Places downwind of the Great Lakes experienced significant lake-effect snow this week. Three feet of snow fell east of Lake Ontario, and more is forecast. Lake-effect snow is common in this area, but in November and December, not February. What’s the story?
Lake-effect snow occurs when cold air moves over a relatively warm, unfrozen lake. It’s most intense in December, on average. In January the Lakes start freezing over, and they generally remain frozen in February. That’s not the case this year. Current ice coverage is a mere 7.8% of the Lakes. This is modern record low.
While ice coverage is likely to grow in the next few days, the maximum ice coverage for 2016 will still be much below average. This is quite a change from 2014 and 2015 when ice coverage was around 90%! Such variation, while extreme, is actually fairly common, as shown below.
This year, the cause of the low ice cover is easy to identify. The eastern United States experienced one of the warmest Novembers on record followed by the warmest December on record. Buffalo’s first snowfall made national news because it occurred exceptionally late — December 18.
January temperatures were also warmer than normal. As a result, the Lakes are much warmer and less icy than normal, and lake-effect snow season is occurring in February instead of December. With more cold in the forecast, folks that live downwind of the Lakes can expect a snowy Valentine’s/President’s Day weekend. I guess this makes up for the unusual “Green Christmas” of 2015.