Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231551

Area Forecast Discussion
National Weather Service Buffalo NY
1051 AM EST Mon Jan 23 2017

A large low pressure system over the Mid Atlantic will churn
northward along the east coast today and tonight bringing widespread
precipitation. This will start as rain today and change to snow
tonight with portions of central NY receiving significant snow
accumulations. Colder air will then slowly filter into the region
into weekend with lake effect snows increasing east of the lower
Great Lakes.


...Significant snowfall expected for central NY tonight into

The only changes to continuity with this late morning package was
to continue the trend of delaying the onset of pcpn. Have backed
off by some 6 hours on the onset...largely based on radar trends.
This slower timing is supported by the newer guidance packages...
and also by the general synoptics that include a dry sfc high
nosing south across the North Country to the Finger Lakes Region.
While this will have an impact on the amount of rain that much of
Wrn NY picks up by evening...the brunt of the upcoming storm in
tonights time period is not expected to be affected.

That being said...WV imagery late this morning displays a large
stacked storm system churning northeast from South Carolina. The
greatest pressure falls are found off the general
track of this storm as per the 06z guidance looks good.
Precipitation ahead of this large storm system is just now (15z)
working into the northern tier counties of PA...which is several
hours (conservative estimate) slower than earlier forecasts.

During the course of the afternoon...the leading edge of the
steady pcpn will make its way north of the PA border and advance
across the western counties. While the pcpn will initially be in
the form of will gradually mix with snow and sleet by
late in the day before changing to just wet snow later tonight.
Since there will be little cold air for the advancing storm system
to tap into...the bulk of the cold air will be generated
internally through cooling due to per the 06z GFS

A closer look at the overall synoptic set up shows continued
support for widespread precipitation across western and central
NY. Upper level diffluence ahead of the 500 mb low coupled with
ample Atlantic moisture flux convergence into the region on the
anomalously strong easterly flow into NY state will produce
widespread precipitation late today and tonight. Highest QPF
amounts around an inch are likely through much of central NY near
the nose of best moisture advection, from Allegany Country through
the Finger Lakes toward the Tug Hill. QPF amounts are expected to
taper off to around a half inch across the Niagara Frontier and
the Saint Lawrence valley.

The various model guidances range from cold enough profiles to
support all snow, to some with stubborn warm noses aloft that
would support sleet or even freezing rain. Have thus leveraged
the colder EC/Canadian solutions to support his change over to all
snow tonight. Snowfall amounts will be highest across central NY
where the best forcing, and highest QPF will track, and thus this
is where confidence was high enough for a Winter Storm Warning.
Snowfall amounts here will most likely range from 6 to 10 inches.
Snowfall rates in the warning area will likely peak around an inch
per hour, with most of the snow coming in a 6 to 10 hour window.
On the northwest periphery of this warning, lower QPF amounts will
amount to advisory snow accumulations of 4 to 7 inches. Amounts
will be lowest across the far Western NY, which will see the least
QPF and least favorable dynamical cooling, with totals of 1 to 4
inches. Thus have excluded far western NY from any highlights at
this time.

All that said, snowfall accumulations will be very sensitive to how
quickly we can make the transition from rain to snow. If this occurs
more slowly than forecast, or if more of a mix of snow and sleet
occurs, then the totals will overall be lower, something that is
certainly possible.

On Tuesday, snow will taper off from west to east. Snow will likely
end across western NY by mid morning on Tuesday, but will likely
linger across the North Country through Tuesday afternoon.

Temperatures throughout this event will indeed be very marginal.
Highs this afternoon will be in the upper 30s to lower 40s, and will
only fall to right around the freezing mark tonight. Temperatures
will recover very little on Tuesday, remain nearly steady near the
freezing mark.


Tuesday night the complex and strong low pressure will move from the
Gulf of Maine into the Canadian Maritimes. Wrap around moisture and
cyclonic flow will linger across the eastern Lake Ontario region
Tuesday evening with a few more snow showers, especially across
higher terrain with an upslope flow component. Any additional
accumulations will be very minor (less than an inch). This will end
overnight as the deeper moisture pulls away. Otherwise the rest of
the area will remain dry as a weak ridge axis briefly builds across
the Lower Great Lakes.

On Wednesday a potent mid level closed low and associated surface
low will move into the central Great Lakes, with a downstream warm
front moving northeast across our area. Model guidance has trended
north and west with the stronger isentropic ascent and deeper
moisture along the warm front, which will initially lessen precip
chances across our area through Wednesday morning. By later in the
day DPVA will increase ahead of the strong mid level low, bringing
an increasing chance of rain showers especially across Western NY
and the eastern Lake Ontario region. Warm advection will push
temperatures into the lower to mid 40s for much of the area, with
mid to upper 30s across the North Country.

