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Area forecast discussion 
National Weather Service Buffalo New York
708 PM EST sun Feb 1 2015

Synopsis...
a storm system organizing in the middle section of the nation will move
into the Ohio Valley tonight then move across Pennsylvania on
Monday. This will produce a wide swath of moderate to heavy snow to
the north of the low track tonight through Monday including all of
western and central New York along with very cold temperatures and
gusty winds. The snow will taper off from west to east Monday
afternoon. Some lake effect snow will develop in its wake...
especially Tuesday east of Lake Ontario.

&&

Near term /through Monday/...
areas of moderate snowfall entering the western southern tier as the
major winter storm gathers force across the lower Ohio Valley.
Expect snow to continue to spread across the forecast area this
evening and tonight...current forecast seems to be right on track.

Details...
merger of northern stream and southern stream systems has now
reached completion over the central Continental U.S....with this storm headed
for the Ohio Valley region. Generally speaking...the supporting
dynamics at the synoptic scale has been addressed in earlier
discussions and remains valid. A check of the latest 12z model suite
guidance yielding no glaring deviations from reality. Given the
consistency of the model trend for a slight northward shift...the
only changes for this forecast package were to shift forecasted
snowfall amounts slightly to the north. Overall this has little
bearing on forecast amounts for the area with general amounts in the
8 to 15 inch range. All warnings continue in place with the
exception of the advisory for Jefferson County. It is entirely
possible that Jefferson County may need to be upgrade eventually to
a warning... however confidence at this point is not as high as feed
of drier northeast flow may limit accumulation potential there.

Regional radars showing the light snow shield shifting into the
western third of the state this afternoon on cue with precipitation
onset meeting earlier forecast expectations. This initial light
snowfall is being driven by outstanding isentropic lift in
combination with very favorable right entrance region dynamics. In
addition...it appears the lead shortwave energy that was earlier
associated with the north half of the Desert Southwest circulation
is arriving on a good trajectory and is at least partially
responsible for the impressive Arch of higher radar reflectivities
currently in place over the southern Great Lakes/Northern Ohio
valley.

It appears that the highest impact portion of this storm for most of
western New York will come roughly between 03z and 12z as this
circulation lifts across our region combined with a plume of higher
Theta-E air which will work into the region at nearly the same time.
Models continue to suggest a well developed and long duration
deformation response striping over the area from 03z-12z as
well...which could lead to the potential for some mesoscale banding.
All this will likely help to enhance snowfall rates upwards of an
inch per hour.

In addition to the snow...another concern will be the increase
northeast winds tonight and Monday morning which may gust in excess
of 35 miles per hour...especially in the corridor from Rochester to Buffalo to
Erie Pennsylvania. This will create significant blowing...drifting
and visibility issues...particularly considering that the snow will
be of lower density. It is highly possible that some roads may
become impassable.

As the storm starts to shift to the coast Monday
morning...lake enhanced snows will become problematic for areas
south of Lake Ontario as the fetch turns more northerly. Profiles
suggesting there will be a window from early Monday morning through
Monday afternoon where decent snowfall rates will likely continue
along the South Shore of Lake Ontario with a continuation risk of
significant blowing and drifting snow.

Outside of the Linger Lake enhanced risk south of Lake Ontario the
departure of the middle level deformation to the east by Monday
afternoon...with a corresponding increase in upper heights filling
eastward late in the day will bring a diminishing trend to the snow.

The resident Arctic air will struggle to respond with temperatures
Monday only reaching the single digits and teens...with wind chill
value below zero.

&&

Short term /Monday night through Wednesday night/...
during the course of Monday night...the center of the winter storm
will lift from Cape Cod into the Canadian Maritimes...while
surface-based ridging and drier air over the Ohio Valley builds
northeastward across the lower Great Lakes. As the deeper synoptic-
scale moisture attendant to the departing low gets stripped away and
large-scale subsidence increases...whatever light snow showers there
are at the start of the evening should quickly taper off to just
some scattered leftover flurries across the bulk of the area...with
just some trifling additional accumulations possible. The one
exception to this will be south and southeast of Lake Ontario...
where some lingering light lake effect snow showers will gradually
become more scattered in nature...while dropping a fresh inch or two
of fluffy snow in the process. With a fresh batch of Arctic air in
place...nighttime lows will range from around zero south of Lake
Ontario to the negative middle teens across the north country...with
colder readings than this possible if skies manage to clear more
significantly than currently forecast. While winds will also be
lightening up...there will still be enough of a gradient in place to
generate some bitterly cold wind chills...with apparent temperatures
potentially reaching advisory criteria across portions of the area.

As we get into Tuesday...a warm advection regime will set up across
the region as the surface ridge axis slides to the Atlantic
coastline...and as a developing clipper system begins to take shape
across the central Great Lakes. This will allow temperatures to
recover some from the previous night's bitter cold...with highs
climbing back to the upper teens to lower 20s in most places.
Precipitation-wise...the day should generally remain dry outside of
areas downwind of Lake Ontario...which will again be subject to some
lingering lake effect snow showers. These will start the day in
scattered form southeast of the lake owing to the limited moisture
and low cap that will be in place...before lifting northward into
the north country over time as the low level flow backs to
southwesterly. As the afternoon progresses...these will also
probably become a little better organized as synoptic-scale moisture
increases in advance of the aforementioned clipper...and have
reflected this in the forecast by bumping probability of precipitation back up into the
likely range by later in the day. This said...any additional
accumulations out of these should remain on the light side.

