Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231940
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
240 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 FRIDAY/...
A slowly deepening surface low is tracking across Quebec this
afternoon with a trailing cold front working across 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 running 3 standard deviations
above normal for this time of year and 40kt low level jet will
accompany the warm front and drive widespread rain showers and
possibly a few isolated thunderstorms lifting across western and
central NY during the second half of tonight into Friday morning.

During the day Friday, the low level jet will drive the band of warm
frontal showers and possibly thunderstorms quickly north across Lake
Ontario leaving western and north-central NY largely dry through the
afternoon hours with chances for showers lingering longest toward
the Saint Lawrence River Valley. The actual surface warm front will
trail behind the showers and mark the line between temperatures in
the 60s-70s to the south and 40s-50s to the north. This will leave a
very tight north-south gradient in temperatures with latest guidance
indicating the front will lift north to around the NYS Thruway. If
this exact position verifies, current forecast temperatures will tie a
record high at Buffalo (67/1906) but fall short at Rochester and
Watertown. The surface temperature gradient will be very
interesting to watch as the surface warm front shifts north
with some bust potential if the front does not make a push as
far north as expected. Winds will become breezy well south of
the warm front but any potential for gusty possibly strong winds
will hold off until behind the cold front on Saturday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
For the majority of western New York...Friday night could prove to
be the warmest night since last October. A deep `cutter` storm
centered over Lower Michigan will push its associated warm front
north of Lake Ontario Friday night...and this will place the western
counties deep within the storms warm sector. The strong southerly
flow of anomalously warm air (H85 10 to 12c) within this portion of
the storm system will mean that temperatures over the western
counties will struggle to drop below 60. Given that normal lows at
this time of year are in the lower 20s...that means we will be
nearly 40 degrees above normal.

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.

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.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Its going to sound like a broken record...but the main feature to
contend during this period will be yet another `cutter`/Colorado
low. Tis the season...albeit a bit early for such a high frequency
of these storms.

The overall pattern during this time frame will be quite
transitory...as a broad low amplitude trough over the country will
give way to a progressive longwave trough that will start over the
western states. If you have been reading these discussions during
the past week or so...you will have learned that significant cutter
storms typically mark the change in the overlying pattern...and this
time period will feature such a storm. The details...

Lake effect snow showers will end east of both lakes Sunday night as
weak warm advection will be found over the region. Otherwise this
should be an eventful night with temperatures settling into the 20s.

On Monday...several strong Pacific shortwaves will dive southward
along the West Coast and re-establish a large trough. This will
promote amplification of a broad ridge over the eastern half of the
country. Closer to home over the Lower Great Lakes...a weak cold
front will attempt to push through the region. While this may be
enough to generate some rain or wet snow showers...rising hgts and
limited moisture should hold any pcpn to a minimum. in other
words...the vast majority (of not all) of the day should be pcpn
free.

Significant cyclogenesis will begin across the central Plains late
Monday and Monday night. For what its worth...the operational ECMWF
looks to be most realistic with this whole storm...so have leaned
more heavily with this guidance package.

The newly formed storm system will track across the Plains to near
Chicago on Tuesday...while its associated far reaching warm frontal
boundary will approach our region. This could lead to some light
rain or snow for our region...which should increase in coverage and
intensity Tuesday night and Wednesday as the parent low is forecast
through the Lower Great Lakes.

In the wake of this system...there will be the risk for strong winds
Wednesday night and Thursday...although guidance is not quite as
impressive looking with it than it was in earlier runs. There is
also markedly more spread in the various ensemble solutions.

Either way you slice it though...strong cold advection will be found
over the region by Thursday. While scattered snow showers should
be found throughout the forecast area...the snowfall will be
enhanced east of the lakes where a lake response should be in
place.

&&

.AVIATION /20Z 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/RSH
LONG TERM...RSH
AVIATION...SMITH
MARINE...SMITH
HYDROLOGY...APFFEL/HITCHCOCK



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