Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
936 PM EST Thursday Dec 5 2013
in the wake of a cold front...progressively colder air will flood
across the region overnight and Friday. This will result in any
lingering rain showers behind the front changing over to snow before
diminishing late tonight...along with a return to much lower
temperatures that will remain in place through the upcoming weekend.
Later Friday into Friday night another wave of low pressure will
lift northeast across the Middle Atlantic States...and this will bring
a period of light to moderate snow to areas south of Lake Ontario.
Near term /through Friday/...
the anomalously mild weather is over.
As of 9 PM...the latest surface analysis shows that the cold front
has pushed completely through our forecast area...with the front now
making its way across the Adirondacks.
Overnight...a wave of low pressure will ride northeastward along the
departing cold frontal boundary...and should spread a second but
brief shot of moisture and lift northeastward across our region.
This will be followed by increasing low level ridging and drying
towards daybreak which should bring an overall diminishing trend in
the precipitation from northwest to southeast. Looking at the 18 and early
00z guidance suites...available forcing and moisture fields
generally suggest a sharp gradient in precipitation chances ranging from
categorical along our southeastern periphery to only low chance
along the Canadian border...which is roughly in line with our
In terms of ptype...expect this second shot of precipitation to
start out in the form of just light rain late this evening...then
cold air advection will force a changeover over to sleet and then
snow before the precipitation diminishes overnight. With fairly limited quantitative precipitation forecast
and only marginal boundary layer temperatures expected following the
changeover...do not anticipate a great deal of sleet and snow
accumulation tonight...with generally only an inch or so falling
across the higher terrain. In a similar vein...model soundings also
suggest that thermal profiles will generally not be supportive of
freezing rain during the changeover...with a quickly deepening layer
of subfreezing air undercutting warmer air aloft...but also
remaining situated above a shallow layer of above freezing air near
the surface...a profile that appears much more favorable for sleet.
With sleet/snowfall accums thus remaining fairly minimal and the
potential for freezing rain looking to be rather low...do not feel
that any winter weather advisories are currently necessary for
On Friday...expect a relative lull during the morning as the remains
of tonight's wave depart off to our south and east...before yet
another and stronger surface wave develops from the Tennessee Valley
into the Middle Atlantic States. During the afternoon...this feature
will spread increasing amounts of moisture and lift back northward
into our region...which will result in some light snow first
breaking out across the southern tier...with the northern edge of
this then slowly spreading north to roughly the New York state thruway corridor
by sunset. While current model/wpc quantitative precipitation forecast consensus and marginal
boundary layer temperatures suggest that most areas north of the southern
tier will see little if any accumulation out of this through late
tomorrow afternoon...areas closer to the Pennsylvania border could
see as much as 1-2 inches...with somewhat greater additional
accumulations expected to follow Friday evening. Taking these
together...we have elected to hoist a Winter Weather Advisory for
our three southern tier counties for tomorrow afternoon and
night...more details on which are provided within the short term
In terms of temperatures...most areas will see lows dipping back
into the lower to middle 30s tonight...with highs then only recovering
some 3-5 degrees on Friday given what should be abundant cloud cover
and continued cold air advection.
Short term /Friday night through Sunday/...
Friday evening widespread light snow will be ongoing from the second
in a series of frontal waves. The wave running along the baroclinic
zone will result in increased differential thermal advection and
frontogenesis...with low level cold advection topped by middle level
warm advection and a general tightening of thermal packing. A strong
150+ knot upper level jet from the Central Lakes to the Canadian
Maritimes will produce strong upper level divergence to support the
low level frontal forcing. This should produce an area of light to
moderate snow to the left of the frontal wave track. The past few
runs of the NAM seem much too high on quantitative precipitation forecast...and we will follow the
more reasonable GFS/ECMWF/sref mean solutions.
The most significant snow will be found close to the PA state line
where the best juxtaposition of moisture and forcing is found. Total
accumulations from Friday afternoon and night may reach 3-5 inches
across chaut/catt/alleg counties with the greatest amounts expected
near the PA state line of southern catt/alleg counties at this time
given the forecast track. Amounts will decrease with northern
extent...with a few inches possible from southern Erie/Wyoming
counties into The Finger lakes. Along the thruway corridor expect an
inch or so with the lowest amounts near the Canadian border. There
will be a tight northern cutoff to the heavier amounts so if any
further model adjustments in the track occur the expected amounts
outlined above may be lower or a little higher.
