The most widespread snow will occur Saturday within the warm
advection regime ahead of the system. A broad area of strong
isentropic ascent will produce a 4-6 hour period of steady
precipitation, developing in the morning across Western NY and
reaching the eastern Lake Ontario region by early afternoon. Across
Western NY, model guidance continues to suggest enough of a warm
layer aloft to support the chance of some sleet mixing in briefly
from late morning through mid afternoon. If sleet lasts for an
extended period of time, it would bring down snow accumulations. By
late in the afternoon, surface temperatures may become warm enough
to change the snow to rain close to the Lake Erie shore, with
southerly downslope winds warming temperatures into the mid to upper
30s. Farther east, precip type will remain all snow from about Wayne
County eastward.
Snow accumulations through early Saturday evening will generally run
2-4 inches, perhaps a little higher across the southern Tug Hill as
southerly upslope flow develops.
Saturday night the widespread precipitation will taper off across
Western NY as a mid level dry slot moves into the area. This will
produce a relative lull in precipitation coverage and amounts
through most of Saturday night. Temperatures will also be above
freezing for a time Saturday night, yielding a rain/snow mix across
Western NY at lower elevations. Later Saturday night colder air will
move back into Western NY, changing everything back to snow. The
airmass will also become cold enough to begin lake enhancement
across the higher terrain east of Lake Erie late Saturday night,
with snowfall rates picking up across the Chautauqua Ridge and
Boston Hills late. Additional accumulations Saturday night will
range from a few inches across the higher terrain east of Lake Erie,
to little or nothing at lower elevations.
Meanwhile, east of Lake Ontario there will be less of a mid level
dry slot, so there will be less of a break in precipitation Saturday
night. Expect periods of snow to continue, especially across the Tug
Hill supported by continued upslope flow. This will support
additional accumulations of a few inches at lower elevations, and 3-
6 inches across the Tug Hill Plateau.
Sunday cold air will pour back into the eastern Great Lakes in the
wake of the low. Boundary layer flow will be westerly most of the
day, targeting areas east of the lakes with heavy lake enhanced
snow. Lake induced equilibrium levels will climb to around 10K feet
by late in the day as cold air deepens. Outside of the main lake
effect areas, snow will be relatively light with minor
accumulations.
East of Lake Ontario, it won`t be pure lake effect, but rather lake
enhanced upslope flow supporting the potential for heavy snow across
the Tug Hill Plateau. This may produce additional accumulations of
up to 5-7 inches across the Tug Hill, and a few inches at lower
elevations. Later Sunday afternoon and evening boundary layer flow
will begin to veer more northwesterly, diminishing the influence of
lake enhancement across the Tug Hill.
East of Lake Erie, it will be a little more of a pure lake effect
setup with less synoptic scale moisture and ascent. Deepening
instability and upslope flow should support persistent moderate snow
across the Chautauqua Ridge, Boston Hills, and hills of Wyoming
County Sunday, and continuing Sunday night for that matter.
Additional accumulations during the day Sunday of 5-7 inches are
possible, with more Sunday night.
Total accumulations from Saturday through late Sunday night will be
highest across the higher terrain east of the lakes. East of Lake
Erie, the Chautauqua Ridge, Boston Hills, and hills of Wyoming
County may see 12-18 inches total. The Tug Hill Plateau will see 12-
18 inches as well, with 7-10 inches for the surrounding lower
elevations east of Lake Ontario. The Buffalo area should see 4-6
inches total over the entire weekend, but this will come in two
batches with some melting between. Rochester may see 4-7 inches
total in several batches with some melting between. The lowest snow
amounts will be across Allegany County and the western Finger Lakes
with little in the way of lake enhanced snow reaching these areas
Sunday.
As far as headlines go, issued a Winter Storm Warning east of Lake
Ontario where the most widespread heavy snow will occur. Issued a
Winter Weather Advisory for the rest of the area for Saturday
through portions of Saturday night and Sunday morning. Also issued a
Winter Storm Watch for the higher terrain east of Lake Erie for late
Saturday night through early Monday morning for lake effect snow.
Note, we are handling the potential for wind gusts to 50 mph within
the winter weather advisories and warnings instead of issuing
separate wind advisory headlines