Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
502 am EST Friday Dec 6 2013
a wave of low pressure passing to the east will bring a wintry mix
across the region this morning. A second wave of low pressure will
then bring another round of snow starting this afternoon and
continuing into tonight. Much colder temperatures will remain in
place today through the upcoming weekend.
Near term /until 6 PM this evening/...
the upper level pattern this morning shows expansive polar low
centered over James Bay extending westward across the southern
prairie provinces to down along the US/Canadian border. A large upper
high is in place over the Gulf of Mexico with an enhanced southwest
flow that extends from central Texas to New England. Water vapor
satellite imagery shows an atmospheric river of moisture embedded
within this southwest flow. At the surface a cold front is extended
from the mouth of the Mississippi River along The Spine of the
Appalachians into New England. Two separate waves of low pressure
are analyzed along this front. One shifting into southern new and
the second across southwest Virginia and western North Carolina.
Have bumped up the start time of the Winter Weather Advisory to be
active this morning and continuing into tonight along with adding
southern Erie...Wyoming...Livingston and Ontario counties. This is
to cover for winter weather impacts from this morning and for
another round of impacts coming later today with the second wave of
As of 5am the first wave is generating a wide area of mixed winter
precipitation from the southern tier northeast across The Finger
lakes to central New York with rain showers observed in the
warmer air across south central New York. Through the rest of the
morning hours we will see this first wave shift further east across
New England with snow...sleet and patchy freezing rain tapering off
across western New York with counties closer to the New York/PA border
being the last to see a break from this wintry precipitation if there is
even a break at all. Looking to the southwest there is still plenty
of radar echos present to continue skirting the southern tier
counties. See the Winter Weather Advisory for specific snow and ice
totals. Counties not included in the advisory will generally receive
and inch of less of snow possibly mixed with some sleet.
Later this morning much of western and north central New York will
see a brief lull in the wintry weather before the second wave of
low pressure works north along the appalachian range toward western
New York. Forecast models show this will start to push the leading
edge of snow back north across western and central New York during
the early to middle afternoon. The leading edge of snow will lift
toward Southern Lake Ontario by this evening then further north
across the north country by midnight. Temperatures with the second
wave look to be colder so expecting mainly snow with little
possibility for any sleet or freezing rain as BUFKIT point
soundings show temperatures through the column to be below freezing. The
only exception may be right at the start where eastern Allegany
County may see some sleet mix in this afternoon.
The deeper moisture and best lift across our area continues to be
located across the southern tier and southern Finger Lakes. The GFS
is more aggressive than the NAM and rgem models as far as how far
north the better snow accums will reach. The forecast calls for
accumulations of an additional 2 to 4 inches across the advisory area
through this afternoon and evening while counties not included in
the advisory will likely only see an additional inch or two as the
wave of low pressure shifts just a little too far to the south of
New York. Temperatures will top out in the low to middle 30s today then
fall into the middle to low 20s tonight. Snow should start to taper
off from west to east later tonight as the surface wave shifts off
the middle-Atlantic coast. The cold air aloft...850mb temperatures dropping to
around -12c will allow for some response from the lakes to develop
closer to the early morning hours of Saturday.
Short term /6 PM this evening through Monday/...
colder air advecting into the region will make for a chilly day on
Saturday with highs only topping out in the upper 20s to lower 30s
and generate enough of a lake response for lingering lake effect
showers the first half of the day before increasing middle-level dry
air/anticyclonic flow kill off activity off Lake Erie by mid-day.
The longer fetch off Lake Ontario may allow light snow showers to
linger through the rest of the day and into Sat night...though by
late Sat night weakening flow as surface high pressure moves
overhead should bring an end to any activity. The aforementioned
area of high pressure will bring light winds Saturday
night...however lingering lake induced cloud cover should limit
radiational cooling across many areas...keeping lows in the 20s.
Portions of the southern tier and north country should still see
enough clearing to manage to drop into the teens overnight.
