Tuesday night and Wednesday our attention turns from the synoptic
scale back to the mesoscale. Colder air will move back over Lake
Ontario with 850MB temps bottoming out around -16C Wednesday
morning. This will allow lake induced equilibrium levels to rise to
8-10K feet Tuesday night and early Wednesday before gradually
lowering late Wednesday. A favorably deep layer of dendritic growth
will be found beneath the inversion, allowing for ideal fluff factor
with thermodynamic profiles supporting large dendrite conglomerates.
Forecast low level wind and thermal profiles suggest a strong land
breeze convergence zone will develop just offshore of the south
shore of the lake, supporting a well organized single band. Boundary
layer flow will be westerly initially Tuesday evening, then veer
slightly to the WNW later Tuesday night through Wednesday.
This setup appears very similar to last night, with the heaviest
snow focused perhaps just a little farther south most of the time.
Expect a band of lake effect snow to organize Tuesday evening over
central or northern Oswego County, then drift south Tuesday night to
southern Oswego County, possibly clipping northern Cayuga County as
well. The band will likely go through several oscillations late
Tuesday night through Wednesday between roughly Scriba Point and
Fair Haven. CIPS analogs support the idea of another localized
warning criteria lake effect snow event at the southeast corner of
Lake Ontario, as does the Canadian RGEM.
Given the above expectations, issued a Watch for Oswego and northern
Cayuga counties from late Tuesday evening through Wednesday night.
Localized accumulations of greater than 9" look possible, especially
across southern and western Oswego County and far northern Cayuga
County.
Lake effect potential looks much weaker off Lake Erie during this
period. A few snow showers will develop on westerly flow Tuesday
night across the higher terrain east of the lake, with spotty
accumulations of 1-2 inches possible. This will taper off by
Wednesday morning as inversion heights lower over the lake.
Outside lake effect areas it will be dry and partly cloudy Tuesday
night through Wednesday morning. A synoptic scale wave will then
pass to the south of the region Wednesday. This may spread some
light snow into the western Southern Tier from late morning through
the afternoon with minor accumulations possible.
A large area of strong Canadian high pressure will continue to ridge
in from the northwest Wednesday night keeping conditions dry across
a good chunk of the region. This will continue to keep any light
snow associated with the synoptic wave passing by to our south over
the western Southern Tier and points south. Otherwise, decent
convergence within the lake aggregate trough over southeastern Lake
Ontario will keep localized lake effect snow going across far
southwestern Oswego and northern Cayuga counties through the first
half of the night. Winds will then turn more northerly during the
second half of Wednesday night. This will eventually weaken the
band, but not before potentially shoving it onshore, possibly
bringing some lighter accumulations to areas along and near the Lake
Ontario shorelines of northeastern Orleans, Monroe and Wayne
counties, before falling apart as it moves further inland by early
Thursday morning. Expect an additional few inches across
northeastern Wayne, northern Cayuga and southwestern Oswego
counties, with an inch or so along the northeastern Orleans to
northwestern Wayne County shorelines Wednesday night. Aside from a
few lingering lake effect snow showers south of Lake Ontario
Thursday morning, expect a mainly dry, but seasonally cold day.