Cold air crossing the relatively warm waters of Lakes Erie and Ontario resulted in lake effect snows.
Off Lake Erie, lake snows developed on a southerly flow across the Niagara Peninsula. The band settled southeastward through the Buffalo Metro area during peak rush hour, between 5pm and 7pm, on Friday evening, while producing high snowfall rates of 3 to 4 inches per hour and thunder and lightning. While this made for a slow going commute, impacts were limited by the southward movement of the band keeping any one area from being impacted for much longer than an hour. By 8pm to 9pm, the band of heavy snow had completely cleared the Buffalo Metro area, skipping over the Southtowns very quickly, where it settled into the western Southern Tier. For the remainder of Friday night and into Saturday, the lake effect snow broke into more multi-banded structure with the westerly flow directing the snow across the western Southern Tier. By Saturday night and into Sunday drying air with high pressure building into the region brought an end to the lake effect snow. The highest snowfall totals were centered over the typical snowbelt locations along the Chautauqua Ridge to the Boston Hills and into western Wyoming County. Specific snowfall reports included:  18 inches at Perrysburg; 15 inches at Little Valley and Fredonia; 14 inches at Cattaraugus, Glenwood and Springville; 12 inches at Franklinville, Colden and Dunkirk; 11 inches at Randolph; 9 inches at Silver Creek; and 8 inches at Ischua and East Aurora.
Off Lake Ontario, disorganized lake snows began over the Thousand Islands region and continued until late Friday evening. As winds veered to west-northwest, an intensifying band of heavy lake effect snow quickly whipped through Jefferson County, producing a quick inch of snowfall for much of the County. The band of heavy lake effect snow settled over the southern Tug Hill late Friday night through early Saturday morning producing snowfall rates over 3 inches per hour. A secondary front dropped across Lake Ontario on Saturday, pushing the band south along the southern Lake Ontario shoreline and across south-central Oswego County then weakened through Sunday afternoon. Specific snowfall reports included:  27 inches at Constableville; 26 inches at Highmarket; 20 inches at Osceola; 17 inches at Redfield; 15 inches at Pulaski; 14 inches at Port Leyden; and 12 inches at Lacona.

Lake-Effect Snow in OSWEGO, NEW YORK
From 15-DEC-17 23:00:00 to 16-DEC-17 13:00:00 (EST-5)
Property damage: 35.00K
Crop damage: 0.00K
Reported by: COOP Observer

Lake-Effect Snow in LEWIS, NEW YORK
From 15-DEC-17 23:00:00 to 16-DEC-17 13:00:00 (EST-5)
Property damage: 40.00K
Crop damage: 0.00K
Reported by: COOP Observer

Lake-Effect Snow in CHAUTAUQUA, NEW YORK
From 15-DEC-17 23:00:00 to 16-DEC-17 15:00:00 (EST-5)
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Lake-Effect Snow in CATTARAUGUS, NEW YORK
From 15-DEC-17 23:00:00 to 16-DEC-17 15:00:00 (EST-5)
Property damage: 35.00K
Crop damage: 0.00K
Reported by: COOP Observer

Lake-Effect Snow in NORTHERN ERIE, NEW YORK
From 15-DEC-17 17:30:00 to 15-DEC-17 23:00:00 (EST-5)
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Public

Lake-Effect Snow in SOUTHERN ERIE, NEW YORK
From 15-DEC-17 17:30:00 to 16-DEC-17 15:00:00 (EST-5)
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Social Media