Wednesday night and Thursday the potent mid level closed low over
the central Great Lakes will open up and accelerate east down the
Saint Lawrence Valley as it merges with another trough crossing
Hudson Bay. Low level cold advection will begin Wednesday night,
then increase later Thursday as a secondary surface trough moves
southeast across the area. The passage of the mid level trough and
associated large scale ascent will support increasing coverage of
precip Wednesday night and Thursday, with the greatest amounts east
of both lakes with frictional convergence and upslope flow into the
higher terrain. It will become marginally cold enough for some lake
enhancement east of the lakes by Thursday, though not cold enough
for pure lake effect yet.

Precip type will be mainly rain Wednesday evening, then slowly mix
with wet snow first across the higher terrain and last on the lake
plains overnight. During the day Thursday expect mainly wet snow
across the high terrain, with a mix of rain and wet snow at lower
elevations. The marginal temperatures will produce elevation
dependent snow amounts, with a few inches likely across the higher
terrain east of both lakes and very little at lower elevations
through late afternoon Thursday.


Typical mid winter weather will become established again through the
long term period after a several week hiatus. A fundamental pattern
change will take place across North America, with a ridge building
over the west and a longwave trough becoming established over the
eastern half of the continent late in the week through next weekend.

Our area will be in the active region near the base of the longwave
trough, with numerous weak shortwaves moving through the base of the
trough. Each of these shortwaves may produce a few light snow
showers across much of the region, and will also bring subtle
variations to the low level flow, moisture depth, and cold air
structure which will impact ongoing lake effect snow.

The pattern appears favorable for a long period of lake effect snow
starting Thursday night and going right through the entire weekend.
Model guidance is in good agreement initially from Thursday night
through Friday night with mean low level flow from the WNW. This
would target the western Southern Tier off Lake Erie and the
Southern Tug Hill and Oswego County off Lake Ontario, possibly into
portions of northern Cayuga and NE Wayne counties at times. By
Saturday and Sunday model guidance begins to show some spread, with
the GFS maintaining WNW flow while the ECMWF backs flow more to the
WSW. Subtle shortwaves will likely produce some variation in low
level flow, although the details are always uncertain at this time

The airmass is not overly cold by late January standards, with 850mb
temps starting at around -8C Thursday night and dropping to around
-12C over the weekend. Temperatures are fairly cold at 700mb
however, and this combined with deep moisture will allow lake
induced equilibrium levels to rise to near 10K feet. The favorable
instability and longevity of the setup suggest significant
accumulations are possible east of the lakes.


Northeast flow off continues off Lake Ontario with plentiful
low level moisture still found around KIAG with IFR cigs
remaining at around 500 feet. KBUF/KROC have improved to MVFR/VFR
cigs late this morning, and expect this to last through this
afternoon. However, expect MVFR vsby at KBUF to remain through
noontime before improvement with daytime mixing. Expect MVFR cigs
to hang in today at KJHW, while VFR conditions will continue
through this afternoon at KART.

A storm system will bring a period of rain to the region. Expect
rain to reach the Southern Tier by early to mid afternoon, KIAG,
KBUF, KROC late this afternoon. Precip at KART will arrive by very
late afternoon/early evening, and may start out as a rain/snow mix
before transitioning to all snow during the evening.
Though conditions may improve to MVFR/VFR briefly before the rain
across western New York, within the rain, expect a deterioration
back to predominantly IFR and MVFR flight conditions. Rain will
transition to a wintry mix and then snow this evening and
overnight. The heaviest snow will fall across central/northcentral
NY, from ELZ to ART where vsbys will drop to a quarter to half
mile at times. Otherwise, light to moderate snow will fall at
most TAF sites overnight, with vsbys generally ranging 2 miles to
a 1/2 mile at times, along with IFR cigs through Tuesday morning.


Tuesday...Areas of MVFR/IFR with wet snow mixed with rain.
Wednesday and Thursday...VFR/MVFR with a chance of rain and snow.
Friday...VFR/MVFR with a chance of snow showers.


Small craft conditions will continue on the south central and south
west shoreline of Lake Ontario as east-northeast winds 20 to 25
knots persist into Tuesday as a strong low pressure system tracks up
the east coast. Winds and waves will remain elevated until the low
pressure system passes on Tuesday. Lake Erie remains less of a
concern as wave action will directed away from the eastern end of
the lake.


NY...Winter Weather Advisory from 7 PM this evening to 7 PM EST
     Tuesday for NYZ007.
     Winter Storm Warning from 7 PM this evening to 7 PM EST
     Tuesday for NYZ005-006-008.
     Winter Storm Warning from 4 PM this afternoon to 10 AM EST
     Tuesday for NYZ004-013-014-021.
     Winter Weather Advisory from 4 PM this afternoon to 10 AM EST
     Tuesday for NYZ003-011-012-020.
MARINE...Small Craft Advisory until 3 AM EST Tuesday for LOZ030.
         Small Craft Advisory until 1 PM EST Tuesday for LOZ042-043.
         Small Craft Advisory from 4 AM to 1 PM EST Tuesday for



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