Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
1123 PM EST Friday Dec 6 2013
a weak area of low pressure will exit the region overnight with a
few light snow showers lingering. Light lake effect snow will
linger into Saturday and Saturday evening before ending as high
pressure provides the region with dry weather on Sunday.
Near term /through Saturday/...
will drop the Winter Weather Advisory as surface observations and
latest radar scans are continuing to show an improvement. Light
synoptic snow showers will likely linger through the overnight but
accumulations will be minor.
Within the northwest flow over Lake Ontario temperatures will drop
to around -13c by morning. Here synoptic moisture is a little
greater and 2 to 3 inches of lake effect snow are possible later
tonight and into the morning hours of Saturday. The flow will be west-northwest
aloft with dry air aloft...limiting or even eliminating any chance
for lake effect snow east of Lake Erie.
Later off Lake Ontario...there may be a bit more moisture aloft
later afternoon...with some better chances for accumulating snow
from about kfzy into southern portions of the Tug Hill. A special
12z 1.3km run of the NAM fire weather nested run along with other high
res runs show this idea nicely...with some streamers late in the day
in roughly the above mentioned areas. Any connection to the Georgian
Bay remains just out of reach and near the mouth of the St Lawrence
River by the end of the day. It is worthy of noting that the modis
estimated lake temperatures are about 5c warmer over the eastern end
of the lake compared to the western end. This may be enough to
provide just a bit more land breeze convergence and eventual lift
over the eastern shoreline. For now will keep the probability of
measurable precipitation low throughout the day with a slight
increase during the afternoon.
Short term /Saturday night through Monday night/...
this period will open with strong surface-based ridging and drier
air building across New York state Saturday night. While a lingering
west-northwesterly flow of cold air across Lake Ontario will support
some snow showers southeast of the lake...these should remain
scattered and fairly minimal in scope given relatively low inversion
heights of 5-6 kft...and a rather limited snow growth region/less
than ideal moisture below the capping inversion. Downwind of Lake
Erie...an even less favorable setup should lead to a few flurries at
worst...with the rest of the area just quiet...dry...and cold.
Expect overnight lows to range from 10-15 across interior portions
of the southern tier and north country...to around 20 along the
On Sunday...any scattered snow showers southeast of Lake Ontario
should get quickly squelched during the morning thanks to a further
lowering of the cap and the weakening/increasingly sheared low level
flow. Once these are gone...dry and seasonably cold conditions
should be the rule for the rest of the day...albeit with some
increase in middle and high cloud cover in advance of the next system.
Daytime highs should be a touch warmer than Saturday/S...and
generally within a few degrees of 30 at any given location.
Sunday night and Monday...a complex and double-barreled area of low
pressure will lift across the Great Lakes and Middle Atlantic States...
with the primary surface low tracking from the lower Ohio Valley to
James Bay...and a secondary coastal low lifting from the Carolina
coast to just offshore of Cape Cod. While all guidance packages
remain in good agreement on keeping the best large-scale forcing/
moisture and consequently the heaviest precipitation off to our northwest
and southeast and in closer proximity to the aforementioned low
tracks...there is also good agreement that a connecting surface
trough/warm front will lift northeastward across New York state
during this time frame. This should help force a round of much
lighter but still fairly widespread precipitation across our
area...with the bulk of this coming between Sunday night and Monday
morning...before quickly tapering off from southwest to northeast as
a surge of drier air spreads into the region. At this point...a
model quantitative precipitation forecast consensus suggests a total of one to two tenths of an inch
of precipitation south of Lake Ontario...with perhaps an additional tenth
or two across the north country.
With respect to precipitation type...model forecast soundings and
plan views suggest the precipitation starting off as all snow Sunday
evening...before quickly changing to sleet/freezing rain and then to
rain overnight and Monday morning as warm advection causes the
atmospheric column to warm above freezing. Given that precipitation
amounts should be relatively light and also that the window for
freezing precipitation looks to be rather brief...feel that it/S best to
just continue highlighting this potential within the severe weather potential statement and hold
off on issuing an advisory...though one may eventually be required
for at least the southern tier and portions of The Finger lakes.
