Area Forecast Discussion
Issued by NWS Buffalo, NY

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500
FXUS61 KBUF 230931
AFDBUF

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TUESDAY/...
...Significant snowfall expected for central NY tonight into
Tuesday...

A large low pressure system seen on WV imagery this morning across
the southeast will move northward through the Mid Atlantic today and
tonight and finally off the New England coast on Tuesday. The result
is a high confidence forecast in widespread precipitation across the
region from today through tonight and into Tuesday morning. However,
there still remains lower confidence in the precipitation type and
snow accumulations due to very marginal thermal profiles.

The synoptic dynamics are very favorable 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. 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.

Again, the challenging part of this forecast remains the very
marginal thermal profiles. This event will start as all rain across
the region today. However, as we get into the later part of the
afternoon and this evening, marginally cooler air will be advected
in on the easterly flow from the cooler airmass over New England.
This, combined with increasing precipitation rates by this evening,
will allow for dynamically cooling to further cool the column and
support a change over from rain to possibly some wintry mix and then
over to snow tonight. This is the tricky part of the forecast. The
various model guidances range from easily cold enough to support all
snow, to some with stubborn warm noses aloft that would support
sleet or even freezing rain. Expect that dynamical cooling in the
high precipitation rates, something the models usually do not
capture well enough, will be enough to push the profile cold enough
to support all snow. 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.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
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
range.

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.

&&

.AVIATION /10Z MONDAY THROUGH FRIDAY/...
Northeast flow off Lake Ontario with plentiful low level moisture
will maintain low IFR stratus around 300 feet at KBUF/KIAG/KROC
through sunrise Monday before improvement with daytime mixing.
Visibilities may also decrease at these sites overnight, with IFR or
lower possible at times. This low stratus will also impact the hill
tops of the southern Tier bringing low IFR conditions to JHW. KART
will see mainly MVFR conditions prevail with offshore flow
overnight.

Monday a storm system will bring a period of rain to the region.
Expect rain to reach the Southern Tier around daybreak, KIAG, KBUF,
KROC just after noontime, and KART by late afternoon. Though
conditions may improve to MVFR/VFR briefly before the rain, within
the rain, expect a deterioration back to IFR and MVFR flight
conditions. Rain will turn to a wintry mix late in the TAF cycle.

Outlook...

Monday night...Areas of MVFR/IFR with rain changing to wet snow.
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.

&&

.MARINE...
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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
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 1 PM EST Tuesday for LOZ042-043.
         Small Craft Advisory from 4 AM to 1 PM EST Tuesday for
         LOZ044.

&&

$$

SYNOPSIS...CHURCH
NEAR TERM...CHURCH
SHORT TERM...HITCHCOCK
LONG TERM...HITCHCOCK
AVIATION...CHURCH
MARINE...CHURCH



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