Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
658 am EST Friday Dec 13 2013
an Arctic cold front will drop south across our region today...and
this will bring an end to the significant lake effect snows. A storm
system will track from the Tennessee Valley to the Middle Atlantic
States during the weekend though...and this will produce a
widespread accumulating snowfall across all of western and north
central New York. Otherwise it will remain very cold into early next
week with temperatures averaging some 10 to 15 degrees below normal.
Near term /through tonight/...
after several days of significant...and at times even intense...lake
effect snow...the weather across our region will shift from mesoscale
to synoptic in nature. That should not be construed as good news
though for those that appreciate the milder weather...as it will
most certainly remain quite cold.
An Arctic cold front stretching from the upper Great Lakes across
southern Ontario to the lower St Lawrence Valley will drop south
across our region today. This will bring an end to the on-going lake
effect snow east of both lakes...but not before another 3 to 6
inches of fresh fluffy snow accumulates. The two main areas that
will remain the target of this lake effect will be parts of the southern
tier...and from the Tug Hill southwards across Oswego County to
portions of Wayne and Cayuga counties.
First...off Lake Erie...
while a well aligned 280 flow will be in place over the lake for the
bulk of today...a fairly pronounced cap around 6k feet will limit the
convective cloud depth. This should keep snowfall rates from
exceeding an inch an hour...but there will certainly still be enough
snow to cause some travel problems.
As advertised...the nebulous area of lake effect over the southern
tier has blossomed over the past few hours with the addition of a
deeper synoptic moisture field. Radar returns have increased to
30-35 dbz...but the activity still lacks the intensity of the past
couple days. Similar returns should remain in place through the
During the midday and afternoon...the aforementioned Arctic front
will settle south across the region and disrupt the lake induced
convection. The lake snows will taper off and gradually hand the
precipitation process off to a swath of synoptically induced low level
convergence that will stretch across much of the southern tier. The
result will be light snow and flurries that will increase in
intensity during the overnight. More on that in a moment.
Now...off Lake Ontario...
an all too familiar plume of moderate to heavy lake snow was found
over the Tug Hill early this morning where snowfall rates of 2 to 3
inches is being suggested by the ktyx radar. This seems quite
reasonable given the temperatures and 30-40 dbz reflectivity. The low
sheared 270-280 flow should keep this snowband in place through
about 13z...after which time the approaching Arctic cold front
will push the band south across the southern half of Oswego County
to Wayne and northern Cayuga counties. Snowfall rates will lower as
the band comes off the lake...but enough snow should fall over parts
of Wayne and noreen Cayuga County to warrant a lake Snow Advisory.
This flag will run through 20z.
Outside of the lake effect areas today...it will be cloudy and cold
with flurries giving way to some steadier snow showers brought about
by the passage of the cold front. These snow showers could bring an
inch or so of fresh snow to sites outside of the lake effect snow
bands. Slightly higher amounts will be possible due to a northerly
upslope flow across the higher terrain of the southern tier. Temperatures
will struggle into the lower 20s for most areas by midday...then
will remain nearly steady or will fall into the teens in the wake of
the front during the afternoon. Wind chill values will generally
remain in the single digits.
Tonight...disorganized low pressure over the Central Plains will
track east across the lower Mississippi Valley. A convergent low
level flow over the southern tier during the evening will then be
complimented with a little jet induced lift during the course of the
overnight to initiate a period of steady light snow that will spread
to the northeast during the course of the overnight.
Temperatures tonight will drop to between 10 and 15 for most
sites...with readings tumbling below zero across the north country.
Short term /Saturday 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 /12z Friday through Tuesday/...
an Arctic cold front will press south across the region today...and
this will likely produce MVFR ceilings along with areas of snow that
could briefly reduce visibilities.
The main areas of concern though will remain east and southeast of
both lakes where moderate to heavy lakes snows this morning will be
accopanied by LIFR ceilings/visibilities for sites such as kjhw and kelz. This
lake effect will weaken during the afternoon as an Arctic cold front
moves south through the region.
VFR conditions will be found at most sites for the first half of
tonight...with the exception of kjhw where MVFR ceilings are expected.
During the overnight...light snow will spread northeast across the
region with MVFR conditions coming back into play.
Saturday and Sunday...IFR with snow...tapering off early Sunday
Monday...MVFR with a chance for snow showers. IFR with lake effect
snow likely southeast of the lakes.
Tuesday...MVFR 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 6 am Saturday to 6 am EST Sunday
Lake effect snow warning until 1 PM EST this afternoon for
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
Marine...Small Craft Advisory until 11 am EST this morning for lez020.
Small Craft Advisory until 7 PM EST this evening for
Small Craft Advisory until 11 am EST this morning for
Small Craft Advisory until 7 PM EST this evening for
Gale Warning until 10 am EST this morning for loz043>045-