Look for a quiet day Sunday as high pressure drifts off to the east
across New England. Increasing southerly flow ahead of an
approaching warm front will bring increasingly cloudy skies from the
south during the day.
Isentropic uplift along the warm front lifting north across the
region ahead of a developing surface low over the central Great
Lakes will generate widespread precipitation across the region starting
near the PA border Sunday evening and working its way into the north
country after midnight. At this point general consensus among models
is that the best dynamics/DPVA will remain over Canada while deeper
moisture advection will be found to our east across central and
eastern PA/New York on the northern periphery of a secondary coastal low.
Therefore...expect precipitation to remain relatively light with only a
tenth of an inch or two at best. Regarding precipitation type...expect
precipitation to initially start out as light snow in the evening before
changing over to freezing rain as the warm nose aloft makes its way
over the area before changing over to rain as the boundary layer
warms above freezing towards morning. Given the expectation that
precipitation will be relatively light and the fact the temperatures
should warm above freezing...thus keeping the window for icing
rather small...will hold off on an advisory at this point...though
should the axis of deeper moisture wind up farther west this may
change. Nonetheless...motorists should be prepared for a period of
slick Road conditions...particularly across the southern
The bulk of the precipitation will taper off from southwest to northeast
on Monday as the warm front lifts into New England. Temperatures
will top out in the upper 30s to near 40 the axis of warmest air
crosses the area before temperatures fall back into the 30s during
the afternoon as the cold airmass currently over the northern plains
begins to filter across the Great Lakes. However...temperatures
should stay just warm enough to prevent lake effect from getting
going until Monday night.
Long term /Monday night through Thursday/...
latest GFS and European model (ecmwf) runs continue to show a deep middle level longwave
trough centered near Hudson Bay Monday night...with broad cyclonic
westerly flow developing across the Great Lakes region. The airmass
becomes plenty cold enough to support a lake response...with about
-16c at 850mb on Tuesday and perhaps a few degrees colder than that
Wednesday. The synoptic scale pattern fits the analog for
significant lake effect snow east of the lakes. The pattern would
suggest numerous small scale shortwaves traversing the mean west-northwest flow
aloft. Current guidance shows the most notable of these passing
just north of the lakes Tuesday night. Each of these waves can
result in subtle low level flow changes which can move lake bands
around and also modulate intensity and organization.
While the details cannot be predicted with any confidence at this
lead time...the pattern nonetheless appears very favorable for
significant lake snows east of the lakes. Stay tuned.
It appears most if not all of the snow Tuesday through Thursday will
be lake effect...so outside of lake effect areas expect just partly
As far as temperatures go...it will turn well below average by
midweek with highs only in the low to middle 20s and lows in the
teens...with single numbers possible in the normally colder
Aviation /10z Friday through Tuesday/...
the bulk of any associated IFR restrictions remain largely south of
a kbuf-kroc-kart axis this morning as snow briefly tapers across
western New York. VFR conditions should prevail along and to the
north of this line through the morning. Expect a brief lull in the
precipitation later this morning with general MVFR to VFR
conditions. Then...by this afternoon another wave of low pressure
spreads light to moderate snow and IFR conditions northward across
western and central New York through the afternoon and into the
tonight...a period of snow and associated IFR south of Lake
Ontario in the evening...diminishing overnight.
Saturday...VFR/MVFR with a chance of snow showers southeast of the
Sunday night and Monday...VFR/MVFR with snow and rain likely.
Tuesday...mainly VFR with a chance of snow showers/MVFR east of the
expect winds and waves to subside through today and generally
remain below advisory levels through the weekend as only a weak to
modest pressure gradient will be in place across the lower lakes
New York...Winter Weather Advisory until 4 am EST Saturday for nyz012>014-
Marine...Small Craft Advisory until 10 am EST this morning for loz042-
Small Craft Advisory until 2 PM EST this afternoon for