It's another signpost along the trail of misery that much of the United States has been on this winter -- ice cover on the Great Lakes. On March 6, 2014 we received word from NOAA's Great Lakes Environmental Research Laboratory that the Great Lakes were 92.2% covered by ice; the second-highest ice cover on record.
The only other winter where a greater percentage of the Great Lakes was iced over was in 1978-1979 when 94.7% of the lakes' surface was frozen; the last winter where ice cover even came close to this winter's was in 1993-1994. Both were truly cold winters in the upper Midwest.
Ice-cover figures are arrived at by interpreting Canadian and U.S. satellite imagery, so ice-cover records only go back to the beginning of the satellite era -- about 40 years.
This period also corresponds to a period of warmer temperatures across the globe -- particularly in the upper Midwest. If a reliable ice-cover record existed from the 1800s (a much colder time, by land-based climate records), there is no doubt that it would show many more years with near-total ice coverage on the lakes. Yet, still, this year's ice cover "achievement" is another yardstick against which this winter will be measured for generations to come.
Ice cover varies from lake-to-lake for a variety of reasons, not all of which are weather-related. Winds & currents play a large role in determining where and when ice forms, as does the depth, or bathymetry, of each lake. Lake Ontario is the deepest of the Great Lakes, and rarely freezes completely, while it's very common for Lake Erie to completely freeze over.
It's worth noting that this weekend's ice-cover analysis shows that we may be turning a corner in the ice-making department. Total ice cover across the Great Lakes has decreased to 90.8%.
Extensive ice cover means that Great Lakes water temperatures will be slow to warm through the spring, and that air temperatures onshore and downwind of the lakes will also be colder-than-average through spring. Maybe it's worth, then, taking these final icy days to trek to a site (and sight) that is becoming increasingly rare: the ice caves of Lake Superior's Apostle Islands. The coldest winter in decades is making the caves accessible for the first time since 2009, provided you're ready for the mile-long walk to get there. Check out WCCO's report from February 2014 on the caves here.