The synoptic snow will quickly end late Friday night and should be
done by daybreak Saturday. The airmass will become cold enough to
turn our attention to the mesoscale and lake effect potential. 850mb
temperatures will bottom out around -14c on Saturday...cold enough to
support a lake response. Major negatives will include a very dry
background environment...anticyclonic low level flow...and a
generally poor synoptic scale environment. This should keep lake
effect very limited.
Off Lake Erie lake induced equilibrium levels only peak around 5-6k
feet...so this will only support a few scattered snow showers across
the western southern tier. Conditions are marginally better off Lake
Ontario with equilibrium levels of 7-8k feet. This may allow for a
better likelihood of snow showers from Oswego County to the southern
Tug Hill...but dry air should keep intensity and organization
Lake effect will slowly end Saturday night as high pressure crests
over the lower lakes. Otherwise expect at least some partial
clearing outside of any lake effect cloud areas.
Sunday morning high pressure crests over the lower lakes before
moving off into New England during the afternoon. Any morning
sunshine will fade behind thickening middle/high clouds as middle/upper
level warm advection increases ahead of the next system.
Temperatures through the weekend will run a little below average...
with highs both days in the upper 20s to around 30 at lower
elevations and middle 20s across higher terrain. Saturday night may be
chilly if skies clear under building high pressure. If this occurs
radiational cooling would support teens in most areas...with a few
high single numbers possible in the colder southern tier valleys and
Tug Hill region.
Long term /Sunday night through Thursday/...
Sunday night our attention turns to the next synoptic scale system.
Medium range guidance remains consistent in ejecting a shortwave out
of the western trough and towards the upper lakes. An associated
weak surface low will track from the Ohio Valley into the Central
Lakes. Weak large scale ascent and increasing warm advection ahead
of this system will support light snow developing from southwest to
northeast Sunday night. Given the track of the surface low to our
west...a strong push of warm air aloft will nose into the lower
lakes later Sunday night and Monday. This will support a change from
snow to sleet/freezing rain and eventually rain from southwest to
northeast. Forcing and moisture look relatively weak with this
feature...so just expect relatively light amounts of snow and ice.
There will be enough to produce a few hours of slick travel...but
Precipitation with this system will end quickly from west to east Monday
morning. Cold advection will increase again late in the day with
colder air coming back in force Monday night. This will set the
stage for an extended period of lake effect snow potential from
Tuesday through Thursday.
Latest 12z GFS and European model (ecmwf) continue to show a deep middle level longwave
trough centered near Hudson Bay...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 12z
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 /03z Friday through Tuesday/...
as of 03z...a cold frontal boundary was making its way across the
Adirondacks with cold advection found back across all of western and
north central New York. Expect only isolated light showers early
tonight with conditions generally remaining VFR...though some areas
of MVFR ceilings will be found across the southern tier and east of Lake
As we progress through the overnight...the cold front will push east
to the Atlantic coastline...with another wave of low pressure
rippling northeast along this boundary and eventually leading to
another round of rain. The bulk of this rain will be focused across
the southern tier and interior portions of The Finger lakes. Over
time...progressively colder air overspreading the area in the wake
of the front will force any rain to changeover to sleet and then
snow...which will then diminish overnight and early Friday morning.
At this point...it appears that the bulk of any associated IFR/MVFR
restrictions will remain largely south of a kbuf-kroc-kart
axis...with mainly VFR conditions continuing along and to the north
of this line.
On Friday...expect a relative lull in the precipitation Friday
morning with general MVFR to VFR conditions...before yet another
approaching wave of low pressure spreads light to moderate snow and
IFR conditions northward across areas south of kbuf-kroc-kfzy during
Friday night...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
in the wake of a cold front...brisk westerly winds will produce
advisory-level conditions on Lake Erie early tonight...and into
Friday on Lake Ontario. After that...expect winds and waves to fall
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 region.
New York...Winter Weather Advisory from 1 PM Friday to 4 am EST Saturday
Marine...Small Craft Advisory until 10 PM EST this evening for lez040-
Small Craft Advisory until 10 am EST Friday for
Small Craft Advisory until 2 PM EST Friday for loz044-045.