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Currently (April 2014), the fraction of the Great Lakes covered by ice is more than ten times the median amount for this time of year, the median amount being indicated by the green line in the below graph and representing the 1980-2010 time period. The source of the graph is the Canadian Ice Service.

enter image description here

(in the graph, the x-axis is year, 1980-2014; the y-axis is percent ice cover 0-40%; Link to graph)

While the data in the graph are only back to 1980, looking at data from the NOAA Atlas of Great Lakes Ice Cover it can be seen that the amount of ice for this time of year is unprecedented back to 1973, the earliest year in the atlas.

My question is, how far back would one have to go to find a year with an equal or greater amount of ice coverage on the Great Lakes at this time of the year? Obviously the Great Lakes were glaciated thousands of years ago :), but is there any historical record of a similar ice coverage event?

update 4/29/2014:

enter image description here

(x-axis is year, 1980-2014; the y-axis is percent ice cover 0-30% Link to graph)

As we close out April, the amount of ice remaining on the Great Lakes is more than 4 times greater than any other year in the 1980-2014 time period, and about 50 times the median value for this time of year.

Vast areas of Lake Superior which were considered by Canadian Ice Service as having a zero-probablity of ice-cover at this time of year are in fact covered in very thick ice:

enter image description here

update 6/2/14

A small amount of ice still remains on Lake Superior. This is the first time in the satellite era (1973-) that ice has been present in June.

enter image description here

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April and later ice cover is primarily on Lake Superior, since this lake is in the coldest region and also because it is the largest lake.

Raymond Assel analyzed the Great Lakes ice coverage for the winters of 1897-1982 in AN ICE-COVER CLIMATOLOGY FOR LAKE ERIE AND LAKE SUPERIOR FOR THE WINTER SEASONS 1897-1898 to 1982-1983 INTERNATIONAL JOURNAL OF CLIMATOLOGY, VOL. 10,731-748 (1990).

According to table IV of Assel, in the winter of 1911-12 Lake Superior had an ice cover of 80% or greater for 74 days. No other winter had more than 52 such days.

According to this NOAA file in the winter of 2013-14 Lake Superior has an ice cover of 80% or greater on 68 days.

Assel also studied Lake Erie, and finds that 1911-12 had 72 days with 80% or greater ice cover. This compares to 70 such days in 2013-14.

Based on the above, it is very likely that 1911-12 was the most recent winter with similar April ice cover to 2013-14.

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It's unprecedented for March going back to 1973. It is not quite unprecedented; February 1979 is still the champ with 94.7% ice cover on the Great Lakes in recent history.

What about before that? Measurements were intermittent and not all that accurate. Earth observation satellites are needed to do this kind of measurement frequently and accurately. That's why the records start with 1973. (Note: Something similar happens with hurricanes records. Meteorologists didn't know how many tropical storms and hurricanes never reached shore until the advent of modern weather satellites.)

Temperatures have been rising since the mid 19th century. There were eight times in the 19th century when the East River froze solid enough to walk on. Since then? None. The winters of 1815-1816 and 1816-1817 are especially good bets for even greater ice coverage on the Great Lakes. 1815 was the "year without summer", thanks to the 1815 eruption of Mount Tambora. The summer of 1815 wasn't, and the winters that followed were just brutal.

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  • $\begingroup$ It don't think it's true that ice coverage wasn't measured before 1973. For example A Historic Perspective of Lake Michigan Ice Coverage has maximum ice cover back to 1963 for Lake Michigan (table 2). Yes, I understand 1979 had a greater maximal ice cover, my question is about this time of year, April. I'm looking for data, not necessarily satellite, for example airplane or ship based data. $\endgroup$ – DavePhD Apr 24 '14 at 16:41
  • $\begingroup$ I'll change that to intermittent and less accurate. It's before airplanes where such measurements just weren't made. The pre-satellite era airplane-based measurements just don't compare in frequency, breadth, and accuracy to satellite-based measurements. Weather satellites drastically changed the entire science of meteorology. $\endgroup$ – David Hammen Apr 24 '14 at 17:01
  • $\begingroup$ The winters of 1815-16 and 1816-17 were not severe in the Great Lakes region. Those winters are not in the list of the 22 coldest winters from 1779 to 1978 in Table 5 of glerl.noaa.gov/ftp/publications/tech_reports/glerl-031/… $\endgroup$ – DavePhD Feb 18 '15 at 13:56

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