showers outside of lake effect areas. The airmass
will grow cold enough for a lake response, with lake induced
equilibrium levels rising to 6-8K feet. Boundary layer flow will be
westerly Saturday night, possibly veering a little more to WNW by
Sunday morning. This will target most of the snow across the Western
Southern Tier off Lake Erie, and the Tug Hill and Oswego County off
Lake Ontario. The relatively dry air should limit the intensity of
lake effect snow, with light to marginally moderate accumulations
possible. The lake effect snow will gradually diminish later Sunday
and Sunday night as high pressure builds from the Ohio Valley to the
Mid Atlantic, with ridging extending northward into the lower Great
Lakes.

Mother Nature will reload the upper level pattern for yet another
significant `cutter` storm during this period. This pattern...more
typical of the second half of March through April...will lead to
renewed warming with anomalous warmth once again possible by mid
week. This cutter may also bring another round of strong winds to
our region.

As we open this period on Monday...a relatively low amplitude flow
will be found over the Great Lakes region while a weak cold front
will try to pass through our forecast area. This feature may have
enough forcing and moisture for a few scattered rain and wet snow
showers, as temperatures reach the upper 30s to lower 40s in many
areas later in the day.

On Tuesday...several robust Pacific shortwaves will dig into...and
amplify...a trough over the western states. This will amplify a
downstream ridge over the eastern half of the country...thereby re-
opening a direct flow out of the GOMEX to the Great Lakes. All of
this will take place while another round of cyclogenesis will be
taking place over the central Plains. While our region will be
mainly rainfree on Tuesday...there will be a low chc for some light
rain showers within the warming airmass.

The weather will deteriorate Tuesday night and Wednesday as the the
deepening cyclone will eject out of the Plains and makes its way to
the Great Lakes. This will lead to more rain for the region...which
could be followed by the potential for strong winds Wednesday night.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Patchy MVFR CIG are in place this afternoon ahead of a weak cold
front that will cross the region this afternoon/evening. The will be
some widely scattered rain showers that form along the cold front as
it makes its way across western and central NY. However drier air
will quickly spill into the region behind the front temporarily
lifting cigs to VFR.

Early tonight the weak cold front will settle south to near the
NY/PA border then lift back north as a warm front late tonight. This
will bring a period of widespread showers and some IFR cigs/vis
across western NY the second half of tonight. The showers should
hold short of KART until around 12z Friday. The surface front will
lift north to about the southern shore of Lake Ontario through
Friday and possibly in between KBUF/KIAG. Some improvement to at
least MVFR and possibly VFR is likely behind the warm front with
some breezy southerly winds.

Outlook...

Saturday...Periods SHRA with MVFR and local IFR, then windy.
Sunday...VFR but IFR to MVFR in lake effect snow SE of both lakes.
Monday...VFR, possible MVFR...depending on low location with a
chance of rain and snow showers.
Tuesday...Chance of rain with MVFR/IFR possible.

&&

.MARINE...
A weak cold front will move across the lake this afternoon/evening
but low level moisture will continue to keep patchy fog possible on
the waters tonight. Winds and waves will hold below advisory levels.

A warm front will lift north across the eastern Great Lakes through
Friday with rain showers and possibly an isolated thunderstorm but
winds and waves are not expected to build until late Friday night
and Saturday when a powerful cold front will cross the Lower Great
Lakes from west to east. Strong, possibly gale force winds will be
found in the wake of the front Saturday and Saturday night.

&&

.HYDROLOGY...
There is a potential for flooding across the Eastern Lake
Ontario Region starting late Friday night and lasting into
early next week.

While the snow pack has largely melted across Western New York,
a significant snow pack remains east of Lake Ontario, including
the Black River basin. Snow water equivalent values are about
130% of normal, with this snow pack expected to become
increasingly ripe through the end of the week due to the warm
weather.

On Saturday, a strong system will pass to our north with
a prolonged period of warm (50+ degree) temperatures expected
late Friday through Saturday until the passage of a cold front
drops temperatures below freezing Saturday night. This will be
combine with gusty winds and high dewpoints to rapidly melt a
significant portion of the snow pack in place. This system will
also bring a period of rain Saturday, with amounts expected to
average around an inch.

This may result in multiple issues east of Lake Ontario. First,
the combination of snowmelt and rain may cause areal flooding on
small, faster responding creeks and rivers starting late
Saturday. Some ice jams are also possible. After this, runoff
will cause the Black River and its tributaries that drain the
Tug Hill Plateau and the western Adirondacks to respond
Saturday night and Sunday and lasting into next week. MMEFS
ensembles show a low probability for flooding at McKeever and
Boonville, but chances may be higher than indicated if surface
temperatures exceed the model consensus. The risk is greater for
the Watertown forecast point, extending upstream to Lyons Falls
with extensive snow pack contributing to the runoff for the
entire basin. Flooding is also possible on the Salmon River and
other rivers in northern Oswego County that drain the western
slopes of the Tug Hill. With this in mind, a flood watch has
been issued for Oswego, Jefferson, and Lewis counties from
Friday night through Sunday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch from Friday evening through Sunday evening for
     NYZ006>008.
MARINE...None.

&&

$$

SYNOPSIS...CHURCH/SMITH
NEAR TERM...SMITH
SHORT TERM...HITCHCOCK
LONG TERM...HITCHCOCK/RSH
AVIATION...SMITH
MARINE...SMITH
HYDROLOGY...APFFEL/HITCHCOCK



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