Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
133 PM EST Friday Dec 13 2013
an Arctic cold front will drop south across our region through this
evening with snow showers and lake effect snow gradually
diminishing. An area of low pressure will then move across the
region over the weekend with widespread accumulating snow Saturday
and Saturday night. Some lake effect snow will linger southeast of
the lakes Sunday before diminishing Monday. Another system may bring
the next round of snow on Tuesday with some limited lake effect snow
possible through midweek.
Near term /through Saturday/...
the lake enhanced snow off Lake Erie continues across the western
southern tier and portions of southern Erie and Wyoming counties.
Latest mesoscale model guidance suggests it may remain in place
through much of the afternoon before falling apart this evening as
low level flow becomes north to northeast. With this in mind...have
extended the lake snow warning for this area through 7pm to account
for another 3-5 inches in persistent bands.
The Lake Ontario band has merged with a low level convergence zone
along an advancing Arctic front...and has left a rather large area
of light to moderate snow across much of the Niagara Frontier. This
will persist for several more hours before very slowly diminishing
to scattered snow showers in place. Until then...it may produce up
to 2 inches of fluffy accumulation across the northern suburbs of
Buffalo into portions of Genesee County.
Farther east...not much is showing on radar behind the Arctic cold
front...but suspect light to moderate lake effect snow is still
falling in multiple narrow bands across Wayne/N.Cayuga/Oswego
counties. The warnings and advisories will continue through middle
Through the evening hours lake effect snow southeast of Lake Erie
should steadily diminish as flow becomes northeast. Off Lake
Ontario...mesoscale model guidance suggests lake effect may try to
make a resurgence to some extent on cold northeast flow. The band
should get organized by middle to late evening from western Oswego
County into Wayne County on northeast flow...then move steadily west
along the shoreline past Monroe County and into Orleans/Niagara
County right along the immediate Lakeshore by daybreak Saturday.
Equilibrium levels remain shallow at 6-7k feet...but with a very
cold low level airmass and the potential for some land breeze
convergence...this may allow for some decent snowfall rates of very
fluffy snow. The band should remain Mobile...so for now have kept
amounts sub-advisory in the 2-4 inch range...with the majority of
that in a narrow zone right along the Lakeshore.
Our attention then turns back to the synoptic scale as a system
approaches the Ohio Valley. An initial somewhat unrelated Wing of
warm advection will develop later tonight across the western
southern tier. Increasing isentropic upglide will produce an area of
light snow late tonight across the western southern tier. This may
produce an inch or two of additional snow from midnight to daybreak
across the southern tier.
On Saturday low pressure will move into the Ohio Valley...and by the
end of the day secondary coastal cyclogenesis will be starting along
the middle Atlantic coast. Low/middle level warm advection will support
increasing isentropic upglide...and a lead shortwave will provide
some large scale ascent. Perhaps most important...a coupled upper
level jet structure will develop across the lower lakes and provide
organized upper level divergence.
This should all support a widespread steady snow...which will
already be ongoing by 7am as far north as the thruway from The
Finger lakes westward. This will very slowly spread northeast...not
reaching the north country until late in the day or early evening.
Expect 2-3 inches of snow from The Finger lakes and Genesee Valley
westward with 3-4 inches closer to the PA state line.
Short term /Saturday night through Sunday night/...
during this period...our main forecast concern continues to be the
potential for a widespread significant snowfall between Saturday and
The 00z guidance suite remains in pretty good agreement on a strong
northern stream shortwave over central Canada digging southeast and
leading to the development of a closed low Saturday and Sunday...
while a somewhat weaker but still significant southern stream
impulse lifts from the Southern Plains to the Virginia coast...then
out into the western Atlantic. At the surface...an incipient weak
wave over the deep south Saturday morning will lift northeast into
the Ohio Valley Saturday...before transferring its energy to a
rapidly strengthening and increasingly dominant secondary low taking
shape off the Delaware-Maryland-Virginia coastline Saturday night. This coastal low
will then continue to deepen as it lifts northeastward just offshore
of the New England coast on Sunday...while remnant surface troughing
lingers across the Great Lakes.
In advance of the first wave lifting northeast into the Ohio Valley
on Saturday...increasing warm air advection/isentropic lift will
spread a swath of fairly steady light snow northeastward across New
York state. Then as the initial low lifts into PA and transfers its
energy to the secondary coastal low Saturday night...overall
isentropic forcing and moisture will become maximized across our
area...which should result in the snow picking up in intensity for
about a 6-9 hour period. After this time...expect the snow to again
become lighter in nature and rapidly diminish from southwest to
northeast later Saturday night and Sunday morning as the coastal low
becomes dominant and draws the best forcing and deepest moisture off
to our northeast.
