As of Monday PM, Great Lakes surface ice extent was at 14.3%. Lake Michigan ice cover was 14.8%. Lake Huron had the highest percentage of ice cover at 26.8% and Lake Superior had the least at 5.3%.
It may seem strange that Lake Superior has the least amount of ice extent. Whether the Great Lakes or smaller inland lakes – the deeper the lake, the longer it will take to form ice cover (other factors equal). Lake Erie’s deepest point is 210 feet, while the deepest point in Lake Superior is 1,333 feet – more than six times the deepest point in Lake Erie.
Wind also plays a factor. The ice extent goes up and down as strong winds act to break up surface ice. There’s also the factor of ships breaking up the ice. If you go to www.marinetraffic.com you can see that while shipping has taken a winter pause on Lake Superior, we still have ships out on the other Great Lakes…not as many as summer, but some ships continue moving cargo in winter as long as they can get into ports.
Here’s a graph that shows the maximum ice extent each year on the Great Lakes as a whole. It starts with the start of frequent satellite images in 1973. The average maximum ice extent is 53.1%, though there are significant fluctuations from year-to-year.
You can see the period of cold winters and high ice extent we had from 1977 – 1982 and the period of milder winters from 1998 – 2002.
Maximum ice extent usually occurs between mid-February and early March. Last year we reached 45.8%, just a little below average. We had La Nina last year and we have a similar La Nina this year, so we’ll see if maximum extent is similar to last year.
There is a Gale Warning for Lake Michigan from 4 pm this (Tue.) to 7 am Wed. Beginning at 7 am tomorrow, we’ll have small craft advisories.