It's been several decades since Lake Superior has completely frozen over, but experts project this year might be the year it does once more. According to NOAA's Great Lakes Coastal Forecasting System, estimated total ice area for February 12, 2014 is at 87.1%. The last time the ice extent was above 75% was in 1996. Last year the maximum extent was 38.4%.
The current estimated mean thickness of the ice on Superior is 28 cm, but actual thicknesses vary greatly across the lake. The current ice concentration on the lake is 88.8%, but forecasters predict that number could max at 95% or greater in the coming days.
For the Great Lakes as a whole, the record maximum ice coverage on record is 94.7% set back in 1979, the lowest just 9.5% in 2002.
The extensive ice will create less lake effect snow (the water isn't evaporating to make snow), and for the same reason, the spring thunderstorm season will often be delayed until that ice melts in years like this.