As for temperatures...expect Sunday night/S lows to come fairly early in
the night...with steady warm air advection then forcing readings to
rise through the remainder of the night and into Sunday morning. For
most locations...highs should peak in the upper 30s to near 40
between late Monday morning and early Monday afternoon...before
falling back some during the remainder of the day following the
passage of a cold front.
By Monday evening...our airmass will become cold enough to support a
lake response northeast of the lakes and will continue to get even
colder through the night under a steady cold air advection regime.
This stated...surface-based ridging and drier air will be
simultaneously building across the lower Great Lakes...and will
produce both a fairly low cap of around 4-5 kft and notable drying
below the inversion...which should keep any lake effect snow showers
limited in nature. With this in mind...have confined probability of precipitation northeast
of the lakes to the low-middle chance range Monday night...with the
rest of the area remaining mainly dry. Given the continued cold
advection pattern...expect overnight lows to drop back to the upper
teens to middle 20s.
Long term /Tuesday through Friday/...
the latest medium range guidance remains consistent in depicting a
deep upper trough slowly drifting from Hudson Bay to northern Quebec
Tuesday through Thursday...before ejecting eastward into the
Canadian Maritimes on Friday. This feature will maintain a broad
cyclonic westerly flow of progressively colder air across the Great
Lakes at least through Thursday...with 850 mb temperatures falling to
around -15c Tuesday and to -18c/-20c by Wednesday and Thursday. Such
a pattern is climatologically favorable for significant lake effect
snows east of the lakes...and in this particular case looks to
become most favorable sometime from later Tuesday afternoon/evening
through Thursday in conjunction with an uptick in background
synoptic scale moisture.
At this still-distant juncture...depicting the exact location and
intensity of the lake effect bands at any given point in time
remains a highly difficult exercise given the presence of numerous
smaller scale shortwaves passing through the large scale trough...
which will produce undulations in the large-scale flow that
subsequently affect both band placement and intensity. This
stated...the medium range guidance has remained consistent on
depicting the most noteworthy of these passing through our region
between Tuesday and Tuesday night...with some suggestions of a more
steady-state westerly flow potentially setting up after that time.
Outside of the Main Lake effect areas...the period should be largely
characterized by mainly dry and colder weather...with daytime highs
settling into the Lower-Middle 20s for the middle portions of the
week...and nighttime lows falling off into the 5-15 degree range.
While some moderation in temperatures may eventually become possible by
Friday as the upper trough begins to lift out...expect that readings
will still remain below normal through the end of the period.
Aviation /06z Saturday through Wednesday/...
for the 06z tafs some MVFR flight conditions in light snow will
still be likely...mainly over the southern tier...and then southeast
of Lake Ontario where a minor band of lake effect snow may develop.
Elsewhere overnight expect mainly VFR flight conditions.
Through the daylight hours across the 5 taf sites expect mainly VFR
flight conditions...with a west to northwest wind flow. These winds
at times may gust to 20 to 25 knots across Lake Ontario and
neighboring taf sites just south of the lake.
Tomorrow evening winds will diminish some...still from a westerly
flow. Will mention vcsh in the Art taf as a band of lake effect snow
may enhance later tomorrow afternoon and evening and lift towards
Sunday night and Monday...VFR/MVFR with snow and rain likely.
Tuesday and Wednesday...mainly VFR but IFR with lake effect snow
east of the lakes.
northwest flow over the eastern Great Lakes will bring an increase
in waves through the late overnight and during the day Saturday. As
winds become near 20 knots on Lake Ontario waves will crest over 4
feet...and small craft advisories have been issued for the near
shore waters of Lake Ontario through the day Saturday...and
remaining through Saturday night. With the westerly flow waves will
likely remain just below small craft advisories on Lake Erie.
Marine...Small Craft Advisory from 9 am Saturday to 7 am EST Sunday for
Small Craft Advisory from 9 am Saturday to 5 am EST Sunday
Small Craft Advisory from noon Saturday to 7 am EST Sunday