Lake Effect Summary: December 18-20, 2015

Maximum Snowfall: Lake Erie 12.2" (Perrysburg); Lake Ontario 36" (Lyonsdale)

Duration:  36 hours +/-

Flake Scale: 2 flakes **

Our second lake effect snow event comes a full two months after our first lake effect snow event of the winter season. Within an El Nino winter pattern, snow has been hard to come by early this winter, and this event is the first widespread significant snow event east of the lakes.

A strong mid-level trough and surface low moved through the western Great Lakes Thursday December 17^th, then north to James Bay on Friday, December 18^th.  Behind this storm system, a cold westerly flow advected across the eastern Great Lakes region to initiate bands of lake effect snow, first off Lake Erie on Friday then later that night off Lake Ontario.

Falling temperatures behind a cold front steepened lapse rates over a lake surface that was still in the middle 40s. This instability formed lake effect snow that began in the early afternoon hours over Lake Erie. Ahead of a shortwave trough, lake induced equilibrium levels rose to near 15 thousand feet and southwest winds initially brought these clusters of lake effect snow inland across metro Buffalo area. The winds backed enough such that the snow briefly reached the airport, bringing the Buffalo airport its first measurable snowfall of the season, with one tenth of an inch measured. As this mid-level trough crossed the area Friday evening, winds veered and sent the intensifying band of snow southward. Early in the evening Friday across the Southtowns thunder snow occurred along with snowfall rates increasing to an inch per hour. These snowfall rates would increase upwards of an inch and a half per hour over Ski County Friday night, when the band of snow was most intense. Through the night snow primarily fell across the western Southern Tier, with a westerly push bringing intense snow as far inland as Allegany County. Later in the night as inversion heights lowered behind the upper level trough, the band of snow east of Lake Erie weakened and became disorganized. Through the morning hours of Saturday this band of snow continued to weaken, producing another inch or so of snow east of the Lake.   

Off Lake Ontario the westerly flow along the lake brought the band of snow across the Tug Hill region.  The 270-280 wind flow had a bit of wind shear initially with the passing of the upper level shortwave trough, and this kept the band of snow loosely organized through Friday evening and into the early overnight hours. By later in the night the band of snow organized into a more impressive plume of snow yielding snowfall rates up to 3 inches per hour across inland Oswego County and southern Lewis County.  Saturday morning the band of snow off Lake Ontario was reaching peak intensity, though contrary to its upstream Lake Erie counterpart, this band of snow off Lake Ontario did not register any thunder. By late in the day Saturday a more northwesterly flow brought the band of snow southward across Oswego County, with the band brushing by far northern Cayuga County. Through the day on Sunday as high pressure from the south expanded northward across the eastern Great Lakes region the band of snow off Lake Ontario began to track northward, and diminished in intensity as drier air entrained into the snow band.   

Given the timing of the event, with much of the snow falling through the weekend hours, there was just a moderate impact on the general public. Roads remained open, though there was an increase in the amount of fender benders. A sizable amount of snow fell east of Lake Ontario with up to three feet of snow falling, but primarily in lesser dense populated area. This event will therefore earn two flakes**.