Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240600
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
100 AM EST Fri Feb 24 2017

.SYNOPSIS...
Unseasonable warmth will continue through Saturday morning. Through
this morning, a warm front will bring 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 TODAY/...
A developing storm system will move into the Central Plains
through the overnight hours with strong warm air advection ahead
of the storm causing the surface front lying near the
Pennsylvania 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
through this 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 /TONIGHT 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 THURSDAY/...
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 /06Z FRIDAY THROUGH TUESDAY/...
Ceilings will deteriorate to MVFR and then IFR overnight through this
morning as warm front with numerous showers and isolated thunder
lifts north across the region. Some MVFR/IFR visibilities are also
likely in the heavier showers or thunderstorms, especially in the
higher terrain of the Southern Tier early this morning.

Conditions will improve to VFR from south to north today as cloud
cover scatters out in the warm sector of an approaching surface low.
The surface warm front will likely stall just north of the NYS
Thruway this afternoon, with northeast winds and MVFR/IFR ceilings
lingering, while locations south of this should clear out to VFR
with southerly winds. Then tonight the warm front will lift well
north of the area, but conditions will deteriorate to MVFR with added
moisture ahead of the approaching cold front for Saturday morning.

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...
Winds and waves will hold well below advisory levels overnight.

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 this evening through Sunday evening for
     NYZ006>008.
MARINE...None.

&&

$$

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



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