Tuesday night...west-southwesterly flow lake effect snow showers
will continue across the north country during the evening...before
giving way to an advancing larger-scale shield of snow associated
with the encroaching clipper. The clipper itself will then bodily
cross the area on Wednesday with a general snowfall continuing...
before the snow then diminishes/transitions to some northwesterly
flow lake effect snow showers in the wake of this system Wednesday
night. At this point...both moisture and lift attendant to the
clipper appear plenty sufficient to warrant bumping probability of precipitation up to the
high likely range...with current model guidance suggesting the
potential for a total general snowfall of 2 to 4 inches out of this
system between later Tuesday night and Wednesday night. As for
temperatures...a milder southwesterly flow out ahead of the clipper
should allow readings to briefly moderate back into the upper 20s
and lower 30s on Wednesday...before the arrival of a new Arctic
airmass results in temperatures plunging back into the single digits
Wednesday night.

&&

Long term /Thursday through Sunday/...
in the wake of wednesday's clipper...a fresh northwesterly flow of
Arctic air will continue to pour across the lower Great Lakes on
Thursday. With 925 mb temperatures likely falling to between the negative
middle teens and the lower minus twenties per a consensus of the latest
medium range guidance...daytime highs will likely only average
within a few degrees of ten above...with wind chills generally
running between zero and ten below. The cold air should also help to
generate some scattered snow showers south and southeast of Lake
Ontario...however these should remain fairly light and limited in
scope due to the very dry nature of the Arctic airmass and rapidly
crashing inversion heights.

Thursday night and early Friday...the axis of surface-based ridging
will slide across New York state. In conjunction with further drying
and subsidence...this should result in any lingering lake effect
snow showers southeast of Lake Ontario disintegrating into some
leftover flurries while gradually lifting northward in response to a
general backing of the low level flow. Elsewhere...conditions should
be dry. Temperature-wise...Thursday night looks to be bitterly cold
as the ridge axis crests overhead and allows for skies to partially
clear...and this in conjunction with light winds should allow
readings to really plummet. Lows of 5 to 10 below zero should be
commonplace south of Lake Ontario...while readings will likely fall
to between 15 and 20 below zero across the north country. On the
backside of the departing surface ridge...the beginnings of warm air
advection will then allow temperatures to rebound a little on
Friday...though readings should still be well below average with
highs still only averaging out in the middle to upper teens.

Next weekend...the medium range guidance seems to be coming into
better agreement on yet another Arctic cold front easing across the
area during the course of Saturday and Saturday night...with this
boundary then stalling out a bit to our south on Sunday as a wave of
low pressure develops over the lower Ohio Valley. This should
translate into another round of scattered snow showers Saturday and
Saturday night...with developing northeasterly-flow lake enhancement
on the backside of the front resulting in some of these lingering
into Sunday across portions of western New York. As for
temperatures...warm advection out ahead of the front should allow
highs to recover into the middle 20s in most places...before yet
another fresh batch of Arctic air results in another downward trend
in temperatures to close out the weekend.

&&

Aviation /00z Monday through Friday/...
generally light snow across western New York this evening with moderate
snow entering the western southern tier. Once the snow arrives visibility
will drop to IFR...and remain there through the night and much of
Monday. The snow and IFR will be delayed until after about 06z
across the north country including kart. There will be embedded
bands of moderate to occasionally heavy snow with visibility possibly
dropping below airfield minimums at times from middle evening through
Monday morning. Expect ceilings to run MVFR at lower elevations and IFR
across higher terrain during the snow event.

The snow will begin to taper off from west to east during Monday
afternoon with visibility improving but likely remaining IFR much of the
time through late afternoon. Heavier snow may persist longer at kroc
due to lake enhancement off Lake Ontario.

Outlook...
Tuesday...VFR/MVFR with a chance of snow showers and local IFR east
of Lake Ontario.
Wednesday...MVFR/IFR with snow likely.
Thursday...MVFR with a chance of snow showers.

&&

Marine...
northeast winds will continue to increase tonight as low pressure
organizes and moves into the lower Ohio Valley...with high pressure
remaining in place over Quebec. The tightening pressure gradient
between the approaching low and strong high pressure over southeast
Canada combined with strong cold air advect will bring a period of
gale force winds to Lake Ontario tonight through Monday morning.
Winds will begin to diminish and become more northerly Monday
afternoon as the low pulls off the southern New England coast and
the pressure gradient relaxes.

Heavy freezing spray will be likely on Lake Ontario tonight through
Monday morning.

&&

Buf watches/warnings/advisories...
New York...Winter Storm Warning until 4 PM EST Monday for nyz010>014-
019>021-085.
Winter Weather Advisory from 1 am to 7 PM EST Monday for
nyz007.
Winter Storm Warning until 7 PM EST Monday for nyz005-006-008.
Winter Storm Warning until 7 PM EST Monday for nyz001>004.
Marine...heavy freezing spray warning until 7 PM EST Monday for
loz042>045-062>065.
Gale Warning from 11 PM this evening to 1 PM EST Monday
for loz042>044-062>065.
Small Craft Advisory from 11 PM this evening to 4 PM EST
Monday for loz045.

&&

$$

Synopsis...tma
near term...tma/wch
short term...jjr
long term...jjr
aviation...tma/wch
marine...tma

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