Compared to yesterday...the 00z guidance has trended somewhat
heavier with the quantitative precipitation forecast from this system...with a consensus of the main
operational models and wpc guidance now suggesting the potential
for 0.50-0.70" inches of liquid equivalent precipitation...with the greatest
quantitative precipitation forecast generally indicated across portions of The Finger lakes and
north country. Using typical snowfall ratios for warm advective
precipitation /which are generally between 10:1 and 15:1/...such quantitative precipitation forecast
would likely translate into roughly 6-9" of snow falling over a
24-30 hour period...with the greatest portion of this coming
during Saturday night. Taking into account local 24-hour warning
criteria...such amounts would generally fall within the upper end
of the advisory range if realized...with eastern sections
potentially having a shot at lower-end warning criteria snowfall
The above stated...given noticeably lower quantitative precipitation forecast seen in previous model
cycles...and the fact that the exact amount of precipitation we'll see out
of this system will ultimately depend upon how quickly energy
transfers from the primary to the secondary low /a factor that is
never easy to nail down/...we do not yet have enough confidence to
justify upgrading portions of the area from the current blanket
Winter Weather Advisory to a Winter Storm Warning. With all this in
mind...for now will elect to just stick with the existing advisory
while bumping up snowfall amounts to the higher end of the advisory
range...and allow the day shift to peruse the 06z/12z guidance
cycles before making a call on any potential adjustments to our
Following the departure of this system on Sunday...a broad west-
northwesterly flow of colder air will develop...resulting in the
redevelopment of lake snows east-southeast of the lakes by later in
the afternoon. While over-lake instability looks to sufficient...at
this point moisture and shear profiles do not appear to be overly
favorable for significant accumulations.
Long term /Monday through Thursday/...
while west to northwesterly flow lake effect will likely be ongoing
at the start of the period...high pressure and drier air nosing down
from central Canada and the upper Great Lakes will likely limit
significant accumulations as the favorable dendritic snow growth
region and available moisture diminish...and lake-induced eqls lower
dramatically. Coupled with increasing shear and developing warm air
advection in advance of the next approaching clipper system...this
should result in the lake snows winding down by later Monday.
After that...the medium range models remain in fairly close
agreement on bringing a clipper-type low across the region in the
Monday night to Tuesday night time frame along with some light warm
advective snows. Behind this clipper...another shot of modified
Arctic air may reinvigorate lake snows across the region for
midweek...however this may be brief as another clipper low arrives
on the scene by Thursday.
Aviation /19z Friday through Wednesday/...
an Arctic cold front will slowly sag south across the area with lake
enhancement southeast of the lakes through late afternoon or early
evening. Fairly widespread IFR visibility to the south of Lake Ontario
will gradually shrink in coverage...and by this evening most of the
IFR should be confined to the western southern tier and a few local
spots of lake effect between kroc and kfzy.
Low pressure moving into the Ohio Valley will then allow a general
snowfall to overspread the region late tonight through Saturday with
visibility deteriorating to IFR from southwest to northeast. Widespread
IFR visibility will continue through Saturday night in snow.
Sunday...MVFR/IFR with snow showers likely and areas of lake snow
southeast of the lakes.
Monday...Lake effect snow showers with local IFR southeast of the
Tuesday...possible MVFR/IFR with a chance of snow showers.
Wednesday...mainly VFR with a chance of snow showers.
with a deep pool of cold air over the eastern Great Lakes right into
the weekend...and passage of several surface waves/low pressures
across the Great Lakes solid advisory-level conditions will persist
through the end of the week. The exception will be the eastern half
of Lake Ontario where gale force winds will be place through midday.
Winds across both lakes will gradually subside during the midday and
afternoon with no wind based flags expected by this evening.
New York...Winter Weather Advisory from 10 am Saturday to 10 am EST
Sunday for nyz006>008.
Lake effect snow warning until 4 PM EST this afternoon for
Lake effect Snow Advisory until 3 PM EST this afternoon for
Winter Weather Advisory from 6 am Saturday to 6 am EST Sunday
Lake effect snow warning until 7 PM EST this evening for
Marine...Small Craft Advisory until 7 PM EST this evening for lez040-
Small Craft Advisory until 7 PM EST this evening for